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Lymphocytic Colitis (cont.)

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What diseases are not colitis?

Patients with irritable bowel syndrome (IBS) do not have colitis, even though they are sometimes referred to as having "spastic colitis," but they frequently have symptoms that mimic colitis such as diarrhea, abdominal pain and mucous in stool. Nevertheless, there is no inflammation of the colon (not even microscopic colitis) in patients with IBS. The cause of symptoms in IBS is not clearly known; it may be caused by either abnormal motility (abnormal contractions) of the intestinal muscles or abnormally sensitive nerves in the intestines (visceral hypersensitivity).

What is microscopic colitis?

Microscopic colitis refers to inflammation of the colon that is only visible when the colon's lining is examined under a microscope. The appearance of the inner colon lining in microscopic colitis is normal by visual inspection during colonoscopy or flexible sigmoidoscopy. The diagnosis of microscopic colitis is made when a doctor, while performing colonoscopy or flexible sigmoidoscopy, takes biopsies (small samples of tissue) of the normal-appearing lining, and then examines the biopsies under a microscope.

There are two types of microscopic colitis; lymphocytic colitis and collagenous colitis. In lymphocytic colitis, there is an accumulation of lymphocytes (a type of white blood cell) within the lining of the colon. In collagenous colitis, there is an additional layer of collagen (scar tissue) just below the lining. Some experts believe that lymphocytic colitis and collagenous colitis represent different stages of the same disease.

The inflammation and the collagen probably interfere with absorption of water from the colon, and cause the diarrhea.

What are the symptoms of microscopic colitis?

The primary symptom of microscopic colitis is chronic, watery diarrhea. Patients with microscopic colitis can have diarrhea for months or years before the diagnosis is made. This chronic diarrhea of microscopic colitis is different from the acute diarrhea of infectious colitis, which typically lasts only days to weeks. Some patients with microscopic colitis also may report mild abdominal cramps and pain. Blood in the stool is unusual.

How common is microscopic colitis and who is at risk?

The prevalence of microscopic colitis in the U.S. is not clearly known. It is estimated that 10-20% of patients with chronic diarrhea may have microscopic colitis. It is this author's experience, that the condition is becoming more common in recent years. It is not clear, however, whether there is an actual increase in the frequency of microscopic colitis or whether doctors are just better at diagnosing it.

Microscopic colitis most commonly occurs in middle aged to elderly patients and is more common among women than men.

What causes microscopic colitis?

The cause(s) of microscopic colitis is unknown. Some doctors suspect that microscopic colitis is an autoimmune disorder similar to the autoimmune disorders that cause chronic ulcerative colitis and Crohn's disease. (Please read the Ulcerative Colitis and Crohn's disease articles for more detailed discussion.)

One study has implicated long term (longer than 6 months) use of nonsteroidal antiinflammatory drugs (NSAIDs) as a cause of microscopic colitis. Some patients' diarrhea improves after stopping the NSAIDs.



Next: How is microscopic colitis diagnosed? »

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