Idiopathic inflammatory myopathies: epidemiology, classification, and diagnostic criteria

The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of immune-mediated disorders, that may present in an isolated form, or in association with another autoimmune or connective tissue disease, a malignancy, or, rarely, an infection or other environmental exposure. This article summarizes recent findings on epidemiologic aspects of the three major varieties of IIM (dermatomyositis, polymyositis and inclusion body myositis) and proposes schemes for the classification and diagnostic criteria for these conditions.