Colitis has been recognised in humans for many centuries. until the 19th century, when a classical description of ulcerative colitis was made, all episodes of colitis were thought to be due to infection.

In 1932 Dr Crohn and his co-workers described inflammation of the last section of the small bowel (also called the terminal ileum) and this condition is now known as Crohn’s disease. It was not until the 1960’s that a clear distinction was made between ulcerative colitis and Crohn’s disease of the colon.

The term inflammatory bowel disease is now used to describe both ulcerative colitis and Crohn’s disease. These disorders are chronic inflammatory conditions of the wall of the gastrointestinal tract. The cause is still unknown. At the time of diagnosis, it is sometimes hard to differentiate which condition is present, but later it usually becomes clear whether it is either ulcerative colitis or Crohn’s disease.

Ulcerative Colitis

Ulcerative colitis is inflammation of the mucous membrane or lining of the large bowel (the colon) and the last section of the large bowel (the rectum). If only the rectum is involved, it is called ulcerative proctitis. This is less serious and rarely progresses to involve the whole colon.

Crohn’s Disease

Crohn’s disease is inflammation of the full wall thickness of the intestine rather than just the lining. It may involve any part of the digestive tract but most frequently occurs in:

• the terminal ileum (the last section of the small bowel) – and is called ileitis
• the large bowel – called colitis
• both the small and large bowel – called ileo-colitis

Differentiating the two conditions

Both ulcerative colitis and Crohn’s disease involve chronic inflammation of the bowel wall. Microscopic examination of the tissue obtained by biopsy or surgery can help a pathologist differentiate between the two conditions.

Ulcerative colitis is confined to the superficial layers lining the bowel wall. It is most severe in the rectum and may spread throughout the colon.

Crohn’s disease, on the other hand, can appear in any part of the gastrointestinal tract. Mast commonly it involved the colon or small bowel, especially the ileum. It can involve the mouth, oesophagus, stomach, or anus but this is rare. Crohn’s disease may be discontinuous, skipping areas of the bowel so that part of the bowel in inflamed and ulcerated, and part is normal. Crohn’s disease involves all layers of the bowel wall and tends to form strictures (areas of narrowing) and fistulae (connections between the bowel and another loop of the bowel, or between the bowel and other organs such as skin, bladder, vagina).

The cause of ulcerative colitis and Crohn’s disease are unknown. It is thought that factors within the body as well as environmental factors may be important in causing a change in the gut of individuals who are susceptible to inflammatory bowel disease. The specific nature of these factors is unknown.

Genetic factors– The exact nature of genetic factors that are important in the development of inflammatory bowel disease are obscure. Family and twin studies show an increased frequency of inflammatory bowel disease in related individuals. However, children of those with inflammatory bowel disease are rarely affected and family screening is not needed.

Diet – Despite many studies, no specific dietary factors have been shown to cause inflammatory bowel disease.

Infectious Agents – There have been many studies bet there is no convincing evidence that inflammatory bowel disease is caused by infectious agents such as viruses or bacteria. Inflammatory bowel disease is not contagious.

Drugs– Drugs used to treat arthritis and rheumatism (non-steroidal anti-inflammatory drugs or NSAIDS), may precipitate relapses of inflammatory bowel disease.

Smoking – Ulcerative colitis is less common in smokers. There is evidence that both initial attacks and relapses may be associated with stopping smoking. However, smoking is not recommended as therapy.

Psychogenic factors– There is no evidence that particular personality types or emotional stress cause inflammatory bowel disease. However, emotional stress may increase suffering and the severity of the symptoms. The disease or its treatment may have a psychological influence which may cause depression.

Immune System – A disturbance of the immune system may be involved in inflammatory bowel disease.