The Irritable Bowel Syndrome (IBS)

This is the commonest functional gastrointestinal disorder, the one year prevalence being ~19% but only a third present to their GPs.¹ If the strict Rome III criteria for IBS are used,² it affects around 5-11% of individuals, with similar prevalence in developed or developing countries.³

It may present at any age (peak prevalence in 30s and 40s - female predominance is most obvious in the 3rd decade and declines afterwards).³
Symptoms may emanate from the whole gut rather than just the colon.
There is no structural lesion, but it may be explained by abnormal smooth muscle activity ± visceral hypersensitivity (there appears to be an association with bronchial hyper-responsiveness)⁴ and abnormal central processing of painful stimuli.

There appears to be a significant subgroup of patients in whom IBS is precipitated by an episode of bacterial gastroenteritis (~10% in one study)⁵ - they have predominantly diarrhoeal symptoms, less psychiatric illness, and increased serotonin-containing enterochromaffin (EC) cells compared with other IBS patients.⁶

Further notes on IBS features

• Most patients have abdominal pain and disordered bowel habit, continuous or intermittent. This may be predominantly diarrhoea, predominantly constipation, or alternating between the two. A "morning rush" is common: patients feel the urgent need to defecate several times on getting up, during and after breakfast.
• Symptoms are chronic, with remissions interrupted by relapses precipitated by stress or changes in bowel flora produced by antibiotics.
• Symptoms may begin following an episode of gastroenteritis.⁶
• Upper GI symptoms may include nausea, heartburn, dysphagia, and early satiety.
• Extra-intestinal symptoms such as headaches and migraine, asthma, backache, lethargy, dyspareunia, urinary frequency, and urgency are more commonly reported by patients with IBS. Psychological problems (anxiety and depression) are also more common, although some psychological morbidity appears to be associated with health care-seeking rather than with IBS per se.

Subclasses of IBS⁹

• Approximately one third of patients have IBS with constipation (IBS-C) = loose stools <25% and hard stools >25% of the time.
• Approximately one third of patients have IBS with diarrhoea (IBS-D) = loose stools >25% and hard stools <25% of the time.
• The remainder have IBS-mixed (IBS-M) = both hard and soft stools >25% of the time.

Signs

On abdominal examination, signs may be few and nonspecific (eg tender, palpable colon). A rectal ± pelvic examination may be appropriate.

The condition has a considerable impact on quality of life - comparable with type 2 diabetes, IHD or depression.¹⁰

Colonic cancer; inflammatory bowel disease, Coeliac disease,¹¹ gastroenteritis (eg giardiasis), ischaemic colitis, gynaecological problems (eg endometriosis, ovarian tumours), anxiety ± depression, somatization and panic disorders.

• Carefully and sympathetically elicit a history and carry out an appropriately thorough physical examination.
• Check FBC and inflammatory markers (CRP and either ESR or plasma viscosity).⁷
• Serological testing for coeliac disease,⁷ particularly in patients with IBS-D, and in areas of high incidence, as this diagnosis is easily missed.
• TFTs ± stool culture are not normally indicated but may be appropriate in patients with recent onset IBS-D.
• Ask about a family history of inflammatory bowel disease or colon cancer aged <50 - as this should lower threshold for investigation/referral.³
• Lactose intolerance testing (lactose breath hydrogen test) and/or measuring faecal fats (malabsorption?) may be helpful in some cases.

Refer patients when there is diagnostic uncertainty, alarm symptoms, or severe resistant symptoms (e.g. for more specialist treatments, exclusion diets, etc.) - GPs refer about one in seven cases to specialists.

Gastroenterology referral:
• Lower bowel investigations - colonoscopy, or sigmoidoscopy ± barium enema. A rectal biopsy may be appropriate (to diagnose inflammatory bowel disease).
• Gastroscopy may be appropriate if upper GI symptoms predominate.
• Gynaecological referral may help rule out endometriosis and pelvic infection.
• Consider psychological referral if main problems are inability to cope with symptoms.

Beware of unnecessary specialist referral and interventions eg hysterectomy and cholecystectomy. Referral may prolong anxiety as much as allay it.

Having confidently made the diagnosis, reassurance and explanation are vital, including frank explanation of the likely course of disease. Many patients may have a fear of cancer, but only careful and often repeated explanations of the nature of the disease reduces this.

