BASDAI versus ASDAS in evaluating axial involvement in patients with psoriatic arthritis: a pooled analysis of two phase 3 studies

Abstract

Abstract Objective In the absence of axial psoriatic arthritis (axPsA)-specific tools, the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS) are used to assess axial symptoms in patients with PsA. Here, we assessed the performance of BASDAI and ASDAS in patients with PsA. Methods Patients with active PsA in DISCOVER-1 and DISCOVER-2 (ClinicalTrials.gov: NCT03162796 and NCT03158285, respectively) with or without axPsA but with available baseline BASDAI information were analyzed; those with investigator-identified axial symptoms and imaging-confirmed sacroiliitis comprised the axPsA cohort. Correlations between BASDAI/ASDAS and clinical variables were assessed with Pearson’s coefficient (r). Longitudinal effects of enthesitis (Leeds Enthesitis Index [LEI]), swollen joint count (SJC), and presence versuss absence of axPsA on BASDAI/ASDAS (normalized 0–10 scale) were analyzed with mixed models for repeated measures. Results At baseline in the axPsA (n = 312) and non-axPsA (n = 124) cohorts, BASDAI scores showed no or weak correlation with SJC (0.18–0.20), tender joint count (0.12–0.29), LEI (–0.04–0.24), and physician global assessment (0.35–0.43); moderate correlation with fatigue (both –0.56); and strong correlation with patient global assessment of disease activity (0.62–0.69) and patient-reported pain (0.66–0.70). Similar correlations were observed for ASDAS. Axial involvement versuss noninvolvement was associated with higher BASDAI/ASDAS scores (all β ≥ 0.5), without differences between instruments; longitudinal associations between SJC (β  ≤ 0.06)/LEI (β  ≤ 0.19) and BASDAI/ASDAS were clinically unimportant. Conclusion BASDAI and ASDAS performed similarly in patients with active PsA and axial involvement, independent of peripheral disease involvement, supporting their performance in assessing axial disease activity. Clinical Trial Registration Trials are registered at ClinicalTrials.gov (NCT03162796 and NCT03158285).