To Örebro University

Background: Perianal diseases are more common in patients with Crohn's disease (CD) than in the general population, but data are scarce in other inflammatory bowel disease (IBD) subtypes.

Method: Using data from the Swedish National Patient Register (NPR) and SWIBREG, the national quality register for IBD, we estimated the cumulative incidence of perianal fistula/abscess and perianal diseases (fistula, abscess, stenosis, fissure or procedure code for perianal surgery) in relation to diagnosis, and the prevalence in 2023, in individuals with CD, ulcerative colitis (UC) and IBD-unclassified (IBD-U), and in a matched (age, sex, calendar year and region of residence) IBD-free cohort from the general population.

Results: We identified 38,364 patients with incident IBD 2007-2017, and 98,229 patients with prevalent IBD as of 31 December 2022. The cumulative incidence of fistula/abscess was 6.7% at diagnosis, 8.3% at 1 year and 10.4% at 5 years in CD. The corresponding percentages in UC were 0.9%, 1.3% and 2.1%, and in IBD-U 2.4%, 3.1% and 4.5%, respectively. In 2023, 12.8%, 3.1% and 4.1% of patients with prevalent CD, UC and IBD-U had a history of fistula/abscess, compared to 0.8% in the general population. The corresponding numbers for perianal diseases were 19.7%, 7.4%, 8.6% and 2.2%.

Conclusions: The cumulative incidence and prevalence of perianal diseases in Swedish patients with CD was in parity with reports from other countries, and in patients with UC and IBD-U, it was 3-4 times higher than in the population.