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by Zach Davis, Stuart Enoch, PhD, Noor Sash, PhD u.a.
Everything you ever wanted to know about medicine – in one package!
Lecturio’s “Medicine Flat Rate” includes all current and prospective medical courses. It will provide you with invaluable guidance and comprehensive support for your study and training – not only for medical students, but also for nurses and non-medical practitioners.
You will get access to an impressive variety of lectures held by renowned experts, such as the editor-in-chief of The American Journal of Medicine, Prof. Joseph Alpert.
Our team of highly qualified medical professionals will guide you through the following main topics:
NCLEX-RN Review Course
The courses “Basic and Further Science”, “Internal Medicine” and “Specialties” will be added soon.
The apophysis is a secondary ossification center found on non-weight-bearing segments of bones. It is the site of ligament or tendon insertion and is involved in the peripheral growth of bones. These secondary growth centers are generally open during childhood and do not close until early adulthood. Chronic apophyseal injury (traction apophysitis) almost always happens in adolescent athletes during periods of growth. Types of chronic apophyseal injury include Sever disease (posterior calcaneal apophysitis), Osgood-Schlatter disease (tibial tuberosity apophysitis), little league elbow (medial epicondyle apophysitis), and Sinding-Larsen-Johansson syndrome (inferior patella apophysitis). Diagnosis is generally made clinically. Chronic apophyseal injuries are generally treated with a conservative approach and rarely require surgical intervention.
The spleen is the largest ductless gland and largest single lymphatic organ in the human body. The main functions of the spleen are immunologic surveillance and red blood cell breakdown. The spleen can be affected by diseases of different origins, such as inflammatory, congenital, infectious, neoplastic, and vascular diseases. Ultrasonography (US) is usually used as the 1st-line imaging modality due to its easy accessibility and lack of ionizing radiation, but CT and MRI with contrast can also be helpful. Contrasted imaging modalities can delineate lesions and help differentiate disorders.
The mediastinum is the central part of the chest cavity containing many vital structures, such as the heart, great vessels, trachea, thoracic esophagus, lymph nodes, multiple nerves, sympathetic chains, and thoracic spine. Mediastinal pathology (e.g., masses) can be noted on conventional radiographs as part of evaluating chest-related symptoms, or it can be incidentally detected. To elucidate the characteristics of the mediastinal abnormality, further imaging studies are warranted. Common additional modalities are CT and MRI.
Cranial nerve palsy is a congenital or acquired dysfunction of 1 or more cranial nerves that will, in turn, lead to focal neurologic abnormalities in movement or autonomic dysfunction of its territory. Head/neck trauma, mass effect, infectious processes, and ischemia/infarction are among the many etiologies for these dysfunctions. Diagnosis is initially clinical and supported by diagnostic aids. Management includes both symptomatic measures and interventions aimed at correcting the underlying cause.
Informed consent (IC) is a medicolegal term describing the documented conversation between a patient and their physician wherein the physician discloses all relevant and necessary information to a patient who is competent to make an informed and voluntary decision regarding their care. Competency, disclosure, and voluntariness are the key elements upon which IC is based. The patient's well-being and autonomy are the 2 key fundamental moral values that are preserved by IC. Medical care decisions requiring IC range from the choice to undergo a defined medical or surgical treatment to participation in a research study. The IC represents shared decision-making between the patient and their caregiver and is thus mandatory for both clinical care and enrollment in research studies. Informed consent is usually documented in a signed written form.
Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Surface receptors are bound to the cell membrane, receive signals from their surrounding environment, and transmit those signals into the cell, often via the generation of 2nd messengers (like cyclic adenosine monophosphate (cAMP)) or through phosphorylation cascades. There are multiple different subclasses of surface receptors, and 3 of the most important classes include ligand-gated ion channel receptors, enzyme-linked receptors (the most common of which are receptor tyrosine kinases (RTKs)), and G-protein-coupled receptors (GPCRs). Intracellular receptors, on the other hand, are located within the cytoplasm and often act as transcription factors, directly interacting with DNA and affecting gene expression.
Diagnostic modalities such as chest X-rays provide static images of the thoracic cavity, including the lungs and airways. While providing a wealth of anatomical information necessary for the diagnosis of pulmonary disease, chest X-rays do not give much information about the individual's respiratory function. Pulmonary function tests are a group of diagnostic procedures yielding useful, quantifiable information about the rate of the flow of air through the individual's airways, lung capacity, and the efficiency of gas exchange in relation to time. The most commonly utilized tests include spirometry (before and after bronchodilator use), lung volumes, and quantitation of diffusing capacity for carbon monoxide (CO). The tests can be influenced by the individual's effort/fatigue, disease state, or anatomical malformation.
Nerve tissue consists of 2 principal types of cells: neurons and supporting cells. The neuron is the structural and functional/electrically excitable unit of the nervous system that receives, processes, and transmits electrical signals to and from other parts of the nervous system via its cell processes. There are multiple types of neurons that are classified based on their anatomic structure and function as sensory neurons, motor neurons, and interneurons. The functional components of a neuron include dendrites (to receive signals), a cell body (to drive cellular activities), an axon (to conduct impulses to target cells), and synaptic junctions (specialized junctions between neurons that facilitate the transmission of impulses between neurons; they are also found between axons and effector/target cells, such as muscle and gland cells). Supporting cells are called neuroglial cells and are located close to the neurons; however, these cells do not conduct electrical signals. The CNS consists of 4 types of glial cells: oligodendrocytes, astrocytes, microglia, and ependymal cells, each having a different function. In the PNS, the supporting cells are called peripheral neuroglia and include Schwann cells, satellite cells, and various other cells having specific structures and functions. Schwann cells surround the processes of nerve cells and isolate them from adjacent cells and the extracellular matrix by producing a lipid-rich myelin sheath, ensuring the rapid conduction of nerve impulses. Satellite cells are similar to Schwann cells, but they surround the nerve cell bodies. In the CNS, oligodendrocytes produce and maintain the myelin sheath. A nerve is composed of a collection of bundles (or fascicles) of nerve fibers. Within the CNS, the brain and spinal cord tissue can be classified as gray or white matter, depending on the tissue composition. White matter is most notably composed of myelinated nerve fibers, whereas gray matter is made up of neuronal cell bodies.
Invasive mechanical ventilation (IMV) is an advanced airway modality used for individuals with immediate or impending respiratory failure and/or in preparation for surgery. The IMV technique involves positive pressure ventilation delivered to the lungs through an endotracheal tube via a ventilator. The ventilator can be set to specific modes that determine how the machine assists with breathing. The modes are tailored to the individual's needs. The mode refers to the characteristics of mechanical ventilation and mainly includes trigger (how inspiration begins), cycle (how inspiration ends), and limit (when inspiration should be aborted). The most commonly used mode is assist-control ventilation, which is usually followed by pressure-support ventilation for weaning. Careful consideration should be exercised while planning extubation, as IMV is associated with complications.
In the pediatric population, imaging often plays a critical diagnostic role, especially in diagnosing congenital anomalies. In children, CT scans are avoided if at all possible due to the high risk of radiation exposure. In addition, both CT and (especially) MRI require children to hold still for significant periods of time and often require sedation to complete the study. For these reasons, plain radiography (often with contrast), fluoroscopy, and ultrasound are the imaging modalities of choice for most suspected cases involving GI pathology. Some conditions that can be diagnosed using imaging include hypertrophic pyloric stenosis, necrotizing enterocolitis, midgut malrotation with or without volvulus, intestinal atresia intussusception, appendicitis, Hirschsprung disease, mesenteric lymphadenitis, and obstructions of the biliary tree.
Chest abnormalities are a common presenting pathology of the pediatric population. Imaging modalities such as chest X-rays are the initial diagnostic test of choice used in urgent/emergent pediatric cases. Imaging modalities aid in differentiating the causes of respiratory distress in infants and finding the underlying infectious, traumatic, or congenital disorder. Computed tomography (CT) is a useful adjunctive modality in the pediatric population when conventional radiography fails to adequately characterize pathology. Given the common occurrence with many cardiac or vascular anomalies, specific protocols are necessary to highlight potentially abnormal anatomical structures. Pediatric chest imaging is a multimodality process at most centers used to help answer clinical questions and adequately care for individuals.
Imaging of the intestines is typically performed utilizing a multimodal approach, with clinical suspicion being the primary indicator for which study should be completed and in what order. There are also many differences between outpatient imaging versus emergency or inpatient imaging of the intestines. Imaging varies widely based on the patient's history, symptoms, and physical exam findings. The patient's age will also play a factor in the modality chosen. For example, appendicitis is typically 1st evaluated via ultrasound in the pediatric population versus CT in adults.
Surgical complications are conditions, disorders, or adverse events that occur following surgical procedures. The most common general surgical complications include bleeding, infections, injury to the surrounding organs, venous thromboembolic events, and complications from anesthesia. In addition, patients may also experience a variety of cardiac, pulmonary, renal/urologic, and CNS complications, especially if the patient is elderly and/or has underlying medical comorbidities. The clinician should be aware of all of these potential complications and their presenting symptoms in order to quickly identify and treat them. Some of the most common signs and symptoms suggestive of a potential complication include tachycardia, hypoxia, fever, pain, and mental status changes.
Congenital infections are acquired in utero or during passage through the birth canal at birth and can be associated with significant morbidity and mortality for the infant. The TORCH infections are a group of congenital infections grouped due to their similar presentation. The acronym TORCH arises from the names of the infectious agents that cause the diseases included in this group: toxoplasmosis, other agents (syphilis, varicella zoster virus (VZV), parvovirus B19, and HIV), rubella, CMV, and herpes simplex.
The primary goals of antepartum testing and monitoring are to assess fetal well-being, identify treatable situations that may cause complications, and evaluate for chromosomal abnormalities. Antepartum tests for aneuploidy are typically performed in the 1st and 2nd trimesters. These tests are divided into screening tests (which include cell-free DNA testing, serum analyte testing, and nuchal translucency measurements), and diagnostic tests, which provide a definitive diagnosis of aneuploidy and include chorionic villus sampling (CVS) and amniocentesis. Antepartum monitoring is done in the 2nd and 3rd trimesters to evaluate fetal well-being and assess the risk of fetal death. Antepartum monitoring tests include continuous cardiotocography (i.e., fetal heart rate tracings), the non-stress and contraction stress tests (NST and CST, respectively), the fetal biophysical profile (BPP), and umbilical artery Doppler studies.
In the human brain, information is transmitted in the form of bioelectrical impulses and chemical signaling molecules. These molecules, called neurotransmitters, are protein molecules used by neurons to emit a specific signal. The signals are picked up in the plasma membrane of adjacent neurons by receptors, which are complexes of protein subunits responsible for sensing relevant stimuli and setting in motion the cellular machinery required to produce the desired response.
Cancer immunotherapy is a rapidly advancing medical therapy that takes advantage of the immune system to contain or eliminate cancer cells. Currently, immunotherapies have been incorporated into treatment regimens for different types of cancer. Various therapeutic approaches exist, including using cytokines, vaccines, oncolytic viruses, T-cell manipulation or cellular adoptive immunotherapy, or antibodies to immune checkpoint molecules. These therapies provide new options for advanced cancers, including melanoma, renal cell carcinoma, prostate adenocarcinoma, lung cancer, urothelial carcinoma, Hodgkin lymphoma, and refractory B-cell ALL. With the immune system involved, these agents carry serious and potentially fulminant adverse effects and toxicities.
Homeostasis is the steady state of equilibrium. Similarly, in biochemistry, energy homeostasis is the balance point between energy supplied and energy dissipated (i.e., a constant energy state) that the human body seeks to maintain for optimal performance. The hypothalamus plays a central role in regulating energy homeostasis. Inefficient energy homeostasis is thought to be a major factor in the obesity epidemic. Many models have been proposed to explain and further understand the mechanism of energy homeostasis.
The prenatal period begins with the formation of the embryo and continues through the development of the fetus, terminating with birth. Neonatal physiology during prenatal life differs significantly from that during postnatal life. Before birth, nutrient, gas exchange, and elimination of waste products occur via the placenta. The fetus receives oxygenated blood via the umbilical vein, and deoxygenated blood is removed via the umbilical arteries. The 3 shunts that help redirect the fetal circulation are the ductus venosus, foramen ovale, and ductus arteriosus. These shunts close after birth, leaving behind vestigial remnants. Postnatally, the fetal circulatory system and organ systems adapt to the extrauterine environment. Placental blood supply is cut off, causing the neonate to make adaptive changes.
Estrogen and progesterone are the sex hormones produced by the ovaries in premenopausal women. These agents are responsible for developing and maintaining female sex organs and secondary sexual characteristics. Estrogen and progesterone are used to treat hypogonadism (primary ovarian insufficiency), menopausal symptoms, and gender dysphoria in transgender women. Risks and side effects include uterine bleeding, predisposition to cancer, breast tenderness, hyperpigmentation, migraines, hypertension, and mood changes. Contraindications are estrogen-dependent neoplasms, thromboembolic disorders, and liver disease.
Immunoassays are plate-based techniques that can detect and quantify many types of molecules through antibody-antigen reactions. An immunoassay typically involves an analyte, a targeted antibody, and labels. Classification of immunoassays is based on the type of label utilized, which includes enzymes (ELISA), light-emitting molecules/tracers (e.g., chemiluminescence and fluorescence immunoassays), and radioactive isotopes (radioimmunoassays). These specialized immunoassays are relatively sensitive, specific, inexpensive, and rapid, and are widely used in a clinical setting. Immunoassays are used in the diagnosis of infectious diseases, identification of tumor markers, allergy testing, and monitoring drug levels.
Blotting techniques involve the separation (via electrophoresis) and transfer of DNA, RNA, or proteins onto a blotting membrane. This separation is generally followed by complexing of the target with a labeled molecule for detection. Southern blotting is used to evaluate for specific DNA sequences and may be used in identification of genetic mutations and in forensics. Northern blotting focuses on RNA sequences and is helpful in assessing gene expression. Western blotting identifies proteins and antibodies and has applications in diagnosing infectious diseases, protein abnormalities (such as prion disease), and autoimmune conditions. Although these tests have good specificity, they have significant disadvantages owing to their expense, labor-intensiveness, and slow turnaround time.
An abnormal amount of lipid in blood is called dyslipidemia, which includes abnormal levels of cholesterol, triglycerides, and/or lipoproteins. Dyslipidemia may be primary (familial) or secondary (acquired). Both primary and secondary causes can lead to the development of premature cardiovascular (atherosclerosis) disease. Familial causes are classified according to the Fredrickson system, which looks into the pathology and the lipids that are elevated. Certain types do not increase the risk of premature atherosclerotic disease but still impact overall cardiac risk and chance of cardiovascular events in the future. Screening, early diagnosis, and strict control and management are the keys to prevention of cardiovascular events.
Proteins have an extensive range of functions in the body. Structural proteins help maintain the physical integrity of cells and allow movement of substances within cells. Catalytic proteins are enzymes, which are critical in almost all biologic functions (e.g., metabolism, coagulation, digestion). Communication, signaling, and regulatory proteins are critical in coordinating responses throughout the organism, and include receptors, hormones, neurotransmitters, intracellular signaling molecules (such as kinases and G-proteins), and transcription factors. Additionally, proteins are involved in transportation of substances through the bloodstream, as well as across cell membranes. Proteins also play a critical role in the immune system.
The ankle is a hinged synovial joint formed between the articular surfaces of the distal tibia, distal fibula, and talus. The ankle primarily allows plantar flexion and dorsiflexion of the foot. The subtalar joint and the other tarsal bones create many synergistic articulations, allowing for a wide range of motion (ROM)–plantar flexion, dorsiflexion, eversion, inversion, abduction, and adduction. The movements are generated by large muscle groups that originate in the leg and insert as well as act upon the bones of the foot and tarsus.
There is a global consensus that quality health care should be safe, effective, and patient-centered, yet adverse events during hospital care cause death and disability worldwide. Almost half of these adverse events are preventable in high-income countries, and that proportion is even higher in low- and middle-income countries. The growing complexity of health care systems has been linked to an increase in medical errors resulting in health-care-related adverse events. The term "error" has negative connotations, and the goal of patient safety measures is to prevent adverse events by following accepted practice at a system or individual level. Sentinel events that result in unexpected mortality or major harm to a patient signal the need for investigation and response. Types of medical errors include adverse drug events, incorrect or delayed diagnosis, and errors during procedures and surgeries. The science and culture of patient safety are based on the premise that human error will occur and that we can build systems that prevent and reduce these occurrences. This culture provides a framework for balanced accountability of the individual and the organization in designing workplace systems that are safe and reliable. Many strategies have been implemented to prevent and address medical errors that affect patient safety.
The primary functions of the GI tract include the digestion of food and the absorption of nutrients. Multiple organs in the GI system secrete various substances into the lumen to assist in digestion and/or the regulation of GI function. The majority of digestive secretions come from the salivary glands, stomach, pancreas, and gallbladder, although the intestines secrete fluids and mucus too, which are critical in protecting their inner walls.
The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons that allow for flexibility as well as dynamic and static support. The foot has 3 primary arches and multiple ligaments that are essential to its structure. The arches are important in absorbing weight during standing, walking, and running and the ability to adapt to uneven terrain during locomotion.
Proteins are 1 of the 3 primary macronutrients in the body and are synthesized from individual building blocks called amino acids (AAs). Amino acids are bound together by peptide bonds, which link the amino end of one AA to the carboxy end of the next AA, generating a protein's primary structure. The strand of AAs then undergoes additional folding, ultimately generating complex 3-dimensional structures. Proteins have a wide variety of functions, including catalytic, structural, regulatory, transport, storage, and immunologic functions. They are digested by proteases and peptidases secreted by the stomach and pancreas and absorbed as individual AAs in the small intestines through specialized transporters. There are countless medical conditions related to protein abnormalities, including abnormalities related to enzymes, receptors, membrane channels, hormones, accumulation of proteins, and autoimmune disorders.
Pharmacokinetics is the science that analyzes how the human body interacts with a drug. Pharmacokinetics examines how the drug is absorbed, distributed, metabolized, and excreted by the body. Pharmacodynamics is the science that studies the biochemical and physiologic effects of a drug and its organ-specific mechanism of action, including effects on the cellular level. Another way to describe the difference between the 2 disciplines is to say that pharmacokinetics is "what the body does to the drug," whereas pharmacodynamics is "what the drug does to the body." When prescribing medications, physicians must take into account both the drug's pharmacodynamics and its pharmacokinetics to determine the correct dosage and to ensure the appropriate effect.
Cholestasis in neonates and young infants is conjugated hyperbilirubinemia in the 1st 3 months of life due to impaired bile excretion. Biliary tract malformations involving the gallbladder and bile duct are grouped into cystic and noncystic obliterative cholangiopathies, the most common of which is biliary atresia. Less common causes include the genetic Alagille syndrome, infectious causes, and metabolic disorders. Clinical presentation is with obstructive jaundice. Ultrasonography and MRCP are useful diagnostic tools, and a prenatal diagnosis is sometimes made with ultrasonography. Cystic causes frequently require surgery to correct the defect and allow for normal child growth. Liver transplantation may be needed in cases of biliary atresia with portal hypertension.
Volume status is a balance between water and solutes, the majority of which is Na. Volume depletion (also known as hypovolemia) refers to a loss of both water and Na, whereas dehydration refers only to a loss of water. Dehydration is primarily caused by decreased water intake and presents with increased thirst and can progress to altered mental status and low blood pressure if severe. Volume depletion can be caused by GI losses, renal losses, bleeding, poor oral Na intake, or third spacing of fluids. The clinical presentation has relatively nonspecific symptoms but will ultimately cause low blood pressure if severe. The diagnosis of these imbalances is based on lab findings in addition to clinical symptoms and signs, which can be subtle and unreliable. Management requires differentiation between these 2 conditions. The treatment is to administer fluids with tonicity similar to those lost; isotonic fluids are used for volume depletion, and hypotonic fluids are used for dehydration.
The hepatobiliary system is composed of the liver, gallbladder, and bile ducts (within the liver and external to the liver). The liver produces bile, which is a fluid made of cholesterol, phospholipids, conjugated bilirubin, bile salts, electrolytes, and water. Bile, which assists in digestion and helps eliminate waste products, is stored in the gallbladder. The hepatobiliary system can be affected by infections, cysts, solid masses, ischemia, and mechanical flow obstruction, which mandate the presence of reliable imaging tests to determine the etiology. The methods that evaluate structural changes in the liver and biliary tract include ultrasonography, CT scan, and MRI (including magnetic resonance cholangiopancreatography). Additionally, cholescintigraphy, a functional imaging study, helps identify gallbladder pathology by tracking the biliary pathway.
Examination of the lower limbs involves assessment of the hips, knees, ankles, and feet to evaluate for signs of pathology. The examination includes inspection, palpation, assessment of range of movement, and provocative maneuvers. A good history should be taken and concurrently used with the exam findings to obtain a presumptive diagnosis.
Noninvasive ventilation (NIV) is an advanced respiratory support that does not require an artificial, invasive airway. This technique is commonly used during acute respiratory failure. The most common forms of NIV are noninvasive positive pressure ventilation (NIPPV) and high-flow nasal cannula (HFNC). In acute respiratory failure, NIV is frequently used to prevent intubation for invasive mechanical ventilation, if there are no contraindications. There are more established contraindications to NIPPV in comparison to HFNC, but NIPPV has demonstrated clear mortality benefit in chronic obstructive pulmonary disease and congestive heart failure exacerbations.
Imaging of the internal female reproductive organs (including the uterus, ovaries, and fallopian tubes) is indicated to diagnose common gynecologic complaints, most commonly in cases of abnormal bleeding, pelvic pain, and to evaluate masses, congenital anomalies, and infertility. Ultrasound is almost always the 1st-line imaging modality of choice, whereas MRI is typically reserved for complicated or indeterminate cases as a follow-up. Computed tomography is almost never used for primary gynecologic assessments. Fallopian tubes are not visible on either ultrasound or MRI if they are normal. The best way to assess tubal patency is by using hysterosalpingography, a fluoroscopic exam in which a dye is injected into the uterine cavity, followed by the study of its flow through the fallopian tubes.
The renal system is composed of 2 kidneys, 2 ureters, a bladder, and a urethra. These structures function to filter blood and excrete urine, which contains waste products of metabolism. Varying conditions such as infections, cysts, solid masses, ischemia, and mechanical obstruction can affect the renal system. Evaluation of diseases rely on imaging methods such as radiography, ultrasonography, CT, and MRI. Some of these are also used to guide tissue sampling (e.g., renal biopsy).
Female breasts, made of glandular, adipose, and connective tissue, are hormone-sensitive organs that undergo changes along with the menstrual cycle and during pregnancy. Breasts may be affected by various diseases, in which different imaging methods are important to arrive at the correct diagnosis and management. Mammography is used for breast cancer screening and diagnostic evaluation of various breast-related symptoms. Ultrasonography is rarely used for screening, but it is typically used for diagnostic workup and during procedures (e.g., breast biopsy). MRI of the breasts is used as a supplementary screening tool for those at high risk for developing breast cancer. Additionally, in individuals with breast implants, inconclusive mammographic and/or breast ultrasound findings, and diagnosed breast cancer needing evaluation pretreatment and posttreatment, MRI is an important breast radiologic tool.
Chromosomal testing can be accomplished using several techniques, all of which can identify chromosomal abnormalities. Karyotyping is the staining, organization, and visualization of chromosomes, which can help identify aneuploidy and major structural changes. Karyotyping is not sensitive in identifying small abnormalities and is a labor-intensive process. Chromosomal microarray analysis is a comparative technique that utilizes fluorescence to identify and quantify specific genetic sequences and is much more sensitive in identifying copy number variants, such as microdeletions or microduplications. However, chromosomal microarray analysis is not useful in identifying certain variations such as balanced translocations. Fluorescence in situ hybridization utilizes fluorescent probes to identify and locate specific genes on chromosomes. Compared with karyotyping, FISH is much more sensitive and specific in determining several abnormalities (except for point mutations) but is limited by the currently available gene probes.
Function of the GI system is highly regulated through neural and hormonal signaling. Much of this regulation comes from the ANS. Parasympathetic stimulation is excitatory, triggering digestive secretions, an increase in GI blood flow, and movement of material through the tract, while sympathetic stimulation is inhibitory and has the opposite effects. The GI tract also has its own enteric nervous system, which controls numerous local GI reflexes. For example, the presence of a particular nutrient may be detected by chemoreceptors and may trigger release of a particular digestive enzyme, which is coordinated entirely by the enteric nervous system (without input from the brain). In addition, there are numerous hormones and paracrine signaling molecules released by GI organs that similarly affect GI function.
The primary functions of the GI tract are digestion and absorption, which require coordinated contractions of the smooth muscles present in the GI tract. Peristaltic waves, segmentation contractions, and the migrating motor complex are all important contraction patterns that help to mix contents, get them in contact with the intestinal walls (where they are further digested by brush-border enzymes and absorbed into the enterocytes), and propel material down the tract at appropriate times and in appropriate amounts.
An airway, breathing, and circulation (ABC) assessment is the mainstay for evaluating and treating critically ill individuals. The airway assessment helps identify individuals with potential obstruction of the airway, which may benefit from airway management techniques to ensure adequate ventilation and oxygenation. Measures to relieve and prevent soft-tissue obstruction in an unconscious individual can include special positioning maneuvers and airway adjuncts (such as oropharyngeal or nasopharyngeal airways). By relieving obstruction, assisted breathing with a bag-mask is more effective. Endotracheal intubation provides a more definitive way to ensure airway patency and protection.
Congestive heart failure (CHF) is a progressive syndrome characterized by the failure of the heart to maintain the metabolic demands of the body either due to systolic or diastolic dysfunction. Treatment of CHF is centered around lifestyle modifications (salt and fluid restriction, smoking cessation, and weight loss) and pharmacologic management. Acute worsening of heart failure is often secondary to other medical conditions and is managed with aggressive diuresis and interventions to support cardiac and ventilatory functions. Angina is defined as chest pain or discomfort resulting from myocardial ischemia. Therapy for angina is targeted at limiting platelet aggregation and adhesion (with antiplatelet agents), reducing O2 demand (with beta-blockers), reducing preload (with nitrates), and preventing the progression of atherosclerotic disease (using statin therapy), along with the management of comorbidities.
Non-Hodgkin lymphomas (NHLs) are a diverse group of hematologic malignancies that are clonal proliferative disorders of mature or progenitor B cells, T cells, or natural killer (NK) cells. Most pediatric cases are aggressive and high-grade (but curable); in adults, low-grade subtypes are more common. Like Hodgkin lymphoma, which has distinct pathologic features and treatments, NHL often presents with constitutional signs of fever, night sweats, and weight loss. Clinical features include lymphadenopathy and hepatosplenomegaly, but some individuals present with extranodal involvement and abnormal lab findings. B-cell NHLs include diffuse large B-cell lymphoma, follicular lymphoma, Burkitt lymphoma, mantle cell lymphoma, and marginal zone lymphoma. T-cell NHLs include adult T-cell lymphoma and mycosis fungoides. Diagnosis is made by lymph node biopsy, bone marrow biopsy, or both. Management is with chemotherapy or targeted drugs. Radiation therapy is used in adults but not in children, and stem cell transplantation is used for patients with aggressive disease.
Immune responses against pathogens are divided into the innate and adaptive immune response systems. The adaptive immune response, also called the acquired immune system, consists of 2 main mechanisms: the humoral- and cellular-mediated immune responses. Humoral immunity is mediated through B cells (producing antibodies), whereas cell-mediated immunity involves T cells, and this response is activated when the innate immune system fails to control an infection. As the 2nd line of defense, the adaptive immune system is slower and responds over a longer period of time, but the effect generally leads to specific immunological memory. The 2 important characteristics of adaptive response are specificity (with antigen recognition) and memory (immune response mounted with reinfection).
Gender dysphoria, formerly known as gender identity disorder, is the emotional discomfort felt by a patient because of the incongruence between their experienced gender and the gender they were assigned at birth (continuous inner conflict between gender identity and sexual identity). The 1st signs of cross-gender behaviors begin around age 3, the time when gender identity is established. Management involves a multidisciplinary approach (medical and psychological) to best support the patient.
Glycogen storage disorders (GSDs) are genetic defects leading to disorders of carbohydrate metabolism. The disorders are caused by pathogenic variants in genes that affect enzymes involved in glycogen breakdown. Deficiency of 1 of these enzymes may occur in the liver or muscles and can cause hypoglycemia and/or abnormal glycogen deposition in tissues. Presentations vary from being fatal in the neonatal period to having their initial presentation with symptoms in adulthood. There are at least 14 types of GSDs, and the 4 most common and significant are von Gierke disease, Pompe disease, Cori disease, and McArdle disease. Diagnosis is clinical; detection of glycogen in tissues is by biopsy and confirmed by DNA analysis. Management aims to treat or avoid hypoglycemia, hyperuricemia, hyperlipidemia (HLD), and lactic acidosis. No cure is currently available, but genetic therapies are being tested.
Digestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body. Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Carbohydrates, proteins, lipids, and micronutrients are digested and absorbed differently and require several enzymes and transport proteins to complete the process.
Diagnostic procedures in gynecology are useful in identifying the presence of disease, determining the progression of disease, and monitoring the response of the organs to treatment. The major diagnostic procedures include speculum examinations, sonography (ultrasound), colposcopy, cervical biopsy and endocervical curettage, loop electrosurgical excision procedures, vulvar biopsy, endometrial biopsy, hysteroscopy, and hysterosalpingography (HSG). All of these procedures can be performed in the office setting or in a radiology suite, though in certain situations they are performed in the OR if more sedation or increased monitoring is required.
Physical examination of the breasts is important both in the evaluation of a breast complaint and screening for asymptomatic breast pathology such as a breast mass. The examination involves inspection of the breasts to look for asymmetry or skin/nipple changes, as well as palpation of the breasts, nipples, and axilla. Coupled with medical history, the outcome of a breast examination can be normal, lead to a clinical diagnosis (e.g., infection), or require additional diagnostic evaluation (e.g., the evaluation of a palpable breast mass or skin/nipple changes).
A female genitourinary exam is performed either as a preventative screening exam or a problem-focused exam to evaluate complaints such as itching, pain, lesions, or infection. The investigation includes inspection, palpation, speculum exam, and bimanual exam. In combination with the subjectâ€™s history, the clinician uses exam findings to diagnose genital and pelvic conditions or to screen for cervical cancer (Pap smear).
Genitourinary examination is an integral part of the male physical examination that provides important information on the normal development in infants and children. Genitourinary examination is used for preventative health exams in adult men and is also a part of problem-focused exams performed to evaluate complaints such as pain, infection, skin lesions, or lumps in the genital or inguinal areas. In subjects with urologic emergencies, such as testicular torsion, an accurate exam leading to prompt treatment can be the defining factor in maintaining fertility. Other significant conditions found on the genitourinary exam are STIs, Peyronie disease, and masses that may need further evaluation to confirm malignancy.
Examination of the upper limbs is the portion of physical examination involving the assessment of the shoulder, elbow, forearm, wrist, and hand to evaluate for signs of pathology. The examination includes inspection, palpation, tests of range of movement, and provocative maneuvers. A good history should be taken and concurrently used with the exam findings to obtain a presumptive diagnosis.
A neurological exam is a systematic assessment of cognitive, sensory, and motor responses to identify pathologies of the nervous system. A neurological exam allows for the localization of neurologic lesions to narrow the differential diagnosis and focus on subsequent laboratory and imaging examinations. The exam should include assessments of the subject's mental status, speech, cranial nerves, motor system, deep tendon reflexes, sensation, balance, and coordination.
Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. From there, the DNA can be visualized with analysis techniques such as gel electrophoresis. The speed, inexpensiveness, ease of use, and high sensitivity and specificity make this technique highly useful for the basic and biomedical sciences, and it has become instrumental in many applications, including forensic analysis, diagnosis of infectious diseases, and diagnosis and screening of genetic abnormalities.
Fatty acid metabolism includes the processes of either breaking down fatty acids to generate energy (catabolic) or creating fatty acids for storage or use (anabolic). Besides being a source of energy, fatty acids can also be utilized for cellular membranes or signaling molecules. Synthesis and beta oxidation are almost the reverse of each other, and special reactions are required for variations (unsaturated fatty acids, very-long-chain fatty acids (VLCFAs)). Synthesis occurs in the cell cytoplasm, while oxidation occurs in mitochondria. Shuttling across membranes within a cell requires additional processes, such as the citrate and carnitine shuttles. In certain physiologic states, an increase in fatty acid oxidation can lead to the production of ketone bodies, which can also be utilized as an energy source, particularly in the brain and muscles.
Smooth muscle is primarily found in the walls of hollow structures and some visceral organs, including the walls of the vasculature, GI, respiratory, and genitourinary tracts. Smooth muscle contracts more slowly and is regulated differently than skeletal muscle. Smooth muscle can be stimulated by nerve impulses, hormones, metabolic factors (like pH, CO2 or O2 levels), its own intrinsic pacemaker ability, or even mechanical stretch. Whatever the stimulus is, it results in an increase in sarcoplasmic Ca levels. This Ca results in a phosphorylation of myosin, which activates it, allowing the myosin to interact with the actin. In smooth muscle, the actin is attached to cytoskeletal proteins located throughout the sarcoplasm and cell membrane known as dense bodies. Therefore, when the myosin pulls on the actin, the actin pulls on the dense bodies, causing the entire cell to â€œscrunchâ€ up and contract.
The cardiac cycle describes 1 complete contraction and relaxation of all 4 chambers of the heart during a standard heartbeat. The cardiac cycle includes 7 phases, which together describe the cycle of ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation. The cycle is frequently represented in a graph known as a pressure-volume loop, which shows how intraventricular volumes and pressures are related to one another throughout the cardiac cycle.
The posterior abdominal wall is a complex musculoskeletal structure that houses the abdominal aorta, the inferior vena cava, as well as important retroperitoneal organs, like the kidneys, renal glands, pancreas, and duodenum. This vital anatomical structure consists of the posterior abdominal muscles, their respective fascia, lumbar vertebrae, and the pelvic girdle. The structure is supported by 12th thoracic rib, lumbar vertebrae, and pelvic rim.
A physicianâ€™s diagnostic and therapeutic tool kit must include a variety of basic procedures that can be performed in the outpatient setting. These procedures include emergency intervention of the airway; drainage of fluid from the abdomen, joints, and spinal canal; and incision and drainage of abscesses. Although these procedures may be of reduced complexity, there are still inherent risks associated with invasive procedures, and these risks must be reduced through consistent aseptic and procedural techniques.
Examination of the skin is a fundamental part of the standard physical exam. This exam consists of a thorough inspection of the skin of the entire body. The assessment focuses on identifying abnormal signs on the skin, such as the scalp, orifices, nails, and mucosal surfaces. Dermatologic findings can represent localized processes or may be a sign of systemic disease.
Doctors routinely prescribe medications and should, therefore, be comfortable with basic calculations used to determine the optimal dosage. A dosing regimen is the manner in which a drug is administered to an individual, and describes the dose and frequency of the medication to be administered. Accuracy in dosing and the frequency of drug administration is necessary to achieve the desired effect while avoiding side effects and toxicity. In a clinical setting, both the prescribing doctor and pharmacist should review the optimal dose. Several medical conditions, including kidney and liver diseases and hypersensitivity, require dose adjustments to achieve the desired therapeutic effect.
Purines and pyrimidines are heterocyclic aromatic compounds, which, along with sugar and phosphate groups, form the important components of nucleotides. Purines include adenine and guanine, while pyrimidines include thymine (in DNA), uracil (in RNA), and cytosine. Purine nucleotide synthesis follows a series of reactions using carbon donors, amino acids (e.g., glutamine, aspartate), and bicarbonate. The de novo pathway generates inosine monophosphate (IMP), which is the precursor of adenosine monophosphate (AMP) and guanosine monophosphate (GMP). Purine synthesis is regulated in the 1st 2 steps. Synthesis of pyrimidine nucleotides also follows different reactions, producing uridine monophosphate (UMP), which is converted to uridine triphosphate (UTP) and cytidine triphosphate (CTP). For thymine, a part of deoxyribonucleotides, ribonucleoside reductase is required to reduce the ribose moiety. Degradation of nucleotides result in xanthine then uric acid production in purines, while pyrimidines produce the amino acids, Î²-alanine, and Î²-aminobutyrate.
Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty acids are integral building blocks of lipids, and can be classified as unsaturated or saturated based on the presence/absence of carbon-carbon double bonds within their nonpolar chains. Eicosanoids are a family of cell-signaling molecules with important physiologic properties derived from the fatty acid, arachadonic acid. In addition, combining fatty acids with different bases, including glycerol, phosphate, and shingosine, results in different lipids with varied functions within the human body. Glycerolipids (triacylglycerols) are important for energy storage and thermal insulation. Glycerophospholipids and sphingolipids are essential constituents of cellular plasma membranes. Another group of lipids is based off of isoprenoids, which are the building blocks of sterols (such as cholesterol). Altered levels of lipids (both an overabundance or deficiency) can result in many potential disease processes.
There are many etiologies of peripheral nerve injuries in the cervicothoracic region. The injuries commonly involve the phrenic nerve, the suprascapular nerve, the dorsal scapular nerve, the long thoracic nerve, or the thoracodorsal nerve. The nerves arise from the cervical plexus and brachial plexus. Causes of injury vary and may include trauma, compression, nerve entrapment, stretch or traction from repetitive movement, infection, surgical injury, or metabolic causes. Clinical presentation depends upon the motor and sensory innervation of the affected nerves. Diagnosis is mostly clinical but may also be confirmed with imaging or electrodiagnostic studies. Depending on the specific injury, management may be either surgical or conservative (physical therapy and avoidance of precipitating movements).
