The disease usually begins in the rectosigmoid area and may extend proximally, eventually to involve the entire colon, or it may include most of the large bowel at once. Crypt abscesses, epithelial necrosis, and mucosal ulceration ultimately develop. The usual manifestations occur as spells of bloody diarrhea varying in intensity and duration, interspersed with asymptomatic intervals. An attack may be acute and fulminant, with sudden violent diarrhea, high fever, signsof peritonitis, and profound toxemia. More often, an attack begins insidiously, with an increased urgency to defecate, mild lower abdominal cramps, and blood and mucus appearing in the stools.
Systemic symptoms are mild or absent.
Malaise, fever, anemia, anorexia, weight loss, leukocytosis,hypoalbuminemia, and elevated ESR may be present with extensive active colitis. Complications Hemorrhage is the most common local complication. In toxic colitis, a particularly severe local complication, transmural extension of the ulcerative process results in localized ileus and peritonitis. As the toxic colitisprogresses, the colon loses muscular tone and within a matter of days or even hours begins to dilate. This is called toxic megacolon.