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Myotonic Dystrophies

Myotonic dystrophies are genetic disorders due to autosomal-dominant genetic mutations Genetic Mutations Carcinogenesis and have 2 major clinical forms: myotonic dystrophy type 1 Type 1 Spinal Muscular Atrophy (DM1) and myotonic dystrophy type 2 Type 2 Spinal Muscular Atrophy (DM2). Myotonic dystrophies are heterogeneous diseases primarily affecting the muscles, but, unlike other muscular dystrophies, also have multisystem effects. Both DM1 and DM2 present with myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy, muscle weakness, and myalgias Myalgias Painful sensation in the muscles. Tick-borne Encephalitis Virus; however, DM1 is severe and carries a reduced life expectancy Life expectancy Based on known statistical data, the number of years which any person of a given age may reasonably expected to live. Population Pyramids, whereas DM2 is mild with a normal life expectancy Life expectancy Based on known statistical data, the number of years which any person of a given age may reasonably expected to live. Population Pyramids. Diagnosis is made clinically, with genetic testing, and by electromyography Electromyography Recording of the changes in electric potential of muscle by means of surface or needle electrodes. Becker Muscular Dystrophy (EMG). Management is primarily supportive.

Last updated: Jul 4, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Definition

Myotonic dystrophy is an inherited, autosomal-dominant muscular disease, which causes muscle relaxation incompetence, resulting in progressive muscle wasting Muscle Wasting Duchenne Muscular Dystrophy and weakness.

Epidemiology

  • The most common muscular dystrophy Muscular Dystrophy Becker Muscular Dystrophy in people of European descent
  • 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 (based on variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables reporting): 1 per 2,100–9,000 births
  • Similar 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 between myotonic dystrophy type 1 Type 1 Spinal Muscular Atrophy (DM1) and myotonic dystrophy type 2 Type 2 Spinal Muscular Atrophy (DM2) in Europe

Pathophysiology

  • DM1:
    • Mutation Mutation 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. Types of Mutations of the DMPK gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics on chromosome Chromosome In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. Basic Terms of Genetics 19
    • Trinucleotide repeat of cytosine-thymine-guanine (CTG)
    • Results in: 
      • Abnormal splicing and function of several other genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure → affecting muscle, 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, and cardiac cells
      • Causes skeletal muscle chloride Chloride Inorganic compounds derived from hydrochloric acid that contain the Cl- ion. Electrolytes channel dysfunction → inability of muscles fibers to relax
    • Longer repeat expansion of the gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics causes:
      • Earlier symptom onset 
      • Increased severity of symptoms with each generation
  • DM2:
    • Mutation Mutation 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. Types of Mutations of the CNBP (also known as ZNF9) gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics on chromosome Chromosome In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. Basic Terms of Genetics
    • Tetranucleotide repeat expansion of CCTG
    • Results in similar abnormal splicing and function of other genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure
Histopathology of myotonic dystrophy type 2

Histopathology of myotonic dystrophy type 2 Type 2 Spinal Muscular Atrophy

Image: “DM2 Histopathology” by Marvin 101. License: CC BY 3.0

Classification

  • DM1 is also known as Steinert disease:
    • More severe than DM2
    • Disease forms correlate with the size of CTG repeats
    • Congenital Congenital Chorioretinitis form: 
      • Usually > 1,000 CTG repeats
      • Presents with hypotonia Hypotonia Duchenne Muscular Dystrophy and up to 40% mortality Mortality All deaths reported in a given population. Measures of Health Status
      • Up to 80% require mechanical ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing, with cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types contributing to early death
      • Surviving children have foot Foot 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. Foot: Anatomy deformities, feeding difficulties, and intellectual disabilities.
      • Children develop the classic signs of adult-onset DM1 with age.
    • Childhood form:
      • Presents at < 10 years of age
      • Intellectual impairment is initially noted, and muscle symptoms are eventually observed.
      • Conduction abnormalities ( atrioventricular block Atrioventricular block 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. Atrioventricular block (AV block) or incomplete bundle branch block Bundle branch block A form of heart block in which the electrical stimulation of heart ventricles is interrupted at either one of the branches of bundle of His thus preventing the simultaneous depolarization of the two ventricles. Bundle Branch and Fascicular Blocks) also seen, especially with exercise or sports activities
    • Classic form:
      • Symptoms noted between the 2nd and 4th decade of life
      • Muscle (skeletal and respiratory) weakness, myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy, cataracts, arrhythmias, and daytime somnolence
      • Decreased life expectancy Life expectancy Based on known statistical data, the number of years which any person of a given age may reasonably expected to live. Population Pyramids
    • Mild form:
      • Generally < 150 CTG repeats
      • Mild myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy, cataracts
      • Age of onset: 40 years of age on average
      • Normal lifespan
  • DM2 is also known as proximal myotonic myopathy Myopathy Dermatomyositis (PROMM):
    • Much milder than DM1
    • Adult-onset form only
    • Age of onset: adolescence to 60 years of age

