Dermatomyositis is a disorder of collagen/connective tissue characterized by nonsuppurative skin inflammation and subcutaneous tissue and muscle fiber necrosis. It may be acute, subacute, or chronic.

The most recent estimates indicate that dermatomyositis occurs at the rate of about 5.5:1,000,000. The frequency seems to be increasing. There is a 2:1 predilection toward females, but no apparent preference for a particular race.

The cause of dermatomyositis is not fully understood. There are suggestions that it is caused by a complement-mediated vascular inflammation. The immunologic abnormalities may be triggered by a wide variety of agents.