Performance of response criteria for assessing peripheral arthritis in patients with psoriatic arthritis: analysis of data from randomised controlled trials of two tumour necrosis factor inhibitors

Background: In recent clinical trials in patients with psoriatic arthritis (PsA), the response criteria and disease activity measures that have been used were those developed for rheumatoid arthritis. However, these have not yet been validated in PsA. Objective: To compare the responsiveness and discriminative capacity of the psoriatic arthritis response criteria (PsARC), American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) response criteria and the Disease Activity Score (DAS) and core-set measures in patients with PsA and peripheral arthritis, using the data from two randomised placebo-controlled trials of tumour necrosis factor inhibitors. Methods: In an infliximab trial, 104 patients with active PsA were randomised to receive placebo or infliximab for 16 weeks. In an etanercept trial, 60 patients with active PsA were randomised to receive placebo or etanercept for 12 weeks. Data from baseline and the end of the intervention phase were used from each study. Responsiveness was assessed using the standardised response mean and effect size. Capacity to discriminate between the active drug and placebo was assessed using t values or a chi(2) test. Measures were ranked in order of their t value or chi(2) value. Results: The EULAR criteria performed better in discriminating the active drug from placebo than the ACR20 improvement criteria, which in turn performed better than the PsARC. It was also found that the pooled indices (DAS and DAS28) were generally more responsive, and performed better in discriminating active drug from placebo, than the single core-set measures. Conclusion: Response criteria and pooled indices developed for rheumatoid arthritis are useful for the assessment of arthritis in PsA clinical trials.