Myositis usually involves a breakdown of muscle tissues, but it can also injure the heart muscle, the lungs, skin areas and the colon. In some cases, the muscles affected may be in only one arm or leg, or a specific muscle group. Patients that have chronic muscle pain and tenderness and fatigue, can take blood tests used to measure the amount of muscle tissue released. The tests include a creatine kinase (CK) or creatine phosphokinase (CPK). People with elevated CK or CPK levels will be evaluated for myositis or rhabdomyolysis.

Other related muscle disorders or "inflammatory myopathies" are called dermatomyositis, polymyositis, and inclusion body myositis.

Doctors do not know how myositis develops, but many scientists believe it is an autoimmune disease in which the body attacks itself. Myositis is significant disorder that is a very high risk factor for the development of rhabdomyolysis, and kidney failure.

Unfortunately there is no regular treatment for most myositis. Corticosteroids and immunosuppressive drugs have little effect, immunoglobulin given intravenously may help in some cases. Patient must watch out for rhabdomyolysis and physical therapy can help the patient maintain motion.