Encouraging results from case reports and early trials suggested that abatacept could be an effective treatment for idiopathic inflammatory myopathy (IIM). Now reported in Arthritis & Rheumatology, a phase III clinical trial of abatacept for IIM failed to meet its primary endpoint, but analysis of the results suggests that abatacept could have benefits in some subtypes of IIM.

In the multicentre, international trial, 149 adults with active, treatment-refractory IIM were randomly allocated to receive subcutaneous abatacept (125 mg weekly) or placebo, in combination with standard treatment. At 24 weeks, 56.0% of the abatacept group and 42.5% of the placebo group met the IMACS definition of improvement. In additional analysis, no between-treatment differences were observed among patients with dermatomyositis, but among those with polymyositis or immune-mediated necrotizing myopathy response rates were higher in the abatacept group than in the placebo group (57.1% versus 32.3%).