Prevalence and Clinical Impact of Immune-Mediated Inflammatory Diseases in Patients with Inflammatory Bowel Disease: Results from a Large Retrospective Observational Study

(1) Background: Inflammatory bowel diseases (IBDs) are chronic inflammatory disorders involving innate and adaptive immune responses. Despite primarily affecting the gut, recent insights highlight systemic implications, expanding our understanding beyond intestinal boundaries. (2) Methods: This retrospective multicentric study explored the association of IBD and immune-mediated inflammatory diseases (IMIDs) and the impact of concurrent IMIDs on the course of IBD. Clinical data were collected from consecutive medical records of patients with IBD. For assessing the impact of concurrent IMIDs, a control group of IBD patients without associated IMIDs was considered. (3) Results: Of 6589 IBD patients, 6.8% exhibited concomitant IMIDs. Notably, 79.8% of these patients had an aggressive disease course. Psoriasis, atopic dermatitis, and type 1 diabetes mellitus prevalence were lower in the IBD population than in the general population. Conversely, multiple sclerosis, primary sclerosing cholangitis, and pyoderma gangrenosum were more prevalent in IBD patients. Among the patients with a concomitant IMID, 79.8% had an aggressive disease course vs. 8.1% in the control group (p < 0.001). (4) Conclusions: This study underscores the frequency of IMIDs in IBD patients and their association with a more aggressive disease course. The recognition of concurrent IMIDs is crucial for comprehensive patient management, influencing therapeutic decisions and potentially improving outcomes.