If treatment is not carefully followed and occasionally in very severe cases, complications may occur, these include:
• Haemorrhage
This is bleeding from the bowel and may require blood transfusions or an operation.

• Perforation
This is a hole in the bowel caused by thinning of the lining due to inflammation. It may cause leaking of the contents into the abdomen (peritonitis) and may require an operation.

• Stricture formation
Strictures are areas of narrowing in the bowel caused by inflammation and scarring. This leads to obstruction and may require surgical removal.

• Abscess formation
Pockets of pus, usually occurring close to the anus, which may require surgical drainage.

• Anorectal disease
Such as fissures. These are painful cracks in the lining causing bleeding on defaecation (passage of a bowel motion). Very occasionally they may lead to a fistula.

• Dysplasia and carcinoma
Patients with long-standing (over 10 years) dysplasia and extensive colitis have an increased risk of bowel cancer.

Dysplasia is a change in the appearance under the microscope of the mucosa, which may alert the doctors to the risk of cancer developing.

• Arthritis
May affect any joints, but especially those in the large joints such as the knees & hips. Inflammation in the bottom of the spine is called sacroileitis. Arthritis is usually related to activity in the bowel and therefore controlling this may help resolve pains in the joints. Arthralgia (painful joints without swelling & deformity) is usually unrelated to bowel activity.

• Pouchitis
When an ileo anal anastomosis has been performed the pouch made from loops of small bowel may become inflamed. This leads to a marked increase in the number of stools passed and sometimes to pain and bleeding. It is believed that pouchitis is due to problems with the bacteria which colonise the pouch after formation. It is therefore treated with courses of antibiotics such as augmentin or ciprofloxacin. Prednisolone may sometimes be helpful and a very exciting new development has been the demonstration that a cocktail of 8 different friendly probiotic bacteria VSL-#3 is effective in preventing pouchitis from recurring.