The precise cause of Crohn's disease is not known. The disease occurs when the immune system
attacks the gastrointestinal tract; for this reason, Crohn's disease is considered an autoimmune disease
. This autoimmune activity produces inflammation in the gastrointestinal tract. For this reason, Crohn's disease is classified as an inflammatory bowel disease
Like many other autoimmune diseases, Crohn's disease is believed to be genetically linked. The highest risk occurs in individuals with siblings who have the disease. Males and females are equally affected. Smokers are three times more likely to develop Crohn's disease.
[/suP] Crohn disease affects between 400,000 and 600,000 people in North America.
estimates for Northern Europe have ranged from 27â€“48 per 100,000.
[/suP] Crohn disease tends to present initially in the teens and twenties, with another peak incidence in the fifties to seventies, although the disease can occur at any age.
The disease was independently described in 1904 by Polish surgeon Antoni Lesniowski
and in 1932 by American gastroenterologistBurrill Bernard Crohn
, for whom the disease was named. Crohn, along with two colleagues, described a series of patients with inflammation of the terminal ileum
, the area most commonly affected by the illness.
[/suP] For this reason, the disease has also been called regional ileitis
[/suP] or regional enteritis.
Crohn's disease is generally classified as an autoimmune disease
. It invariably affects the gastrointestinal tract, most gastroenterologists categorize the presenting disease by the affected areas. Ileocolic
Crohn's disease, which affects both the ileum
(the last part of the small intestine
that connects to the large intestine
) and the large intestine, accounts for fifty percent of cases. Crohn's ileitis, affecting the ileum only, accounts for thirty percent of cases, and Crohn's colitis, affecting the large intestine, accounts for the remaining twenty percent of cases, and may be particularly difficult to distinguish from ulcerative colitis
. The disease can attack any part of the digestive tract, from mouth
. However, individuals affected by the disease rarely fall outside these three classifications, being affected in other parts of the gastrointestinal tract such as the stomach
[/suP] Crohn's disease may also be categorized by the behaviour of disease as it progresses. This was formalized in the Vienna classification of Crohn's disease.
[/suP] There are three categories of disease presentation in Crohn's disease: stricturing, penetrating, and inflammatory
. Stricturing disease causes narrowing of the bowel which may lead to bowel obstruction
or changes in the caliber of the feces
. Penetrating disease creates abnormal passageways (fistulae
) between the bowel and other structures such as the skin. Inflammatory disease (or non-stricturing, non-penetrating disease) causes inflammation without causing strictures or fistulae.