Diabetes mellitus (DM) is a chronic metabolic disorder characterized by persistent hyperglycemia due to impaired insulin secretion (type 1 DM), insulin resistance (type 2 DM), or both (latent autoimmune diabetes in adults (LADA)). The goal of diabetes management is to prevent chronic serious and potentially disabling complications due to damage to various organs. Adequate long-term control of blood glucose is crucial in the prevention of complications. Macrovascular complications include heart disease, stroke, peripheral vascular disease, and CKD in various stages, including end-stage renal disease that requires dialysis. Microvascular disease can cause retinopathy, neuropathy, or symptomatic cardiac disease, which are not seen during stress testing or angiogram that are used to diagnose large vessel diseases.
The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The fallopian tubes receive an ovum after ovulation and help move it and/or a fertilized embryo toward the uterus via ciliated cells lining the tubes and peristaltic movements of its smooth muscle. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Externally, the cervix is lined by stratified squamous cells; however, the cervical canal is lined by columnar epithelium. The transition point is known as the squamocolumnar junction, which is the site of most cervical cancers. These organs are supplied by the uterine and ovarian arteries and innervated by the autonomic nervous system.
Urologic cancer is a broad term that involves cancer of the male and female urinary tracts and male reproductive organs. Risk factors for urologic cancer are smoking; exposure to chemicals such as benzidine and beta-naphthylamine, and arsenic; genetic predisposition; and chronic irritation of the urinary system. Clinical presentation includes painless hematuria, flank and/or suprapubic pain, dysuria, and unexplained significant weight loss. The gold standard for diagnosis is endoscopy of the urologic structures (cystoscopy, cystourethroscopy, ureteropyeloscopy) with biopsy. Additional studies include radiologic imaging, which gives information about the tumor invasion and spread of the disease to other sites or organs. Management includes surgery, chemotherapy, radiotherapy, and supportive treatment, depending on the location, extent, and histology.
Skeletal muscle is striated muscle containing organized contractile structures known as sarcomeres that are made up of overlapping myofilaments: actin and myosin. When a nerve impulse arrives from a motor neuron, the signal triggers an action potential (AP) in the sarcolemma (muscle cell membrane), resulting in the release of Ca ions from the sarcoplasmic reticulum (SR) within the muscle cell. The Ca causes a conformational change in regulator proteins (troponin and tropomyosin), exposing myosin-binding sites on the actin filaments. Using ATP energy, the myosin heads pull the myosin along the actin, shortening the sarcomere and resulting in muscle contraction. The ATP can be produced via anaerobic and aerobic mechanisms, and the primary source of ATP energy in a muscle fiber determines its functional characteristics.
A complex system of coordinated electrical circuitry within the heart governs cardiac muscle activity. The heart generates its own electrical impulses within its pacemaker cells. The signal then travels through specialized myocytes, which act as electrical wiring, distributing the signal throughout the heart. Once the signal â€œleavesâ€ the specialized conduction system, it passes to each myocyte through channels called gap junctions (which connect myocytes to each other) and causes them to contract. An electrical impulse is created by the opening and closing of ion channels, allowing the flow of charged particles across the myocardial cell membrane. The flow of charged particles changes the voltage across the membrane and opens up additional voltage-gated channels, allowing the signal to propagate throughout the heart.
The human eye is a sensory organ whose primary function is vision. They eye has a spheroidal shape and is structured in 3 layers: a supporting outer fibrous layer, a middle vascular layer, and an inner neural layer. The eye can also be subdivided into 3 compartments: the anterior, posterior, and vitreous chambers. Surrounding the eyeball itself are the extraocular muscles, the lacrimal apparatus, various nerves and vessels, and the bony structure of the orbit. Light travels through the compartments of the eye to focus on the retina, which is the location where photoreceptors convert the stimulus into a neural impulse that is carried by the optic nerve to the brain.
Spinal cord injuries are complex injuries that involve damage to the neural tissue within the spinal canal. Spinal cord injuries are commonly the result of trauma. Clinical presentation varies depending on the site of injury and on whether the injury is complete or incomplete. Diagnosis is by clinical exam and imaging. Management is 2-fold, with immediate supportive care and stabilization of spine followed by long-term rehabilitation with physiotherapy and treatment of complications. Spinal cord injuries are associated with multisystem complications.
During exercise, the metabolic demands of the body increase, and changes in the cardiovascular system are required to maintain adequate perfusion. During isometric contraction, blood flow is decreased to the contracting muscle due to direct compression of the arteries. Once the contraction ends, vasoactive metabolites cause significant vasodilation, resulting in an increase in blood flow to the muscle known as active hyperemia. During endurance exercise, repetitive, coordinated movements over a sustained period result in an increase in HR, stroke volume, cardiac output, and systolic blood pressure primarily via sympathetic stimulation and effects of the skeletal muscle pump. Diastolic blood pressure usually decreases slightly due to significant vasodilation in the skeletal muscle vascular beds, resulting in a decrease in systemic vascular resistance.
Circulation is the movement of blood throughout the body through one continuous circuit of blood vessels. Different organs have unique functions and, therefore, have different requirements, circulatory patterns, and regulatory mechanisms. Several of the most vital organs (including the brain, heart, and kidneys) have autoregulatory properties, meaning that they are able to maintain a relatively constant blood flow despite fluctuations in mean arterial pressure (MAP). In other cases, locally produced factors (such as adenosine, CO2, or NO) can produce local vasoconstriction or vasodilation, regulating blood flow under specific physiologic conditions.
Mean arterial pressure (MAP) is the average systemic pressure in the arteries. The MAP is tightly regulated to help maintain appropriate perfusion and is primarily determined by the cardiac output (CO) and the systemic vascular resistance (SVR). Cardiac output is determined by the HR and the stroke volume (the volume of blood ejected by the heart each beat). The HR is primarily regulated by the effects of the ANS on the sinoatrial node in the heart, while stroke volume is determined by the preload, afterload, and inotropy (or contractile strength) of each heartbeat. The SVR is regulated by a number of factors, including the ANS, the arterial baroreflex, circulating catecholamines, the RAAS, and several other hormones.
The adult human body is made up of 60% water and is divided into extracellular and intracellular fluid compartments. Extracellular fluid is present outside the cells and makes up â…“ of the total body water. Intracellular fluid is present inside the cells and makes up â…” of the total body water. Intracellular and extracellular fluids are separated into compartments by semipermeable membranes, and the transport of fluid and ions is maintained by channels in the cell membrane. Each compartment contains different concentrations of ions and osmolar molecules. The relative charge and osmolarity are maintained rigorously by the transport of water and substances between compartments. Hypernatremia, hyponatremia, and edema are the clinical conditions arising from disturbances in the maintenance of osmolarity of the body fluid compartments.
Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular resistance is directly related to the diameter of the vessel (smaller vessels have higher resistance). Mean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors.
Ethics is the field of study dealing with moral principles. Since the beginning, ethics has guided the practice of medicine. The core set of directives are based on the assumptions that all human life has intrinsic value and must be preserved, and all actions of the physician must be congruent with curing disease and in the best interest of the individual. Medical research also operates under these assumptions when seeking better alternatives of care to benefit individuals.
Cholesterol is an important lipid molecule that is used for many biologic functions. Cholesterol can either be synthesized from endogenous acetyl-CoA or absorbed from food in the GI tract. Because cholesterol is lipophilic, it must be transported through the bloodstream via lipoproteins, where it can be picked up by hepatocytes or peripheral tissues. There, cholesterol can be stored, used in cellular membranes, or used as a precursor for steroid hormones. The human body cannot degrade cholesterolâ€™s ring structure, so the only mechanism for potential excretion is through the production of bile acids.
Glycogen is a branched polymer and the storage form of carbohydrates in the human body. Major sites of storage are the liver and skeletal muscles. Glycogen is the main source of energy during fasting or in between meals. Glycogen provides energy for up to 18 hours, after which energy requirements are met by fatty acid oxidation. The 2 metabolic pathways of glycogen are glycogenesis (glycogen synthesis) and glycogenolysis (glycogen breakdown). The key regulatory enzymes in these processes are glycogen synthase (in glycogenesis) and glycogen phosphorylase (in glycogenolysis). These pathways proceed depending on the energy needs of the cells, generally modulated by hormonal and allosteric regulators. Abnormal accumulation of glycogen occurs with enzyme deficiencies causing different types of glycogen storage disorders.
Signaling pathways are complex systems in which a single extracellular signal can elicit multiple intracellular events, some of which may also be triggered by other signaling pathways or may themselves trigger other intracellular events. "Second messengers" is a term used to refer to a diverse group of small molecules or ions that transmit the extracellular signal initiated by a ligand binding to a cell surface receptor to effector proteins inside the cell. In the resting state, small amounts of second messengers exist in a cell; however, their production can rapidly ramp up once a signal has been received. Once released inside the cell, second messengers bind to their target proteins and alter their properties (activity, localization, availability of reaction sites, stability, etc.), causing a change in the cellâ€™s homeostasis and thus transmitting the message.
The glyoxylate cycle is an anabolic pathway that is considered a variation of the tricarboxylic acid (TCA) cycle. The TCA cycle occurs in plants, bacteria, and fungi, and acetyl-CoA is converted into succinate. The glyoxylate cycle was thought not to occur in animals due to the absence of the enzymes isocitrate lyase and malate synthase; however, this hypothesis is being explored. The glyoxylate cycle occurs in glyoxysomes, which are specialized peroxisomes. There are no decarboxylation reactions in the glyoxylate cycle. The glyoxylate cycle allows cells to utilize 2 carbon units of acetate, and convert them into 4 carbon units, succinate, for energy production and biosynthesis. Additionally, each turn of the cycle produces a molecule of FADH2 and NADH.
Heme is an iron-containing porphyrin (which is made of 4 pyrrole groups), synthesized mostly in the bone marrow and the liver. Heme is a component of many crucial substances, including cytochromes, myoglobin, and hemoglobin. Biologic functions include the transportation of gases (e.g., O2), and electron transfer. Biosynthesis of heme is an 8-step process initiated by the synthesis of aminolevulinic acid. Iron availability affects heme production, as the last step involves insertion of ferrous ion. Iron is obtained from the diet and from the breakdown of heme-containing products. In the process of catabolism, heme is converted into bile pigments, out of which bilirubin is excreted. Mutations involving the enzymes in heme synthesis lead to a group of disorders known as porphyrias, and a defect in the catabolism of heme causes hyperbilirubinemias.
Spasmolytics are skeletal muscle relaxants that reduce forceful, involuntary muscle contractions. Spasmolytics have several mechanisms and can either act centrally to inhibit somatic motor neuron signals, or peripherally to prevent Ca+2 release from the sarcoplasmic reticulum. Spasmolytics are often used as temporary adjunctive treatment to alleviate muscle spasms or musculoskeletal pain. Spasmolytics may also be used in the management of spasticity due to upper motor neuron disorders. Most medications readily cross the bloodâ€“brain barrier; thus, CNS depression is a common side effect. It is also important to be aware of dependence and withdrawal symptoms (particularly with CNS depressants and GABA agonists).
Cardiac mechanics refers to how the heart muscle pumps blood and the factors that affect the heart's pumping function. Stroke volume (the volume of blood pumped out during each contraction) is affected by 3 key factors: preload, afterload, and inotropy (also known as contractility). Preload is how much the ventricle has stretched by the end of diastole (and thus how much blood has filled the ventricles). Afterload is the pressures in the aorta that ventricular contraction must overcome in order to open the aortic valve and eject blood into the aorta. Inotropy is the strength of the muscle contraction itself (independent of the preload), which is primarily related to how much intracellular Ca2+ is present.
Body temperature can be divided into external temperature, which involves the skin, and core temperature, which involves the CNS and viscera. While external temperature can be variable, the core temperature is maintained within a narrow range of 36.5â€“37.5ÂºC (97.7â€“99.5ÂºF). Although the reasons are unknown, it has been hypothesized that a narrow temperature range is maintained for the metabolic rate needed for the functioning and optimization of cellular processes. Regulation of the core temperature is one of the most critical functions of the nervous system and is achieved by physiologic and behavioral feedback and feed-forward mechanisms that are mainly regulated by the hypothalamus. Any change in body temperature or environmental temperature triggers responses that lead to the quick and efficient resetting of homeostasis.
Fatty acid oxidation disorders (FAODs) are a group of genetic conditions caused by disruptions in beta-oxidation or the carnitine transport pathway. These disruptions lead to an inability to metabolize fatty acids. All FAOD types are autosomal recessive. Because of the inability of the body to break down fatty acids, these fats accumulate in the liver and other internal organs. The clinical presentations of each disorder vary, but they commonly include hypoglycemia, cardiomyopathy, encephalopathy, seizures, myopathy, and liver dysfunction. Screening of newborns can detect these diseases, and DNA sequencing is usually performed to confirm the diagnosis. Management includes dietary changes or substrate supplementation.
During the 4th week of gestation, limb buds form on the sides of the developing embryo. The tips of these buds condense into the apical ectodermal ridge (AER). The AER continues the elongation of the limb buds and maintains its growth by continuously producing fibroblast growth factor 8 (FGF8). As the AER grows away from the body, tissues differentiate. After the cartilage models are formed in the developing limbs, arteries invade central and peripheral areas, giving rise to primary and secondary centers of ossification. The process of endochondral ossification is completed when those centers meet and the epiphyseal plate is no longer present.
Vascular surgery is the specialized field of medicine that focuses on the surgical management of the pathologies of the peripheral circulation. The main goal of most vascular procedures is to restore circulatory function to the affected vessels by relieving occlusions or by redirecting blood flow (e.g., bypass). Surgical intervention is either open or endovascular. Vascular interventions require a multidisciplinary approach, including vascular surgeons, interventional radiologists, anesthesiologists (or anesthetists), nurses, physiotherapists, and occupational therapists.
Cardiac surgery is the surgical management of cardiac abnormalities and of the great vessels of the thorax. In general terms, surgical intervention of the heart is performed to directly restore adequate pump function, correct inherent structural issues, and reestablish proper blood supply via the coronary circulation. Common interventions treat ischemic and valvular heart disease as well as disorders of the great vessels.
Acute disseminated encephalomyelitis (ADEM) is an immune-mediated, inflammatory, monophasic, demyelinating condition that affects the white matter of the brain and spinal cord. As a rapidly progressive post-infectious encephalomyelitis, ADEM is characterized by demyelination in the brain and spinal cord as a result of inflammation following infection or immunization.
Neuromuscular blockers are skeletal muscle relaxant medications that block muscle contraction through a couple of mechanisms. Depolarizing neuromuscular blockers bind to nicotinic cholinergic receptors (nAChRs), locking the ion channel open. This results in an initial, persistent depolarization, followed by receptor desensitization to result in muscle relaxation and paralysis. Nondepolarizing neuromuscular blockers also bind to these same receptors; however, they act by keeping the channel closed to prevent depolarization. These agents are often used as an adjunct to general anesthesia during surgery, and to facilitate endotracheal intubation. Since these medications also work on muscles associated with breathing, respiratory support should be employed. It is also important that adequate sedation is also given, since these agents do not have a sedative effect. Common adverse effects include anaphylaxis, bradycardia, hypotension, and prolonged paralysis. Physicians should also be aware of the potential for muscle fasciculations and hyperkalemia with succinylcholine.
Mineralocorticoids are a drug class within the corticosteroid family and fludrocortisone is the primary medication within this class. Fludrocortisone is a fluorinated analog of cortisone. The fluorine moiety protects the drug from isoenzyme inactivation in the kidney, allowing it to exert its mineralocorticoid effect. The mechanism of action of mineralocorticoids mimics that of aldosterone. By acting on the mineralocorticoid receptors, fludrocortisone induces the expression of proteins responsible for Na+ reabsorption and K+ excretion by renal tubule cells, which results in Na+ and water retention. Mineralocorticoids are used in the management of diseases characterized by insufficient (or absent) aldosterone activity, such as adrenal insufficiency and congenital adrenal hyperplasia. Adverse effects are related to both mineralocorticoid and glucocorticoid effects and include hypertension, edema, decompensated heart failure, hyperpigmentation, hypokalemia, Cushing syndrome, hyperglycemia, and hypothalamic-pituitary-adrenal axis suppression.
Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. These medications are also used for conditions requiring physiologic glucocorticoid replacement. Despite their extensive use, glucocorticoids can produce many and varied adverse effects and should be used judiciously. Because of their immunosuppressive effect, these medications may predispose individuals to infection and should be avoided in those with uncontrolled infections. In addition, long-term therapy can lead to suppression of the hypothalamic-pituitary-adrenal (HPA) axis, so discontinuation of therapy should be done carefully to avoid adrenal insufficiency.
Spinal disk herniation (also known as herniated nucleus pulposus) describes the expulsion of the nucleus pulposus through a perforation in the annulus fibrosus of the intervertebral disk. Spinal disk herniation is an important pain syndrome with the potential for neurologic impairment and is most commonly caused by degenerative disk disease. Clinical presentation depends on the presence or absence of spinal cord or nerve root compression and the downstream neurologic sequelae (e.g., radicular pain, muscle weakness, sensory deficit, reflex deficit). Diagnosis is initially clinical and can be confirmed with diagnostic imaging (e.g., MRI). Management can range from conservative to surgical, depending on the situation.
A tachyarrhythmia is a rapid heart rhythm, regular or irregular, with a rate > 100 beats/min. Tachyarrhythmia may or may not be accompanied by symptoms of hemodynamic change. Pathologic tachyarrhythmias resulting in hemodynamic instability can be caused by intrinsic cardiac abnormalities, systemic diseases, or medication toxicity. Supraventricular arrhythmias are called narrow-complex tachycardias and originate in the sinoatrial (SA) node, atrial myocardium, or atrioventricular (AV) node. Ventricular arrhythmias originate below the AV node and are characterized by a wide QRS complex. Diagnosis is made by physical exam and ECG. Management is directed toward the type of tachyarrhythmia present and its underlying cause.
The membrane potential is the difference in electric charge between the interior and the exterior of a cell. All living cells maintain a potential difference across the membrane thanks to the insulating properties of their plasma membranes (PMs) and the selective transport of ions across this membrane by transporters. There are 3 types of potential: resting membrane potential, equilibrium potential, and action potential. Membrane potential helps to generate action potential, and these action potentials act as carry-and-relay signals to the CNS and brain for performing a specific movement or action.
The abdominal organs are derived primarily from endoderm, which forms the primitive gut tube. The gut tube is divided into 3 regions: foregut, midgut, and hindgut. The foregut gives rise to the lining of the GI tract from the esophagus to the upper duodenum, as well as the liver, gallbladder, and pancreas. The midgut gives rise to the GI tract lining between the midduodenum and midtransverse colon. The hindgut gives rise to the GI tract lining from the midtransverse colon through the upper anal canal. The mesoderm gives rise to the muscles of the GI tract wall, connective tissue (including the mesenteries and omenta), and the vasculature. The ectoderm gives rise to the nerve tissue and the lining of the lower anal canal.
The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Indentations between arches are known as the pharyngeal clefts, or grooves, externally and the pharyngeal pouches internally. Each pharyngeal arch contains cartilage and muscular components, which are supplied by a cranial nerve (derived from neural crest cells), and an artery, known as a pharyngeal aortic arch. Some of these aortic arches go on to form the great vessels near the heart.
Medical ethics are a set of moral values that guide the decision-making of health care professionals in their daily practice. A sense of ethical responsibility has accompanied the profession of medicine since antiquity, and the Hippocratic oath was the 1st document to codify its core ethical principles (benevolence, autonomy, nonmaleficence, and distributive justice). In the 20th century, bioethics began to explore the moral relationship between humans and their world.
Both gastrulation and neurulation are critical events that occur during the 3rd week of embryonic development. Gastrulation is the process by which the bilaminar disc differentiates into a trilaminar disc, made up of the 3 primary germ layers: the ectoderm, mesoderm, and endoderm. During this process, a structure called the notochord is formed in the midline in the mesodermal layer; the notochord is critical in inducing neurulation. Neurulation is the process by which some of the ectoderm in the trilaminar embryo develops into the neural tube and neural crest cells, which will go on to form all of the neural tissue in the body. This process is completed by the end of the 3rd week.
The psychiatric assessment is the equivalent of a physical exam, tailored to evaluate a patient for psychiatric pathologies. While the psychiatric assessment has a mostly standardized approach, the interviewer can tailor it based on the presenting symptoms of the patient. The psychiatric assessment is designed to systematically assess for various features of psychiatric illnesses and involves both direct questioning and passive observation.
The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 â€œhipâ€ bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. The pelvic ring joints include the pubic symphysis anteriorly and the sacroiliac joints posteriorly. The hip bones are made up of 3 fused bones: the pubis, ischium, and ilium. The pelvic cavity houses various GI, urinary, and reproductive structures, which are supported by the muscles and connective tissue of the pelvic floor. The female pelvis, making accommodations for childbirth, is generally wider and larger than the male pelvis.
Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Pain symptoms are seen every day, by every physician, in every clinic and hospital in the world. Understanding pain physiology is the cornerstone to understanding how to treat it and to providing the individual with their first sigh of relief as definitive management is undertaken.
Veins transport deoxygenated blood and waste products from capillaries in the periphery back to the heart. Veins are capacitance vessels, meaning that they can stretch significantly, increasing the volume of fluid they can hold without significantly increasing their pressure. Veins respond to stimulation from the ANS, as arteries do, but to less of an extent. The effects of either venoconstriction or venodilation, however, impact venous capacitance. As veins constrict, capacitance goes down, forcing more blood back to the heart (i.e., increasing venous return), which in turn affects the amount of blood that can be pumped out of the heart on the next heartbeat. Thus, changes in venous capacitance can significantly affect cardiac output (CO). These effects can be plotted on graphs known as venous function curves.
The anterior abdominal wall is anatomically delineated as a hexagonal area defined superiorly by the xiphoid process, laterally by the midaxillary lines, and inferiorly by the pubic symphysis. From the superficial to deep order, the anterior abdominal wall consists of the skin, subcutaneous tissue, muscle, transversalis fascia, and peritoneum. The lateral abdominal muscles include the external and internal obliques and the transversus abdominis. Anterior abdominal muscles include the rectus abdominis and pyramidalis muscles. The abdominal wall is primarily supplied by epigastric arteries and innervated by thoracoabdominal nerves.
Liver function tests, also known as hepatic function panels, are one of the most commonly performed screening blood tests. Such tests are also used to detect, evaluate, and monitor acute and chronic liver diseases. Liver function tests assess the levels of various hepatic proteins and enzymes to determine the state of liver metabolic activity, homeostasis, bile metabolism, and protein synthesis capacity. The standard hepatic panel includes the levels of total protein, bilirubin, albumin, ALT, AST, AST/ALT ratio, and alkaline phosphatase (ALP).
The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. The bladder acts as a reservoir for urine until micturition is appropriate. Regulation of micturition relies on the CNS and the spinal cord.
The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. Saliva helps keep the oral mucosa lubricated, and it provides antimicrobial protection. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. There are also hundreds of minor salivary glands found in patches around the oral cavity.
The muscles of the neck can be divided into 3 groups: anterior, lateral, and posterior neck muscles. Each of the groups is subdivided according to function and the precise location of the muscles. The muscles of the neck are mainly responsible for the movements of the head (i.e., extension, flexion, lateral flexion-extension, and rotation), but the deep muscles also contribute to more intricate functions (i.e., speaking and swallowing).
Sickle cell disease (SCD) is a group of genetic disorders in which an abnormal Hb molecule (HbS) transforms RBCs into sickle-shaped cells, resulting in chronic anemia, vasoocclusive episodes, pain, and organ damage. Sickle cell trait, which is the heterozygous condition, is the only 1 of the group that is generally benign and rarely associated with serious SCD-like complications. Triggers such as stress and hypoxia can induce or worsen the sickling of RBCs. Individuals with SCD are susceptible to infection, infarction of various organs, and bone marrow aplasia; lung involvement in acute chest syndrome can be rapidly fatal. Sickle cells can usually be seen on the peripheral blood smear, but Hb electrophoresis is needed for diagnosis. The management of painful episodes consists of IV fluids and analgesics, and in severe episodes, exchange transfusions may be required. Survival is improved by vaccination against bacterial infections, prophylactic antibiotics, and aggressive treatment of infections.
The pentose phosphate pathway (also known as the hexose monophosphate (HMP) shunt)) is an important physiological process that can occur in 2 phases: oxidative and nonoxidative. The oxidative phase utilizes glucose-6-phosphate to produce nicotinamide adenine dinucleotide phosphate (NADPH) and ribulose-5-phosphate (which can be converted to ribose-5-phosphate). The nonoxidative phase is a collection of several reversible reactions in which the intermediates are connected to several other pathways, including nucleotide synthesis, aromatic amino acid synthesis, and glycolysis.
Congenital malformations or teratogenic birth defects are developmental disorders that arise before birth during the embryonic or fetal period. The rate of incidence for children born alive is approximately 3%. The cause may be genetic or contingent on external influences or teratogens. Teratogens are environmental factors that result in permanent structural or functional malformations, or the death of the embryo or fetus. Teratogens include infections, certain medications, drugs, and radiation.
The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. The prostate consists of multiple lobes and is made up of glandular and fibromuscular tissue. The glandular tissue has ducts that empty into the prostatic portion of the urethra, and the fibromuscular tissue encircles the urethra.
The inguinal region, or the groin, is located in the RLQ and LLQ of the anterior abdominal wall, bordered by the thigh inferiorly, the pubis medially, and the iliac crest superolaterally. The inguinal canal is a tubular structure that runs in a straight line from the anterior superior iliac spine to the pubic tubercle. The canal contains the spermatic cord in men and the round ligament in women. This region is clinically relevant, as it is the site for the most common type of hernias, such as indirect and direct inguinal hernias. Patients with hernias will present with a unilateral bulge in the groin that may be associated with pain. In symptomatic or high-risk cases, hernias can be repaired surgically.
The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels including the superior vena cava, inferior vena cava, pulmonary arteries, pulmonary veins, and aorta. The mediastinum extends from the upper thoracic aperture to the diaphragm and is bordered by the lungs.
The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. The thalamus consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. The thalamus is divided into anterior, medial, and lateral parts, each containing groups of nuclei that function as relay centers for sensory impulses and for the modulation of motor responses via interconnections with the basal ganglia.
The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. The brain stem contains many nerves, pathways, reflex centers, and nuclei and serves as a major relay station for sensory, motor, and autonomic information. All cranial nerves, except I and II, originate from the brain stem. The brain stem also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle.
Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall laterally by the suspensory ligament of the ovary and to the uterus medially by the utero-ovarian ligament. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes), which are expelled and then â€œcapturedâ€ by the uterine tubes. The primary blood supply to the ovary is provided by the ovarian artery, a direct branch of the abdominal aorta; the ovarian artery anastomoses with the ascending branch of the uterine artery, providing excellent collateral blood flow.
The cerebellum, Latin for "little brain", is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Three paired peduncles link the cerebellum to the brainstem and diencephalon. Much like the cerebral cortex, the cerebellum has a cortex of gray matter on the surface.
The heart is a 4-chambered muscular pump made primarily of cardiac muscle tissue. The heart is divided into 4 chambers: 2 upper chambers for receiving blood from the great vessels, known as the right and left atria, and 2 stronger lower chambers, known as the right and left ventricles, which pump blood throughout the body. Blood flows through the heart in 1 direction, moving from the right side of the heart, through the lungs, and then returning to the left side of the heart, where it is pumped out to the rest of the body. As blood moves through the heart, 4 important valves prevent backflow. The heart muscle itself is supplied by the coronary arteries. The heart also has its own conduction system, triggering its own rhythmic contractions.
Juvenile idiopathic arthritis (JIA), formerly known as juvenile rheumatoid arthritis, is a heterogeneous group of inflammatory diseases characterized by inflammation of 1 or more joints and is the most common pediatric rheumatic disease. Juvenile idiopathic arthritis is classified according to its clinical presentation, and diagnosis is made with examination findings as well as confirmatory lab testing showing evidence of inflammation and characteristic X-ray findings. Treatment is directed at preventing loss of function and controlling or limiting joint damage, with a variable prognosis depending on the type.
Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. These medications are used in the management of a wide range of diseases, most notably in the treatment of overactive bladder, irritable bowel syndrome, chronic obstructive pulmonary disease (COPD), and allergic rhinitis. Atropine specifically is used in emergency medicine in the advanced cardiac life support (ACLS) protocol for severe bradycardia and as an antidote to organophosphate poisoning with insecticides or chemical warfare agents. Atropine is also used in anesthesiology as an antisialagogue or to reverse neuromuscular blocking agents. The term â€œanticholinergicâ€ is often used to describe the adverse effects of drugs with anticholinergic properties (e.g., tricyclic antidepressants); these include dry mouth, constipation, blurred vision, and orthostatic hypotension.
Antiemetics are medications used to treat and/or prevent nausea and vomiting. These drugs act on different target receptors. The main classes include benzodiazepines, corticosteroids, atypical antipsychotics, cannabinoids, and antagonists of the following receptors: serotonin, dopamine, and muscarinic and neurokinin receptors. Anticholinergics and antihistamines are useful in the treatment of vestibular causes of nausea. Serotonin and neurokinin antagonists are effective in the management of chemotherapy-induced nausea and vomiting. Antiemetics should be used with caution, though, because of their adverse effects. Serotonin antagonists and some dopamine antagonists cause QT-interval prolongation. Dopamine antagonists are associated with extrapyramidal symptoms. Additionally, many agents cause sedation and have anticholinergic effects, which can aggravate underlying diseases.
The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. The cortex contains gyri that are separated by sulci. The cerebral cortex provides the neural substrate for the conscious experience of sensory stimuli.
The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. The interconnections between the bones, cartilage, and muscles allow for the rhythmic expansion and reduction of the chest wall during breathing, which facilitates changes in intrathoracic pressure to allow expansion of the lungs during inspiration. The extrinsic muscles have 2 bony attachments; the intrinsic muscles only attach to the thoracic skeleton.
Premenstrual dysphoric disorder (PMDD) refers to a group of mood, somatic, and behavioral symptoms that follow a cyclical pattern experienced by some women prior to menstruation. Unlike premenstrual syndrome (PMS), PMDD is characterized by significant distress and/or functional impairment. Diagnosis is made clinically with history and physical exam. Management is 2-fold: via lifestyle modification and pharmacotherapy with serotonin reuptake inhibitors or oral contraceptives.
Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. The components intricately synapse onto each other to promote or antagonize movement.
Nephritic syndrome is a broad category of glomerular diseases characterized by glomerular hematuria, variable loss of renal function, and hypertension. These features are in contrast to those of nephrotic syndrome, which includes glomerular diseases characterized by severe proteinuria, although there is sometimes overlap of > 1 glomerular disease in the same individual. The clinical presentations of nephritic syndrome are highly varied, from asymptomatic with urinary abnormalities to life-threatening critical illness. Diagnosis is suggested by hematuria, mild-to-moderate proteinuria, and certain serologies (e.g., ANCA); kidney biopsy is necessary in most cases. Management varies as widely as the clinical presentations, from watchful waiting in mild cases to immunosuppression and plasmapheresis in aggressive disease.
The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. The spinal cord is divided into cervical, thoracic, lumbar, and sacral regions, though because the spinal cord is shorter than the vertebral column, these regions do not line up with their corresponding vertebral levels. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Like the brain, the spinal cord is surrounded by 3 layers of connective tissue, collectively known as the meninges; these layers are the dura mater, arachnoid mater, and pia mater. The spinal cord is supplied by 1 anterior and 2 posterior spinal arteries.
Nephrotic syndrome is characterized by severe proteinuria, hypoalbuminemia, and peripheral edema. In contrast, the nephritic syndromes present with hematuria, variable loss of renal function, and hypertension, although there is sometimes overlap of > 1 glomerular disease in the same individual. The primary etiologies of nephrotic syndrome are minimal change disease, membranous nephropathy, and focal segmental glomerulosclerosis. The clinical presentation of nephrotic syndrome includes proteinuria (> 3.5 g/day), hypoalbuminemia (< 3 g/dL), and peripheral edema. Other frequently observed clinical findings are hyperlipidemia and thrombotic disease. Diagnosis is suggested by the clinical findings, and kidney biopsy is necessary in most cases. Management varies with the etiology and usually involves glucocorticoids or other immunosuppressant drugs.
Renal tubular acidosis (RTA) is an imbalance in physiologic pH caused by the kidneyâ€™s inability to acidify urine to maintain blood pH at physiologic levels. Renal tubular acidos3s exist in multiple types, including distal RTA (type 1), proximal RTA (type 2), and hyperkalemic RTA (type 4). Depending on the type of RTA, various mechanisms cause dysfunction of renal acidâ€“base handling, resulting in a nonâ€“anion-gap metabolic acidosis. All RTAs present clinically with some degree of metabolic acidosis; however, distal RTA and proximal RTA also have hypokalemia, while hyperkalemic RTA does not. Diagnosis is primarily through the history and laboratory analysis, including measurement of serum and urine anion gaps. Treatment involves the correction of chronic metabolic acidosis with alkali to prevent its long-term catabolic effects on bone and muscles, as well as addressing any underlying causes leading to the RTA.
Complex regional pain syndrome (CRPS) is a chronic regional neuropathic pain condition characterized by excruciating pain (out of proportion to apparent tissue damage or inciting trauma), paresthesia, allodynia, temperature abnormalities, skin discoloration, edema, reduced range of motion, and bone demineralization. This syndrome is most often associated with an inciting traumatic event (e.g., fracture, surgery, burn) and predominantly affects the limb(s). Diagnosis is clinical, but it is supported by imaging and electrodiagnostic testing. Treatment centers around multidisciplinary pain management and maintenance of function.
Distal radius fractures are one of the most common fractures encountered in practice and are often associated with falling onto an outstretched hand. These fractures are most frequently seen in older individuals, especially women. In this population, these fractures are related to an increase in falls due to gait instability with aging and associated osteoporosis. In younger individuals, distal radius fractures are usually related to high-energy trauma. Individuals often present with pain and a dinner fork deformity of the distal forearm. Diagnosis is clinical and confirmed with x-rays of the wrist. Treatment can be operative or nonoperative depending on the age of the individual, articular involvement, and degree of displacement or angulation.
Antiestrogens are medications decreasing the estrogenic effects in the body. The antiestrogens include selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), aromatase inhibitors, and several others, which include medications suppressing the gonadotropins or counteracting the effects of estrogen. Antiestrogens are most commonly used in the treatment of breast cancer but also treat precocious puberty, gynecomastia, anovulatory infertility, and several gynecologic complaints. Adverse effects include hot flashes, venous thromboembolic events, bone mineral density loss, and ischemic cardiovascular events. Antiestrogens are contraindicated in individuals with known hypersensitivity reactions and pregnancy.
Fetal growth restriction (FGR), also known as intrauterine fetal growth restriction (IUGR), is an estimated fetal weight (EFW) or abdominal circumference < 10th percentile for gestational age. The term small for gestational age (SGA) is sometimes erroneously used interchangeably with FGR. However, SGA refers to babies born with a birth weight < 10th percentile for gestational age. Defining FGR is challenging because each fetus has a different growth potential that may not be accounted for. The most commonly recognized classifications for FGR are symmetrical or asymmetrical. Symmetrical FGR occurs when all parts of the fetus are equally small and is typically the result of a complication early in pregnancy. Asymmetrical FGR occurs when there is disproportionately lagging growth in different body parts; most commonly, the fetus will have a normal size head and a small body. The causes of FGR can be broadly grouped into maternal, fetal, and placental. Fetal growth restriction is diagnosed by ultrasonography and confirmed by weight at birth. Management is often targeted to the underlying etiology, if known. Depending on the etiology, these fetuses may be at increased risk for complications such as preterm birth, intrauterine fetal death, and neurologic sequelae. Close surveillance and delivery planning by a skilled provider is crucial.
Breastfeeding is often the primary source of nutrition for the newborn. During pregnancy, hormonal stimulation causes the number and size of mammary glands in the breast to significantly increase. After delivery, prolactin stimulates milk production, while oxytocin stimulates milk expulsion through the lactiferous ducts, where it is sucked out through the nipple by the infant. Breastfeeding has many benefits for the mother and baby, including a decreased risk of infections, GI distress, and atopic disease for the infant; and a decreased risk of anemia, cardiovascular disease, and breast and ovarian cancer for the mother. True contraindications to breastfeeding exist but are quite rare. Important clinical conditions associated with breastfeeding include engorgement, mastitis, galactocele, breast abscess, and infant jaundice.
Fever is defined as a higher-than-normal body temperature. In modern medicine, fever is defined as a temperature > 38Â°C (100.4Â°F). It is a common symptom in the pediatric population as an isolated symptom or accompanied by other findings that can help narrow the differential diagnosis. Fever is most commonly the bodyâ€™s response to infectious processes; however, it can also be seen in other pathologic processes. In neonates and very young infants, the clinical presentation lacks specificity, so more diagnostic aids are deployed to rule out severe bacterial infection (SBI) and to begin treatment according to age and clinical evolution.
Neurosurgery is a specialized field focused on the surgical management of pathologies of the brain, spine, spinal cord, and peripheral nerves. General neurosurgery includes cases of trauma and emergencies. There are a number of specialized neurosurgical practices, including oncologic neurosurgery, spinal neurosurgery, and pediatric neurosurgery. Common neurosurgery cases treat tumors, masses, herniations, various types of hemorrhages, and radicular pain. Although neurosurgery is a surgical specialty, neurosurgeons must be very competent in neurology, critical care, trauma care, and radiology.
Instances of traumatic force applied to the chest are seen in 10% of the cases of pediatric trauma, usually in the context of motor vehicle accidents and falls. Chest trauma rarely occurs in isolation and is often associated with polytrauma. The 2 major mechanisms involve blunt and penetrating forces. Pneumothorax, hemothorax, flail chest, and lung contusions are the most common injuries. Treatment of affected children is very similar to that of adults, but unique pediatric pathoanatomy dictates important differences in approach and management.
