Crohn's Disease is a chronic inflammatory disease of the alimentary tract and it can involve any part of it - from the mouth to the anus. It typically affects the terminal ileum and well demarcated areas of large bowel with relatively normal bowel disease. It is often associated with auto-immune disorders outside the bowel, such as mouth ulcers and rheumatoid arthritis. Given the high incidence of irritable bowel syndrome among Americans, this can also be a complicating factor.

Crohn's patients typically suffer from chronic diarrhea and disrupted digestion, making it difficult for sufferers in the acute phase of the disease to eat and/or digest food. The inflammation can be extremely painful and debilitating. Other common complications of Crohn's include fistulas of the colon, hemorrhoids, lipid, absorption problems, and anemia.

The disease typically first appears in a sufferer by age 30 or so, though it is not unknown for symptoms to first appear quite late in life. It quite commonly appears in childhood. Some estimates suggest that up to 1,000,000 Americans have the disease, suggesting that the prevalence of it is around 1 in 300. Some ethnic groups have significantly higher rates of prevalence than others. Increased rates of disease have also been noted in some families, leading to speculation of a possible genetic link, especially in the HLA-B27 MHC allele. Epidemiological research indicates that Crohn's is a disease of civilization, in other words, the incidence of the disease is much higher in industrialized countries than elsewhere.

The disease has long been suspected of being due to a Mycobacterium because of the similarity of many features to human tuberculosis and veterinary Ovine Jonnes Disease, but to date no specific organism has been detected. It is probably a combination of an infection from one or several organisms together with an altered immune response. A class of organisms know as "cell wall-deficient bacteria," which can prime autoimmune reactions, is a current topic of research.

The bowel shows segmental "hose pipe" thickening and shows full thickness chronic inflammation, giant cell granulomas, and fissures with acute inflammation. Fistula formation is quite common in Crohn's. Bowel obstruction is a known complication which may require surgical resection. Approximately 50% of surgical cases require additional surgery within five years because the disease tends to reappear at the site where the bowel was rejoined, and some patients eventually develop short bowel syndrome which makes it extremely difficult to digest food. For this reason, surgery is considered by many doctors only as a last resort in the treatment of Crohn's.

There is currently no cure for Crohn's; treatment for Crohn's disease is mainly symptomatic. Some patients find some foods (such as foods high in fiber, and dairy foods) make their symptoms worse, but the disease cannot be controlled simply through diet modifications. Therapies include treatment with anti-inflammatory drugs that act in the intestines, and, if symptoms cannot be controlled with other drugs, with steroids (although long-term steroid therapy is discouraged because of its well-known side effects).

A well-established group of drugs, especially in the mild-to-moderate disease,
are salicylates -  5-ASA derivates - 5-aminosalicylic acid compounds such
as sulfasalazine (brand name Asacol), mesalamine (brand nams Pentasa), olsalazine, and balsalazide.  Immunomodulating drugs such as azathioprine and mercaptopurine as well as infliximab (brand name Remicade) are given mainly in moderate-to-severe cases. Research trials are being conducted on treatment with drugs in the same family as thalidomide.

Some patients can be treated with the existing drugs quite effectively and can go into long-term remission, sufficient to allow the sufferer to lead a normal life. Patients are at somewhat larger risk of colon cancers, and should have regular colonoscopies both to check for precancerous growths and to monitor the success of treatment. It does not seem to have as great a risk of malignancy compared to ulcerative colitis.

Crohn's disease and ulcerative colitis are quite distinct diseases but in practice there are sometimes difficulties distinguishing between them, especially in mild cases - these are usually simply classified as "chronic inflammatory bowel disease".

Crohn's disease is often misdiagnosed as food poisoning, gastroenteritis, appendicitis (due to the common locus of pain in the lower right-hand quadrant of the abdomen), and irritable bowel syndrome.

Crohn's disease was first described by Giovanni Battista Morgagni (1682-1771), and subsequent cases were described by John Berg in 1898, and by Polish surgeon Antoni Leśniowski in 1904. Scottish physician T. Kennedy Dalziel described nine cases in 1913. Burrill Bernard Crohn, an American gastroenterologist, described fourteen cases in 1932, characterizing the disease as "Terminal ileitis: A new clinical entity"; the description was changed to "Regional ileitis" on publication. It is by virtue of alphabetization rather than contribution that Crohn's name appeared as first author: because this was the first time the condition was reported in a widely-read journal, and the disease has come to be known as Crohn's disease for reasons of publicity rather than precedence.

In Poland the disease is known as Leśniowski-Crohn disease.

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See also: Gastroenterology