POLYMYOSITIS

a chronic, progressive inflammation of skeletal muscles, particularly the muscles of the shoulders and pelvis. The term polymyositis means "many muscles inflamed." Initially muscles may be swollen slightly, and the first symptoms to appear are usually muscle weakness and sometimes pain. A weakening of muscles close to the torso is common. Occasionally muscles of the esophagus and larynx are affected, which causes difficulty in swallowing and speaking. When muscles of the lungs are involved, difficulty in breathing may result. Muscles of the heart and the gastrointestinal tract also may be affected. As the disease progresses, the affected muscles atrophy and harden. Disease symptoms may abate and increase in alternating cycles of remission and exacerbation. The muscle cell damage that occurs in polymyositis is believed to result from an attack on muscle tissue by white blood cells called T lymphocytes, which normally are produced by the immune system to fight infection. This self-destructive malfunctioning of the immune system is called an autoimmune response. The factor that precipitates it is not known, but there is evidence that viral infections trigger some cases of polymyositis. Polymyositis arises in both children and adults and is more prevalent in women. It sometimes is associated with an increased incidence of several types of malignancies, including lung, colon, and breast cancers. The disorder dermatomyositis, which involves the skin as well as muscles, shares many characteristics with polymyositis, but the two are believed to arise from different causes. The drugs most commonly used to treat polymyositis are corticosteroids, such as prednisone. A number of immunosuppressive drugs, such as methotrexate, also are used. Early diagnosis and treatment tends to reduce the severity of the disease.