Inflammatory Myopathies

Inflammatory myopathies represent a small but important group of acquired muscular disorders. The most important forms of immunogenic inflammatory myopathies are dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM). A hallmark of all types of immunogenic inflammatory myopathies is infiltration (B-cells, CD4+ and CD8+ T cells and macrophages) in muscle tissue. In DM, inflammatory infiltrates with B-cells and CD4+ T cells are found predominantly in perivascular and perifascicular regions, producing the picture of a myositis of the perifascicular type. There are striking lesions of the small intramuscular vessels with CD5b9 complement deposits and tubulovesicular inclusions seen on electron microscopy. In PM infiltrates are predominantly endomysial, producing the picture of a diffuse myositis. Immunhistologically, cytotoxic CD8+ lymphocytes are the predominant cells that invade non-necrotic muscle fibers. IBM is characterized by endomysial infiltrations with CD8+ lymphocytes. In addition, rimmed vacuoles with eosinophilic cytoplasmatic inclusions can be found. On electron microscopy filamentous inclusions in the cytoplasm and nuclei are pathognomonic. First-line treatment strategies of DM and PM are corticosteroids and Immunosuppressives. High-dose Immunoglobulins are only necessary in relatively seldom cases in which the first-line drugs are not successful or severe side effects are prominent. In inclusion body myositis the only therapeutic possibility is the administration of immunoglobulins. Newer studies on drugs against cytokines, such as TNF-alpha inhibitors are underway.