Irritable bowel syndrome

The essentials 

- IBS is the commonest gastrointestinal disorder seen in primary care.

- In more than half of patients, a stressful event precedes onset of IBS.

- Both excess of and lack of dietary fibre may provoke symptoms.

- Under-60s with typical IBS symptoms do not usually need further tests.

- Some complementary therapies have good evidence of benefit.

1. WHAT IS IRRITABLE BOWEL SYNDROME?

Irritable bowel syndrome (IBS) is a functional gastroenterological disorder of the colon in which abdominal pain or discomfort is associated with change in bowel habit and bloating or distension.

IBS is the most common gastrointestinal disorder seen in primary care.

Despite this, only about 25 per cent of IBS sufferers seek medical attention.

The British Society of Gastroenterology has acknowledged the significance of the problem by the publication of comprehensive guidelines for its diagnosis and management (www.bsg.org.uk).

More relevant to GPs are the Primary Care Society for Gastroenterology (PCSG) guidelines for the primary care management of IBS (pcsg.lchost.co.uk and box, right).

The size of the problem

A number of community surveys agree that about 12 per cent of the population experiences IBS symptoms in any 12-month period.

The precise incidence of the condition is not accurately known, but it has been estimated at almost 1 per cent per year.

In general, women are twice as likely to suffer as men, although men are more likely to present with certain specific symptoms, notably frequent and loose stools.

IBS patients consult frequently with GI complaints. They also consult more frequently with non-GI complaints, and are more prone to problems such as lethargy and low back pain.

It has been calculated that each consulting IBS sufferer costs the NHS £90 per year. In the UK, given the incidence of new cases, the overall number of consultations probably reaches 240,000 per year. This translates into an annual cost to the NHS of around £22 million.

KEY POINTS

- As many as 12 per cent of the population suffer from IBS.

- Only a quarter of IBS patients seek medical attention.

- IBS patients consult more frequently with both GI and non-GI problems.

- The annual cost to the NHS is £22 million.

THE PCSG GUIDELINES

- Key symptoms are pain or discomfort, altered bowel habit and abdominal bloating.

- Associated non-colonic problems include upper GI symptoms, urinary and gynaecological problems, back pain, lethargy, and sometimes migraine, asthma and depression.

- Older patients with new symptoms and any patients with alarm symptoms need referral.

- Patients with predominant constipation are most likely to benefit from a high-fibre diet.

- Dietary manipulation is controversial but some patients say symptoms are strongly related to certain foods.

2. AETIOLOGY

Most IBS patients managed in primary care do not have any serious psychological morbidity. However, referred patients display a higher than normal incidence of psychological symptoms and psychiatric disease.

The role of stress Studies have shown that, in more than 50 per cent of referred patients, the onset of symptoms is associated with a stressful life event, such as work-related problems, bereavement, a surgical operation or relationship difficulties.

The pain of IBS appears to be due to visceral hypersensitivity. IBS patients exhibit decreased pain thresholds in response to balloon distension of the gut. It is probable that the central processing of visceral afferent stimuli is involved.

The significance of infection Chronic bowel dysfunction is seen in 25 per cent of patients following Campylobacter, Shigella and Salmonella gastroenteritis. Previously infected patients are more sensitive to rectal distension, and rectal biopsies indicate microscopic structural abnormalities.

In one study of 584,000 patients, the occurrence of bacterial gastroenteritis was the strongest predictor of new-onset IBS in the 12 months after enteric infection, with a relative risk of 11.9.

Is diet important?

Although many patients believe that some types of food exacerbate their IBS symptoms, evidence that the gut is sensitive to certain food types is limited.

On the other hand, studies that have incorporated dietary restrictions followed by sequential introduction of single foods have reported food intolerance in between one and two thirds of IBS patients.

The most common food intolerances in the UK involve wheat, dairy products and coffee. The introduction of a lactose-free diet may improve IBS symptoms in some patients, although even lactose malabsorbers do not experience symptoms if their daily intake is less than 0.25 litres of milk per day.

KEY POINTS

- There is evidence of lowered pain thresholds in IBS sufferers.

- Bacterial gastroenteritis is a strong predictor of new IBS cases.

- Evidence that the gut is sensitive to certain types of food is limited.

- Lactose-free diets may help a limited number of patients, but only where the intake was previously high.

3. HISTORY AND INVESTIGATIONS

A careful and detailed history is important, and is often developed over several consultations. This history should identify any relevant psychological factors, family history, and personal circumstances.

A dietary history is also useful as this will help identify any unusual dietary habits or triggering medications. For example, both excess and lack of dietary fibre may provoke symptoms in susceptible individuals.

The same is true of excesses of poorly absorbed sugars such as fructose.

Drug history

Several drugs can affect the likelihood of patients experiencing diarrhoea or constipation. Diarrhoea-predominant effects have been reported with ACE inhibitors, beta-blockers, antibiotics, chemotherapeutic agents, proton-pump inhibitors and NSAIDs. In contrast, constipation-predominant effects have been seen with opiate analgesics, calcium-channel blockers and tricyclic antidepressants.

Further assessment

If symptoms are typical and the patient is under 60 years, no further investigation beyond physical examination is usually necessary to establish a working diagnosis. However, if atypical features are present or the history is short, it may be appropriate to perform further tests to eliminate other serious conditions. These might include thyroid function tests, stool microscopy, lactose intolerance testing, endomysial antibody test (for coeliac disease) and colonic imaging.

