Crohn's Disease

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Crohn's disease is a condition where there is inflammation in the gut (gastrointestinal tract). The disease flares up from time to time. Symptoms vary, depending on the part of the gut affected and the severity of the condition. The most common symptoms are diarrhoea, abdominal pain and feeling generally unwell. Medication can often ease symptoms when they flare up. Surgery to remove sections of the gut is needed to treat some flare-ups. Medication taken regularly may prevent symptoms from flaring up.

Crohn's disease is a condition that causes inflammation of the wall of the gut (gastrointestinal tract). Any part of the gut can be affected. This can lead to various symptoms (detailed below). Crohn's disease is named after Dr Crohn, the person who first described the disease in the 1930s.

When doctors talk of inflammatory bowel disease they usually mean people who either have Crohn's disease or ulcerative colitis. Both these conditions can cause inflammation of the colon and rectum (large bowel or large intestine) with similar symptoms, such as bloody diarrhoea, etc. Although these conditions are similar and treatments are similar, there are differences. For example, the inflammation of ulcerative colitis tends to be just in the inner lining of the gut (gastrointestinal tract), whereas the inflammation of Crohn's disease can spread through the whole wall of the gut. Also, ulcerative colitis only affects the colon and rectum, whereas Crohn's disease can affect any part of the gut. See separate leaflet called Ulcerative Colitis for more details.

However, about 1 in 20 people with inflammatory bowel disease affecting just the colon cannot be classified as having either Crohn's disease or ulcerative colitis because they have some features of both conditions. This is sometimes called indeterminate colitis.

Note: inflammatory bowel disease is sometimes shortened to IBD. This is not the same as IBS which is short for irritable bowel syndrome - a very different disease.

The gut (gastrointestinal tract) is the long tube that starts at the mouth and ends at the anus. When we eat, food passes down the gullet (oesophagus), into the stomach and then into the small intestine.

The small intestine has three sections - the duodenum, jejunum and ileum. In the small intestine, food is digested and absorbed into the bloodstream. The structure of the gut then changes to become the large intestine (colon and rectum, sometimes called the large bowel).

The colon absorbs water, and contains food that has not been digested, such as fibre. This is passed into the last part of the large intestine, where it is stored as stools (faeces). Faeces are then passed out of the anus into the toilet.

The Gut - simple

Crohn's disease is diagnosed in about 1 in 10,000 people every year. About 145 in every 100,000 people in the UK have Crohn's disease. It can develop at any age but most commonly starts between the ages of 15 and 30. Crohn's disease is more common in people who smoke. If you have a family member with Crohn's disease, you are more likely to develop the condition yourself. It is also more common in people who have had their appendix removed, for the first five years after the operation.

In Crohn's disease, one or more patches of inflammation develop in parts of the gut (gastrointestinal tract). Any part of the gut can be affected. However, the most common site for the disease first to start is the last part of the small intestine (the ileum). The ileum is affected in about half of cases. Other parts of the small intestine and the colon are also commonly affected. The mouth, gullet (oesophagus) and stomach are affected much less commonly.

A patch of inflammation may be small, or spread quite a distance along part of the gut. Several patches of inflammation may develop along the gut, with normal sections of gut in between. In about 3 in 10 cases, the inflammation occurs just in the small intestine. In about 2 in 10 cases the inflammation occurs just in the colon. In a number of cases, the inflammation occurs in different places in the gut.

The cause is not known. About 3 in 20 people with Crohn's disease have a close relative who also has it. This means there may be some genetic factor. However, other factors such as a germ (bacterium or virus) may be involved. One theory is that a germ may trigger the immune system to cause inflammation in parts of the gut (gastrointestinal tract) in people who are genetically prone to develop the disease.

Crohn's disease has become more common in recent years but the reason for this is not known. It is more common in smokers than in non-smokers. Smokers also tend to have more severe disease compared with non-smokers. The oral contraceptive pill and non-steroidal anti-inflammatory tablets (usually used for joint inflammation) have also been implicated as possible factors in triggering the disease to start.

