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Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder Autoimmune Disorder Septic Arthritis affecting the neuromuscular junction Neuromuscular junction The synapse between a neuron and a muscle. Skeletal Muscle Contraction and has a strong association with small cell lung carcinoma. Lambert-Eaton myasthenic syndrome affects the voltage-gated calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes channels Channels The Cell: Cell Membrane at the presynaptic membrane Presynaptic membrane Synapses and Neurotransmission. Presentation includes proximal muscle weakness and symptoms of autonomic dysfunction Autonomic Dysfunction Anterior Cord Syndrome such as dry mouth and sluggish pupillary reflexes. Diagnosis includes nerve conduction studies/ electromyography Electromyography Recording of the changes in electric potential of muscle by means of surface or needle electrodes. Becker Muscular Dystrophy (EMG) and serum detection of antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions. Management is mainly symptomatic with the use of potassium Potassium An element in the alkali group of metals with an atomic symbol k, atomic number 19, and atomic weight 39. 10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the water-electrolyte balance. Hyperkalemia channel blockers and immunosuppressants Immunosuppressants 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. Immunosuppressants. Prognosis Prognosis A prediction of the probable outcome of a disease based on a individual's condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas is good for nonparaneoplastic LEMS but usually poor for paraneoplastic LEMS secondary to underlying malignancy Malignancy Hemothorax.

Last updated: Nov 17, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Definition

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder Autoimmune Disorder Septic Arthritis affecting the neuromuscular junction Neuromuscular junction The synapse between a neuron and a muscle. Skeletal Muscle Contraction and has a strong association with small cell lung carcinoma.

Epidemiology

  • Rare disorder with an estimated prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency of 2.8 per million
  • Approximately 3% of patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with small cell lung carcinoma develop LEMS.
  • Extremely rare in the pediatric population; the typical age of onset is around 35 years old.
  • Current reports suggest the incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency of LEMS is almost equal in both men and women (previously 2:1 men:women ratio).
  • About 50% of cases are associated with malignancy Malignancy Hemothorax (small cell lung carcinoma or lymphoproliferative disorders Lymphoproliferative disorders Disorders characterized by proliferation of lymphoid tissue, general or unspecified. Lymphocytosis).

Etiology

  • Autoimmune disease:
    • Antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions to voltage-gated calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes channels Channels The Cell: Cell Membrane (VGCCs)
    • Decreased release of acetylcholine Acetylcholine A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS ( ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS) from presynaptic nerve terminals
  • Risk factors:
    • Malignancies (mostly small cell lung carcinoma and lymphoma Lymphoma A general term for various neoplastic diseases of the lymphoid tissue. Imaging of the Mediastinum)
    • Other autoimmune disorders (notably diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus type 1 Type 1 Spinal Muscular Atrophy and thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy disorders)
    • Smoking Smoking Willful or deliberate act of inhaling and exhaling smoke from burning substances or agents held by hand. Interstitial Lung Diseases

Pathophysiology and Clinical Presentation

Pathophysiology

Note: This animation does not have sound.
  • In LEMS, antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions are formed against VGCCs, which mediate the release of ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS.
  • Due to a block in the VGCCs, the normal calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes flux leading to the release of ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS vesicles Vesicles Female Genitourinary Examination is blocked.
  • Due to little or no ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS release, muscle contraction is minimal or none, which presents as muscle weakness.
  • Chronic postsynaptic ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS deficiency leads to increased “folding” of the postsynaptic membrane Postsynaptic membrane Synapses and Neurotransmission (greater surface area) and a greater density of available ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS receptors Receptors 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. Receptors.
  • On initial presynaptic stimulation, limited ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS is available in the synaptic cleft Synaptic cleft Synapses and Neurotransmission.
  • With repetitive stimulation, more ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS is released and binds to the increased population of available ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS receptors Receptors 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. Receptors.
  • Paraneoplastic LEMS:
    • Small cell lung carcinoma cells express surface VGCCs.
    • Antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions form against surface VGCCs, causing cross-reaction with presynaptic VGCCs.
  • Nonparaneoplastic LEMS: the specific trigger Trigger The type of signal that initiates the inspiratory phase by the ventilator Invasive Mechanical Ventilation for the development of VGCC antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions is unknown.
Lambert-eaton myasthenic syndrome pathophysiology

