Lymphocytic Colitis (cont.)
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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