Pathomechanisms of inflammatory myopathies: recent advances and implications for diagnosis and therapies

Abstract

The main subtypes of inflammatory myopathies include dermatomyositis (DM), polymyositis (PM), necrotising myopathy (NM) and sporadic inclusion body myositis (sIBM). Recent observations have helped us to understand better the unique pathomechanisms of each subset. Advances in the pathogenesis of these disorders have led to a more precise diagnosis and specific therapeutic strategies. A critical review regarding tissue biomarkers for the diagnosis of DM, PM, NM and sIBM is provided and an outline for more effective treatment strategies is discussed, particularly in sIBM, for which there is no effective therapy. The reader will gain an objective overview of the different pathomechanisms of the major forms of myositis, the best means of arriving at the correct diagnosis, and a critical outline of the present and future therapeutic strategies. Whereas DM is mainly mediated by humoral mechanisms, a T-cell-mediated cytotoxicity is operational in PM and sIBM. NM is multifactorial, but a subset is autoimmune, mediated by macrophages and possibly antibodies. Accumulation of aberrant molecules contributes to the pathology of sIBM. Muscle biopsy is required for the correct diagnosis of each entity. Standard immunotherapy is effective in DM and PM, but not usually in sIBM, for which new treatment strategies are discussed.