Impact of Sex in Axial Spondyloarthritis: Insights from the Brazilian Registry of Spondyloarthritis

Background: Sex differences in axial spondyloarthritis (axSpA) are increasingly recognized, with women often reporting higher disease burden despite similar objective inflammatory markers. This study aimed to compare clinical features, disease activity, function, quality of life, and treatment patterns between men and women with axSpA and identify sex-specific predictors of disease outcomes using data from the Brazilian Registry of Spondyloarthritis (RBE). Methods: This was a cross-sectional, observational study based on data from the RBE, a nationwide multicenter cohort including 828 patients (568 men and 260 women) from 17 referral centers across Brazil. Standardized clinical and demographic data were collected using the REDCap platform. Disease activity (ASDAS-CRP, BASDAI), physical function (BASFI), spinal mobility (BASMI), and quality of life (ASQoL) were assessed with validated instruments. Sex-stratified multivariable linear regression models were constructed to identify independent predictors of each outcome. Results: Women presented higher disease activity (median BASDAI 4.5 vs. 3.2; ASDAS-CRP 2.2 vs. 1.9), greater functional limitation (BASFI 5.0 vs. 4.0), and poorer quality of life (ASQoL 9.0 vs. 7.0) compared to men, despite similar CRP levels. Psychological distress was more frequent in women, while men had worse spinal mobility (BASMI 4.0 vs. 3.5) and higher HLA-B27 positivity. Regression models revealed that shoulder and hip pain were relevant predictors of disease activity in both sexes, but psychological factors and work activity more strongly influenced outcomes in women. Men’s disease burden was more associated with structural damage and cardiometabolic comorbidities. Conclusions: This study highlights distinct sex-related clinical patterns in axSpA. Women reported higher symptom burden, functional limitations, and reduced quality of life, largely influenced by subjective symptoms and comorbidities. Conversely, men presented greater structural impairment and different comorbidity profiles. These findings support the need for sex-informed clinical assessments and individualized management strategies in axSpA to tailor the care of these sex-specific disease trajectories, which may enhance equity and outcomes in real-world settings.