Myotonic dystrophy.

Myotonic dystrophy is an autosomal dominant disorder that results in skeletal muscle weakness and wasting, myotonia, and numerous nonmuscular manifestations including frontal balding, cataracts, gonadal dysfunction, cardiac conduction abnormalities, respiratory insufficiency, and hypersomnolence. Although the gene defect in myotonic dystrophy has been mapped to chromosome 19, the exact metabolic abnormalities responsible for this disorder are unknown. Skeletal muscle has been found to be relatively insulin-resistant in myotonic dystrophy, and a decrease in the anabolic action of insulin on skeletal muscle may be related to muscle wasting in this disorder. Laboratory studies, including electromyography, electrocardiography, and muscle biopsy, are helpful in evaluating patients for this disorder, but the clinical aspects and a careful family history remain the mainstays of diagnosis. A number of management strategies preserve function and prevent complications in myotonic dystrophy.