Inflammatory myopathies (IM) are a heterogeneous group of autoimmune
muscle disorders of unknown origin that share clinical symptoms such as
muscle weakness and histological features with the presence in muscle of inflammatory infiltrate. Based on clinical, histological and serological characteristics, IM can be divided into
polymyositis, dermatomyositis, overlap
myositis,
cancer-associated
myositis, immune-mediated necrotizing
myopathy, and
inclusion-body myositis. Because of their resistance to
corticosteroids and immunosuppressive drugs,
inclusion-body myositis will be treated separately in this issue. Major obstacles in conducting high quality randomized controlled trials in
inflammatory myopathies include the low prevalence and the heterogeneity of these diseases as well as the lack of international consensus on the outcome measures. In the absence of adequate controlled therapeutic trials, treatment of these disorders remains largely empirical.
Corticosteroids are the cornerstone
therapy. Due to the chronic course of the disease, there is a frequent need to use additional immunosuppressive treatment both to improve the disease response and to reduce the side effects of
corticosteroids.
Intravenous immunoglobulin infusion is a costly treatment option that is reserved in the presence of refractory
dermatomyositis based on a trial showing superior efficacy against control in patients with impaired swallowing or with
contraindications to immunosuppressive drugs. In patients who fail second-line
therapy, which usually consists of
methotrexate plus
corticosteroids, the diagnosis should be carefully reassessed before considering other treatment options including
methotrexate plus
azathioprine or
biological agents such as
rituximab.