ABSTRACT
The inflammatory myopathies are divided into three major and distinct subsets: polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM).1-6 Although their cause is unknown, autoimmune mechanisms are implicated, as supported by their association with other putative or definite autoimmune diseases or viruses, the evidence for a T cell-mediated myocytotoxicity or complement-mediated microangiopathy, and the presence of various autoantibodies.1-6 This is also true for IBM, in spite of the coexistence of various degenerative features in these patients’ muscle biopsies.7,8
Clinical experience indicates that patients with PM and DM respond to prednisone in some degree and for varying periods.9-11 In some patients the response may be dramatic and, if prudently used, prednisone may have a longlasting effect with minimal side-effects.12 In other patients, however, the response is mild to moderate, and in still others the steroid-induced side-effects are severe, necessitating the use of other immunosuppressive drugs. Azathioprine, methotrexate, cyclosporin, cyclophosphamide and mycophenolate are commonly used immunosuppressants which offer a mild or, at the very best, a modest benefit, but with considerable toxicity after long-term use. Plasmapheresis is ineffective.13 IBM is almost always unresponsive to steroids or other immunosuppressants. The need for more effective therapies and the encouraging results from pilot or uncontrolled studies14-17 have prompted the need to examine the therapeutic efficacy of high-dose intravenous immunoglobulin (IVIg), an
immunomodulating drug with prohibitive cost but minimal toxicity. This chapter summarizes the value of IVIg in DM based on controlled studies the authors performed at the National Institutes for Health (NIH). The role of IVIg in the other inflammatory myopathies will not be discussed here as it is beyond the scope of this book, and because these patients do not present to dermatologists. The accessibility of muscle biopsy tissues before and after therapy has also offered the opportunity to study the mechanism of action of IVIg and provide information useful in understanding how IVIg works, not only in inflammatory myopathies but also in other autoimmune neurological and dermatological disorders.
