Incidence and Prevalence of Microscopic Colitis Between 2001 and 2016: A Danish Nationwide Cohort Study

BACKGROUND AND AIMS: Epidemiological studies suggest an increasing global incidence of microscopic colitis, including collagenous colitis and lymphocytic colitis. We aimed to investigate the incidence and prevalence of microscopic colitis in Denmark. METHODS: In a nationwide cohort study, we included all incident patients with a recorded diagnosis of collagenous colitis or lymphocytic colitis in the Danish Pathology Register between 2001 and 2016. RESULTS: A total of 14 302 patients with microscopic colitis-8437 [59%] with collagenous and 5865 [41%] with lymphocytic colitis-were identified during the study period. The prevalence in December 2016 was estimated to be 197.9 cases per 100 000 inhabitants. Microscopic colitis was more prevalent among females (n = 10 127 [71%]), with a mean annual incidence of 28.8, compared with 12.3 per 100 000 person-years among males. The overall mean incidence during the study period was 20.7 per 100 000 person-years. Mean age at time of diagnosis was 65 years (standard deviation [SD]:14) for microscopic colitis, 67 [SD:13] for collagenous colitis, and 63 [SD:15] for lymphocytic colitis. The overall incidence increased significantly from 2.3 cases in 2001 to 24.3 cases per 100 000 person-years in 2016. However, the highest observed incidence of microscopic colitis was 32.3 cases per 100 000 person-years in 2011. Large regional differences were found, with the highest incidence observed in the least populated region. CONCLUSIONS: The incidence of microscopic colitis in Denmark has increased 10-fold during the past 15 years and has now surpassed that of Crohn's disease and ulcerative colitis. However, incidence has stabilised since 2012, suggesting that a plateau has been reached.