Dr John Wright

Gastroenterologist
MbChB MRCP(UK) PhD

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Irritable Bowel Syndrome: Back to Basics

Dr John P Wright
Updated: 28 April 2013

Of all gastrointestinal conditions irritable bowel syndrome (IBS) is the most misunderstood. It is a physiological disturbance rather than a disease. Most people will have some symptoms of IBS but view these as a normal consequence of life itself. Others are highly stressed by them and further aggravated by their understanding of a normal diet. Unfortunately the perceived healthy diet includes lots of vegetables and fruit, the two factors that commonly aggravate IBS symptoms. While the medical profession struggles with the physiology and treatment of IBS legions of health shops, alternative practitioners, nutritionists and popular magazines claim to have the answer. A certain distrust of the profession at the health promotion level gives disproportionate power to these alternative sources and the lady in the checkout queue(1).

We, the traditional scientific medical practitioners, have spent too much effort on defining the condition. The Rome Criteria are regularly refined in an attempt to encapsulate the clinical presentation of these patients(2).. This misses the point that IBS is a syndrome of disturbed intestinal physiology with deranged processes that lead to the clinical symptoms. The clinical approach is therefore to identify the disturbed physiology, exclude other pathology and manipulate the physiology back towards normal. To achieve this, the most important investigation is the clinical history. The aim is not to check the boxes of diagnostic criteria but understand where and how the symptoms originate. The clinical history therefore needs to concentrate on the pathophysiology demonstrated by the patient.

The 4 pillars of IBS pathophysiology are

  1. Intestinal dysmotility(3).
  2. Hypersensitivity of the intestinal tract to distension. (4).
  3. Psycho-social factors(5).
  4. Dietary factors(6).

Numerous studies have addressed the above problems and a logical all-encompassing model has not yet been formed or accepted by the scientific community. Based on the above factors treatment is usually random and ineffectual with a sub-conscious nod to a perceived hypochondriacal patient.

The first factors to elucidate are

  1. Is the bowel habit one of constipation, diarrhoea or variable? IBS patients with diarrhoea need to be approached differently as many diseases such as coeliac disease or inflammatory bowel disease need to be ruled out.
  2. Is the patient bloated?
  3. Is there excessive flatus?
  4. Is there cramping abdominal pain which can be related to gastrointestinal function?

Let us now associate these symptoms with the underlying pathophysiology.

  1. Constipation is the inevitable consequence of non propulsive motility and inadequate stool formation. This leads to a colon full of stool and an associated increase in gas production. Small stools and excessive mucous production are well recognised by patients who often revert to intestinal stimulants to improve bowel function. Fruit and other laxatives are used which may encourage defaecation but increase the hypersensitivity of the intestinal tract and completes the vicious circle which makes up IBS.
  2. Bloating is due to relaxation of abdominal muscles and downward movement of the diaphragm(7).. Although most bloated patients produce excessive flatus the mechanism is completely different. Bloating is a posture common to most mammals in response to intestinal spasm…
  3. Excessive flatus comes from three possible sources. The most important is from the stool retention associated with constipation and the bacterial substrate it contains(8,9).. This can be reduced by avoiding the gas producing leaves such as cabbage, broccoli and cauliflower. Aerophagia due to stress will cause primarily belching but also odourless flatus. Gas from malabsorbed carbohydrate such as lactose and fructose may complicate the diagnosis of IBS but are not the primary cause.
  4. Cramping abdominal pain is usually related to bowel function. This is most common prior to defaecation but also during and after defaecation. The pain can be very severe. Protalgia fugax is a related severe, searing and stabbing rectal pain which characteristically wakes the patient at night(10).