Collagenous colitis (CC), a form of microscopic colitis, is characterized by a thick subepithelial collagen layer in the colon in the presence of chronic nonbloody watery diarrhoea and macroscopically normal-appearing colonic mucosa. Typically affecting elderly adults, CC is rare in children with only 12 cases previously reported in the literature. We report the case of a 4-year-old girl with CC associated with eosinophilic gastritis, which was clinically responsive to treatment with ketotifen, a benzocycloheptathiophene derivative, and H1 class of antihistamine that stabilizes mast cells and potentially impairs eosinophil migration to target organs. We review the published cases of paediatric-onset CC and summarize the links between eosinophils and CC in the clinical and basic science literature.
Conclusion: CC is a rare cause of chronic diarrhoea in children and may relate to mast cell and eosinophil activity.