Background: It is unknown whether the subtypes of microscopic colitis (MC) represent distinct nosologic entities or related presentations of the same disease. Our aim was to search for epidemiologic differences among its various histopathologic subtypes.
Methods: In a computerized database of 789,568 colon pathology reports, we compared the characteristics of 8,745 MC patients with those of the remaining population.
Results: MC was diagnosed as three distinct histopathologic subtypes: lymphocytic colitis (LC) in 51 %, collagenous colitis (CC) in 43 %, and incomplete colitis (IC) in 6 % of patients. Only 0.65 % was simultaneously diagnosed with more than one subtype of MC. The prevalence of all three subtypes showed an age-dependent rise, with the average age (SD) being 63.3 (14.3) years in LC, 66.4 (12.1) years in CC, and 67.3 (12.7) years in IC (p < 0.0001). There was a striking female predominance in all three subtypes, the female fraction being 72 % in LC, 82 % in CC, and 79 % in IC (p < 0.0001). All three subtypes showed similar geographic distributions among different US states. They were similarly associated with diarrhea and weight loss, the odds ratios for all MC being 45.92 (43.35-48.63) and 5.12 (4.68-5.60), respectively, compared to control patients without MC. All three subtypes also harbored significantly less colonic adenomas, the overall odds ratio being 0.11 (0.10-0.12).
Conclusion: MC comes in three distinct histopathologic entities, which show striking similarities of their general epidemiologic features. The slight differences in their demographic characteristics could point at varying sets of environmental influences that affect the occurrence of subtypes.