Abstract： @@ Dermatomyositis (DM) and polymyositis (PM) are idiopathic inflammatory myopathies with unknown etiology.The incidence of both diseases is estimated at 4 to 10 cases per million people per year~1.Classical DM patients display characteristic cutaneous manifestations,proximal muscle weakness,and laboratorial evidence of myositis.Skin manifestations include the classic periorbital heliotrope,cutaneous Gottron's papules and signs,and violaceous erythema of the upper trunk and extremities.Muscle involvement may be revealed by elevated muscle-derived enzymes such as creatine kinase (CK),lactate dehydrogenase (LDH),aldolase,alanine aminotransferase (ALT) or aspartate transaminase (AST).Additional testing,including electromyography (EMG),magnetic resonance imaging (MRI),or even muscle biopsies,may be performed if other tests are inconclusive~2.