The exact cause of dermatomyositis is unknown, but the disease shares many characteristics with autoimmune disorders, in which your immune system attacks normal body components.

Normally, your immune system works to protect your healthy cells from attacks by foreign substances, such as bacteria and viruses. If you have polymyositis, an unknown cause may act as a trigger for your immune system to begin producing autoimmune antibodies (autoantibodies) that attack your body's own tissues. Many people with polymyositis show a detectable level of autoantibodies in their blood.

Small blood vessels in muscular tissue are particularly affected in dermatomyositis. Inflammatory cells surround the blood vessels and eventually lead to degeneration of muscle fibers.

Jul. 07, 2011