Development of a disease activity and responder index for psoriatic arthritis--report of the Psoriatic Arthritis Module at OMERACT 11.

This module reflected work within the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) to develop and validate composite disease activity measures in psoriatic arthritis (PsA). At the Outcome Measures in Rheumatology (OMERACT) 8 Meeting, a core set of domains to be assessed in randomized controlled trials (RCT) and longitudinal observational studies of PsA was agreed upon. At OMERACT 10, 5 proposed composite responder definitions for PsA were reviewed and discussed, including new data from the GRACE (GRAppa Composite Exercise) study. At OMERACT 11, ongoing retrospective analyses of RCT data using the 3 proposed measures (Composite Psoriatic Disease Activity Index, Psoriatic Arthritis Disease Activity Score, and Arithmetic Mean of the Desirability Function) were discussed in detail. There was agreement that developing composite outcome measures for use in RCT and longitudinal observational studies in PsA was important. Concerns were expressed regarding development of a single measure that encompassed diverse domains, such as joint counts, quality of life (QOL), and disability measures. It was emphasized that the use of any composite measure should include the ability to differentiate between activity in individual domains, such as enthesitis or psoriasis, such that the effect of each could be assessed independently. It was also agreed that patients would be systematically involved in further development and refinement of composite measures. Future plans include qualitative work with patients to explore their experience of disease activity and statistical modeling to explore how each of the proposed measures will perform in different disease subgroups.