To most clinicians nonspecific ulcerative colitis is a disease, of undetermined origin, characterized clinically by severe and progressive diarrhea, fever, emaciation and anemia, characterized pathologically by an ulcerating process which, beginning in the superficial mucosa of the colon, invades the walls of that hollow viscus and spreads remorselessly over the various segments until, in the severe cases, the whole mucosal surface of the large intestine is involved. The popular and familiar concept is of a disease which has its usual point of selection in the rectum and lower sigmoid, where usually the oldest ulcers and the greatest invasion and cicatrization take place. Hence the inflammation and ulceration spread orally to involve proximal segments; in advanced cases the descending and the transverse colon soon participate; in the most severe type the hepatic flexure, the ascending colon, the cecum and even the terminal ileum eventually participate in the suppurative ulcerating process.
CROHN BB, BERG AA. RIGHT-SIDED (REGIONAL) COLITIS. JAMA. 1938;110(1):32-38. doi:10.1001/jama.1938.02790010034007