Duchenne muscular dystrophy

Definition

Duchenne muscular dystrophy is an inherited disorder that involves rapidly worsening muscle weakness.

Alternative Names

Pseudohypertrophic muscular dystrophy; Muscular dystrophy - Duchenne type

Causes, incidence, and risk factors

Duchenne muscular dystrophy is a rapidly-worsening form of muscular dystrophy. Other muscular dystrophies (including Becker's muscular dystrophy) get worse much more slowly.

Duchenne muscular dystrophy is caused by a defective gene for dystrophin (a protein in the muscles). However, it often occurs in people without a known family history of the condition.

Because of the way the disease is inherited, males are more likely to develop symptoms than are women. The sons of females who are carriers of the disease (women with a defective gene but no symptoms themselves) each have a 50% chance of having the disease. The daughters each have a 50% chance of being carriers.

Duchenne muscular dystrophy occurs in approximately 1 out of every 3,600 male infants. Because this is an inherited disorder, risks include a family history of Duchenne muscular dystrophy.

Symptoms

Symptoms usually appear before age 6 and may appear as early as infancy. They may include:

• Fatigue
• Mental retardation (possible, but does not worsen over time)
• Muscle weakness
  • Begins in the legs and pelvis, but also occurs less severely in the arms, neck, and other areas of the body
  • Difficulty with motor skills (running, hopping, jumping)
  • Frequent falls
  • Rapidly worsening weakness
• Progressive difficulty walking
  • Ability to walk may be lost by age 12

By age 10, the person may need braces for walking. By age 12, most patients are confined to a wheelchair.

Signs and tests

A complete nervous system (neurological), heart, lung, and muscle exam may show:

• Abnormal heart muscle (cardiomyopathy)
• Congestive heart failure or irregular heart rhythm (arrhythmias) -- rare
• Deformities of the chest and back (scoliosis)
• Enlarged calf muscles, which are eventually replaced by fat and connective tissue (pseudohypertrophy)
• Loss of muscle mass (wasting)
• Muscle contractures in the heels, legs
• Muscle deformities
• Respiratory disorders, including pneumonia and aspiration of food or fluid into the lungs (in late stages of the disease)

Tests may include:

• Electromyography (EMG)
• Genetic tests
• Muscle biopsy
• Serum CPK

Treatment

There is no known cure for Duchenne muscular dystrophy. Treatment aims to control symptoms to maximize quality of life. Gene therapy may become available in the future.

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 to care for yourself.

Support Groups

You can ease the stress of illness 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.

Expectations (prognosis)

Duchenne muscular dystrophy leads to quickly worsening disability. Death usually occurs by age 25, typically from lung disorders.

Complications

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

Calling your health care provider

Call your health care provider if:

• Your child has symptoms of Duchenne muscular dystrophy
• Symptoms worsen, or new symptoms develop, particularly fever with cough or breathing difficulties

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.

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References

Kliegman RM, Behrman RE, Jenson HB, Stanton BF. Muscular dystrophies. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa:Saunders Elsevier; 2007:chap 608.