A colorectal mosaic pattern might be an endoscopic feature of collagenous colitis.

Background And Aims: The endoscopic aspect of the colorectal mucosa in those patients with collagenous colitis is usually normal, or with non-specific changes. Until now it had never been related to a mucosal pattern of mosaic type. Our aim was to determine the diagnostic accuracy of the presence of mosaic pattern in the colorectal mucosa for collagenous colitis.

Methods: Patients who had undergone a colonoscopy with random biopsies performed in the diagnostic evaluation of chronic diarrhea between 2004 and 2008 were studied. We defined patients with chronic diarrhea and mosaic mucosal pattern as "cases", and patients with chronic diarrhea without mosaic pattern as "controls". The odds ratio (OR) of finding a collagenous colitis in view of a mosaic pattern in colon was determined; as well as sensitivity and specificity; positive and negative likelihood ratios (LR+, LR-), considering this finding as a diagnostic instrument for collagenous colitis.

Results: 252 patients who had undergone colonoscopy with biopsy due to chronic diarrhea were analyzed. In 6 patients, a mosaic pattern was identified in the colorectal mucosa. The histological diagnose of 36 of the 252 patients (14%) was microscopic colitis, 27 of which (11%) had collagenous colitis. The colonoscopy was found normal in 21 of these 27 patients; in 2 patients, congestion or petechiae was found in the rectum; and in 4 patients (15%), all women, a mosaic pattern was found in the rectosigmoid mucosa. The OR of this finding was 19.4 (CI 95% 3.9-95.4) for collagenous colitis. It had a sensitivity of 14.8% (CI 95% 6.8-20), a specificity of 99.1% (CI 95% 98.2-99.7), LR+ of 16.6 (CI 95% 3.7-76.4), and LR- of 0.86 (CI 95% 0.80-0.95) for a collagenous colitis.

Conclusion: The mosaic pattern in the colorectal mucosa of patients studied due to chronic diarrhea could be a distinguishing feature of collagenous colitis.