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Other Forms of Muscular Dystrophy

By Michael Rubin, MDCM, Professor of Clinical Neurology;Attending Neurologist and Director, Neuromuscular Service and EMG Laboratory, Weill Cornell Medical College;New York Presbyterian Hospital-Cornell Medical Center

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 of varying severity.

Facioscapulohumeral dystrophy is the most common form of muscular dystrophy. Duchenne muscular dystrophy is the second most common and the most severe form. Becker muscular dystrophy is closely related to Duchenne muscular dystrophy but starts later in a child's life and causes milder symptoms. Several uncommon forms of muscular dystrophy, all inherited, also cause progressive muscle weakness.

Congenital muscular dystrophy

Congenital muscular dystrophy is not a single disorder but instead refers to muscular dystrophy that is seen at birth. Congenital muscular dystrophies result from mutations in a variety of different genes including the genes needed for normal muscle structure and function.

Newborns who have a congenital muscular dystrophy have severely reduced muscle tone (hypotonia, or "floppiness").

Doctors suspect the diagnosis of congenital muscular dystrophy in any newborn who has floppy muscle tone. Doctors usually do a muscle biopsy and genetic testing to confirm the diagnosis.

Treatment

  • Physical therapy

Treatment of congenital muscular dystrophy includes physical therapy, which may help maintain muscle function.

Emery-Dreifuss dystrophy

This dystrophy is inherited in various ways. Only males are affected, but females may be carriers of the gene that causes the disorder. Carriers are people who have an abnormal gene for a disorder but who do not have any symptoms or visible evidence of the disorder.

Symptoms

Muscles become weak and waste away (atrophy) any time before age 20 years. The most affected muscles are those of the upper arms, lower legs, and heart. The muscles of the arms and legs tighten in permanent, flexed positions called contractures. The heart muscle can also be affected. An affected heart commonly causes sudden death.

Diagnosis

Doctors suspect the diagnosis of Emery-Dreifuss dystrophy based on the boy's symptoms and family history. To confirm the diagnosis, doctors usually do blood tests to measure levels of the enzyme creatine kinase in the blood, electrical studies of muscle function (electromyography), muscle biopsy (examination of a sample of the weak muscle tissue under a microscope), and genetic testing.

Treatment

  • Therapy to prevent contractures

Physical therapy can help prevent contractures.

Heart pacemakers may help prolong life if heart rhythms are abnormal.

Facioscapulohumeral muscular dystrophy (Landouzy-Dejerine muscular dystrophy)

Facioscapulohumeral muscular dystrophy (FSHMD) is inherited via an autosomal dominant gene. Therefore, a single abnormal gene is sufficient to cause the disorder, and the disorder can appear in either males or females. It is the most common form of muscular dystrophy and occurs in about 7 out of 1,000 people.

Symptoms

Symptoms of facioscapulohumeral muscular dystrophy usually begin gradually between the ages of 7 and 20. The facial and shoulder muscles are always affected, so that a child has difficulty whistling, closing the eyes tightly, or raising the arms. Some people with the disease also develop a footdrop (the foot flops down). People also frequently have hearing loss and eye problems.

The weakness is rarely severe, and many people are not disabled and have a normal life expectancy. However, other people need to use a wheelchair in adulthood. In one form that develops in infancy, children have rapidly progressive muscle weakness and severe disability.

Diagnosis

The diagnosis of facioscapulohumeral muscular dystrophy is based on characteristic symptoms, the person's age when symptoms began, family history, and the results of genetic testing.

Treatment

  • Physical therapy

There is no treatment for the weakness, but physical therapy may help maintain muscle function.

Limb-girdle muscular dystrophies

These dystrophies can be inherited in various ways. They cause weakness in the muscles of either the pelvis (Leyden-Möbius muscular dystrophy) or the shoulder (Erb muscular dystrophy). Males and females are affected equally. These inherited disorders often begin in early childhood but may not begin until adulthood. They rarely cause serious weakness.

Diagnosis

The diagnosis of limb-girdle dystrophy is based on characteristic symptoms, the person's age when symptoms began, and family history. Doctors usually do a muscle biopsy and genetic testing to confirm the diagnosis.

Treatment

  • Maintenance of function and prevention of contractures

Treatment of limb-girdle dystrophy is focused on maintaining muscle function and preventing the muscles from freezing in permanent, flexed positions called contractures.

Mitochondrial myopathies

These myopathies are muscle disorders inherited through faulty genes in mitochondria (the energy factories of cells, which carry their own genes) or in the nuclear genes that control mitochondrial function.

These rare disorders sometimes cause increasing weakness in one or a few muscle groups, such as the eye muscles (ophthalmoplegia), and often affect many other organs, such as the heart, intestines, or brain. One mitochondrial myopathy is called Kearns-Sayre syndrome.

Myotonia congenita (Thomsen disease)

This dystrophy is a rare autosomal dominant disorder (only one affected parent is needed to pass the trait on to offspring) that affects males and females. Symptoms of myotonia congenita usually start in infancy. The hands, legs, and eyelids become very stiff because of an inability to relax the muscles. Muscle weakness, however, is usually minimal.

Diagnosis

The diagnosis of myotonia congenita is made from the child’s characteristic appearance, inability to relax the grip of the hand rapidly after closing the hand, and prolonged contraction after the doctor taps a muscle.

An electromyogram (a test in which electrical impulses from muscles are recorded) is needed to confirm the diagnosis.

Treatment

  • Drugs to relieve muscle stiffness

Myotonia congenita is treated with phenytoin, quinine, procainamide, or mexiletine to relieve muscle stiffness and cramping. However, each of these drugs has undesirable side effects. Regular exercise may be beneficial.

People with myotonia congenita have a normal life expectancy.

Myotonic dystrophy (Steinert disease)

This dystrophy is an autosomal dominant disorder affecting males and females. Myotonic dystrophy affects about 1 in 8,000 people.

Symptoms

Symptoms of myotonic dystrophy begin during adolescence or young adulthood.

The disorder causes myotonia. Myotonia is the delayed 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) and the heart rhythm may become abnormal.

Symptoms of myotonic dystrophy begin during adolescence or young adulthood and 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 (in men), irregular heartbeats, diabetes, and intellectual disability. They usually die by about age 54.

Mothers with myotonic dystrophy may have children with a severe form of myotonia that appears during infancy. Infants 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 respiratory failure and perhaps cardiomyopathy. Up to 60% of survivors have intellectual disability.

Diagnosis

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

  • Drugs to relieve muscle stiffness

Treatment with mexiletine or other drugs (for example, quinidine, phenytoin, carbamazepine, or procainamide) 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.

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Drugs Mentioned In This Article

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  • DILANTIN
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  • QUALAQUIN
  • TEGRETOL