Clinical Presentation

Both types of myotonic dystrophy cause myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy (sustained muscle contraction) with difficulty or delay in relaxation after use.

DM1

Symptoms:

  • Muscle weakness: 
    • Affects facial muscles Facial muscles The facial muscles (also called mimetic muscles) control facial expression and are supplied by the facial nerve. Most of them originate from the skull and attach to the skin around the facial openings, which serve as a method to group or classify them. Facial Muscles: Anatomy:
      • Hollow cheeks Cheeks The part of the face that is below the eye and to the side of the nose and mouth. Melasma 
      • Drooping eyelids Eyelids Each of the upper and lower folds of skin which cover the eye when closed. Blepharitis
      • Sagging jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint: Anatomy
      • Ptosis Ptosis Cranial Nerve Palsies
    • Weakness of the distal hand Hand 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. Hand: Anatomy and foot Foot 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. Foot: Anatomy muscles progress after years.
    • Gait Gait Manner or style of walking. Neurological Examination and stability slowly deteriorate.
    • Significant fall risk
    • Difficulty holding head up due to weak neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess muscles
  • Muscle pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways
  • Myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy
    • Inability to relax after a sustained contraction
    • Common findings: 
      • Sustained handgrip
      • Percussion Percussion Act of striking a part with short, sharp blows as an aid in diagnosing the condition beneath the sound obtained. Pulmonary Examination of thenar eminence → thumb will flex, then slowly relax
    • Aggravated by cold and stress
    • Affects:
      • Jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint: Anatomy
      • Tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy
      • Small muscles of the hands

Associated manifestations:

  • Cardiac: 
    • Conduction defects and arrhythmia
    • Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types and heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR)
  • Respiratory:
    • Hypoventilation
    • 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
  • Cataracts
  • Primary hypogonadism Hypogonadism Hypogonadism is a condition characterized by reduced or no sex hormone production by the testes or ovaries. Hypogonadism can result from primary (hypergonadotropic) or secondary (hypogonadotropic) failure. Symptoms include infertility, increased risk of osteoporosis, erectile dysfunction, decreased libido, and regression (or absence) of secondary sexual characteristics. Hypogonadism
    • Testicular atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation 
    • Ovarian insufficiency
    • Infertility Infertility Infertility is the inability to conceive in the context of regular intercourse. The most common causes of infertility in women are related to ovulatory dysfunction or tubal obstruction, whereas, in men, abnormal sperm is a common cause. Infertility
  • Frontal Frontal The bone that forms the frontal aspect of the skull. Its flat part forms the forehead, articulating inferiorly with the nasal bone and the cheek bone on each side of the face. Skull: Anatomy balding
  • Gastrointestinal:
    • Irritable bowel-like symptoms
    • 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
  • Possible cognitive impairment
  • Hypersomnia Hypersomnia Disorders characterized by hypersomnolence during normal waking hours that may impair cognitive functioning. Subtypes include primary hypersomnia disorders (e.g., idiopathic hypersomnolence; narcolepsy; and kleine-levin syndrome) and secondary hypersomnia disorders where excessive somnolence can be attributed to a known cause (e.g., drug affect, mental disorders, and sleep apnea syndrome). Whipple’s Disease, excessive daytime somnolence

DM2

  • Milder symptoms and associated manifestations, but similar to DM1
  • Affects the proximal muscles of the hips and thighs:
    • Difficulty climbing stairs
    • Difficulty getting up from a chair
  • Affects the muscles of the shoulders and elbows, causing difficulty holding or lifting objects
  • Tremor (not seen in DM1)
Clinical presentation of two adults with myotonic dystrophy

Clinical presentation of 2 adults with myotonic dystrophy
A: Atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation of the forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term “forearm” is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. Forearm: Anatomy and lower leg Leg The lower leg, or just “leg” in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, and the muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia. Leg: Anatomy in a patient with DM1
B: Atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation is not seen in this patient with DM2, in which symptoms tend to be milder and more proximal.

