About 25% of Inflammatory Bowel Disease (IBD) cases occur in individuals under 18 years old, and its incidence in childhood—especially early childhood—is rising globally. Paediatric IBD differs notably from adult-onset disease in clinical presentation, histology, severity and genetic background. Children are often diagnosed earlier in the disease course, before complications or classic mucosal changes appear. The disease tends to be more extensive and aggressive, partly due to longer cumulative inflammation and higher genetic and environmental susceptibility. However, symptoms and biopsies may be less characteristic, making diagnosis challenging [1].
The ESPGHAN revised Porto criteria guide the diagnostic work-up in children. They recommend ileocolonoscopy, upper GI endoscopy and histological examination, with biopsies from all gastrointestinal segments in suspected cases. Infectious and other alternative diagnoses must be excluded. Once IBD has been established, paediatric cases are classified into typical Ulcerative Colitis (UC), atypical UC, Crohn’s Disease (CD), colonic CD and IBD-unclassified (IBD-U), according to ESPGHAN and ECCO definitions [2]. IBD-U is more common in children than in adults because of atypical patterns and limited specificity of histological and laboratory findings. These patients show patchy inflammation without granulomas or classic continuous UC involvement. IBD-U is more frequent in those aged under 10 years and progresses rapidly to pancolitis; many cases are later reclassified, although a significant proportion of patients retain the diagnosis. Prognosis may be worse than that of UC, especially regarding postoperative pouch complications [3, 4].
Paediatric UC is typically more extensive but shows milder inflammation and less architectural distortion compared to adult UC. Several atypical patterns occur more frequently in children: rectal sparing, short disease duration resulting in lack or paucity of chronicity features, caecal patches, upper GI involvement and Acute Severe Colitis with backwash ileitis. Children with CD more commonly present with colonic disease involving the rectum, making differentiation from UC difficult in comparison with adults, who often present with terminal ileitis. Discontinuous inflammatory changes across multiple colonic biopsies and a higher frequency of granulomas favour CD in paediatric cases. Upper gastrointestinal involvement, including of the oesophagus, stomach and duodenum, is also more frequent in children. Given these atypical patterns, complete assessment with ileocolonoscopy, oesophagogastroduodenoscopy, multiple biopsies and small bowel imaging (e.g. capsule endoscopy) is essential for accurate diagnosis [5, 6].
Most IBD in older children and adults is polygenic, with over 200 risk loci identified. In contrast, very early onset IBD (VEO-IBD, diagnosed before age 6 years) can result from monogenic or digenic mutations, often linked to primary immunodeficiencies. These patients tend to have more severe and extensive disease. Additional clues favouring a monogenic cause include family history, consanguinity, failure to thrive, autoimmune phenomena, recurrent infections or fevers, early treatment failure, severe perianal disease, immune dysregulation syndromes, intestinal obstruction or atresia, skin or dental abnormalities and malignancies [7]. Histologically, these cases show heterogeneous inflammatory patterns and are often termed “IBD-like colitis”. Three main patterns can be recognised on biopsy [8]:
Paediatric IBD presents earlier, more extensively and often with atypical clinical and histological features compared to adult-onset disease. Accurate diagnosis requires comprehensive endoscopy with biopsies and careful exclusion of other causes. Classification into UC or CD is more difficult in children due to overlapping and evolving features, and IBD-U is more common. Distinct histological patterns, especially in VEO-IBD, may reflect underlying monogenic disorders and demand higher clinical suspicion. Early, accurate classification is key to timely therapy and improved outcomes in this population.
