[Pathogenesis of the idiopathic inflammatory myopathies]

The inflammatory myopathies, commonly described as idiopathic, are a group of acquired diseases characterized by an inflammatory infiltrate of the skeletal muscle. On the basis of clinical and immuno-pathological features, three major diseases can be identified: dermatomiositis (DM), polymyositis (PM) and inclusion body myositis (IBM). Immunopathogenesis mechanisms are crucial for discriminating between the three different subsets of inflammatory myopathies. DM is a complement-mediated microangiopathy affecting skin and muscle. PM and IBM are T cell-mediated disorders, where CD8-positive cytotoxic T cells invade muscle fibres expressing MHC class I antigens. This article summarizes the main immunopathological markers. The impact of this new knowledge must be defined in relation to potential therapeutic targets for idiopathic inflammatory myopathies.