Microscopic colitis is a common cause of watery diarrhea, particularly in the elderly. Although the incidence is comparable to ulcerative colitis and Crohn's disease, the etiology is unknown. Understanding the etiology of microscopic colitis is an important step in developing logical interventions to decrease the burden from microscopic colitis. This research could provide critical insights into the etiology of this poorly studied condition.

Microscopic colitis (MC) is a chronic condition that is a common cause of watery diarrhea, particularly in the elderly. The etiology is unknown but widely considered to be an abnormal immune reaction to luminal antigens in predisposed hosts. Drugs and autoimmunity have also been implicated. The aims of the study are: 1) To quantitatively classify microscopic colitis using image analysis microscopy to determine whether the degree of lymphocytic infiltration correlates with etiology, symptoms and prognosis. 2) To investigate the etiology of microscopic colitis by examining medical and lifestyle risk factors including medications, autoimmunity, diet, and smoking 3) To evaluate the association between the adherent microbial flora and MC to assess whether bacterial dysbiosis is linked to presence of MC. As an exploratory aim we will evaluate whether CYP2C19 polymorphisms are more common in purportedly drug-induced disease since the diverse drugs that have been associated with MC are all substrates for this gene.

To conduct the study the investigators will obtain detailed dietary, medical and lifestyle information on study subjects who undergo complete colonoscopy for diarrhea. The investigators will obtain colon biopsies from the right, transverse and left colon to evaluate adherent bacterial organisms. The investigators will draw blood to evaluate CYP2C19 polymorphisms and for future genetic studies. The prospective design corrects important limitations of prior research on MC. Successful completion of the study aims will improve the understanding of risk factors, set the stage for more scientifically grounded future research, and potentially suggest new interventions for a disease that is currently poorly understood.

Inclusion Criteria:

Colonoscopy for diarrhea

Exclusion Criteria:

1. Fewer than 4 loose bowel movements per day.
2. Failure to visualize the entire colon to the cecum or preparation less than good or excellent.
3. Age under 35 years. There will be no upper age limit.
4. Inability to understand and cooperate with the interview.
5. Indication for colonoscopy other than diarrhea.
6. Prior history of inflammatory bowel disease (Crohn's disease or ulcerative colitis).

Patients who undergo colonoscopy for diarrhea at the University of North Carolina