Idiopathic inflammatory myopathies (IIMs) are heterogeneous disorders characterized by chronic muscle weakness and muscle fatigue and mononuclear cell infiltration into skeletal muscle.[1] The most common subgroups in adults are dermatomyositis (DM), polymyositis (PM), amyopathic DM (ADM), inclusion body myositis (IBM), and juvenile DM (JDM). Several diagnostic or classification criteria for IIM have been developed.[2?5] Classification criteria are mostly used in research and clinical trials, not daily in practice. Great efforts have been dedicated in pursuing new criteria in the past decades.