S1983 Prevalence, Etiology, and Outcomes of Microscopic Colitis: A Retrospective Single-Centre Cohort Study

Introduction: Microscopic Colitis (MC) is an inflammatory disease of the colon that commonly presents with non-bloody watery diarrhea, weight loss, and nocturnal stools. It has a high prevalence in older females affecting 1 in 115 women during their lifetime. The exact etiology of MC is not well understood but it is believed to involve a combination of genetic, environmental, and immune factors. Endoscopically, it presents with normal-appearing colonic mucosa, although erythema with or without edema may also be observed. However, the diagnosis is made on colon biopsies. There are 2 subtypes of MC, lymphocytic colitis (LC) which consists of lymphocytic inflammation of the lamina propria, and intraepithelial lymphocytosis, or collagenous colitis (CC) which consists of subepithelial collagen band thickening. We aim to create a database of patients in Manitoba with MC based on histological diagnosis. Methods: A retrospective review of pathology reports of patients undergoing a colonoscopy from 2006-2018 within the Winnipeg health region. Results: 914 patients (9.7%) were identified with MC from the initial 9377 pathology reports that were screened. 490 (53.6%) patients had CC, of whom 79 (16.1%) were males and 411 (83.8%) were females. The mean age at diagnosis was 62.9 ± 12.4 years old (range 28-90) for males and 61.8 ± 13.3 years old (range 20-91) for females. In contrast, 409 (44.7%) patients had LC, of whom 94 (22.9%) were males and 315 (77.0%) were females. The mean age at diagnosis of LC was 61.9 ± 17.2 years old (range 23-90) for males and 59.2 ± 13.7 years old (range 18-91) for females. Fifteen (1.6%) patients had an unspecified diagnosis on their pathology report. Seventy-four people had more than one colonoscopy during the study period. Finally, there was a signal of an increase in the incidence of both subtypes in recent years. In males, there was a trend towards a higher incidence of LC (R² = 0.60) in recent years vs a higher incidence of CC in females (R² = 0.82). Initial data shows that 31.1% used a PPI (most commonly omeprazole) and 23.8% were on a Selective Serotonin Reuptake Inhibitors (SSRI). 1.4% had celiac disease and 1.9% had a proceeding CDI pre-MC diagnosis compared to 2.7% post. Conclusion: There was a strong female predominance, albeit comparable age at diagnosis, in both MC subtypes with a trend towards increased incidence in recent years. A higher prevalence of CC was noted especially in middle-aged years. Finally, there was a high correlation between PPI and SSRI use and new cases.