Crohn's disease is a form of inflammatory bowel disease (IBD), which involves ongoing (chronic) inflammation of the gastrointestinal tract. Crohn's-related inflammation usually affects the intestines, but may occur anywhere from the mouth to the anus (the end of the rectum).

See also: Ulcerative colitis

While the exact chain of events that lead to Crohn's disease is unknown, the condition is linked to a problem with the body's immune system response. Normally the immune system helps protect the body from harmful substances. But in patients with Crohn's disease and other types of inflammatory bowel disease (IBD), the immune system can't tell the difference between good substances and foreign invaders. The result is an overactive immune response that leads to chronic inflammation. This is called an autoimmune disorder.

There are five different types of Crohn's disease:

• Ileocolitis is the most common form. It affects the lowest part of the small intestine (ileum) and the large intestine (colon).
• Ileitis affects the ileum.
• Gastroduodenal Crohn's disease causes inflammation in the stomach and first part of the small intestine, called the duodenum.
• Jejunoileitis causes spotty patches of inflammation in the top half of the small intestine (jejunum).
• Crohn's (granulomatous) colitis only affects the large intestine.

A person's genes and environmental factors seem to play a role in the development of Crohn's disease.

The inflammation related to Crohn's disease frequently occurs at the end of the small intestine that joins the large intestine, but it may occur in any area of the digestive tract. There can be healthy patches of tissue in between diseases areas. The ongoing inflammation causes the intestinal wall to become thick.

The disease may occur at any age, but it usually occurs in persons between ages 15 and 35. Risk factors include a family history of Crohn's disease, Jewish ancestry, and smoking.

Symptoms depend on what part of the gastrointestinal tract is affected. Symptoms range from mild to severe, and can come and go with periods of flare-ups.

The main symptoms of Crohn's disease are:

• Crampy abdominal (belly area) pain
• Persistent, watery diarrhea
• Fever
• Fatigue

Other symptoms may include:

• Rectal bleeding and bloody stools
• Loss of appetite
• Unintentional weight loss
• Constipation
• Abdominal fullness and gas
• Gastrointestinal bleeding
• Foul-smelling stools
• Tenesmus (pain with passing stool)
• Fistulas (usually around the rectal area, may cause draining of pus, mucus, or stools)
• Liver inflammation
• Joint pain
• Skin rash
• Swollen gums
• Eye inflammation
• Kidney stones
• Clotting problems (deep vein thrombosis)

A physical examination may reveal an abdominal mass or tenderness, skin rash, swollen joints or mouth ulcers. The doctor may use a stethoscope to listen to the belly area. Abdominal sounds (borborygmus, a gurgling or splashing sound heard over the intestine) may be heard.

Tests to diagnose Crohn's disease include:

• Endoscopy
• Colonoscopy
• Sigmoidoscopy with small bowel biopsy
• Small bowel x-ray series
• Barium enema
• Upper GI series
• Stool guaiac test

A stool culture may be done to rule out other possible causes of the symptoms.

This disease may also alter the results of the following tests:

• Fecal fat
• Liver function tests
• Albumin