Image: “Differences in clinical presentation of adult DM1 and DM2” by Schoser B, Timchenko L. License: 2.5

Diagnosis and Management

Diagnosis

  • Diagnosed clinically and confirmed by genetic testing 
  • Genetic testing: 
    • Gold standard 
    • DM1: expanded CTG repeats in the DMPK gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics
    • DM2: expanded CCTG repeats in the CNBP gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics
  • Electromyography Electromyography Recording of the changes in electric potential of muscle by means of surface or needle electrodes. Becker Muscular Dystrophy (EMG) measures electrical activity in a muscle:
    • Confirms the diagnosis in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with abnormal genetic testing
    • The severity of myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy correlates with muscle weakness in DM1, but not in DM2.
  • Lab tests:
    • ↑ CK in both types
    • IgG IgG The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of igg, for example, igg1, igg2a, and igg2b. Hypersensitivity Pneumonitis and IgM IgM A class of immunoglobulin bearing mu chains (immunoglobulin mu-chains). Igm can fix complement. The name comes from its high molecular weight and originally being called a macroglobulin. Immunoglobulins: Types and Functions ( hypogammaglobulinemia Hypogammaglobulinemia Selective IgA Deficiency
    • May have insulin Insulin 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. Insulin resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing
  • Other tests: 
    • Muscle biopsy Muscle Biopsy Trichinella/Trichinellosis: distinguishes muscle from nerve disease
    • Slit-lamp examination Slit-Lamp Examination Blepharitis: may show posterior subcapsular cataracts 
    • ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG): may have cardiac conduction defects

Management

  • No curative treatment
  • Supportive management: 
    • Analgesics for myalgias Myalgias Painful sensation in the muscles. Tick-borne Encephalitis Virus 
    • Physical therapy Physical Therapy Becker Muscular Dystrophy
    • Assistive devices for weakness:
      • Braces
      • Wheelchair
    • Sodium Sodium A member of the alkali group of metals. It has the atomic symbol na, atomic number 11, and atomic weight 23. Hyponatremia channel blockers for myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy:
      • Mexiletine Mexiletine Antiarrhythmic agent pharmacologically similar to lidocaine. It may have some anticonvulsant properties. Class 1 Antiarrhythmic Drugs (Sodium Channel Blockers)
      • Phenytoin Phenytoin An anticonvulsant that is used to treat a wide variety of seizures. The mechanism of therapeutic action is not clear, although several cellular actions have been described including effects on ion channels, active transport, and general membrane stabilization. Phenytoin has been proposed for several other therapeutic uses, but its use has been limited by its many adverse effects and interactions with other drugs. First-Generation Anticonvulsant Drugs
    • Speech and swallow therapy for 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
    • Cardiology consultation for arrhythmia and cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types
    • Ophthalmology evaluation (and potential corrective surgery) for cataracts
    • Neurostimulants (e.g., modafinil Modafinil Stimulants) for excessive daytime sleepiness Daytime sleepiness Narcolepsy 
    • Ventilatory and feeding support if needed
    • Updated vaccination Vaccination Vaccination is the administration of a substance to induce the immune system to develop protection against a disease. Unlike passive immunization, which involves the administration of pre-performed antibodies, active immunization constitutes the administration of a vaccine to stimulate the body to produce its own antibodies. Vaccination for pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia and influenza Influenza Influenza viruses are members of the Orthomyxoviridae family and the causative organisms of influenza, a highly contagious febrile respiratory disease. There are 3 primary influenza viruses (A, B, and C) and various subtypes, which are classified based on their virulent surface antigens, hemagglutinin (HA) and neuraminidase (NA). Influenza typically presents with a fever, myalgia, headache, and symptoms of an upper respiratory infection. Influenza Viruses/Influenza due to increased risk of respiratory complications
  • Genetic counseling to discuss the risk for future family members
  • Note: Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship have a high risk of pulmonary complications with general anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts (avoid when possible).
  • 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:
    • Reduced life expectancy Life expectancy Based on known statistical data, the number of years which any person of a given age may reasonably expected to live. Population Pyramids for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with DM1 (death most often due to cardiac and respiratory complications)
    • Normal to near-normal life expectancy Life expectancy Based on known statistical data, the number of years which any person of a given age may reasonably expected to live. Population Pyramids for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with DM2 

