Progression of collagenous colitis to Crohn's disease.

Collagenous colitis is a condition usually characterized by watery diarrhoea, macroscopically normal colonic mucosa and a typically thickened subepithelial collagen band on histological examination. It is rare in children, and coexistence with other inflammatory bowel diseases has been reported only rarely. We describe a case of diarrhoea presenting in infancy subsequently proved to be collagenous colitis that progressed to the typical features of Crohn's disease.