Clinical phenotypes of very early onset inflammatory bowel disease in Australian children: A single‐centre retrospective study

Abstract Objectives Very early onset inflammatory bowel disease (VEO‐IBD), diagnosed at <6 years old, includes a subset of infantile onset IBD (IO‐IBD, ≤2 years). We describe presenting clinical features, phenotypes, and early management of children with VEO‐IBD at a single tertiary centre. Methods Retrospective cohort study of children with VEO‐IBD diagnosed at Queensland Children's Hospital from January 2010 to March 2025. Results In 52 children, (24 IO‐IBD; 28 VEO‐IBD), median Paediatric Ulcerative Colitis Activity Index on presentation was 35 (interquartile range [IQR] 15), similar in both groups (35 IO‐IBD; 39.5 VEO‐IBD). Ulcerative colitis (UC) was the most frequent diagnosis (50%; 38% Crohn's disease; 12% IBD‐Unclassified [IBD‐U]). Among children with UC/IBD‐U, pancolitis was common in both groups (57.1% IO‐IBD; 66.7% VEO‐IBD). Paris‐classified anatomic phenotype did not differ between IO‐IBD and VEO‐IBD. Atypical colitis, upper gastrointestinal involvement, and granulomas occurred in 23%, 38% and 35% of cases, respectively. Prior allergic/atopic diagnoses were documented in 44%. Primary sclerosing cholangitis (PSC) was identified in 8% within 12 months of IBD diagnosis. Two monogenic disorders were identified, among 38 genotyped children, with severe perianal disease and successful bone marrow transplantation. Corticosteroids were used in 67% (35/52); 86% (30/35) responded without biologic rescue; five required anti‐tumour necrosis factor therapy. One child required early colectomy. Conclusions IO‐IBD and VEO‐IBD demonstrated substantial overlap in presenting clinical and intestinal phenotypes. Monogenic disease was confined to IO‐IBD, while early PSC was a notable secondary finding. These data support phenotype‐guided genetic evaluation and further study of early hepatobiliary disease in VEO‐IBD.