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Tests and diagnosis
By Mayo Clinic staffYour doctor will likely start the diagnostic process by culturing your stool to rule out an infectious cause of the watery diarrhea.
Your doctor may also refer you to a specialist to perform either a colonoscopy or a flexible sigmoidoscopy. Both of these tests involve threading a tube through your rectum and into your colon, allowing your doctor to view the interior of your large intestine with the help of a small camera on the tip of the instrument. Because the colonoscopy tube is inserted into the entire length of the colon, rather than simply the first one-third of the colon as in a sigmoidoscopy, a colonoscopy is more thorough.
These tests may be as important in ruling out other conditions as in making a definitive diagnosis of collagenous colitis or lymphocytic colitis. In fact, if either disorder is present, the inflammation that results won't be visible during an examination of the colon's lining; the colon looks normal during these exams. However, when these diseases are suspected, biopsies of the colon can be performed as part of the colonoscopy or sigmoidoscopy.
During the biopsy, small samples of tissue from your colon are removed and sent to a laboratory for evaluation under a microscope — hence, the umbrella term "microscopic colitis." Because the inflammation can occur in patches rather than along the entire length of the large intestine, tissue in several areas of the colon needs to be evaluated. The findings of the lab examination can differentiate between the two conditions:
- If you have collagenous colitis, the doctor evaluating the biopsy (pathologist) will see an increase in the thickness of a nonelastic, protein band of connective tissue (collagen) inside the colon lining.
- If you have lymphocytic colitis, the laboratory analysis will reveal an increased level in the number of specialized white blood cells (lymphocytes) found between the cells that line the large intestine. However, unlike with collagenous colitis, there are no apparent changes in the collagen.
Without biopsies, these conditions can be misdiagnosed as other digestive conditions such as irritable bowel syndrome (IBS). In most cases, IBS has a long-term course of alternating constipation and diarrhea, while collagenous colitis and lymphocytic colitis are characterized primarily by diarrhea.
Blood tests aren't usually helpful in diagnosing collagenous colitis and lymphocytic colitis, because findings tend to be normal. The same is true with tests of urine and stool samples. However, your doctor may use blood tests to check for celiac disease, which is associated with both collagenous colitis and lymphocytic colitis.
Because the treatment for collagenous colitis and lymphocytic colitis are the same, many doctors believe it's not crucial to differentiate between them as part of the diagnostic process. However, your doctor will want to eliminate other conditions affecting the colon as a possible diagnosis.
- Collagenous Colitis and Lymphocytic Colitis. National Digestive Diseases Information Clearinghouse. http://digestive.niddk.nih.gov/ddiseases/pubs/collagenouscolitis/. Accessed Aug. 12, 2008.
- Collagenous Colitis and Lymphocytic Colitis. Merck Manual. http://www.merck.com/mmhe/sec09/ch126/ch126d.html. Accessed Aug. 12, 2008.
- Dietrich CF. Lymphocytic and collagenous colitis (microscopic colitis). http://www.uptodate.com/patients/content/topic.do?topicKey=inflambd/5666. Accessed Aug. 12, 2008.
- Wall, Geoffrey C. Pharmacotherapy for Microscopic Colitis. Pharmacotherapy. 2007;27(3):425-433.http://www.medscape.com/viewarticle/555432_1. Accessed Aug. 12, 2008.
- Colitis: A cause of persistent diarrhea in older adults. Mayo Clinic Health Letter.Vol. 25, No. 3, March 2007.
- Antidiarrheal Medicines: OTC Relief for Diarrhea. American Academy of Family Physicians. http://familydoctor.org/online/famdocen/home/otc-center/otc-medicines/855.html#ArticleParsysMiddleColumn0010. Accessed Aug. 12, 2008.
