Irritable bowel syndrome

Published on 08/04/2015 by admin

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Chapter 9 IRRITABLE BOWEL SYNDROME

KEY POINTS

• Irritable bowel syndrome (IBS) is a highly prevalent condition affecting 15% of the population.
• IBS is defined by chronic or relapsing abdominal symptoms (pain and/or discomfort) associated with an abnormality of bowel movements (loose or hard, or more or less frequent stools at pain onset) in the absence of structural lesions.
• In the absence of alarm features (e.g. weight loss, vomiting, rectal bleeding) or advanced age, a diagnosis of IBS usually can be made with no additional testing.
• Communicating the diagnosis and explaining the prognosis is key for further treatment.
• A proportion of patients with IBS suffer from concomitant anxiety or depressive disorders.
• Proper dietary assessment and advice may help identify triggers for symptoms.
• Target the dominant symptoms (i.e. abdominal pain, constipation or diarrhoea) when planning symptomatic treatment.
• Low-dose tricyclic antidepressants, psychological interventions or hypnotherapy can be considered in patients with severe symptoms not responding to the conventional therapies.

DEFINITIONS AND CATEGORIES

In less than 50% of patients with chronic or relapsing symptoms such as abdominal pain or discomfort, structural or biochemical abnormalities can be found that explain these symptoms. On the other hand, even if there are structural abnormalities, such as diverticula in the sigmoid colon, these abnormalities may not explain the symptoms in patients presenting for assessment. If there are no abnormalities explaining symptoms, a functional gastrointestinal disorder can be diagnosed.

If there is no structural abnormality to explain the symptoms, and symptoms such as pain or discomfort are associated with changes in bowel habit, irritable bowel syndrome (IBS) can be diagnosed. The most stringent definitions for functional gastrointestinal disorders have been provided by the Rome Committee, an international working party. The Rome III criteria for IBS are summarised in Table 9.1. Essentially, IBS can be diagnosed when structural lesions are absent (or unlikely based upon the clinical presentation) and the patient suffers from chronic or relapsing abdominal discomfort or pain associated with an abnormality of bowel movements (constipation, diarrhoea or alternating diarrhoea and constipation). Bloating is also common.

TABLE 9.1 Diagnostic criteria for irritable bowel syndrome (Rome III)

Recurrent abdominal pain or discomfort for at least 3 months, and symptoms at least 3 days/month associated with two or more of the following:

1. Relief of pain or discomfort with defecation
2. Onset of pain or discomfort associated with a change in bowel frequency
3. Onset of pain or discomfort associated with a change in form (appearance) of stool (loose or hard stools)

Based upon the symptoms, patients with IBS are usually categorised into one of three groups: IBS with predominant diarrhoea (IBS-D) or predominant constipation (IBS-C) or a mixed pattern of diarrhoea and constipation. Alternating refers to changing from diarrhoea to a constipation pattern (IBS-A). There is a group of patients who develop IBS symptoms after an episode of acute infectious diarrhoea, sometimes accompanied by fever, nausea and vomiting. This syndrome is now labelled post-infectious or PI-IBS. Interestingly, post-infectious IBS is usually associated with diarrhoea predominant IBS. Chronic abdominal pain or discomfort in the absence of abnormalities in stool pattern is not IBS, but is called chronic functional abdominal pain.

EPIDEMIOLOGY

The prevalence of IBS ranges from 10% to 20% in Western countries, and it is just as common in India, Japan and China. Only one out of three people who have symptoms of IBS seek medical attention. Generally, those who have more severe symptoms seek medical help. IBS is more prevalent in females. While IBS is not life-threatening, it is remarkable that affected patients have a substantial number of days off work, and thus society has to cope with the burden of IBS too.

PATHOPHYSIOLOGY OF IBS

A number of mechanisms are believed to be involved in the manifestation of IBS. Indeed, there is evidence accumulating that IBS is not one disease, but most likely represents a group of disorders with different pathophysiologies.

Genetic and environment

IBS runs in families. It is reasonable to speculate that specific genetic factors in combination with the exposure to specific environmental factors cause IBS. The environmental influences (e.g. infections or stress) most likely have different effects based upon an array of factors that include genetic predisposition.

Sensorimotor dysfunction

There is sufficient evidence from numerous studies that, at least in a proportion of patients, abnormal gut sensory function is present (increased sensitivity to innocuous stimuli in the gut).

Food intolerance

A proportion of patients report intolerance of specific foods. There is evidence for hypersensitivity but usually not food allergy. However, diets that carefully exclude these nutrients rarely succeed in providing long-lasting relief.

Gastrointestinal flora and bacterial overgrowth

Emerging evidence suggests that, at least in a subgroup of patients, small intestinal bacterial overgrowth may be present. Antibiotic therapy has improved symptoms, especially bloating, more than the placebo, but more data are needed.

Psychological factors

Up to two-thirds of patients with IBS referred to a tertiary centre suffer from depression or anxiety disorders. In addition, it is striking that IBS patients are more likely to report a history of physical or sexual abuse. However, IBS is not simply a psychological disorder.

MANAGEMENT

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