Irritable bowel syndrome

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


Even though IBS does not carry any risk for excess mortality, effective management of and treatment for these patients is important since this disorder can cause severe and sometimes disabling symptoms, impairment of quality of life and, if inappropriately treated, may trigger unnecessary costs for diagnostic and therapeutic measures. Establishing the diagnosis is the first step and, for further management, the most important step. IBS can be diagnosed in the majority of patients without any tests, simply based upon the clinical presentation. While a colonoscopy may not find structural lesions that explain the chronic symptoms in the majority of patients, it may still be helpful to reassure the patient or, if the patients are 50 years of age or older, may be a preventive measure with regard to the early detection of colonic polyps and cancer.



Diagnostic tests


For many years, IBS was considered a diagnosis of exclusion. Patients with alarm symptoms or signs (red flags) such as weight loss, fever, rectal bleeding, malnutrition (or laboratory abnormalities such as anaemia, a low albumin level or an elevated white blood count) need to undergo a diagnostic work-up before the diagnosis of IBS can be made. However, current best evidence does not support the routine use of tests in order to exclude organic gastrointestinal disease in patients with typical IBS symptoms without alarm features. Serological testing for coeliac sprue only might be useful (5% with IBS-type symptoms may have coeliac disease). However, alarm features or persistent non-responsive symptoms should prompt a more detailed diagnostic evaluation.


The diagnosis of IBS is based on patient descriptions of common symptoms and, in particular, abdominal pain or discomfort accompanied by changes in stool form or frequency, often associated symptoms such as bloating and distension. A review of the literature shows that, in patients with no alarm symptoms, the Rome criteria have a positive predictive value of approximately 98%, and that additional diagnostic tests have a yield of 2% or less. The diagnostic evaluation ideally should also include a psychosocial assessment specifically addressing any history of sexual or physical abuse because these issues significantly influence management strategies and treatment success.


While the evidence for a comprehensive diagnostic work-up to establish the diagnosis of IBS is poor, it needs to be acknowledged that the response to treatment is frequently disappointing. Even treatments that are considered to be effective only yield a gain over placebo that does not exceed 10%–20%. Thus, a large proportion of patients that are diagnosed on clinical grounds as having IBS ultimately will have further diagnostic measures simply because the symptoms do not respond to therapy or symptoms relapse after a while.


If tests are being considered, a complete blood count, erythrocyte sedimentation rate (or C-reactive protein), serum chemistry and albumin, and stool examination for ova and parasites can be ordered. However, the cost-benefit of these tests is not established. Coeliac disease serological testing (e.g. transglutaminase) should be ruled out by appropriate serological testing and appears to be cost effective. While not necessary from the perspective of establishing the diagnosis of IBS, in patients over 50 years of age, a colonoscopy is recommended due to the increased probability of colon cancer. In younger patients, colonoscopy or sigmoidoscopy with biopsies can be performed, based upon relevant clinical features (e.g. diarrhoea to exclude microscopic colitis).


The need for additional diagnostic tests such as thyroid stimulating hormone (TSH) may depend on the symptom subtype. For example, for constipation-predominant symptoms, a therapeutic trial of fibre supplementation may be sufficient. The American Gastroenterological Association guidelines recommend that in patients who do not respond to fibre, confirmation of slow colonic transit with a whole gut transit test, or evaluation for obstructed defecation with anorectal motility and balloon expulsion test, might be indicated. In patients with diarrhoea-predominant symptoms, clinical judgment will determine the further diagnostic work-up. In patients with relapsing or chronic loose/watery stools, a lactose/dextrose H2 breath test for bacterial overgrowth, serology for coeliac sprue or biopsies of the small intestine (for Giardia, small bowel malabsorption) or colon (for microscopic colitis) might be necessary. Small intestine imaging might be required to rule out Crohn’s disease. Other imaging procedures such as computed tomography (CT) or magnetic resonance imaging (MRI) scan may be justified in very selected patients with severe symptoms not responding to therapy, and patients whose symptoms appear to worsen over time. However, none of these can be considered routine diagnostic measures. If clinically indicated, lactose intolerance should be excluded by breath test or an exclusion diet.

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Mar 29, 2017 | Posted by in GASTROENTEROLOGY | Comments Off on Irritable bowel syndrome

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