Absence of focally enhanced gastritis in macaques with idiopathic colitis

Background: Focally enhanced gastritis has been described in association with Crohn's disease and ulcerative colitis, but is rare in the general population. The study aim was to test whether idiopathic colitis in macaques was associated with any characteristic changes of the gastric mucosa resembling similar changes in humans. Methods: The presence or absence of idiopathic colitis was established by gross and microscopic examination of the colons of rhesus macaques (Macaca mulatta), which died at the Oregon National Primate Research Center. Gastric tissue specimens were compared between a case population of 26 macaques with idiopathic colitis and a control population of 21 macaques without colitis. The specimens were histologically assessed by two independent pathologists blinded to the presence or absence of idiopathic colitis. Differences between cases and controls were compared using a two-sided Fisher's exact test. Results: Of the 26 cases of macaques with colitis, 11 animals (42%) harbored signs of chronic gastritis. Of the 21 control macaques without colitis, nine animals (43%) harbored signs of chronic gastritis, P = 1.0000. Of all animals with gastritis, 1/11 animals with colitis and 2/9 control animals showed rare active gastritis as evidenced by the presence of neutrophils, P = 0.5658. Lymphocytic infiltrates of the gastric mucosa were seen in 4/11 colitis cases and 0/9 controls, P = 0.0942. No gastric specimens with focally enhanced gastritis were found among any of the case or control animals. Conclusions: Unlike chronic inflammatory bowel disease in humans, idiopathic colitis in macaques is not associated with focally enhanced gastritis or any other type of specific gastritis.