Crohn's Disease

Crohn's disease is a chronic (ongoing) disorder that causes inflammation of the digestive or gastrointestinal (GI) tract. Although it can involve any area of the GI tract from the mouth to the anus, it most commonly affects the small intestine and/or colon.

The disease is named after Dr. Burrill B. Crohn. In 1932, Dr. Crohn and two colleagues, Dr. Leon Ginzburg and Dr. Gordon D. Oppenheimer, published a landmark paper describing the features of what is known today as Crohn's disease. Crohn's and a related disease, ulcerative colitis, are the two main disease categories that belong to a larger group of illnesses called inflammatory bowel disease (IBD).

Because the symptoms of these two illnesses are so similar, it is sometimes difficult to establish the diagnosis definitively. In fact, approximately 10 percent of colitis cases are unable to be pinpointed as either ulcerative colitis or Crohn's disease and are called indeterminate colitis.

Both illnesses do have one strong feature in common. They are marked by an abnormal response by the body's immune system. The immune system is composed of various cells and proteins. Normally, these protect the body from infection. In people with Crohn's disease, however, the immune system reacts inappropriately. Researchers believe that the immune system mistakes microbes, such as bacteria that is normally found in the intestines, for foreign or invading substances, and launches an attack. In the process, the body sends white blood cells into the lining of the intestines, where they produce chronic inflammation. These cells then generate harmful products that ultimately lead to ulcerations and bowel injury. When this happens, the patient experiences the symptoms of IBD.

Although Crohn's disease most commonly affects the end of the small intestine (the ileum) and the beginning of the large intestine (the colon), it may involve any part of the GI tract. In ulcerative colitis, on the other hand, the GI involvement is limited to the colon. In Crohn's disease, all layers of the intestine may be involved, and there can be normal healthy bowel in between patches of diseased bowel. In contrast, ulcerative colitis affects only the superficial layers (the mucosa) of the colon in a more even and continuous distribution, which starts at the level of the anus.