Androgens are naturally occurring steroid hormones responsible for development and maintenance of the male sex characteristics, including penile, scrotal, and clitoral growth, development of sexual hair, deepening of the voice, and musculoskeletal growth. Androgens are primarily given to treat hypogonadism, gender dysphoria in transgender men, and low testosterone in older men (controversial). Antiandrogenic drugs decrease the effect of androgens. Classes include androgen receptor blockers, 5Î±-reductase inhibitors, and androgen synthesis inhibitors. Both men and women may use antiandrogens, which treat advanced prostate cancer, benign prostatic hyperplasia (BPH), alopecia, and hirsutism.
Tricyclic antidepressants (TCAs) are a class of medications used in the management of mood disorders, primarily depression. These agents, named after their 3-ring chemical structure, act via reuptake inhibition of neurotransmitters (particularly norepinephrine and serotonin) in the brain. In effect, there is an increased concentration of neurotransmitters in the synapse. Histaminic, muscarinic, and adrenergic receptors are also blocked, leading to a wide array of side effects. For decades, TCAs have been utilized for depression and are considered alternative antidepressant options to selective serotonin reuptake inhibitors (SSRIs). Full effects take a latent period of around 2â€“3 weeks. Overdose can lead to cardiac toxicity, seizures, and coma. Other uses include treatment for anxiety disorders, chronic pain syndrome, and nocturnal enuresis.
Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. General anesthesia is induced via the administration of gaseous or injectable agents before surgical procedures or other medical interventions. On the other end of the spectrum is local anesthesia, which is achieved via the use of topical agents or the local administration of injectable anesthetics to the area of concern. The use of anesthetics has been well documented in history, but the practice of modern anesthesiology only began by the end of the 18th century.
Pharmacological treatment of pulmonary hypertension (PH) (characterized by an elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure) includes various classes of drugs. These medications fall into the following drug categories: phosphodiesterase type-5 (PDE-5) inhibitors, soluble guanylate cyclase (sGC) stimulants, prostacyclin receptor agonists, endothelin receptor antagonists, and calcium channel blockers (CCBs). Via differing pathways, the overall effect of the medications is vascular smooth muscle relaxation and vasodilation resulting in a fall in pulmonary arterial pressure. Contraindications, adverse events, and drug interactions are dependent on the class of drugs.
Neuropathy is a nerve pathology presenting with sensory, motor, or autonomic impairment secondary to dysfunction of the affected nerve. The peripheral nerves (outside the brain and spinal cord), are derived from several plexuses, with the brachial and lumbosacral plexuses supplying the major innervation to the extremities. Mononeuropathy (affecting a single nerve) and plexopathy (affecting the plexus) can occur from trauma, compression, and systemic diseases. The clinical presentation varies according to location, type of nerves affected, and cause of the damage. Diagnosis requires a thorough physical examination, and diagnostic tests include laboratory tests, imaging and a confirmatory nerve conduction study, and electromyography. Management depends on the etiology but centers around physical therapy, supportive care, and treatment of underlying issues.
Brain aneurysms, also known as intracranial or cerebral aneurysms, are dilations of the arteries along points of weakness in the brain. The majority of the aneurysms are berry (saccular) in nature and located within the anterior circulation of the circle of Willis. Unruptured aneurysms are typically asymptomatic, unless the aneurysm compresses surrounding structures. The majority of these aneurysms are detected on rupture and presentation of a subarachnoid hemorrhage (SAH). Rarely, they may be detected incidentally on brain imaging done for other reasons. Diagnosing an aneurysm is done via imaging with CTA or MRA. Management depends on the size, risk of rupture, risk of intervention complications, and individual preference. This may include risk factor modifications, surveillance with serial imaging, and interventional measures (such as surgical clipping or endovascular coiling). Ruptured aneurysms carry a high morbidity and mortality rate.
Staphylococcus is a medically important genera of Gram-positive, aerobic cocci. These bacteria form clusters resembling grapes on culture plates. Staphylococci are ubiquitous for humans, and many strains compose the normal skin flora. Staphylococcus aureus is the most virulent species; S. epidermidis and S. saprophyticus are less virulent but are also clinically significant. Infection can cause a wide array of disease, including cellulitis, abscesses, endocarditis, osteomyelitis, and medical device infections. Toxins formed by S. aureus can cause gastroenteritis, SSSS, and toxic shock syndrome (TSS). Antibiotic management varies based on the type of infection, severity, and sensitivity data.
Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Chromosomal mutations occur when an abnormal number of chromosomes is inherited. Point mutations occur when a nucleotide is swapped for another nucleotide and can be missense, nonsense, or silent mutations. Frameshift mutations occur when a nucleotide is added or deleted, and expansion mutations occur when a given trinucleotide sequence is repeated along the chromosome. Genetic mutations are the basis for most inherited diseases. Common disorders caused by DNA mutations include sickle cell disease, Huntington disease, and Tay-Sachs disease.
Gregor Mendel (1822â€“1884), the "father of genetics", was an Augustine monk and mathematician who performed cross-breeding experiments with peas and beans from a monastery garden. Based on the experiments, Mendel deduced hereditary factors may be passed from the parental generation to the filial generation. From the deductions, the father of genetics formed Mendel's laws of heredity: the law of segregation, the law of independent assortment, and the law of dominance. Mendel's laws described the inheritance of uncoupled autosomal genes based on statistical predictions. The gene traits follow the laws of mendelian inheritance.
Transplantation is a procedure that involves the removal of an organ or living tissue and placing it into a different part of the body or into a different person. Organ transplantations have become the therapeutic option of choice for many individuals with end-stage organ failure. Transplantation can offer the individual a definitive treatment for a given disease entity. Over the past 50 years, organ transplantation has become established worldwide, with ever-improving results, conferring an immense benefit to hundreds of thousands of individuals. Both solid organs and bone marrowâ€“derived hematopoietic cells can be successfully transplanted for a number of different indications. Tolerance of the transplanted organ by the immune system of the host is achieved through the use of immunosuppressive and immunomodulating strategies. The main complications of transplantation are organ rejection or graft failure; however, chronic immunosuppression also carries the risk of serious complications, including potentially life-threatening infections.
The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. The epithelium is classified according to the cells (squamous, cuboidal, columnar), the number of layers, and other unique characteristics either due to function (transitional epithelium allowing distention) or appearance (pseudostratified epithelium giving a false impression of multiple layers). The surface epithelium has multiple functions, which include protection, secretion, filtration, and sensory reception.
The urogenital system is derived from intermediate mesoderm. The intermediate mesoderm differentiates into nephrogenic cords (which will go on to form the urinary system) and an adjacent area known as the gonadal ridge (which will go on to form the gonads). The nephrogenic cords elongate in a caudal direction and sequentially develop 3 different structures: the pronephros (rudimentary and nonfunctional), the mesonephros (forms the primitive urinary system), and the metanephros (forms the permanent kidney). Concurrently, the genital system develops in close association with the urinary system. Genital development depends on chromosomal sex, which determines whether the primitive gonads differentiate into testes or ovaries. The gonads then secrete certain hormones, which direct further development of both the internal and external genital structures.
The ANS is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ANS consists of the sympathetic and parasympathetic nervous systems. The efferent nerve fibers that terminate in the endocrine, vascular, and visceral structures coordinate the inner workings of the body in response to several afferent inputs. The sympathetic and parasympathetic neural circuits coordinate stress responses and relaxation responses, respectively. The enteric nervous system regulates visceral organ function. A balance between these systems results in homeostasis, whereas an imbalance leads to pathological conditions.
The neck is considered to be quadrangular. This shape is the basis to study various components of the neck and their relations. The boundaries of the quadrangular shape include the mandible, upper border of the clavicle, midline of the neck, and anterior margin of the trapezius. The quadrangular shape is divided into an anterior and posterior triangle by the sternocleidomastoid muscle (SCM). The anterior and posterior triangles are the 2 primary subdivisions and are delineated by easily recognized anatomic structures. Each triangle houses muscles, nerves, vasculature, lymphatics, and adipose tissue.
Second-generation antipsychotics (SGAs) are also called atypical antipsychotics. Medications in this class include aripiprazole, asenapine, brexpiprazole, cariprazine, clozapine, iloperidone, lumateperone, lurasidone, olanzapine, paliperidone, pimavanserin, quetiapine, risperidone, and ziprasidone. The SGAs act primarily by antagonizing dopamine (D2) and serotonin (5-hydroxytryptamine 2 (5-HT2)) receptors. Clinical indications include the treatment of schizophrenia, bipolar disorder, and treatment-resistant depression. In comparison to 1st-generation antipsychotics (FGAs), the SGAs cause fewer extrapyramidal symptoms but more metabolic adverse effects.
Immunosuppressants are a class of drugs widely used in the management of autoimmune conditions and organ transplant rejection. The general effect is dampening of the immune response. There are multiple targets in the immune system, as well as varied mechanisms in inhibiting inappropriate immune activity. Biologic agents are medications derived from living organisms that target particular components of the immune system. The targets can be tumor necrosis factor (TNF), interleukins (ILs), or B- or T-cell activity. Calcineurin inhibitors halt the activity of calcineurin, a phosphatase involved in T-cell activation. Corticosteroids interfere with the cell cycle of inflammatory cells and modify the activity of other immune components. mTOR inhibitors are proliferation signal inhibitors, reducing immune-cell proliferation. Some immunosuppressants, such as cytotoxic agents, have antineoplastic activity; these are used in rheumatoid arthritis, as prophylaxis for transplant rejection, and for malignant diseases.
Le Fort fractures are a group midface fracture patterns classified into 3 types: Le Fort I, II, and III. Le Fort fractures represent 10%–20% of all facial fractures and can be caused by any significant blunt trauma to the face, most commonly from motor vehicle accidents. Clinical presentation includes severe facial bleeding and edema and mobility of different bone segments, depending on the type in question. Diagnosis is clinical, supported by imaging techniques. Initial management centers around stabilization of the individual and control of bleeding. Definitive management is surgical. Long-term management concerns preservation and rehabilitation of facial function.
Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. Risk factors for infection include conditions or agents that may lead to an immunocompromised state, disruption of the normal flora, and/or disturbance of the mucosal barrier. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). The diagnosis is made by identifying Candida on KOH preparation, cultures, or tissue biopsy. Treatment depends on the extent and site of infection, and includes topical or systemic antifungal medications
Mendelian inheritance is defined as a pattern of segregation of genes, originating from any 1 of the parents, into gametes. Autosomal inheritance is a key component of Mendelian inheritance. Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. As such, autosomal diseases are inherited at equal rates among both genders. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited, whereas autosomal dominant diseases are expressed when only 1 copy of the dominant allele is inherited. Inborn errors of metabolism are classically autosomal recessive, whereas inherited structural abnormalities are classically inherited in an autosomal-dominant manner.
There are 2 types of sex chromosomes in humans: X and Y. Chromosomal sex is male when a Y chromosome is present (e.g., 46,XY or 47,XXY) and female when the Y chromosome is absent (e.g., 46,XX or 45,X0). Male phenotypes develop when a specific gene, called the SRY gene (usually found on the Y chromosome), is present, stimulating differentiation of the gonads into testes. The testes then produce testosterone (triggering development of the penis and scrotum externally and the ejaculatory system internally) and antimüllerian hormone (AMH), which causes regression of the müllerian ducts. Without the SRY gene, ovaries develop; without testosterone, external female genitalia develop; and without AMH, the müllerian ducts persist and differentiate into the fallopian tubes, uterus, and upper vagina.
The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. The skin is composed of surface epithelium, exocrine components, connective tissue, muscles, and nerves. The primary role of the skin is to serve as a protective barrier between the internal body and the external environment; it also protects the body from excessive fluid loss.
Before the developing blastocyst reaches the uterine wall, it needs to undergo several stages of differentiation. After a continuous process of cleavage and compaction, the morula gives rise to the trophoblast and embryoblast, which are the primary components of the blastocyst. Uterine fluid passes through the zona pellucida to form the blastocyst cavity. When the blastocyst reaches the endometrium, implantation begins by the trophoblast dividing into the cytotrophoblast and syncytiotrophoblast, with the syncytiotrophoblast primarily being responsible for invading the endometrium. The embryoblast divides into the epiblast and hypoblast, which are responsible for creating the amniotic cavity and yolk sac, respectively.
The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. The kidneys also play a major role in homeostatic processes, including electrolyte concentration, blood pressure, and acid–base regulation. Grossly, they consist of an outer cortex and inner medulla. Microscopic functional units known as nephrons filter the blood through a structure called the glomerulus, and this filtrate is then modified and concentrated as it moves through a complex tubular system. The renal arteries supply the kidneys via a central opening, known as the renal hilum, on its medial side; large renal veins empty directly into the vena cava.
Labor is defined as regular, effective uterine contractions resulting in cervical changes that culminate in expulsion of the fetus and products of conception. Complications may arise during childbirth that necessitate prompt recognition and management by the delivering team. Four important complications/topics related to the moments surrounding delivery include episiotomy and lacerations, operative vaginal deliveries (forceps and vacuum-assisted deliveries), shoulder dystocia, and amniotic fluid embolism.
Targeted therapy exerts antineoplastic activity against cancer cells by interfering with unique properties found in tumors or malignancies. The types of drugs can be small molecules, which are able to enter cells, or monoclonal antibodies, which have targets outside of or on the surface of cells. Among the areas in malignant cells that are blocked or inhibited by targeted therapy are signal pathways (as seen in protein kinase inhibitors), which lead to decreased proliferation and subsequent tumor cell apoptosis. Other means of reducing cancer cells is by eliminating the capacity for DNA repair (seen in poly(ADP-ribose) polymerase inhibitors), blocking the ligand-receptor binding (growth factor inhibitors), and increasing immune activity against the neoplasm (immunotherapies). These agents are used in multiple types of cancer and in combination with traditional chemotherapeutic agents.
Thrombolytics, also known as fibrinolytics, include recombinant tissue plasminogen activator (TPa) (i.e., alteplase, reteplase, and tenecteplase), urokinase, and streptokinase. The agents promote the breakdown of a blood clot by converting plasminogen to plasmin, which then degrades fibrin. Thrombolytics are particularly helpful for conditions related to vascular obstruction by a blood clot (e.g., acute STEMI, pulmonary embolism (PE), deep venous thrombosis (DVT), and acute ischemic stroke). Efficacy declines the longer tissue ischemia persists; therefore, timing of therapy is particularly important in myocardial infarction and stroke. Life-threatening bleeding and allergic reactions are potentially serious complications. Weighing the risks and benefits of thrombolytics and evaluating individuals for contraindications/bleeding risk before initiating therapy is important.
Gout medications include antiinflammatory and urate-lowering medications. Colchicine is an antiinflammatory medication that can be used for acute gout flares. The urate-lowering drug classes include the xanthine oxidase inhibitors, uricosuric agents, and uricases. These medications are beneficial for the prevention of gout exacerbations and work through a variety of mechanisms. Xanthine oxidase inhibitors are the most commonly used urate-lowering therapy; these work by inhibiting the enzyme necessary for the conversion of purines to uric acid. Uricosuric agents reduce reabsorption of uric acid by the proximal tubule, thereby increasing renal excretion. Lastly, the urases are recombinant enzymes that metabolize uric acid to allantoin. In addition to gout, urate-lowering treatment can also be used for other indications, such as the prevention of tumor lysis syndrome and uric acid nephrolithiasis.
Antihistamines are drugs that target histamine receptors, particularly H1 and H2 receptors. H1 antagonists are competitive and reversible inhibitors of H1 receptors. First-generation antihistamines cross the blood-brain barrier and can cause sedation. Additionally, with the ability to block muscarinic receptors, anticholinergic effects are also observed with this class of drugs. The 1st-generation H1 antagonists include chlorpheniramine, diphenhydramine, dimenhydrinate, and meclizine. Second-generation antihistamines generally do not cause drowsiness as these agents do not cross the blood-brain barrier. Examples of 2nd-generation antihistamines include loratadine, desloratadine, and cetirizine. Due to their antihistaminic activity, H1 antagonists are prescribed to treat allergy symptoms. Moreover, 1st-generation antihistamines are also used to treat motion sickness, nausea, and vomiting. H2 antagonists (blockers) target the H2 receptor, reducing gastric acid production and secretion. Thus, the general indications of H2 blockers include treatment of GERD and gastric and duodenal ulcers.
Peripheral nerve damage affecting the upper extremities is a common occupational injury and also occurs in individuals who participate in recreational sports. Injuries can affect the axillary, musculocutaneous, median, ulnar, or radial nerves. The most common causes of these injuries are overuse, compression or entrapment, or nerve trauma; degenerative or demyelinating disorders; radiation therapy; and mass lesions. Clinical presentation is with motor and/or sensory deficits. Diagnosis is made clinically and based on electrodiagnostic and imaging studies. Treatment in most cases is conservative, although surgical intervention may occasionally be necessary.
Brown-Séquard syndrome (BSS) is a rare neurologic injury that causes hemisection of the spinal cord, resulting in weakness and paralysis of one side of the body and sensory loss on the opposite side. This syndrome is most often due to trauma, but it may also occur with disc herniation, hematoma, or tumor. Clinical presentation is consistent with ipsilateral damage to the corticospinal tracts and posterior columns (weakness, loss of proprioception, and vibration sensation) below the level of the lesion, and contralateral anterior column symptoms owing to the unilateral involvement of the spinothalamic tract (loss of pain and temperature sensation). Diagnosis is confirmed with MRI. Management depends on the etiology and site of injury, and timely intervention is associated with a favorable prognosis and recovery.
The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force, and its contraction leads to flattening of the dome of the diaphragm. This flattening increases the volume of the thoracic cavity and allows the lungs to expand during inspiration.
The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival.
Membranoproliferative glomerulonephritis (MPGN) is also known as mesangiocapillary glomerulonephritis. Membranoproliferative glomerulonephritis is a pattern of glomerular injury characterized by mesangial hypercellularity, endocapillary proliferation, and thickening of the glomerular basement membrane (double contour formation). The changes are due to the deposition of Igs, complement factors, or both, in the glomerular mesangium and along the glomerular capillary walls. The pathogenic variants include immune complex/monoclonal Ig-mediated (e.g., from infections, autoimmune diseases) and complement-mediated MPGN. In rare cases, MPGN is not associated with Igs and the complement system, such as in the case of endothelial injury. With multiple etiologies, the presentation and clinical course vary. Presenting features can be asymptomatic proteinuria and hematuria, nephrotic syndrome, nephritic syndrome, or chronic renal failure. Definitive diagnosis requires renal biopsy, although additional laboratory and imaging tests may point to the associated disease. Treatment is based on the underlying cause. Steroids, immunosuppressants, and kidney transplantation are among the commonly used treatment modalities.
Anticonvulsant drugs are pharmacological agents used for seizure control and/or to prevent seizure episodes. Anticonvulsants encompass various drugs with different mechanisms of action, including ion-channel (Na+, calcium) blocking and inhibition of GABA reuptake. Second-generation anticonvulsants exert their effects via these mechanisms and are associated with good efficacy, fewer toxic effects, and better tolerability, and generally do not require blood level monitoring. Medications in this class include felbamate, gabapentin, pregabalin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, zonisamide, and lacosamide. Anticonvulsant drugs are indicated for focal seizures, generalized tonic-clonic seizures, myoclonic seizures, and Lennox-Gastaut syndrome. Some anticonvulsants are also indicated in conditions unrelated to seizures (e.g., bipolar disorder). The most common adverse effects include dizziness, headache, and somnolence.
Cell junctions are proteinaceous structures that physically hold 2 surfaces (cell-to-cell or cell-to-matrix) together. Cell junctions aid in communication and structural support and act as a barrier. They are classified as occluding (tight junctions), anchoring (adherens, desmosomes and hemidesmosomes), and communicating (gap junctions). Type II hypersensitivity has been noticed with autoantibody production against the components of anchoring junctions, resulting in pathology such as pemphigus vulgaris and bullous pemphigoid.
The vitreous body is a transparent, gelatinous substance that is present in the space between the lens and the retina, providing structural stability and maintaining the shape of the eye. Some conditions that can affect the vitreous body are posterior vitreous detachment, vitreous hemorrhage, synchysis scintillans, asteroid hyalosis, and persistent fetal vasculature. The conditions can be asymptomatic or present with floaters in the field of vision, photopsia, and decreased visual acuity. Funduscopy and slit-lamp microscopy are commonly used in the diagnosis of these diseases. Treatment methods depend on the condition and severity, but may include observation, vision correction, and surgery.
Intravenous anesthetics have been used in modern anesthesia practice since the 20th century. Modern anesthesia began with inhaled anesthetics; however, intravenous agents were adopted because injected or infused doses could be more closely controlled with little wasted medication. Several groups of agents are currently available (e.g., barbiturates, benzodiazepines, and dissociatives), but the most widely used are fentanyl, midazolam, and propofol.
Child and adolescent care is the area of healthcare dedicated to individuals who are beyond the immediate neonatal age through adulthood. These individuals do not present a uniform group, but are a series of patient populations, each with evolving healthcare needs (both preventive and pathologic) unique to them. Appropriate care aims to ensure optimal overall health to promote the physical, emotional, and social well-being of these often-challenging populations. Primary care physicians are usually responsible for child and adolescent care. Well-child visits are scheduled yearly for this purpose. These visits are an opportunity to obtain a detailed clinical history, monitor physiologic and psychologic development, assess growth parameters, and perform a thorough physical examination. Age-specific screenings, counseling, and vaccinations should also be completed at these times.
Phosphodiesterase (PDE) inhibitors are a group of drugs that act by inhibiting PDE enzymes. Phosphodiesterase inhibitors have various mechanisms of action depending on the subtype of PDE targeted, but their main action is increasing the amount of intracellular cAMP or cGMP, which in turn results in physiologic effects such as reducing inflammation, promoting smooth muscle relaxation, and vasodilation. Phosphodiesterase inhibitors are indicated in a wide variety of medical conditions, such as intermittent claudication, decompensated heart failure, chronic obstructive pulmonary disease, psoriasis, atopic dermatitis, erectile dysfunction, pulmonary artery hypertension, and benign prostatic hypertrophy. Contraindications, adverse effects, and warnings are category- and drug-dependent.
Antidepressants encompass several classes of medications and are used to treat individuals with depression, anxiety, and other psychiatric conditions, as well as to manage chronic pain and menopausal symptoms. Bupropion is an atypical antidepressant that acts by increasing neurotransmitter levels and alleviates the symptoms of depression. Brexanolone is a neurosteroid mainly used for the management of postpartum depression.
Monoamine oxidase inhibitors are a class of antidepressants that inhibit the activity of monoamine oxidase (MAO), thereby increasing the amount of monoamine neurotransmitters (particularly serotonin, norepinephrine, and dopamine). The increase of these neurotransmitters can help in alleviating the symptoms of depression. Selective inhibitors of MAO type B can also be used for the treatment of Parkinson disease. Other uses include for bulimia nervosa and panic disorder. The major adverse effects include serotonin syndrome and hypertensive crisis. Special care should be taken to avoid other serotonergic medications and tyramine-containing foods.
Cholinomimetic drugs, also known as parasympathomimetics or cholinergic agonists, increase acetylcholine (ACh), which acts on cholinergic muscarinic and nicotinic receptors. Other cholinomimetic drugs result in a net cholinergic effect by inhibiting the cholinesterase enzyme. Muscarinic receptors are found in the CNS and are part of the parasympathetic nervous system, which responds to cholinomimetics. Nicotinic receptors are found in the CNS at the neuromuscular junction. Physiologic effects on muscarinic receptors include bronchoconstriction, lacrimation, and bradycardia. Physiologic effects on nicotinic receptors include vasoconstriction, tachycardia, and elevated blood pressure. Cholinergic activation of muscarinic receptors on vascular endothelial cells cause an increase in nitric oxide, which diffuses to the adjacent vascular smooth muscle cells, resulting in smooth muscle relaxation/vasodilation and a paradoxical effect of the cholinomimetics on bronchial smooth muscle (constriction) and vascular smooth muscle (relaxation). Clinical uses of cholinomimetic agents include treatment of dementia, glaucoma, and as an aid for smoking cessation. The primary adverse effect of cholinergic drugs is overstimulation of the parasympathetic nervous system. Symptoms result from excessive levels of ACh in synapses, glands, smooth muscles, and motor endplates.
The testicles, also known as the testes or the male gonads, are a pair of egg-shaped glands suspended within the scrotum. The testicles have multiple layers: an outer tunica vaginalis, an intermediate tunica albuginea, and an innermost tunica vasculosa. The testicles are composed of testicular lobules (contain interstitial tissue) and seminiferous tubules (produce spermatozoa). Blood supply to the testicles is primarily provided by the testicular artery. Venous drainage is through testicular veins.
The breasts are found on the anterior thoracic wall and consist of mammary glands surrounded by connective tissue. The mammary glands are modified apocrine sweat glands that produce milk, which serves as nutrition for infants. Breasts are rudimentary and usually nonfunctioning in men. The shape and size of the breasts change during a womanâ€™s life and menstrual cycles. Breasts are supplied by the axillary, internal thoracic, and intercostal arteries, and they are innervated by branches of the cervical plexus.
The ear is a sensory organ responsible for the sense of hearing and balance. Anatomically, the ear can be divided into 3 parts: the outer ear, the middle ear, and the inner ear. The outer ear consists of the auricle and ear canal. The middle ear houses the tympanic structures and ossicles, which are responsible for the detection and initial transmission of sound. Finally, the inner ear contains the bony labyrinth, along with other structures essential for spatial orientation, hearing, and balance.
The auditory and vestibular pathways are anatomically related but discrete pathways that permit conscious perception of and reaction to sound and spatial orientation. Stimulation of specialized hair cells in the cochlea and vestibular apparatus excite and send signals through partitions of the vestibulocochlear nerve (CN VIII) to the brainstem, where they synapse on various targets, send and receive other projections, and ultimately contribute to spatial orientation and perception of sound.
Class 3 antiarrhythmics are drugs that block cardiac tissue K channels. The medications in this class include amiodarone, dronedarone, sotalol, ibutilide, dofetilide, and bretylium. The main mechanism of action includes blocking the cardiac K channels to prolong repolarization. However, some medications in this class also exert effects on Na channels, calcium channels, and adrenergic receptors. Indications vary among the medications, but include both atrial and ventricular arrhythmias. Because these medications prolong the QT interval, torsades de pointes is a potential complication of therapy.
Hematopoietic growth factors are a family of glycoproteins responsible for the proliferation and differentiation of hematopoietic progenitor cells in the bone marrow. Pharmacologic erythropoietin, thrombopoietin, granulocyte colony-stimulating factor (G-CSF), and granulocyte macrophage colony-stimulating factor (GM-CSF) are used in certain cases in which normal hematopoiesis is impaired owing to treatment (e.g., chemotherapy) or underlying disease (e.g., aplastic anemia). Commonly, erythropoiesis-stimulating agents (ESAs) are given as part of the treatment of chemotherapy-induced anemia and anemia secondary to CKD. G-CSF and GM-CSF are administered to treat chemotherapy-induced neutropenia. Thrombopoiesis-stimulating agents are used in the prevention or treatment of thrombocytopenia.
Non-insulinotropic diabetes medications are used to treat type 2 diabetes by methods other than increasing insulin secretion. This group of medications includes the biguanides, thiazolidinediones, alpha-glucosidase inhibitors, sodium–glucose transport protein 2 inhibitors, and amylin analogs. Mechanisms of action vary, but they can include increasing peripheral insulin sensitivity, reducing glucagon release, inhibiting gluconeogenesis, slowing glucose absorption, and increasing satiety. Metformin is the initial medication of choice; others may be used as an alternative monotherapy or as adjunctive therapy. Most of these medications are not associated with severe hypoglycemia, except for amylin analogs or when medications are used in conjunction with other hypoglycemic agents.
Antimetabolite chemotherapy agents belong to the cell-cycle–specific drugs, which act on a specific phase of the cell cycle. Cancer cells more rapidly divide (or cycle) than normal cells, making them an easy target for chemotherapy. The different cell-cycle phases include G1, S, G2, and M. Antimetabolites target the S phase, when DNA replication occurs, thus inhibiting DNA synthesis of tumor cells. In this group, the drugs include antifolates (which block folic acid activity, an essential component of DNA and RNA precursors), pyrimidine and purine analogs (which interfere with the process of DNA synthesis), and ribonucleotide reductase inhibitors (which reduce production of deoxyribonucleotides). Cell-cycle–specific chemotherapy drugs cannot differentiate healthy from cancerous cells, thus adverse effects are seen. Myelosuppression is a common finding during treatment.
Alkylating agents are cell cycle–independent antineoplastic drugs that work primarily by binding alkyl groups to various parts of DNA. The overall action produces cross-linking of DNA, leading to inhibition of DNA replication and DNA damage. The general effect is cancer (CA) cell death. The subgroups of drugs are nitrogen mustards, nitrosoureas, alkyl sulfonates, triazines, ethylenimines, and methylmelamines. Platinum coordination complexes belong to the group of alkylating agents by producing the same effect, but their mechanism is via formation of covalent metal adducts with DNA. Myelosuppression and toxicity to organ systems such as the kidneys, liver, and lungs are common adverse reactions.
Microtubule and topoisomerase inhibitors target cellular structures and processes to inhibit cancer cell proliferation. Microtubule inhibitors act on the cytoskeleton, while topoisomerase inhibitors act on an enzyme that is important in DNA replication and transcription. The microtubule system, along with microfilaments and intermediate filaments, form the cellular cytoskeleton. These components are essential for cell division, movement, and signaling. Taxanes and vinca alkaloids interfere with microtubule function, and thus in effect, inhibit mitosis. Topoisomerase assists DNA replication by creating double- and single-stranded breaks to relieve supercoils. Inhibiting the enzyme causes termination of DNA replication and DNA damage. There are multiple chemotherapeutic agents in each class that commonly produce myelosuppression as an adverse effect.
There are multiple different types of malignancies that can affect the vulva. The most common histologic type is squamous cell carcinoma (SCC), which accounts for approximately 75%–85% of all vulvar cancers. Other types include melanoma, basal cell carcinoma, sarcoma, malignancy of the Bartholin glands, and Paget disease of the vulva (an adenocarcinoma). Squamous cell carcinoma is typically associated with either high-risk HPV infection or lichen sclerosus. Vulvar cancer presents as vulvar lesions that can have a variety of appearances, which may include warty or nodular masses, scaly plaques, pigmented lesions, and ulcers; pruritus is also common. Diagnosis usually requires a biopsy, and management is primarily with surgical excision. Unfortunately, lymph node metastasis occurs early in the natural history of the disease and is associated with a poor prognosis.
Insulinotropic diabetes medications treat type 2 diabetes mellitus by increasing insulin secretion, which results in decreased glucose levels. The group of medications includes sulfonylureas, meglitinides, glucagon-like peptide-1 (GLP-1) receptor agonists, and DPP-4 inhibitors. The agents are usually used in combination with other therapies for diabetes management. Sulfonylureas and meglitinides are associated with weight gain, while GLP-1 agonists may provide the added benefit of weight loss. Other side effects vary between the drug classes. None of the medications should be used in the treatment of type 1 diabetes mellitus or diabetic ketoacidosis.
Labor is the normal physiologic process defined as uterine contractions resulting in dilatation and effacement of the cervix, which culminates in expulsion of the fetus and the products of conception. Labor has 3 stages: the 1st stage starts with the onset of regular contractions, the 2nd stage starts with full cervical dilation, and the 3rd stage starts immediately after fetal delivery and ends with delivery of the placenta. The primary factors required for labor to progress normally are the three Ps: power (uterine contractions), passenger (the fetus), and passage (the maternal pelvis). Labor may become abnormally protracted and require augmentation, usually with oxytocin, to prevent maternal and fetal complications.
Primary vaginal cancers are malignant tumors that originate from cells in the vagina. Squamous cell carcinoma (SCC) is by far the most common (80%–85%); other histologic types include adenocarcinomas, sarcomas (including sarcoma botryoides, typically seen in children), and melanomas. Vaginal SCC is most commonly associated with HPV infections, while clear cell adenocarcinomas are associated with in utero exposure to diethylstilbestrol (DES). Individuals typically present with vaginal bleeding and/or an irregular mass or lesion on exam; other symptoms may include abnormal discharge, pain, and urinary or defecatory symptoms. A biopsy is required for diagnosis. Staging is based on tumor size, extent of local invasion, and metastasis. Management may be surgical for stage I disease, but surgery is typically avoided in advanced disease, which is instead managed with radiation and chemotherapy.
Endometrial hyperplasia (EH) is the abnormal growth of the uterine endometrium. This abnormal growth may be due to estrogen stimulation or genetic mutations leading to uncontrolled proliferation. Endometrial carcinoma (EC) is the most common gynecologic malignancy in the developed world, and it has several histologic types. Endometrioid carcinoma (known as type 1 EC) typically develops from atypical endometrial hyperplasia, is hormonally responsive, and carries a favorable prognosis. Other histologic types are known as type 2 EC; they tend to present at more advanced stages, are not hormonally responsive, and carry a far worse prognosis. Women with both EH and EC tend to present with postmenopausal or irregular menstrual bleeding. Diagnosis is histologic. Management most often involves progestin therapy, surgery, and adjuvant radiation therapy (for advanced disease).
Spontaneous abortion, also known as miscarriage, is the loss of a pregnancy before 20 weeks' gestation. However, the layperson use of the term “abortion” is often intended to refer to induced termination of a pregnancy, whereas “miscarriage” is preferred for spontaneous loss. Most spontaneous abortions occur within the 1st 12 weeks of gestation and can be caused by several factors such as infection, trauma, and genetic and autoimmune causes. There are different types of spontaneous abortions, including threatened, inevitable, incomplete, complete, and missed abortions. Spontaneous abortions are diagnosed based on history, physical examination, and ultrasound findings. Management options include expectant, medical, or surgical therapy.
Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. There are several forms of insulin, and they differ in their time of onset, peak effect, and duration. Insulin can be classified as fast acting, short acting, intermediate acting, or long acting. A combination of classes can be used to maintain glucose control throughout the day. Common adverse effects include hypoglycemia, weight gain after initiation of an insulin regimen, and local injection site changes.
Multiple pregnancy, or multifetal gestation, is a pregnancy with more than 1 fetus. Multiple pregnancy with more than 2 fetuses is referred to as a higher-order multiple pregnancy and the most common type of multiple pregnancy is a twin pregnancy. Due to advanced maternal age and evolving assisted reproductive technology, the rates of multiple pregnancies have steadily increased over the past 3 decades. However, rates have slowly plateaued with the increase of the single embryo transfer. The perinatal mortality and morbidity rates of twin pregnancies are 3–7x higher than singleton pregnancies primarily because of higher rates of preterm delivery. Multiple pregnancies also carry a higher risk of obstetric complications such as congenital anomalies, preeclampsia, and gestational diabetes. Multiple pregnancies are classified as high-risk and require astute obstetric care.
Infant care is provided primarily by the child’s parents or other caregiver. A physician can greatly impact the quality of this care during the regularly scheduled outpatient visits, also known as well-child visits. During these visits, the physician has an opportunity to perform a comprehensive assessment of the child’s health, gauge caregivers’ apprehension about their role, and evaluate the overall growth environment of the child. Routine visits should be scheduled at regular intervals, with additional visits for acute concerns. The physician should conduct a history and physical examination; assess growth, development, and nutritional status; encourage administration of vaccinations; and provide anticipatory guidance and counseling to parents or caregivers, making sure to address any questions and concerns and to foster optimal development and support.
Ovarian cancer is a malignant tumor arising from the ovarian tissue and is classified according to the type of tissue from which it originates. The 3 major types of ovarian cancer are epithelial ovarian carcinomas (EOCs), ovarian germ cell tumors (OGCTs), and sex cord-stromal tumors (SCSTs). By far, EOCs are the most common, tend to present in postmenopausal women with advanced disease, and carry a poor prognosis. On the other hand, OGCTs and SCSTs frequently affect younger women, tend to present earlier, and carry a better prognosis. Affected individuals are frequently asymptomatic, although they may present with nonspecific symptoms such as fatigue, increasing abdominal girth, GI symptoms, and pelvic pain. Moreover, if the tumor secretes hormones, abnormal bleeding may be a presenting symptom. Diagnosis is suspected based on imaging studies and confirmed with histologic examination. Treatment is primarily surgical and often with adjuvant chemotherapy.
Geriatric care includes the prevention and diagnosis of diseases, as well as the management of diseases, disabilities, and other health concerns in individuals ≥ 65 years of age. Special consideration is given when addressing multiple aspects that are specific to aging. Preventive measures such as vaccinations as well as cancer and disease screening are essential in this age group because of the high risk for infections and developing cancer and chronic diseases. A majority of older individuals have at least 1 chronic medical condition, which increases the likelihood of polypharmacy and adverse drug reactions. Vision, hearing, cognitive function, gait, and balance are among the functions that decline in the geriatric population. These disease- and age-related factors affect the activities of daily living. Assessing the financial and social resources of the elderly is also important, given the direct impact of these factors on their health. A multidisciplinary approach involving various professionals in the healthcare field is important in achieving comprehensive care for the elderly.
Knee pain is a common presentation to primary care physicians. The diagnosis can be challenging as the pain may arise from the joint, surrounding tissues, or referred to the joint from distant structures. The differential diagnosis of knee pain is broad and categorizing the various diagnoses related to the timing (acute or chronic) is useful. A thorough understanding of pertinent anatomy, appropriate physical examination, and common problems of the knee joint are essential for diagnosis and proper management of knee pain. Exercise-based therapy is often the 1st-line management of many knee disorders, but surgical intervention is warranted for specific diagnoses.
