Incidence of collagenous and lymphocytic colitis: a 5-year population-based study.

OBJECTIVE: The incidence of collagenous and lymphocytic colitis is not well known. We sought to assess the incidence of collagenous and lymphocytic colitis in a well-defined population during a 5-yr study period.
METHODS: From January 1, 1993, to December 31, 1997, all new patients diagnosed with collagenous or lymphocytic colitis living in the catchment area of the Hospital Mutua de Terrassa (Barcelona, Spain) were identified. Since 1993 all patients with chronic diarrhea were referred for a diagnostic colonoscopy. Multiple biopsy sampling of the entire colon was performed when appearance of the colonic mucosa was grossly normal.
RESULTS: Twenty-three cases of collagenous colitis and 37 of lymphocytic colitis were diagnosed. The female:male ratios were 4.75:1 and 2.7:1 for collagenous and lymphocytic colitis, respectively. The mean age at onset of symptoms was 53.4+/-3.2 (range, 29-82) yr for collagenous colitis, and 64.3+/-2.7 (range, 28-87) yr for lymphocytic colitis (p = 0.012). The mean annual incidence per 100,000 inhabitants based on the year of onset of symptoms was 1.1 (95% confidence interval [CI], 0.4-1.7) for collagenous colitis, and 3.1 (95% CI, 2.0-4.2) for lymphocytic colitis. A peak incidence was observed in older women in both diseases. A rate of microscopic colitis of 9.5 per 100 normal-looking colonoscopies performed in patients with chronic watery diarrhea was observed. Normal rectal biopsies were found in 43 % and 8% of patients with collagenous and lymphocytic colitis, respectively.
CONCLUSIONS: The incidence of lymphocytic colitis is three times higher than that of collagenous colitis. Microscopic colitis should be considered as a major possibility in the work-up of chronic diarrhea in older women.