Symptomatic overlap between irritable bowel syndrome and microscopic colitis

Background: Microscopic colitis is diagnosed on the basis of histologic criteria, and irritable bowel syndrome (IBS) is diagnosed by symptom-based criteria. There has been little investigation into the symptomatic overlap between these conditions. Our aim was to assess the prevalence of symptoms of irritable bowel syndrome in a population-based cohort of patients with microscopic colitis. Methods: The Rochester Epidemiology Project (REP), a medical records linkage system providing all health care data for the defined population of Olmsted County, Minnesota, was used to identify all county residents with a diagnosis of microscopic colitis between 1985 and 2001. The medical records of these individuals were reviewed to ascertain symptoms consistent with Rome, Rome II, and Manning criteria for irritable bowel syndrome. Results: One hundred thirty-one cases of microscopic colitis were identified. Median age at diagnosis was 68 years (range, 24-95); 71% were women. Sixty-nine (53%) and 73 (56%) met Rome and Rome II criteria for irritable bowel syndrome, respectively. Fifty-four (41%) had three or more Manning criteria. Forty-three (33%) had previously been diagnosed with irritable bowel syndrome. Conclusions: In this population-based cohort of histologically confirmed microscopic colitis, approximately one-half met symptom-based criteria for the diagnosis of irritable bowel syndrome. The clinical symptom-based criteria for irritable bowel syndrome are not specific enough to rule out the diagnosis of microscopic colitis. Therefore, patients with suspected diarrhea-predominant irritable bowel syndrome should undergo biopsies of the colon to investigate for possible microscopic colitis if symptoms are not well controlled by antidiarrheal therapy.