What are the risk factors?
There is a small genetic link, with around 25 per cent of patients having a history of bowel inflammation. Acute stress can play a major role in triggering relapses. Smoking has contradictory effects; smokers are more prone to Crohn’s than non-smokers, but are less prone to UC. Environmental factors such as diet and lifestyle may play a role.
How does IBD present?
Patients with IBD present with non-specific symptoms, such as severe diarrhoea, abdominal pain, cramping, fever, anorexia, nausea and vomiting. Symptoms tend to be of long duration and fail to respond to treatment. Patients with severe diarrhoea of more than 24 hours’ duration should be referred to a GP.
Other features include very frequent bowel movements with stools consisting of little more than blood, mucus and perhaps pus, malaise, and weight loss.
Inflammatory bowel disease (IBD) is a collective term covering two chronic diseases that mainly affect the GI tract. It affects one in 500 people in the UK and is characterised by progressive damage to the gut wall, usually in the large and/or small intestine, with resultant abdominal pain, diarrhoea and eventual deteriorating function.
Although IBD is mainly a disease of the bowel, there can also be serious inflammatory damage to other tissues, such as the eye and the joints.
IBD consists of Crohn’s disease and ulcerative colitis (UC), the former being the more serious. Crohn’s can affect any part of the gut, progresses faster than UC, is more likely to have serious complications and is more resistant to treatment. Patients with Crohn’s tend to have poorer outcomes.
By contrast, UC is generally less debilitating. It is restricted to the rectum and colon and fewer patients are seriously ill for long periods. It also affects an older group of patients than Crohn’s. See table 1, below, for a comparison of the clinical aspects of the two conditions.
|Table 1. Comparison of ulcerative colitis and Crohn’s disease|
|Ulcerative colitis||Crohn’s disease|
|Most common site||Sigmoid colon/rectum||Anywhere in gastrointestinal tract|
Mainly terminal ileum/colon
|Pathology||Epithelial inflammation||Transmural inflammation|
|Age range||Onset usually in 20-40 years or 50-70 years||Onset usually in younger patients|
|Severity/effect on life||Many patients can live normal lives most of the time||Severely affects life of most patients|
|Relapses||May not be frequent||Frequent|
|Complications – GI||Dehydration, fluid/electrolyte imbalance Megacolon; colon cancer||Malabsorption|
Obstruction, perforation, fistulae,
extra – intestinal
|Arthritis, spondylitis, iritis, uveitis, hepatitis, dermatitis||Arthritis, spondylitis, iritis, uveitis,|
|Management||Drugs and possibly surgery; stoma||More intensive drug therapy;|
surgery more common; stoma
Causes and risk factors
As with most autoimmune diseases, IBD has some genetic links, but these are not strong: about 25 per cent of patients have a family history of bowel inflammation, and the concordance rate for identical twins is about 35 per cent for CrohnÕs and 10 per cent for UC.
Certain HLA (histocompatibility) genes predict a predisposition to IBD, and there is overlap with other autoimmune conditions. For example, HLA-B27 is found in IBD and ankylosing spondylosis.
It is currently believed IBD is caused by a fault in immune recognition, which persuades the body to mount an inflammatory-immune response to gut tissues. This is commonly associated with or triggered by an intestinal microbe, such as the measles virus. However, the precise connection of microbes to the disease process is uncertain.
Other aetiological factors for IBD have been sought but no unequivocal influences have been found. Industrialised countries have the highest rates of IBD, which are increasing in these areas. Certain ethnic groups have different prevalence, for example Crohn’s is more common among people of Jewish descent. Dietary and other lifestyle factors have also been implicated, with prevalence changing following migration to another area suggesting environmental factors.
Acute stress can play a major role in triggering relapses. Smoking has contradictory effects; smokers are more prone to Crohn’s than non-smokers, but are less prone to UC. Both genders are equally affected.
Crohn’s and UC can both start in early adulthood, although patients with Crohn’s tend to be younger. A further cohort of patients can suffer their first UC attack in middle age.
In Crohn’s disease the entire thickness of the gut wall is affected, with inflammatory swelling significantly reducing the gut lumen. In severe cases this can lead to intestinal obstruction.
Inflammatory lesions can occur simultaneously in various parts of the gut, and appear anywhere from the mouth to the anus, although in 95 per cent of patients only the small and/or large intestine is affected. These discontinuous disease areas are referred to as skip lesions.
In UC usually only one, continuous, strip of gut is affected, most commonly either in the rectum or the distal (sigmoid) colon. Inflammation is restricted to the gut lining, so obstruction is not a problem. Indeed the opposite, toxic megacolon, is a potential complication.
