Family doctor

What is Crohn's disease?

Inflammatory bowel diseases (IBD) are a group of chronic disorders that cause inflammation of the small and large intestines. There are two major members - ulcerative colitis which affects only the large intestine, and Crohn's disease which can affect the whole of the gastrointestinal tract from the mouth to the anus. Ulcerative colitis involves only the inner lining of the bowel whereas Crohn's disease involves the full thickness of the bowel.

Usually in Crohn's the inflammation is concentrated to certain areas of the bowel. The gastrointestinal tract starting from the mouth is serially oesophagus (gullet), stomach, small bowel (duodenum, jejunum, and ileum), large bowel (ascending colon, transverse colon, descending colon, sigmoid colon), rectum and anus. Crohn's disease most often affects the ileum and/or the large bowel and characteristically develops what are called skip lesions with normal bowel between two areas of inflammation.

What causes Crohn's disease?

In the early part of the 20th century tuberculosis was a common cause of inflammation of the ileum. Dr Crohn identified some patients with inflammation in the ileum (ileitis) but could not find any evidence of tuberculosis. Suspecting that there must be some other infecting organism, he searched assiduously but could not find an infection causing the disease. Since then many have looked for an infection without success. While some hold to an infectious theory of causation, it is now commonly believed that it is not due to an infection.

There has been accumulation of evidence to show that genetic factors play a role. There is an increased occurrence in family members most marked in identical twins but not in dissimilar twins. There is no increase in spouses. There are at least 7 genes which have an association with the development of Crohn's. Grouping of more of these may be critical in determining the probability of developing the disease.

No one single agent has been identified as causing the disease. However, it is commonly accepted that environmental factors are important. It may be a toxin, a food, or even an acute infection which temporarily damages the lining of the bowel in persons with the collection of genes necessary to establish the immune reactions that are characteristic of Crohn's. Once established there is an immune reaction which is finely balanced to counteract a host of environmental factors including reactions to some foods, bacterial products, and to produce actions outside the bowel such as skin lesions, arthritis, etc.

How common is Crohn's disease?

The incidence is highest in white populations and low in black and Polynesian races. The incidence (the number of new cases diagnosed each year) is increasing, making the disease, formally considered to be rare, to be considered in people with chronic bowel symptoms. The incidence in New Zealand is thought to be greater than 1 in 10,000. The prevalence in New Zealand has not been calculated but is probably 1 in several thousand.

What is the natural history of Crohn's disease?

Crohn's is a chronic condition usually with exacerbations and remissions. Once the disease is established it is considered to be a life-long illness. Many patients will have variable periods of remission and a few can have very long remissions.

A number of complications can occur including anaemia, narrowing of the bowel (stricture), with a variable degree of obstruction, communications (fistula) between adjacent loops or the skin, or arthritis.

What symptoms can be expected with Crohn's disease?

The most common symptoms of Crohn's disease is abdominal pain, often in the right lower abdomen and with or without diarrhoea. Joint pains, loss of appetite, weight, and fever are common. Sores and abscesses may occur in the anal area. People with Crohn's frequently have recurring mouth ulcers.

How is Crohn's disease diagnosed?

Crohn's may be seen at any age but it appears most frequently during the third decade of life. It is said that men and women are equally affected but there is a change developing, with it occurring more frequently in women.

A thorough history and a physical examination will often raise the possibility of Crohn's. This will be followed by blood tests to determine if there is anaemia or other abnormalities and a test of faeces to exclude an infectious cause of diarrhoea.

A flexible tube examination of the large bowel and extending into the lower part of the small bowel may show inflammation, ulceration, and a generally thickened bowel wall. Small pieces of bowel lining are taken for examination under the microscope.

An x-ray examination of the large bowel will usually be done to show the extent and severity of the disease. These examinations will include an upper series (enteroclysis) and a lower series (barium enema). Barium is put in the bowel. The barium appears white on the x-ray giving a shadow showing inflammation and ulceration.

What can be done for Crohn's disease?

All treatments carry risks. Non-treatment also carries risk: the risks of treatment and non-treatment must be carefully considered.

The goals of treatment are to correct nutritional deficiencies; to control inflammation; and to relieve abdominal pain, diarrhoea, and bleeding.

There is no special diet for Crohn's disease and most patients do not require dietary restriction. When the disease is very active a bland diet low in fibre is often better tolerated than one high in fibre and containing a lot of fat and spices. If there is narrowing of the small intestine, a semi-fluid diet may be needed as a temporary measure.

When there are nutritional deficiencies shown these should be managed by temporary supplementation. Common supplements which may be needed are iron, zinc, calcium, vitamin B12, and folate. Large doses of vitamins are useless and can even cause harmful side effects. A few patients lack the enzyme that breaks down milk sugar (lactose) and these should have reduced milk in their diet.

There are two groups of drugs available - those can be described as specific because they reduce the inflammation and those which are non-specific but reduce symptoms.

Salazopyrine (sulphasalazine) often lessens the inflammation. This is best in ulcerative colitis but is still used in some patients with large bowel Crohn's. The significant active component of salazopyrine had been modified by some clever biotechnology to release the active ingredients at the site of the inflammation. Such drugs are Dipentum, Pentasa, and Asacol.

Steroids (prednisone, prednisolone and ACTH) are used to treat moderate or severe attacks. They are very effective in reducing inflammation and swelling of the bowel. They are usually used in a dose customised to the severity of the attack.

More severe cases may require antibiotics, or drugs that act through the bodies immune system.

What are the complications of Crohn's disease?

The most common complication is a blockage (obstruction) of the intestine. Blockage occurs when there is swelling of the bowel wall and/or fibrous scar tissue has formed. The former may be temporary and responds to medications which reduce inflammation.

Crohn's may be accompanied by very deep ulcers which can burrow through the bowel wall into surrounding tissues such as adjacent bowel, the skin, the urinary bladder, or the vagina. These burrowings (fistula) often cause pockets of infection and abscess formation.

Crohn's may cause complications affecting other parts of the body. Arthritis, inflammation of the eyes, kidney stones, and inflammation of the liver are some of the complications arising outside the bowel and are manifestations of the immune system operating in Crohn's disease.

Does surgery have a place in the management of Crohn's disease?

Crohn's can be helped by surgery. If the disease is confined to the large bowel colectectomy (removal of the large bowel) with the formation of an opening for the small bowel on the skin (ileostomy) is of great benefit. Patients need careful instruction in the management of an ileostomy so that this becomes an accepted part of daily living.

Other indications for surgery are the relief of fibrous bands that are narrowing the bowel (stricturectomy), drainage of abscesses, and the repair perforations.

Can people with Crohn's disease develop cancer?

It is believed that cancer of the colon is a little higher in patients with Crohn's colitis than in the normal population. Cancer of the small bowel is very rare but patients with Crohn's of the small bowel have a slightly higher prevalence than the general population of developing small intestinal cancer.

Future trends

Crohn's disease is subject to intensive research. That research has led to better understanding of the disease process. New treatments are being extensively tested and there is every reason to be optimistic that Crohn's treatment will soon offer new and exciting management programmes.