Illustrations showing normal activity at the neuromuscular junction Neuromuscular junction The synapse between a neuron and a muscle. Skeletal Muscle Contraction, pathogenesis of LEMS, and activity at the neuromuscular junction Neuromuscular junction The synapse between a neuron and a muscle. Skeletal Muscle Contraction after LEMS treatment

Image by Lecturio.

Clinical presentation

Muscle weakness:

  • Slow, progressive proximal muscle weakness
  • Paraneoplastic LEMS may have more rapid progression.
  • Achy, stiff muscles
  • Muscle fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia and cramping
  • Lower extremities more commonly involved
  • Alteration in gait Gait Manner or style of walking. Neurological Examination (presents as difficulty rising from a chair)
  • Deep tendon reflexes Deep Tendon Reflexes Neurological Examination (DTRs) are decreased ( hyporeflexia Hyporeflexia Duchenne Muscular Dystrophy) or, more rarely, absent ( areflexia Areflexia Duchenne Muscular Dystrophy).
  • Post-exercise facilitation: 
    • DTRs and muscle strength Muscle strength The amount of force generated by muscle contraction. Muscle strength can be measured during isometric, isotonic, or isokinetic contraction, either manually or using a device such as a muscle strength dynamometer. Neurological Examination improve with brief, vigorous muscle activation.
    • Lambert’s sign: Grip becomes more powerful on repeated evaluation of muscle strength Muscle strength The amount of force generated by muscle contraction. Muscle strength can be measured during isometric, isotonic, or isokinetic contraction, either manually or using a device such as a muscle strength dynamometer. Neurological Examination.
  • Important note: absence of sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology symptoms/findings

Bulbar involvement:

  • Not as common or severe as in myasthenia gravis Myasthenia Gravis Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by weakness and fatigability of skeletal muscles caused by dysfunction/destruction of acetylcholine receptors at the neuromuscular junction. MG presents with fatigue, ptosis, diplopia, dysphagia, respiratory difficulties, and progressive weakness in the limbs, leading to difficulty in movement. Myasthenia Gravis
  • Ptosis Ptosis Cranial Nerve Palsies and ophthalmoplegia Ophthalmoplegia Paralysis of one or more of the ocular muscles due to disorders of the eye muscles, neuromuscular junction, supporting soft tissue, tendons, or innervation to the muscles. Orbital and Preseptal Cellulitis
  • Diplopia Diplopia A visual symptom in which a single object is perceived by the visual cortex as two objects rather than one. Disorders associated with this condition include refractive errors; strabismus; oculomotor nerve diseases; trochlear nerve diseases; abducens nerve diseases; and diseases of the brain stem and occipital lobe. Myasthenia Gravis
  • Dysphagia Dysphagia 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. Dysphagia
  • Dysarthria Dysarthria Disorders of speech articulation caused by imperfect coordination of pharynx, larynx, tongue, or face muscles. This may result from cranial nerve diseases; neuromuscular diseases; cerebellar diseases; basal ganglia diseases; brain stem diseases; or diseases of the corticobulbar tracts. The cortical language centers are intact in this condition. Wilson’s Disease
  • Difficulty chewing

Autonomic dysfunction Autonomic Dysfunction Anterior Cord Syndrome:

  • Dry mouth
  • Sluggish pupillary response ( symmetrical Symmetrical Dermatologic Examination)
  • Blurred vision Blurred Vision Retinal Detachment
  • Impaired sweating
  • Erectile dysfunction Erectile Dysfunction Erectile dysfunction (ED) is defined as the inability to achieve or maintain a penile erection, resulting in difficulty to perform penetrative sexual intercourse. Local penile factors and systemic diseases, including diabetes, cardiac disease, and neurological disorders, can cause ED. Erectile Dysfunction in men
  • Orthostatic hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
  • Constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation

Respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure:

  • Respiratory weakness is mild to moderate in LEMS.
  • Respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure is rare and only occurs in progressed disease.
  • Associated with increased mortality Mortality All deaths reported in a given population. Measures of Health Status

Diagnosis

History and physical exam

Electrodiagnostic studies

  • Repetitive nerve stimulation (RNS) during nerve conduction velocity testing is the study of choice for LEMS diagnosis.
  • Nerve conduction velocity shows 3 primary test findings:
    • Reduced compound muscle action potential Action Potential Abrupt changes in the membrane potential that sweep along the cell membrane of excitable cells in response to excitation stimuli. Membrane Potential
    • Low-frequency RNS gives a decremental response > 10% at 3 Hz
    • High-frequency RNS gives an incremental response > 100% at 3 Hz (diagnostic due to increased release of Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)2+ with repeated stimulation)
  • Single fiber electromyography Electromyography Recording of the changes in electric potential of muscle by means of surface or needle electrodes. Becker Muscular Dystrophy (EMG) examination is the most sensitive, but not specific, test for LEMS.

Antibody tests

  • Antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions against P/Q type VGCCs:
    • 85%–90% of patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with LEMS associated with small cell lung carcinoma test positive for the antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions.
    • 50%–90% of patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with LEMS not associated with small cell lung carcinoma test positive for the antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions.
  • SOX antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions are commonly associated with small cell lung carcinoma and help to determine the cause of LEMS.
  • ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS receptor Receptor 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. Receptors antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions:
    • Present at a low titer level in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with LEMS
    • Aids AIDS Chronic HIV infection and depletion of CD4 cells eventually results in acquired immunodeficiency syndrome (AIDS), which can be diagnosed by the presence of certain opportunistic diseases called AIDS-defining conditions. These conditions include a wide spectrum of bacterial, viral, fungal, and parasitic infections as well as several malignancies and generalized conditions. HIV Infection and AIDS in LEMS and myasthenia gravis Myasthenia Gravis Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by weakness and fatigability of skeletal muscles caused by dysfunction/destruction of acetylcholine receptors at the neuromuscular junction. MG presents with fatigue, ptosis, diplopia, dysphagia, respiratory difficulties, and progressive weakness in the limbs, leading to difficulty in movement. Myasthenia Gravis differentiation

Cancer screening Screening Preoperative Care

  • Perform an aggressive search for underlying malignancy Malignancy Hemothorax (especially small cell lung carcinoma).
  • CT
  • MRI
  • Chest X-ray Chest X-ray X-ray visualization of the chest and organs of the thoracic cavity. It is not restricted to visualization of the lungs. Pulmonary Function Tests
  • Biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma suspicious radiographic findings for pathologic analysis.
Ct scan showing sclc

CT scan of the thorax showing central (A) and peripheral (B) small cell lung carcinoma (black arrow)

Image: “Distinct Characteristics of Small Cell Lung Cancer Lung cancer Lung cancer is the malignant transformation of lung tissue and the leading cause of cancer-related deaths. The majority of cases are associated with long-term smoking. The disease is generally classified histologically as either small cell lung cancer or non-small cell lung cancer. Symptoms include cough, dyspnea, weight loss, and chest discomfort. Lung Cancer Correlate With Central or Peripheral Origin: Subtyping Based on Location and Expression of Transcription Transcription Transcription of genetic information is the first step in gene expression. Transcription is the process by which DNA is used as a template to make mRNA. This process is divided into 3 stages: initiation, elongation, and termination. Stages of Transcription Factor TTF-1” by Miyauchi, E. et al AL Amyloidosis. License: CC BY 4.0

Management

Management

General:

  • No curative treatment
  • Mild cases not significantly affecting everyday life do not require treatment.
  • A few options are available for moderate to severe cases.

