What kind of condition is dermatomyositis?

Autoimmune. It is an autoimmune disease with the collagen vascular diseases and is treated by rheumatologist. It affects skin and muscle with proximal muscle weakness of the hips and shoulders. Diagnosis is made by muscle weakness, typical rash on face and hands, muscle biopsy , skin biopsy, and blood tests. Treatment is oral steroids and steroid sparing drugs such as cytoxan, (cyclophosphamide) imuran, methotrexate.
Muscle disease. Dermatomyositis causes inflammation of blood vessels leading to muscle damage, skin rashes, and calcium deposits under the skin if left untreated. It is an autoimmune disease and is treatable with steroids and immunosuppressants.