Duchenne muscular dystrophy

Definition

Duchenne muscular dystrophy is an inherited disorder that involves muscle weakness, which quickly gets worse.

Alternative Names

Pseudohypertrophic muscular dystrophy; Muscular dystrophy - Duchenne type

Causes

Duchenne muscular dystrophy is a form of muscular dystrophy that worsens quickly. 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, boys are affected, not girls. 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 about 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
• Learning difficulties (the IQ can be below 75)
• Mental retardation (possible, but does not get worse 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
  • Trouble getting up from a lying position or climbing stairs
  • Weakness quickly gets worse
• Progressive difficulty walking
  • Ability to walk may be lost by age 12, and the child will have to use a wheelchair
  • Breathing difficulties and heart disease usually start by age 20

Exams 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 muscles of the calves, buttocks, and shoulders (around age 4 or 5). These muscles 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 poor swallowing, with food or fluid passing 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 improve quality of life.

Steroid drugs can slow the loss of muscle strength. They may be started when the child is diagnosed or when muscle strength begins to decline.

Other treatments include:

• Albuteral--a drug used for people with asthma
• Amino acids
• Carnitine
• Coenzyme Q10
• Creatine
• Fish oil
• Green tea extracts
• Vitamin E

However, the effects of these treatments have not been proven. Stem cells and gene therapy may be used in the future.

Activity is encouraged. Inactivity (such as bedrest) can make the muscle disease worse. Physical therapy may be helpful to maintain muscle strength and function. Speech therapy is often needed.

Other treatments may include:

• Assisted ventilation (used during the day or night)
• Drugs to help heart function, such as angiotensin-converting-enzyme inhibitors, beta-blockers, and diuretics
• Orthopedic appliances (such as braces and wheelchairs) to improve mobility
• Proton pump inhibitors (for people with gastroesophageal reflux)

Several new treatments are being studied in trials.

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.

Outlook (Prognosis)

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

Possible 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

When to Contact a Medical Professional

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.

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.

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