Collagenous Colitis
A microscopic colitis, (i.e. only seen under the microscope) caused by the formation of a collagen band (a tough and inelastic tissue) under the lining of the bowel. The main feature of the disease is watery diarrhoea.

Lymphocytic Colitis
A microscopic colitis which, under the microscope, demonstrates increased levels of lymphocytes (white cells) and is characterised by watery diarrhoea, usually without blood.

Ischaemic Colitis
Inflammation caused by partial death of tissue (infarct) due to either a blockage in the blood supply, e.g. after major abdominal surgery or a reduced supply, e.g. poor cardiac output in heart disease. It occurs almost entirely in the elderly and is characterised by violent bloody diarrhoea and abdominal pain. It can mimic Crohn's disease as it is variable in extent, location and severity.

Diversion Colitis
Inflammation developing from the diversion of the faecal stream following colostomy or ileostomy. Colitis may develop in the portion of the bowel which no longer has faeces passing through.

Behçet's Syndrome
This is a rare disease causing inflammation in the blood vessels and can affect many organs in the body. When present in the bowel, it can mimic Crohn's disease as it tends to occur in the ileocaecal area and segments of the colon.

Infective Colitis
Certain infections caused by various organisms can result in damage to the lining or other layers of the intestine which may mimic Crohn's disease or ulcerative colitis. For example:
• yersinia
• cytomegalovirus (CMV)
• clostridium dificile

It is therefore important to exclude this possibility before making a diagnosis of chronic inflammatory bowel disease.

Indeterminate Colitis
Indeterminate colitis (IC) is the name doctors give to inflammation in the large bowel which could be caused either by either Ulcerative Colitis (UC) or Crohn's disease.

Histological changes and biopsies do not allow the pathologists to decide which disease is present. It is customary to treat IC in a similar way to UC.