Pathophysiology and Management of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a chronic relapsing disorder of the gastrointestinal function, the main features of which are abdominal pain or discomfort and an alteration of bowel habit. IBS has a complex, multifactorial etiology and is recognised as the most common disorder diagnosed by gastroenterologists; it is also very commonly encountered in primary care practice. Consequently, it has a huge socioeconomic impact on health care resources in most industria lised societies 1 , 2 ) . Definitions of IBS have continued to evolve over the last two decades, initiated by the seminal study of Manning et al ) in which several symptoms which typically cluster together in IBS were identified. These included: pain relief by defecation, more frequent stools occurring at the onset of pain, looser stools occurring at the onset of pain, visible abdominal distension, passage of rectal mucus and a sensation of incomplete evacuation after defecation. Several years ago, an international consensus definition of IBS was termed the "Rome criteria", based largely on the Manning criteria. In the Rome classification, functional (painless) diarrhea and functional (painless) constipation were regarded as separate entities from IBS. Over the last five years, the Rome criteria for IBS have become accepted as the stateoftheart criteria for research studies. Recently, they have been refined, focusing on the essential components of abdominal pain and an altered bowel pattern (Table 1) . Work is underway to further determine the specificity of these criteria, particularly in the light of new potential pathophysiological markers which include visceral hyperalgesia and detectable histological and immunohistochemical alterations in the small and large intestine. The importance of the Rome criteria lies in the fact that they can be used to diagnose IBS positively, in conjunction with the selective use of investigations to exclude "organic" disease. The prevalence of IBS varies according to the diagnostic symptom criteria employed (for example, the Rome I or II criteria, the Manning criteria etc.), but ranges from about 3% in the US ) to up to 20% in population samples ) : the incidence of IBS is 1-2% per year. Although the Rome II consensus does not recommend formal subgrouping of IBS according to the predominant bowel pattern, it does provide working definitions for constipationand diarrheapredominant subgroups, if required . A third subgroup, socalled alternating IBS, can be recognised clinically; it is generally recognised that the above three subgroups each constitute about onethird of IBS cases. Recently, a Swedish report ) has characterised, by cluster analysis, three different subcategories of IBS the first distinguished by hard stools , varying stool consistency and a highly disturbed stool passage; the second by loose stools and urgency; and the third by normal stools with little disturbance in stool passage, but with considerable abdominal pain and bloating. Interestingly, in this study no relationship was found between pain/bloating and bowel habit in terms of the subgrouping. Postprandial exacerbation of symptoms is common in IBS , a factor not specifically included in the Rome criteria . Finally, extraintestinal symptoms are also common in IBS, including headache, backache, urinary and gynecological symptoms, and fatigue; these appear to be more common in the IBSconstipation subgroup. In Western countries , women tend to present to doctors with symptoms of IBS more frequently than men, and a femaletomale ratio of up to 3:1 has been reported in some studies 9 , 10 ) . The apparently higher prevalence of IBS in women is seen in all age groups P a t h o p hy s io lo g y a n d Ma n a g e m e n t o f Ir r it a b le Bo w e l S y n d r o m e