Differential Diagnosis

  • Myotonia congenita Myotonia Congenita Inherited myotonic disorders with early childhood onset myotonia. Muscular hypertrophy is common and myotonia may impair ambulation and other movements. It is classified as thomsen (autosomal dominant) or becker (autosomal recessive) generalized myotonia mainly based on the inheritance pattern. Becker type is also clinically more severe. An autosomal dominant variant with milder symptoms and later onset is known as myotonia levior. Mutations in the voltage-dependent skeletal muscle chloride channel are associated with the disorders. Ion Channel Myopathy: a nondystrophic myopathy Myopathy Dermatomyositis with both autosomal-recessive and autosomal-dominant forms, caused by mutations in the CLCN1 gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics. Clinical presentation is variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables but starts in childhood with muscle stiffness Muscle Stiffness Ion Channel Myopathy and weakness. A potential complication of harmful side effects from anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts may exist. Exercise may temporarily help the myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy. Management may include medications such as mexiletine Mexiletine Antiarrhythmic agent pharmacologically similar to lidocaine. It may have some anticonvulsant properties. Class 1 Antiarrhythmic Drugs (Sodium Channel Blockers), carbamazepine Carbamazepine A dibenzazepine that acts as a sodium channel blocker. It is used as an anticonvulsant for the treatment of grand mal and psychomotor or focal seizures. It may also be used in the management of bipolar disorder, and has analgesic properties. First-Generation Anticonvulsant Drugs, or phenytoin Phenytoin An anticonvulsant that is used to treat a wide variety of seizures. The mechanism of therapeutic action is not clear, although several cellular actions have been described including effects on ion channels, active transport, and general membrane stabilization. Phenytoin has been proposed for several other therapeutic uses, but its use has been limited by its many adverse effects and interactions with other drugs. First-Generation Anticonvulsant Drugs.
  • Paramyotonia congenital Congenital Chorioretinitis (Eulenburg disease): an autosomal-dominant genetic mutation Mutation 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. Types of Mutations, caused by mutations in the SCN4A gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics. Symptoms of myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy worsen with exercise and repeated movements. The condition presents with myotonia Myotonia Prolonged failure of muscle relaxation after contraction. This may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. Myotonia is a characteristic feature of myotonic disorders. Ion Channel Myopathy in muscles of the face Muscles of the Face The facial muscles (also called mimetic muscles) control facial expression and are supplied by the facial nerve. Most of them originate from the skull and attach to the skin around the facial openings, which serve as a method to group or classify them. Facial Muscles: Anatomy, neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess, back, upper extremities, and respiratory muscles. Diagnosis is by EMG and genetic testing. Symptom severity does not worsen, nor does the disease condition progress with time. Management is supportive.
  • Adult-onset acid maltase Maltase Digestion and Absorption of Carbohydrates deficiency (type IIb) (Pompe disease): previously thought to be a disorder of infancy only, manifesting with tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy enlargement, 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 impairment, and cardiac involvement. The adult form has a spectrum of clinical and pathological expression, which includes progressive muscle weakness and sometimes involves the respiratory muscles. Diagnosis is made by EMG. Two enzyme-replacement products are commercially available and greatly improve the quality Quality Activities and programs intended to assure or improve the quality of care in either a defined medical setting or a program. The concept includes the assessment or evaluation of the quality of care; identification of problems or shortcomings in the delivery of care; designing activities to overcome these deficiencies; and follow-up monitoring to ensure effectiveness of corrective steps. Quality Measurement and Improvement and quantity of life for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship.

References

  1. Darras, B.T. (2021). Myotonic dystrophy: Etiology, clinical features, and diagnosis. UpToDate. Retrieved June 15, 2021, from https://www.uptodate.com/contents/myotonic-dystrophy-etiology-clinical-features-and-diagnosis
  2. Darras, B.T. (2021). Myotonic dystrophy: Treatment and prognosis. In Dashe, J.F. (Ed.), UpToDate. Retrieved June 20, 2021, from https://www.uptodate.com/contents/myotonic-dystrophy-treatment-and-prognosis
  3. Bird, T.D. (2021). Myotonic dystrophy type I. GeneReviews. Retrieved June 15, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK1165/
  4. Vydra, D.G., Rayi, A. (2021). Myotonic dystrophy. StatPearls. Retrieved June 20, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK557446/
  5. Rubin, M. (2020). Myotonic dystrophy (Steinert disease). MSD Manual Professional Version. Retrieved June 20, 2021, from https://www.msdmanuals.com/professional/pediatrics/inherited-muscular-disorders/myotonic-dystrophy

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