Crohn's Disease

What is Crohn’s disease?

Crohn’s disease is one of the chronic inflammatory bowel diseases (IBD) that cause long-standing inflammation in the digestive tract.

The last part of the small intestine (the terminal ileum) and the large bowel are most often affected. But the disease can arise anywhere in the digestive tract, from mouth to anus.

In Crohn’s disease the inflammation may not stay at the surface of the bowel; it can extend into the deeper layers of the bowel wall. This explains why strictures, abscesses or fistulas can develop over time in some patients.

The disease generally runs in periods of flare and remission.

Crohn’s disease is not contagious.

What causes Crohn’s disease?

The exact cause is not yet known.

It is now thought that Crohn’s disease arises not from a single cause but from a combination of genetic susceptibility, an inappropriate response of the immune system, the microorganisms of the bowel and environmental factors.

Normally the immune system works in a controlled balance with the microorganisms in the bowel. In Crohn’s disease this balance may be upset and inflammation may continue in the bowel for longer than it should.

Smoking matters particularly in Crohn’s disease. It can increase the risk of developing the disease, and can contribute to existing Crohn’s running a more severe course, recurring, and requiring surgery more often.

Which parts does Crohn’s disease affect?

The disease can differ considerably from person to person.

Most often it affects:

• The last part of the small intestine,
• The large bowel,
• Both the small and the large bowel.

In some patients the mouth, the stomach or the upper digestive tract may also be involved.

One of the important features of Crohn’s disease is that it can show “skip lesions” — segments of entirely normal-looking bowel may lie between the diseased sections.

What happens in the bowel?

At the outset small aphthous-like ulcers may develop on the surface of the bowel.

As the inflammation advances, deeper ulcers may form and the bowel wall may thicken.

Prolonged or recurrent inflammation may in some people lead to scarring of the bowel wall and to a stricture (stenosis).

When the inflammation passes through the whole thickness of the bowel wall, abnormal connections may develop between neighbouring parts of the bowel, the bladder, the skin or other structures. These are called fistulas.

For this reason Crohn’s disease is not regarded merely as “inflammation of the bowel surface”.

What are the symptoms?

Symptoms vary with the site, extent and severity of the disease.

The commonest complaints are:

• Prolonged or recurrent diarrhoea,
• Abdominal pain,
• Weight loss,
• Loss of appetite,
• Weakness and tiredness,
• Fever,
• Blood in the stool in some patients.

In people with small bowel involvement, absorption of iron, vitamin B12 or other nutrients may become impaired.

In children and young people, failure to grow and develop may sometimes be one of the important signs of the disease.

Does Crohn’s affect only the bowels?

No.

Symptoms can arise outside the bowel in Crohn’s disease.

Some patients may have:

• Joint pain or inflammation,
• Inflammation in the eye,
• Skin lesions,
• Recurrent mouth ulcers,
• Certain conditions of the liver and bile ducts.

These findings sometimes rise and fall with the activity of the bowel disease and sometimes run independently of the bowel symptoms.

Are there different types of Crohn’s disease?

The behaviour of Crohn’s disease can differ over time.

In the inflammatory type the main problem is active inflammation; no marked stricture or fistula has yet formed.

In the stricturing type, chronic inflammation and fibrosis in the bowel wall may narrow the bowel channel. Obstructive symptoms such as cramp after meals, bloating and vomiting may appear.

In the penetrating/fistulising type the inflammation may pass through the bowel wall and form a fistula or abscess.

The behaviour of the disease matters in choosing treatment.

What is perianal Crohn’s disease?

Crohn’s disease can affect the area around the anus in some people.

Here there may be:

• Fistulas,
• Abscesses,
• Fissures,
• Swelling and discharge.

Treating complex perianal Crohn’s disease in particular usually requires gastroenterology, colorectal surgery and, where needed, radiology teams working together. The current ECCO approach likewise stresses the importance of planning medical and surgical treatment together in complex perianal disease.

How is the diagnosis made?

There is no single blood test that shows Crohn’s disease.

The diagnosis is made by assessing together the patient’s symptoms, blood and stool tests, endoscopy, biopsy and imaging of the bowel.

The 2025 European diagnostic guideline recommends ileocolonoscopy with biopsies, and assessment of the small bowel by intestinal ultrasound or MR enterography, among the first-line investigations in patients suspected of having Crohn’s disease.

Blood tests

Anaemia, inflammation, vitamin and mineral deficiencies and the effects of the disease on the body can be investigated.

Markers of inflammation such as CRP may be useful but do not on their own establish a diagnosis of Crohn’s.

Faecal calprotectin

Faecal calprotectin is an important stool test that gives information about inflammation in the bowel.

It can be used both in people suspected of having Crohn’s disease and in monitoring known disease.

But a raised calprotectin does not on its own mean that Crohn’s disease is present.

Colonoscopy and biopsy

This is one of the mainstays of diagnosis.

The large bowel and, where possible, the terminal ileum are assessed. Biopsies are taken from the diseased areas and from wherever else is thought necessary.