Signs and symptoms
The classic features of an acute IBD attack or exacerbation may superficially resemble nonspecific abdominal upset, gastroenteritis or acute abdomen, with severe diarrhoea, abdominal pain, cramping, fever, anorexia, nausea and vomiting.
Key features to look for when a patient first presents with IBD include the duration and chronicity of the condition, and failure to respond to standard non-specific remedies. Patients who present with severe diarrhoea of more than 24 hours’ duration should be referred to a GP.
Other features include very frequent bowel movements (often more than 10 times daily) with stools consisting of little more than blood, mucus and perhaps pus; malaise; and weight loss. Crohn’s is usually more insidious in onset, and is associated with greater weight loss than UC.
Blood tests in a patient with IBD will reveal typical signs of systemic inflammation, with a raised erythrocyte sedimentation rate (ESR) and plasma C-reactive protein.
There will also usually be anaemia, perhaps exacerbated by iron deficiency from malabsorption and anorexia. In Crohn’s, malabsorption may also cause hypoalbuminaemia and possibly hypovitaminosis (eg folate, B12).
In either disease, severe and prolonged acute attacks of diarrhoea may cause dehydration, with reduced blood pressure, tachycardia and possibly hypokalaemia. Other tests required include liver function tests and stool examination for pathogenic microbes and blood.
The definitive diagnosis of IBD relies on imaging. For colonic disease, a barium enema or colonoscopy/sigmoidoscopy is standard. If disease in the ileum is suspected, access is more difficult as colonoscopes cannot penetrate further back than the caecum. Similarly, duodenoscopes cannot penetrate very far along the ileum from the stomach.
Alternatively, a barium meal with follow-through can be used, where a radio-opaque test meal is followed radiologically for an extended period. Areas affected by Crohn’s will show up as a grossly narrowed lumen (called the ‘string sign’). It is also possible to inject radio-labelled leucocytes and scan the patient for hotspots, because inflammatory cells will concentrate at sites of inflammation.
CT and MRI scanning may also be used. Otherwise, laparotomy may be needed, using modern keyhole techniques to inspect the abdomen directly with an endoscope. Endoscopy also allows tissue samples to be taken for biopsy, which may help in identifying inflammatory cells or possible neoplasia.
An emerging technique is capsule endoscopy. In this a miniaturised video camera is fitted inside a capsule small enough to be swallowed. It transmits pictures of the interior of the gut wirelessly at intervals, until expelled in the faeces. This technique can be used when all other tests have failed to locate a lesion, but it is expensive as the instrument is not reusable.
The course of IBD
IBD is a chronic progressive disease characterised by relapses and remissions. In about 10 per cent of patients the disease remits permanently, while about 20 per cent of patients progress to severe disease, with almost continuous ill health and the eventual need for surgery.
However, most patients with UC experience long periods of relatively normal health, although they usually require maintenance therapy. Life expectancy is not significantly reduced, and the effect on work may be minimal.
Crohn’s tends to follow a more debilitating course, with a greater proportion of sufferers experiencing prolonged ill health, more frequent relapses and hospital admissions, and greater weight loss. Life expectancy is slightly reduced.
Up to three quarters of Crohn’s patients will need surgery. However, surgical excision of one or more problem areas (with rejoining of the gut) rarely solves the problem; the disease tends to subsequently flare up again elsewhere in the gut.
Because frequent operations have a cumulative risk and a progressively debilitating effect in themselves, surgery is delayed as long as possible. On the other hand, surgery for UC patients may be practically curative, although it may leave the patient with a stoma.
In UC, sudden gross swelling of the colon (toxic megacolon), often associated with infection, may occur. This may cause perforation of the intestinal wall and resultant peritonitis.
Crohn’s disease tends to cause more frequent intestinal perforation than UC, because although the GI wall is thickened in the condition it is insubstantial and has deep, ulcerated clefts. It therefore tends to cause fistulas through to other intestinal organs, such as the bladder, or even through to the surface of the abdominal wall. Perforation and abscesses are also quite common, and obstruction can occur.
These should be considered a medical emergency requiring surgery. Both Crohn’s and UC predispose patients to colon cancer after about 10 years, especially if the condition is poorly controlled. Therefore regular screening is necessary.
There are also possible extra-intestinal inflammatory complications that may affect patients with Crohn’s or UC. These include limb joint arthritis (up to 20 per cent of patients), spondylitis, iritis, hepatitis and dermatitis. These may either follow the course of the underlying disease, or follow an independent course (and may be the cause of first presentation).