Inflammatory bowel disease does not confer higher disease activity or greater radiographic progression in axial spondyloarthritis.

To examine whether inflammatory bowel disease (IBD) influences disease activity and radiographic progression in patients with axial spondyloarthritis (axSpA). This was a longitudinal cohort study of axSpA patients from a tertiary referral centre. Active axSpA was assessed using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI ≥4) in a dataset of 1268 patients. Radiographic progression, defined as a ≥ 2-unit increase in the modified Stoke Ankylosing Spondylitis Score (mSASSS) over 2 years, was evaluated in a subset of 471 patients with available longitudinal radiographic data. Generalized estimating equation models were used to assess associations between IBD and each outcome, adjusting for key confounders. Among 1451 axSpA patients, 184 (13%) had IBD. Compared with axSpA-only patients, those with IBD had lower HLA-B27 positivity and higher rates of uveitis, peripheral arthritis, and elevated C-reactive protein. However, IBD was not associated with an increased risk of active axSpA (OR 0.98, 95% CI 0.75-1.28) or radiographic progression (OR 1.45, 95% CI 0.78-2.73). Sensitivity analyses accounting for time-varying IBD status confirmed these findings. AxSpA-IBD patients exhibited distinct clinical features but did not have worse disease activity or greater radiographic progression than those with axSpA alone. These findings suggest that while IBD and axSpA share overlapping immunopathogenic mechanisms, IBD does not exacerbate axSpA severity. Further research is needed to explore the effects of IBD severity and duration on long-term axSpA outcomes to delineate the interaction between these two diseases.