Autoimmune Myopathies: Updates on Evaluation and Treatment

Abstract

The major forms of autoimmune myopathies include dermatomyositis (DM), polymyositis (PM), myositis associated with antisynthetase syndrome (ASS), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). While each of these conditions has unique clinical and histopathological features, they all share an immune-mediated component. These conditions can occur in isolation or can be associated with systemic malignancies or connective tissue disorders (overlap syndromes). As more has been learned about these conditions, it has become clear that traditional classification schemes do not adequately group patients according to shared clinical features and prognosis. Newer classifications are now utilizing myositis-specific autoantibodies which correlate with clinical and histopathological phenotypes and risk of malignancy, and help in offering prognostic information with regard to treatment response. Based on observational data and expert opinion, corticosteroids are considered first-line therapy for DM, PM, ASS, and IMNM, although intravenous immunoglobulin (IVIG) is increasingly being used as initial therapy in IMNM related to statin use. Second-line agents are often required, but further prospective investigation is required regarding the optimal choice and timing of these agents.

Keywords: Autoimmune myopathy; Immune-mediated myopathy; Inflammatory myopathy; Necrotizing myopathy.

Fig. 1

Characteristic distribution of weakness and atrophy in inclusion body myositis. (a) Quadriceps atrophy. (b) Asymmetric atrophy of flexor muscles in the forearm, with asymmetric weakness of the deep finger flexors (including the flexor pollicis longus) > superficial finger flexors (the patient was asked to curl his fingers and thumbs)