Polymyositis is a connective-tissue disorder characterized by
inflammation and weakening of the muscles. It may occur with
dermatomyositis. The cause is unknown, but it may be an autoimmune disease, in which the immune system, for reasons not yet understood, forms antibodies that attack the body's own tissues. Thus, microscopic examination of muscle tissue, to look for cell degeneration and other structural changes, is helpful in diagnosing the disorder. Elevated levels of muscle enzymes in the blood serum and abnormal electrical
activity in the muscles are other diagnostic criteria.
Polymyositis affects people of all ages; generally, it begins acutely in children but more subtly in adults. Treatment with corticosteroids usually is effective in relieving
inflammation and returning muscle enzyme levels to normal. Analgesics and the application of heat may be prescribed to relieve pain. Patients also are advised to limit physical activity until inflammation subsides, although range-of-motion exercises are advised to minimize muscle atrophy.