How does ibs differ from crohn's disease or ulcerative colitis?

Apples and oranges: Ibs: irritable bowel syndrome is not inflammation. Anatomy normal, but functional abnormality. Can occur after a GI infection.Sx occur on and off. Uc and cd are inflammatory; chronic, can have mild or severe consequences/complications. Uc: inflamed lining of colon, starting in rectum, variable extent. Cd-full thickness infl of bowel from lips to anus, can skip areas ibd rx meds +/- surgery.

Very different: Though the diseases may have similar symptoms they are in fact, very different. By definition, a patient with irritable bowel has no inflammation or other significant abnormalities found in their GI tract which would explain their symptoms. Crohn's patient have visible inflammation somewhere which can be confirmed with biopsy. Both commonly have abdominal pain and/or diarrhea.