There are several benign vulvar diseases, but some of the most common are Bartholin cyst and abscess, lichen sclerosus, and lichen simplex chronicus. Bartholin cysts are formed due to an obstruction in the excretory duct that causes retention of their secretions (lubricating mucus). Bartholin cysts present as nontender fluctuant masses at the 4 and/or 8 o'clock positions in the labia. If a Bartholin cyst becomes infected, it can develop into an extremely painful abscess. Lichen sclerosus is a chronic dermatologic condition that causes progressive thinning and fibrosis of the vulvar, perineal, and perianal skin, and presents classically with itching and white plaques. Lichen simplex chronicus is a thickening of the vulvar skin due to chronic itching or rubbing, which often occurs in the setting of atopic or contact dermatitis.
Hormonal contraceptives (HCs) contain synthetic analogs of the reproductive hormones estrogen and progesterone, which may be used either in combination or in progestin-only formulations for contraception. These formulations act synergistically to produce antiovulatory effects and can also affect the endometrial lining (typically decreasing bleeding and pain associated with menstruation), which is why they are also used to treat a variety of gynecologic issues. Available formulations include oral contraceptive pills (combined and progestin-only), transdermal patches, vaginal rings, progestin injections, subdermal implants, and intrauterine devices. Common adverse effects include nausea, headaches, mood changes, and irregular bleeding. Importantly, estrogens increase the risk of venous thromboembolism (VTE) and are contraindicated in individuals at risk for VTE. Other important contraindications include pregnancy, liver disease, and breast cancer.
Cannabinoids are a class of compounds interacting with cannabinoid receptors. The 3 types of cannabinoids are phytocannabinoids (naturally derived from flora), endocannabinoids (endogenous), and synthetic cannabinoids (artificially produced). Endocannabinoids are endogenous neuropeptide neurotransmitters found in the human nervous system. Cannabinoids have a psychotropic effect, which leads to frequent recreational use, but the unique effects of cannabinoids on the CNS also provide pharmacological indications. Prescription cannabinoids treat pain, nausea, vomiting, and seizure disorders and also serve as appetite stimulants.
Multitrauma occurs when 2 or more traumatic injuries occur in at least 2 areas of the body. A systematic management approach is necessary for individuals who have undergone trauma to maximize outcomes and reduce the risk of undiscovered injuries. Assessment of multitrauma starts with a primary survey followed by the A-B-C-D-E scheme, involving securing of the airway (A), and evaluating breathing (B), circulation (C), recognition of neurologic deficits or disability (D), and exposure to environmental control (E). Once the primary survey is completed, a secondary survey is performed to obtain pertinent history and nature of the trauma based on a thorough examination and diagnostic studies. The A-B-C-D-E approach is crucial for the overall stabilization, treatment, and identification of any missed injuries.
Cerebellar disorders are a specific set of neurologic signs and symptoms caused by local or systemic conditions that affect the cerebellum; the classic sign is ataxia, in addition to several other motor abnormalities that affect coordination. The causes of cerebellar disorders range from acute alcohol intoxication to inherited conditions. Clinical presentation is with incoordination of voluntary muscle movement, affected ocular movements, speech, gait, balance, and muscle tone. The diagnosis is initially made clinically and then followed by imaging studies to determine the etiology; management depends on the specific etiology.
Antitumor antibiotics, also known as antineoplastic antibiotics, are the product of soil microbes, Streptomyces bacteria. The commonly used types of antitumor antibiotics—bleomycin, dactinomycin, and anthracyclines—have a wide spectrum of activity against hematologic malignancies and solid tumors. Bleomycin differs from the rest of the drugs owing to its cell cycle–specific action during the G2 phase. Mechanisms of actions of these drugs include free radical damage to DNA, topoisomerase II inhibition, binding of DNA via intercalation, and alteration of cell membrane fluidity and transport of ions. Important adverse effects include cardiotoxicity (acute and chronic) and myelosuppression.
Vertigo is defined as the perceived sensation of rotational motion while remaining still. A very common complaint in primary care and the ER, vertigo is more frequently experienced by women and its prevalence increases with age. Vertigo is classified into peripheral or central based on its etiology. Vertigo is a clinical diagnosis, differentiated through history and physical examination findings, most notably nystagmus. Further testing may be required in malignant cases. Management depends on the etiology but certain maneuvers such as the Epley maneuver can be diagnostic and therapeutic.
Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Diagnostic evaluation relies on history, physical examination (including otoscopic and tuning fork examinations), and audiology testing. Management is directed toward the underlying cause of the hearing loss to choose the appropriate course of treatment.
Ménière disease is a condition characterized by episodes of vertigo, tinnitus, and hearing loss, likely caused by endolymphatic hydrops of the labyrinthine system in the inner ear. The risk factors include a family history of Ménière disease, preexisting autoimmune disorders, allergies, and trauma to the head or ear. A diagnosis is made clinically, by audiometry, by vestibular testing, and occasionally by imaging. Management can be by diet and lifestyle modification, vasodilators, diuretics, antihistamines, benzodiazepines, antiemetics, glucocorticoids, surgical intervention, or hearing aids.
Carpal tunnel syndrome (CTS) is a complex of signs and symptoms caused by compression of the median nerve as it crosses the carpal tunnel. Presentation is with pain and paresthesia of the dermatomal target tissues innervated by the median nerve as well as weakness and atrophy of the nerve's myotomal targets. Risk factors that cause a predisposition to CTS include obesity, female sex, pregnancy, diabetes, inflammatory conditions, genetic predisposition, and occupational factors. A clinical diagnosis may be made on the basis of history and physical examination and confirmed with electrodiagnostic testing. Conservative management includes splinting and physical therapy; more severe cases may require surgical correction.
Anticonvulsant drugs are pharmacological agents used to achieve seizure control and/or prevent seizure episodes. Anticonvulsants encompass various drugs with different mechanisms of action including ion-channel (Na+ and Ca+2) blocking and GABA reuptake inhibition. Phenobarbital, phenytoin, carbamazepine, valproic acid, and ethosuximide are the 1st-generation antiseizure drugs. Anticonvulsant drugs generally have complicated pharmacokinetics, multiple drug interactions, and narrow therapeutic ranges compared with new-generation drugs.
The brachial plexus is a network of nerves that originate from the lower cervical and upper thoracic nerve roots. The causes of brachial plexopathies include traumatic injuries, birth-related injuries, iatrogenic procedures, neoplastic processes, and previous treatment with radiation. Patients present with sensory and motor deficits related to the site of the lesion and the nerves involved. Diagnosis is made based on clinical findings, imaging, and electrodiagnostic studies. Treatment is related to the underlying cause and may be medical or surgical.
The term “persistent vegetative state,” also called unresponsive wakefulness, describes the condition of individuals with severe anoxic brain injury who have progressed to a state of wakefulness without any meaningful response to their environment. A persistent vegetative state is distinguished from a coma in that individuals in a persistent vegetative state have intermittent sleep–wake cycles. The individual's eyes may be open and there may be some yawning, grunting, or other vocalizations. In both cases, the individual is alive, but the brain does not function fully. Persistent vegetative state is most commonly associated with anoxic brain injury due to cardiac arrest, trauma, metabolic causes, or infections. Diagnosis is made by fulfilling specific diagnostic criteria. Treatment is controversial and ethically challenging. Recovery of consciousness from a posttraumatic persistent vegetative state is unlikely after 12 months, while recovery from a nontraumatic persistent vegetative state after 3 months is exceedingly rare.
Guillain-Barré syndrome (GBS), once thought to be a single disease process, is a family of immune-mediated polyneuropathies that occur after infections (e.g., with Campylobacter jejuni). Typical GBS is characterized by acute monophasic neuromuscular paralysis, which is symmetric and ascending in progression. If the paralysis reaches the respiratory muscles, GBS can progress into respiratory failure, which requires prolonged hospitalization. Management is mostly supportive and may require either plasma exchange or IV immunoglobulin.
Trigeminal neuralgia (TN) is an often chronic and recurring pain syndrome involving the sensory distribution of the trigeminal nerve (cranial nerve (CN) V). The pain is typically unilateral and described as an acute, sharp, electric-shock–like pain involving the maxillary or mandibular areas and often associated with spasm of facial muscles. Trigeminal neuralgia occurs in multiple, short-acting episodes. Most cases are usually due to vascular compression of the trigeminal nerve, although secondary causes can be from aneurysms, neuromas, or other neurologic disorders. A detailed history is the hallmark for diagnosis. Neuroimaging with MRI is useful to determine the exact pathology involving the trigeminal nerve root. The 1st line of therapy is pharmacologic (carbamazepine). Other treatment options include botulinum toxin injections or surgical procedures in refractory cases.
Antiadrenergic agents are drugs that block the activity of catecholamines, primarily norepinephrine (NE). There are 2 major types of adrenergic receptors–alpha and beta receptors—and there are several subtypes of each. Antiadrenergic drugs can be classified according to their specificity for the different receptors, with the major classes including selective beta-1 receptor blockers, nonselective beta-blockers, mixed alpha- and beta-blockers, selective alpha-1 receptor blockers, and nonselective alpha-blockers. There are many beta receptors in the heart, so these medications are primarily used for cardiac indications, including MI, angina, heart failure (HF) (stable), and hypertension (as an alternative agent). Alpha receptors are prominent in smooth muscle, especially in the vasculature. Alpha-blockers cause significant vasodilation and are indicated in hypertension and benign prostatic hyperplasia (BPH). Significant adverse effects are possible.
Dystonia is a hyperkinetic movement disorder characterized by the involuntary contraction of muscles, resulting in abnormal postures or twisting and repetitive movements. Dystonia can present in various ways as may affect many different skeletal muscle groups. Dystonia may be inherited, acquired, or idiopathic. The diagnosis is made clinically, and genetic testing is recommended in individuals with a family history of dystonia. Management is with botulinum toxin or other drugs that target the various neurotransmitters involved in the pathogenesis of dystonia.
Posterior cord syndrome (PCS) is an incomplete spinal cord syndrome affecting the dorsal columns, the corticospinal tracts (CSTs), and descending autonomic tracts to the bladder. Posterior cord syndrome is rare but has a diverse range of etiologies, including demyelinating disorders, degenerative spinal conditions, neoplastic causes, vascular abnormalities, and hereditary neurodegenerative disorders. Clinical symptoms include gait ataxia, paresthesias with loss of position and vibration sense, and urinary incontinence. The diagnosis is made clinically and with neuroimaging. Management addresses treatment of the underlying cause.
Ataxia-telangiectasia, also known as Louis-Bar syndrome, is a neurocutaneous syndrome, which involves multiple systems but mainly affects the neurological system. Ataxia-telangiectasia is an autosomal recessive genetic disorder caused by a mutation in the ATM gene (ATM serine/threonine kinase or the ataxia-telangiectasia mutated gene). Ataxia-telangiectasia presents with progressive ataxia, telangiectasias, extrapyramidal symptoms, dermatological manifestations, immune dysfunction, and progressive pulmonary disease. Diagnosis is based on clinical presentation and confirmed with neuroimaging and genetic testing. Management is supportive with symptom management. Prognosis is poor secondary to numerous complications.
Sympathomimetic drugs, also known as adrenergic agonists, mimic the action of the stimulators (α, β, or dopamine receptors) of the sympathetic autonomic nervous system. Sympathomimetic drugs are classified based on the type of receptors the drugs act on (some agents act on several receptors but 1 is predominate). Clinical uses of sympathomimetics include the treatment of hypotension, asthma, and anaphylaxis. The primary drugs used as IV vasopressors in the hospital are dopamine and norepinephrine. Dobutamine is given IV as an inotrope. Albuterol is used via nebulizer or metered-dose inhaler for asthma. Sympathomimetics may produce a wide range of adverse effects, which generally resemble excessive stimulation of the sympathetic nervous system. The effects may include palpitations, tachycardia, and/or arrhythmias due to stimulation of cardiac β receptors.
Neurofibromatosis type 2 is a neurocutaneous disorder that can arise from mutations in the NF2 gene located in chromosome 22 and may be inherited in an autosomal dominant fashion or occur from de novo mutations. The main clinical features are bilateral vestibular schwannomas, intracranial/spinal meningioma, and intramedullary and extramedullary spinal tumors. Other features can include eye lesions such as cataracts, skin lesions, and peripheral neuropathy. Diagnosis is made clinically from history and examination and confirmed with MRI, molecular testing, and histopathology. Tumor surveillance and follow-up with screening of at-risk family members is recommended. Management includes surgical interventions, radiation therapy, and/or monoclonal antibody therapy with bevacizumab.
Stimulants are used by the general public to increase alertness and energy, decrease fatigue, and promote mental focus. Stimulants have medical uses for individuals with ADHD and sleep disorders, and are also used in combination with analgesics in pain management. Stimulants are used in beverages and as over-the-counter medications, prescription medications, and drugs of abuse. Caffeine and nicotine are commonly used psychostimulants. Amphetamines are used in a clinical setting for specific indications, but are more often used illegally as drugs of abuse along with cocaine. Each agent has its idiosyncrasies with respect to effects, withdrawal, and overdose.
Neurofibromatosis type 1 (NF1), also known as phakomatosis, is a neurocutaneous disorder that is most commonly of autosomal dominant inheritance due to mutations in the NF1 gene. Neurofibromatosis type 1 presents a range of clinical manifestations with the most prominent features being various pigmented skin lesions called café au lait macules (CALMs), benign nerve-sheath tumors called neurofibromas, freckling of the inguinal and axillary regions, and iris hamartomas, referred to as Lisch nodules. At least half of the individuals with NF1 have learning disabilities. Neurofibromatosis type 1 may also cause osteodysplasia and malignant transformation of tumors. The diagnosis is based on the typical clinical presentation and can be confirmed with genetic testing. Management depends on the clinical presentation and may vary from surgical removal to chemotherapy/radiotherapy for tumors, occupational therapy and PT for motor impairments, treatment with growth hormone, and bracing in the case of bone abnormalities.
Inhaled anesthetics are chemical compounds, which can induce and maintain general anesthesia when delivered by inhalation. Inhaled anesthetics can be divided into 2 groups: volatile anesthetics and gases. Volatile anesthetics include halothane, isoflurane, desflurane, and sevoflurane. Nitrous oxide (N2O) is the most common of the anesthetic gases; cyclopropane and xenon are less commonly used. While the exact mechanism of action of the inhaled anesthetics is unknown, the drugs are believed to have variable effects on GABA, glycine, glutamate, and NMDA receptors in the CNS. Inhaled anesthetics have been used for medical purposes for the last 200 years.
Idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri, is a clinical disorder that presents with symptoms due to increased intracranial pressure (ICP; ≥ 20 mm Hg) or CSF pressure (> 250 mm H2O), with no structural changes or other attributable causes. The condition is most commonly observed in obese women and after intake of certain drugs, such as growth hormones, tetracycline antibiotics, and high dosages of vitamin A. Classic manifestations include headache, vision loss or visual-field defects, and papilledema. Diagnosis is made by clinical exam, imaging, and lumbar puncture. Management is aimed at decreasing ICP and includes medication, therapeutic CSF removal, and shunting.
Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope is not a distinct disease entity; rather, it is a symptom of another pathologic process, whether it be transient or a more established disease process. Syncope may be accompanied by other symptoms, such as light-headedness, sweating, palpitations, nausea, feeling warm or cold, and visual blurring. Workup includes a detailed history and physical examination, electrocardiography, echocardiography, provocative testing (tilt-table test), or imaging of the suspected culprit vasculature. In many cases, a definite etiology is not found. Management is based on the underlying cause and can include physical countermaneuvers, stopping offending drugs, volume resuscitation, blood transfusion, and/or cardiac or vascular interventions.
Anthelmintic drugs are used to treat infections caused by parasitic helminths. Helminths include both flatworms (flukes and tapeworms) and roundworms. Anthelmintic medications are categorized on the basis of the class of helminths they are used for. Nematicidal agents include the benzimidazoles (albendazole, mebendazole, and triclabendazole), diethylcarbamazine, ivermectin, and pyrantel pamoate. Praziquantel is a trematocidal and cestodicidal agent. The mechanisms of action of the anthelmintic drugs vary, but many work by disrupting the normal function of the organism, inducing paralysis, and/or causing death. Most of these drugs are well absorbed, which can allow for treatment of systemic infections. Pyrantel pamoate, on the other hand, is poorly absorbed and is better suited to treating luminal nematodes. The benzimidazoles’ absorption is changed by the presence of food, which allows for some control in treating luminal or invasive infections (such as cysticercosis). Adverse effects of anthelmintics vary, but all classes of these drugs are associated with GI side effects.
Amebicides are drugs toxic to amoebas such as Entamoeba histolytica (the causative organism of amebiasis). Parasites enter the GI tract where trophozoites can penetrate the intestinal wall and cause an invasive infection. Amebicides are classified based on where the drug is most effective: intestinal lumen or tissues. Intestinal-lumen amebicides include iodoquinol and paromomycin. Tissue amebicides include the nitroimidazole drug class (e.g., metronidazole, tinidazole). Treatment of symptomatic disease usually requires a combination of both classes.
Antiresorptive drugs are used to treat osteoporosis. Bisphosphonates are generally used as 1st-line therapy, but other options are available for individuals who fail or cannot tolerate therapy. The drug classes include exogenous hormone therapy (teriparatide, calcitonin, estrogen, and vitamin D), selective estrogen receptor modulators, and RANKL inhibitors. Most of these drugs inhibit osteoclast activity to decrease bone resorption. A notable exception is teriparatide, which stimulates osteoblast activity to promote bone formation. Adverse effects vary greatly among drug classes.
Antiviral agents against human herpesviruses (HHVs) include acyclovir, cidofovir, and foscarnet. Human herpesviruses are DNA viruses in the Herpesviridae family. Herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), and HHV-8 belong to the Herpesviridae family. Antivirals against the group generally act via inhibition of DNA polymerase. Acyclovir (the prototypical nucleoside analog) requires viral kinase for phosphorylation to become a triphosphate, which is incorporated in viral DNA. Cidofovir requires phosphorylation by host cellular kinase, which allows cidofovir to have activity against mutated viruses and become deficient in viral kinase. Foscarnet (a pyrophosphate analog) does not require phosphorylation. Nephrotoxicity is a shared adverse effect in the agents. Acyclovir can also cause obstructive crystalline nephropathy and foscarnet carries a risk of electrolyte abnormalities and seizures. The nephrotoxic effect of cidofovir can be reduced with IV saline and probenecid.
Normal intracranial pressure (ICP) is defined as < 15 mm Hg, whereas pathologically increased ICP is any pressure ≥ 20 mm Hg. Increased ICP may result from several etiologies, including trauma, intracranial hemorrhage, mass lesions, cerebral edema, increased CSF production, and decreased CSF absorption. Increased ICP can lead to brain herniation and death if not treated promptly. Clinical presentation includes headache, drowsiness or altered level of consciousness, and papilledema. Diagnosis is suspected based on the clinical presentation and confirmed with urgent brain imaging. Immediate management includes measures to decrease ICP, medications including diuretics, and surgery.
Glandular epithelia, composed of epithelial tissue, are specialized structures that play a role in the production and release of enzymes, hormones, sweat, oil, and mucus in organisms. The secretion and release of these substances are prompted by either external or internal stimuli. Products of glandular epithelia are released either into ducts leading to the surface of the epithelium or into the blood. The 2 types of glands are exocrine and endocrine glands. The classification is based on the number and location of secreting cells and the type of secretions, among other factors.
Antivirals for hepatitis B include the nucleoside/nucleotide analogs, also known as nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs). Because of their similar chemical structure to nucleosides and nucleotides, NRTIs are able to integrate into viral DNA during the replication process. This process inhibits the function of viral RNA-dependent DNA polymerase, resulting in chain termination. All of these medications are administered orally and are excreted by the kidneys. Indications include chronic hepatitis B infection, and some (such as lamivudine) are also used for HIV. Adverse effects include GI symptoms, evidence of mitochondrial toxicity (such as lactic acidosis), and rebound infection upon discontinuation.
Intracerebral hemorrhage (ICH) refers to a spontaneous or traumatic bleed into the brain parenchyma and is the 2nd-most common cause of cerebrovascular accidents (CVAs), commonly known as stroke, after ischemic CVAs. Trauma, hypertension, vasculopathy, vascular malformations, tumors, coagulopathy, and hemorrhagic conversion of ischemic stroke may all be causative factors. Clinical presentation may vary depending on the size and location of the hemorrhage and may range from headache, neurologic signs and symptoms, and altered level of consciousness to coma. Treatment includes stabilization, stopping or reversing of anticoagulation, blood pressure control, monitoring in a neurologic ICU, and possible neurosurgical intervention. Intracerebral hemorrhage is associated with significant morbidity and mortality.
Diarrheagenic Escherichia coli is a strain of pathogenic bacteria that can cause intestinal infection. Transmission is often through the fecal–oral route via the consumption of contaminated food or water. Pathogenesis varies based on the strain, but it can include toxin production, invasion of the mucosal surface, and adhesion with alteration of enterocyte structure. Noninvasive disease tends to present with watery diarrhea, while invasive infections cause bloody diarrhea. The diagnosis can be established with PCR. Management generally consists of supportive therapy (fluids and electrolytes). Antibiotics are reserved for severe or persistent infections and are contraindicated with enterohemorrhagic E. coli because of the risk of hemolytic uremic syndrome.
Bone, while seemingly inert, is an active, growing, and changing part of the human body, in addition to being the body's primary calcium reservoir. In the correct homeostatic conditions, bone can remodel in response to damage, stress, or hormonal signaling (parathyroid hormone and calcitonin). Osteocytes located deep in the bone sense damage and signal bone-lining cells that will begin the process of remodeling. This process is vital not only for damage repair but also to adapt to a new environment and conditions.
Intravenous fluids (IVFs) are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Crystalloids and colloids have different general compositions, which affect distributions through the body’s fluid compartments and guide clinical use. Crystalloid solutions are typically used for patients who are hypovolemic, dehydrated, or have ongoing fluid losses. Colloidal solutions may be used in cases of low oncotic pressure. Providers should choose fluid types based on the clinical scenario and best available evidence. All recipients of IVFs should be closely monitored to determine the goal and status of the fluid therapy.
Epidural hemorrhage (EDH) is an event characterized by bleeding into the epidural space between the dural layers of the meninges and the skull. The primary mechanism triggering bleeding is trauma (i.e., closed head injury), which causes arterial injury, most commonly middle meningeal artery injury. Epidural hemorrhage presents acutely, usually immediately (seconds to hours) following head trauma, with an altered level of consciousness that may span from a momentary loss of consciousness to coma. Diagnosis is based on clinical suspicion following head trauma and is confirmed with neuroimaging (i.e., noncontrast head CT). Management includes stabilization, stopping (possibly, the reversal) of all anticoagulants, monitoring in a neurologic ICU, and neurosurgical intervention.
To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. An ectopic pregnancy occurs if the zygote does not reach the uterus before the zona pellucida degrades.
Subdural hemorrhage (SDH) is bleeding into the space between the dural and arachnoid meningeal layers surrounding the brain. The most common mechanism triggering the bleeding event is trauma (e.g., closed head injury) causing a tearing injury to the extracerebral “bridging” veins, but rupture of small arteries within this space or intracranial hypotension may also be causative. Acute SDH presents, immediately following head trauma, with an altered level of consciousness that may span from a momentary loss of consciousness to coma, which makes it a potentially life-threatening condition. Chronic SDH may also occur, presenting with a more gradual neurologic deterioration. Diagnosis is based on clinical suspicion following head trauma and confirmed with neuroimaging (e.g., noncontrast head CT). Management includes stabilization, stopping (possibly reversing) all anticoagulants, monitoring in a neurologic ICU, and neurosurgical intervention.
Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. The basic pathophysiology of all etiologies of hyponatremia is an abnormal increase in total body water (TBW), which dilutes the total body sodium (TBNa+) concentration. The clinical presentation varies greatly, from asymptomatic to subtle cognitive deficits, seizures, and death. Management is guided by etiology, acuity, and duration of symptoms, usually involving oral fluid restriction or administration of IV fluids that contain Na. Sodium must be replaced slowly, as overly rapid correction of hyponatremia can lead to irreversible neurologic complications and death, known as the osmotic demyelination syndrome (ODS).
Rapidly progressive glomerulonephritis (RPGN) is a syndrome of severe glomerular disease with progressive loss of kidney function within weeks to months. Rapidly progressive glomerulonephritis is associated with nephrotic syndrome and is a manifestation of different diseases. Histologically, crescents (the proliferation of epithelial cells and the infiltration of monocytes/macrophages in the Bowman space) are found in the glomeruli and arise from immunologic injury. The major mechanisms of immunologic injury are classified into anti-glomerular basement membrane (anti-GBM) disease, pauci-immune crescentic glomerulonephritis, and immune complex-mediated injury. Rapidly progressive glomerulonephritis can manifest with hematuria, proteinuria, and varying degrees of edema and hypertension. Diagnosis is by presentation, laboratory tests, imaging, and renal biopsy. Prompt treatment is essential because RPGN can develop into end-stage renal disease within a short period of time. Modalities include corticosteroids, cyclophosphamide or other immunosuppressants, and plasmapheresis (depending on the underlying disease).
Subarachnoid hemorrhage (SAH) is a type of cerebrovascular accident (stroke) resulting from intracranial hemorrhage into the subarachnoid space between the arachnoid and the pia mater layers of the meninges surrounding the brain. Most SAHs originate from a saccular aneurysm in the circle of Willis but may also occur as a result of trauma, uncontrolled hypertension, vasculitis, anticoagulant use, or stimulant use. The most classic symptom is a sudden-onset (thunderclap) headache along with neck stiffness, vomiting, a decreased level of consciousness, and seizure. As with any stroke, focal neurologic deficits are commonly present, and rapid neurologic deterioration may ensue without prompt diagnosis and intervention. An SAH should be suspected in any person presenting with thunderclap headache and neurologic symptoms, and the diagnosis can be confirmed with neuroimaging or lumbar puncture (LP). Treatment consists of reversal of anticoagulation, control of blood pressure, and neurosurgical intervention to contain the bleed and/or relieve elevated intracranial pressure (ICP). Even with prompt neurosurgical intervention, SAH carries a high mortality rate.
Gametogenesis is the development of gametes from primordial germ cells. This process differs between the sexes. In males, spermatogenesis produces spermatozoa. In females, oogenesis results in an ovum. The process starts with the migration of primordial germ cells from the yolk sac to the gonadal ridge. Oogenesis starts during the embryonic and fetal periods, whereas spermatogenesis starts at puberty. However, the phases of gametogenesis are similar, with germ cells progressing through mitosis, meiosis I, meiosis II, and maturation. This process results in gametes that are haploid, with 23 chromosomes.
Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. The major cellular response involves neutrophils and macrophages to phagocytose and lyse the injurious organism or repair necrosed tissue after injury. Inflammation can be pathologic if it is prolonged or when normal processes create an excessive response (such as with atherosclerosis). There are multiple mediators of inflammation that overlap with innate immunity when they respond to injurious stimuli. Inflammation can become chronic, resulting in the formation of granulomas, tissue damage, and the loss of organ function.
Paraneoplastic syndromes are a heterogeneous group of disorders caused by an abnormal immune response to a neoplasm. The substances produced are not due to the direct effect of the tumor, such as metastasis, mass effect, or invasion. Antibodies, hormones, cytokines, and other substances are generated and affect multiple organ systems. About 10% of cases of cancer are affected by paraneoplastic syndromes. The common cancers that present with paraneoplastic syndromes include cancer of the lung, breast, ovaries, kidney, liver, and stomach and lymphomas.
The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th‒11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. The spleen can also activate immune responses, produce antibodies, and function as a reservoir for platelet storage. There are 2 primary types of splenic tissue: red pulp, which contains dense fibrovascular networks for filtering the blood, and white pulp, which is primarily made up of lymphoid tissue surrounding the larger vessels. The spleen has a relatively weak capsule; thus, it can rupture more easily than other abdominal organs and lead to life-threatening hemorrhage.
Portal hypertension is increased pressure in the portal venous system. This increased pressure can lead to splanchnic vasodilation, collateral blood flow through portosystemic anastomoses, and increased hydrostatic pressure. There are a number of etiologies, including cirrhosis, right-sided congestive heart failure, schistosomiasis, portal vein thrombosis, hepatitis, and Budd-Chiari syndrome. Most individuals are asymptomatic until complications arise, including esophageal varices, portal hypertensive gastropathy, ascites, and hypersplenism. The diagnosis is clinical, but it can be supported by ultrasound findings (and hepatic venous pressure gradient measurement in unclear cases). Management requires treating the underlying etiology and managing the complications. This can include nonselective beta blockers to prevent bleeding from varices, diuretics and sodium restriction for ascites, and transjugular intrahepatic portosystemic shunt for refractory complications.
Cystoisospora and Cyclospora are genera within the Coccidia subclass of protozoans. These single-celled, obligate intracellular parasites cause intestinal infections in humans. Humans are the only host for these species, and they are both transmitted through the fecal–oral route. The symptoms of cystoisosporiasis and cyclosporiasis are watery diarrhea, abdominal pain, and fever. Severe cystoisosporiasis can occur in immunocompromised individuals, particularly those with HIV/AIDS, and can lead to malabsorption, weight loss, and dehydration. Both diseases are self-limited in immunocompetent individuals, though cyclosporiasis has a longer course. Diagnosis is made by identifying the oocysts in stool samples. Antimicrobial therapy, such as trimethoprim–sulfamethoxazole, can be used (particularly in immunocompromised individuals).
The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). The peritoneum supports and suspends the organs within the abdominal cavity and provides an important conduit for the neurovasculature supplying these organs. There are several peritoneal folds, known as mesenteries, omenta, and ligaments. The greater and lesser omenta divide the peritoneal cavity into greater and lesser sacs, which are important anatomic spaces within the cavity. Organs located behind the posterior parietal peritoneum are known as retroperitoneal, while organs that protrude into the cavity and are fully covered by visceral peritoneum are known as intraperitoneal.
Hepatitis C is an infection of the liver caused by the hepatitis C virus (HCV). Hepatitis C virus is an RNA virus and a member of the genus Hepacivirus and the family Flaviviridae. The infection can be transmitted through infectious blood or body fluids and may be transmitted during childbirth or through IV drug use or sexual intercourse. Hepatitis C virus can cause both acute and chronic hepatitis, ranging from a mild to a serious, lifelong illness including liver cirrhosis and hepatocellular carcinoma (HCC). Hepatitis C infection is diagnosed by testing for the presence of HCV antibodies and HCV RNA. Management is supportive but includes direct antiviral agents (DAAs) if infection does not resolve spontaneously.
Malnutrition is a clinical state caused by an imbalance or deficiency of calories and/or micronutrients and macronutrients. The 2 main manifestations of acute severe malnutrition are marasmus (total caloric insufficiency) and kwashiorkor (protein malnutrition with characteristic edema). Malnutrition is almost always associated with an underlying disease process, which can be classified into 4 categories: decreased nutrient intake, decreased absorption of micronutrients and macronutrients, increased nutrient loss, and increased energy expenditure. The clinical presentation of marasmus varies based on severity, duration of caloric restriction, and vitamin/mineral deficiencies. The clinical presentation of kwashiorkor includes peripheral pitting edema, muscle atrophy, and abdominal distention. Anthropometry is essential in the diagnosis of malnutrition. The 3-step approach to treat malnutrition includes resuscitation, rehabilitation, and relapse prevention.
Hepatitis B virus (HBV) is a partially double-stranded DNA virus, which belongs to the Orthohepadnavirus genus and the Hepadnaviridae family. Hepatitis B virus is transmitted by exposure to infectious blood or body fluids. Examples of types of exposure include sexual intercourse, IV drug use, and childbirth. The virus can cause potentially life-threatening liver disease. Most individuals with acute HBV infection are asymptomatic or have mild, self-limiting symptoms. Chronic infection can be asymptomatic or create hepatic inflammation, leading to liver cirrhosis and hepatocellular carcinoma (HCC). Management of acute hepatitis is typically supportive. Administration of antivirals or liver transplantation may be necessary in fulminant and chronic cases.
The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal incontinence can occur if this function is disturbed. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Peristaltic waves within the rectal muscularis, involuntary relaxation of the internal anal sphincter (controlled by the ANS), and voluntary relaxation of the external anal sphincter (controlled by the cerebral cortex) are essential for defecation to occur. The rich plexus of veins surrounding the anal canal can develop into hemorrhoids if dilated.
Mitochondria are located in a cell’s cytoplasm and contain circular DNA, called mitochondrial DNA (mtDNA). This DNA exists separately from a cell’s nuclear genome and is inherited solely through the maternal lineage—nonmendelian inheritance. Genetic mutations in mtDNA give rise to various rare diseases such as Leber hereditary optic neuropathy (LHON) and myoclonic epilepsy with ragged red fibers (MERRF).
The electron transport chain (ETC) sends electrons through a series of proteins, which generate an electrochemical proton gradient that produces energy in the form of adenosine triphosphate (ATP). Proteins generate energy through redox reactions that create the proton gradient. The complete aerobic catabolism of 1 molecule of glucose yields between 36 and 38 ATPs, mostly through energy obtained as the reduced coenzymes NADH and FADH2 are conveyed through the electron transport system. Three of the 4 respiratory complexes that make up the mitochondrial respiratory chain, as well as ATP synthase, are embedded in the inner mitochondrial membrane. Coenzyme Q and cytochrome c transfer electrons between complexes, which will ultimately meet oxygen and generate H2O.
Urea cycle disorders (UCDs) are caused by genetic defects and result in deficiencies of enzymes and transporters of the urea cycle. As a result of the defects, individuals are unable to rid the body of nitrogen waste. Common symptoms include vomiting, lethargy, seizures, and respiratory alkalosis. Most defects are autosomal recessive and definitive diagnosis is by molecular genetic testing. Treatment aims to reduce ammonia concentration in plasma. In less severe cases, acute episodes can be prevented through dietary restriction of protein. Untreated disease may lead to seizures, coma, or death.
Olfaction represents an ancient, evolutionarily critical physiologic system. Humans have the ability to detect and discriminate at least 10,000 different odorants. The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction is responsible for the detection of hazards, pheromones, and food.
The limbic system is a neuronal network that mediates emotion and motivation, while also playing a role in learning and memory. The extended neural network is vital to numerous basic psychological functions and plays an invaluable role in processing and responding to environmental stimuli.
The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. The palate is formed between weeks 7 and 10 of gestation, and deformities of this structure (cleft palate) are usually relevant because of its role in feeding, especially in infants.
The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. The muscles of the pharynx receive innervation from the vagus and glossopharyngeal nerve to propel food from the oral cavity into the esophagus.
Heart sounds are brief, transient sounds produced by valve opening and closure and by movement of blood in the heart. They are divided into systolic and diastolic sounds. In most cases, only the first (S1) and second (S2) heart sounds are heard. These are high-frequency sounds and arise from aortic and pulmonary valve closure (S1), as well as mitral and tricuspid valve closure (S2). The third heart sound (S3) may be physiologic (e.g., athletes) or pathologic (e.g., congestive heart failure), and is related to abnormally rapid deceleration of early diastolic left ventricular inflow. The fourth heart sound (S4) is associated with contraction of the atria into partially-filled and non-compliant (stiff) ventricles. S4 is a pathologic sign in the young, but may be found in older individuals due to an age-related decrease in ventricular compliance. Additional sounds include murmurs (physiologic and pathologic), clicks, and snaps. These sounds are heard in individuals with structural abnormalities of the heart such as septal defects, valvular stenosis, and mitral regurgitation.
The nose is the human body's primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. There are 12 cranial bones that contribute to the structure of the nose's walls and nasal conchae.
Genital herpes infections are common sexually transmitted infections caused by herpes simplex virus (HSV) type 1 or 2. Herpes simplex virus type 1 is more commonly associated with non-genital herpes, while HSV-2 is more commonly associated with genital herpes. Primary infection often presents with systemic, prodromal symptoms followed by clusters of painful, fluid-filled vesicles on an erythematous base, dysuria, and painful lymphadenopathy. Primary infection can also be asymptomatic. Herpes infections are unique in that the virus is able to remain dormant in the neuronal ganglia, which allows for recurrent infections. Recurrent outbreaks are usually less severe than the initial infection. Treatment is with antiviral therapy, primarily acyclovir.
Pseudomembranous colitis is a bacterial disease of the colon caused by Clostridium difficile. Pseudomembranous colitis is characterized by mucosal inflammation and is acquired due to antimicrobial use and the consequent disruption of the normal colonic microbiota. C. difficile infections account for the most commonly diagnosed hospital-acquired diarrheal illnesses. C. difficile infections can range from asymptomatic colonization to diarrhea and progress to fulminant colitis with systemic sepsis in severe cases. The diagnosis is established based on stool studies. Management of pseudomembranous colitis is mainly using antibiotics. Fecal transplant is considered in a few cases, whereas surgical intervention is required in severe cases.
Perforated viscus or GI perforation represents a condition in which the integrity of the GI wall is lost with subsequent leakage of enteric contents into the peritoneal cavity, resulting in peritonitis. The causes of perforated viscus include trauma, bowel ischemia, infections, or ulcerative conditions, all of which ultimately lead to a full-thickness disruption of the intestinal wall. Perforated viscus presents as sudden onset of abdominal pain, distention, nausea, vomiting, obstipation, and symptoms of peritonitis. Diagnosis relies on the medical history as well as imaging studies, including abdominal and pelvic CT scan and X-ray. Treatment includes bowel rest, the use of a nasogastric tube, antibiotics to avoid severe infections or sepsis, analgesics, and surgical repair.
The most common complications include pneumonia, respiratory failure and acute respiratory distress syndrome (ARDS), sepsis and septic shock, cardiomyopathy, acute kidney injury (AKI), and pulmonary thromboembolism. Other complications include acute stroke, arrhythmias, acute cardiac injury, and dermatologic manifestations.
Fungi belong to the eukaryote domain and, like plants, have cell walls and vacuoles, exhibit cytoplasmic streaming, and are immobile. Almost all fungi, however, have cell walls composed of chitin and not cellulose. Fungi do not carry out photosynthesis but obtain their substrates for metabolism as saprophytes (obtain their food from dead matter). Mycosis is an infection caused by fungi.
