Definition and epidemiology of inflammatory bowel disease.

Inflammatory bowel disease (IBD) includes two major disorders: ulcerative colitis (UC) and Crohn's disease (CD). Both usually involve severe diarrhea, pain, fatigue and weight loss. IBD can be debilitating and sometimes leads to life-threatening complications. UC is characterized by relapsing and remitting episodes of inflammation limited to the mucosal layer of the colon. It involves the rectum and typically extends in a proximal of the colon. In CD, inflammation often spreads deep into affected tissues. CD is characterized by transmural inflammation and by skip lesions in the entire gastrointesti- nal tract from mouth to perianal area. The transmural inflammation leads to fibrosis, strictures and microperforations or fistulae. Multiple studies have evaluated the epidemiology of IBD in various geographic regions.