Irritable Bowel Syndrome

Manning criteria

Pain relieved by defecation

More frequent stools at the onset of pain

Looser stools at the onset of pain

Visible abdominal distension

Passage of mucus

Feeling of incomplete evacuation

Rome I criteria

Abdominal pain or discomfort for at least 3 months with at least one of the following symptoms:

Relief upon defecation

Association with a change in the frequency of stools

Associated with a change in the form of stools and two more of the following symptoms:

Altered stool frequency and/or form, altered stool passage

Passage of mucus

Bloating or abdominal distension

Rome II criteria

At least 12 weeks (not necessarily consecutive) in the preceding 12 months of abdominal discomfort or pain that has two of three features:

Relieved with defecation

Onset associated with a change in the frequency of stool

Onset associated with a change in the form (appearance) of stool

Symptoms that cumulatively support the diagnosis of IBS:

Abnormal stool frequency

Abnormal stool passage (straining, urgency, or feeling of incomplete evacuation)

Passage of mucus

Bloating or feeling of abdominal distension

Rome III criteria

Diagnostic criteria ^afor IBS: recurrent abdominal pain or discomfort ^bat least 3 days per month in the past 3 months associated with two or more of the following:

1. Improvement with defecation

2. Onset associated with a change in the frequency of stool

3. Onset associated with a change in the form (appearance) of stool

Subtyping IBS by predominant stool pattern:

1. IBS with constipation (IBS-C): hard or lumpy stools ≥25 % and loose (mushy) or watery stools <25 % of bowel movements

2. IBS with diarrhea (IBS-D): loose (mushy) or watery stools ≥25 % and hard or lumpy stools <25 % of bowel movements

3. Mixed IBS (IBS-M): hard or lumpy stools ≥25 % and loose (mushy) or watery stools ≥25 % of bowel movements

4. Unsubtyped IBS: insufficient abnormality of stool consistency to meet criteria for IBS-C, -D, or -M

^aCriteria fulfilled for the past 3 months, with symptom onset at least 6 months before diagnosis

^b Discomfort means an uncomfortable sensation not described as pain. In pathophysiology research and clinical trials, a pain/discomfort frequency at least 2 days a week during screening evaluation is required for subject eligibility

IBS-related symptoms overlap with those of other diseases. Experienced clinicians often diagnose these disorders on symptoms alone, but because functional disorders are much more common than organic diseases, any diagnostic strategy is likely to have a deceptively high positive predictive value.

13.2 Epidemiology

IBS is one of the most common disorders seen in gastrointestinal clinical practice. The overall prevalence is similar (10–20 %) in most industrialized countries. These findings reflect the tremendous impact of IBS on social costs related to health care use, drug consumption, and absences from work. The exact prevalence of IBS is poorly defined, probably because of the different definitions and clinical criteria used to define the syndrome.

This certainly underestimates the real prevalence of IBS, as only one in three patients seeks treatment. Those who do consult a doctor report more severe symptoms and an increased level of psychological disturbance (anxiety, depression, and sleep disturbance) than those who do not.

IBS is commonly believed to be a female-predominant disease. IBS symptoms are at least twice as common in women as in men. The reasons why women seem to be more prone to IBS than men are unknown, although health-seeking behavior and other factors may play a role in this gender difference. The first presentation of patients to a physician often occurs between the ages of 30 and 50 years, and reporting frequency decreases among older people.

13.3 Etiology/Pathophysiology

Since the mid 1990s, significant advances have been made in the understanding of the pathophysiology of IBS. However, interactions/interrelationships between causal and secondary alterations are unclear. For many patients the most consistent, and probably interrelated, characteristics are:

Altered intestinal motility
Visceral hypersensitivity
Bowel dysfunction after infection (altered intestinal microbiota)
Dietary factors
Stress and psychological comorbidity

13.3.1 Altered Motility

Abnormal small-intestinal and colonic motility has been demonstrated in patients with IBS, and in some patients it has been shown to correlate with symptoms. Abnormalities of intestinal motility may lead not only to the onset of pain but also to bloating and, if the abdominal motility results in changes in intestinal transit, constipation and diarrhea.