Pituitary adenomas are tumors that develop within the anterior lobe of the pituitary gland. They are classified by size (either micro- or macroadenomas) and by their ability to secrete hormones. Non-functioning or non-secretory adenomas do not secrete hormones but can compress surrounding pituitary tissue, leading to hypopituitarism. Secretory adenomas secrete various hormones depending on the cell type from which they evolved, leading to hyperpituitarism.
Rhinitis refers to inflammation of the nasal mucosa. The condition is classified into allergic, nonallergic, and infectious rhinitis. Allergic rhinitis is due to a type I hypersensitivity reaction. Non-allergic rhinitis is due to increased blood flow to the nasal mucosa. Infectious rhinitis is caused by an upper respiratory tract infection. All 3 types present with nasal congestion, rhinorrhea, and sneezing. Diagnosis is mainly clinical. Management includes antihistamines, decongestants, and immunotherapy.
Diphtheria is an infectious disease caused by Corynebacterium diphtheriae that most often results in respiratory disease with membranous inflammation of the pharynx, sore throat, fever, swollen glands, and weakness. The hallmark sign is a sheet of thick, gray material covering the back of the throat. Diphtheria can also manifest as cutaneous disease leading to nonspecific skin lesions. In advanced stages, diphtheria can damage the heart, kidneys, and nervous system. It is diagnosed via a culture of pharyngeal swabs and treated with antibiotic therapy and the diphtheria antitoxin.
Pleuritis, also known as pleurisy, is an inflammation of the visceral and parietal layers of the pleural membranes of the lungs. The condition can be primary or secondary and results in sudden, sharp, and intense chest pain on inhalation and exhalation. Etiologies include infection, trauma, cardiac ischemia, and lung cancer. The most common primary infectious cause is a viral infection, and underlying lung infections account for the majority of secondary infectious causes. Management consists of pain control and the treatment of the underlying condition.
Sinusitis refers to inflammation of the mucosal lining of the paranasal sinuses. The condition usually occurs concurrently with inflammation of the nasal mucosa (rhinitis), a condition known as rhinosinusitis. Acute sinusitis is due to an upper respiratory infection caused by a viral, bacterial, or fungal agent. Viral etiologies are the most common cause. Sinusitis presents with facial pain over the affected sinus and purulent rhinorrhea. Diagnosis is usually clinical and management is supportive, although it may require antibiotics.
Hemolytic anemia (HA) is the term given to a large group of anemias that are caused by the premature destruction/hemolysis of circulating red blood cells (RBCs). Hemolysis can occur within (intravascular hemolysis) or outside the blood vessels (extravascular hemolysis). Extravascular destruction of RBCs is affected by macrophages of the liver, spleen, bone marrow, and lymph nodes. Other than the site of destruction, HA can also be classified according to the type of RBC defect that causes their destruction. If the RBC has an intrinsic and usually inherited defect such as a hemoglobinopathy, a membrane defect, or a metabolic defect, its destruction is called intracorpuscular hemolysis. If the RBC is normal but is damaged by an external force such as an antibody, mechanical trauma, or a pathogen, then its destruction is classified as extracorpuscular hemolysis, which is almost always an acquired disorder.
Gestational trophoblastic diseases are a spectrum of placental disorders resulting from abnormal placental trophoblastic growth. These disorders range from benign molar pregnancies (complete and partial moles) to neoplastic conditions such as invasive moles and choriocarcinoma. Diagnosis is confirmed by elevated serum beta human chorionic gonadotropin (hCG) and ultrasound findings, which are dependent on the disorder. Treatment is primarily through dilation and curettage and/or methotrexate.
Enzyme inhibitors bind to enzymes and decrease their activity. Enzyme activators bind to enzymes and increase their activity. Molecules that decrease the catalytic activity of enzymes can come in various forms, including reversible or irreversible inhibition. Reversible inhibition can be competitive, non-competitive, or uncompetitive.
Enzyme kinetics describes the sequence of enzyme-catalyzed reactions with a dependence on various parameters such as temperature, pH, and substrate concentration. The reaction rate is measured and the effects of varying the conditions of the reaction are investigated.
Amino acids (AAs) can be acquired through the breakdown of intracellular or ingested dietary proteins. Amino acids can enter 3 metabolic routes within the body. They can 1) be recycled to synthesize new proteins; 2) combine with cofactors and substances to create amino acid derivatives; or 3) be catabolized into their functional groups and carbon skeletons. This process releases ammonium, which moves into the urea cycle and produces intermediates for energetic metabolic pathways.
Laryngitis is an inflammation of the larynx most commonly due to infection or trauma that can be either acute or chronic. In this condition, the 2 folds of mucous membranes that make up the vocal cords become inflamed and irritated. The inflammation results in a distortion of the voice produced, resulting in a hoarse sound that may lead to an inability to produce any sound (aphonia) in severe cases. In the presence of an infectious cause, patients often also present with rhinorrhea, cough, and mild sore throat.
Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Determining the causative agent based on symptoms alone is difficult. Thus, a throat swab is often performed to rule out a bacterial cause. The mainstay of treatment is symptomatic and supportive, with bacterial causes requiring antibiotics.
Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Treatment is directed at the removal of excess fluid and decreasing oxygen demand of the heart. Prognosis depends on the underlying cause, compliance with medical therapy, and presence of comorbidities.
Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular fibrillation is most commonly caused by underlying ischemic heart disease. It leads to death within minutes unless advanced cardiac life support measures are started immediately.
Granulomatosis with polyangiitis (GPA) is a rare autoimmune disease of unknown etiology. It leads to a necrotizing granulomatous inflammation of small and medium-sized blood vessels of the nose, sinuses, throat, lungs, and kidneys. Early stages of GPA often present with localized manifestations such as infections of the upper respiratory tract, skin lesions, and/or constitutional symptoms. Later stages can present with renal failure and severe respiratory disease. Early diagnosis and treatment of granulomatosis with polyangiitis (which involves the administration of corticosteroids and immunosuppressive agents such as methotrexate) may lead to a full remission but without treatment, the condition has a high mortality rate.
Epidemiologists use specific measures of morbidity and mortality to characterize the degree to which illness and disease are present in a population and in how much this affects the population’s health and death rate.
Common variable immune deficiency (CVID), also known as humoral immunodeficiency, is a disorder of the immune system characterized by reduced serum levels of immunoglobulins G, A, and M. The underlying causes of CVID are largely unknown. Patients with this condition are prone to infections in the gastrointestinal tract and the upper and lower respiratory tracts. CVID is also associated with a higher risk of developing autoimmune disorders, granulomatous diseases, and malignancy.
Personality disorders are ego-syntonic behaviors that begin in childhood or adolescence and are classified into 3 clusters: A, B, and C. They can considerably interfere with a patient’s adherence to medical treatment for a variety of reasons. It is important to rule out organic causes of a mental disorder (e.g., endocrine hormone imbalances, medication adverse effects, alcohol and/or substance use, other mental health co-morbidities) before ascribing a personality disorder to a patient. Cluster B includes antisocial, borderline, histrionic, and narcissistic personality disorders, which can be behaviorally described as dramatic, erratic, and threatening/disturbing.
Personality disorders are ego-syntonic behaviors that begin in childhood or adolescence and are classified into 3 clusters: A, B, and C. They can considerably interfere with a patient’s adherence to medical treatment for a variety of reasons. It is important to rule out organic causes of a mental disorder (e.g., endocrine hormone imbalances, medication adverse effects, alcohol and/or substance use, other mental health co-morbidities) before ascribing a personality disorder to a patient. Cluster C includes avoidant, dependent, and obsessive-compulsive personality disorders, which can be behaviorally described as anxious and apprehensive.
X-linked agammaglobulinemia, also known as Bruton's agammaglobulinemia or Bruton's disease, is a rare, recessive genetic disorder characterized by the improper development of B cells, leading to a lack of mature B cells capable of responding to stimulation by cell-mediated immune responses or certain antigen-presenting cells. X-linked agammaglobulinemia is more likely to be found in males than females and is due to mutations in the Bruton’s tyrosine kinase gene on the X chromosome. The result of this mutation is a complete or near-complete lack of all antibodies. Presentation includes recurrent bacterial infections after the first few months of life. Management consists of IV immunoglobulins and prophylactic use of antibiotics.
Malignant mesothelioma (usually referred to as simply "mesothelioma") is the malignant growth of mesothelial cells, most commonly affecting the pleura. The majority of cases are associated with occupational exposure to asbestos that occurred > 20 years before clinical onset, which includes dyspnea, chest pain, coughing, fatigue, and weight loss. Chest computed tomography (CT) scan shows multifocal pleural thickening and pleural effusion. Pleural biopsy is required for confirmation and to rule out metastases from lung or breast cancer. Treatment is rarely effective, with an average survival time of < 1 year.
Selective immunoglobulin A (IgA) deficiency is the most common type of primary immunodeficiency. The condition is a hypogammaglobulinemia characterized by a lack or reduced levels of IgA. This antibody mainly resides in the mucous membranes of the mouth, airways, and digestive tract. The exact cause is unknown. The disease is usually asymptomatic, although some patients can present with recurrent respiratory and gastrointestinal infections as well as autoimmune and malignant disorders. Diagnosis is made with a measure of exceptionally low IgA levels in the serum in the presence of normal IgG and IgM levels.
46,XX gonadal dysgenesis is a disorder present in individuals who are phenotypic females with normal karyotypes of 46,XX and who have streak gonads with no functional ovarian tissue. It is also called “pure gonadal dysgenesis” to differentiate these patients from those who present with the phenotype of Turner's syndrome (webbed neck, short stature, widely spaced nipples). Patients present with a normal development during childhood, primary amenorrhea, infertility, and a lack of secondary sexual characteristics. Management includes hormone replacement therapy and prophylactic gonadectomy.
Jaundice is the abnormal yellowing of the skin and/or sclera caused by the accumulation of bilirubin. Hyperbilirubinemia is caused by either an increase in bilirubin production or a decrease in the hepatic uptake, conjugation, or excretion of bilirubin. Etiologies often involve the liver and can be prehepatic, intrahepatic, or posthepatic. Other symptoms of hyperbilirubinemia include pruritus, pale stools, and darkened urine. The diagnosis is made based on liver function tests and imaging. Management is focused on treatment of the underlying condition.
IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome is a rare congenital T-cell deficiency associated with transcription factor FOXP3 dysfunction. This factor regulates the development of a regulatory T cell line and dysfunctions usually result in autoimmunity. The condition manifests as autoimmune enteropathy, eczematous dermatitis, nail dystrophy, autoimmune endocrinopathies, and autoimmune skin conditions. The only form of management for IPEX is bone marrow transplantation.
Long QT syndrome (LQTS) is a disorder of ventricular myocardial repolarization that produces QT prolongation on electrocardiogram (ECG). Long QT syndrome is associated with an increased risk of developing life-threatening cardiac arrhythmias, specifically torsades de pointes. The condition may be congenital or acquired. Congenital LQTS is attributed to genetic mutations affecting cardiac ion channels. Acquired LQTS usually results from drug therapy and/or electrolyte abnormalities. Patients can be asymptomatic or present with palpitations, syncope, seizures, and even sudden cardiac death. Diagnosis is established with ECG along with medical and family history, laboratory workup, and other cardiac tests. Treatment is determined by etiology. Acquired LQTS requires removal of the offending drug and correction of electrolyte abnormalities. Congenital LQTS management involves avoidance of triggers of arrhythmia, intake of beta-blockers, and placement of an implantable cardioverter-defibrillator (ICD).
Autosomal dominant hyper-IgE syndrome (AD-HIES), also known as Job's syndrome, is a rare form of primary immunodeficiency disorder that affects various organs systems in addition to the immune system. Some cases of AD-HIES are caused by mutations in the STAT3 gene, resulting in abnormal neutrophil chemotaxis. In other cases, the cause is unknown. Patients with AD-HIES experience recurrent pneumonia, skin infections, rashes, blisters, and abscesses.
Cri du chat is the French term for "cat-cry" or "call of the cat." The term refers to the cat-like cry of a pediatric patient with cri-du-chat syndrome. The condition is a rare genetic disorder caused by deletion mutations on chromosome 5. Cri-du-chat syndrome is more common in females than in males. Aside from the characteristic cry, the condition also presents with dysphagia, low birth weight, poor growth, and severe cognitive, speech, and motor disabilities.
Crohn's disease is a chronic, recurrent condition that causes patchy transmural inflammation that can involve any part of the gastrointestinal tract. It is a type of inflammatory bowel disease (IBD) along with ulcerative colitis (UC). The terminal ileum and proximal colon are usually affected. Crohn's disease typically presents with intermittent, non-bloody diarrhea and crampy abdominal pain. Extraintestinal manifestations may include calcium oxalate renal stones, gallstones, erythema nodosum, and arthritis. Diagnosis is established via endoscopy with biopsy that shows transmural inflammation, characteristic “cobblestone” mucosa, and noncaseating granulomas. Management is with corticosteroids, azathioprine, antibiotics, and anti-TNF agents (infliximab and adalimumab). Complications include malabsorption, malnutrition, intestinal obstruction or fistula, and an increased risk of colon cancer.
Severe combined immunodeficiency (SCID), also called “bubble boy disease,” is a rare genetic disorder in which the development of functional B and T cells is disturbed due to several genetic mutations that result in reduced or absent immune function. It is the most severe form of primary immunodeficiency and is characterized by dysfunction in both humoral and cell-mediated immune responses. Multiple mutations can result in heterogeneous types of SCID. Patients present with severe and recurrent infections within the first months of life. Management includes IV immunoglobulins and bone marrow transplantation. If left untreated, SCID is usually fatal within the 1st year of life.
5-alpha-reductase deficiency is an autosomal recessive intersex or “disorder of sex development” (DSD) condition caused by a loss-of-function mutation in a gene on chromosome 2. The affected subjects have a 46,XY karyotype, bilateral testes, and normal testosterone production but have impaired virilization during embryogenesis due to defective conversion of testosterone to dihydrotestosterone (DHT), which is a significantly more potent androgen. This leads to male pseudohermaphroditism or ambiguous genitalia in males. Also known as pseudovaginal perineoscrotal hypospadias, these patients present with a clitoris-like phallus, cryptorchidism, bifid scrotum, and a rudimentary prostate. No Müllerian structures are present.
Seborrheic dermatitis is a common chronic, relapsing skin disorder that presents as erythematous plaques with greasy, yellow scales in susceptible areas (scalp, face, and trunk). Seborrheic dermatitis has a biphasic incidence, occurring in two peaks: first in infants, then in adolescence and early adulthood. Although the exact etiology is unknown, pathologic mechanisms have been observed involving the sebaceous glands and Malassezia on the skin. Topical medications are used for acute exacerbation or maintenance treatment. These options aim to inhibit skin colonization (antifungal agents), reduce inflammation (steroids, calcineurin inhibitors), and loosen scales and crusts (keratolytic agents). Severe and refractory seborrheic dermatitis may warrant the use of systemic antifungal medications.
Type II hypersensitivity, also known as antibody-mediated cytotoxic hypersensitivity, is caused by immunoglobulin G (IgG) and IgM antibodies directed against antigens on cells or extracellular materials. The reaction leads to cytotoxic processes involving antibodies and the complement system. Interference with the normal cellular operation generating either stimulatory or inhibitory dysfunction is another mechanism that occurs. The inciting antigen can be intrinsic or part of the host cell. Extrinsic antigens such as blood products or medications can provoke a similar reaction. For diagnosis, laboratory tests and invasive procedures are utilized, depending on the system affected. Management of resulting disease ranges from supportive care to antibiotics, immunosuppressive medications, and surgery.
By refraction, the light that enters the eye is focused onto a particular point of the retina. The main refractive components of the eye are the cornea and the lens. When the corneal curvature, the refractive power of the lens, does not match the size of the eye, ametropia or a refractive error occurs. The types of refractive errors include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (which can occur in both myopia and hyperopia). The use of a proper refractive device helps correct the visual impairment. Laser in situ keratomileusis (LASIK) is the most common corrective surgical procedure.
Friedreich's ataxia is an autosomal recessive disorder characterized by progressive spinocerebellar degeneration. It presents in the 1st to 2nd decades of life with progressive gait ataxia, weakness, tremor, dysarthria, dysphagia, hypertrophic cardiomyopathy, and/or diabetes. Patients eventually become bedridden. Diagnosis is confirmed by genetic testing showing trinucleotide repeat expansion in the FXN gene. Treatment is supportive and most patients die of heart disease in the 4th or 5th decade of life.
Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Pain is a subjective experience. Acute pain lasts < 3 months and typically has a specific, identifiable cause. Chronic pain lasts > 3 months and may exist in the absence of tissue damage or after healing would have been expected to occur. Pain management involves a combination of addressing underlying causes and using a systematic approach tailored to the clinical scenario.
Type III hypersensitivity, also known as immune complex-mediated hypersensitivity, occurs when antibodies and antigens form immune complexes (ICs) in circulation and deposit in susceptible tissues. The complement system triggers the immune response, leading to leukocyte recruitment and tissue injury. There is no single clinical syndrome for this hypersensitivity. Symptoms reflect the impairment of multiple organ systems based on sites of IC deposition. Diagnostic workup depends largely on the history and includes laboratory tests, imaging, and biopsy of the affected organ. Treatment consists of removal or avoidance of offending agents and, in severe conditions, glucocorticoids or immunosuppressive therapy.
Neonatal polycythemia is a hematocrit (HCT) that is 2 standard deviations above the average values for gestation and postnatal age. Neonatal polycythemia can develop from increased fetal hematopoiesis (secondary to placental insufficiency, maternal endocrinopathies, genetic disorders, etc.) or passive erythrocyte transfusion (placental-, feto-, or maternal-fetal transfusion). Patients may be asymptomatic or present with plethora, cardiorespiratory distress, and other symptoms. Continuous monitoring of vital signs and metabolic derangements is important. Treatment includes partial exchange transfusion.
The elimination disorders that most commonly occur in childhood are enuresis (urinary incontinence) and encopresis (fecal incontinence in inappropriate situations). Enuresis is usually diagnosed when children > 5 years of age continue to wet the bed. Enuresis can occur both in the daytime (diurnal) and at night (nocturnal). The incidence of nocturnal enuresis spontaneously resolves at a rate of approximately 15% per year. Management of nocturnal enuresis primarily consists of behavior and lifestyle modifications but can include desmopressin. Encopresis is most often secondary to underlying constipation, although emotional stressors may also be involved. Management is primarily through treating constipation.
Type IV hypersensitivity reaction, or delayed-type hypersensitivity, is a cell-mediated response to antigen exposure. The reaction involves T cells, not antibodies, and develops over several days. Presensitized T cells initiate the immune defense, leading to tissue damage. A cytokine-mediated process is activated by T-helper cells while cytotoxic T cells directly release cytotoxins to infected or dysfunctional cells, causing cell lysis. Clinical manifestations depend on the system involved, so diagnostic tests rely on history and findings. Treatment includes controlling the effects of the immune response with glucocorticoids and immunosuppressive therapy while managing the associated disease complications.
Blepharitis is an ocular condition characterized by eyelid inflammation. Anterior blepharitis involves the eyelid skin and eyelashes, while the posterior type affects the meibomian glands. Often, these conditions overlap. The typical presentation of blepharitis includes eyelid edema with itching and redness, crusts and scales around the eyelashes, and gritty sensation. Diagnosis is clinical, with a slit-lamp examination providing details of the structural changes affecting the eye. The mainstay of treatment is eyelid hygiene using warm compresses and eyelid scrubs. In moderate-to-severe cases, topical and oral antibiotics are utilized. Topical glucocorticoids also help improve symptoms but require an ophthalmology evaluation due to potential adverse effects.
Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Diagnosis is clinical. Management requires treating the underlying disease, managing complications, and, if required, liver transplantation.
Thoracic aortic aneurysm (TAA) is the abnormal dilation of a segment of the thoracic aorta, usually the ascending aorta. Most TAAs are due to degenerative aortic disorders, commonly in patients > 65 years of age. Genetic TAAs account for 20% of cases and are frequently found in younger patients. Most TAAs are asymptomatic (incidentally found in imaging) but could present with symptoms from its effects on surrounding structures. Aortic rupture is a life-threatening emergency. Among diagnostic imaging studies, computed tomography (CT) angiography is the most widely utilized. In asymptomatic cases, aortic expansion is monitored. Operative repair is recommended for symptomatic TAAs and increasing aortic diameter (criteria varies with location and underlying condition).
Precocious puberty (PP) is the appearance of secondary sexual characteristics due to elevated sex hormones before the age of 6–8 in girls and 9 in boys. Excess hormone secretion may occur only at the level of the sex hormone or may involve the whole hypothalamic-pituitary-gonadal axis. Measurement of sex hormone levels, as well as X-rays to evaluate skeletal maturity, are used to diagnose and characterize PP. Correcting the hormonal excess at its root cause can appropriately delay the onset of puberty. A primary goal of treatment is the preservation of normal height potential.
Uveitis is the inflammation of the uvea, the pigmented middle layer of the eye, which comprises the iris, ciliary body, and choroid. The condition is categorized based on the site of disease; anterior uveitis is the most common. Uveitis can be caused by an infection or systemic disease, but in some cases the cause is idiopathic. Patients present with blurred vision, eye redness, and pain (frequently in anterior uveitis) or reduced vision and floaters (in intermediate and posterior uveitis). Diagnosis is by dilated funduscopy and slit-lamp examination. Treatment for anterior uveitis is topical steroids, while uveitis in deeper locations requires an injection. Uveitis from infections and systemic disorders requires etiology-directed therapy.
Benign breast epithelial lesions are grouped histologically as nonproliferative, proliferative without atypia, and atypical hyperplasia. The classifications are based on subsequent cancer risk in either breast. The nonproliferative type carries no risk, while fibroadenoma, the most common benign tumor, is a proliferative breast lesion (i.e., has a slight increase in malignancy risk). Because atypical hyperplasia shares some features with breast carcinoma in situ, future cancer potential is increased. Management ranges from frequent monitoring to surgical excision, depending on certain factors, including the inherent risk of the pathologic diagnosis. Other breast disorders without malignant possibility are associated with underlying infection or systemic disease, so treatment differs. Benign breast diseases are common but present diversely. It is important to distinguish between them to determine the likelihood of cancer and the best course of treatment.
Glaucoma is an optic neuropathy characterized by typical visual field defects and optic nerve atrophy seen as optic disc cupping on examination. The acute form of glaucoma is a medical emergency. Glaucoma is often, but not always, caused by increased intraocular pressure (IOP). Frequently, there is peripheral vision loss that eventually leads to loss of central vision. The 2 main types of glaucoma are open-angle and angle-closure. Overproduction or reduced excretion of the aqueous humor leads to open-angle glaucoma. Onset of symptoms is gradual. Angle-closure glaucoma results from blockage in the angle (of the iris and cornea), preventing drainage of the aqueous fluid. Diagnosis involves IOP determination (tonometry) and angle visualization with slit lamp (gonioscopy). Treatment includes topical medications that reduce IOP, and eye surgery.
Cor pulmonale is right ventricular (RV) dysfunction caused by lung disease that results in pulmonary artery hypertension. The most common cause of cor pulmonale is chronic obstructive pulmonary disease. Dyspnea is the usual presenting symptom. Clinical findings include signs of right-sided heart failure and hypoxemia. While right cardiac catheterization is the gold standard test, most patients are diagnosed clinically and through the use of noninvasive testing. Echocardiography shows RV enlargement and elevated pulmonary arterial systolic pressure. Management is first focused on the underlying disease. Oxygen therapy improves disease progression, while diuretics reduce RV filling pressure. Lung transplantation is an option for those refractory to therapy.
A cataract is a condition defined as painless clouding or opacity of the lens. It causes visual impairment, as the lens provides part of the eye’s refractive power. Although all age groups can be affected, the age-related or senile type of cataract is the most common. Aside from age, there are multiple risk factors, including systemic diseases, medications, or trauma. Patients present with blurry vision, glare sensitivity, and color vision change. Ophthalmologic inspection often shows darkening of or opacities in the red reflex. Slit-lamp examination will show the extent and location of the cataract. The treatment is surgery, which is indicated when loss of vision function interferes with daily function.
Hyperbilirubinemia of the newborn is a broad term that refers to various conditions that can cause accumulation of bilirubin during the first few days after birth. The condition is often noted because of visible yellowing of the skin and sclera secondary to bilirubin deposition. Because hyperbilirubinemia arises from physiological processes that accompany birth, it is usually an expected finding. However, hyperbilirubinemia in the neonate can also have pathological etiologies, including breastfeeding-related, blood group isoimmunization, metabolic disorders, and infection. Regardless of etiology, the primary goal of therapy in neonatal jaundice is to prevent the neurotoxic effect of indirect bilirubin, mainly kernicterus. When indicated, treatment mainly includes phototherapy and exchange transfusion.
Age-related macular degeneration (AMD) is visual impairment due to changes in the macula, the area responsible for high-acuity vision. It is marked by central vision loss with peripheral vision relatively spared. Risk factors include advanced age, smoking, family history, and cardiovascular disease. The 2 types of AMD are exudative (wet) or non-exudative (dry). The difference between these 2 types is the presence of choroidal neovascularization in wet AMD, which manifests as visual distortion or loss. The more frequently occurring dry AMD is usually asymptomatic but in a minority of cases leads to vision loss. There is no treatment for early dry AMD but Age-Related Eye Disease Study 2 (AREDS 2) supplements are recommended for advanced disease. Inhibitors of vascular endothelial growth factor are used for wet AMD.
Dacryocystitis is inflammation of the lacrimal sac due to nasolacrimal duct obstruction and the subsequent stasis of tears. The condition can have an acute or chronic onset. Acute dacryocystitis presents within hours or days with redness, swelling, tenderness, and excessive tearing. The chronic type has a gradual course, often manifesting with epiphora. By etiology, dacryocystitis can be congenital or acquired. Nasolacrimal duct obstruction affects 6% of newborns. Acquired cases occur due to trauma, systemic diseases, or tumors. Diagnosis is made clinically. In some cases, laboratory tests and imaging help determine abnormal structures and underlying disease. Initial treatment includes conservative measures such as Crigler massage, warm compresses, and antibiotics, if indicated. If these fail, surgical options are tried.
The embryological development of craniofacial structures is an intricate sequential process involving tissue growth and directed cell apoptosis. Disruption of any step in this process may result in the formation of a cleft lip alone or in combination with a cleft palate. As the most common craniofacial malformation of the newborn, the diagnosis of a cleft is clinical and usually apparent at birth. The type and severity of the defect cause various degrees of difficulty with speech development, feeding, swallowing, tooth eruption, and cosmetic issues. Ultimate correction is through surgical repair.
A cataract is a condition defined as painless clouding or opacity of the lens. Cataracts cause visual impairment, as the lens provides part of the eye’s refractive power. The condition is one of the most common causes of pediatric blindness. Cataracts can be present from birth (congenital) or can develop after infancy (acquired). Genetic mutations, systemic diseases, trauma, and medications can lead to cataract development. Children present with an abnormal red reflex, leukocoria, or decreased visual acuity. An ophthalmologic examination reveals the morphology and location of the cataract. Management depends on age of presentation and visual defects. When opacity is of a certain size or is causing visual impairment, strabismus, and nystagmus, cataract surgery is recommended.
Anorectal atresia refers to a spectrum of congenital anorectal malformations with an unclear etiology. These anomalies range from a simple imperforate anus in an otherwise normal anorectal region to complex anomalies involving the urogenital system. Anorectal atresia is sometimes seen as an isolated finding, but it may also occur as part of a multi-organ syndrome. Diagnosis is often made during initial newborn examination or after a delay in passage of meconium for over 24 hours after birth. Prognosis varies based on complexity. Treatment is primarily surgical.
Congenital diaphragmatic hernias are embryologically derived defects in the diaphragm through which abdominal structures can pass into the chest cavity. The presence of intestines and intra-abdominal organs in the chest interferes with embryonic development of the lungs, which is the major cause of pathology postnatally. Prenatal diagnosis is commonly made by ultrasound during pregnancy followed by confirmation on chest X-ray after birth. Immediate respiratory resuscitation at birth with endotracheal intubation and mechanical ventilation are required. Surgical repair is the only curative option. Prognosis varies, but children with diaphragmatic hernias usually suffer from lifelong pulmonary complications.
Anal fistulas are abnormal communications between the anorectal lumen and another body structure, often to the skin. Anal fistulas often occur due to extension of anal abscesses but are also associated with specific diseases such as Crohn's disease. Symptoms include pain or irritation around the anus; abnormal discharge or purulent drainage; and swelling, redness, or fever if an abscess is present. Management is primarily surgical, with fistulotomy, but can include antibiotics if infection is present. Treatment is surgical. Complications after surgery include recurrence and incontinence.
Retinal detachment is the separation of the neurosensory retina from the retinal pigmented epithelium and choroid. Rhegmatogenous retinal detachment, the most common type, stems from a break in the retina, allowing fluid to accumulate in the subretinal space. In the setting of an intact retina, detachment occurs when the vitreous pulls on the retina (traction) or when an underlying condition leads to increased leakage of fluid (exudative). Symptoms of photopsia, floaters, and visual defects can present over hours or gradually over weeks. Retinal detachment with visual loss is an emergency. Once macular detachment occurs, visual prognosis is poor. Symptomatic rhegmatogenous retinal detachment with intact central acuity warrants urgent surgery. For non-rhegmatogenous retinal detachments, treatment is directed toward the primary process.
A population pyramid graphically illustrates the age and gender distribution of a given population. The shape of the pyramid conveys details about life expectancy, birth, fertility, and mortality rates. Additional data that can be extrapolated from a population pyramid include the effects of historical events, economic development, and future demographic trends. This information helps direct plans for the subsequent social and economic needs of a given population.
In order to cope with their environment, cells undergo structural and functional changes. These cellular adaptations are reversible responses that allow cells to survive and continue to adequately function. Adaptive processes consist of increased cellular size and function (hypertrophy), increase in cell number (hyperplasia), decrease in cell size and metabolic activity (atrophy), or a change in the phenotype of the cells (metaplasia). If the stress or stimulus is removed, the cell can return to its original state. However, when the limits of the adaptive responses are exceeded, cellular function is adversely affected, leading to cellular injury.
A retinal vessel occlusion is a blockage in a major artery or vein of the retina. Depending on the location, the occlusion can be classified as central retinal artery occlusion (CRAO), branch retinal artery occlusion (BRAO), central retinal vein occlusion (CRVO), or branch retinal vein occlusion (BRVO). Typically, a retinal vessel occlusion is a thromboembolic event. Risk factors include hypertension, diabetes mellitus, and cardiac valvular disease. Central retinal artery occlusion is characterized by sudden, unilateral, painless loss of vision and/or transient vision loss (amaurosis fugax). Treatment options are limited in all cases and usually ineffective. When the macula is involved, prognosis is especially poor, leading to permanent vision loss.
A chalazion is one of the most common inflammatory lesions of the eyelid. It is caused by obstruction of the Meibomian or Zeis glands, leading to granulomatous inflammation and resulting in a firm, rubbery, slow-growing nodule that is typically non-tender. Diagnosis is based on history and physical exam findings. Most chalazia will resolve with conservative management.
A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Larger PFOs and PFOs associated with paradoxical thromboembolic stroke or other cardiac anomalies may require treatment with anticoagulation. Surgical or percutaneous closure may be indicated in select cases.
Substances can accumulate in the cytoplasm, nucleus, or organelles as a result of an intrinsic cellular dysfunction or metabolic abnormalities. Commonly seen substances are pigments, calcium, iron, fat, cholesterol, and glycogen. These substances are produced by the cell and can increase in amount when there is inadequate removal of the substance or failure of metabolite degradation. Defective protein folding, packaging, and transport, both genetic and acquired, also produce substance accumulation. In some instances, deposition is from an external source, such as coal dust. The cell does not have an inherent mechanism of elimination, so material builds up in the exposed site.
The cubital fossa is the region anterior to the elbow joint. The cubital fossa is seen as the triangular depression between the brachioradialis and pronator teres muscles. Except for the ulnar nerve, which runs posteriorly, most of the major neurovascular structures transition from the arm to the forearm via the cubital fossa. The 4 important structures of the cubital fossa (from lateral to medial) are the radial nerve, tendon of the biceps brachii muscle, brachial artery, and median nerve.
Omphalocele is a congenital anterior abdominal wall defect in which the intestines are covered by peritoneum and amniotic membranes. The condition results from the failure of the midgut to return to the abdominal cavity by 10 weeks' gestation. Omphalocele is frequently associated with genetic syndromes and chromosomal abnormalities. Prenatal diagnosis can be made by prenatal ultrasound, maternal blood elevated ⍺-fetoprotein, and fetal chromosomal analysis. Treatment includes immediate hemodynamic stabilization followed by primary or staged surgical repair.
Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed NTD) to very severe malformations of the spine or brain (open NTD). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. The most common type of open NTD is meningomyelocele, which involves both the meninges and neural tissue. The etiologies of NTD are multifactorial, ranging from maternal nutrition to genetic determinants. Prenatal diagnosis by ultrasound and maternal α-fetoprotein level is common. Management of open NTDs is mainly surgical.
A hordeolum is an acute infection affecting the meibomian, Zeiss, or Moll glands of the eyelid. Stasis of the gland secretions predisposes to bacterial infection. Staphylococcus aureus is the most common pathogen. The condition presents as a painful, localized, erythematous mass in the anterior (external hordeolum) or posterior (internal hordeolum) lamella of the eyelid. A hordeolum usually resolves spontaneously and can be managed with warm compresses, massage, and lid hygiene. In certain cases of significant swelling, topical antibiotics with steroids may be needed. If there is no resolution, incision, and drainage are performed.
The menstrual cycle is the cyclic pattern of hormonal and tissular activity that prepares a suitable uterine environment for the fertilization and implantation of an ovum. The menstrual cycle involves both an endometrial and ovarian cycle that are dependent on one another for proper functioning. There are 2 phases of the ovarian cycle (follicular and luteal) and 3 phases of the endometrial cycle (desquamation or menses, proliferative, and secretory). The menstrual cycle is regulated by the hypothalamic-pituitary-ovarian axis via follicle-stimulating hormone (FSH) and luteinizing hormone (LH). A woman’s 1st menstrual cycle is referred to as menarche, and cycles continue until menopause.
Atrioventricular septal defects (AVSDs) are a category of congenital defects of the endocardial cushion and atrioventricular valves (AVVs) resulting in abnormal interatrial and/or interventricular communication. Severe forms present early during infancy with failure to thrive and recurrent pneumonia, and require early surgical correction to avoid pulmonary hypertension.
Ascites is the pathologic accumulation of fluid within the peritoneal cavity that occurs due to an osmotic and/or hydrostatic pressure imbalance secondary to portal hypertension (cirrhosis, heart failure) or non-portal hypertension (hypoalbuminemia, malignancy, infection). Patients often present with progressive abdominal distention and weight gain. Abdominal exam may reveal shifting dullness and a positive fluid wave. Diagnosis is established with an ultrasound, and etiologies can be distinguished by ascitic fluid analysis from paracentesis. Treatment involves dietary sodium restriction, diuretics, and treatment of the underlying cause.
Psoriasis is a common T-cell–mediated inflammatory skin condition. The etiology is unknown, but is thought to be due to genetic inheritance and environmental triggers. There are 4 major subtypes, with the most common form being chronic plaque psoriasis. Plaques are well-circumscribed and salmon-colored, with silvery scales. Plaques commonly appear on the scalp and extensor surfaces of the extremities. Diagnosis is clinical. Treatment options are determined by the percentage of body surface area (BSA) affected and include topical corticosteroids, retinoids, calcineurin inhibitors, disease-modifying antirheumatic drugs (DMARDs), biologics, and phototherapy.
Ethanol is a chemical compound that is produced in small amounts within the small intestine and is also ingested from alcoholic drinks. Ethanol's digestion involves a complex catabolic pathway that mainly takes place in the liver. Ethanol is turned into acetaldehyde, then to acetate, and finally into acetyl-CoA, which becomes a substrate for the citric acid cycle and produces energy. Excessive ethanol intake can have pathologic metabolic consequences including alcoholism, liver disease, and cancer.
Chronic pancreatitis is due to persistent inflammation, fibrosis, and irreversible cell damage to the pancreas, resulting in a loss of endocrine and exocrine gland function. The most common etiologies are alcohol abuse and pancreatic duct obstruction. Patients often present with recurrent epigastric abdominal pain, nausea, and features of malabsorption syndrome (diarrhea, steatorrhea, and weight loss). Characteristic computed tomography (CT) findings include pancreatic atrophy, dilated pancreatic ducts, and pancreatic calcifications. Therapy focuses on alcohol cessation, diet changes, pain management, and treatment of pancreatic insufficiency.
Hypertension has many adverse effects on the eye, of which retinopathy is the most common presentation. Hypertensive retinopathy consists of retinal vascular changes that develop as a direct effect of elevated blood pressure. In acute increases of blood pressure, autoregulation results in retinal arteriolar narrowing. In chronic hypertension, structural changes consistent with arteriosclerosis affect the retinal vasculature. Endothelial wall damage ensues and various signs appear including hemorrhages, cotton-wool spots, and exudates. In severe cases of uncontrolled hypertension, papilledema is seen. Management is focused on controlling hypertension. Patients with severe hypertensive retinopathy have an increased risk for coronary artery disease and stroke; therefore, detection and treatment of underlying hypertension are important.
Actinic keratosis (AK) is a precancerous skin lesion that affects sun-exposed areas. The condition presents as small, non-tender macules/papules with a characteristic sandpaper-like texture that can become erythematous scaly plaques. Actinic keratosis is usually diagnosed clinically but suspicious features warrant a biopsy to rule out invasive squamous cell carcinoma. The majority of AK lesions remain non-malignant, but it is difficult to distinguish those that will resolve from those that will become cancerous. Actinic keratosis has multiple types of treatment, including cryotherapy, shave removal, excision, topical medications, and photodynamic therapy. Lesions with features that are suggestive of cancer warrant removal and pathologic evaluation.
