Inflammatory Myopathies

Idiopathic inflammatory myopathies (IIM) are a diverse group of disorders ranging from focal varieties to diffuse forms. The most common varieties encountered in clinical practice are dermatomyositis (DM), polymyositis (PM), and inclusion body myositis (IBM), each of which has distinctive clinical and histopathologic features, and may occur in an isolated form or in association with a systemic connective tissue disease, other autoimmune disorders, retroviral infection, or malignancy. Myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA) increase the complexity of classification. MSA indicate specific phenotypes while MAA are usually seen in overlap syndrome and serve as biomarkers. Muscle biopsy is mandatory to confirm the diagnosis of an inflammatory myopathy and to allow unusual varieties such as eosinophilic, granulomatous, parasitic myositis, and macrophagic myofasciitis. The treatment of inflammatory myopathies remains largely empirical and relies upon the use of corticosteroids, immunosuppressive agents, intravenous immunoglobulin, and biological agents, all of which have nonselective effects on the immune system.