Irritable bowel syndrome (IBS) is a common condition, with reported UK prevalence rates varying from 5 to 22 per cent. It has been found to occur twice as frequently in women.
The current standard definition is based on the Rome II criteria for IBS (see box, right). There are no pathognomonic features, therefore the diagnosis is one of exclusion.
The pathophysiology of IBS is unclear. It is likely to be multifactorial in origin.
Current suggestions include gastrointestinal motility disorders, visceral hypersensitivity, psychiatric disease, abnormal illness behaviour such as hypochondriac beliefs, smooth muscle abnormalities not specific to the GI tract and diet.
A detailed history should be taken covering at least the previous few months.
Psychological, social, personal and family histories are important. A diagnosis of IBS is likely if the patient is under 45 years of age, with long-standing and fluctuating symptoms, no family history of colorectal carcinoma, a normal physical examination and no alarm features.
Other non-gastrointestinal features that support a diagnosis of IBS include lethargy, fibromyalgia and dyspareunia. The diagnosis is confirmed by continued observation.
Reasons to refer include age over 45 at presentation (onset in old age is rare), atypical symptoms, new symptoms in a patient with an existent diagnosis of IBS, alarm features (anorexia, weight loss, rectal bleeding), family history of carcinoma of colon, breast, ovary or uterus, and severe, more constant, or poorly responsive symptoms, or where the GP cannot supply adequate reassurance.
Differential diagnoses include gastrointestinal malignancy, inflammatory bowel disease, malabsorption, gastrointestinal infection (for example giardiasis), gastrointestinal disorders such as diverticulitis, urological, gynaecological, endocrine and psychological disorders.
The patient’s concerns need exploration and reassurance is essential. In up to 70 per cent of cases, treatment produces an initial placebo effect.
Lifestyle advice should be given. A daily diary recording symptoms along with stressful events and food taken might suggest areas for modification.
Constipation may be improved by increasing dietary fibre and fluid. Excess fibre, dietary fat, alcohol and caffeine may cause diarrhoea.
Some patients notice that certain foods trigger symptoms (for example dairy foods). Wheat bran may help some patients, but on the other hand 55 per cent find it causes exacerbation of symptoms; in such cases ispaghula husk may help if additional fibre is required.
Patients without marked psychological disorders may benefit from relaxation therapy, hypnotherapy and biofeedback.
Those with pronounced psychiatric disorders may be suitable for cognitive behavioural therapy, dynamic psychotherapy, or psychiatric referral.
Pharmacological treatments are of long-term benefit in only a few patients and may make the situation worse if there is underlying, untreated psychological illness.
Treatment may be preferable for those with periodic symptoms. Tricyclic antidepressants are most effective, having an effect on motility of the gut and they also treat any underlying depression .
Abdominal pain treatments include antispasmodics (mebeverine), antimuscarinics (hyoscine butylbromide), tricyclic antidepressants and peppermint oil.
Lactulose may worsen abdominal distension. There is insufficient evidence for use of stimulant laxatives in IBS.
Diarrhoea treatments include loperamide and can be used prophylactically. It also helps with symptoms of urgency. Codeine may help but problems include sedation and risk of dependency. Bile salt induced diarrhoea may be treated with cholestyramine.
Dr Price is a medical examiner for the Department for Work and Pensions and a former GP in Hampshire
At least 12 weeks (which need not be consecutive) in the preceding 12 months of abdominal discomfort or pain that has two of the following three features:
- Relieved by defaecation.
- Onset associated with a change of frequency of stool.
- Onset associated with a change in form of stool.
Symptoms supporting the diagnosis of IBS:
- Abnormal stool frequency.
- Abnormal stool form.
- Abnormal stool passage.
- Passage of mucus.
- Bloating feeling or abdominal distension.
- British Society of Gastroenterology guidelines for the management of irritable bowel syndrome. Gut 2000; 47: ii1–ii9.
- Drossman et al. Rome II the functional gastrointestinal disorders. Second edition. Degmon Associates , McLean, UA 2000.