Comparison of disease activity measures in early psoriatic arthritis in usual care.

Objectives: To compare responsiveness and longitudinal validity of Disease Activity Score 28 (DAS28), Disease Activity index for PSoriatic Arthritis (DAPSA), Composite Psoriatic Disease Activity Index (CPDAI), Psoriatic ArthritiS Disease Activity Score (PASDAS), GRAppa Composite scorE (GRACE) and Minimal Disease Activity (MDA) in usual care PsA patients, within 1 year after diagnosis.

Methods: Data collected in the Dutch southwest early PsA cohort (DEPAR) were used. Responsiveness was assessed using effect size (ES), standardized response mean (SRM), and discrimination between different general health states. Longitudinal validity was tested using mixed models with outcomes health-related quality of life (HRQOL), productivity and disability.

Results: Responsiveness was highest for PASDAS, with ES 1.00 and SRM 0.95, lowest for DAPSA, with ES 0.73 and SRM 0.71, and in between for DAS28, CPDAI and GRACE. Differences in general health were best discriminated with PASDAS and GRACE. Patients reporting stable or worsening general health could not be distinguished by DAS28 or CPDAI. Discrimination was better using DAPSA, but worse than when using PASDAS and GRACE. Longitudinal evolvement of HRQOL and productivity had the highest association with low disease activity according to GRACE, followed by PASDAS, MDA, DAPSA, DAS28, with the lowest association for CPDAI.

Conclusion: PASDAS and GRACE were superior with respect to responsiveness, and together with MDA best related to longitudinal evolvement of HRQOL, productivity and disability. Responsiveness and longitudinal validity of most outcomes were inferior for DAS28, DAPSA and CPDAI. As alternatives to the continuous measure DAPSA, use of PASDAS or GRACE should be considered.