Measuring treatment response in psoriatic arthritis: comparison between PSoriatic Arthritis Response Criteria and Disease Activity Score-28

Abstract Objectives Despite current UK guidelines recommending the use of the PSoriatic Arthritis Response Criteria (PsARC) to assess response to advanced targeted therapies in Psoriatic Arthritis (PsA) patients, some clinicians use the Disease Activity Score 28 (DAS-28) primarily developed for Rheumatoid Arthritis. Concordance of the two scores in PsA patients commencing advanced therapies has not previously been explored and is investigated here. Methods Utilising data from the ‘Outcomes of Treatment in Psoriatic Arthritis Study Syndicate’ (OUTPASS – RDN-CPMS 13910) cohort; a UK, multi-centre, observational study, component of PsARC and DAS-28 scores were calculated at baseline (pre-treatment), 3-months (3M) and 6-months (6M), following treatment, where available. DAS-28-basedgood/moderate response were combined and compared with PsARC responder status and agreement tested using the Prevalence-adjusted Bias-adjusted Kappa test. Results Of 413 patients, 78% were classified as responders by PsARC at 3M and 73% at 6M, and 80% by DAS-28 at both 3M & 6M. Of 218 visits, where data was recorded for patients with both PsARC and DAS28, at 3M or 6M, 17.9% were overall discordant. Prevalence-adjusted Bias-adjusted Kappa revealed ‘substantial agreement’ (64.22%) between the two scores. Further analysis between the overall concordant/discordant populations showed significant difference with PsARC Patient’s Global Assessments (PtGA), (P = 0.02). Conclusion PsARC and DAS-28-based response criteria show ‘substantial agreement’, supporting the use of either score in patients commencing advanced therapies. PsARC PtGA was the sole subcomponent significantly different (P < 0.05) between the discordant and concordant groups, highlighting an importance in considering patient-perspectives and psycho-social factors affecting response to treatment.