Inflammatory Bowel Disease: Intestinal Problems (cont.)
What kind of malabsorption occurs in IBD?
Malabsorption means abnormal intestinal absorption. Crohn's disease usually affects the
small intestine, which is the part of the gut that absorbs most nutrients.
Remember that Crohn's disease involves the small bowel and/or the colon, while
ulcerative colitis involves
only the colon. Crohn's disease of the upper part (duodenum) and middle part (jejunum) of the
small intestine may interfere with the absorption of proteins, sugars, iron,
vitamins, and fats. This widespread malabsorption in Crohn's disease, which does not occur in
ulcerative colitis, may lead to weight loss and malnutrition. In addition, some unabsorbed
nutrients can cause the small or large intestine to secrete increased amounts of
liquid, which worsens the diarrhea in Crohn's disease. (As previously mentioned, diarrhea is
the most common symptom in patients with IBD, with or without the intestinal
complications.) The lower end (ileum) of the small intestine is the part of the
bowel most commonly involved in Crohn's disease. In ulcerative colitis, however, the function of the ileum is
normal. When the ileum is involved in patients with Crohn's disease (or surgically removed),
a decreased absorption of vitamin B12 may occur. If a deficiency of B12
develops, a particular type of anemia called pernicious anemia can result.
The ileum is also the major area for intestinal absorption of bile acids. The bile
acids are compounds that are secreted in the bile by the liver into the
duodenum. The major function of bile acids is to help transport and absorb fats,
mostly in the jejunum. Bile acids that are not absorbed by a diseased or removed
ileum pass into the colon. The bile acids then induce the colon to secrete
liquid, which aggravates the diarrhea. If the bile acids are not sufficiently
absorbed in the colon and consequently become deficient, fat malabsorption and
more diarrhea can result.
Extensive Crohn's disease, usually involving the surgical removal
of several intestinal segments over the years, can lead to a debilitating
condition known as short bowel syndrome. In this condition, the patients have
many of the intestinal complications of Crohn's disease, including severe malabsorption. They
can also suffer from the previously mentioned complications not directly
affecting the intestinal tract (extraintestinal). Additionally, these patients
frequently have certain other extraintestinal complications, such as
osteoporosis (thin or porous bones), osteomalacia (soft bones), gallstones, and
kidney stones.
How is malabsorption in IBD treated?
The treatment of malabsorption in patients with IBD includes medications to
treat the underlying intestinal inflammation. Decreasing the inflammation can
improve the intestinal absorption of the nutrients that were malabsorbed. The
malabsorption or deficiency of B12 may need to be treated by administering the
vitamin in the vein or into the muscle. Diarrhea that is induced by bile acids
can be treated with cholestyramine, a compound that works by binding the bile
acids.
Supplemental calories and nutrients may be administered as special liquid
diets. These so-called elemental diets are composed of proteins, carbohydrates,
vitamins, and fats that are broken down into smaller particles that are easier
for the intestine to absorb. Unfortunately, however, these diets often do not
smell or taste very good. Nevertheless, they can be administered through a small
tube inserted through the nose (enteral feeding). For patients who are unable to
tolerate any food or liquid by mouth or by enteral feeding, nutrition may need
to be given solely through the veins (total parenteral nutrition). Finally, a
small bowel transplant can now be done for patients with severe Crohn's disease or otherwise
unmanageable short bowel syndrome.
- The inflammatory bowel diseases (IBD) are Crohn's
disease (CD) and ulcerative colitis (UC). The intestinal complications of
Crohn's disease and ulcerative colitis differ because of the
characteristically dissimilar behaviors of the intestinal inflammation in
these two diseases.
- The intestinal complications of IBD are caused by
intestinal inflammation that is severe, widespread, chronic, and/or extends
beyond the inner lining (mucosa) of the intestines.
- While ulcerative colitis involves only the large
intestine (colon), Crohn's disease occurs throughout the gastrointestinal
tract, although most commonly in the lower part of the small bowel (ileum).
- Intestinal ulceration and bleeding are complications
of severe mucosal inflammation in both ulcerative colitis and Crohn's disease.
- Intestinal inflammation in Crohn's disease involves
the entire thickness of the bowel wall, whereas the inflammation in ulcerative
colitis is confined to the inner lining. Accordingly, complications such as
intestinal strictures, fistulas, and fissures are far more common in Crohn's
disease than in ulcerative colitis.
- Intestinal strictures and fistulas do not always
cause symptoms. Strictures, therefore, may not require treatment unless they
cause significant intestinal blockage. Likewise, fistulas may not require
treatment unless they cause significant abdominal pain, infection, external
drainage, or bypass of intestinal segments.
- Small intestinal bacterial overgrowth (SIBO) in
Crohn's disease can result from an intestinal stricture, is diagnosed by a
hydrogen breath test, and is treated with antibiotics.
- Because of an increased risk of colon cancer in
ulcerative colitis, yearly monitoring with colonoscopies and biopsies of the
colon for premalignant cells (dysplasia) and cancer is recommended for
patients after 8 to10 years of chronic inflammation of the colon (colitis).
- Narcotics, codeine, and anti-diarrheal medications
such as Lomotil and Imodium should be avoided during severe episodes of
colitis because they might induce a toxic megacolon.
- In Crohn's disease of the duodenum
and jejunum, malabsorption of nutrients can cause malnutrition, weight loss, and
diarrhea, whereas in Crohn's disease of the ileum, malabsorption of bile salts can cause
diarrhea and malabsorption of vitamin B12 can lead to anemia.
Last Editorial Review: 9/18/2005
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