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Definition of IBS

A relapsing functional bowel disorder presenting with abdominal discomfort, change in bowel habit and bloating in the absence of clear organic cause.


Prevalence of IBS

  • Approximately 10-20% in the UK at some point
  • Women more than men


Presentation of IBS

  • Abdominal pain or discomfort (especially cramping)
  • Bloating (key feature – less common in other conditions)
  • May present as recurrent non-cardiac chest pain
    • Angina-like but tends to radiate to the back
    • All cardiac investigations negative


Differential diagnosis of IBS

  • Inflammatory bowel disease
  • Colonic malignancy
  • Chronic gastroenteritis (e.g. giardiasis)
  • Ischaemic colitis
  • Diverticular disease
  • Gynaecological pathology
    • Endometriosis, pelvic inflammatory disease, ovarian cancer
  • Psychological overlay
    • Anxiety and depression
    • Somatisation


NICE diagnostic criteria for IBS

A six-month history of either:

  • Abdominal pain or discomfort
    • Usually relieved by defecation
  • Bloating
  • Change in bowel habit (25% have constipation, 25% diarrhoea, 50% alternating)

AND  at least 2 of the following:

  • Altered passage of stool (straining, urgency, incomplete evacuation)
  • Abdominal bloating or distension
  • Aggravation with food
  • Passage of mucous

Lethargy, nausea, backache and bladder symptoms may be used to support diagnosis.


Pathophysiology of IBS

  • Increased motor activation within the bowel
  • Increased sensory thresholds
    • Balloon dilatation in the bowel gives lower pain thresholds in those with IBD than those without


Investigations in IBS

Note that IBS is a clinical diagnosis; these investigations are to rule out other pathology.

  • TGA (Coeliac)
  • TFTs
  • Ca-125 in women
  • Consider lactose breath test and faecal fats


Management of IBS

  • Overview

    • Be nice. Be understanding. This is a functional disorder. That means it is as real as any other issues, it is just a problem with function (either motor or sensory) as opposed to structure.
    • A key feature of good response to treatment in IBS is the doctor-patient relationship. There therefore needs to be a constructive dialogue from the start.


  • Lifestyle

    • Dietary advice [note this is completely different from what is normally advised for health and will need to be explained in terms of fibre being an irritant to the GI tract, hence the removal of fibre-heavy foods].
      • Low fibre
        • Remove cereals first. Then remove vegetables, then fruit (or at least try to cut down).
    • Good hydration
    • Cut out caffiene
    • Stop smoking


NHS video on IBS. Note the mention of dietary fibre which is often noted by patients to be related to symptoms. However, contrary to popular belief high dietary fibre is likely to worsen IBS symptoms as opposed to alleviating them.



  • Antispasmodics (e.g. mebevirine)
  • Loperamide ( if diarrhoea and infective causes ruled out)
  • Laxatives (if constipation if the predominant symptom)
    • e.g. movicol – NOT fibre-based laxatives such as lactulose
  • Low dose TCA is very effective
    • Amitriptilline (10mg, titrate to 50mg)
      • Note this is far less than antidepressant dosing
    • Nortriptylline tends to have less side-effects so may be better tolerated
      • Works on sensory GI pathways
  • Treat co-existent depression or anxiety
    • SSRI can help anxiety if this is the predominant feature
  • Hypnotherapy can be effective in 70% but only available in specialist centres


Prognosis in IBS

  • More than 50% will continue to have symptoms after 5 years