The development of the brain, spinal cord, and face involve several complex processes that occur simultaneously to achieve correct organ development. Beginning with neurulation, the neural tube and neural crest cells form the central and peripheral nervous systems. Beginning at the 4th week, the face begins to develop as well, and through the creation of frontonasal, medial, lateral, and mandibular prominence, recognizable facial features can be observed from the 14th week onward.
The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. The afferent pathway for visual function starts from the retina and moves through the optic tracts and lateral geniculate nuclei, terminating in the visual cortex. Light stimulus is conducted by the parasympathetic system to the midbrain, while psychosensory reaction is processed by the sympathetic system. Efferent pathways produce the appropriate response: miosis and mydriasis from the parasympathetic and sympathetic innervations, respectively. Pupillary disorders result from defects in areas of the visual afferent and efferent pathways. Presentation varies with pupillary size along with response to light and medication.
Tricuspid regurgitation (TR) is a valvular defect that allows backflow of blood from the right ventricle to the right atrium during systole. Tricuspid regurgitation can develop through a number of cardiac conditions that cause dilation of the right ventricle and tricuspid annulus. A blowing holosystolic murmur is best heard at the left lower sternal border. Mild TR may be asymptomatic or present with systemic venous congestion due to increased right atrial and venous pressures. Echocardiography can establish the diagnosis. Treatment focuses on heart failure management, and surgery is reserved for severe disease.
Tricuspid stenosis (TS) is a valvular defect that obstructs blood flow from the right atrium to the right ventricle during diastole. This condition most commonly results from rheumatic heart disease or a congenital defect, and is usually found in conjunction with other valvular disease. A mid-diastolic murmur is best heard at the lower left sternal border. Mild TS may be asymptomatic or present with systemic venous congestion due to increased right atrial and venous pressures. Echocardiography can establish the diagnosis. Treatment focuses on heart failure management, and surgery is reserved for severe disease.
Nonalcoholic fatty liver disease is a spectrum of liver pathology that arises due to accumulation of triglycerides in hepatocytes. Risk factors include diabetes mellitus, insulin resistance, obesity, and hypertension, among others. Nonalcoholic fatty liver disease ranges from fatty liver or hepatic steatosis but can lead to nonalcoholic steatohepatitis (NASH), which features fatty deposits and inflammation. Progressive liver injury and fibrosis irreversibly develop into cirrhosis and, possibly, primary liver cancer. Patients are usually asymptomatic but may present with hepatomegaly and right upper quadrant discomfort. Although liver biopsy is the diagnostic gold standard, the diagnosis can also be established by clinical history, imaging, and laboratory tests. The mainstay of management is lifestyle modifications (weight loss and exercise) with control of associated comorbidities.
Renal artery stenosis (RAS) is the narrowing of one or both renal arteries, usually caused by atherosclerotic disease or by fibromuscular dysplasia. If the stenosis is severe enough, the stenosis causes decreased renal blood flow, which activates the renin-angiotensin-aldosterone system (RAAS) and leads to renovascular hypertension (RVH), which only accounts for a small fraction of all cases of hypertension. Renovascular hypertension can be associated with abdominal bruits, renal insufficiency, or progressive renal atrophy. Diagnosis is by clinical presentation followed by imaging studies, including duplex ultrasonography, magnetic resonance angiography (MRA), computed tomography angiography (CTA), and sometimes catheter-based angiography. Revascularization is usually reserved for cases in which medical therapy has failed.
Stevens-Johnson syndrome (SJS) is a cutaneous, immune-mediated hypersensitivity reaction that is commonly triggered by medications, including antiepileptics and antibiotics. The condition runs on a spectrum with toxic epidermal necrolysis (TEN) based on the amount of body surface area (BSA) involved. Stevens-Johnson syndrome is characterized by keratinocyte necrosis and separation of the epidermis from the dermis. Patients will present with a flu-like prodrome, followed by cutaneous bullae and sloughing on the face, thorax, and mucous membranes. Stevens-Johnson syndrome is considered a medical emergency, and management is largely supportive. Withdrawal of the causative agent is required. Monitoring for, and treating, superinfection is essential due to the high risk of associated death in these patients.
Valvular disorders can arise from the pulmonary valve, located between the right ventricle (RV) and the pulmonary artery (PA). Valvular disorders are diagnosed by echocardiography. Pulmonary stenosis (PS) is valvular narrowing causing RV outflow tract obstruction. Patients are often asymptomatic unless they have other congenital cardiac anomalies or severe PS. Symptoms (exertional dyspnea, chest pain, and syncope) are due to RV failure. Severe PS is treated surgically.
Neisseria is a genus of bacteria commonly present on mucosal surfaces. Several species exist, but only 2 are pathogenic to humans: N. gonorrhoeae and N. meningitidis. Neisseria species are non-motile, gram-negative diplococci most commonly isolated on modified Thayer-Martin (MTM) agar. These pathogens have many virulence factors, including fimbriae, lipooligosaccharide envelope proteins, a polysaccharide capsule (unique to N. meningitidis), and IgA protease. Gonococcal infections are sexually or perinatally transmitted and include gonorrhea, pelvic inflammatory disease, septic arthritis, and neonatal conjunctivitis. Meningococcal infections are transmitted via respiratory and oral secretions. They most commonly cause meningococcemia with petechial hemorrhages and meningitis.
The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. The muscles of the hand are classified as extrinsic (forearm-based) or intrinsic (hand-based) depending on the location of the muscle belly. These muscles are also grouped by area or type: thenar, hypothenar, lumbricals, and interossei.
Budd-Chiari syndrome is a condition resulting from the interruption of the normal outflow of blood from the liver. The primary type arises from a venous process (affecting the hepatic veins or inferior vena cava) such as thrombosis, but can also be from a lesion compressing or invading the veins (secondary type). The patient typically presents with hepatomegaly, ascites, and abdominal discomfort. Onset is often subacute or chronic. Diagnosis is confirmed by Doppler ultrasound. Treatment involves addressing the underlying condition that caused the venous occlusion. Further management involves prevention of further clotting (anticoagulation), restoration of blood flow, and decompressing the liver. Liver transplantation is considered if initial treatment fails and/or the patient has decompensated liver cirrhosis.
The cell undergoes a variety of changes in response to injury, which may or may not lead to cell death. Injurious stimuli trigger the process of cellular adaptation, whereby cells respond to withstand the harmful changes in their environment. Overwhelmed adaptive mechanisms lead to cell injury. Mild stimuli produce reversible injury. If the stimulus is severe or persistent, injury becomes irreversible. The principal targets of cell injury are the cell membranes, mitochondria, protein synthesis machinery, and DNA. Multiple cellular abnormalities resulting from the damage result in cell death. The 2 main types of cell death are necrosis and apoptosis. Necrosis is an uncontrolled cell death characterized by inflammatory changes in a pathologic condition. Apoptosis is programmed cell death, a mechanism with both physiologic and pathologic effects.
Primary biliary cholangitis (PBC) is a chronic disease resulting in autoimmune destruction of the intrahepatic bile ducts. The typical presentation is that of a middle-aged woman with pruritus, fatigue, and right upper quadrant abdominal pain. Elevated liver enzymes and antimitochondrial antibodies (AMAs) establish the diagnosis. Medical management is limited to using ursodeoxycholic acid, a disease-modifying agent. Definitive treatment is liver transplantation, which is performed in late stages (cirrhosis).
Altitude sickness refers to a spectrum of symptoms caused by physiological changes in the human body at altitudes above 2,500 m. Altitude sickness includes acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). Hypobaric hypoxia is a common pathophysiologic trigger. Acute mountain sickness and HACE represent 2 extremes of a neurologic disorder, from benign to life-threatening. High-altitude pulmonary edema is primarily a pulmonary problem, not necessarily preceded by AMS or HACE. The risk of altitude sickness can be reduced by gradual ascent and other precautionary measures, including medications. The symptoms of altitude sickness can be reduced with hyperbaric oxygen therapy.
A femoral hernia is an uncommon type of groin hernia in which intra-abdominal contents herniate under the inguinal ligament and through the femoral ring into the femoral canal. More common in adults than in children, femoral hernias usually present with swelling that protrudes into the femoral triangle (inferiorly to the inguinal ligament and medial to the femoral vein). Although uncommon, femoral hernias are frequently associated with complications, secondary to the small size of the canal, leading to hernia incarceration and/or strangulation.
Acute cholangitis is a life-threatening condition characterized by fever, jaundice, and abdominal pain which develops as a result of stasis and infection of the biliary tract. Septic shock, liver abscess, and multi-organ dysfunction are potential serious complications. The diagnosis is confirmed with ultrasound showing dilation of the common bile duct (CBD) or gallstones, elevated liver function tests, and leukocytosis. Treatment includes hemodynamic stabilization, broad-spectrum antibiotics, urgent biliary drainage, and cholecystectomy to prevent recurrence.
Decompression sickness (DCS), known informally as “the bends,” is a condition caused by compression and decompression of gases contained in the body during descent and rapid ascent while diving. Clinical presentation of DCS may be nonspecific and variable, with a time of onset that can vary from immediately to 12 hours after surfacing. Diagnosis is made clinically. Management is early supportive therapy and hyperbaric recompression treatment carried out in a specialized facility.
Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. The 1st-degree block is due to delayed conduction through the AV node. The 2nd-degree block is characterized by progressive conduction delay or intermittently blocked conduction. The 3rd-degree block involves total interruption in conduction between the atria and ventricles, causing complete AV dissociation. Patients may be asymptomatic or may present with syncope, chest pain, dyspnea, and bradycardia depending on the severity of the block. Electrocardiography (ECG) establishes the diagnosis, and treatment is based on the type of block and hemodynamic stability of the patient.
Acute pancreatitis is an inflammatory disease of the pancreas due to autodigestion. Common etiologies include gallstones and excessive alcohol use. Patients typically present with epigastric pain radiating to the back. Diagnosis requires 2 of 3 criteria, including: characteristic abdominal pain, serum amylase and lipase 3 times the upper limit of normal, or characteristic radiology findings. Ranson’s criteria is commonly used to assess the severity. Management includes aggressive intravenous (IV) hydration, analgesia, nutritional support, and treatment of the underlying cause.
Congenital renal abnormalities arise from embryologic/genetic defects and cause a variety of isolated or syndromic renal disorders, including renal agenesis, dysgenesis, and ectopia. Congenital renal abnormalities are generally identified prenatally and represent approximately ⅓ of all prenatal anomalies. Because of the fetal kidney’s role in the production of amniotic fluid, oligohydramnios detected on prenatal ultrasounds often prompts the workup that identifies congenital renal anomalies. Unilateral renal involvement in the presence of a functioning contralateral kidney may only be an incidental finding later in life. In many cases, treatment is supportive.
Complement component 3 (C3) deficiency is the absence, reduction, or dysfunction of complement factor C3 and its fragments, C3a and C3b. Complement factors are key components of the innate immune system. Reduced levels of C3b increase the probability of developing infections with encapsulated organisms (e.g., Pneumococcus, Haemophilus influenza, Neisseria meningitidis), especially respiratory infections, due to reduced opsonization. Individuals with C3 deficiencies are also more susceptible to type III hypersensitivity reactions because a reduced clearance of antigen-antibody C3b complexes from the circulation causes an increased risk of hypersensitivity reactions.
Gastroenteritis is inflammation of the stomach and intestines, commonly caused by infections from bacteria, viruses, or parasites. Transmission may be foodborne, fecal-oral, or through animal contact. Common clinical features include abdominal pain, diarrhea, vomiting, fever, and dehydration. Diagnostic testing with stool analysis or culture is not always required, but can help determine the etiology in certain circumstances. The majority of cases of gastroenteritis are self-limited; therefore, the only required treatment is supportive therapy (fluids). However, antibiotics are indicated in severe cases.
The most common benign liver tumors include hepatic hemangiomas, focal nodular hyperplasia, and hepatic adenomas. These tumors are mostly asymptomatic and/or found incidentally on abdominal imaging. While these tumors are benign, large lesions can cause symptoms such as upper abdominal pain, or produce complications such as bleeding. Malignant potential is a concern for hepatic adenoma, depending on risk factors. The diagnosis is based on imaging studies, with characteristic findings defining the tumor. Biopsy generally is reserved for equivocal cases. Management is observation for most small, asymptomatic, and non-growing tumors. However, high-risk factors, symptoms, increasing tumor size, and complications dictate the need for surgical intervention.
Lynch syndrome, also called hereditary non-polyposis colorectal cancer (HNPCC), is the most common inherited colon cancer syndrome, and carries a significantly increased risk for endometrial cancer and other malignancies. Lynch syndrome has an autosomal dominant inheritance pattern involving pathogenic variants in one of the mismatch repair (MMR) genes or epithelial cell adhesion molecule (EpCAM). Diagnosis is made by genetic testing of the index patient and their family members. Management consists of an earlier screening of individuals with defective MMR genes, as well as total colectomy if colorectal neoplasia is discovered. Prophylactic hysterectomy plus salpingo-oophorectomy are recommended for women beyond reproductive age.
Treacher Collins syndrome is a rare genetic condition with autosomal dominant inheritance. Treacher Collins syndrome is also referred to as mandibulofacial dysostosis or Franceschetti syndrome and is characterized by significant craniofacial deformities and conductive hearing loss. Treacher Collins syndrome is strictly a physical disease and does not affect cognition or other spheres of development. Diagnosis is confirmed with genetic testing. Management of the airway, feeding ability, and hearing loss are the primary concerns in the first few years of life. Ultimately, facial reconstructive surgery is needed. Life expectancy is normal.
Hereditary angioedema (HAE), also known as C1 esterase inhibitor (C1-INH) deficiency, is an autosomal dominant disorder characterized by recurrent episodes of severe swelling (angioedema). Hereditary angioedema commonly affects the limbs, face, intestinal tract, and upper airway. Swelling in the airway can restrict breathing and lead to a life-threatening airway obstruction. Hereditary angioedema has 3 subtypes distinguished by their underlying etiologies and levels of C1 inhibitor in the blood. Management includes treatment with danazol, kallikrein inhibitors, and C1-INHs. Hereditary angioedema is self-limiting, but may be fatal if the airway becomes compromised.
Small bowel obstruction (SBO) is an interruption of the flow of the intraluminal contents through the small intestine, and is classified as mechanical (due to physical blockage) or functional (due to disruption of normal motility). The most common cause of SBO in the Western countries is post-surgical adhesions. Small bowel obstruction typically presents with nausea, vomiting, abdominal pain, distention, constipation, and/or obstipation. The diagnosis is established via imaging. Up to 80% of all cases will resolve with supportive management (bowel rest, intravenous (IV) hydration, and nasogastric decompression). However, surgery is required for persistent or complicated cases.
The gluteal region is located posterior to the pelvic girdle and extends distally into the upper leg as the posterior thigh. The gluteal region consists of the gluteal muscles and several clinically important arteries, veins, and nerves. The muscles of the gluteal region help to move the hip joint during walking, running, standing, and sitting and are specialized for bearing weight and maintaining the horizontal balance of the pelvis.
Fibromuscular dysplasia (FMD) is a nonatherosclerotic, noninflammatory, medium-sized angiopathy due to fibroplasia of the vessel wall. The condition leads to complications related to arterial stenosis, aneurysm, or dissection. The clinical presentation can differ depending on which arteries are affected, but may include secondary hypertension from renal artery stenosis (RAS), neurologic deficits from cerebrovascular involvement, claudication due to limb involvement, and intestinal angina from mesenteric artery disease. The diagnosis is confirmed with imaging, such as computed tomography with angiography. Treatment includes lifestyle modifications, antihypertensive therapy for RAS patients, and potential revascularization.
Klinefelter syndrome is a chromosomal aneuploidy characterized by the presence of 1 or more extra X chromosomes in a male karyotype, most commonly leading to karyotype 47,XXY. Klinefelter syndrome is associated with decreased levels of testosterone and is the most common cause of congenital hypogonadism. Symptoms are often not noticed until adolescence or adulthood. Individuals with this condition tend to present as tall, phenotypic men with small testes, decreased body hair, gynecomastia, and infertility. Treatment consists of life-long testosterone replacement therapy.
Dysphagia is the subjective sensation of difficulty swallowing. Symptoms can range from a complete inability to swallow, to the sensation of solids or liquids becoming “stuck.” Dysphagia is classified as either oropharyngeal or esophageal, with esophageal dysphagia having 2 sub-types: functional and mechanical. Common causes of functional dysphagia include achalasia, scleroderma, and diffuse esophageal spasm (DES). Mechanical causes of dysphagia include esophageal rings, webs, strictures, and cancer. Oropharyngeal dysphagia may be due to structural abnormalities or abnormal neuromuscular function and coordination. The diagnostic workup depends on the patient’s presenting symptoms, but may include manometry, barium esophagram, or direct visualization with nasopharyngeal laryngoscopy or endoscopy. Treatment varies depending on the underlying cause.
Actinomyces is an anaerobic, gram-positive, branching, filamentous rod. Actinomyces israelii is the most common species involved in human disease. The organism is commonly found as part of the normal flora in the oral cavity, gastrointestinal tract, and reproductive tract. The disease is caused when the organism is displaced even by minor trauma or procedure, allowing the organism to move beyond the mucosal barrier. Reaching areas of low oxygen leads to the organism's multiplication. Actinomyces is associated with cervicofacial infection, which forms draining sinus tracts. Actinomyces can also affect the thoracic, abdominal, and pelvic areas. Drainage or infected tissue may have the characteristic yellow sulfur granules associated with Actinomyces. Management is with long-term penicillin and surgery, if needed.
Nocardia is a branching, filamentous, gram-positive bacilli. It is partially acid fast due to the presence of mycolic acids in the cell wall. Nocardia is a ubiquitous soil organism that most commonly affects immunocompromised patients. Nocardia is transmitted via inhalation of aerosolized bacteria or less commonly, via direct contact with wounds. Nocardia causes opportunistic infections, primarily pulmonary infections (pneumonia, abscess, or cavitary lesions), which may spread to form brain abscesses. In immunocompetent patients, Nocardia can cause a cutaneous infection. Treatment for nocardiosis is with trimethoprim–sulfamethoxazole and/or surgical intervention as indicated.
Pseudomonas is a non-lactose-fermenting, gram-negative bacillus that produces pyocyanin, which gives it a characteristic blue-green color. Pseudomonas is found ubiquitously in the environment, as well as in moist reservoirs, such as hospital sinks and respiratory equipment. Pseudomonas has a sweet, grape-like odor. The most clinically relevant species is Pseudomonas aeruginosa (P. aeruginosa), which has a wide array of clinical manifestations from benign diseases, such as swimmer’s ear and “hot tub” folliculitis, to disseminated bacteremia and osteomyelitis. Risk factors for infections include: neutropenia, cystic fibrosis, asplenia, burn injuries, and indwelling catheters/endotracheal intubation. Management is primarily with piperacillin/tazobactam.
Large bowel obstruction is an interruption in the normal flow of intestinal contents through the colon and rectum. This obstruction may be mechanical (due to the actual physical occlusion of the lumen) or functional (due to a loss of normal peristalsis, also known as pseudo-obstruction). Malignancy and volvulus are the most common causes of mechanical large bowel obstruction. Typical symptoms include intermittent lower abdominal pain, abdominal distention, and obstipation. Diagnosis is established with imaging. Mechanical large bowel obstruction requires surgery in most cases.
Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. The replication cycle differs between viruses that infect bacteria (bacteriophages) and viruses that infect eukaryotic cells. Bacteriophages have either a lytic or lysogenic replication cycle, while eukaryotic viruses have a defined 6-step replication process.
A Meckel’s diverticulum is a persistent remnant of the omphalomesenteric (vitelline) duct. A Meckel’s diverticulum is usually located in the antimesenteric border of the ileum. The mucosal lining of the diverticulum may contain heterotopic mucosa (most commonly gastric). Though frequently asymptomatic, a Meckel’s diverticulum can cause ulceration and present with lower gastrointestinal (GI) bleeding. Other complications include diverticulitis or small bowel obstruction (SBO). A Meckel’s scan can detect the diverticulum in hemodynamically stable patients. For those with active bleeding, arteriography is the diagnostic option. The treatment for a symptomatic Meckel’s diverticulum is surgery.
Brucellosis (also known as undulant fever, Mediterranean fever, or Malta fever) is a zoonotic infection that spreads predominantly through ingestion of unpasteurized dairy products or direct contact with infected animal products. Clinical manifestations include fever, arthralgias, malaise, lymphadenopathy, and hepatosplenomegaly. The clinical manifestations, exposure history, serology, and culture data are used in the diagnosis. Treatment involves a combination of antibiotics, including doxycycline, rifampin, and aminoglycosides. Preventative measures include avoiding unpasteurized dairy products, vaccinating livestock, and using caution around animals.
The primary visual pathway consists of a relay system, beginning at the retina, whose ganglion cell axons form the optic nerve. The optic nerve fibers from each eye hemidecussate in the optic chiasm (OC), with nasal fibers joining the temporal fibers of the contralateral nerve. The nasal fibers continue as the optic tract on each side, synapsing with the lateral geniculate nucleus (LGN) of the thalamus. Signals are then transmitted to the primary visual cortex of the occipital lobe. The right and left visual fields are processed by opposite hemispheres. Lesions along the pathway result in vision loss or visual field deficits. Based on the type of presentation, the location of the lesion in the pathway can be ascertained.
Colorectal cancer (CRC) is the 2nd-leading cause of cancer-related death in the United States. Almost all cases of CRC are adenocarcinoma and the majority of lesions come from the malignant transformation of an adenomatous polyp. As most CRCs are asymptomatic, screening is essential in detecting early disease. Screening is recommended to start at the age of 45 years, utilizing various screening tools available with colonoscopy, flexible sigmoidoscopy, and fecal tests among them. For high-risk individuals, earlier and more frequent screening is recommended. Other stool-based strategies and visualization tests are also available for CRC screening.
Giardiasis is caused by Giardia lamblia (G. lamblia), a flagellated protozoan that can infect the intestinal tract. Giardia transmission occurs most commonly through consumption of cysts in contaminated water or through the fecal-oral route. Excystation occurs in the gastrointestinal (GI) tract, and trophozoites attach to the intestinal wall villi and cause malabsorption. The hallmark symptom of giardiasis is foul-smelling steatorrhea. Patients who develop chronic infections may experience weight loss, failure to thrive, and vitamin deficiencies as a result of malabsorption. The diagnosis is made through detection of Giardia organisms, antigens, or deoxyribonucleic acid (DNA) in the stool. Management includes supportive treatment and antimicrobial therapy with metronidazole, tinidazole, or nitazoxanide. Prevention measures include proper handwashing and water treatment.
Mycoplasma is a species of pleomorphic bacteria that lack a cell wall, which makes them difficult to target with conventional antibiotics (particularly penicillins and other beta-lactam antibiotics that target cell wall synthesis) and causes them to not gram stain well. Mycoplasma bacteria commonly target the respiratory and urogenital epithelium. Mycoplasma pneumoniae (M. pneumoniae), the causative agent of atypical or “walking” pneumonia, is the most clinically relevant species. Antibiotics, particularly macrolides, are the most effective mode of therapy.
Anthrax is an infection caused by the bacterium Bacillus anthracis, which usually targets the skin, lungs, or intestines. Anthrax is a zoonotic disease and is usually transmitted to humans from animals or through animal products. The Bacillus spores can persist in soil for a long time. The Bacillus spores have also been used as a biological weapon. Symptoms depend on which organ system is affected. The skin forms small blisters with surrounding swelling that often turn into a painless ulcer with a black center. Inhalational exposure causes severe fulminant pneumonia. Intestinal exposure causes mucosal ulcers, bloody diarrhea, abdominal pain, nausea, and vomiting. Diagnosis is established with cultures, tissue examination, and polymerase chain reaction (PCR). Management involves antibiotics, antitoxins, and frequently hospital/critical care admission. Mortality from systemic disease remains high.
Delayed puberty (DP) is defined as the lack of testicular growth in boys past the age of 14 and the lack of thelarche in girls past the age of 13. Delayed puberty affects up to 5% of healthy boys and girls, and half of all cases are due to constitutional growth delay. Classified as central or gonadal, delayed puberty has multiple etiologies, expressed as a lack of development of secondary sexual characteristics. Diagnosis is made by clinical criteria and confirmed through laboratory testing. Management involves sex-steroid replacement therapy when indicated.
Shigella is a genus of gram-negative, non-lactose-fermenting facultative intracellular bacilli. Infection spreads most commonly via person-to-person contact or through contaminated food and water. Humans are the only known reservoir. Because it is resistant to acid, Shigella spp. survive transit through the stomach; thus, only a small amount of inoculum is needed to cause disease. Shigellosis (Shigella dysentery) results in fever, abdominal pain, and bloody diarrhea, which are effects of the toxins and epithelial-cell invasion of the organism. In the majority of cases, symptoms resolve within a few days. However, complications of dehydration, hemolytic uremic syndrome, toxic megacolon, or reactive arthritis can arise. Treatment is primarily using fluid and electrolyte replacement and antibiotics.
Cardiac myxoma is the most common of the primary tumors of the adult heart, all of which are very rare. Cardiac myxoma is a benign neoplasm that arises from primitive multipotent mesenchymal cells. Most occur sporadically, but some are a part of some familial syndromes. All 4 chambers may give rise to myxoma, but 90% originate and grow in the atria, with a left-to-right ratio of approximately 4:1. Diagnosis is made by echocardiography, cardiac magnetic resonance imaging (MRI), or cardiac computed tomography (CT). Complete surgical excision is required because of the substantial risk of embolization and cardiovascular complications, including sudden death.
Leptospira is a spiral or question mark–shaped, gram-negative spirochete with hook-shaped ends. The disease, leptospirosis, is a zoonosis, infecting animals. Rodents are the most important reservoir. Bacteria shed in the urine of rodents and other animals can be transmitted to humans via contaminated water. The major clinical species is Leptospira interrogans, which causes a mild flu-like illness in a majority of cases. The manifestations are biphasic, with Leptospira found in the blood initially. In the immune phase, the bacteria disappear from the bloodstream and can be detected in the urine. In about 10% of infections, icterohemorrhagic leptospirosis develops, manifesting as hemorrhage, renal failure, and jaundice. Bacterial culture takes weeks, so other diagnostic tests such as serology and dark field microscopy are used. Treatment is primarily with penicillin.
The human immunodeficiency virus (HIV) is a species of Lentivirus, a genus of the family Retroviridae, which causes HIV infections and acquired immunodeficiency syndrome (AIDS). The virus has high genetic variability and is divided into 2 major types, HIV type 1 (HIV-1) and HIV type 2 (HIV-2). The human immunodeficiency virus is a single-stranded, positive-sense, enveloped RNA virus, which targets and destroys WBCs, leading to frequent opportunistic infections and, eventually, death.
Cervical cancer is the 3rd most common gynecologic cancer. More than 90% of cervical cancer cases are associated with high-risk human papillomavirus (hrHPV), which is transmitted by sexual contact. Cervical cancer can be prevented by early detection and treatment of precancerous lesions caused by hrHPV. The methods of detection are cervical cytology and HPV testing. Screening is recommended by the age of 21 and is generally repeated every 3 years up to the age of 29 in an average-risk individual. By age 30, HPV testing with cytology is obtained. Since the screening program was initiated, there has been a 75% decline in the incidence of and mortality from cervical cancer.
Bacteroides is a genus of opportunistic, anaerobic, gram-negative bacilli. Bacteroides fragilis is the most common species involved in human disease and is part of the normal flora of the large intestine. Infection most commonly occurs when the colon wall is breached and bacteria enter the peritoneal cavity, which can cause intra-abdominal infections and intra-abdominal abscess formation. Management involves antibiotics and abscess drainage.
Gas gangrene, also known as clostridial myonecrosis, is a life-threatening muscle and soft tissue infection that usually develops after traumatic inoculation with Clostridium perfringens (C. perfringens), but can also develop spontaneously in association with other Clostridium species. Sudden, severe muscle pain classically develops shortly after the injury. Skin color changes (red/purple to black), tenderness, bullae formation, and crepitus are also present and progress rapidly. Most of the time, diagnosis is established clinically. Once the diagnosis is suspected, intravenous (IV) antibiotic therapy should be started and emergent surgical debridement should be performed.
Chiari malformations (CMs) are a group of central nervous system (CNS) conditions characterized by the underdevelopment of the posterior cranial fossa with subsequent protrusion of neural structures through the foramen magnum. There are 4 types of CM, with type I being the most common. Headaches are the most common symptom. Diagnosis is made by clinical findings and confirmed by magnetic resonance imaging (MRI). Treatment is surgical, based on decompression of the posterior fossa and restoration of CNS flow. Prognosis depends on the type of malformation.
Penetrating chest injuries (PCIs) are caused by an object puncturing the chest wall. Penetrating chest injuries can be high velocity, such as with gunshot wounds (GSWs); medium velocity, such as with pellet gunshots; or low velocity, such as with stab wounds. Penetrating chest injuries have a higher mortality rate than blunt chest injuries but are less common. Performing the standardized trauma evaluation (primary and secondary surveys), as well as ordering proper imaging, is critical to determining the diagnosis and aiding in management decisions. The majority of PCIs do not require major surgery and can be managed by observation or tube thoracostomy, although surgical repair of injuries may be needed.
Transposition of the great vessels (TGV) is a cyanotic congenital heart disease characterized by “switching” of the great arteries. There are 2 presentations: the dextro (D)- and levo (L)-looped forms. The L-looped form is rare and congenitally corrected, as the ventricles are also switched. The D-looped form accounts for 3% of all cases of congenital heart disease. The condition occurs within the neonatal phase of life with cyanosis that is unresponsive to oxygen therapy. Diagnosis is confirmed by echocardiogram and a chest X-ray showing the classic “egg on a string” pattern. Treatment is primarily surgical, and the prognosis for surgically corrected cases is good.
Foreign body aspiration can lead to choking and death by obstructing airflow at the larynx or trachea. Foreign bodies may also become lodged deeper in the bronchi; this may not affect breathing but can cause infection or erosion of bronchial walls. Foreign bodies (FBs) are more frequently aspirated by children, who may present with coughing or wheezing. As FBs are rarely visible on X-ray, other modalities of imaging, such as computed tomography or flexible bronchoscopy, must be employed when prompted by symptoms and clinical suspicion. The relative frequency with which various objects are aspirated varies based on patient demographics. Prompt removal of the FB is the definitive treatment.
Campylobacter ("curved bacteria") is a genus of thermophilic, S-shaped, gram-negative bacilli. There are many species of Campylobacter, with C. jejuni and C. coli most commonly implicated in human disease. The mode of transmission is primarily through the consumption of undercooked food contaminated with Campylobacter. Infection is most often associated with self-limiting gastroenteritis and is also a major cause of bloody diarrhea, especially in children. Two associated complications of Campylobacter gastroenteritis are Guillain-Barré syndrome and reactive arthritis.
Vibrio is a genus of comma-shaped, gram-negative bacilli. It is halophilic, acid labile, and commonly isolated on thiosulfate-citrate-bile-sucrose (TCBS) agar. There are 3 clinically relevant species. Vibrio cholerae (V. cholerae) is found in brackish and marine waters. Vibrio cholerae is associated with cholera, which causes severe, secretory “rice-water” diarrhea. The other 2 species are Vibrio vulnificus (V. vulnificus) and Vibrio parahaemolyticus (V. parahaemolyticus), which are transmitted through raw or undercooked shellfish and are associated with wound infections, septicemia, and diarrhea.
Legionella is a facultative intracellular, gram-negative bacilli. Legionella does not grow on common culture media because it requires certain supplementation (cysteine and iron). Legionella can be isolated on a buffered charcoal yeast extract (BCYE) medium. The habitat for Legionella is aquatic systems including human-constructed reservoirs, such as cooling towers and hot water tanks. Transmission occurs primarily through inhalation of aerosolized water droplets, causing pulmonary infection. Legionella pneumophila (L. pneumophila) accounts for the majority of human infections. The clinical presentation includes Legionnaires’ disease, atypical pneumonia, and Pontiac fever. Diagnosis is by culture, urine antigen test, and/or polymerase chain reaction (PCR). Fluoroquinolones and macrolides are the main treatments.
Flail chest is a life-threatening traumatic injury that occurs when 3 or more contiguous ribs are fractured in 2 or more different locations. Patients present with chest pain, tachypnea, hypoxia, and paradoxical chest wall movement. Management includes oxygen supplementation, pain control, ventilation if respiratory failure presents, and possible surgery. Severe traumatic intrathoracic injuries, such as pulmonary contusions, pneumothorax, and cardiac injuries, are often seen in conjunction with flail chest.
Atrial septal defects (ASDs) are benign acyanotic congenital heart defects characterized by an opening in the interatrial septum that causes blood to flow from the left atrium (LA) to the right atrium (RA) (left-to-right shunt). Atrial septal defects account for approximately 15% of all cases of congenital heart disease (CHD), making ASDs the 2nd most common CHD. There are 4 types of ASD based on the location of the defect along the atrial septum, but the most common is the ostium secundum defect. Atrial septal defects are usually detected during a routine physical examination and confirmed by an echocardiogram. In infancy, most small ASDs close spontaneously by 2 years of age. Only patients that are symptomatic require surgical closure. In general, most patients with ASD can expect a good overall outcome.
Airway obstruction is a partial or complete blockage of the airways that impedes airflow. An airway obstruction can be classified as upper, central, or lower depending on location. Lower airway obstruction (LAO) is usually a manifestation of chronic disease, such as asthma or chronic obstructive pulmonary disease (COPD). Upper airway obstruction (UAO) and central airway obstruction (CAO) refers to a mechanical blockage of the large airways and are potentially life-threatening events, which need to be recognized and managed promptly.
Aromatase deficiency is a very rare genetic condition with autosomal recessive inheritance. Aromatase deficiency is characterized by congenital estrogen deprivation with increased levels of testosterone due to decreased levels of the aromatase enzyme. Affected females present with abnormal development of the external genitalia, virilization, primary amenorrhea, and tall stature. Males usually develop symptoms later in life, including hyperinsulinemia and lipid metabolism disorders. Individuals affected by aromatase deficiency have an increased risk of developing osteoporosis. Treatment involves hormone replacement therapy.
Bordetella is a genus of obligate aerobic, Gram-negative coccobacilli. They are highly fastidious and difficult to isolate. The most important pathologic species is Bordetella pertussis (B. pertussis), which is commonly isolated on Bordet-Gengou agar. Bordetella pertussis is highly infectious via respiratory droplets and is only known to infect humans, causing the clinical syndrome of pertussis. Pertussis is characterized by 3 distinct phases: catarral, paroxysmal, and convalescent. Pertussis is rare in developed countries due to widespread use of the diphtheria, tetanus, and acellular pertussis (DTaP) combined vaccine.
Antiphospholipid syndrome (APLS) is an acquired autoimmune disorder characterized by the persistent presence of antiphospholipid antibodies, which create a hypercoagulable state. These antibodies are most commonly discovered during a workup for a thrombotic event or recurrent pregnancy loss, which are the 2 most common clinical manifestations of APLS. Patients with APLS are at risk for both arterial and venous thrombosis, and after a thrombotic event, patients are managed with long-term anticoagulation therapy.
Corynebacteria are gram-positive, club-shaped bacilli. Corynebacteria are commonly isolated on tellurite or Loeffler's media and have characteristic metachromatic granules. The major pathogenic species is Corynebacterium diphtheriae, which causes diphtheria—a severe upper respiratory infection. The characteristic findings of diphtheria include pharyngeal pseudomembranes (grayish tonsillar exudates), severe pharyngitis, and “bull’s neck” lymphadenopathy. Treatment is primarily through passive immunization with antitoxin and antibiotics. Prevention is via the diphtheria toxoid vaccine.
Reactive arthritis is a seronegative autoimmune spondyloarthropathy that occurs in response to a previous gastrointestinal (GI) or genitourinary (GU) infection. The pathophysiology of this disease is unclear, but a significant proportion of affected patients are positive for HLA-B27. The disease manifests as asymmetric oligoarthritis (particularly of large joints in the lower extremities), enthesopathy, dactylitis, and/or sacroiliitis. Ocular, mucocutaneous, GI, GU, and cardiac manifestations may also occur. The diagnosis is clinical, and efforts should be made to rule out alternative diagnoses. Management focuses on controlling symptoms, typically with nonsteroidal anti-inflammatory drugs. An active infection should also be treated, particularly Chlamydia trachomatis.
Splenic rupture is a medical emergency that carries a significant risk of hypovolemic shock and death. Injury to the spleen accounts for nearly half of all injuries to intra-abdominal organs. The most common reason for a rupture of the spleen is blunt abdominal trauma, specifically, motor vehicle accidents. For individuals with splenomegaly, however, even minimal trauma may result in splenic injury or rupture. Patients often present with LUQ abdominal pain; however, pain may be referred to the left shoulder. Patients are at risk for hemodynamic instability due to blood loss. The diagnosis is generally made with CT imaging, and management, ranging from observation to splenectomy, depends on the patient’s hemodynamic stability.
Clostridia species comprise a group of spore-forming, obligate anaerobic, gram-positive bacilli. Major pathogenic species include Clostridium perfringens (C. perfringens), which is associated with gas gangrene; Clostridioides difficile, which is associated with pseudomembranous colitis; C. tetani, which causes tetanus; and C. botulinum, which causes botulism. Clostridium perfringens (C. perfringens), Clostridioides difficile, C. tetani, and C. botulinum have broad-spectrum invasiveness and clinical manifestations that are summarized below. Note that Clostridium difficile has been reclassified as Clostridioides difficile. However, exams will likely not have the updated genus for several years.
