What is New in Idiopathic Inflammatory Myopathies: Mechanisms and Therapies

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of disorders that cause muscle weakness and also have extramuscular manifestations involving various organ systems; namely the lung, skin, heart, and joints. Previously classified broadly as dermatomyositis (DM) and polymyositis now the spectrum of the disease has evolved into more clinical subtypes. There are now five clinicoserological subtypes recognized worldwide DM, antisynthetase syndrome (AS), overlap myositis (OM), immune mediated necrotizing myopathy (IMNM), and inclusion body myositis. Each of these subtypes has a unique phenotype and specific antibodies associated. With the evolving treatment options from the use of immunosuppressive medications to the use of targeted therapy with biologic agents, and further understanding of the pathogenesis of inflammatory myositis, we may have more effective treatment options. We discuss in this review, various myositis-associated antibodies associated with each clinicoserological subtype of IIM and their role. We also describe the evolving therapies and the evidence for the newer biologic therapies in the treatment of IIMs.