Dermatomyositis and polymyositis: new treatment targets on the horizon

Polymyositis (PM) and dermatomyositis (DM) are rare idiopathic inflammatory myopathies (IIM) with a presumed autoimmune pathogenesis. Typical features are subacute onset, proximal, symmetric muscle weakness, elevated serum creatine kinase, and mononuclear cell infiltrates in the muscle biopsy. Strong support for an autoimmune pathogenesis comes from histopathological findings in biopsies of affected muscles. Furthermore, the association with autoantibodies supports the notion that immune-mediated inflammation is involved. PM and DM may occur in isolation or in connection with a connective tissue disease or cancer. The current treatment for IIM consists of first-line high-dose steroids and various conventional second-line treatments. Improvements in treatment for IIM are hampered by difficulties in the design of trials and the low incidence and prevalence of the disease. Cytokines and chemokines are factors involved in the inflammatory process in IIM, and are candidates for future therapeutic targets. Preliminary data with anti-tumour necrosis factor therapy are not very promising, but results of blockers of the lymphotoxin signalling pathway are to be awaited. Anti-B cell therapy may be a valuable therapeutic option for treatment of refractory IIM. The effects of anti-interferon-alpha in IIM are to be awaited, as are results of other anti-cytokine therapies and anti-chemokine therapy. Outcome measures to be used in clinical trials in IIM include at present the core sets of outcome proposed by the International Myositis Assessment Clinical Study Group (IMACS).