The Spectrum of Inflammatory Myopathies: Dermatomyositis, Polymyositis, Necrotizing Myositis, Anti-synthetase Syndrome-overlap Myositis, and Inclusion-Body Myositis

Abstract

The inflammatory myopathies constitute a heterogeneous group of acquired myopathies that have in common progressive muscle weakness associated with muscle autoimmunity. Based on currently evolved distinct clinical, histological and autoantibody features, these disorders are best classified in five subsets: Dermatomyositis (DM), Polymyositis (PM), Necrotizing Autoimmune Myositis (NAM), Anti-synthetase syndrome-overlap myositis (Anti-SS-OM), and Inclusion-Body-Myositis (IBM). Polymyosiitis is very rare-if it exists as a single entity-but it is included for historical reasons on classic muscle immunopathology. Because prognosis and response to immunotherapies is variable according to each subtype, correct identification is fundamental from the outset to avoid disease mimics. The paper describes the main clinicopathologic characteristics of each subset highlighting the need for careful neurological examination, precise reading of muscle pathology and careful interpretation of the various autoantibodies and immunopathologic findings to avoid erroneous diagnoses and initiate the correct therapeutic schemes.