Becker's Muscular Dystrophy
Definition
Becker's muscular dystrophy is an inherited disorder that involves slowly progressive muscle weakness of the legs and pelvis.
Becker's muscular dystrophy is very similar to Duchenne's muscular dystrophy, except that it progresses at a much slower rate.
The disorder is inherited with an X-linked recessive inheritance pattern -- the gene is located on the X chromosome. Since women have two X chromosomes, if one X chromosome has the defective gene, the second X chromosome will have a working copy of the gene to compensate. In these cases, some women have much milder symptoms because of this ability to compensate.
Men have an X and a Y and because they don't have another X to compensate for the defective gene, they will develop symptoms if they inherit the defective gene.
People with this disorder experience 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 as in the lower half of the body.
Calf muscles initially enlarge (an attempt by the body to compensate for loss of muscle strength), but 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. Bones develop abnormally, causing skeletal deformities of the chest and other areas.
Cardiomyopathy (damage to the heart) does not occur as commonly with this disorder as it does with Duchenne's muscular dystrophy. Cognitive problems may accompany the disorder, but they are not inevitable and do not worsen as the disorder progresses.
Becker's muscular dystrophy occurs in approximately 3-6 in 100,000 male births. Symptoms usually appear in men at about age 12, but may sometimes begin later. The average age of becoming unable to walk is 25-30. Women rarely develop symptoms.
Because this is an inherited disorder, risks include having a family history of Becker's muscular dystrophy.
Symptoms
- Muscle weakness, slowly progressive, causing difficulty with muscle skills (running, hopping, jumping)
- Progressive difficulty walking
- Ability to walk may continue into adulthood (up to age 40)
- Frequent falls
- problems breathing
- Cognitive dysfunction
- Skeletal deformities, chest and back (scoliosis)
- Muscle deformities, contractures of heels, legs
- Pseudohypertrophy of calf muscles
- Fatigue
- Heart disease
Signs and tests
The pattern of symptom development resembles that of Duchenne's muscular dystrophy, but with a much slower rate of progression. Muscle wasting 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 may occur, but the development of congestive heart failure or arrhythmias (irregular heartbeats) is rare.
The ability to walk may continue to age 40 or older.
CPK may be higher than normal. EMG (electromyography) shows if weakness is caused by destruction of muscle tissue rather than by damage to nerves. Muscle biopsy or genetic test (blood test) confirms the diagnosis.
Treatment
There is no known cure for Becker's muscular dystrophy. Treatment is aimed at control of symptoms to maximize the 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
The stress of illness can often be helped by joining a support group where members share common experiences and problems.
Expectations (prognosis)
Becker's muscular dystrophy results in slowly progressive disability. Death usually occurs in the fifth decade but some patients live to an advanced age.
Complications
- Deformities
- Permanent, progressive disability
- Decreased mobility
- Decreased ability to care for self