Cumulative incidence of perianal manifestations in pediatric‐onset inflammatory bowel disease: A nationwide Swedish cohort study

Perianal disease is a recognized complication of pediatric Crohn's disease (CD), but data on ulcerative colitis (UC) and inflammatory bowel disease unclassified (IBD-U) are limited. We examined the occurrence of perianal disease before, at, and after diagnosis of pediatric-onset IBD compared with matched (age, sex, and geographical region) population comparators. Using Swedish nationwide registers, we identified 3501 children with CD, 3821 with UC, and 1081 with IBD-U diagnosed 1990 to 2019, and 81,861 matched IBD-free individuals. The 10-year cumulative incidence of perianal disease was 24.8% in CD, 13.4% in IBD-U, and 7.4% in UC, compared with 1.1% in comparators. Fistula incidences were 18.1%, 7.1%, 2.9%, and 0.3%. Perianal disease was associated with subsequent diagnostic reclassification, particularly from UC and IBD-U to CD. Perianal disease is common in pediatric CD and occurs substantially more often in UC and IBD-U than in the general population, highlighting its clinical relevance across pediatric IBD subtypes.