Because polymyositis and dermatomyositis (PM/DM) are uncommon conditions, few randomized placebo controlled studies have been performed in these patients. The first line of therapy consists in high-dose oral prednisone, prescribed at 1mg/kg/day, then progressively tapered based on patients' clinical response. In patients who do not improve with corticosteroids alone, methotrexate is added, the therapeutic effect of which being observed within 8weeks. If PM/DM patients are refractory to corticosteroids and methotrexate, intravenous immunoglobulins can be added. In patients who fail to respond to this therapeutic strategy, it is crucial to make sure that the correct diagnosis has been made and we strongly recommend to perform a new muscle biopsy in order to exclude other myopathies. If the diagnosis of PM/DM is confirmed, a number of therapeutic agents may be proposed, including mycophenolate mofetil and rituximab. Importantly, TNF-α antagonists should not be considered in PM/DM patients, as these agents have been shown to favor exacerbation of interstitial lung disease and myositis and increase the risk of severe pyogenic and opportunistic infections in PM/DM patients.
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