Pathophysiology of Irritable Bowel Syndrome (IBS) :- IBS encompasses a wide range of symptoms and a single cause is unlikely. It is generally believed that most patients develop symptoms in response to psychosocial factors, altered gastrointestinal motility, altered visceral sensation or luminal factors. 1. Psychosocial factors Most patients seen in general practice do not have psychological problems but about 50% of patients referred to hospital meet the criteria for a psychiatric diagnosis. A range of disturbances are identified, including anxiety, depression, somatisation and neurosis. Panic attacks are also common. Acute psychological stress and overt psychiatric disease are known to alter visceral perception and gastrointestinal motility in both irritable bowel patients and healthy people. There is an increased prevalence of abnormal illness behaviour with frequent consultations for minor symptoms and reduced coping ability. These factors contribute to but do not cause IBS. 2. Altered gastrointestinal motility A range of motility disorders are found but none is diagnostic. Patients with diarrhoea as a predominant symptom exhibit clusters of rapid jejunal contraction waves, rapid intestinal transit and an increased number of fast and propagated colonic contractions. Those who are predominantly constipated have decreased orocaecal transit and a reduced number of high-amplitude, propagated colonic contraction waves but there is no consistent evidence of abnormal motility. 3. Abnormal visceral perception IBS is associated with increased sensitivity to intestinal distension induced by inflation of balloons in the ileum, colon and rectum, a consequence of altered central nervous system processing of visceral sensation. This is more common in women and in diarrhoea-predominant IBS. 4. Infection and allergy Between 7 and 32% of patients develop IBS following an episode of gastroenteritis, more commonly young women and those with existing background psychological problems. Others may be intolerant of specific dietary components, particularly lactose and wheat. Abnormalities of gut microflora leading to increased fermentation and gas production and minimal inflammation have also been postulated. Some patients have subtle, histologically undetectable mucosal inflammation, possibly leading to activation of inflammatory cells and release of cytokines, nitric oxide and histamine. These may trigger abnormal secretomotor function and sensitise enteric sensory nerve endings. ► Tejin ► [Davidson’s Principles and Practice of Medicine Twenty-first edition 2010]
Posted on: Wed, 10 Jul 2013 16:16:14 +0000
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