In Crohn’s disease, skip inflammation, aphthous ulcers, deep ulcers and, in some patients, a cobblestone appearance may be seen.

MR enterography and intestinal ultrasound

Because Crohn’s disease can affect the whole thickness of the bowel wall and parts of the small intestine that colonoscopy cannot reach, imaging matters.

MR enterography is particularly valuable in assessing small bowel involvement, strictures, fistulas and other complications.

Intestinal ultrasound is also increasingly used in diagnosis and follow-up in centres equipped for it.

Treatment of Crohn’s disease

Treatment is not the same for everyone.

The site and severity of the disease, the presence of a stricture or fistula, drugs used previously, the patient’s age and the risk of complications are all weighed together.

The main aim is to bring the inflammation under control, to achieve remission and to maintain that well-being for a long time.

It is no longer regarded as enough that diarrhoea or abdominal pain has settled. Because inflammation continuing silently in the bowel can lead to lasting damage over time, the disease is also monitored by objective methods. The current ECCO approach stresses the importance of early treatment and close monitoring in reducing long-term complications.

Corticosteroids

Cortisone-group drugs can be used to bring active disease under control quickly.

In mild to moderate disease confined to the ileum and right colon, budesonide may be preferred in suitable patients.

Systemic corticosteroids may be needed in more severe flares.

But cortisone is not a long-term maintenance treatment. Because long use can cause important side effects, the aim is to keep the disease under control without making the patient steroid-dependent.

Treatments that modify the immune system

Immunomodulator drugs may be used in some patients.

But treatment options have now widened considerably, particularly in moderate to severe Crohn’s disease.

Biological and targeted treatments

There are modern treatments that target particular inflammatory pathways of the disease.

These may include:

Anti-TNF treatments, vedolizumab, ustekinumab, biological treatments targeting the IL-23 pathway and, in suitable patients, oral targeted small-molecule treatments.

Which treatment is most suitable is decided for each person. The current ECCO treatment guideline supports more than one advanced treatment option in moderate to severe Crohn’s disease.

Is surgery needed?

In some patients, yes.

Surgery may be needed particularly for:

• A stricture that cannot be controlled with drug treatment,
• Bowel obstruction,
• An abscess,
• A fistula,
• Perforation,
• Bleeding that cannot be controlled.

But surgery does not mean that Crohn’s disease has gone completely. The disease may reappear outside the removed segment of bowel, or later at the surgical join.

Suitable follow-up after surgery, and preventive treatment in some patients, are therefore needed.

Nutrition in Crohn’s disease

There is no single “Crohn’s diet” that holds for everyone with the disease.

Nutrition should be arranged according to whether the disease is active or quiet, whether there is a stricture in the bowel, previous surgery and any nutritional deficiencies.

Unnecessary and prolonged food restrictions can lead to malnutrition.

Deficiencies of iron, vitamin B12, vitamin D and other nutrients are investigated and replaced where needed.

In patients with a stricture, the advice about fibrous and hard-to-digest foods may differ from that given to other patients with Crohn’s.

Does Crohn’s disease lead to cancer?

In some patients with Crohn’s colitis affecting a significant part of the large bowel over many years, the risk of colorectal cancer may be increased.

But this does not mean that patients with Crohn’s will get cancer.

A colonoscopic follow-up programme suitable for the person is drawn up taking account of the duration and extent of the disease, the severity of the inflammation, family history and certain accompanying conditions.

ECCO recommends screening colonoscopy for colorectal cancer about eight years after the first symptoms begin in IBD affecting the colon, with the subsequent interval determined by the person’s risk. Patients with small bowel Crohn’s alone do not need the same IBD-specific bowel cancer follow-up programme.

Does Crohn’s disease heal completely?

Crohn’s disease is a chronic disease, and there is at present no single treatment that removes it definitively.

But this does not mean the patient will always be unwell.

Long remission can be achieved with modern treatments; many patients carry on normally with their education, their work and their daily life.

The aim of treatment is not merely to make the patient “feel well” but, as far as possible, to bring the inflammation in the bowel under control and to prevent the lasting bowel damage that could otherwise follow.

When is emergency assessment needed?

Medical assessment is needed without delay if a patient with Crohn’s develops any of the following:

• Severe or increasing abdominal pain,
• Marked swelling of the abdomen with inability to pass wind or stool,
• Persistent vomiting,
• High fever,
• Heavy bleeding,
• Fainting or serious weakness,
• Severe pain, swelling, fever or discharge around the anus.

These may be signs of bowel obstruction, an abscess, perforation or another complication.

Currency: This information was prepared taking account of the 2024 ECCO guideline on the treatment of Crohn’s disease and the 2025 ECCO-ESGAR-ESP-IBUS guideline on the diagnosis and monitoring of inflammatory bowel disease.

This content is for general information. The plan for diagnosis, treatment and follow-up of Crohn’s disease should be determined by a gastroenterologist according to the site, activity and behaviour of the disease and the person’s own circumstances.