Abstract
OBJECTIVE: In the absence of axial psoriatic arthritis (axPsA)-specific tools, the 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 analysed; 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 and presence versus absence of axPsA on BASDAI/ASDAS (normalized 0-10 scale) were analysed 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 swollen joint count (0.18-0.20), tender joint count (0.12-0.29), LEI (-0.04 to 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 versus non-involvement was associated with higher BASDAI scores and ASDAS (all β ≥ 0.5), without differences between instruments; longitudinal associations between swollen joint count (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. TRIAL REGISTRATION: ClinicalTrials.gov, http://clinicaltrials.gov, NCT03162796 and NCT03158285.