Microscopic Colitis–Defining Incidence Rates and Risk Factors: A Population-Based Study

Background & Aims: The burden and determinants of microscopic colitis (MC) in North America are inadequately defined. We determined the incidence rate of and risk factors for MC in a well-defined North American population. Methods: A population-based cohort study was conducted between April 1, 2002, and March 31, 2004. All adults with a pathologic diagnosis of MC were identified and comprehensive chart review was undertaken to confirm the diagnosis and identify risk factors. Category-specific risks for developing MC were reported as rate ratios (RRs) with exact 95% confidence intervals (CIs). Results: MC was identified in 164 individuals for an annual incidence rate of 10.0 per 100,000 person-years (lymphocytic colitis, 5.4; collagenous colitis, 4.6 per 100,000). Patients older than the age of 65 were more than 5 times more likely to develop MC (RR, 5.6; 95% CI, 4.0–7.7). Women were at higher risk of acquiring MC for both collagenous colitis (RR, 3.44; 95% CI, 2.07–5.97) and lymphocytic colitis (RR 6.29; 95% CI, 3.21–13.74). Elderly women with a history of malignancy were associated with a higher risk of MC (RR, 3.59; 95% CI, 1.68–7.01), as were patients with celiac disease (RR, 7.9; 95% CI, 4.0–14.2) and hypothyroidism (RR, 6.1; 95% CI, 3.5–10.0). Conclusions: This was a large population-based cohort study of MC and our incidence rates were consistent with previously reported population-based studies in North America and Europe. An increased incidence of MC was observed in several disease states with the novel finding of an increased risk of MC with malignancy.