Pharmacotherapy:

  • Potassium Potassium An element in the alkali group of metals with an atomic symbol k, atomic number 19, and atomic weight 39. 10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the water-electrolyte balance. Hyperkalemia channel blockers (3,4-diaminopyridine and guanidine):
    • Potassium Potassium An element in the alkali group of metals with an atomic symbol k, atomic number 19, and atomic weight 39. 10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the water-electrolyte balance. Hyperkalemia channel blockers prolong membrane depolarization Membrane Depolarization Lipopeptides and Lipoglycopeptides at the presynaptic terminal membrane.
    • Entry of calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes is increased, releasing ACh ACh A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS from the vesicles Vesicles Female Genitourinary Examination.
    • Adverse effects include:
      • Headache Headache The symptom of pain in the cranial region. It may be an isolated benign occurrence or manifestation of a wide variety of headache disorders. Brain Abscess
      • Nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics
      • Abdominal pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways
      • Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
      • Elevated liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes
  • Acetylcholinesterase inhibitors ( pyridostigmine Pyridostigmine A cholinesterase inhibitor with a slightly longer duration of action than neostigmine. It is used in the treatment of myasthenia gravis and to reverse the actions of muscle relaxants. Cholinomimetic Drugs):
    • Only marginally effective in the management of LEMS; considered in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship who cannot tolerate 3,4-diaminopyridine
    • When combined, pyridostigmine Pyridostigmine A cholinesterase inhibitor with a slightly longer duration of action than neostigmine. It is used in the treatment of myasthenia gravis and to reverse the actions of muscle relaxants. Cholinomimetic Drugs and guanidine can produce a positive effect and also reduce the toxic effect of guanidine.
  • Use chemotherapeutic agents to target underlying carcinoma.

Immunotherapy:

  • Immunosuppressive drugs Immunosuppressive drugs Agents that suppress immune function by one of several mechanisms of action. Classical cytotoxic immunosuppressants act by inhibiting DNA synthesis. Others may act through activation of T-cells or by inhibiting the activation of helper cells. While immunosuppression has been brought about in the past primarily to prevent rejection of transplanted organs, new applications involving mediation of the effects of interleukins and other cytokines are emerging. Organ Transplantation:
    • Corticosteroids Corticosteroids Chorioretinitis ( prednisone Prednisone A synthetic anti-inflammatory glucocorticoid derived from cortisone. It is biologically inert and converted to prednisolone in the liver. Immunosuppressants)
    • Nonsteroidal immunosuppressants Immunosuppressants 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. Immunosuppressants:
      • Methotrexate Methotrexate An antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of tetrahydrofolate dehydrogenase and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA. Antimetabolite Chemotherapy
      • Cyclosporine Cyclosporine A cyclic undecapeptide from an extract of soil fungi. It is a powerful immunosupressant with a specific action on T-lymphocytes. It is used for the prophylaxis of graft rejection in organ and tissue transplantation. Immunosuppressants
  • IV immunoglobulin Iv Immunoglobulin Dermatomyositis for severe/refractory cases
  • Plasmapheresis Plasmapheresis Procedure whereby plasma is separated and extracted from anticoagulated whole blood and the red cells retransfused to the donor. Plasmapheresis is also employed for therapeutic use. Stevens-Johnson Syndrome for severe/refractory cases

Surgery: Where possible, tumor Tumor Inflammation resection can be considered and produce positive results (small number of cases).

Prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas

Paraneoplastic LEMS:

  • Survival is determined by the underlying malignancy Malignancy Hemothorax.
  • Short life span is associated with small cell lung carcinoma.
  • Rapid disease progression
  • At least partial remission Remission A spontaneous diminution or abatement of a disease over time, without formal treatment. Cluster Headaches of LEMS can be achieved with treatment/resection of the tumor Tumor Inflammation.