Lifestyle, diet and physical activity

• Provide information about self help covering lifestyle, physical activity, diet and symptom-targeted medication.
• Encourage patients to identify and make best use of leisure time, and create times in the day for relaxation.
• Assess physical activity levels (eg General Practice Physical Activity Questionnaire, GPPAQ) and give advise on increasing activity if appropriate.
• Give general advise on diet:

• Constipation Predominant (IBS-C)
  • Encourage patients to eat at regular intervals and increase exercise.
  • Increase dietary insoluble fibre (eg wholegrain cereals) and soluble fibre (other cereals, fruit and vegetables) - but be aware that increasing the latter may increase bloating and wind. Ispaghula husk (soluble fibre - bulking agent) has been shown to increase stool frequency (better tolerated than wheat bran) and improves overall symptoms and IBS related constipation (insoluble fibre only helps the constipation).¹⁵
  • Supplement if necessary with an osmotic laxative (eg lactulose or magnesium hydroxide) or stool softener (liquid paraffin) - avoid stimulant laxatives (can cause cramping pains).
  • Selective serotonin 4 (5-HT4) receptor agonists (eg tegasarod) have prokinetic activity and are licensed in many parts of the world for short term use in IBS-C. They appear to improve overall symptomatology, but there is little data on their effect on quality of life.¹⁶
• Diarrhoea predominant (IBS-D)
  • Symptoms may respond to low fat diet, reduced caffeine intake and stopping smoking.
  • Some fibre helps - but patient may need to reduce a particularly high fibre intake. Excessive supplements (eg vitamin C or magnesium) can also cause diarrhoea, as can a high fructose intake in some individuals.
  • Loperamide (opioid analogue) reduces stool frequency and urgency, and improves stool consistency without the sedation and drug dependency of codeine. Titrate dose carefully to avoid constipation.
  • Low dose tricyclic antidepressants help pain,¹⁷ and as they also tend to cause constipation, they may have particular benefit in IBS-D.
  • 5-HT3 receptor antagonists (eg ondansetron) are being developed.
• Abdominal spasms
  • Smooth muscle relaxants (eg mebeverine and alverine) appear to improve global rating of symptoms and reduce pain in IBS patients.¹⁷ They have relatively few adverse effects but only benefit some patients.
  • Antimuscarinics (hyoscine and dicycloverine/dicyclomine) are occasionally helpful, but anticholinergic side-effects limit use.
  • Peppermint oil is a commonly recommended as a smooth muscle relaxant It may help symptoms of abdominal pain, distension, and stool frequency (more evidence needed).¹³
  • Transcutaneous nerve stimulation (TENS) may be effective for pain, but usually has no effect on other symptoms.

• Low dose tricyclic antidepressants may be effective in reducing pain.¹⁷ If depression is a feature a standard antidepressive dose may be appropriate¹⁸ - tricyclics tend to constipate and SSRI's may cause diarrhoea. Nice recommends trying tricyclics before SSRIs.⁷
• Only use tranquillisers (eg Diazepam) if symptoms are stress-related; and then only use short-term.
• Chinese herbal medicine has been used with success¹⁹ (as long as drugs like aristolochia, stephania and clematis are avoided). Recent RCT has shown a commercially available herbal preparations containing nine plant extracts (STW 5) is effective in reducing symptoms in IBS; (as was a research herbal preparation STW 5-II containing six plant extracts).²⁰
• Short term therapy with probiotics such as Lactobacillus Plantarum LP01 and Bifidocterium Breve BR0 shows some benefit in reducing symptoms, but more research is needed.²¹ If a patient wants to try these - take only recommended dose for at least 4 weeks while monitoring effects.⁷
• New drugs, such as cholecystokinin, neurokinin, and corticotropin receptor antagonists are being developed.
• Aloe vera is not recommended.⁷

The diagnosis of IBS rarely alters over time, but be prepared to reconsider the diagnosis if the clinical picture changes. More than 50% will continue to have symptoms after 5 years. IBS is not associated with the long-term development of any serious disease, although IBS patients are more likely to undergo certain surgical operations, (e.g. hysterectomy or cholecystectomy) than controls.²² Patients with a long history being less likely to improve. The post infective subgroup appear to have a better prognosis, symptoms resolved within 6 years in about half of patients.⁵