Yersinia is a genus of bacteria characterized as gram-negative bacilli that are facultative anaerobic with bipolar staining. There are 2 enteropathogenic species that cause yersiniosis, Y. enterocolitica and Y. pseudotuberculosis. Infections are manifested as pseudoappendicitis or mesenteric lymphadenitis, and enterocolitis. The bacteria are transmitted through consumption of contaminated food products or water. Manifestations include fever, abdominal pain, and/or diarrhea. The gastrointestinal illness is usually self-limiting. Antibiotics are given for severe infection and in immunocompromised patients.
The plague is a bacterial infection caused by Yersinia pestis (Y. pestis), which primarily infects rodents. The disease is transmitted to humans via a fleabite. Inhalation of infectious droplets and handling infected animals or laboratory specimens are other means of transmission. The plague has 3 forms: bubonic (most common form), septicemic, and pneumonic. Bubonic plague results in swollen and tender lymph nodes called buboes in the inguinal area. Pneumonic and septicemic plague can arise as the primary presentation, but also can result from hematogenous spread from the bubonic disease. Diagnosis includes clinical history and findings, culture, polymerase chain reaction (PCR), and serology. The mortality rate is high, so prompt diagnosis and treatment with antibiotics are necessary.
Osgood-Schlatter disease, or apophysitis of the tibial tubercle, is a common orthopedic condition seen in children between 10 and 15 years of age. The disease is caused by the repetitive application of mechanical forces on the knee, leading to microtrauma on the ossification center at the site of insertion of the distal patellar ligament. Patients present with localized knee pain, tenderness, and swelling at the proximal anterior tibia. Diagnosis is clinical and treatment is focused on symptomatic relief. Osgood-Schlatter disease is a self-limiting condition that resolves with skeletal maturity.
Ebstein's anomaly (EA) is a cyanotic congenital heart disease (CHD) characterized by the downward displacement of the septal and posterior leaflets of the tricuspid valve (TV). Ebstein's anomaly accounts for less than 1% of all cases of CHD. Maternal use of lithium is a common cause of EA. Clinical presentation varies, with the most common symptom being cyanosis. The age of presentation varies from in utero to adulthood and is proportional to the severity of the TV displacement, most cases present during adolescence. Ebstein's anomaly presents with multiple comorbidities, especially Wolff-Parkinson-White syndrome. The diagnosis is confirmed by echocardiography and definitive treatment is surgical. Patients who are managed appropriately still have a reduced life expectancy.
Bacillus are aerobic, spore-forming, gram-positive bacilli. Two pathogenic species are Bacillus anthracis (B. anthracis) and B. cereus. Bacillus anthracis has a unique polypeptide capsule composed of D-glutamate and is associated with cutaneous, gastrointestinal, and pulmonary anthrax. Importantly, B. anthracis is classified as a bioterrorism agent. Bacillus cereus is associated with 2 forms of food poisoning, diarrheal and emetic, both of which are self-limited and require only supportive care.
Proteus spp. are gram-negative, facultatively anaerobic bacilli. Different types of infection result from Proteus, but the urinary tract is the most common site. The majority of cases are caused by Proteus mirabilis (P. mirabilis). The bacteria are part of the normal intestinal flora and are also found in the environment. Proteus spp. exhibit a characteristic swarming motility and strong urease activity, which enable initiation of infection. Hydrolysis of urea by urease leads to alkaline urine with an ammonia-like odor. With the elevated pH in the urine, struvite renal stones form, which eventually can cause obstruction and renal failure. Treatment is with antibiotics (e.g., trimethoprim-sulfamethoxazole) for the infection and surgical removal of the stones, if present.
Toxic shock syndrome (TSS) is an acute, multi-systemic disease caused by the toxin-producing bacteria, Staphylococcus aureus and Streptococcus pyogenes. Staphylococcal TSS is more common and associated with tampons and nasal packing. Streptococcal TSS is commonly due to invasive group A streptococcal (GAS) infections, such as bacteremia and necrotizing fasciitis, and has a higher mortality rate. Patients present with fever, tachycardia, hypotension, an erythematous rash, and evidence of multi-system organ dysfunction. The diagnosis is based on clinical, laboratory, and culture data. Management involves intravenous fluid (IVF) resuscitation, antibiotics, vasopressor support, and identification and management of the potential infectious source.
Slipped capital femoral epiphysis (SCFE) is an orthopedic disorder of early adolescence characterized by the pathologic “slipping” or displacement of the femoral head, or epiphysis, on the femoral neck. Considered a type I Salter-Harris growth plate fracture, SCFE affects boys twice as often as girls. Thought to be due to a combination of biomechanical and endocrine factors, diagnosis is made with hip X-rays and treatment ranges from conservative to surgical. Prognosis depends on the severity of the slip or displacement.
Injuries due to cold weather are common among children and athletes who are involved in sports played in cold conditions. There are multiple cold-related injuries, with frostbite being the most common. Frostbite is a direct freezing injury to the peripheral tissues and occurs when the skin temperature drops below 0℃ (32°F). Common sites of frostbite include the nose, ears, fingers, and toes. Clinical signs include skin pallor, anesthesia, blistering, and tissue necrosis. The main treatment is rapid rewarming.
Compartment syndrome is a surgical emergency usually occurring secondary to trauma. The condition is marked by increased pressure within a compartment that compromises the circulation and function of the tissues within that space. Long bone fractures are the most common cause, with the leg and forearm compartments frequently affected. Patients present with pain out of proportion to the injury and may also have pallor, pulselessness, paresthesia, poikilothermia, and paralysis (the 6 Ps of compartment syndrome). Diagnosis is clinical but compartment pressure measurement can be used. Management is an emergency fasciotomy. Failure to diagnose and manage the condition results in limb loss.
Carbon monoxide (CO) is an odorless, colorless, tasteless, nonirritating gas formed by hydrocarbon combustion (e.g., fires, car exhaust, gas heaters). Carbon monoxide has a higher affinity to hemoglobin than oxygen, forming carboxyhemoglobin (COHb). Increased levels of COHb lead to tissue hypoxia and brain damage. Symptoms of CO poisoning include headache, nausea, weakness, chest pain, shortness of breath, seizures, coma, and even death. Oxygen therapy is key to the management of CO poisoning.
Scleroderma (systemic sclerosis) is an autoimmune condition characterized by diffuse collagen deposition and fibrosis. The clinical presentation varies from limited skin involvement to diffuse involvement of internal organs. Diagnosis is established by a combination of physical findings and serology. There is no curative treatment. Management options are limited and include immunosuppressive medications as well as specific organ- or symptom-directed drugs. The overall 5-year survival of patients with scleroderma is about 80%.
Erythema infectiosum is a rash illness caused by parvovirus B19. Erythema infectiosum is also known as fifth disease, being 5th in the historical list of rash-causing childhood infectious diseases: measles (1st), scarlet fever (2nd), rubella (3rd), Dukes' disease (4th), and roseola (6th). Transmission is through respiratory secretions. Diagnosis is generally clinical, suspected in patients presenting with an erythematous malar rash with circumoral pallor (“slapped cheek”). A rash over the trunk and extremities occurs afterward. The illness is self-limited and has no specific therapy. Complications can occur, however, due to the viral tropism for erythrocyte precursors. Patients with hemoglobinopathies can experience aplastic crisis, while the immunocompromised may have chronic infection producing pure red cell aplasia.
Benign prostatic hyperplasia (BPH) is a condition indicating an increase in the number of stromal and epithelial cells within the prostate gland (transition zone). Benign prostatic hyperplasia is common in men > 50 years of age and may greatly affect their quality of life. The development of BPH involves modifiable and non-modifiable risk factors, which lead to anatomic obstruction and downstream effects on other organ systems. Clinically, patients present with a combination of obstructive and bladder storage symptoms. Diagnosis is made by determining the severity of voiding symptoms through a variety of non-invasive (voiding diary, history, physical examination) and invasive (cystoscopy, urodynamics, transrectal ultrasound imaging) tools. Treatment is multimodal with medical and surgical components (prostatectomy) utilized in combination.
Rickettsiae are a diverse collection of obligate intracellular, gram-negative bacteria that have a tropism for vascular endothelial cells. The vectors for transmission vary by species but include ticks, fleas, mites, and lice. The most clinically relevant pathogens are R. rickettsii, which causes Rocky Mountain spotted fever; R. prowazekii, which causes epidemic (louse-borne) typhus; R. typhi, which causes endemic typhus; and R. akari, which causes rickettsialpox. All of these diseases are a form of inflammatory vasculitis and commonly present with fever, headache, and rash. Treatment is with doxycycline.
Klebsiella are encapsulated gram-negative, lactose-fermenting bacilli. They form pink colonies on MacConkey agar due to lactose fermentation. The main virulence factor is a polysaccharide capsule. Klebsiella pneumoniae (the most important pathogenic species) is commonly associated with lobar aspiration pneumonia in patients with alcohol-use disorder. It also causes nosocomial infections, such as hospital-acquired pneumonia and urinary tract infections, as well as tissue-destructing abscesses (liver, lung, spleen). Treatment is with cephalosporins for sensitive strains. However, many Klebsiella species have plasmids that confer multidrug resistance.
Leishmania species are obligate intracellular parasites that are transmitted by an infected sandfly. The disease is endemic to Asia, the Middle East, Africa, the Mediterranean, and South and Central America. Clinical presentation varies, dependent on the pathogenicity of the species and the host’s immune response. The mildest form is cutaneous leishmaniasis (CL), characterized by painless skin ulcers. The mucocutaneous type involves more tissue destruction, causing deformities. Visceral leishmaniasis (VL), the most severe form, presents with hepatosplenomegaly, anemia, thrombocytopenia, and fever. Management is based on the clinical severity and patient's immune status. Some cutaneous lesions spontaneously resolve or require local therapy. Systemic treatment (amphotericin B), however, is needed for VL.
The apophysis is a secondary ossification center found on non-weight-bearing segments of bones. The apophysis is also the site of ligament or tendon insertion and is involved in the peripheral growth of the bone. These secondary growth centers are generally open in late childhood and may not close until early adulthood. With overuse, the apophysis may become inflamed and painful, becoming vulnerable to tearing and avulsion. An acute apophyseal avulsion fracture occurs when a portion of the apophysis is pulled off by the ligament, usually secondary to explosive movements and eccentric muscular contractions. Apophyseal avulsion fractures are primarily treated conservatively, but may require surgical repair if the avulsed fragment is large or significantly displaced.
Borrelia are gram-negative microaerophilic spirochetes. Owing to their small size, they are not easily seen on Gram stain but can be visualized using dark-field microscopy, Giemsa, or Wright stain. Spirochetes are motile and move in a characteristic spinning fashion due to axial filaments in the periplasmic space. The ability of Borrelia to express different repertoires of surface proteins allows for bacterial transmission and evasion of the host immune system. Borrelia utilizes Ixodes ticks, Ornithodoros ticks, and the human body louse as vectors, and the resulting diseases include Lyme disease and relapsing fever.
The bones of growing children exhibit unique characteristics, which, combined with the unique mechanisms of injury seen in children, result in fracture patterns differing significantly from those common in adults. The greenstick fracture is an incomplete fracture usually seen in long bones. The bone is typically bent, and the fracture extends only partway through the bone. Greenstick fractures are at high risk for refracture and should be completely immobilized. Greenstick fractures rarely require reduction but should be managed cautiously to prevent malunion or angulation deformities. A patient with a greenstick fracture should be referred for orthopedic follow-up.
A “toddler’s fracture” is a spiral or oblique fracture of the distal tibia in toddlers resulting from a low-energy trauma with a rotational/twisting component. These fractures are often seen in children who are learning to walk and who do not have a specific history of trauma. The child can sometimes present with a painful limp or refusal to bear weight on the affected limb. Management comprises analgesia and immobilizing the injured leg for several weeks.
Antiretroviral therapy (ART) targets the replication cycle of the human immunodeficiency virus (HIV) and is classified based on the viral enzyme or mechanism that is inhibited. The goal of therapy is to suppress viral replication to reach the outcome of undetected viral load. Currently, reverse transcriptase, protease, integrase, and entry inhibitors are used in combined ART (cART) regimens. Combination therapy (3-drug regimen) is used to prevent drug resistance and cross-resistance, which develop through genetic mutations.
Rocky Mountain spotted fever (RMSF) is a bacterial infection caused by the obligate intracellular parasite Rickettsia rickettsii. Transmission occurs through an arthropod vector, most commonly the American dog tick (Dermacentor variabilis). Rocky Mountain spotted fever is prevalent in the southeastern United States. Early signs and symptoms of RMSF are nonspecific and include a high fever, severe headache, and rash. The rash is characteristic in that it begins peripherally and moves centrally, and also appears on the hands and soles. A high clinical suspicion is required for diagnosis, and empiric treatment with doxycycline is recommended within 5 days of symptoms onset.
The bones of growing children exhibit unique characteristics. These characteristics, combined with the unique mechanisms of injury seen in children, result in fracture patterns that differ significantly from those that are common in adults. When axial loads are applied, particularly to long bones in children, compressive forces may result in buckling of the bone without disruption of the periosteum. These fractures are called buckle or torus fractures and are considered generally stable, requiring only immobilization.
A gastrinoma is a tumor that secretes excessive levels of the hormone gastrin and is responsible for Zollinger-Ellison syndrome (ZES). Gastrinomas are frequently associated with multiple endocrine neoplasia 1 (MEN 1) and can arise from the pancreas, stomach, duodenum, jejunum, and/or even from the lymph nodes. Gastrinoma tumors are often malignant and frequently metastasize to the liver, lymph nodes, and bone. Zollinger-Ellison syndrome (ZES) is characterized by high gastrin levels, elevated gastric acid production, peptic ulcers, gastroesophageal reflux, and diarrhea. Diagnosis is based on fasting serum gastrin levels. Management consists of surgical resection of the gastrinoma and/or symptomatic management for unresectable disease.
Vascular rings are a group of rare malformations featuring congenital abnormalities of the aortic arch. The aberrant arteries often form a ring around the esophagus and trachea, putting pressure on these structures. Clinical symptoms range from stridor, respiratory distress, and/or dysphagia in neonates, to asymptomatic forms, noted incidentally in adults. Diagnosis is confirmed through X-ray and echocardiography, but may be further defined with a computed tomographic (CT) scan. Definitive treatment is surgical, and the prognosis is excellent as clinical recovery is immediate.
Salmonellae are gram-negative bacilli of the family Enterobacteriaceae. Salmonellae are flagellated, non-lactose-fermenting, and hydrogen sulfide-producing microbes. Salmonella enterica, the most common disease-causing species in humans, is further classified based on serotype as typhoidal (S. typhi and paratyphi) and nontyphoidal (S. enteritidis and typhimurium). Transmission occurs through the fecal-oral route and consumption of contaminated foods and water. Bacteria penetrate the intestinal cells through microfold cells of Peyer’s patches and cause abdominal symptoms. Pathogens can also disrupt sodium and chloride transport in the intestine (causing diarrhea) and invade the bloodstream (causing sepsis and nonintestinal infection). Major clinical presentations include typhoid or enteric fever, foodborne enterocolitis, and bacteremia. Antibiotic treatment is considered in severe illness and chronic carrier states.
Relapsing fever is a vector-borne disease caused by multiple species of the spirochete Borrelia. There are 2 major forms of relapsing fever: tick-borne relapsing fever (caused by multiple species, such as B. hermsii, B. miyamotoi, and B. turicatae) and louse-borne relapsing fever (caused by B. recurrentis). Patients go through recurrent stages of fever, crisis phase, and afebrile periods. Severe manifestations can include myocarditis, ARDS, and meningitis. Diagnosis is based on the clinical history and visualization of spirochetes on a thick and thin blood smear obtained during a febrile episode. Management of relapsing fever is with antibiotics, such as doxycycline, penicillin, or ceftriaxone. Patients should be monitored closely for Jarisch-Herxheimer reaction.
Hashimoto's thyroiditis, or chronic lymphocytic thyroiditis, is the most common cause of hypothyroidism in iodine-sufficient regions. The condition is an autoimmune disorder leading to destruction of the thyroid cells and thyroid failure. The gradual clinical course of Hashimoto's thyroiditis starts with a transient hyperthyroid state (“hashitoxicosis”) followed by subclinical hypothyroidism. Eventually, progression to overt hypothyroidism occurs, which is permanent. Patients may have a painless goiter, but in later stages, the gland is atrophic. Diagnosis is by laboratory tests showing elevated thyroid-stimulating hormone (TSH), low free thyroxine (T4), and positive antibodies against thyroglobulin and thyroid peroxidase. In uncertain cases, imaging is required. Radioactive iodine uptake will show low iodine uptake and ultrasound demonstrates diffuse symmetric enlargement. Biopsy shows lymphocytic infiltration with Hurthle cells. Treatment is lifelong thyroid hormone replacement.
An abscess is a collection of pus in the dermis or subcutaneous tissue. Abscesses are one of the commonly encountered skin and soft tissue infections. Although abscesses may occur spontaneously, predisposing factors such as abrasions and punctures are often identified. A patient with a skin abscess usually presents with a localized, fluctuant, tender mass that appears red and warm. Incision and drainage are the mainstay of management, but antibiotics can be used depending on the size of the abscess as well as the patient’s risk factors for severe infection.
Graves' disease is an autoimmune disorder characterized by the presence of circulating antibodies against the thyroid-stimulating hormone (TSH) receptors, thereby causing the thyroid gland to hyperfunction. Clinical features include hyperthyroidism (of which Graves' disease is the most common cause), orbitopathy, goiter, and dermopathy/pretibial myxedema. Manifestations reflect the muti-systemic effects of a hyperactive thyroid, including heat intolerance, sweating, palpitations, tremors, pretibial myxedema, and exophthalmos. Diagnosis is by thyroid laboratory tests showing a low TSH, elevated thyroid hormones (thyroxine (T4) and triiodothyronine (T3)) and thyrotropin-receptor antibodies (particularly the thyroid-stimulating immunoglobulins subtype). If initial tests are nondiagnostic, radioactive iodine uptake (increased uptake) and thyroid ultrasound (diffuse thyroid enlargement) provide diagnostic information. Treatment options include thionamides, radioiodine ablation, and surgery.
Chlamydial infections are a group of infectious diseases caused by bacteria belonging to the Chlamydiaceae family. The 3 species that can infect humans are Chlamydia trachomatis, C. pneumoniae, and C. psittaci. The most common infection is an STI caused by C. trachomatis, which affects the genitourinary tract. Chlamydia is the most common sexually transmitted bacterial infection in the United States. Other species of Chlamydia mainly cause respiratory infections. Diagnosis is based on nucleic acid amplification tests. Management is with antibiotics. Untreated chlamydial infections may have serious consequences, including sterility, ectopic pregnancies, spontaneous abortions, and chronic pelvic inflammatory disease.
Tricuspid valve atresia (TVA) is a congenital heart defect (CHD) causing an absent or rudimentary tricuspid valve (TV) associated with an interatrial or ventricular septal defect. Patients present with cyanosis at birth due to blood mixing between the right atrium (RA) and right ventricle (RV). Diagnosis can be made in utero or confirmed after birth with an echocardiogram. Definitive management involves a staged surgical procedure beginning in the neonatal period.
Total anomalous pulmonary venous return (TAPVR) is a cyanotic congenital heart defect wherein the pulmonary veins drain into anatomical sites other than the left atrium. The most common sub-type is the supra cardiac form, where the drainage is into the superior vena cava. Patients are usually cyanotic from birth and present with respiratory and heart failure right after birth. On examination there is a fixed, wide split-second heart sound, and a chest X-ray might reveal the “snowman” sign. Diagnosis is confirmed by an echocardiogram, which can be prenatal. All patients require surgery for survival and medical management is used to bridge the gap to surgery.
Serotonin syndrome is a life-threatening condition caused by large increases in serotonergic activity. This condition can be triggered by taking excessive doses of certain serotonergic medications or taking these medications in combination with other drugs that increase their activity. Hallmarks of this condition are autonomic hyperactivity, neuromuscular instability, and altered mental status. Management involves discontinuation of all serotonergic agents, sedation with benzodiazepine, and cyproheptadine (a serotonin antagonist) if supportive measures fail.
Primate erythroparvovirus 1 (generally referred to as parvovirus B19, B19 virus, or sometimes erythrovirus B19) ranks among the smallest DNA viruses. Parvovirus B19 is of the family Parvoviridae and genus Erythrovirus. In immunocompetent humans, parvovirus B19 classically results in erythema infectiosum (5th disease) or “slapped cheek syndrome.” Other manifestations vary with the immunologic and hematologic status of the host due to the viral tropism for erythrocyte precursors. Diagnosis is primarily clinical and management is generally supportive.
A volvulus is the twisting or axial rotation of a portion of the bowel around its mesentery. The most common site of volvulus in adults is the colon; most frequently the sigmoid volvulus. Patients typically present with symptoms of bowel obstruction such as abdominal pain, distension, vomiting, and constipation/obstipation. In severe cases, signs of bowel ischemia and gangrene (tachycardia, hypotension, hematochezia, and peritonitis) may also be present. Clinical suspicion prompts imaging to confirm the diagnosis and surgery is the definitive treatment. For stable patients with sigmoid volvulus, surgery may be preceded by endoscopic detorsion. However, immediate surgery is required for colon perforation or ischemia.
Polymyositis (PM) is an autoimmune inflammatory myopathy caused by T cell-mediated muscle injury. The etiology of PM is unclear, but there are several genetic and environmental associations. Polymyositis is most common in middle-aged women and rarely affects children. Patients present with progressive and symmetric proximal muscle weakness and constitutional symptoms. Complications may arise from respiratory, cardiac, or GI involvement. Diagnosis is based on clinical presentation and laboratory studies and confirmed using muscle biopsy. Management is with systemic glucocorticoids, immunosuppressants, and physiotherapy. All patients should undergo cancer screening because there is a strong association with malignancy.
A VIPoma is a rare neuroendocrine tumor arising primarily in the pancreas that releases large amounts of vasoactive intestinal polypeptide (VIP). This process leads to chronic watery diarrhea with concomitant hypokalemia and dehydration, as well as wheezing and flushing (known as Verner-Morrison or WDHA (chronic Watery Diarrhea, Hypokalemia, Achlorhydria) syndrome). Most tumors arise sporadically, but some are associated with MEN 1. Diagnosis is established by measuring serum VIP levels. Treatment consists of medical management of symptoms and complete surgical removal of the tumor when possible.
IgA nephropathy (Berger's disease) is a renal disease characterized by IgA deposition in the mesangium. It is the most common cause of primary glomerulonephritis in most developed countries. Patients frequently present in the second and third decades of life and, historically, with a preceding upper respiratory or GI infection. Common presenting features are gross hematuria or asymptomatic, microscopic hematuria on urinalysis. The course is often benign, with the definitive diagnostic procedure, renal biopsy, performed only in cases of severe, progressive renal disease. Treatment depends on the severity of proteinuria, renal function, and pathologic changes. ACE inhibitors or angiotensin-receptor blockers (ARBs) are given to reduce disease progression. Persistent proteinuria and increasing creatinine are indications for immunosuppressive therapy that includes glucocorticoids and, possibly, cytotoxic agents.
Sick sinus syndrome (SSS), also known as sinus node dysfunction, is characterized by degeneration of the sinoatrial (SA) node, the heart’s primary pacemaker. Patients with SSS may be asymptomatic or may present with tachycardia or bradycardia. In cases of bradycardia, patients can experience fatigue, light-headedness, and syncope. Diagnosis is made by physical exam and ECG. Management can include a pacemaker.
Supracondylar fractures are the most common elbow fractures in the pediatric population. The most common mechanism of injury involves a fall on an outstretched hand, resulting in a fracture of the distal humerus. Patients frequently present with pain, visible deformity, and limited range of motion of the injured elbow. This fracture often requires immediate orthopedic consultation secondary to the displacement of the fracture and the frequency of concomitant neurovascular injury.
Subclavian steal syndrome occurs when narrowing/occlusion of the subclavian artery proximal to the origin of the vertebral artery causes a reversal of blood flow in the ipsilateral vertebral artery to continue perfusing the ipsilateral arm. The most common cause is atherosclerosis. Symptoms are rare, but when they occur are usually triggered by physical exertion of the arm and subsequent hypoperfusion of the arm or brain. Patients may present with claudication, pain, pallor, paresthesias, and weakened pulse in the affected extremity. Patients may also present with transient neurologic disturbances concerning for a stroke. Diagnosis is made by clinical findings and imaging (ultrasound, CT, MRI). In addition to appropriate management of atherosclerosis, symptomatic patients may need angioplasty/stenting or surgical revascularization.
Prostate cancer is one of the most common cancers affecting men. In the United States, the lifetime risk of being diagnosed with prostate cancer is approximately 11%, and the lifetime risk of death is 2.5%. Prostate cancer is a slow-growing cancer that takes years, or even decades, to develop into advanced disease. Several men with prostate cancer are asymptomatic. Late-stage cancer can present with bone pain, urinary symptoms, and/or weight loss. Most cases of prostate cancer are identified based on diagnostic tests to determine prostate-specific antigen (PSA) levels and are confirmed based on image-guided transrectal biopsy. Management of prostate cancer depends on age, life expectancy, comorbidities, risk stratification, and preferences of the patient. Management options include active surveillance, androgen deprivation therapy, radiotherapy, chemotherapy, and radical prostatectomy.
Uterine leiomyomas (or uterine fibroids) are benign tumors arising from smooth muscle cells in the uterine myometrium. Leiomyosarcomas, however, are malignant tumors, arising de novo (not from fibroids). With a lifetime risk of > 70% for both African American and Caucasian women, fibroids are common. Conversely, leiomyosarcomas are rare. Leiomyosarcomas may present similarly to uterine fibroids making preoperative diagnosis challenging. Both conditions present with abnormal bleeding, pelvic pain, and/or bulk symptoms. A fibroid is identified as a hypoechoic, well-circumscribed, round mass on pelvic ultrasound. A leiomyosarcoma is usually diagnosed on a postoperative specimen. Depending on patient symptoms and preference, treatment for leiomyoma may include surgical resection or medical options to reduce bleeding and/or bulk. Management of leiomyosarcoma, which carries a poor prognosis, may include adjuvant chemotherapy based on stage.
A glucagonoma is a glucagon-secreting neuroendocrine tumor that originates from the α-cells in the pancreatic islets. Most glucagonomas are malignant, and many of them are part of the autosomal dominant condition known as multiple endocrine neoplasia syndrome type 1 (MEN 1). Elevated levels of glucagon lead to increased gluconeogenesis and glycogenolysis, resulting in an increase in free glucose in the bloodstream and the depletion of fat and amino acid stores. Patients often present with diabetes, a characteristic rash called necrolytic migratory erythema, weight loss, anemia, deep vein thrombosis, and neuropsychiatric symptoms. Laboratory findings demonstrate an elevated glucagon level, and imaging shows a pancreatic mass. Management is usually supportive and includes glucagon inhibition with octreotide (a somatostatin analog). Surgical resection is attempted if disease is localized, though this is frequently palliative. Chemotherapy and targeted molecular agents are also used in advanced disease.
Rosacea is a chronic inflammatory disease of the skin that is associated with capillary hyperreactivity. This condition is predominantly seen in middle-aged women, and is more common in fair-skinned patients. Patients may have facial erythema, flushing, telangiectasia, papules, pustules, phymatous changes, and ocular manifestations. The diagnosis is clinical. Management includes avoidance of triggers, gentle skincare, topical (and/or oral) antibiotics, and laser (or surgical) therapies.
Dilated cardiomyopathy (DCM) is the most common type of non-ischemic cardiomyopathy and a common cause of heart failure (HF). The cause may be idiopathic, familial, or secondary to a variety of underlying conditions. The disease is characterized by the enlargement of 1 or both ventricles and reduced systolic function. Patients typically present with symptoms of HF such as shortness of breath, fatigue, weakness, and peripheral edema. Blood tests, ECG, X-rays, echocardiography, and other cardiac studies and procedures are typically done to obtain the diagnosis. Treatment includes medications used to reduce volume overload (e.g., diuretics) and manage HF (e.g., beta-blockers). Devices such as pacemakers and cardioverter-defibrillators may also be needed. In severe cases, a heart transplant is required. Complications include thromboembolic events and sudden cardiac death.
Becker muscular dystrophy (BMD) is an X-linked recessive genetic disorder that is caused by a mutation in the DMD gene. Abnormal, partially functional muscle dystrophin protein is produced, which leads to progressive muscle weakness and the eventual loss of ambulation. The clinical course is highly variable, but symptoms generally occur by adolescence. The diagnosis is based on muscle enzymes, genetic testing, and muscle biopsy (if necessary). Management of BMD is supportive and aimed at slowing disease progression and complications. Dilated cardiomyopathy is the leading cause of death.
A thyroid nodule is a disordered growth of thyroid cells that produces a mass in the thyroid gland. Most thyroid nodules are benign and detected either by the patient or by the clinician on examination. In other cases, a thyroid nodule is found in radiologic imaging incidentally. Ruling out of malignancy is important. Workup includes thyroid-stimulating hormone (TSH) and thyroid ultrasound followed by radioactive iodine (RAI) uptake scan or thyroid scan if initial tests suggest the presence of hyperthyroidism. Fine-needle aspiration biopsy (FNAB) is recommended in patients with suspicious ultrasound findings, "cold" nodules (iodine uptake < surrounding tissue) on thyroid scan, large nodules (generally > 1.5 cm), or risk factors for malignancy. Management is dictated by pathology findings and can range from periodic ultrasound monitoring to surgery.
Nephritic syndrome is a renal condition with signs and symptoms produced by inflammation of the glomeruli (glomerulonephritis) and increased permeability of the glomerular barriers. Defining features include hematuria, proteinuria (but below nephrotic range), RBC casts with dysmorphic RBCs on urine microscopy, and increased serum creatinine. Causes can be genetic, autoimmune, idiopathic, or post-infectious. The most common cause is acute post-streptococcal glomerulonephritis. General clinical findings include edema, hypertension, and oliguria. Diagnosis is made based on history, physical exam, and laboratory data. A renal biopsy is sometimes necessary to establish the underlying cause. There can be a combined nephritic-nephrotic picture, especially in the chronic presentation. Treatment and prognosis depend on cause and severity.
Lentigo maligna is melanoma in situ, a precancerous lesion that may progress to an invasive melanoma (specifically lentigo maligna melanoma subtype). This condition typically occurs in sun-damaged areas (e.g., face and neck) of elderly patients. Lentigo maligna presents as a brown macule with color variegation and asymmetrical borders that grow slowly. The lesion should be biopsied to confirm a diagnosis and surgical excision with a safety margin is the 1st-line treatment.
Dermatomyositis (DM) is an autoimmune and inflammatory myopathy. Although the etiology of DM is unclear, it has several genetic and environmental associations. Dermatomyositis is common in women around the age of 50 years. Patients present with symmetrical, proximal weakness, characteristic skin manifestations, and systemic symptoms. Diagnosis is based on clinical presentation and laboratory studies and confirmed on the basis of muscle biopsy. Myositis-specific antibodies, including anti-Mi-2, are specific markers in DM. Management is with systemic glucocorticoids, immunosuppressants, and physiotherapy. As there is a strong association of DM with malignancy, all patients should undergo cancer screening.
Opioid use disorder (OUD) is a substance use disorder characterized by pathologic consumption of opioids. Opioids are central nervous system depressants that are used medically as potent analgesics. However, they are often misused for their euphoric effects. Features of opioid intoxication include respiratory depression, drowsiness, and pinpoint pupils. Intoxication can be managed with administration of naloxone. If discontinued, patients may develop withdrawal symptoms such as irritability, piloerection, and stomach cramps. Withdrawal may be managed by methadone or buprenorphine. Chronic OUD is managed with psychotherapy as well as medications. Prognosis is poor without adequate management and prevention of relapse and overdose.
Alport syndrome, also called hereditary nephritis, is a genetic disorder caused by a mutation in the genes encoding for the alpha chains of type IV collagen, resulting in the production of abnormal type IV collagen strands. Patients present with glomerulonephritis, hypertension, edema, hematuria, and proteinuria, as well as with ocular (cataract, retinopathy) and auditory (sensorineural hearing loss) findings. Diagnosis is established with urinalysis, urine microscopy, and a renal function panel. A renal biopsy showing characteristic glomerular basement membrane splitting may be used to confirm the diagnosis. Treatment for Alport syndrome is focused on limiting disease progression with angiotensin receptor blockers and angiotensin-converting enzyme inhibitors. Hearing aids are used for hearing loss associated with Alport syndrome.
Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. The borders are not clearly delineated. The lower extremities are the most frequent site of infection, but cellulitis can occur anywhere on the body. Diagnosis is usually clinical, and management involves oral and/or parenteral antibiotics. Coverage for MRSA may be added, depending on the presence of risk factors.
Chorioamnionitis, commonly referred to as intraamniotic infection (IAI), is a common obstetric complication involving infection and inflammation of the fetal membranes, amniotic fluid, placenta, or the fetus itself. Chorioamnionitis is typically caused by a polymicrobial infection that ascends from the lower genitourinary tract. Primary risk factors include prolonged rupture of membranes and prolonged labor. Chorioamnionitis is diagnosed by clinical findings, including maternal fever. Chorioamnionitis is managed with antibiotics, and by ensuring continued labor progress (or initiating progress) toward delivery. Chorioamnionitis typically resolves soon after delivery. Significant maternal and fetal complications are possible, warranting prompt diagnosis and treatment.
Rashes are a group of diseases that cause abnormal coloration and texture to the skin. The etiologies are numerous but can include irritation, allergens, infections, or inflammatory conditions. Rashes that present in only 1 area of the body are called localized rashes. Generalized rashes occur diffusely throughout the body. Rashes can be classified by their distribution, configuration, and morphology. The diagnosis is often clinical and based on the patient’s history and physical exam findings. Management is dependent on identifying the correct condition and varies depending on the etiology.
Cocaine use disorder is a substance use disorder defined by pathologic consumption of the recreational drug cocaine. Cocaine is an indirect sympathomimetic that blocks the reuptake of dopamine, serotonin, and norepinephrine from the synaptic cleft. This process causes stimulant effects on the body and mind such as euphoria, increased energy, irritability, psychosis, decreased appetite, and weight loss. Cocaine overdose can cause death secondary to cardiac arrhythmia, myocardial infarction, seizure, or respiratory depression. Prognosis is poor as there is no approved pharmacological treatment, but psychosocial interventions have been associated with improved outcome.
Strongyloidiasis is a common parasitic disease caused by infection with the roundworm Strongyloides stercoralis. Transmission occurs through skin penetration, most commonly from walking barefoot. Strongyloides has a unique life cycle that can be entirely completed in the human host, migrating from the skin to the pulmonary system and then to the GI system. Symptoms include cutaneous irritation, constipation, diarrhea, dry cough, and wheezing, depending on where the parasite is in its life cycle. Effective eradication of the parasite can be obtained with anthelmintic medications, usually ivermectin.
Adenomyosis is a benign uterine condition characterized by the presence of ectopic endometrial glands and stroma within the myometrium. Adenomyosis is a common condition, affecting 20%–35% of women, and typically presents with heavy menstrual bleeding and dysmenorrhea. Diagnosis is often made with pelvic imaging. Usually, transvaginal ultrasound is adequate, though MRI can be helpful in indeterminate cases. Management is based on the patient’s preference regarding future childbearing and may include hysterectomy (definitive treatment), other surgical options, or medical hormonal suppression (usually with progestins).
Endometrial polyps are pedunculated or sessile projections of the endometrium that result from overgrowth of endometrial glands and stroma around a central vascular stalk. Endometrial polyps are a few millimeters to a few centimeters in size, can occur anywhere within the uterine cavity, and, while usually benign, can be malignant, particularly in postmenopausal women. Endometrial polyps present with abnormal uterine or postmenopausal bleeding, although many are asymptomatic and discovered incidentally. Endometrial polyps are best diagnosed with a saline-infusion sonogram, and are usually treated with hysteroscopic resection.
Carotid artery stenosis is a chronic atherosclerotic disease resulting in narrowing of the common and internal carotid arteries. Common risk factors include family history, advanced age, hyperlipidemia, smoking, and diabetes mellitus. Patients may present with or without symptoms of decreased cerebral perfusion. Carotid artery stenosis is commonly diagnosed via ultrasound. Management includes lifestyle modifications to control progression of atherosclerosis. Treatment is with statins, anti-hypertensive and antiplatelet agents, and, in some cases, surgical revascularization. The most serious complication of carotid artery stenosis is stroke.
Thrombotic thrombocytopenic purpura (TTP) is a life-threatening condition due to either a congenital or an acquired deficiency of ADAMTS-13, a metalloproteinase that cleaves multimers of von Willebrand factor (VWF). The large multimers then aggregate excessive platelets resulting in microvascular thrombosis and an increase in consumption of platelets. Clinical presentation can consist of thrombocytopenia, hemolytic anemia, hematuria, gastrointestinal symptoms, neurological symptoms, and renal involvement. Diagnosis is established based on a combination of clinical symptoms and laboratory tests. Thrombotic thrombocytopenic purpura is a medical emergency and almost always fatal if appropriate treatment is not initiated promptly. Emergency management includes plasma exchange and immunosuppressive therapies.
Osteosarcoma is a primary malignant tumor of the bone characterized by the production of osteoid or immature bone by the tumor cells. The disease is most common in children and young adults and most frequently affects growth plates of the long bones, although it can involve any bone. Osteosarcoma can present with pain, swelling, and palpable mass, and sometimes with a pathologic fracture. Diagnosis is established with imaging studies and biopsy. Treatment involves systemic chemotherapy and surgical resection. Long-term survival can be expected with appropriate treatment in the absence of macrometastatic disease.
