Clinical Features Focusing on Extraintestinal Manifestations in Japanese Patients with Inflammatory Bowel Diseases: Far East 1000

Background: Patients with inflammatory bowel diseases (IBD) can develop extraintestinal manifestations (EIMs) during the disease course, which sometimes impact their quality of life. Objectives: This study aimed to clarify the prevalence and types of EIMs using a hospital-based IBD cohort in Japan. Methods: A patient cohort with IBD was established in 2019, as participated by 15 hospitals in Chiba Prefecture of Japan. Using this cohort, the prevalence and types of EIMs, which are defined based on previous reports and the Japanese guidelines, were investigated. Results: This cohort enrolled 728 patients, including 542 ulcerative colitis (UC) and 186 Crohn's disease (CD). Of these patients with IBD, 10.0% were identified with one or more EIMs (57 (10.5%) with UC and 16 (8.6%) with CD). Arthropathy and arthritis were the most common EIM in 23 (4.2%) patients with UC, followed by primary sclerosing cholangitis (PSC) (2.6%). Arthropathy and arthritis were also the most common in patients with CD, but no cases of PSC were observed. EIMs were more frequently observed in patients with IBD treated by specialists than in those treated by non-specialists (12.7% vs. 5.5%, p = 0.011). The incidence of EIMs in patients with IBD was not significantly different over time. Conclusions: The prevalence and types of EIMs in our hospital-based cohort in Japan did not significantly differ from those reported in previous or Western studies. However, the incidence might be underestimated due to the limited ability of non-IBD specialists to discover and describe EIMs in patients with IBD.