Myotonic dystrophy is the second most common form of 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 needed for normal muscle structure and function are defective, leading to muscle weakness and muscle wasting (dystrophy) of varying severity.
Myotonic dystrophy is the second most common form of muscular dystrophy. It is an autosomal dominant 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.
Myotonic dystrophy may be present at birth or may begin during adolescence or early adulthood.
Symptoms of Myotonic Dystrophy
Symptoms of myotonic dystrophy usually begin in adolescence or early 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. Some people with the disorder also develop a footdrop (the foot flops down).
The heart muscle also becomes weak (cardiomyopathy), and the heart rhythm may become abnormal.
Symptoms of myotonic dystrophy can range from mild to severe. People with the most severe form of the disorder have extreme muscle weakness and many other symptoms, including cataracts, small testes (in men), premature balding in the front of the scalp (in men), irregular heartbeats, diabetes, and intellectual disability.
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, 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) 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.
Genetic testing is done to confirm the diagnosis.
Treatment of Myotonic Dystrophy
Medications to relieve muscle stiffness
The only treatment for muscle weakness is supportive measures, such as ankle braces (for footdrop) and other devices.
Prognosis for Myotonic Dystrophy
Death is most commonly caused by problems with breathing and the heart. People who develop irregular heartbeats and severe muscle weakness at a younger age are at increased risk of premature death. They usually die by about age 54.
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
Muscular Dystrophy Association: Information on research, treatment, technology, and support for people living with myotonic dystrophy
