ILEAL INVOLVEMENT IS AGE-DEPENDENT IN PAEDIATRIC CROHN??S DISEASE

Abstract

Aims: Lymph follicles (LFs) have been suggested to play a role at the early stage of Crohn's disease (CD) lesions. In the small bowel, LF are grouped forming Peyer's patches (PPs) which develop early in fetal life, grow in size and number until puberty and then undergo involution. In contrast, colonic LFs are isolated and undergo little change during life. As a result, if LFs play a role in the occurrence of CD lesions, the distribution of ileal and colonic lesions is expected to be altered in small children. Methods: Medical records of two independent French (n = 136) and Swedish (n = 55) cohorts of consecutive paediatric CD were reviewed. Disease sites and age of onset were recorded and the age-dependent probability to develop ileal lesions was computed. The CARD15/NOD2 genotype was also analysed when available (n = 99). Results: The curves of disease occurrence were significantly different in case of CD with or without ileal lesions (p < 0.0001). At the age of 8 years, the probability (95% CI) of small bowel involvement in CD patients is was 0.19 (0.07-0.39). It increases until 16 years to 0.61 (0.54-0.68). It was slightly higher in patients carrying one or more CARD15/NOD2 mutations [0.75 (0.55-0.89)] than in wild-type patients [0.46 (0.34-0.58)]. CARD15 mutations also influenced the age of onset of ileal disease (p < 0.02). Summary and Conclusions: In children, ileal CD lesions are delayed when compared to colonic lesions. This observation is in agreement with the previously proposed hypothesis of a pathophysiological role of PP in ileal CD. The rarity of small bowel flesions incites to be cautious when classifying chronic colitis in small children.