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Becker's muscular dystrophy

Definition

Becker's muscular dystrophy is an inherited disorder that involves slowly worsening muscle weakness of the legs and pelvis.

Alternative Names

Benign pseudohypertrophic muscular dystrophy; Becker's dystrophy

Causes

Becker's muscular dystrophy is very similar to Duchenne's muscular dystrophy, except that it gets worse at a much slower rate.

The disorder is inherited. Women rarely develop symptoms. Men will develop symptoms if they inherit the defective gene.

Becker's muscular dystrophy occurs in approximately 3 - 6 out of every 100,000 males.

Because this is an inherited disorder, risks include having a family history of Becker's muscular dystrophy.

Symptoms

Symptoms usually appear in men at about age 12, but may sometimes begin later.

Symptoms may include:

• Cognitive problems (these do not get worse over time)
• Fatigue
• Loss of balance and coordination
• Muscle weakness in the arms, neck, and other areas (not as severe as in the lower body)
• Muscle weakness of the legs and pelvis that slowly worsens, causing
  • Difficulty walking that worsens over time
    • Frequent falls
    • The average age of becoming unable to walk is age 25 - 30
  • Difficulty with muscle skills (running, hopping, jumping)
  • Loss of muscle mass (wasting)
• Problems breathing

Exams and Tests

The health care provider will do a nervous system (neurological) and muscle examination. A careful medical history is also important, because the pattern of symptom development resembles that of Duchenne's muscular dystrophy. However, Becker's muscular dystrophy gets worse much more slowly.

An exam may find:

• Abnormally developed bones, leading to deformities of the chest and back (scoliosis)
• Abnormality of heart muscle function (cardiomyopathy)
• Congestive heart failure or irregular heartbeat (arrhythmias) - rare
• Muscle deformities
  • Contractures of heels and legs
  • Fat and connective tissue (pseudohypertrophy) in calf muscles
• Muscle wasting that begins in the legs and pelvis, then progresses to the muscles of the shoulders, neck, arms, and respiratory system

Tests include:

• CPK
• Electromyography (EMG)
• Muscle biopsy or genetic test (blood test)

Treatment

There is no known cure for Becker's muscular dystrophy. Treatment tries to control symptoms to maximize quality of life. Some doctors prescribe steroids to help keep a patient walking for as long as possible.

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

Genetic counseling may be advisable. Sons of a man with Becker's muscular dystrophy do not develop the disorder, but daughters may be carriers. The daughters' sons may develop the disorder.

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.

Outlook (Prognosis)

Becker's muscular dystrophy leads to slowly worsening disability. Death may occur in the 50s or 60s, but patients can live longer than that.

Possible Complications

• Cardiomyopathy
• Deformities
• Permanent, worsening disability
  • Decreased ability to care for self
  • Decreased mobility
• Mental impairment (varies) -- see mental retardation
• Pneumonia or other respiratory infections
• Respiratory failure

When to Contact a Medical Professional

Call your health care provider if:

• Symptoms of Becker's muscular dystrophy appear
• A person with Becker's muscular dystrophy develops new symptoms (particularly fever with cough or breathing difficulties)
• You are planning to start a family and you or other family members have been diagnosed with Becker's muscular dystrophy

Prevention

Genetic counseling may be advised if there is a family history of Becker's muscular dystrophy.

References

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

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