Massive haemorrhage- it is seen in around 1% of patients with severe form of disease.
Toxic Megacolon- It is rapid swelling of the large bowel and presents itself with fever, tachycardia, leucocytosis, anaemia and X-ray finding of dilatation of colon. It is potentially lethal condition. 50% of acute episodes respond to medical therapy alone. Perforation is the most dangerous local complication of toxic megacolon.
Toxic Colitis and Ulceration- in such cases bowel may perforate without first dilating.
Obstructions- Formation of stricture causing obstruction, around 1/3rd of the strictures occurring in the rectum.
Other complications- Cancer, anal fissures, perianal abscesses and haemorrhoids