Irritable bowel syndrome functional bowel disorders

Pathophysiology/epidemiology

Irritable bowel syndrome (IBS) is one of several functional bowel disorders, including noncardiac chest pain, functional dyspepsia, epigastric pain syndrome, postprandial distress syndrome and chronic proctalgia, which represent diagnoses of exclusion that are based on symptomatology [22]. IBS has been demonstrated to be associated with abnormalities of motility and/or sensation in different subpopulations. The diagnosis of IBS is given to 40-70% of referrals to gastroenterologists.

IBS typically presents in the third or fourth decades of life and has a female to male ratio of 2:1. In general populations, up to 20% of women and 10% of men experience symptomatology consistent with IBS, but most people with these symptoms do not seek medical care. Of those who do seek care, 50-60% have significant symptomatology consistent with depression and/or an anxiety disorder [23, 24]. IBS symptomatology is present in many cultures, with similar prevalences noted in Britain, China, India, Japan, New Zealand, the United States and South America. Other disorders without identifiable histopathology such as fibromyalgia and mixed headaches are common co-morbidities [24].

There exist many diverse hypotheses related to the etiology of IBS, ranging from the purely psychosocial to neuropathic processes producing visceral hyper-sensitivity (the equivalent of somatic hyperalgesia/ allodynia). Peripheral sensitizing substances such as cytokines released by mast cells have been hypothesized as mechanistic agents of hypersensitivity [25].

Evaluation and treatment

The diagnosis of IBS requires the positive findings of disturbed bowel habits and a history of pain/discomfort coupled with negative findings for neoplas-tic, infectious or inflammatory causes. It is defined by the Rome criteria, now in their third form [26], as 3 months of continuous or recurrent symptoms of abdominal pain or discomfort associated with two of the following: an improvement with defecation and/ or a change in stool consistency (appearance) and/or a change in stool frequency. At least three different clinical presentations are given the diagnosis of IBS, two of which have pain/discomfort as a minor component (watery diarrhea group and alternating constipation/diarrhea group respectively). There is a third subgroup of IBS patients who have abdominal pain as their primary symptom and altered bowel movements as a secondary or exacerbating complaint. In this group, pain is typically in the left lower quadrant or in the suprapubic region and may be precipitated by food ingestion and a need to defecate. Bloating, mucus in the stools and flatulence are often prominent, and anxiety may exacerbate these symptoms. Although there is great variation between patients, the particular symptom complex for a given patient generally remains constant. Generalized abdominal tenderness to palpation is common. The classic physical finding is a tender, palpable sigmoid colon in the left lower quadrant.

As a diagnosis of exclusion, imaging and laboratory findings should be negative for neoplasm, inflammatory bowel disease, infection, diverticulosis or other intra-abdominal processes. Colonoscopy and/

or barium enema radiography should be negative for any focal lesions. Stool samples should not have occult blood or infectious agents present. It is generally agreed that the colons of most patients with IBS are exceptionally reactive to physiologic stimuli such as eating [27]. Unfortunately, this finding is only supportive evidence for the diagnosis. Motility studies and sensation evocation with a distending balloon in the rectum or sigmoid colon may prove valuable in the stratification of patients into different subgroups.

Irritable bowel syndrome has frequent exacerbations and may have spontaneous resolution. As a consequence, open trials are of limited value due to high placebo rates. Interventional treatments are not a major component of therapy because, by definition of the disease, there is no structural pathology to treat. Life-threatening pathology can be ruled out without an exhaustive investigation. However, the patient needs to be assured that their symptoms are believed. There are no universally accepted treatments for IBS [26-28] but some therapeutic options are listed in Box 15.2. Due to the typically stable nature of a patient's symptom complex, once significant pathology has been ruled out, additional or repeat investigation is not necessary unless the symptom complex changes.

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