Definition - one of a group of muscle diseases that involve inflammation of the muscles or associated tissues; the inflammatory cells of the immune system directly attack muscle fibers

Cause - the cause is unclear; researchers suspect viruses or exposure to certain drugs might trigger the misdirected immune response

Onset - usually begins after age 20; more common in females than in males

Symptoms - weakness of the muscles of the hips, thighs, upper arms, top part of the back, shoulders and muscles that move the neck; pain or tenderness in affected areas; possible heart, respiratory and swallowing problems

Progression - gradual; immunosuppressant medications often effectively control symptoms

Inheritance - not a genetic disease, though a genetic predisposition may exist

Facts About Inflammatory Myopathies