Immunotherapy of inflammatory myopathies: practical approach and future prospects

Abstract

The inflammatory myopathies, a group of chronic myopathic conditions, are potentially treatable, so proper diagnosis and early initiation of therapy are necessary. The most common types are polymyositis (PM), dermatomyositis (DM), necrotizing autoimmune myopathy (NAM), and inclusion body myositis (IBM). This review provides practical advice on treatment and identifies emerging new therapies. Although IBM is difficult to treat, PM, DM, and NAM respond to appropriate immunotherapies, if diagnosed early and treated aggressively. In uncontrolled studies, PM and DM respond to prednisone to some degree and for a period of time. The commonly used immunosuppressive drugs (azathioprine, cyclosporine, mycophenolate, or methotrexate) may offer some non-evidence-based "steroid-sparing" effect but provide minimal benefit on their own. As a result, the second-line therapy is intravenous immunoglobulin (IVIg), which a controlled study has shown to be effective in DM and which appears to be effective in PM and NAM; it offers minimal and transient benefit to only a small number of IBM patients, however. Uncontrolled series have suggested that rituximab and tacrolimus may offer additional benefit to some patients not adequately controlled with the aforementioned therapies. IBM is usually resistant to most therapies, but early initiation of therapy may be helpful at times. Emerging agents against T cells, B cells, transmigration, or transduction molecules are discussed as potential new treatment options.