Inflammatory Myopathies

Abstract

Therapies that suppress or modify the immune system remain the primary treatment for the idiopathic inflammatory myopathies. Dermatomyositis (DM) and polymyositis (PM) are the two conditions that respond best to immunotherapy. Although there are no randomized controlled trials, corticosteroids, specifically high-dose oral prednisone, remain the cornerstone of management. Recent controlled clinical trials show that intravenous immunoglobulin (IVIg) is an efficacious treatment in DM. Expert clinicians are generally using this as a second-line agent or as an adjunct to prednisone. IVIg has a relatively benign side effect profile compared with chronic steroid use, but the cost of treatment, the need for repetitive treatment cycles, and the potential for serious adverse effects have kept it from being a first-line agent in DM. There have been no trials performed using IVIg in PM. Chronic immunosuppressant medications, including azathioprine, cyclosporine, and methotrexate, are also available for long-term management in patients with recalcitrant disease or side effects from extended corticosteroid use. These agents lack the troubling side effects of prednisone and are less costly than IVIg, but require close medical monitoring for adverse reactions to blood, kidney, lung, or liver. Newer medications with potentially more benign side effect profiles, such as mycophenolate mofetil and etanercept, are currently being studied, but knowledge of how effective they are and how quickly they work are not yet available. Inclusion body myositis has proven resistant to immunosuppressive medications. The response has been so consistently poor and so easily contrasted with DM that the authors wonder why these conditions are so routinely lumped together in chapters and review articles. Clearly, this is based solely on the common pathologic feature of inflammation, rather than a clear understanding of how these conditions occur, or why they do or do not respond to treatment.