Ulcerative colitis is an inflammatory disease of the colon, the large intestine, which is characterized by inflammation and ulceration of the innermost lining of the colon. Symptoms characteristically include diarrhea with or without rectal bleeding and often abdominal pain. Ulcerative colitis may affect only the lowest part of the colon, the rectum, and be termed ulcerative proctitis . If the disease affects only the left side of the colon, it is called limited or distal colitis . If it involves the entire colon, it is termed pancolitis .
Ulcerative colitis differs from another inflammatory bowel disease, Crohn's disease.
Ulcerative colitis affects only the colon. Ulcerative colitis affects only the innermost lining of the colon, whereas Crohn's disease can affect the entire thickness of the bowel wall. Ulcerative colitis and Crohn's disease are different from spastic colon or irritable bowel syndrome, which is a motility disorder of the gastrointestinal tract. Irritable bowel syndrome bears no direct relationship to either ulcerative colitis or Crohn's disease. It is estimated that there are up to 2,000,000 Americans with either ulcerative colitis or Crohn's disease, roughly half of that number for each disease.