Polymyositis (pol-e-mi-o-SI-tis) is a persistent inflammatory muscle disease that causes weakness of the skeletal muscles, which control movement. Medically, polymyositis is classified as a chronic inflammatory myopathy — one of only three such diseases.

Polymyositis can occur at any age, but it mostly affects adults in their 30s, 40s or 50s. It's more common in blacks than in whites, and women are affected more often than men are. Polymyositis signs and symptoms usually develop gradually, over weeks or months.

Remissions — periods during which symptoms spontaneously disappear — are rare in polymyositis. However, treatment can improve your muscle strength and function.

Jul. 07, 2011