Crohn's Disease
Medical Revising Author:
Dennis Lee, MD
Medical Revising Editor: Jay W. Marks, MD
Previous contributing author: Lori Kam, MD
What is Crohn's disease?
Crohn's disease is a chronic inflammatory disease of the intestines. It
primarily causes ulcerations (breaks in the lining) of the small and large
intestines, but can affect the digestive system anywhere from the mouth to the
anus. It is named after the physician who described the disease in 1932. It also
is called granulomatous enteritis or colitis, regional enteritis, ileitis, or
terminal ileitis.
Crohn's disease is related closely to another chronic inflammatory condition
that involves only the colon called ulcerative colitis. Together, Crohn's disease and ulcerative colitis are
frequently referred to as inflammatory bowel disease (IBD).
Ulcerative colitis and Crohn's disease have no medical cure. Once the diseases begin, they tend to
fluctuate between periods of inactivity (remission) and activity (relapse). They
affect approximately 500,000 to two million people in the United States. Men and
women are equally affected. IBD most commonly begins during adolescence and
early adulthood, but it also can begin during childhood and later in life.
Crohn's disease tends to be more common in relatives of patients with Crohn's
disease. It also is more common among relatives of patients with ulcerative
colitis.
What causes Crohn's disease?
The cause of Crohn's disease is unknown. Some scientists suspect that
infection by certain bacteria, such as strains of mycobacterium, may be the
cause of Crohn's disease. To date, however, there has been no convincing
evidence that the disease is caused by infection. Crohn's disease is not
contagious. Although diet may affect the symptoms in patients with Crohn's
disease, it is unlikely that diet is responsible for the disease.
Activation of the immune system in the
intestines appears to be important in IBD. The immune system
is composed of immune cells and the proteins that these immune cells produce.
Normally, these cells and proteins defend the body against harmful bacteria, viruses,
fungi, and other foreign invaders. Activation of the immune system causes inflammation
within the tissues where the activation occurs. (Inflammation is an important
mechanism of defense used by the immune system.)
Normally, the immune system is activated only when the body is exposed to
harmful invaders. In patients with IBD, however, the immune system is abnormally
and chronically activated in the absence of any known invader. The continued
abnormal activation of the immune system results in chronic inflammation and
ulceration. The susceptibility to abnormal activation of the immune system is
genetically inherited. Thus, first degree relatives (brothers, sisters,
children, and parents) of patients with IBD are more likely to develop these
diseases. Recently a gene called NOD2 has been identified as being associated
with Crohn's disease. This gene is important in determining how the body
responds to some bacterial products. Individuals with mutations in this gene are
more susceptible to developing Crohn's disease.
Next: How does Crohn's disease affect the intestines? »
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