Informing response criteria for Psoriatic Arthritis (PsA). II: Further considerations and a proposal - The PsA joint activity index

Objective. To develop a recommended measure of response for use in psoriatic arthritis (PsA) clinical trials and observational cohort studies reflecting joint involvement. Methods. Previously, we used data from phase III randomized placebo-controlled trials of anti-tumor necrosis factor (TNF) agents to determine models, based primarily on statistical considerations but with some clinical input when necessary, that best distinguish drug-treated from placebo-treated patients. For the same data, we examine response criteria currently used for PsA and logistic regression models based on the individual components of these response criteria. Comparison with our previously developed models, based primarily on statistical consideration, is made. Results. A simplified score, the PsA Joint Activity Index (PsAJAI), based on components of the ACR30, performed better than the ACR20 and PsARC, and comparable to our previously developed models. The PsAJAI is a weighted sum of 30% improvement in core measures with weights of 2 given to the joint count measure, the C-reactive protein laboratory measure, and the physician global assessment of disease activity measure. Weights of 1 should be given to the remaining 30% improvement measures including pain, patient global assessment of disease activity, and the Health Assessment Questionnaire. Conclusion. We recommend the PsAJAI be used as an outcome measure for assessing joint disease response in PsA clinical trials. The Journal of Rheumatology