BACKGROUND:Chronic constipation in children can be caused by cows' milk intolerance (CMI), but its pathogenesis is unknown.AIMS:To evaluate the histology and manometry pattern in patients with food intolerance-related constipation.PATIENTS AND METHODS:Thirty-six consecutive children with chronic constipation were enrolled. All underwent an elimination diet and successive double-blind food challenge. All underwent rectal biopsy and anorectal manometry.RESULTS:A total of 14 patients were found to be suffering from CMI and three from multiple food intolerance. They had a normal stool frequency on elimination diet, whereas constipation recurred on food challenge. The patients with food intolerance showed a significantly higher frequency of erosions of the mucosa, and the number of intra-epithelial lymphocytes and eosinophils. The rectal mucous gel layer showed that the food-intolerant patients had a significantly lower thickness of mucus than the other subjects studied. Manometry showed a higher anal sphincter resting pressure and a lower critical volume in food intolerance patients than in the others suffering from constipation unrelated to food intolerance. Both histology and manometry abnormalities disappeared on the elimination diet.CONCLUSIONS:Food intolerance-related constipation is characterized by proctitis. Increased anal resting pressure and a reduced mucous gel layer can be considered to be contributory factors in the pathogenesis of constipation.