Inflammatory muscle diseases.

Inflammatory myopathies are the largest group of potentially treatable myopathies in children and adults. They constitute a heterogeneous group of disorders that are best classified, on the basis of distinct clinicopathologic features, in four subtypes: dermatomyositis, polymyositis, necrotizing autoimmune myositis, and inclusion-body myositis (throughout this review, I use this term to refer specifically to sporadic inclusion-body myositis).1-6 A fifth subtype, termed overlap myositis, is also beginning to be recognized. The identification of the correct subtype and the distinction of these conditions from other diseases that have characteristics that mimic these conditions is fundamental, because each subtype has a different prognosis and response to therapies. This review reflects the current knowledge of these conditions, highlights how best to avoid erroneous diagnoses, describes the main clinicopathologic and immunologic features, and provides practical guidelines regarding therapies.