Collagenous and Lymphocytic Colitis

Collagenous colitis (CC) was described concurrently in 1976 by Lindstrom and by Freeman. In 1980, Read described microscopic colitis, which is clinically indistinguishable from CC but is differentiated from it by colonic biopsy features. Later, the term lymphocytic colitis (LC) was proposed by Lazenby to replace the term microscopic colitis and to distinguish it from infectious colitis and inflammatory bowel disease (ulcerative colitis and Crohn disease). The term microscopic colitis is now used to describe both CC and LC, and these conditions should be considered in any patient with unexplained nonbloody diarrhea. Patients undergoing either sigmoidoscopy or colonoscopy for unexplained diarrhea who have normal endoscopic findings should have biopsy samples taken to diagnose or rule out either form of microscopic colitis.

LC and CC are relatively rare conditions that are diagnosed when a patient with chronic watery nonbloody diarrhea has an endoscopically or radiographically normal colon, but colonic biopsies show unique inflammatory changes. Because the mucosa is not ulcerated or otherwise disrupted, the diarrhea generally does not contain blood or pus.

• The characteristic feature of LC is an infiltration of lymphocytes into the colonic epithelium. CC shares this feature but additionally shows a distinctive thickening of the subepithelial collagen table. LC and CC have been suggested to represent different phases of a single pathophysiologic process, with LC possibly being a precursor or earlier phase of CC; however, this has not been proven.

• The diarrhea in CC is more likely due to the inflammatory process than to the subepithelial collagen layer, although this layer may serve as a cofactor in the role of a diffusion barrier.

• Increased levels of immunoreactive prostaglandin E2 in stool water may contribute to a secretory diarrhea.

• Some patients with CC and concurrent collagenous infiltration of the duodenum and/or the ileum have demonstrated altered small bowel dysfunction, demonstrated by reduced D-xylose absorption.

• Some individuals have bile acid malabsorption demonstrated by the Se-75-homotaurocholate (SeHCAT) test, in which a positive test result is shown by retention of less than 11% of the administered dose of radioactivity after 7 days.

• Some patients with CC may have increased mucosal secretion of vascular endothelial growth factor, a fibrosis-enhancing peptide.

United States

True incidence is not known. The disease has been increasingly diagnosed over the past 20 years, but it is still uncommon. A recently published population-based study found the incidence of microscopic colitis to increase significantly from 1.1 per 100,000 persons in the late 1980s to 19.6 per 100,000 persons by the end of 2001. Rates increased with age. Prevalence at the end of the study period was 103.0 per 100,000 persons (39.3 for CC and 63.7 for LC).

Morbidity is limited to the consequences of diarrhea and malabsorption, including metabolic abnormalities such as hypokalemia and dehydration, weight loss, fatigue, and vitamin deficiencies. This is not considered a life-threatening condition; however, profuse watery diarrhea may lead to severe dehydration and electrolyte abnormalities requiring intensive resuscitation.

LC affects similar numbers of men and women, while CC is up to 20 times more frequent in women than in men.

Both conditions are observed most commonly in people older than 40 years, with peak incidence in the sixth and seventh decades of life, and the incidence of both conditions increases with age. Isolated cases have been reported in younger populations, including children.