Responsiveness and Minimum Clinically Important Difference in Patient‐ReportedOutcome Measures Among Patients With Psoriatic Arthritis: A Prospective Cohort Study

To determine the responsiveness to therapy and minimum clinically important improvement (MCII) for patient‐reported outcome measures in psoriatic arthritis (PsA) and to examine the impact of baseline disease activity on the ability to demonstrate change. A longitudinal cohort study was performed within the PsA Research Consortium. Patients completed several patient‐reported outcomes, including the Routine Assessment of Patient Index Data, the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), the Psoriatic Arthritis Impact of Disease 12‐item (PsAID12) questionnaire, and others. The mean change in the scores between visits and standardized response means (SRMs) were calculated. The MCII was calculated as the mean change in score among patients who reported minimal improvement. SRMs and MCIIs were compared among subgroups with moderate to highly active PsA and those with lower disease activity. Among 171 patients, 266 therapy courses were included. The mean ± SD age was 51 ± 13.8 years, 53% were female, and the mean swollen and tender joint counts were 3 and 6, respectively, at baseline. SRMs and MCII for all measures were small to moderate, although greater among those with higher baseline disease activity. BASDAI had the best SRM overall and for less active PsA, and the clinical Disease Activity of PsA (cDAPSA) and PsAID12 were best for those with higher disease activity. SRMs and MCII were relatively small in this real‐world population, particularly among those with lower disease activity at baseline. BASDAI, cDAPSA, and PsAID12 had good sensitivity to change, but selection for use in trials should consider the baseline disease activity of patients to be enrolled.