Natural disease course of inflammatory bowel disease unclassified in a prospective European population-based inception cohort-the Epi-IBD cohort

Background: The precise diagnosis of inflammatory bowel disease (IBD) cannot always be established. Thus, a proportion of patients will be diagnosed as IBD Unclassified (IBDU). A significant proportion of these patients will remain unclassified throughout their disease course. Only very few population-based cohorts have investigated the disease course of IBDU. Methods: The Epi-IBD cohort is a prospective population-based cohort of 1289 unselected, uniformly diagnosed patients with IBD diagnosed in 2010 in centres from Western and Eastern European countries. Clinical data were captured prospectively throughout the follow-up period. The aim of the study was to investigate the disease course and prognosis of patients diagnosed with IBDU from diagnosis and during the first 5 years of follow-up. Results: A total of 112 (9%) patients were initially diagnosed with IBD). Patient characteristics are shown in Table 1. After 5 years of follow-up, 28 (25%) patients changed diagnosis to either ulcerative colitis (UC) (n = 20, 71%) or Crohn’s disease (CD) (n = 8, 29%) while 84 (7% of the total cohort) remained as IBDU. The median time to a definite IBD diagnosis was 7 months (range: 1–63) with no difference between those changing to UC or CD. A total of 17 (15%) patients were hospitalised for their IBD during follow-up after a median of 10 months (range: 0–63). Of those, 9 (45%) patients changed diagnosis to UC during follow-up, while no patient changing diagnosis to CD was hospitalised. 8 (7%) patients had surgery (7 colectomies, 1 resection) after a median of 19 months (range: 3–63). Most surgeries (n = 6, 75%) were performed in patients who changed diagnosis to UC, and 3 of those led to a definite diagnosis of UC where the other 3 were performed after the change of diagnosis. No patient changing diagnosis to CD had surgery. The cumulative exposure to medical treatments in IBDU patients including t[...]