Abstract: The review authors identified 14 relevant RCTs. They excluded four trials. The 10 included studies, four of which have been added in this update, included a total of 258 participants. Six studies compared an immunosuppressant or immunomodulator with placebo control, and four studies compared two immunosuppressant regimes with each other. Most of the studies were small (the largest had 62 participants) and many of the reports contained insufficient information to assess risk of bias. Amongst the six studies comparing immunosuppressant with placebo, one study, investigating intravenous immunoglobulin (IVIg), showed statistically significant improvement in scores of muscle strength in the IVIg group over three months. Another study investigating etanercept showed some evidence of a longer median time to relapse in the etanercept group, a secondary outcome in this review, but no improvement in other assessed outcomes. The other four randomised placebo-controlled trials assessed either plasma exchange and leukapheresis, eculizumab, infliximab or azathioprine against placebo and all produced negative results. Three of the four studies comparing two immunosuppressant regimes (azathioprine with methotrexate, ciclosporin with methotrexate, and intramuscular methotrexate with oral methotrexate plus azathioprine) showed no statistically significant difference in efficacy between the treatment regimes. The fourth study comparing pulsed oral dexamethasone with daily oral prednisolone and found that the dexamethasone regime had a shorter median time to relapse but fewer side effects. Immunosuppressants were associated with significant side effects. This systematic review highlights the lack of high quality RCTs that assess the efficacy and toxicity of immunosuppressants in inflammatory myositis.

Plain-language summary: Amongst the six studies comparing immunosuppressant with placebo, one study, investigating intravenous immunoglobulin (IVIg), showed statistically significant improvement in scores of muscle strength in the IVIg group over three months. Another study investigating etanercept showed some evidence of a longer median time to relapse in the etanercept group, a secondary outcome in this review, but no improvement in other assessed outcomes. The other four randomised placebo-controlled trials assessed either plasma exchange and leukapheresis, eculizumab, infliximab or azathioprine against placebo and all produced negative results. Three of the four studies comparing two immunosuppressant regimes (azathioprine with methotrexate, ciclosporin with methotrexate, and intramuscular methotrexate with oral methotrexate plus azathioprine) showed no statistically significant difference in efficacy between the treatment regimes. The fourth study comparing pulsed oral dexamethasone with daily oral prednisolone and found that the dexamethasone regime had a shorter median time to relapse but fewer side effects. Most of the studies were small (the largest had 62 participants) and many of the reports contained insufficient information to assess risk of bias. Immunosuppressants were associated with significant side effects. The small number of RCTs of immunosuppressants and immunomodulatory therapies are inadequate to decide whether these agents are beneficial in dermatomyositis and polymyositis. Two small trials, one of IVIg in dermatomyositis, the other of etanercept in dermatomyositis suggested that they are beneficial. More RCTs are needed.