Crohn’s disease

What is Crohn’s disease?

Crohn’s disease is a long-term condition that causes inflammation in the gut – the lining of the digestive system. The inflammation usually occurs in the last section of the small intestine (ileum) or the large intestine (colon), but any part of the gut can be affected. There may be a small patch of inflammation, or it may spread quite a way along the gut, or there may be several patches in different places.


In a few people, the mouth, gullet or stomach may be involved. More rarely, the condition also triggers inflammation outside the intestine leading to arthritis, eye inflammation or skin complaints.


In mild Crohn’s disease, there are patches of inflammation with groups of small ulcers, similar to mouth ulcers. In moderate or severe Crohn’s disease, the ulcers are larger and deeper. The inflammation can thicken the intestine, blocking the passage of digested food. In some cases, deep ulcers break through the intestine wall causing infection – an abscess – outside the bowel. This infection or abscess can spread to a nearby part of the body, often around the anus, and this is called a fistula. Scar tissue can form as the inflammation heals, and in some cases this leads to a blockage in the intestine.

Who gets Crohn’s disease?

Crohn’s disease is a rare condition. It can develop at any age, but usually starts between the ages of 15 and 30, and between the ages of 60 and 80. Crohn’s disease affects slightly more women than men, and is more common in white people than in black or Asian people. It is most common among those descended from European Ashkenazi Jewish communities.


The condition runs in families, so those who have a family member with Crohn’s disease are more likely to develop the condition too. It is also more common in people who have had their appendix removed, for the first five years after the operation.

What is inflammatory bowel disease?

Crohn’s disease is one of two conditions known as ‘inflammatory bowel disease’, the other being ulcerative colitis.


Both these conditions can cause inflammation of the colon and rectum, with similar symptoms and treatments. The main differences are that the inflammation of ulcerative colitis is usually found just in the inner lining of the gut, while in Crohn’s disease the inflammation can spread through the whole wall of the gut. In addition, ulcerative colitis only affects the colon and rectum, while Crohn’s disease can affect any part of the gut.


Inflammatory bowel disease is sometimes shortened to IBD. This is not the same as IBS, which is short for irritable bowel syndrome, and which is a very different condition.

What causes Crohn’s disease?

The exact cause is unknown. Most researchers think that it is caused by a combination of factors. These include:

Genetics:Inherited genes may increase the risk of developing Crohn’s disease. Because Crohn’s disease is more common in some ethnic groups also suggests that genetic factors play an important role.

Immune system: One theory is that the immune system – the body’s natural defence against infection and illness – is responsible for the inflammation in the digestive system. Crohn’s disease disrupts the immune system, so that it no longer recognises the ‘friendly bacteria’ that help to digest food.


Previous infection: A previous infection, possibly in childhood, may trigger an abnormal response from the immune system.


Environmental factors: Crohn’s disease is most common in countries with a modern western lifestyle, such as the UK, and least common in poorer parts of the world, such as Africa. This suggests that the environment has a part to play.


Smoking: Smokers are twice as likely to develop the disease compared with non-smokers. Smokers with Crohn’s disease usually have more severe symptoms than non-smokers.

What are the symptoms?

The symptoms vary and depend on which part of the intestine is inflamed.There may be long periods that last for weeks or months with very mild or no symptoms, known as remission. This may be followed by periods when the symptoms are particularly troublesome, known as flare-ups.


Common symptoms include one or more of the following:

  • recurring diarrhoea, often with a feeling of urgency to get to the toilet or a feeling of wanting to go to the toilet but with nothing to pass
  • abdominal pain and cramping, which is usually worse after eating
  • extreme tiredness (fatigue)
  • weight loss.

Less common symptoms include:

  • high temperature (fever) of 38°C (100°F) or above
  • feeling sick (nausea)
  • being sick (vomiting)
  • joint pain and swelling (arthritis)
  • inflammation and irritation of the eyes
  • skin rashes
  • blood and mucus in poo, which may be the result of an ulcer bleeding
  • anaemia, which may occur if there is a lot of blood loss
  • mouth ulcers.
How is Crohn’s disease diagnosed?

The starting point during an initial assessment is for your GP to ask about the pattern of symptoms, and possible reasons for the persistent diarrhoea and abdominal pain. These might include diarrhoea as a result of recent travel abroad, the side-effects of any medication you are taking and whether you have a family history of Crohn’s disease or ulcerative colitis.An examination will look for signs of inflammation, such as tenderness in the abdomen.


If your doctor suspects that the symptoms might point to Crohn’s disease, a referral will be made to a specialist for diagnostic tests.

Is there a link with bowel cancer?

People with Crohn’s disease have an increased risk of developing bowel cancer and should be monitored regularly. The risk is related to the length of time that inflammation has been present, and the site and severity of the disease.


Several studies estimate the risk by following patients over a period of 10–40 years. Some did not show an associated risk, but others predicted an increase that was twice that of the general population for developing bowel cancer. If the disease is confined to the colon, this risk is estimated at around five times greater.


The risk of small intestinal cancer has been estimated at around six times that of the general population, but as this is an extremely rare cancer in the general population, the risk in Crohn’s disease is still small.


(Please note that the above figures are only estimates and may vary among different studies.)


The signs and symptoms may vary according to the site and extent of the cancer, but mostly show a general worsening of the symptoms associated with Crohn’s disease.


While Crohn’s disease and bowel cancer are two very different conditions, it is important to note that many of the symptoms are the same for both. People with Crohn’s disease are often unaware that they have bowel cancer, as the initial symptoms are similar to Crohn’s disease, such as blood in your stool, diarrhoea and abdominal pain. Because of this, you will probably be advised to have a colonoscopy every few years to check that no cancer has developed.

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