Abstract Background Rare Crohn’s disease (CD) phenotypes, such as isolated perianal, oral, or genital involvement, are not captured by the current Montreal/Paris phenotypic classifications and are often under-recognised or misdiagnosed in clinical practice. This study aimed to describe rates, demographics and outcomes of children and young people presenting with these atypical forms. Methods A retrospective cohort study conducted within our prospective paediatric IBD incident database, included all regional CD cases diagnosed before 16 years of age between 01.01.11-30.06.23, with follow-up to 31.08.25. Patients presenting with “rare phenotype” - isolated perianal fistulae/abscesses, orofacial lesions, or genital swelling without evidence of luminal disease and therefore unclassifiable by Montreal/Paris - were compared with those showing a classifiable “typical phenotype”. Outcomes assessed included time to classifiable luminal disease, resectional surgery, initiation of anti-TNFα and second-line advanced therapies. Results Thirty-one (13%) of 249 children presented with a “rare phenotype”: isolated perianal (n = 8), orofacial (n = 17), genital (n = 2), and combined perianal and orofacial (n = 4); 74% were male. Median age at diagnosis was lower in the “rare phenotype” group 11.6 years (IQR 9.9–13.4) vs 13.4 years (IQR 11.3–14.8); p = 0.008. Median time from onset to “rare phenotype” diagnosis was 12 months (IQR 4–29). After a median of 10 months (IQR 3–43), 26/31 (84%) developed luminal disease. Over a median follow-up of 78 months (IQR 46–116), 5/12 (42%) patients presenting with perianal ± orofacial CD did not develop luminal involvement, in contrast to none in the other subgroups (p = 0.004). Disease location and behaviour classifiable by Montreal/Paris did not differ from the “typical” group. Anti-TNFα therapy was more frequently used (84% vs 67%; p = 0.05) but started later 46.5 months (IQR 20.8–77.3) vs 4 months (IQR 1–15); p 0.001 in the “rare phenotype” group. Rates of second-line advanced therapy 19% vs 16%; p = 0.4 and resectional surgery 10% vs 4%; p = 0.144 were comparable between groups. Conclusion In our population, one in eight children with CD presented with an isolated and unclassifiable rare phenotype by current classifications. Rare phenotypes were associated with prolonged time to diagnosis and delayed anti-TNFα treatment but not increased need for second-line advanced therapy or surgery. These findings underscore the need to refine current phenotypic classifications to include this individually uncommon but collectively significant subset of cases representing relevant CD presentations. Conflict of interest: Pochesci, Saverio: No conflict of interest Wilson, Adele: No conflict of interest Henderson, Paul: Personal Fees: Speaker Honorarium from Vertex Pharmaceuticals Armstrong, Katherine: No conflict of interest Russell, Richard K.: Grant: Nestec Other: Abbvie, Celltrion, Janssen, Lilly, Nestle, Pharmacosmos, Pfizer Wilson, David: No conflicts
Pochesci et al. (Thu,) studied this question.