This is inflammation of the lining of the large bowel and usually confined to the rectum - in a small number of patients it can affect the whole bowel. Some patients have only one attack with inflammation confined to the rectum - this is called 'proctitis'.
Others have recurrent attacks of extensive inflammation requiring surgery - occasionally this has to be done as an emergency for life threatening disease. Fortunately this is quite rare and most patients require just one episode of treatment and others can be kept very fit on maintenance treatment.