Definition of Dermatomyositis:

Dermatomyositis is a muscle disease that causes inflammation and a skin rash. It is a type of inflammatory myopathy.

Causes, incidence, and risk factors:

The cause is unknown. Experts think it may be due to a viral infection of the muscles or a problem with the body's immune system.

Anyone can develop dermatomyositis, but it most commonly occurs in children age 5 to 15 and adults age 40 - 60. Women develop this condition more often than men.

Polymyositis is a similar condition, but the symptoms occur without a skin rash.