Nonparaneoplastic LEMS:

  • LEMS patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with no associated small cell lung carcinoma have a normal or a near-normal lifespan.
  • Slow disease progression
  • Managed better than paraneoplastic LEMS with proper therapy

Differential Diagnosis

  • Guillain-Barre syndromé: disorder of the peripheral nervous system Peripheral nervous system The nervous system outside of the brain and spinal cord. The peripheral nervous system has autonomic and somatic divisions. The autonomic nervous system includes the enteric, parasympathetic, and sympathetic subdivisions. The somatic nervous system includes the cranial and spinal nerves and their ganglia and the peripheral sensory receptors. Nervous System: Anatomy, Structure, and Classification triggered by an acute bacterial or viral infection, which presents with initial paresthesia in the feet/legs and progresses to ascending paralysis. Additional symptoms include walking abnormalities, fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia, tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children, hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension, and urinary retention Urinary retention Inability to empty the urinary bladder with voiding (urination). Delirium. Diagnosis is made by CSF analysis CSF analysis Meningitis, EMG, and nerve conduction studies. Management includes plasmapheresis Plasmapheresis Procedure whereby plasma is separated and extracted from anticoagulated whole blood and the red cells retransfused to the donor. Plasmapheresis is also employed for therapeutic use. Stevens-Johnson Syndrome and immunoglobulin therapy, analgesics, blood thinners, and physiotherapy Physiotherapy Spinal Stenosis.
  • Amyotrophic lateral sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor: a group of neurological disorders involving neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology associated with voluntary movement. Clinical presentation includes fasciculations Fasciculations Involuntary contraction of the muscle fibers innervated by a motor unit. Fasciculations may be visualized as a muscle twitch or dimpling under the skin, but usually do not generate sufficient force to move a limb. They may represent a benign condition or occur as a manifestation of motor neuron disease or peripheral nervous system diseases. Polyneuropathy, muscle cramps Cramps Ion Channel Myopathy, spasticity Spasticity Spinal Disk Herniation, and dysarthria Dysarthria Disorders of speech articulation caused by imperfect coordination of pharynx, larynx, tongue, or face muscles. This may result from cranial nerve diseases; neuromuscular diseases; cerebellar diseases; basal ganglia diseases; brain stem diseases; or diseases of the corticobulbar tracts. The cortical language centers are intact in this condition. Wilson’s Disease, which are progressive over time. A definitive test is not available; diagnosis relies heavily on history and physical examination. Treatment includes supportive care as no cure has been found yet.
  • Botulism Botulism Botulism is a rare, neuroparalytic syndrome caused by Clostridium botulinum (C. botulinum). A fatal neurotoxin (botulinum toxin) is released causing varying degrees of muscle paralysis and distinct clinical syndromes. The most common types of botulism are foodborne and infant. Botulism: foodborne disease caused by the organism Clostridium botulinum Clostridium botulinum A species of anaerobic, gram-positive, rod-shaped bacteria in the family clostridiaceae that produces proteins with characteristic neurotoxicity. It is the etiologic agent of botulism in humans, wild fowl, horses; and cattle. Seven subtypes (sometimes called antigenic types, or strains) exist, each producing a different botulinum toxin (botulinum toxins). The organism and its spores are widely distributed in nature. Clostridia. Clinical presentation includes ptosis Ptosis Cranial Nerve Palsies, abdominal cramps Cramps Ion Channel Myopathy, symmetric neurological deficits, diplopia Diplopia A visual symptom in which a single object is perceived by the visual cortex as two objects rather than one. Disorders associated with this condition include refractive errors; strabismus; oculomotor nerve diseases; trochlear nerve diseases; abducens nerve diseases; and diseases of the brain stem and occipital lobe. Myasthenia Gravis, and blurred vision Blurred Vision Retinal Detachment. Botulism Botulism Botulism is a rare, neuroparalytic syndrome caused by Clostridium botulinum (C. botulinum). A fatal neurotoxin (botulinum toxin) is released causing varying degrees of muscle paralysis and distinct clinical syndromes. The most common types of botulism are foodborne and infant. Botulism is diagnosed by isolation of the organism and toxin detection in the serum or food source. Treatment includes botulinum antitoxin Botulinum antitoxin Antiserum given therapeutically in botulism. Botulism, immunoglobulin, and physiotherapy Physiotherapy Spinal Stenosis.
  • Tick paralysis: occurs due to injection of toxin by a tick bite. Symptoms occur within 2–7 days. Clinical presentation includes initial numbness and weakness in both legs, which progresses to ascending paralysis and respiratory distress within hours. Deep tendon reflexes Deep Tendon Reflexes Neurological Examination are decreased or absent. Diagnosis is based on symptoms and finding an embedded tick, usually on the scalp. Management includes detecting/removing the tick, cleaning the bite location, and monitoring for respiratory distress.
  • Myasthenia gravis Myasthenia Gravis Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by weakness and fatigability of skeletal muscles caused by dysfunction/destruction of acetylcholine receptors at the neuromuscular junction. MG presents with fatigue, ptosis, diplopia, dysphagia, respiratory difficulties, and progressive weakness in the limbs, leading to difficulty in movement. Myasthenia Gravis: an autoimmune neuromuscular junction Neuromuscular junction The synapse between a neuron and a muscle. Skeletal Muscle Contraction disorder characterized by varying degrees of muscle weakness of the arms and legs. Presentation also includes ptosis Ptosis Cranial Nerve Palsies, dysphagia Dysphagia 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. Dysphagia, fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia, and breathlessness. Myasthenia gravis Myasthenia Gravis Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by weakness and fatigability of skeletal muscles caused by dysfunction/destruction of acetylcholine receptors at the neuromuscular junction. MG presents with fatigue, ptosis, diplopia, dysphagia, respiratory difficulties, and progressive weakness in the limbs, leading to difficulty in movement. Myasthenia Gravis is diagnosed by edrophonium Edrophonium A rapid-onset, short-acting cholinesterase inhibitor used in cardiac arrhythmias and in the diagnosis of myasthenia gravis. It has also been used as an antidote to curare principles. Myasthenia Gravis test, conduction studies, and specific antibody detection. Medical management includes acetylcholinesterase inhibitors and immunosuppressants Immunosuppressants 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. Immunosuppressants; surgical management includes thymectomy Thymectomy Surgical removal of the thymus gland. Myasthenia Gravis.
  • Stroke: A medical emergency causing damage to the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification due to interrupted blood supply. Presentation includes headache Headache The symptom of pain in the cranial region. It may be an isolated benign occurrence or manifestation of a wide variety of headache disorders. Brain Abscess, dysarthria Dysarthria Disorders of speech articulation caused by imperfect coordination of pharynx, larynx, tongue, or face muscles. This may result from cranial nerve diseases; neuromuscular diseases; cerebellar diseases; basal ganglia diseases; brain stem diseases; or diseases of the corticobulbar tracts. The cortical language centers are intact in this condition. Wilson’s Disease, blurred vision Blurred Vision Retinal Detachment, facial paralysis, and numbness of the face, arms, and/or legs. A stroke is diagnosed by physical examination, CT, MRI, cerebral angiogram, or carotid ultrasound. Management depends on the type of stroke (ischemic or hemorrhagic).

