One of the causes of chronic diarrhea is microscopic colitis; its etiology is unknown. Collagenous colitis and lymphocytic colitis are considered to be two histologically and clinically similar types of microscopic colitis. Histologic examination of a biopsy specimen is the only way to diagnose this entity because the colon appears normal during endoscopy. In addition, distribution of the lesions is nonuniform and has a relevant clinical implication. Is colonoscopy with biopsies from multiple sites the preferred method of diagnosing microscopic colitis, or is flexible sigmoidoscopy with biopsies limited to the left colon sufficient? Matteoni and associates conducted this study to determine if biopsies from the left colon could detect microscopic colitis, precluding the need for colonoscopy.

Patients diagnosed with collagenous or lymphocytic colitis between 1987 and 1999 were enrolled in the study if they had undergone a total colonoscopy and if biopsy specimens were available from the right colon (considered the right and transverse colon) and the left colon (considered the distal to the transverse colon).

Of 98 patients identified with microscopic colitis, 58 met inclusion criteria for analysis of distribution of disease; 24 patients had collagenous colitis and 34 had lymphocytic colitis. Of the 58 participants, 28 had previously undergone a barium enema or a colonoscopy (without biopsy) as part of an evaluation of chronic diarrhea; the results were normal. The current colonoscopy was being performed in this group to obtain biopsy specimens. Collagenous colitis was diagnosed from left colon biopsy specimens in all 24 patients with that diagnosis. Overall, the mean number of biopsies performed was 1.8 ± 0.8 from the descending colon, 1.1 ± 0.6 from the sigmoid colon and 1.0 ± 0.7 from the rectum. Lymphocytic colitis was diagnosed from left colon biopsy specimens in 33 of 34 patients. The mean number of biopsies performed was 1.3 ± 0.7 from the descending colon, 0.9 ± 0.5 from the sigmoid colon and 1.4 ± 0.8 from the rectum.

Colonoscopy is a commonly accepted part of an evaluation of persons with chronic diarrhea (in developed countries). Many patients with chronic diarrhea have previously undergone a colonoscopy (without biopsy) or barium enema with normal results. Of these patients, approximately 10 percent will have microscopic colitis. Based on the results of this study, the diagnosis of microscopic colitis would have been missed in one of 58 patients if a flexible sigmoidoscopy had been performed rather than a colonoscopy. This patient had a single left colon biopsy, and the authors suggest that it is likely the diagnosis would have been made by obtaining more biopsy specimens from the left side.

The authors conclude that the results of this study support the concept that microscopic colitis affects the entire colon. Flexible sigmoidoscopy with multiple biopsy sites from the left colon will detect almost all patients with microscopic colitis and may preclude the need for a colonoscopy.