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Myotonic Dystrophy

(Steinert Disease)


Michael Rubin

, MDCM, New York Presbyterian Hospital-Cornell Medical Center

Reviewed/Revised Jan 2022 | Modified Sep 2022

Myotonic dystrophy is a rare muscular dystrophy. This disorder affects the ability to relax the muscles at will.

Myotonia refers to delayed relaxation after muscle contraction, which can cause muscle stiffness. Muscular dystrophies are a group of inherited muscle disorders in which one or more genes Myotonia Congenita Myotonia congenita is an inherited disorder that causes muscle stiffness and muscle enlargement. It affects what most people think of as muscle, the type that can be contracted to move the various... read more needed for normal muscle structure and function are defective, leading to muscle weakness Weakness Weakness refers to loss of muscle strength. That is, people cannot move a muscle normally despite trying as hard as they can. However, the term is often misused. Many people with normal muscle... read more and muscle wasting (dystrophy) of varying severity.

Myotonic dystrophy is an autosomal dominant Dominant x-linked disorders Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body or code for functional RNA molecules.... read more disorder, which means only one affected parent is needed to pass the trait on to offspring. This dystrophy affects males and females and about 1 in 8,000 people.

Symptoms of Myotonic Dystrophy

Symptoms of myotonic dystrophy begin during adolescence or young adulthood.

The disorder causes myotonia. Myotonia is a delay in the ability to relax the muscles after contracting them. Other main symptoms are weakness and wasting of arm and leg muscles (especially in the hands) and muscles in the face. Drooping eyelids are also common. The heart muscle also becomes weak (cardiomyopathy Overview of Cardiomyopathy Cardiomyopathy refers to progressive impairment of the structure and function of the muscular walls of the heart chambers. There are three main types of cardiomyopathy: Dilated cardiomyopathy... read more Overview of Cardiomyopathy ) and the heart rhythm may become abnormal.

Congenital myotonic dystrophy

Mothers with myotonic dystrophy may have children with a severe form of myotonia that appears during infancy. This disorder is called congenital myotonic dystrophy, which should not be confused with myotonia congenita Myotonia Congenita Myotonia congenita is an inherited disorder that causes muscle stiffness and muscle enlargement. It affects what most people think of as muscle, the type that can be contracted to move the various... read more , which is a separate disorder. Infants with congenital myotonic dystrophy have severely reduced muscle tone (hypotonia, or "floppiness"), feeding and breathing problems, bone deformities, facial weakness, and delays in development of thought processes and physical movement. Up to 40% of infants do not survive, usually because of difficulty breathing (respiratory failure Respiratory Failure Respiratory failure is a condition in which the level of oxygen in the blood becomes dangerously low or the level of carbon dioxide in the blood becomes dangerously high. Conditions that block... read more ) and perhaps cardiomyopathy. Up to 60% of survivors have intellectual disability.

Diagnosis of Myotonic Dystrophy

  • Genetic testing

The diagnosis of myotonic dystrophy is based on characteristic symptoms, the person's age when symptoms began, and family history.

Treatment of Myotonic Dystrophy

  • Drugs to relieve muscle stiffness

Treatment of myotonic dystrophy with mexiletine or other drugs (for example, lamotrigine, phenytoin, or carbamazepine) may relieve the stiffness, but these drugs do not relieve the weakness, which is the most bothersome symptom to the person. Also, each of these drugs has undesirable side effects. The only treatment for muscle weakness is supportive measures, such as ankle braces (for footdrop) and other devices.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Lamictal, Lamictal CD, Lamictal ODT, Lamictal XR, Subvenite
Dilantin, Dilantin Infatabs, Dilantin-125, Phenytek
Carbatrol, Epitol , Equetro, Tegretol, Tegretol -XR
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