To Örebro University

Background: The Epi-IBD cohort is a prospective European population-based cohort of 1,508 patients diagnosed in 2010 and 2011 with inflammatory bowel disease (IBD) according to Copenhagen criteria in centres across 17 European countries. The study aims to describe treatment strategies, disease course and prognosis of IBD unclassified (IBDU) across Europe.

Methods: Patients with IBDU were defined as not fulfilling the Copenhagen diagnostic criteria of Crohn’s disease (CD) or ulcerative colitis (UC), but still required IBD related treatment and monitoring. They were followed prospectively from the time of diagnosis until December 31st, 2020, death, emigration or loss of follow-up. Clinical data on surgery, hospitalizations, and medical treatment were captured throughout the follow-up period and entered into a validated web-database, www.epi-ibd.org. Patients with IBDU were categorised as CD-like, UC-like or mixed CD-UC based on disease location and continuity of the affected bowel segments at diagnosis.

Results: In total, 129 IBDU patients aged ≥15 years from 22 centres were included. They comprised 8.5% (N=129/1,508) of the total cohort. The disease location was reported in Table 1 where 4 patients had unknown disease location at baseline. At diagnosis, 16% (N=25/129) were CD-like, 52% (N=62/129) were UC-like and 32% (N=42/129) were mixed CD-UC.During the 10-year follow-up, 32% (N=41/129) were re-classified as either CD (N=16) or UC (N=25). The crude 1-, 5-, and 10-year rates for re-classification of diagnosis were 19%, 26% and 32%. The time to initiation of therapies and the distribution of therapies according to re-classification of IBDU diagnosis at baseline are presented in Figure 1 A-B . Advanced therapies were used in 13% (N=17/129) of patients over the 10-year follow-up, and was initiated after a median period of 1.9 years (inter-quartile range 0.9-8.1). An intestinal resection was required in 7% (N=9/129). After 1, 5, and 10 years, 9%, 19% and 26% of the patients diagnosed with IBDU at baseline, respectively, required hospitalisation.

Conclusion: After 10 years of follow-up, a third of patients initially diagnosed with IBDU were re-classified as either CD or UC. The disease course was in general mild with a low number of patients requiring advanced therapy, intestinal resection, and hospitalization. However, patients who were re-classified as CD or UC were more frequently treated with medical therapies.