Collagenous colitis

Collagenous colitis
Micrograph of collagenous colitis. H&E stain.
Specialty	Gastroenterology

Collagenous colitis is an inflammatory condition of the colon. Together with the related condition lymphocytic colitis, it is a subtype of microscopic colitis, which is characterized by inflammation that specifically affects the colon (i.e. colitis), and a clinical presentation that involves watery diarrhea but a lack of rectal bleeding. Microscopic colitis does not usually cause macroscopic changes to the colon that allow a visual diagnosis during colonoscopy, instead causing microscopic changes that can be detected through histopathological examination of colonic biopsies. The nature of these microscopic changes is what differentiates collagenous from lymphocytic colitis, with the characteristic finding in collagenous colitis being depositions of collagen in the connective tissue between the colonic glands.^[1] Collagenous colitis, and microscopic colitis as a whole, is sometimes considered to be an inflammatory bowel disease (IBD) along with Crohn's disease and ulcerative colitis. However, little is known about the etiology of microscopic colitis, and so the degree of similarity to the inflammatory bowel diseases is uncertain.^[1][2]

Although cases are known to occur in all age groups, the disease is most frequently diagnosed in late middle aged or elderly people, with the average person being diagnosed in their 60s. Women are more frequently affected than men, with different studies finding female-male incidence ratios of between 3 and 8. Epidemiological studies have found large increases in diagnosed cases of microscopic colitis, of which collagenous colitis cases are a majority, over the past few decades, with cases of microscopic colitis now outnumbering those of Crohn's disease and ulcerative colitis at least in some regions.^[3][4]