ABC of colorectal diseases. Non-specific inflammatory bowel disease.

Incidence Non-specific inflammatory bowel diseases are those for which there is no discernible aetiological agent. The two most important of these diseases affecting the large bowel are ulcerative colitis and Crohn's disease. Ulcerative colitis is always confined to the large bowel, although a few centimetres of the terminal ileum may be affected by "backwash" ileitis. On the other hand, Crohn's disease affects the whole of the gastrointestinal tract, although the only manifestation may be in the large bowel.