Dermatomyositis (DM) is a connective-tissue disease related to polymyositis (PM) that is characterized by inflammation of the muscles and the skin.The cause is unknown, but it may result from either a viral infection or an autoimmune reaction. In the latter case it is a systemic autoimmune disease. Many people diagnosed with dermatomyositis were previously diagnosed with infectious mononucleosis and Epstein-Barr virus. Some cases of dermatomyositis actually "overlap" (are combined with) other autoimmune diseases such as: Sjögren's syndrome, lupus, scleroderma, or vasculitis. Several cases of polymyositis and dermatomyositis were reported as being triggered by the use of various statin drugs used to control blood cholesterol.
The main symptoms include skin rash and symmetric proximal muscle weakness which may be accompanied by pain. The pain may resemble the type experienced after strenuous exercise.Skin findings occur in dermatomyositis but not PM and are generally present at diagnosis.Gottron's sign is an erythematous, scaly eruption occurring in symmetric fashion over the MCP and interphalangeal joints.The heliotrope or "lilac" rash is a violaceous eruption on the upper eyelids and in rare cases on the lower eyelids as well, often with itching and swelling.Shawl (or V-) sign is a diffuse, flat, erythematous lesion over the back and shoulders or in a "V" over the posterior neck and back or neck and upper chest, worsens with UV light.Calcinosis cutis is usually seen in juvenile dermatomyositis, not adult dermatomyositis.