Measuring Outcomes in Psoriatic Arthritis: Comparing Routine Assessment of Patient Index Data and Psoriatic Arthritis Impact of Disease.

Objective: To examine the construct validity of Routine Assessment of Patient Index Data 3 (RAPID3) and Psoriatic Arthritis Impact of Disease (PsAID) in patients with psoriatic arthritis (PsA). In examining construct validity, we also addressed scores among subgroups with severe psoriasis, poly articular disease, enthesitis, and dactylitis, and evaluated influences of sociodemographic factors and comorbidities (contextual factors) on these patient-reported outcomes (PRO).

Methods: Patients with PsA were enrolled in the Psoriatic Arthritis Research Consortium (PARC) between 2014 and 2016. PARC is a longitudinal observational cohort study conducted at 4 US institutions. In this cross-sectional study, construct validity was assessed by examining Spearman correlation coefficients for RAPID3 and PsAID with physician-reported disease activity measures and other PRO [e.g., Medical Outcomes Study Short Form-12 physical component summary/mental component summary (SF-12 PCS/MCS), Functional Assessment of Chronic Illness Therapy-Fatigue scale (FACIT-F)]. Contextual factors and disease subgroups were assessed in multivariable linear regression models with RAPID3 or PsAID12 as outcomes of interest and the hypothesized contextual factors as covariates.

Results: Among 401 patients enrolled in PARC, 347 completed RAPID3 or PsAID12. Of these, most were white females with a mean age of 51.7 years (SD 14.02). RAPID3 and PsAID were highly correlated (r = 0.90). These measures were also correlated with the SF-12 PCS (r = -0.67) and FACIT-F (r = -0.77). Important contextual factors and disease subgroups included enthesitis, joint counts, education, insurance type, and depression.

Conclusion: RAPID3 and PsAID12 have excellent construct validity in PsA and are strongly correlated despite differing items. Contextual factors (i.e., the presence of depression and obesity) should be considered when interpreting raw scores of the RAPID3 and PsAID12.