Alternate Names: Pseudohypertrophic muscular dystrophy; Muscular dystrophy - Duchenne type

Causes and Risks:

Duchenne muscular dystrophy is a rapidly progressive form of muscular dystrophy. A slowly progressive muscular dystrophy that is very similar to Duchenne also exists (Becker muscular dystrophy). Duchenne muscular dystrophy is an inherited disorder. However, it is not unusual to find no family history.

Symptoms appear before age 6 and may appear as early as infancy. There is progressive muscle weakness of the legs and pelvis, which is associated with a loss of muscle mass (wasting). Muscle weakness also occurs in the arms, neck, and other areas, but not as severely or as early as in the lower half of the body.

Calf muscles initially enlarge -- the enlarged muscle tissue is eventually replaced by fat and connective tissue (pseudohypertrophy). Muscle contractures occur in the legs and heels, causing inability to use the muscles because of shortening of muscle fibers and fibrosis of connective tissue.

Symptoms usually appear in males 1 to 6 years old. By age 10, braces may be required for walking, and by age 12, most patients are confined to a wheelchair. Bones develop abnormally, causing skeletal deformities of the spine and other areas.

Muscular weakness and skeletal deformities contribute to frequent breathing disorders. Cardiomyopathy occurs in almost all cases. Intellectual impairment can be observed, but it is not inevitable and does not worsen as the disorder progresses.

The cause of this muscle impairment is related to an abnormal gene for dystrophin protein (a specific type of protein in the muscles). This gene is on the X chromosome. Duchenne muscular dystrophy is inherited in an X-linked recessive inheritance pattern. Boys with an abnormal gene have symptoms. Females with an abnormal gene are carriers (i.e., usually do not have symptoms). However, the sons of carrier females each have a 50% chance of having the disease, and the daughters each have a 50% chance of being carriers.

Duchenne muscular dystrophy occurs in approximately 2 out of 10,000 people. Because this is an inherited disorder, risks include a family history of Duchenne muscular dystrophy.

Prevention: Genetic counseling is advised if there is a family history of the disorder. Duchenne muscular dystrophy can be detected with about 95% accuracy by genetic studies performed during pregnancy.

Symptoms:

• Muscle weakness
  • Rapidly progressive
  • Frequent falls
  • Difficulty with motor skills (running, hopping, jumping)
• Progressive difficulty walking
  • Ability to walk may be lost by age 12
• Fatigue
• Intellectual retardation (possible)
• Skeletal deformities
  • Chest and back (scoliosis)
• Muscle deformities
  • Contractures of heels, legs
  • Pseudohypertrophy of calf muscles

Signs and Tests: Muscle wasting (atrophy) begins in the legs and pelvis, then progresses to the muscles of the shoulders and neck, followed by loss of arm muscles and respiratory muscles. Calf muscle enlargement (pseudohypertrophy) is quite obvious. Cardiomyopathy is commonly present, but signs of congestive heart failure or arrhythmias (irregular heartbeats) are rare. Respiratory disorders are common during the later stages, including pneumonia and aspiration of food or fluid into the lungs.

• A serum CPK is highly elevated.
• A neurologic exam demonstrates weaness and lack of coordination or balance.
• An EMG (electromyography) shows that weakness is caused by destruction of muscle tissue rather than nerve damage.
• A muscle biopsy confirms the diagnosis.

Treatment: There is no known cure for Duchenne muscular dystrophy. Treatment is aimed at control of symptoms to maximize the quality of life.

Activity is encouraged. Inactivity (such as bedrest) can worsen the muscle disease. Physical therapy may be helpful to maintain muscle strength and function. Orthopedic appliances (such as braces and wheelchairs) may improve mobility and the ability for self-care.

Support Groups: The stress of illness can often be helped by joining a support group where members share common experiences and problems. See muscular dystrophy - support group. The Muscular Dystrophy Association is an excellent source of information on this disease.

Prognosis: Duchenne muscular dystrophy results in rapidly progressive disability. Death usually occurs by age 15, typically from respiratory (lung) disorders.

Complications:

• Deformities
• Permanent, progressive disability
  • Decreased mobility
  • Decreased ability for self-care
• Mental impairment (varies, usually minimal)
• Pneumonia or other respiratory infections
• Respiratory failure
• Cardiomyopathy
• Congestive heart failure (rare)
• Heart arrhythmias (rare)

Call your health care provider if symptoms indicate Duchenne muscular dystrophy.

Call your health care provider if symptoms worsen, or new symptoms develop, particularly fever with cough or breathing difficulties.