Diarrhea (cont.)
What are common causes of chronic diarrhea?
Irritable bowel syndrome. The
irritable bowel syndrome (IBS) is a
functional cause of diarrhea or constipation.
Inflammation does not typically exist in the affected bowel. (Nevertheless,
recent information suggests that there MAY be a component of inflammation in
IBS.) It may be caused by several different underlying problems, but it is
believed that the most common cause is rapid passage of the intestinal contents
through the colon.
Infectious diseases. There
are a few infectious diseases that can cause chronic diarrhea, for
example, Giardia lamblia . Patients with
AIDS often have chronic infections of their intestines that cause diarrhea.
Bacterial overgrowth of the small intestine. Because of small intestinal
problems, normal colonic bacteria may spread from the colon and into the small
intestine. When they do, they are in a position to digest food that the small
intestine has not had time to digest and absorb. The mechanism that leads to the
development of diarrhea in bacterial overgrowth is not known.
Post-infectious. Following acute viral, bacterial or parasitic
infections, some individuals develop chronic diarrhea. The cause of this type of
diarrhea is not clear, but some of the individuals have
bacterial overgrowth of
the small intestine. This condition also is referred to as post-infectious IBS.
Inflammatory bowel disease (IBD). Crohn's disease and
ulcerative
colitis, diseases causing inflammation of the small intestine and/or colon,
commonly cause chronic diarrhea.
Colon cancer. Colon cancer can cause either
diarrhea or constipation. If the cancer blocks the passage of stool,
it usually causes constipation. Sometimes, however, there is secretion of water behind the
blockage, and liquid stool from behind the blockage leaks around the cancer and
results in diarrhea. Cancer, particularly in the distal part of the colon, can
lead to thin stools. Cancer in the rectum can lead to a sense of incomplete
evacuation.
Severe constipation. By blocking the colon, hardened stool can lead to
the same problems as colon cancer, as discussed previously.
Carbohydrate (sugar) malabsorption. Carbohydrate or
sugar malabsorption is an inability to digest and absorb sugars. The most well-recognized
malabsorption of sugar occurs with lactase deficiency (also known as
lactose
or milk intolerance) in which milk products containing the milk sugar,
lactose, lead to diarrhea. The lactose is not broken up in the intestine because
of the absence of an intestinal enzyme, lactase, that normally breaks up
lactose. Without being broken up, lactose cannot be absorbed into the body. The
undigested lactose reaches the colon and pulls water (by osmosis) into the
colon. This leads to diarrhea. Although lactose is the most common form of sugar
malabsorption, other sugars in the diet also may cause diarrhea, including
fructose and sorbitol.
Fat malabsorption. Malabsorption of fat is the inability to digest or
absorb fat. Fat malabsorption may occur because of reduced pancreatic secretions
that are necessary for normal digestion of fat (for example, due to pancreatitis
or pancreatic cancer) or by diseases of the lining of the small intestine that
prevent the absorption of digested fat (for example, celiac disease). Undigested
fat enters the last part of the small intestine and colon where bacteria turn it
into substances (chemicals) that cause water to be secreted by the small
intestine and colon. Passage through the small intestine and colon also may be
more rapid when there is malabsorption of fat.
Endocrine diseases. Several endocrine diseases (imbalances of hormones) may cause
diarrhea, for example, an over-active thyroid gland (hyperthyroidism) and an
under-active pituitary or adrenal gland (Addison's disease).
Laxative abuse. The abuse of laxatives by individuals who want attention or
to lose weight is an occasional cause of chronic diarrhea.
Next: What are the complications of diarrhea? »
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