BECKER'S MUSCULA...

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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, incidence, and risk factors

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

Signs 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)

Reviewer Info: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine; and Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc., 12/17/2008