Purpose The diagnosis microscopic colitis (MC) consisting of collagenous colitis (CC)
and lymphocytic colitis (LC) relies on histological assessment of mucosal biopsies
from the colon. The optimal biopsy strategy for reliable diagnosis of MC is controversial.
The aim of this study was to evaluate the distribution of histopathological features
of MC throughout the colon. Methods Mucosal biopsies from multiple colonic segments
of patients with MC who participated in one of the three prospective European multicenter
trials were analyzed. Histological slides were stained with hematoxylin-and-eosin,
a connective tissue stain, and CD3 in selected cases. Results In total, 255 patients
were included, 199 and 56 patients with CC and LC, respectively. Both groups exhibited
a gradient with more pronounced inflammation in the lamina propria in the proximal
colon compared with the distal colon. Similarly, the thickness of the subepithelial
collagenous band in CC showed a gradient with higher values in the proximal colon.
The mean number of intraepithelial lymphocytes was > 20 in all colonic segments in
patients within both subgroups. Biopsies from 86 to 94% of individual segments were
diagnostic, rectum excluded. Biopsies from non-diagnostic segments often showed features
of another subgroup of MC. Conclusion Conclusively, although the severity of the histological
changes in MC differed in the colonic mucosa, the minimum criteria required for the
diagnosis were present in the random biopsies from the majority of segments. Thus,
our findings show MC to be a pancolitis, rectum excluded, questioning previously proclaimed
patchiness throughout the colon.