Secondary amenorrhea is defined as the absence of menses for 3 months in a woman with previously regular menstrual cycles or for 6 months in a woman with previously irregular cycles. Etiologies involve either disruptions to the hypothalamic–pituitary–ovarian (HPO) axis or acquired obstructions in the uterus or outflow tract. The most common cause of secondary amenorrhea is pregnancy. The most common pathologic etiologies include functional hypothalamic amenorrhea, polycystic ovary syndrome, hyperprolactinemia, premature ovarian insufficiency, and Asherman's syndrome. The diagnosis is made with a thorough history and physical examination, measurement of hormone levels, a pregnancy test, and imaging with pelvic ultrasonography. A progestin and/or combined estrogen–progestin challenge can help further identify the location of the abnormality. Management depends on the underlying etiology, clinical presentation, and patient desires regarding fertility. Treatment can include lifestyle, medical, and surgical management options.
Appendectomy is an invasive surgical procedure performed with the goal of resecting and extracting the vermiform appendix through either an open or a laparoscopic approach. The most common indication is acute appendicitis, which is why appendectomies are usually carried out in an urgent fashion. It is one of the most commonly performed emergent abdominal procedures. It can be associated with a number of postoperative complications; however, the majority of patients do very well and recover quickly.
Acne vulgaris, also known as acne, is a common disorder of the pilosebaceous units in adolescents and young adults. The condition occurs due to follicular hyperkeratinization, excess sebum production, follicular colonization by Cutibacterium acnes, and inflammation. Acne can present as open or closed comedones, papules, pustules, nodules, or cysts. The diagnosis is based on clinical exam. Management depends on the severity, but includes skin care techniques, topical therapies, antibiotics, and retinoids.
Amyloidosis is a disease caused by abnormal extracellular tissue deposition of fibrils composed of various misfolded low-molecular-weight protein subunits. These proteins are frequently byproducts of other pathological processes (e.g., multiple myeloma). These misfolded proteins can become deposited in different tissues, interfere with normal organ functions, and cause tissue-specific diseases (e.g., renal amyloidosis causes proteinuria). Diagnosis is established clinically and confirmed with tissue biopsy. Treatment should be directed toward the underlying cause and the reduction of amyloid deposition.
Basal cell carcinoma is the most common skin malignancy. This cancer arises from the basal layer of the epidermis. The lesions most commonly appear on the face as pearly nodules, often with telangiectatic blood vessels and ulceration in elderly individuals. Diagnosis is established by tissue biopsy. Despite having low metastatic potential, basal cell carcinoma should be treated adequately because it is locally aggressive and destructive to tissues. Complete surgical excision is the main treatment method. Long-term prognosis is excellent with adequate management.
Leprosy, also known as Hansen's disease, is a chronic bacterial infection caused by Mycobacterium leprae complex bacteria. Symptoms primarily affect the skin and peripheral nerves, resulting in cutaneous manifestations (e.g., hypopigmented macules) and neurologic manifestations (e.g., loss of sensation). Leprosy is known for its historical stigma and psychosocial effects on infected persons, prompting the World Health Organization (WHO) to pursue a disease elimination plan that led to significant reduction in the prevalence of leprosy. The diagnosis of leprosy is established clinically and supported with skin biopsy. It is treated with long-term multidrug antibiotic combinations. Untreated leprosy leads to disability and permanent damage to the skin, nerves, limbs, and eyes.
Preterm labor refers to regular uterine contractions leading to cervical change prior to 37 weeks of gestation; preterm birth refers to birth prior to 37 weeks of gestation. Preterm birth may be spontaneous due to preterm labor, preterm prelabor rupture of membranes (PPROM), or cervical insufficiency. Preterm birth may also be initiated by the provider for a variety of maternal or fetal indications. Diagnosis involves assessments to detect cervical change and monitoring for regular uterine contractions. Management depends on gestational age, but typically includes administration of corticosteroids (to improve fetal lung maturity), magnesium sulfate (for fetal neuroprotection against cerebral palsy), group B streptococcus (GBS) prophylaxis, and 48 hours of tocolytics to help patients complete a full course of steroids.
Chancroid is a highly transmissible STD caused by Haemophilus ducreyi. The disease presents with painful ulcer(s) on the genital tract (termed chancroid or “soft chancre”). Up to 50% of patients will develop painful inguinal lymphadenopathy. Furthermore, of that percentage, 25% may develop complications of the suppurative lymph nodes. Given the growth of H. ducreyi on a special medium (often not readily available), chancroid is diagnosed based upon clinical appearance and tests to rule out both syphilis and herpes (the most common causes of genital ulcers). Although the disease can resolve spontaneously, antibiotics (azithromycin or ceftriaxone) are the treatment of choice. Treatment should involve both patients and their sexual contacts.
Tetanus is a bacterial infection caused by Clostridium tetani, a gram-positive obligate anaerobic bacterium commonly found in soil that enters the body through a contaminated wound. C. tetani produces a neurotoxin that blocks the release of inhibitory neurotransmitters and causes prolonged tonic muscle contractions. It presents with lockjaw, neck stiffness, opisthotonus, rigid abdomen and severe painful muscle spasms. Diagnosis is made on clinical grounds, as it is rarely possible to isolate the infectious agent from the wound. It is treated with antibiotic therapy and the human tetanus antitoxin. Untreated tetanus can lead to respiratory failure and cardiovascular complications and can be fatal. With appropriate treatment, however, most patients will recover.
Staphylococcal scalded skin syndrome (SSSS), also known as Ritter disease and staphylococcal epidermal necrolysis, is a toxin-mediated condition caused by Staphylococcus aureus. The exfoliative toxin produced disseminates and cleaves desmoglein 1 in the epidermis, causing separation and detachment of the skin. SSSS most commonly affects young children. Prodromal symptoms precede diffuse cutaneous erythema, tenderness, bullae formation, and superficial desquamation. The mucous membranes are spared. The diagnosis is made clinically and can be confirmed with culture data (targeting possible primary infection sites) and biopsy. However, cultures of bullae are not useful. Antibiotics and supportive care should be initiated as soon as the diagnosis is suspected.
A brief resolved unexplained event (BRUE) is defined as a reported, sudden, brief (< 1 minute) event in a child < 1 year of age, which is resolved at the time of presentation. The definition includes ≥ 1 finding of either change in color (cyanosis or pallor), breathing pattern (absent, decreased, or irregular), muscle tone (hypertonia or hypotonia), or level of consciousness. The findings are based on a report given by a parent or caregiver. Adopted by the American Academy of Pediatrics in 2016, the new term was to replace the previously used terms “apparent life-threatening event” (ALTE) and “near sudden infant death syndrome”. The change in terminology was to better define an unexplained event after a thorough evaluation, stratify high- and low-risk groups, identify those needing further evaluation, and avoid unnecessary testing and admissions. Importantly, BRUE can be diagnosed only if there is no other explanation for the episode after a careful history and physical examination.
An embolus is an intravascular solid, liquid, or gaseous material that is carried by the blood to a site distant from its point of origin. Emboli of all types warrant immediate medical attention. The majority of emboli dislodge from a thrombus, forming a thromboembolus. Other less common nonthrombotic types of emboli are cholesterol, fat, air, amniotic fluid, and tumor emboli. The cause of the embolus depends on the type, as does the clinical presentation, diagnosis, and management of each embolic condition. Due to their effects on circulation, all emboli have the potential to result in end-organ failure and death.
Hypoaldosteronism is a hormonal disorder characterized by low levels of aldosterone. These low levels can be caused by decreased aldosterone production or a peripheral resistance to aldosterone. When hypoaldosteronism occurs as a result of an acquired decrease in renin production, the condition is more commonly referred to as renal tubular acidosis (RTA) type 4. Patients are usually older, with underlying renal disease (e.g., diabetic nephropathy). Hypoaldosteronism usually presents as hyperkalemia with a mild hyperchloremic metabolic acidosis (normal anion gap). Most patients are asymptomatic and routine lab evaluation demonstrates hyperkalemia, prompting a further workup. The condition is diagnosed using serum and urine tests that demonstrate reduced aldosterone levels and a reduced transtubular potassium gradient, among other characteristic findings. Patients are managed based on their underlying etiology.
Pulmonary hypoplasia is the lack of normal fetal development of the pulmonary parenchyma. The condition is characterized by a decreased number of alveoli and bronchial generations. Oligohydramnios is a notable cause, but conditions that restrict lung development or lead to fetal lung compression can also result in pulmonary hypoplasia. A diagnosis of pulmonary hypoplasia can be suspected on prenatal ultrasound. Findings include reduced amniotic fluid, congenital abnormalities, and characteristic anatomical measurements. A more complete picture at birth points to the diagnosis based on clinical findings (respiratory distress, typical anomalies) and further evaluation (reduced lung volume on imaging). Treatment is focused on antenatal lung maturity and postnatal ventilatory support, with subsequent correction of associated causes and defects. Survival depends on the degree of lung underdevelopment.
Mycobacterium is a genus of the family Mycobacteriaceae in the phylum Actinobacteria. Mycobacteria comprise more than 150 species of facultative intracellular bacilli that are mostly obligate aerobes. Mycobacteria are responsible for multiple human infections including serious diseases, such as tuberculosis (M. tuberculosis), leprosy (M. leprae), and M. avium complex infections. While lungs are the most common site of infection, mycobacteria can colonize and infect other organ systems including the lymph nodes, skin, sinuses, eyes, ears, bones, CNS, and urinary tract.
Restrictive cardiomyopathy (RCM) is a fairly uncommon condition characterized by progressive stiffening of the cardiac muscle, which causes impaired relaxation and refilling of the heart during diastole, resulting in diastolic dysfunction and eventual heart failure. It most often occurs secondary to scarring, damage, and/or infiltration of the heart muscle, with amyloidosis being the most common cause. Infrequently, it may be idiopathic or inherited. Signs and symptoms include shortness of breath, low exercise tolerance, fatigue, and peripheral edema. Diagnosis is made through clinical suspicion and confirmed through ECG, X-ray, echocardiography, and cardiac MRI. Treatment includes medications for heart failure, implantable devices such as pacemakers and cardioverter–defibrillators, and heart transplantation in refractory cases.
Ehrlichiosis and anaplasmosis are tick-borne bacterial infections. The most common causative species include Ehrlichia chaffeensis and Anaplasma phagocytophilum, which infect and multiply within monocytes and granulocytes, respectively. The clinical presentation can vary widely, but often includes fever, malaise, headache, myalgia, and arthralgias. A maculopapular or petechial rash occurs in some patients. Gastrointestinal, neurologic, and respiratory symptoms are also possible. The diagnosis is based on clinical suspicion and confirmed PCR or antibody testing. Management is with doxycycline.
Babesiosis is an infection caused by a protozoa belonging to the genus, Babesia. The most common Babesia seen in the United States is B. microti, which is transmitted by the Ixodes tick. The protozoa thrive and replicate within host erythrocytes. Lysis of erythrocytes and the body’s immune response result in clinical symptoms. Patients usually present with a flu-like illness and jaundice. In severe cases, organ damage may occur. The diagnosis is confirmed by the visual presence of parasites within RBCs, which are often noted to be in a “Maltese Cross” configuration. Serological testing and PCR are also used in the diagnosis. Azithromycin and atovaquone are often used in management. Coinfection with Borrelia and Anaplasma is common.
Post-transcriptional modifications (PTMs) are processes that facilitate the generation of mature, functional RNA. These rapidly responsive regulatory mechanisms allow different proteins to be produced from one gene and act as regulators of the phenotype and proliferation rate. These modifications also play a role in some forms of cancer and neurodegenerative diseases. The pre-messenger RNA (mRNA), called heterogeneous nuclear RNA (hnRNA), is modified by adding a 5’ 7-methylguanosine cap and a 3’ poly-A (polyadenylate) tail for stability and protection. Moreover, hnRNA that contains introns (noncoding sequences) among the expressed sequences or exons undergo splicing. This process removes introns to produce a mature mRNA carrying the coding sequence for translation. Alternative splicing, on the other hand, also excludes the introns, but varying combinations of exons are linked, producing different proteins from the original mRNA. In RNA editing, the mRNA sequence is altered and differs from the transcribed DNA template. Transfer RNA and ribosomal RNA start from longer precursor molecules and go through steps that include methylation, trimming, and addition of nucleotides.
Caustic agents are acidic or alkaline substances that damage tissues severely if ingested. Alkali ingestion typically damages the esophagus via liquefactive necrosis, whereas acids cause more severe gastric injury leading to coagulative necrosis. Ingestion of large volumes and high concentrations of caustic agents can lead to severe and extensive injuries. Additionally, aspiration affects the laryngeal and tracheobronchial structures. Signs and symptoms include oral pain, burns, dysphagia, vomiting, and abdominal pain. Severe injuries can present with shock, abdominal rigidity, respiratory distress, and/or altered mental status. Diagnosis is based on laboratory tests, abdominal and chest imaging, and endoscopy within 24 hours (if without contraindications) to determine the extent of damage. Management involves stabilizing the cardiorespiratory status, decontamination, and supportive therapy. Severe injury may require surgery.
Cannabis use disorder (CUD) is characterized by the pathologic consumption of cannabis, which is the most commonly used illicit substance worldwide. While cannabis has some beneficial medical uses, it also has the potential to cause intoxication characterized by psychosis or cognitive impairment, especially in chronic use. Unlike most other substances, withdrawal symptoms are mild. There is currently no strong evidence for long-term benefits of pharmacologic or psychosocial interventions in the management of cannabis use disorder. Other factors such as underlying mood or personality disorders or comorbidity with other substance use disorders are associated with a poor prognosis.
Amphetamine use disorder (AUD) is a condition characterized by pathologic use of psychostimulants. Amphetamines produce their effect by increasing the release and blocking the reuptake of neurotransmitters (dopamine, norepinephrine, serotonin). Medically, they are used for the treatment of ADHD and narcolepsy. Methamphetamines and so-called designer drugs have no clinical use. Intoxication results in euphoria, pupillary dilation, hypertension, skin excoriation, paranoia, and severe aggression. Fatal complications can arise from myocardial infarction and coma. The prognosis for AUD is poor, as there is no FDA-approved pharmacotherapy, but psychosocial interventions have been associated with improved outcomes.
In the context of acute or chronic kidney failure, renal function may diminish to a point at which it is no longer able to adequately support life. When this happens, renal replacement therapy is indicated. Renal replacement therapy refers to dialysis and/or kidney transplantation. Dialysis is a procedure by which toxins and excess water are removed from the circulation. Hemodialysis and peritoneal dialysis (PD) are the two types of dialysis, and their primary difference is the location of the filtration process (external to the body in hemodialysis versus inside the body for PD).
Hyperaldosteronism is defined as the increased secretion of aldosterone from the zona glomerulosa of the adrenal cortex. Hyperaldosteronism may be primary (resulting from autonomous secretion), or secondary (resulting from physiological secretion due to stimulation of the RAAS). Classically, hyperaldosteronism presents with hypertension, hypokalemia, and metabolic alkalosis, although recent studies have suggested that hypokalemia is less common than originally thought in primary hyperaldosteronism. Patients with hypertension who are treatment resistant and/or associated with hyperkalemia should be screened for hyperaldosteronism by determining their plasma aldosterone concentration and plasma renin activity. Confirmatory tests and an abdominal CT scan are required to conclusively diagnose primary hyperaldosteronism. Management involves the use of aldosterone receptor antagonists and surgical excision of any aldosterone-secreting tumors.
Lactose intolerance (LI) describes a constellation of symptoms due to lactase deficiency (LD), the enzyme located in the brush border of the adsorptive cells in the small intestine. Lactose is the disaccharide present in milk and requires hydrolysis by lactase to break it down into its 2 absorbable constituents, glucose and galactose. Lactose intolerance typically presents with bloating, abdominal cramping, diarrhea, and flatulence. The diagnosis of LI can be suspected clinically based on symptoms after consumption of a lactose-containing meal. The most commonly used test for confirmation of the diagnosis is the lactose hydrogen breath test. The treatment goal is to eliminate symptoms while maintaining sufficient intake of calcium and vitamin D. Alternative diagnoses to LI should always be sought, as many people wrongly attribute their symptoms to LI.
The kidneys are primarily in charge of the maintenance of water and solute homeostasis through the processes of filtration, reabsorption, secretion, and excretion. Glomerular filtration is the process of converting the systemic blood supply into a filtrate, which will ultimately become the urine. Complex regulatory processes ensure that only the appropriate substances in the systemic blood are lost in the urine and that the urine flow is satisfactorily balanced to maintain adequate systemic volume status. Abnormalities of the glomerulus can cause several clinically important conditions.
Bariatric surgery refers to a group of invasive procedures used to surgically reduce the size of the stomach to produce early satiety, decrease food intake (restrictive type) and/or alter digestion, and artificially induce malabsorption of nutrients (malabsorptive type). The ultimate goal of bariatric surgery is drastic weight loss. Bariatric surgery is currently the only modality that provides significant long-term weight loss in morbidly obese individuals and cures or significantly improves obesity-related complications. The 2 modalities currently in wide use are the Roux-en-Y gastric bypass and sleeve gastrectomy.
Extranodal marginal zone lymphoma (EMZL) of mucosa-associated lymphoid tissue (also called MALToma, MALT lymphoma, and pseudolymphoma) is a group of non-Hodgkin’s lymphomas that have historically been grouped together because they appear to arise from postgerminal center marginal zone B cells and share a similar immunophenotype. MALT lymphoma is thought to arise in the setting of chronic immune stimulation, which is usually due to bacterial, viral, or autoimmune stimuli. MALT lymphomas present with symptoms due to localized involvement of glandular epithelial tissues in the specific site where they develop. Diagnosis of MALT lymphoma is made by morphologic, immunophenotypic, and genetic analysis of biopsy samples. Helicobacter pylori–positive gastric MALT lymphoma is treated with H. pylori eradication therapy, and H. pylori–negative gastric MALT lymphoma is treated with radiation therapy. Nongastric MALT lymphoma is treated based on the involved area and extent of disease. MALT lymphoma patients have a good prognosis, with a median survival of > 10 years.
Hyperparathyroidism is a condition associated with elevated blood levels of parathyroid hormone (PTH). Depending on the pathogenesis of this condition, hyperparathyroidism can be defined as primary, secondary or tertiary. Primary hyperparathyroidism is an inherent disease of parathyroid glands associated with abnormal secretion of PTH. Secondary hyperparathyroidism results from abnormalities of calcium metabolism, which, if left untreated, can progress to tertiary hyperparathyroidism, which is associated with hypertrophy of the parathyroid gland and oversecretion of PTH even if the primary cause is eliminated. Diagnosis is based on biochemical parameters, which include serum PTH, calcium, and phosphate levels as well as urinary calcium. Management relies mostly on surgical parathyroidectomy for primary and tertiary hyperparathyroidism. Management of secondary hyperparathyroidism is focused on treatment of the underlying disease.
Seborrheic keratosis (SK) is the most common benign epithelial cutaneous neoplasm. The condition consists of immature keratinocytes. Seborrheic keratosis is the most common benign skin tumor in middle-aged and elderly adults and presents as a sharply demarcated, exophytic, skin lesion that may be tan or black and has a “stuck-on” appearance. Pruritus or pain can occur if these lesions become secondarily inflamed by trauma, especially if they are within the skin folds. Genetics are thought to play a role, but the pathogenesis is uncertain. The most common mutations involve two oncogenes: fibroblast growth factor receptor 3 (FGFR3) and PIK3CA. There is a familial predisposition to develop a high number of seborrheic keratoses. Treatment is not necessary, as this is a benign condition, but cryotherapy, curettage or electrodesiccation can be performed for discomfort or cosmetic concerns.
Thyroiditis is a catchall term used to describe a variety of conditions that have inflammation of the thyroid gland in common. It includes pathologies that cause an acute illness with severe thyroid pain (e.g., subacute thyroiditis and infectious thyroiditis) as well as conditions in which there is no clinically evident inflammation and the manifestations primarily reflect thyroid dysfunction or a goiter (e.g., painless thyroiditis and fibrous Riedel’s thyroiditis). The etiology of thyroiditis is varied and includes autoimmune inflammation (most common), bacterial or viral infection, and drug-induced reactions. The inflammation of the thyroid leads to a sequential pathologic process that can result in signs and symptoms of hyperthyroidism followed by signs and symptoms of hypothyroidism. The resulting damage can be temporary or permanent, and the treatment depends on the underlying cause.
Bronchiolitis obliterans is an obstructive lung disease triggered by a bronchiolar injury, which leads to inflammatory fibrosis and narrowing of the distal bronchioles. The triggering bronchiolar injury is often due to inhalation of a noxious substance, infection, or drug toxicity. Bronchiolitis obliterans is also associated with rheumatic disease and is an important complication to recognize following a lung or hematopoietic stem-cell transplant. Following bronchiolar injury, there is an abnormal fibroproliferation within the bronchioles, which results in small-airway obstruction. Patients present with a persistent progressive cough and dyspnea. Diagnosis is usually made based on pulmonary function tests (showing a non-reversible obstructive pattern, air trapping, and decreased gas exchange) and high-resolution CT (showing air trapping and bronchial-wall thickening). Management involves supportive care, bronchodilators, glucocorticoids, and/or macrolide antibiotics. Immunosuppressive therapy is usually increased in patients who have undergone transplantation, and retransplantation may be required if the condition worsens.
Potassium is the main intracellular cation in all cells and is distributed unevenly between the intracellular fluid (98%) and extracellular fluid (2%). This large disparity is necessary for maintaining the resting membrane potential of cells, and explains why K+ balance is tightly regulated. The GI tract secretes 5%–10% of the absorbed K+ daily; however, the kidneys are responsible for 90%–95% of the overall K+ regulation. While most of the K+ is reabsorbed in the proximal tubules, the majority of regulation occurs in the principal and α-intercalated cells of the collecting ducts. The most important regulatory mechanisms include aldosterone, plasma K+ concentration, distal urinary flow rate, and the distal delivery of Na+ and water. Hyperkalemia and hypokalemia can result when K+ regulation is abnormal.
Dog and cat bites can cause superficial and deep tissue destruction, as well as serious wound infections. Dog bites occur more frequently in men and children and often cause crushing or tearing trauma. Cat bites are more frequent in adult women and result in puncture wounds. Because puncture wounds allow inoculation of bacteria into the deep tissues, cat bites are more frequently associated with infection. The diagnosis is clinical, and cultures should be obtained if the wound appears infected. Management requires fastidious wound care and antibiotics for high-risk or infected wounds.
Coagulation studies are a group of hematologic laboratory studies that reflect the function of blood vessels, platelets, and coagulation factors, which all interact with one another to achieve hemostasis. Coagulation studies are usually ordered to evaluate patients with bleeding or hypercoagulation disorders.
Mumps is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae and the subfamily Rublavirinae. The mumps virus is contagious and spreads only among humans by respiratory droplets or direct contact transmission from an infected person or fomite. Mumps is typically a disease of childhood, which manifests initially with fever, muscle pain, headache, poor appetite, and a general feeling of malaise, and is classically followed by parotitis. Complications include meningitis, pancreatitis, permanent deafness, and testicular inflammation, which can result in infertility. Mumps is managed with supportive care and is preventable by vaccination.
Hydrogen cyanide is an extremely poisonous, colorless, flammable liquid used in multiple industries and includes rubber, plastic, and household paints. Exposure to cyanide can occur via inhalation, dermal contact, or intestinal ingestion. Cyanide poisoning is a common complication of closed-space fires since cyanide is a byproduct of plastics combustion. Symptoms develop within seconds to minutes and involve cardiovascular, respiratory, and neurological changes. Management includes sodium thiosulfate, nitrites, and hydroxocobalamin. If not recognized and treated promptly, cyanide poisoning is frequently lethal.
Osteochondritis dissecans (OCD) is an orthopedic disorder characterized by the detachment of a focal segment of subchondral bone and cartilage as a result of focal aseptic necrosis. This can occur at any age, but it is most commonly seen in adolescents who participate in competitive sports. Patients can be asymptomatic or may present with joint pain, stiffness, and swelling that is worse with activity. The diagnosis can be made with imaging. Management depends on the severity, but can include restricted weight-bearing activity, physical therapy, or surgery.
Primary ciliary dyskinesia (PCD), also known as immotile-cilia syndrome, is an autosomal recessive disorder leading to an impairment that affects mucociliary clearance. Primary ciliary dyskinesia is caused by defective ciliary function in the airways and is characterized by the loss of oscillation (immotility), abnormal oscillation (dyskinesia), or absence of cilia (aplasia). In most cases, PCD commonly presents with recurrent infections of the upper and lower respiratory tract. Clinical features include bronchiectasis, chronic rhinosinusitis, and situs inversus. There is no gold standard diagnostic test for PCD, as several tests are used in the diagnosis. Treatment is individualized, and the primary goal is to remove trapped mucus and treat infections. Patients with PCD usually have a regular lifespan.
A cell is a complex unit that performs several complex functions. An organelle is a specialized subunit within a cell that fulfills a specific role or function. Organelles are enclosed within their own lipid bilayers or are unbound by membranes. If a cell is viewed as an organism, the organelles are an equivalent of the cell’s internal organs. Cell organelles carry out various functions from maintaining the shape of the cell to reproduction, movement, protein synthesis, energy production, and the transport of substances in and out of the cell.
Intestinal hookworm infections that affect humans are caused mainly by Necator americanus and Ancylostoma duodenale. Millions of people are infected around the world, mainly in tropical regions, where warm and moist environments facilitate larva survival in the soil. Transmission is via dermal penetration by the larvae. From entry, the parasite undergoes a transpulmonary passage, reaching the trachea and pharynx, where it is swallowed. In the small intestine, worms mature and attach to the duodenum. Diarrhea, nausea, and vomiting are GI symptoms. Blood loss (leading to anemia) and subsequent malnutrition are complications. Diagnosis is by stool microscopy showing the hookworm eggs and by PCR. Management targets prevention through proper sanitation and regular deworming of high-risk groups. Treatment involves the use of anti-parasitic medications, with iron supplements for anemia.
Short bowel syndrome is a malabsorptive condition most commonly associated with extensive intestinal resection for etiologies such as Crohn's disease, bowel obstruction, trauma, radiation therapy, and vascular insufficiency. The short length of bowel results in insufficient surface area for fluid and electrolyte absorption. Patients typically present with diarrhea, electrolyte abnormalities, and dehydration. Management options include antimotility agents, antisecretory agents, and total parenteral nutrition for patients who cannot maintain themselves with oral intake. Last-resort options include surgical intestinal lengthening procedures and small bowel transplant.
Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder affecting the neuromuscular junction and has a strong association with small cell lung carcinoma. Lambert-Eaton myasthenic syndrome affects the voltage-gated calcium channels at the presynaptic membrane. Presentation includes proximal muscle weakness and symptoms of autonomic dysfunction such as dry mouth and sluggish pupillary reflexes. Diagnosis includes nerve conduction studies/electromyography (EMG) and serum detection of antibodies. Management is mainly symptomatic with the use of potassium channel blockers and immunosuppressants. Prognosis is good for nonparaneoplastic LEMS but usually poor for paraneoplastic LEMS secondary to underlying malignancy.
Hypocoagulable conditions, also known as bleeding disorders or bleeding diatheses, are a diverse group of diseases that result in abnormal hemostasis. Hemostasis is the innate, stepwise process resulting in bleeding cessation from a damaged blood vessel. Physiologic hemostasis is dependent on the integrity of endothelial cells and subendothelial matrix, platelets, and coagulation factors. The hypocoagulable states result from abnormalities in one or more of these contributors, resulting in ineffective thrombosis and bleeding.
Trichinellosis is an illness caused by infection with Trichinella. The most common causative parasite is Trichinella spiralis, which is usually found in pigs and transmitted to humans through the ingestion of undercooked meat. Once ingested, the parasite grows and matures within the intestinal walls. The adult forms mate, and the larvae produced spread through the bloodstream, reaching striated muscles. Symptoms occur during larval migration. Patients may have GI symptoms within a few weeks after consumption of the infected meat, and systemic symptoms such as fever, chills, myalgia, and periorbital edema may follow. Diagnosis can be made by serologic examination and confirmed by the presence of cysts or larvae in a muscle biopsy. Mild infections are self-limited, but systemic disease is managed with antiparasitic medications and corticosteroids. Infection can be prevented by proper meat handling and cooking techniques.
Basic surgical intervention in the thoracic cavity has the primary goal of alleviating any malady that mechanically affects the function of the heart and lungs, which can be secondary to underlying pathologies or, most commonly, trauma. Interventions such as tube thoracostomy and thoracentesis are performed to evacuate fluid, blood, or air that is occupying the thoracic cavity in order to restore thoracic negative pressure. When direct intervention to the heart and mediastinum is required, an emergency thoracotomy is performed. Once the immediate mechanical problems are addressed, more advanced reparative surgery involving heart, lungs, or mediastinal structures can then be performed as necessary.
The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Between both layers, there is a well-lubricated potential space called the pleural cavity, which eases the respiratory movements of the lungs and helps avoid friction.
Edwards syndrome, or trisomy 18, is a genetic syndrome caused by the presence of an extra chromosome 18. The extra chromosome is either from 3 full copies of chromosome 18 or an additional segment of chromosome 18. As the 2nd most common trisomy, Edwards syndrome is seen in 1 out of every 5,500 live births and increases with maternal age. Many cases are detected prenatally with maternal screening and ultrasound findings. Abnormalities include intrauterine growth restriction (IUGR), overlapping fingers, typical craniofacial features, rocker-bottom feet, and congenital heart defects. Trisomy 18 frequently results in fetal loss. For term pregnancies, most deaths occur during the 1st 6 months of life. Delivery in a specialized center is recommended for full-term pregnancies and intervention is based on associated abnormalities.
Q fever is a bacterial zoonotic infection caused by Coxiella burnetii. Transmission occurs primarily through the inhalation of contaminated aerosols and exposure to infected animal products. The clinical presentation can vary and often result in mild disease with flu-like symptoms. Other manifestations include pneumonia, hepatitis, endocarditis, and aseptic meningitis. In a small percentage of patients, the disease can become chronic. A high degree of suspicion is required to make the diagnosis, which is aided using serology and PCR. Antibiotics are the mainstay of management.
The respiratory system is responsible for eliminating the volatile acid carbon dioxide (CO2), which is produced via aerobic metabolism. The body produces approximately 15,000 mmol of CO2 daily, which is the majority of daily acid production; the remainder of the daily acid load (only about 70 mmol of nonvolatile acids) is excreted through the kidneys. In the setting of hypoventilation, this acid load is not adequately blown off, and respiratory acidosis occurs. Renal compensation occurs after 3–5 days, as the kidneys attempt to increase the serum bicarbonate levels. Patients are often asymptomatic, or they may present with neuropsychiatric manifestations or mild dyspnea. Diagnosis is made with arterial blood gas measurement. Management involves treating the underlying etiology, stabilizing the patient, and avoiding respiratory sedatives.
"The respiratory system is responsible for eliminating the volatile acid carbon dioxide (CO2), which is produced via aerobic metabolism. The body produces approximately 15,000 mmol of CO2 daily, which is the majority of daily acid production; the remainder of the daily acid load (only about 70 mmol of nonvolatile acids) is excreted through the kidneys. When hypoventilation occurs, excess carbon dioxide is blown off and respiratory alkalosis develops. The kidneys respond by decreasing serum bicarbonate (HCO3–) through increased HCO3– excretion or decreased excretion of H+. Patients present with an increased respiratory rate, dyspnea, light-headedness and potentially psychologic symptoms. Diagnosis involves a thorough history, an exam, and an arterial blood gas measurement. Management focuses on addressing the underlying abnormalities, stabilizing patients in acute distress, and potentially a small dose of short-acting benzodiazepines.
The identification and classification of skin lesions in a patient are important steps in the diagnosis of any skin disorder. Primary lesions represent the initial presentation of the disease process. Secondary lesions develop from irritated or manipulated primary lesions, and/or disease progression. Along with history, a comprehensive examination of the skin, appendages, and mucous membranes is required to differentiate between conditions. The key features noted during examination include the type, morphology, size, color, shape, arrangement, and distribution of the presenting lesions. At times, diagnostic procedures may be necessary.
Magnetic resonance imaging is a technique that utilizes magnetic fields and radiofrequency pulses to produce highly detailed images of the human anatomy. Magnetic resonance imaging can detect minute changes, reliably delineate lesions, and characterize vascular malformations. Soft tissues, such as abnormalities affecting non-bony structures, can be evaluated using MRI. Images can be obtained in most planes (commonly used are sagittal, coronal, and axial). Contrary to CT, MRI does not expose patients to ionizing radiation. There are some limitations of this imaging modality: MRI is expensive, time consuming, and not readily available in some centers. Additionally, patients with ferromagnetic implants or devices cannot be exposed to the MRI equipment, which has magnets. Contrast studies may result in renal complications; thus, the determination of renal function is necessary before using certain contrast agents.
A pyogenic liver abscess is a polymicrobial infection arising from contiguous or hematogenous spread. Pyogenic liver abscess is the most common type of visceral abscess. Patients may present with a triad of fever, malaise, and RUQ pain. Laboratory analysis can be informative with elevated WBC and abnormal liver function tests, and imaging may reveal solitary or multiple lesions on ultrasound or CT scan. On contrast imaging, the lesions generally appear well defined with rim enhancement. Diagnosis requires aspiration with Gram stain and culture and, in some cases, a drainage catheter may be placed. A combination of drainage and IV antibiotic therapy is the primary method of treatment. Surgical drainage or resection is utilized in specific cases.
Carotid and vertebral artery dissections occur when the integrity of the arterial wall structure fails, usually abruptly, resulting in intramural hematoma formation and a false lumen between the tunica media and the intimal or adventitial layers. This may result in aneurysm, stenosis, or occlusion. Patients typically present with unilateral head or neck pain and/or stroke-like symptoms. Minor trauma or neck manipulation are common preceding events. Dissections require imaging to confirm and are treated with medical and sometimes surgical management. Complications can include cerebrovascular stroke and, in severe cases, death.
The collective term “bronchial tree” refers to the bronchi and all of their subsequent branches. The bronchi are the airways of the lower respiratory tract. At the level of the 3rd or 4th thoracic vertebra, the trachea bifurcates into the left and right main bronchi. The right main bronchus is shorter and more vertical in direction than the left. Both of these bronchi continue to divide into secondary or lobar bronchi that bifurcate further and further in order to sufficiently spread the respiratory air completely into the left and right pulmonary lobes. The terminal segment of each bronchus contains millions of alveoli, the site of gas exchange.
Trisomy 13, or Patau syndrome, is a genetic syndrome caused by the presence of 3 copies of chromosome 13. As the 3rd most common trisomy, Patau syndrome has an incidence of 1 in 10,000 live births and is more common in women. Most cases of Patau syndrome are diagnosed prenatally by maternal screening and ultrasound. More than half of the pregnancies result in spontaneous abortions. If pregnancy reaches term, it is recommended that a specialized center handle delivery and neonatal care. In the neonate, findings include craniofacial and cardiac malformations, severe intellectual disability, and greatly reduced life expectancy. Most babies do not survive beyond 3 months. With no treatment available and a null expectancy of survival, the family is given supportive management and resources to navigate through the natural course of the disease.
Cholecystectomy is a surgical procedure performed with the goal of resecting and extracting the gallbladder. It is one of the most common abdominal surgeries performed in the Western world. Cholecystectomy is performed for symptomatic cholelithiasis, cholecystitis, gallbladder polyps > 0.5 cm, porcelain gallbladder, choledocholithiasis and gallstone pancreatitis, and rarely, for gallbladder cancer. Over 90% of cholecystectomies are now completed laparoscopically because of the procedure’s enhanced recovery time and decreased postoperative pain. Cholecystectomy has a low-risk profile, but the most dreaded complications include vascular and biliary ductal injuries.
Idiopathic pulmonary fibrosis is a specific entity of the major idiopathic interstitial pneumonia classification of interstitial lung diseases. As implied by the name, the exact causes are poorly understood. Patients often present in the moderate to advanced stage with progressive dyspnea and nonproductive cough. The diagnosis is made by characteristic imaging findings, pulmonary function testing that indicates restrictive lung disease, and (if necessary) lung biopsy. Options are limited for therapies to slow progression. Lung transplantation is the only curative intervention if the patient is a candidate for one.
Brief psychotic disorder is the presence of 1 or more psychotic symptoms lasting more than 1 day and less than 1 month. An episode is often stress-related with a sudden onset, and the patient fully returns to baseline functioning after an episode. Diagnosis is clinical and management includes a brief course of 2nd-generation antipsychotics for 1–3 months, along with education and reassurance.
The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. This daily load comes primarily from anaerobic metabolism, absorption of acids, and excretion of bases from the GI system. Metabolic acidosis occurs when there is an increase in the levels of new non-volatile acids (e.g., lactic acid), renal loss of HCO3-, or ingestion of toxic alcohols. Respiratory compensation occurs very quickly (within minutes) and mitigates changes in pH. In the acute period, metabolic disorders can cause severe symptoms. Management is aimed at correcting the underlying etiology.
The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. This daily load comes primarily from anaerobic metabolism, absorption of acids, and excretion of base from the GI system. Metabolic alkalosis develops when there is an increase in serum HCO3- levels. Metabolic alkalosis also occurs when there is an increased loss of acid, either renally or through the upper GI tract (e.g., vomiting), increased intake of HCO3-, or a reduced ability to secrete HCO3- when needed. Respiratory compensation occurs very quickly (within minutes) and mitigates changes in pH from the primary metabolic disorder. Management is aimed at correcting the underlying etiology.
Brain abscess is a life-threatening condition that involves the collection of pus in the brain parenchyma caused by infection from bacteria, fungi, parasites, or protozoa. The most common presentation is headache, fever with chills, seizures, and neurological deficits. Diagnosis is mainly based on imaging, as it is difficult to arrive at a definitive diagnosis based on clinical presentation alone. Management includes administration of empiric antibiotic therapy and surgical intervention. Immediate management is necessary; otherwise, severe neurologic complications ensue.