The epidemiology of microscopic colitis: a 10-year pathology-based nationwide Danish cohort study.

Objective. Microscopic colitis (MC) includes two main types: collagenous colitis (CC) and lymphocytic colitis (LC). Previous studies have indicated an increasing incidence, but these have mainly been based on regional databases. We found it important to study the epidemiology based on a comprehensive nationwide cohort. Material and methods. We studied the epidemiological data of MC in Denmark from 2002 to 2011. The cohort consisted of all patients with a recorded diagnosis of either CC or LC in the Danish Pathology Register during the study period. Data on all patients with a registered colon biopsy were also included. Results. A total of 7777 patients, 4749 (61%) with CC and 3028 (39%) with LC, were identified. Over the study period, the annual incidence of diagnosed cases of CC increased from 2.9/105 to 14.9/105 and of LC from 1.7/105 to 9.8/105. In 2011, the incidence of MC was 24.7/105 inhabitants. The age-specific incidence showed that the risk of both CC and LC increased with age. The female/male ratio, distribution of the type of colitis and mean age at diagnosis were relatively stable during the study period. The annual number of registered colon biopsies in the pathology register increased from 21.583 in 2002 to 39.733 in 2011, indicating an increased diagnostic activity. Conclusion. In a nationwide cohort study, the incidence of CC and LC continued to increase from 2002 to 2011. An increased diagnostic activity could in part explain the increase in the number of diagnosed cases.