Inflammatory Bowel Disease: Intestinal Problems (cont.)

Some intestinal complications of IBD occur in both ulcerative colitis and Crohn's disease. For example, ulceration of the inflamed inner intestinal lining (mucosa), which causes abdominal pain and intestinal bleeding, may complicate both diseases. Since both ulcerative colitis and Crohn's disease involve the colon, complications that are associated with the colon, such as toxic megacolon and colon cancer, occur in both diseases. Additionally, there are no intestinal complications that occur only in ulcerative colitis and not in Crohn's disease. On the other hand, certain intestinal complications of IBD occur predominantly in Crohn's disease (for example, fistulas) or exclusively in Crohn's disease and not in ulcerative colitis (for example, malabsorption and SIBO).

The differences in intestinal complications between ulcerative colitis and Crohn's disease depend on the characteristically dissimilar behaviors of the inflammation associated with these diseases. In Crohn's disease, the inflammation usually extends from the inner lining (mucosa) through the entire thickness of the bowel wall. This spreading inflammatory process may thereby lead to fistulas, abscesses, or strictures of the bowel. By contrast, the inflammation in ulcerative colitis is limited to the inner lining of the colon. The development of these particular complications is, therefore, much less common in ulcerative colitis. Also, Crohn's disease can affect any area of the GI tract from the mouth to the anus, whereas ulcerative colitis is limited to the colon. Therefore, complications involving the small intestine, such as malabsorption and SIBO, as previously noted, occur only in Crohn's disease and not in ulcerative colitis.

Source: MedicineNet.com
http://www.medicinenet.com/inflammatory_bowel_disease_intestinal_problems/article.htm