eMedicine Specialties > Pediatrics: General Medicine > Gastroenterology

Irritable Bowel Syndrome

Author: Mohammad F El-Baba, MD, Assistant Professor of Pediatrics, Division of Pediatric Gastroenterology, Wayne State University School of Medicine; Division Chief of Pediatric Gastroenterology, Children's Hospital of Michigan
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Updated: Jan 13, 2010

Introduction

Background

Irritable bowel syndrome (IBS) is defined as chronic or recurrent abdominal pain, altered bowel habits, and bloating, with the absence of structural or biochemical abnormalities to explain these symptoms. Irritable bowel syndrome is part of a broader group of disorders known as functional GI disorders. It is the most common GI diagnosis among gastroenterology practices in the United States and is one of the top 10 reasons for visits to primary care physicians. Irritable bowel syndrome is recognized in children, and many patients trace the onset of their symptoms to childhood. Children who have a history of recurrent abdominal pain are at increased risk of irritable bowel syndrome during adolescence and young adulthood.

Pathophysiology

Irritable bowel syndromehas no identifiable cause, and laboratory testing is unrevealing. Over the last 5 decades, the understanding of irritable bowel syndrome has evolved from a disorder of motor activities in the upper and lower GI tracts to a more integrated understanding of visceral hypersensitivity and brain-gut interaction.

GI motility abnormalities

Studies evaluating the motor response of the colon to meals, pain, and stress suggest a difference between control subjects and patients with irritable bowel syndrome. Pretreatment with anticholinergic medication in irritable bowel syndrome was demonstrated to reduce meal-stimulated pain and diarrhea. The finding of an abnormal, 3-cycle-per-minute, slow-wave activity in the colon of patients with irritable bowel syndrome was not confirmed by other studies and was noted in some individuals without irritable bowel syndrome.

Abnormal small-bowel motility has also been reported by some investigators. Intestinal transit has been demonstrated to be delayed in patients with constipation-predominant irritable bowel syndrome. In contrast, the transit was accelerated in patients with diarrhea-predominant irritable bowel syndrome. Clustered contractions in the duodenum and jejunum and prolonged propagated contractions in the ileum were noted more frequently in patients with irritable bowel syndrome. Small-bowel motility studies have demonstrated more abnormal findings in patients with irritable bowel syndrome in conscious states than during sleep, suggesting that the condition may result in part from CNS input.

Non-GI smooth-muscle abnormalities

Bladder dysfunction was identified in 50% of patients with irritable bowel syndrome and in only 13% of control subjects. One study found patients with irritable bowel syndrome to have a higher incidence of orthostatic hypotension. A clinical study demonstrated a greater reduction of forced expiratory volumes in 1 second (FEV1) induced by methacholine in patients with irritable bowel syndrome than in control subjects.

Visceral hypersensitivity

Most patients with functional disorders appear to have inappropriate perception of physiologic events and altered reflex responses in different gut regions. Patients with irritable bowel syndrome undergoing balloon distension studies of the colorectum demonstrated awareness of distension and pain at pressures and volumes that were significantly lower than in control subjects. The development of chronic hyperalgesia within the GI tract can be explained by the development of hyperexcitability of neurons in the dorsal horn in response to peripheral tissue irritation or to descending influences from the brain stem. Multiple factors are proposed to alter neuroreceptors and afferent spinal neuron functions. These factors include genetic, inflammatory, local nerve mechanical irritation, motility, and psychological factors.

Brain-gut interaction

The brain-gut axis is a bidirectional pathway that links higher cortical centers with visceral afferent sensation and intestinal motor function. Regulation of these connections occurs via numerous neurotransmitters found in the brain and gut, including cholecystokinin, vasoactive intestinal peptide, substance P, serotonin (5-hydroxytryptamine [5-HT]), and many others. These transmitters act at different sites in the brain and gut and lead to varied effects on gastrointestinal motility, pain control, emotional behavior, and immunity.

Dysregulation of the brain-gut system is becoming an acceptable theory to explain the functional GI disorders. Furthermore, several studies have hypothesized that specific 5-HT receptor antagonists may be beneficial in irritable bowel syndrome. Numerous newer noninvasive imaging techniques (eg, positron emission tomography, functional MRI) have been applied to assess brain-gut interactions in healthy patients and in those with irritable bowel syndrome.

