[Functional diarrheas are not, in most cases, minor clinical forms of lymphocytic or collagenous colitis]

The aim of the study was to test the hypothesis that some patients with functional diarrhea could actually suffer from a mild clinical pattern of collagenous or lymphocytic colitis.

Twenty consecutive patients with chronic diarrhea were included in the study if the colonic mucosa appeared normal during colonoscopy. From multiple colonic biopsies were established a conventional histological diagnosis and a quantitative histological diagnosis. This latter diagnosis was based on the semiquantitative evaluation of epithelial morphological alterations and lamina propria monocellular infiltration, and on the determination of both intraepithelial lymphocyte count and subepithelial collagen layer thickness. Multiple colonic biopsies from 12 control patients without diarrhea were analyzed according to the same protocol.

Among the 20 patients with diarrhea, the quantitative diagnosis of collagenous colitis was made in 3 patients (thickness of the collagen band between 11 and 26 microns) and the diagnosis of lymphocytic colitis in one (21% of intraepithelial lymphocytes). The percentage of intraepithelial lymphocytes did not differ between the 16 remaining patients and the controls (12 +/- 5% and 9 +/- 4%, respectively). Similarly, the score of surface epithelial damage and the score of lamina propria infiltration in patients with diarrhea (1.2 +/- 1.0 et 1.7 +/- 1.5) were not different from the values in the control group (1.3 +/- 1.3 et 1.5 +/- 1.2). The mean fecal weight in patients with diarrhea but without colitis was 161 +/- 130 g/d. All the values of fecal weight were below 300 g/d, except in one patient with a past history of truncular vagotomy.

These results suggest that most of the patients with functional diarrhea do not suffer from mild clinical patterns of collagenous or lymphocytic colitis.