Is microscopic colitis a missed diagnosis in diarrhea-predominant Irritable Bowel Syndrome?

BACKGROUND: There are controversies about the importance of biopsies of normal colon mucosa in the investigation of patients with diarrhea predominant irritable bowel syndrome (IBS). On the other hand, microscopic colitis may be missed based on normal colonoscopy and laboratory examination in this group of patients METHODS: The study took place in Alzahra and Noor hospitals and Poursina Hakim Research Institute, from 2002 to 2004. Eligible patients were those suffering from diarrhea for at least 4 weeks. A total of 138 patients were included in the study after meeting Rome criteria (II) with normal CBC, ESR, stool examination and no endoscopic abnormality. RESULTS: The histologic findings in 138 patients with diarrhea predominant IBS with mean age of 34.7 years (female 55.1% and male 44.9%) were as follows: 10 patients (7.2%) had collagenous colitis and 3 patients (2.2%) were compatible with lymphocytic colitis. No significant diagnostic histologic findings were seen in the rest of patients. Collagenous colitis was detected in 13% of right colon biopsies and in 10% of sigmoid and transverse colon biopsies. Noctumal diarrhea was found in 30% of collagenous colitis patients. CONCLUSIONS: Total colonoscopy and multiple biopsies in diarrhea predominant IBS patients are necessary for early diagnosis of microscopic colitis.