Crohn's disease symptoms are due to inflammation in the wall of the affected parts of the gut (gastrointestinal tract). When the disease flares up, the inflammation may cause one or more of the following:

  • Diarrhoea is the most common first symptom. It can vary from mild to severe. The diarrhoea may be mixed with mucus, pus or blood. An urgency to get to the toilet is common. A feeling of wanting to go to the toilet but with nothing to pass (tenesmus) is also common.
  • Pain occurs in about 7 in 10 cases. The site of the pain depends on which part of the gut is affected. The last part of the small intestine (ileum) is the most common site. Therefore, a common area of pain is the lower right side of the tummy (abdomen). When Crohn's disease first develops it is sometimes mistaken for appendicitis. The severity of pain can vary from person to person. Also, a sudden change or worsening of pain may indicate a complication (see below).
  • Weight loss that is not intentional is another common symptom.
  • Ulcers. An ulcer is a raw area of the lining of the gut which may bleed. You may see blood when you pass stools (faeces).
  • Generally feeling unwell, which may include loss of appetite, high temperature (fever), and tiredness.
  • Anaemia may occur if you lose a lot of blood.
  • Mouth ulcers are common.
  • Anal fissures may occur. These are painful cracks in the skin of the anus. Skin tags (small fleshy wart-like lumps) may also appear around the anus.

Symptoms can vary and depend on which part or parts of the gut are affected - for example:

  • You may not have diarrhoea if the disease is just in the small intestine.
  • A persistent pain in the abdomen without any other symptoms may be due to a small patch of Crohn's disease in the small intestine.
  • A severe flare-up can make you generally very ill.
  • If large parts of the gut are affected, you may not absorb food well and you may become deficient in vitamins and other nutrients.

Other symptoms

Other parts of the body are affected in some people in addition to the gut. These include:

  • Inflammation and pain of some joints (arthritis).
  • Skin rashes.
  • Inflammation of the middle layer of the eye (uveitis).
  • Liver inflammation.

These problems can cause various symptoms.

It is not clear why these other problems occur. The immune system may trigger inflammation in other parts of the body when there is inflammation in the gut. These other problems tend to go when the gut symptoms settle, but not always.

Crohn's disease is a chronic, relapsing condition. Chronic means that it is ongoing. Relapsing means that there are times when symptoms flare up (relapse) and times when there are few or no symptoms (remission). The severity of symptoms and how frequently they occur vary from person to person. The first episode (flare-up) of symptoms is often the worst.

Complications may occur, particularly if flare-ups are frequent or severe. These include the following which often need treatment with surgery:

  • Stricture. This is a narrowing of part of the gut (gastrointestinal tract). It is due to scar tissue that may form in the wall of an inflamed part of the gut. A stricture can cause difficulty in food passing through (an obstruction). This leads to pain and being sick (vomiting).
  • Perforation. This is a small hole that forms in the wall of the gut. The contents of the gut can then leak out and cause infection or an abscess inside the tummy (abdomen). This can be serious and life-threatening.
  • Fistula. This occurs when inflammation causes a channel to form between two parts of the body. For example, a fistula may form between a part of the small intestine and a part of the colon. Fistulas can also form between part of the gut and other organs such as the bladder or womb (uterus). The contents of the gut may then leak into these other organs. A perianal fistula sometimes develops. This is a fistula that goes from the anus or rectum and opens on to the skin near to the anus.
  • Cancer. People with Crohn's disease have a small increased risk of developing cancer of the colon compared with the risk of the general population.
  • 'Thinning' of the bones (osteoporosis). The increased risk of this is related to the poor absorption of food that occurs in some people with severe Crohn's disease.

Your doctor will initially arrange blood tests to help find the diagnosis. You may also be asked to provide stool (faeces) samples for analysis to see if there is an infection in your gut (gastrointestinal tract). A stool sample may also be sent to measure a protein called calprotectin, which can be used to see whether it is likely that you have Crohn's disease.

If it is thought that you may have Crohn's disease you will be referred to a specialist for further investigations. If you are very ill then you may need to be admitted immediately to hospital for these investigations.

Depending on where the symptoms arise from, various tests may be done to confirm the diagnosis, and to determine how much of the gut is affected. For example, if you have symptoms coming from the colon or ileum, a doctor may look inside the colon and ileum, using a special flexible telescope (a colonoscope). The colonoscope is passed through the anus, up into the colon and a little further into the ileum. See separate leaflet called Colonoscopy for more details.

The typical appearance of the inside lining of the colon or ileum suggests Crohn's disease. Small samples (biopsies) of the lining of various parts of the colon and ileum are usually taken. These are looked at under a microscope. The typical pattern of the cells may confirm the diagnosis.

If you have symptoms coming from the upper part of the gut, a doctor may suggest a gastroscopy (endoscopy). This is a procedure in which a thin, flexible telescope is passed down the gullet (oesophagus) into the stomach. This allows a doctor or nurse to look inside. See separate leaflet called Gastroscopy (Endoscopy) for more details.

