Polymyositis
A type of chronic inflammation of the muscles (inflammatory myopathy) related to dermatomyositis and inclusion body myositis. Its name means "inflammation of many muscles" (poly- + myos- + -itis). The inflammation of polymyositis is mainly found in the endomysial layer of skeletal muscle, whereas dermatomyositis is characterized primarily by inflammation of the perimysial layer of skeletal muscles
Treatment is the same as for dermatomyositis, but those with polymyositis tend to do worse.