13.3.2 Visceral Hypersensitivity

Patients with functional bowel diseases exhibit decreased tolerance of pain upon balloon distension of the gut. This was first described in the rectum of patients with IBS almost 30 years ago and was subsequently confirmed by others. It is often also noted with air insufflation during colonoscopy. This phenomenon is referred to as visceral hyperalgesia. Explanations for this include an alteration of the sensitivity of sensory receptors through the recruitment of nociceptors in response to infection, intraluminal factors, ischemia, distension, and psychiatric factors. The neurons in the dorsal horn of spinal cord may experience increase excitability, and centrally there may be differences in the way the brain modulates afferent signals from the dorsal horn neurons through ascending pathways.

13.3.3 Gastrointestinal Infection (Altered Intestinal Microbiota)

There is an increased risk of patients developing IBS symptoms following an episode of gastrointestinal infection. It was shown that approximately one-third of patients hospitalized for infectious diarrhea had developed new IBS [13]. In most cases, persistent bowel dysfunction was noted in patients following documented Campylobacter, Shigella, and Salmonella gastroenteritis. Factors predisposing patients to persisting symptoms are the severity and duration of diarrhea, anxiety, depression, and somatization, as well as adverse life events. Mechanisms underlying IBS after infection are unclear, but immunological abnormalities at the intestinal level have been demonstrated in these patients, as has increased mucosal T lymphocytes and serotonin-producing enteroendocrine cells. Also, response to a pathogen is undoubtedly influenced by genetic factors that in turn influence immune response.

13.3.4 Dietary Factors

Many patients with IBS believe that their symptoms are related to food, and some have considerably restricted their diet by the time they consult a physician. The gut has an extensive immune system, but the current understanding of how food antigens are processed in health and disease is limited. At present, no clinically useful marker is available to test for food hypersensitivity in IBS. Researchers have used both skin tests and serum immunoglobulins (IgG and IgE) as markers of food hypersensitivity in various disorders, including IBS, but published data are equivocal. Moreover, many unscrupulous practitioners benefit from the confusion, leading patients to more and more restricted and illogical diets.

The role of sugar malabsorption in the pathogenesis of IBS is still a debated problem. Demographic data show that the prevalence of sugar malabsorption among patients with IBS is similar to that found in controls. Symptoms such as diarrhea and bloating, can typically be reproduced by lactose intake and reduced once lactose is excluded from the diet. Lactose malabsorption may coexist with IBS. Nevertheless, a lactose-free diet is effective in improving symptoms in only about 10 % of patients with IBS.

True food allergy is much less common. It is usually not difficult to recognize whether food ingestion is associated with urticaria, asthma, eczema, angioedema, and rhinorrhea because of the high incidence of positive skin-prick or high radioallergosorbant scores. Such patients see an allergist rather than a gastroenterologist and are not usually thought to have IBS.

13.3.5 Stress and Psychological Comorbidity

Psychological observations have shown that psychological symptoms of anxiety and depression are more common among patients with IBS than among either healthy volunteers or patients with organic gastrointestinal diseases. More than 50 % of patients linked the onset of their symptoms to a stressful event such as employment difficulties, a death in the family, a surgical procedure, or marital stress. Clinicians agree that stress can cause symptoms of IBS, but it cannot be considered the only cause. The magnitude of psychological stress also correlates with symptomatic outcomes.

13.4 Symptoms

Patients with IBS suffer from various gastroenterological symptoms. These include recurrent abdominal pain, altered bowel function, bloating, abdominal distension, a sensation of incomplete evacuation, and the increased passage of mucus (Table 13.1).
In addition, several nongastroenterological symptoms are more frequent in patients with IBS, such as lethargy, poor sleep, fibromyalgia, backache, urinary frequency, and dyspareunia.
Anxiety, depression, and somatization are frequent but do not reliably discriminate between IBS and other gastrointestinal diseases.
Functional diseases such as IBS usually interfere with patients’ comfort and their daily activities.
On the other hand, IBS is a benign disorder, and there are no long-term organic complications such as cancer or colitis.

13.5 Diagnosis

The focus during diagnosis is on a careful history and the physical examination, supplemented by basic laboratory testing, abdominal ultrasound, and, in women, gynecological examination. After these have been performed, if results are normal, treatment may be started on a trial basis, even without a confirmed diagnosis (see section 13.5.2). This should be decided on an individual basis and is justified particularly in patients with mild, nonprogressive symptoms, but it does not allow a diagnosis of IBS to be made.

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