collagenous colitis

Definition: Collagenous colitis is a subtype of microscopic colitis .

Images

 collagenous colitis

• https://twitter.com/smlungpathguy/status/853997959943528448

Microscopy

 Patchy thickening of subepithelial basement membrane

• thickness : 10 microns or more / 0.01 mm (thickest in transverse colon);
• often spares rectosigmoid;
• lower border of collagen is irregular,
• extends into lamina propria and encircles capillaries,
• may be difficult to measure

 Also increased chronic inflammatory cells (lymphocytes, plasma cells, eosinophils) in lamina propria and within surface epithelium (20+ lymphocytes per 100 epithelial cells)
 Epithelial damage is demonstrated by loss of mucin and irregular orientation of nuclei
 Usually no neutrophilic infiltration, no atrophy, no mucosal architectural distortion
6+ intraepithelial lymphocytes per 100 epithelial cells in terminal ileum is 98% specific and 50-60% sensitive for collagenous/lymphocytic colitis (Am J Surg Pathol 2002;26:1484)
 Increased connective tissue growth factor expression; may be end stage mediator of local fibrosis (Histopathology 2010;57:427)

Diagnosis

 do not base on thickness of collagen, but distorted superficial cell arrangement with areas of epithelial denudation and inflammatory cells in superficial epithelium and the lamina propria;

• Lazenby’s statement: "Focusing solely on the collagen band can result in both over- and underdiagnosis" (Am J Clin Pathol 2008;130:375)

Differential diagnosis

 Chronic ischemic damage: fibrosis in lamina propria
 Lymphocytic colitis: no collagen
 Nonspecific changes
 Scleroderma: affects muscularis propria
 Solitary rectal ulcer syndrome: mucosal architectural distortion, variable collagen deposits but no intraepithelial lymphocytes
 Tangential sectioning of subepithelial basement membrane (lacks inflammation)

Variants

 pseudomembranous collagenous colitis (14508399)

References

 Goldstein NS, Gyorfi T. Focal lymphocytic colitis and collagenous colitis: patterns of Crohn’s colitis? Am J Surg Pathol. 1999 Sep;23(9):1075-81. PMID: 10478667