Biologic Treatment Modification Efficacy in Concurrent Inflammatory Bowel Disease and Ankylosing Spondylitis: A Retrospective Cohort Study at a Single Tertiary Center

Background: The link between ankylosing spondylitis (AS) and inflammatory bowel disease (IBD) is well-established, with concurrent prevalence estimates ranging from 5–10%. However, there are still significant gaps in our understanding, and a comprehensive treatment guideline for these co-diagnosed patients has yet to be established. Our objective was to explore patterns of treatment alterations following the diagnosis of AS in patients previously diagnosed with IBD, and vice versa. Additionally, we sought to determine how these modifications influence clinical outcomes in both conditions. Methods: This retrospective data-based cohort study included patients with coexisting IBD and AS that were diagnosed between the years 2009–2022 and were followed by the gastroenterology and the rheumatology units of the Sheba Medical Center, Israel. The data were extracted from the electronic health record and included demographic information, medication history, treatment modification at the time of second diagnosis, and the characteristics and activity of both IBD and AS at the index time and at the 3-month mark. Results: The study included a total of 68 patients, with a male predominance (40 patients, 59%). The median age was 43 years (IQR 31–55) and 78% had Crohn’s disease (CD). The median duration between the diagnosis of the first disease to the second one was 4 years (IQR 1–9.5). A significant proportion of patients (85%) underwent treatment modification at their second diagnosis. Out of the total cohort, 28% initiated biological therapy, 17.6% switched their biologic regimen, and 16.2% discontinued NSAIDS. Patients who underwent biologic modifications at time of the second diagnosis (the initiation/switch/augmentation of a concurrent regimen) experienced significantly higher rates of clinical improvement in either IBD or AS at the 90-day follow-up compared to patients who did not (68% vs. 32%, p = 0.004), and biologic modification was found to be an independent predictor for clinical improvement (OR 3.69, CI 1.08–12.58, p = 0.037). Conclusions: Our findings suggest that biologic therapy modification at the time of the second diagnosis was associated with a higher rate of improvement in AS/IBD at the 90-day follow-up.