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.

Abbreviations used in this paper: CC, collagenous colitis, CI, confidence interval, LC, lymphocytic colitis, MC, microscopic colitis, RR, rate ratio