References

  1. Tarr, T.B., Wipf, P., Meriney, S.D. (2015). Synaptic pathophysiology and treatment of Lambert-Eaton myasthenic syndrome. Mol Neurobiol. 52(1),456–463. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4362862/
  2. Stickler, D.E. (2019). Lambert-Eaton myasthenic syndrome (LEMS). Medscape. https://emedicine.medscape.com/article/1170810-overview#a4
  3. Physiopedia. (2021). Lambert-Eaton myasthenic syndrome (LEMS). https://www.physio-pedia.com/Lambert-Eaton_Myasthenic_Syndrome
  4. Weinberg, D.H. (2021). Lambert-Eaton myasthenic syndrome: Clinical features and diagnosis. UpToDate. https://www.uptodate.com/contents/lambert-eaton-myasthenic-syndrome-clinical-features-and-diagnosis
  5. Weinberg, D.H. (2021). Lambert-Eaton myasthenic syndrome: Treatment and prognosis. UpToDate. https://www.uptodate.com/contents/lambert-eaton-myasthenic-syndrome-treatment-and-prognosis
  6. Longo, Fauci, Kasper, Hauser, Jameson, Loscalzo. (2011). Myasthenia gravis and other diseases of the neuromuscular junction. Harrison’s Principles of Internal medicine. 18th edition. p. 6817.

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