The most common symptoms of Crohn disease include diarrhea and abdominal pain. Rectal bleeding, fever, weight loss, arthritis, and anemia are indications of moderate to severe disease. Some patients develop fistulas, or abnormal passages connecting the bowel to other organs, such as the bladder or the vagina (vagina). These often lead to abscesses (abscess) ( pus-filled cavities within tissues). The formation of fistulas and the thickening of the intestinal wall—to the point of obstruction—are the only microscopic findings that distinguish Crohn disease from ulcerative colitis, the other type of IBD. In Crohn disease the maximum damage to the intestine occurs beneath the mucosa, and lymphoid conglomerations, known as granulomata, are formed in the submucosa. In addition, Crohn disease attacks the perianal tissues more often than does ulcerative colitis. Crohn disease is diagnosed by a combination of methods, including blood and stool analysis and colonoscopy. Diagnosis may be confirmed by other methods, such as barium enema, which uses X-rays (X-ray) to examine the intestine following rectal insertion of a liquid barium contrast agent, and capsule endoscopy, which examines the intestines via a pill-sized video camera that is swallowed by the patient and transmits images to sensors attached to the patient's body as it passes through the digestive tract.

A combination of immunosuppressive and anti-inflammatory drugs (drug), including corticosteroids and aminosalicylic acid compounds, are used to treat Crohn disease. The drugs are effective both in treating acute episodes and in suppressing the disease over the long term. Depending on the circumstances, hematinics, vitamins (vitamin), high- protein diets, and blood transfusions (blood transfusion) are also used. Surgical resection of the portion of the large bowel affected is often performed. The entire colon may need to be removed and the small intestine brought out to the skin as an ileostomy, an opening to serve as a substitute for the anus.