KEY POINTS

- A detailed history is important.

- Identify any relevant psychological factors.

- Drug history may relate to diarrhoea or constipation-predominant effects.

- Further investigations, such as thyroid function tests and tests for coeliac disease, are needed if there are atypical symptoms or the history is short.

4. DIAGNOSIS

Most IBS patients are diagnosed in primary care, based on the identification of symptoms consistent with the syndrome and the exclusion of organic diseases that have similar clinical presentations.

Patients over the age of 60 with new onset of symptoms, patients with alarm symptoms such as rectal bleeding, anaemia and weight loss should be referred for specialist assessment (see box right).

Criteria for diagnosis

The Rome II criteria are the current and widely accepted standard for the diagnosis of IBS. They are valuable in clinical trials, but in practice many doctors are less restrictive in reaching a diagnosis, especially in primary care.

There should be 12 consecutive weeks or more in the past 12 months when the patient has felt abdominal discomfort or pain that has two out of three features. These features are that the pain is relieved by defaecation, associated with a change in frequency of stool, or associated with a change in consistency of stool.

An accumulation of symptoms also supports the diagnosis of IBS, and these symptoms are abnormal stool frequency, abnormal stool form, abnormal stool passage, passage of mucus, and bloating or feelings of abdominal distension.

Patients aged over 60 years presenting for the first time and/or those with atypical symptoms normally warrant hospital referral.

Similarly, patients who have been diagnosed in primary care with a functional GI disorder but whose symptoms have worsened, possibly as a result of an adverse life event, should also be considered for referral to exclude an alternative diagnosis.

KEY POINTS

- Most IBS patients are diagnosed in primary care.

- Over-60s with new symptoms and any patients with alarm symptoms need referral.

- Inform the specialist about any relevant psychological factors.

- Refer to exclude serious pathology in patients with worsened symptoms and functional GI disorder.

GUIDELINES FOR REFERRAL OF SUSPECTED COLORECTAL CANCER

All ages

- Definite, palpable, right-sided, abdominal mass.

- Definite, palpable, rectal (not pelvic) mass.

- Rectal bleeding with change in bowel habit to more frequent defaecation or looser stools (or both) persistent over six weeks.

- Iron-deficiency anaemia (haemoglobin concentration > 11.0 g/l in men or > 10.0 g/l in postmenopausal women) without obvious cause.

Over 60 years

- Rectal bleeding persistently without anal symptoms (soreness, discomfort, itching, lumps, prolapse, pain).

- Change of bowel habit to more frequent defaecation or looser stools (or both), without rectal bleeding, and persistent for six weeks.

5. TREATMENT STRATEGIES

Treatment includes a thorough explanation of IBS and its symptoms.

Being positive about the diagnosis reassures the patient that their symptoms are explainable and potentially treatable.

Complementary medicine

Hypnosis, biofeedback and psychotherapy all have evidence of benefit in referred patients. A recent trial of CBT demonstrated its effectiveness in a general practice population.

Pharmacological treatments

The evidence for efficacy of drug therapies for IBS is weak. Although there is evidence of benefit for antispasmodic drugs for abdominal pain and global assessment of symptoms, it is unclear whether anti-spasmodic subgroups are individually effective. There is no clear evidence of benefit for antidepressants or bulking agents.

Global assessment of symptoms is a construct containing various dimensions.

For each individual, these will have a different weighting and treatment should be aimed at the most debilitating symptom. Stool problems are by definition part of the IBS symptom complex.

Bulking agents may improve constipation and can be used empirically, but should be evaluated at an early stage for individual benefit.

Antispasmodics are often used to treat abdominal pain. These drugs relax smooth muscle but vary in their specificity.

Antidepressants modify gut motility, and alter visceral nerve responses.

These responses are usually seen long before effects on mood are evident.

5HT-active drugs

Two newer classes of compound that have shown promise in the treatment of IBS act on 5HT receptors. Early reports indicate that 5HT4 agonists improve constipation while 5HT3 antagonists reduce symptoms of diarrhoea.

However, their precise role in the primary care management of patients is not yet established.

Diarrhoea and constipation

For patients with symptoms of diarrhoea, loperamide is effective. It slows large and small intestinal transit, and reduces stool frequency and urgency. Loperamide can also be taken prophylactically to avoid embarrassing incidents during work or leisure pursuits.

For patients with constipation, increased intake of dietary fibre, including those derived from cereals, fruits, and vegetables has been shown to increase stool weight and accelerate gut motility.

KEY POINTS

- Make IBS diagnosis and reassure the patient.

- Simply listening sympathetically about ongoing symptoms can help.

- Some complementary therapies have evidence of benefit.

- Antispasmodics help abdominal pain.

FURTHER RESOURCES

Further reading

Guidelines for the management of IBS in general practice. Primary Care Society for Gastroenterology. www.pcsg.org.uk Quartero A O, Meineche-Schmidt V, Muris J, Rubin G, de Wit N. Bulking agents, antispasmodic and antidepressant medication for the treatment of irritable bowel syndrome. The Cochrane Database of Systematic Reviews 2005, Issue 2.

WEBSITES

See Medicine on the Web, page 57.

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