Identifying Axial Spondyloarthritis in Patients With Inflammatory Bowel Disease Using Computed Tomography

The diagnosis of axial spondyloarthritis (axSpA) is hampered by diagnostic delay. Computed tomography (CT) undertaken for nonmusculoskeletal (non-MSK) indications in patients with inflammatory bowel disease (IBD) offers an opportunity to identify sacroiliitis for prompt rheumatology referral. This study aims to identify what proportion of patients with IBD who underwent abdominopelvic CT for non-MSK indications have axSpA and to explore the role of a standardized screening tool to prospectively identify axSpA on imaging.

Abdominopelvic CT scans of patients with verified IBD, aged 18 to 55 years, performed for non-MSK indications were reviewed by radiologists for the presence of CT-defined sacroiliitis (CTSI), using criteria from a validated CT screening tool. All patients identified were sent a screening questionnaire, and those with self-reported chronic back pain (CBP), CBP duration of greater than 3 months, and age of onset of less than 45 years were invited for rheumatology review.

CTSI was identified in 60 out of 301 (19.9%) patients. Out of these 60 patients, 32 (53%) responded to an invitation to participate, and 27 out of 32 (84.3%) were enrolled. Of these, 8 had a preexisting axSpA diagnosis and 5 did not report CBP. In total, 14 patients underwent rheumatology assessment, and 3 out of 14 (21.4%, 95% CI 4.7-50.8) had undiagnosed axSpA. In total, 11 out of 27 (40.7%, 95% CI 22.4-61.2) patients had a rheumatologist-verified diagnosis of axSpA.

In this study, 5% (3/60) of patients with IBD undergoing abdominopelvic CT for non-MSK indications with CTSI were found to have undiagnosed axSpA and, overall, 18.3% (11/60) were found to have axSpA. This reveals a significant hidden population of axSpA and highlights the need for a streamlined pathway from sacroiliitis detection to rheumatology referral.