Inclusion body myositis.

The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of rare disorders that share many similarities. In addition to sporadic inclusion body myositis (IBM), these include dermatomyositis, polymyositis, and autoimmune necrotizing myopathy. IBM is the most common IIM after age 50 years. Muscle histopathology shows endomysial inflammatory exudates surrounding and invading nonnecrotic muscle fibers often accompanied by rimmed vacuoles and protein deposits. It is likely that IBM is has a prominent degenerative component. This article reviews the evolution of knowledge in IBM, with emphasis on recent developments in the field, and discusses ongoing clinical trials.