Sex differences in patient-reported outcomes and the association with clinical factors in axial spondyloarthritis patients treated with tumour necrosis factor inhibitors

OBJECTIVES To investigate sex differences in patient-reported outcome measures (PROMs) among axSpA patients initiating their first TNFi and identify factors contributing to these disparities over the follow-up. METHODS Data were included from 15 EuroSpA registries and consisted of axSpA patients initiating their first TNFi, with ≥2 measurements for each analysed PROM (BASDAI and BASFI, scale 0-100) taken at any time point. Linear mixed models were employed to analyse sex differences in PROMs over 24 months and to evaluate how baseline characteristics were related to the observed sex differences. RESULTS We analysed 13 102 (38% women) in the BASDAI analyses and 10 623 (38% women) in the BASFI analyses. At follow-up, mean sex differences in BASDAI increased from 4.3 units at baseline (95% CI, 3.5-5.1)-8.0 (7.2-8.8) at 6 months, and in BASFI from 2.2 (1.4-3.1)-4.6 (3.6-5.5), with consistently worse scores in women. Baseline characteristics could not substantially account for the observed sex differences over time; however, the magnitude of the sex differences was reduced by HLA-B27 positivity, longer disease duration, and increased CRP levels, but increased by TNFi initiation in later years and peripheral arthritis. CONCLUSION In axSpA patients initiating their first TNFi, baseline sex differences in BASDAI and BASFI increased two-fold after 6 months of treatment and persisted thereafter, with worse scores in women. Several baseline characteristics moderated the sex differences, though none could fully account for them. These findings improve our understanding of sex differences and underscore their importance in axSpA.