Lymphocytic colitis is diagnosed by correlating clinical and histologic findings.
Specimen: random biopsies from grossly normal colonic mucosa
Histologic features of lymphocytic colitis:
(1) lymphocytes within the epithelial cell layer along the surface and within the crypts
(2) degenerative changes in the epithelial cells (flattening, drop-out, etc)
(3) increase in inflammatory cells in the lamina propria consisting mostly of mononuclear cells
intraepithelial lymphocyte count =
= number of intraepithelial lymphocytes per 100 enterocytes
Confidence in the diagnosis of lymphocytic colitis correlates with the number of intraepithelial lymphocytes. Olesen et al required >= 20 lymphocytes per 100 surface epithelial cells for the diagnosis, but other authors accept smaller numbers ("paucicellular").
Things that are absent:
(1) absence of marked distortion in crypt architecture (crypts normal or mildly distorted)
(2) absence of a thickened subepithelial collagen layer (layer < 10 microns thick)
(3) absence of mucosal erosions, crypt abscesses and inflammatory pseudomembranes
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