Performance of three composite measures for disease activity in peripheral spondyloarthritis.

OBJECTIVE To investigate concurrent validity and discrimination of the Disease Activity Psoriatic Arthritis score (DAPSA), Psoriatic Arthritis Disease Activity Score (PASDAS) and Ankylosing Spondylitis Disease Activity Score (ASDAS) in peripheral spondyloarthritis (pSpA) in clinical practice. METHODS Data from a Dutch registry for SpA (SpA-Net) were used. Predefined hypotheses on concurrent validity of the composite measures with 15 other outcome measures of disease activity, physical function and health-related quality of life were tested. Concurrent validity was considered acceptable if ≥75% of the hypotheses were confirmed. Discrimination was assessed by stratifying patients in DAPSA, PASDAS and ASDAS predefined disease activity states and studying mean differences in health outcomes by one-way ANOVA. Furthermore, the concordance in disease activity states was determined. All analyses were repeated in subgroups with and without psoriasis. RESULTS DAPSA, PASDAS and ASDAS scores were available for 191, 139 and 279 patients with pSpA, respectively. The concurrent validity and discrimination of all composite measures were acceptable as the strength of correlations were as hypothesized in ≥75% of the studied correlations. With increasing disease activity states, scores in nearly all outcome measures worsened significantly. The DAPSA, PASDAS and ASDAS classified 22%, 56% and 48% of the patients, respectively, in the two highest disease activity states. Stratified analyses for concomitant psoriasis revealed no relevant subgroup differences. CONCLUSION The performance of DAPSA, PASDAS and ASDAS in pSpA was acceptable, and independent of concomitant psoriasis. Due to discrepancy in classification, the validity of existing thresholds for disease activity states warrants further study in pSpA.