Low Prevalence of Colon Polyps in Patients with Diarrhea and Microscopic Colitis

Purpose: The term microscopic colitis (MC) encompasses two related clinical entities: collagenous colitis (CC) and lymphocytic colitis (LC). Previous studies have suggested that patients with CC or LC may harbor fewer colon polyps than controls without MC. The objective of this study was to test this hypothesis in a large cohort of patients who underwent colonoscopy for workup of diarrhea. Methods: We used the Miraca Life Sciences database to extract histopathologic, demographic, and clinical information from all adult patients who had a colonoscopy for the investigation of diarrhea with colonic biopsies from 1/2008 to 12/2012. Patients who had a screening colonoscopy, a history or a diagnosis of inflammatory bowel disease, or lower gastrointestinal surgery were excluded. Only the first chronological colonoscopy was included for patients who had multiple procedures. Results: Cases were 9,521 with MC (median age 67 years; range 18-98 years; 77.9% female): 4,183 with CC, 4,784 with LC, and 606 with a mixed form. Controls were 104,439 patients with diarrhea and no MC (median age 57 years, range 18-100 years; 69% female). Hyperplastic polyps (HP) were found in 13.1% of controls and 6.7% of patients with MC (OR 0.48; 95% CI 0.44-0.52; p<.0001), with no significant difference between CC and LC. Tubular adenomas (TA) were detected in 19.9% of controls, 12.3% of patients with LC (OR 0.57; 95% CI 0.52-0.62; p<.0001), and 6.8% of patients with CC (OR 0.30; 95% CI 0.26-0.33; p<.0001). Figure 1 shows the age-dependent prevalence of HP and TA in patients with MC and controls. Not only is the higher TA prevalence independent of age, but the disparity increases in the older age groups, in whom polyps are more prevalent.FigureConclusion: Among patients with diarrhea, those with MC have a significantly lower prevalence of polyps than those without. An endoscopic selection bias appears unlikely, since only patients with diarrhea and without known history of MC were included. The infiltrates found in microscopic colitis consist predominantly of ab-T-cell receptor(+) CD8+ lymphocytes, with an increased ratio of Foxp3/CD8+ cells. Thus, regulatory T-cells are highly represented, suggesting that immunomodulation exerts an inhibitory effect on epithelial proliferation.