A special X-ray of the large intestine (barium enema) or small intestine (barium meal) may be advised. Barium coats the lining of the gut and shows up as white on X-ray films. Typical patterns on the films show which parts of the gut are affected. These X-rays using barium are much less often used now. Other tests such as an MRI or CT scan are now often preferred, depending on the following:

  • Which part of your bowel is affected.
  • Whether there are any complications.
  • Whether these tests are available in your area.

Also, repeat blood tests are helpful from time to time to assess the level of inflammation within the gut, to check for anaemia and other deficiencies, and to assess your general well-being.

You may be asked to provide further stool samples for analysis to check for various germs that are sometimes present in people with Crohn's disease. Very occasionally, you may need to have an operation to diagnose Crohn's disease if your specialist cannot rule out an equally serious condition such as tuberculosis inside the abdomen.

There are two main aspects of treatment:

  • When a flare-up develops - a main aim is to clear symptoms. That is, to cause a remission of the disease.
  • When a flare-up has settled - a main aim is to prevent any further flare-ups of symptoms. That is, to keep you in remission.

The treatment advised can depend on various factors - for example:

  • The severity of the symptoms.
  • The site or sites of the inflammation in the gut (gastrointestinal tract).
  • Whether associated problems have developed, such as eye inflammation.
  • What treatments worked best for you in the past.

Treatment decisions can become complex and a specialist will usually advise. Options that may be considered include the following:

No treatment

This is an option for some people who have mild symptoms. There is a chance that the symptoms will settle on their own. If symptoms become worse, decisions about treatment can be reviewed.

A course of steroids (corticosteroids)

Steroid medicines work by reducing inflammation. The two commonly used steroids for Crohn's disease are budesonide and prednisolone. In about 7 in 10 cases, symptoms are much improved within four weeks of starting steroids. The dose is reduced gradually and then stopped once symptoms ease. A course of steroids for a few weeks is normally safe. Steroids are not usually continued once a flare-up has settled. The aim is to treat any flare-ups but keep the total amount of steroid treatment over the years as low as possible.

Although steroid tablets are commonly used, a steroid enema or suppository is also an option for a mild flare-up confined to the lower large intestine. Steroid injections directly into a vein may be required for a severe flare-up.

Immunosuppressant medicines

Newer powerful medicines that suppress the immune system have become available in recent years. These have made a big impact on the treatment of Crohn's disease in recent years. They tend to be divided into two groups:

These are medicines that modify and suppress the immune system. They include azathioprine, mercaptopurine and methotrexate. They tend to be used in more severe cases and in those where steroid treatment has not helped much.

Biological therapies
These are genetically engineered proteins such as special antibodies called monoclonal antibodies. These can target specific chemicals of the immune system, involved in the inflammation process. In Crohn's disease, a chemical called cytokine tumour necrosis factor alpha (TNF-α) is involved in the inflammation process. Medicines called infliximab and adalimumab (which are really manufactured antibodies) block the action of this chemical and therefore suppress the disease activity. Treatment with infliximab or adalimumab is an option in some cases - for example:

  • In people who do not respond to steroid medication or to immunomodulators; or
  • In certain situations causing severe symptoms.

These medicines need to be given directly into a vein but then typically persist in the body for many weeks with long-lasting effects. People on these medicines should have their disease assessed every twelve months to see whether they still need them.


Antibiotics may need to be added to other treatments if infective complications are suspected - for example, if you develop an infected fistula such as an infected perianal fistula.

Dietary treatments

A very strict liquid diet that contains basic proteins and other nutrients has been found to help in some cases. This is mainly used in children. A flare-up can settle within four weeks in some people who have this diet. After this, a normal diet is gradually restarted. It is not clear why this treatment works. It may have some effect of 'resting' the gut. This may be an alternative for some people when medication has not worked so well, or has caused bad side-effects.


An operation to remove a severely affected section of gut may be needed if other treatments do not work. The gut is cut above and below the affected part which is removed. The two ends are then joined up. Surgery is also usually needed to treat complications such as fistulas, strictures and abscesses.

