12. Becker’s Dystrophy
Definition
Becker’s dystrophy is a genetic variation of Duchenne’s muscular dystrophy. This form is very similar to pseudohypertrophic muscular dystrophy (Duchenne’s), but the onset of the disease occurs later in life and progresses more slowly. However, the ultimate debilitation is the same as with Duchenne’s.
Incidence
The Becker’s dystrophy phenotype occurs at a rate of approximately 24:1,000,000 population. The onset may occur any time from 3 years of age through adulthood, even late adulthood.
Etiology
The genotype for Becker’s dystrophy is the result of a sex-linked transmission on the X chromosome in the Xp 21 stripe. The Becker phenotype correlates with point mutations that preserve reading frame or genetic deletions that cause less structural compromise.
Signs and Symptoms
• Age, usually 10 to 20 years
• Calf enlargement
• Gait disturbances
• Kyphoscoliosis
• Progressive development of muscle weakness
• Progressive diminishment of deep tendon reflexes
• Waning forced vital capacity and other lung volumes
Medical Management
Prednisone is currently the only medication that has demonstrated any benefit in the treatment of Becker’s dystrophy. The dose is 0.75 to 1.5 mg/kg/day in divided doses. The muscle wasting produced by this disease is retarded or delayed by the administration of prednisone. The benefit of prednisone administration may become evident as soon as 1 month after initiation of treatment, but those benefits generally last only about 3 years. These benefits may also be somewhat diminished by sequelae resulting from chronic steroid administration.
The remainder of medical management of Becker’s dystrophy concentrates on measures and strategies to maximize functional status, maintain muscle tone, and delay reliance on a wheelchair for as long as possible. Exercising joints and stretching muscles daily can delay the onset of debilitating contractures. These exercises work synergistically with the application of various supportive braces, such as ankle-foot or knee-ankle-foot orthoses, to help maintain the ability to stand, whether mobile or not, and further contribute to the delay of debilitating contractures and scoliosis.
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