Incidence of Immune-Mediated Inflammatory Diseases Among Patients With Inflammatory Bowel Diseases in Denmark

BACKGROUND & AIMS: It is not clear whether the co-occurrence of immune-mediated inflammatory diseases (IMIDs) affects the course of inflammatory bowel diseases (IBD). We investigated the occurrence of IMIDs in relation to onset of IBD and the effects of concurrent IMIDs on IBD outcomes in a nationwide study of the Danish population. METHODS: We used a nationwide cohort of all individuals diagnosed with IBD, including Crohn's disease (CD) or ulcerative colitis (UC), in Denmark from 2007 through 2016 (n = 14,377). Patients were match with individuals without IBD from the general population (controls, n = 71,885). All cohort members were followed from birth until 2016, their migration, or their death. The occurrence of IMIDs was assessed using the Danish national patient register and Registry of Medicinal Products Statistics. RESULTS: A total of 3,235 patients with a diagnosis of IBD (22.5%) has also received a diagnosis of an IMID; most IMIDs occurred before the onset of IBD (n = 2,600, 80.3%). The most common IMIDs observed were psoriasis, asthma, type 1 diabetes, and iridocyclitis. Patients with IBD treated with infliximab were at reduced risk of developing IMIDs (CD adjusted odds ratio [aOR], 0.52; 95% CI, 0.34-0.81 and UC aOR, 0.47; 95% CI, 0.29-0.76). Co-occurrence of IMIDs increased the risk of surgery in patients with CD that developed IMIDs after CD onset (aOR, 2.30; 95% CI, 1.46-4.20) but not in UC. CONCLUSIONS: In a nationwide study of the Danish population, 22.5% of patients with IBD also had at least 1 concurrent IMID. Co-occurrence of IMIDs increased the risk of surgery in patients with CD.