General measures

  • Iron tablets may be prescribed if you develop anaemia.
  • Vitamins and other nutrient supplements may be needed if a large part of the gut is affected and food is poorly absorbed.
  • Nutritional support such as dripping nutrients directly into a vein (parenteral nutrition) may be needed in severe cases.
  • Painkillers may be needed for a while during flare-ups.
  • Hospital admission for intravenous fluids (a drip) and intensive treatment may be needed if you have a severe flare-up.
  • Vaccinations may be offered to people with Crohn's disease, to protect them from a variety of infections. This is especially important if they are on treatment which stops their immune system from working properly.

Once a flare-up has settled, without treatment, on average there is about a 1 in 2 chance that another flare-up will develop within a year. Certain factors increase the likelihood of more severe and more frequent flare-ups.

For example, the severity of the first flare-up, the extent of the disease in your gut, your age, and the extent of treatment needed to control the initial flare-up. For some people it may not be worthwhile taking regular medication if flare-ups are not frequent, or are mild, and respond well to treatment when they occur. For others, medication to prevent flare-ups can make a big difference to quality of life.

The treatment options that may be considered to prevent flare-ups (which in medical language is to maintain remission) include the following:

  • A regular dose of an immunomodulator (described earlier). This is becoming more widely used as a treatment to prevent flare-ups.
  • A regular dose of a biological therapy (described earlier). For example, an infusion of infliximab every eight weeks. This may be used in selected cases where flare-ups are severe and other treatments have not worked so well.

Each of the above treatments increases the chance of remaining free of flare-ups but they do not always work. There is a balance between the likely benefits and the possible side-effects that occur in some people. Your doctor will advise about the pros and cons of long-term medication and which medication is best for your circumstances. Note: steroid medication is not generally used long-term to prevent flare-ups.

For smokers, giving up smoking may reduce the number and severity of flare-ups. It would always be wise to try to give up smoking. There are treatments that can help smokers to quit. Ask your doctor for advice on this.

The treatment of Crohn's disease is an evolving field. Various new medicines are under investigation and may change the treatment options over the next ten years or so.

If you have Crohn's disease and are planning to become pregnant, it is advised that you discuss this in advance with your doctor. For example, you may need extra folate supplements, and certain medicines which may be used for Crohn's disease, such as methotrexate, must not be used during pregnancy.

The outlook is variable. It depends on which part or parts of the gut (gastrointestinal tract) are affected and how often and how severe the flare-ups are. Without treatment:

  • About 3 in 20 people with Crohn's disease have frequent and/or severe flare-ups.
  • A few people would have just one or two flare-ups in their lives but for most of their lives have no symptoms.
  • Most people would fall somewhere in between - have flare-ups from time to time but have long spells without symptoms.

Sometimes a severe flare-up is life-threatening and a small number of people die as a result of a serious complication such as a perforated gut.

Modern immunosuppressant medicines have made a big impact in recent years. Recent reports suggest that about 15 in 20 people with Crohn's disease remain in work ten years after diagnosis. So, this means that, in the majority of cases, with the help of treatment, the disease is manageable enough to maintain a near-normal life. However, the burden of the disease can be heavy for some people with severe disease.

Up to 8 in 10 people with Crohn's disease require surgery at some stage in their lives for a complication. In about half of people with Crohn's disease, surgery is needed within the first ten years of developing the disease. The most common reason for surgery is to remove a stricture that has formed. Some people need several operations in their lifetime. If you develop Crohn's disease as a young adult, on average you can expect to have two to four operations in your lifetime. However, there is some evidence that the rate of surgery is coming down, probably due to the more modern treatments with medicines now available.

If you have Crohn's disease that affects at least half the surface of your colon (large intestine), you will be at a slightly increased risk of developing cancer.

People with this risk are usually advised to have their large intestine routinely checked after having had Crohn's disease for about ten years. This involves a look into the large intestine by a flexible telescope (colonoscopy) every now and then and taking small samples of bowel (biopsies) for examination. It is usually combined with chromoscopy - the use of dye spray which shows up suspicious changes more easily. Depending on the findings of this test and on other factors, you will be put into a risk category which is called low, intermediate or high. 'Other factors' include:

  • The amount of intestine affected.
  • Whether you have had complications such as small fleshy lumps (polyps).
  • Whether you have a family history of cancer.

The National Institute for Health and Care Excellence (NICE) recommends the next colonoscopy/chromoscopy should depend on the degree of risk of developing colon or rectal cancer.

Original Author:
Dr Tim Kenny
Current Version:
Peer Reviewer:
Dr Laurence Knott
Document ID:
4431 (v42)
Last Checked:
Next Review:
The Information Standard - certified member
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