Immunotherapies in autoimmune inflammatory myopathies: Rationale and therapeutic updates

Autoimmune inflammatory myopathies (AIM) constitute a heterogeneous group of acquired myopathies with endomysial inflammation as a shared feature highlighting a potentially autoimmune inflammatory process amenable to immunotherapies. The disorders can be best classified as dermatomyositis, necrotizing autoimmune myositis, antisynthetase syndrome-overlap myositis, and inclusion body myositis. Because of clinical and immunohistologic heterogeneity but often overlapping pathophysiologic features among all major subsets, a correct diagnosis is critical from the outset to apply the most suitable and subset-specific immunotherapy. Advances in the immunopathologic characterization of autoimmune inflammatory myopathies have identified potentially mechanism-specific disease subsets that promise the application of targeted immunotherapies for better clinical outcomes. A number of recent clinical trials with biologic agents and monoclonal antibodies, regardless of the clinical outcome considering that several were negative, have collectively expanded our knowledge on the main pathogenic markers of autoimmunity associated with each AIM subset including the role of T-cell or B-cell factors, key cytokines, complement and various associated antibodies, or innate immunity factors. The paper summarizes the main clinical and histopathologic features of each myositis subtype, including overlapping or unique concepts of their immunopathogenic mechanisms, being mainly focused on applied immunotherapies and relevant controlled clinical trials discussing evidence-based efficacy according to the currently evolved therapeutic algorithm. The ongoing trials are also discussed highlighting those with promising future, if applied early in the disease, and the new immunotherapeutic interventions for the refractory AIM subsets.