Microscopic colitis in patients with chronic diarrhea and normal colonoscopic findings in Southern China.

BACKGROUND AND OBJECTIVES: Microscopic colitis includes lymphocytic colitis and collagenous colitis. The entity is considered as an important cause for unknown chronic diarrhea, but rarely reported in China before. This study aimed to determine the prevalence of microscopic colitis in patients with chronic diarrhea and normal colonoscopy findings in Southern China, and to reveal the clinical feature of microscopic colitis in these patients.
METHODS: Patients with chronic diarrhea and normal colonoscopic findings were enrolled from three hospitals in Southern China from January, 2009 to June, 2010. Multiple colorectal biopsies were obtained in these patients and histological examination was underwent with hematoxyin and eosin stain, Masson's trichrome stain and immunohistochemistry for tenascin to screen lymphocytic colitis and collagenous colitis. The clinical symptom and risk factor of microscopic colitis were assessed by comparing with controls. The diagnostic overlap between microscopic colitis and irritable bowel syndrome or functional diarrhea was also analyzed.
RESULTS: Randomly mucosal biopsies were performed in 613 patients with chronic diarrhea and normal or near normal colonoscopic finding. Fifty-nine cases of lymphocytic colitis and 28 cases of collagenous colitis were found by histological examination. The rates of rheumatoid arthritis in lymphocytic colitis group (15.4 %) and collagenous colitis group (14.3 %) were significant higher than in control group (2.2 %). Rheumatoid arthritis was confirmed as the risk factor of microscopic colitis by logistic regression analysis. There was no difference on the symptoms among the controls, patients with lymphocytic colitis, and patients with collagenous colitis. There were 13.8 % (12/87) of patients with microscopic colitis fulfilled Rome III criteria of irritable bowel syndrome and 42.5 % (37/87) fulfilled the criteria of functional diarrhea.
CONCLUSIONS: Microscopic colitis is not an uncommon disorder in Chinese population. Rheumatoid arthritis is the risk factor of microscopic colitis. Microscopic colitis has a symptomatic overlap with irritable bowel syndrome and functional diarrhea. It is reasonable to obtain multiple biopsies in patients with chronic diarrhea when the mucosa grossly normal at colonoscopy.