Genetics

Several studies suggest that irritable bowel syndrome may have a genetic basis. The genetic theory is based on twin studies as well as familial aggregation of irritable bowel syndrome. Several twin studies have shown a higher concordance rate for irritable bowel syndrome in monozygotic twins than in dizygotic twins.^1,2,3,4 Studies on familial aggregation have found that patients with irritable bowel syndrome are more likely than controls to present positive family history.^5,6,7 However, familial and twin aggregation studies cannot exclude the influence of environmental and social learning in the development of irritable bowel syndrome.

In a twin study conducted by Levy et al, the proportion of dizygotic twins with irritable bowel syndrome who have mothers with irritable bowel syndrome was greater than the proportion of dizygotic twins with irritable bowel syndrome who have co-twins with irritable bowel syndrome. The data also revealed that having a mother or a father with irritable bowel syndrome are independent predictors of irritable bowel syndrome status and both are stronger predictors than having a twin with irritable bowel syndrome.²  
 
Several investigators have proposed that irritable bowel syndrome may be associated with select gene polymorphisms, including SERT, alpha-adrenergic receptors, interleukin-10, transforming growth factor, tumor necrosis factor-alpha, and sodium channel. However, the data are limited, and studies have failed to identify a specific irritable bowel syndrome gene.^8,9

Psychosocial factors in irritable bowel syndrome

Numerous studies have found an increased prevalence of abnormal psychiatric disorders, including anxiety, major depression, personality disorders, and hysteria, in adult patients with irritable bowel syndrome, especially patients referred to medical facilities. These psychological disturbances are not believed to cause or induce the symptoms of irritable bowel syndrome but are thought to influence the patient's perception of the symptoms and affect the clinical outcome. Stressful events are known to affect GI functions and may lead to exacerbation of symptoms in patients with irritable bowel syndrome.

In addition, antidepressant or antipsychotic therapy is helpful in some patients with irritable bowel syndrome. A meta-analysis has confirmed the relative efficacy of antidepressant medications in irritable bowel syndrome, particularly in predominantly diarrheic patients experiencing severe pain.¹⁰ Studies have reported an increased frequency of prior sexual or physical abuse in patients with irritable bowel syndrome and other functional GI disorders.

Dietary factors

Some studies have proposed that carbohydrate intolerance may produce significant symptoms in patients with irritable bowel syndrome. Ingestion of lactose, sorbitol, or fructose is associated with increased GI symptoms. Likewise, a food allergy may play a minor role in triggering or exacerbating symptoms in some patients with irritable bowel syndrome. A study by Atkinson et al has shown that immunoglobulin (Ig)G food antibodies may have a role in irritable bowel syndrome and food elimination based on IgG antibodies may be effective in reducing irritable bowel syndrome symptoms.¹¹

GI infection and irritable bowel syndrome

Some investigations found a correlation between the development of irritable bowel syndrome and a prior severe GI infection, especially in patients with higher scores for anxiety. Symptoms compatible with irritable bowel syndrome affect 10-15% of adult patients after acute infectious gastroenteritis. Factors that increase risk to develop post infectious irritable bowel syndrome include severe and prolonged infection, female sex, younger age, antibiotic treatment for this infection, and concomitant presence of anxiety.

Studies have demonstrated low-grade lymphocytic infiltration in the intestinal mucosa, increased permeability, and increases in inflammatory components including EC and mast cells.

Some studies have shown that small intestinal bacterial overgrowth is common in subjects with irritable bowel syndrome. A double-blind placebo-controlled study by Pimentel et al (2003) showed that normalization of lactulose breath testing with neomycin correlated with symptom improvement in patients with irritable bowel syndrome.¹³

Frequency

United States

Symptoms consistent with irritable bowel syndrome are present in 10-20% of adolescents and adults. Less than one third of patients seek medical advice. In the pediatric population, irritable bowel syndrome symptoms are reported in 14% of high-school students and 6% of middle-school students. One third of patients with irritable bowel syndrome trace their symptoms to childhood.

International

Prevalence in developing countries is probably lower than in Western countries, but this may be explained by a combination of reduced availability of medical care and different cultural approaches to illness.

Mortality/Morbidity

Irritable bowel syndrome is not a life-threatening condition but can have a serious impact on a patient's daily activities and quality of life. Greater impairments in quality of life are reported in patients with irritable bowel syndrome who sought medical care compared with those who did not consult their physicians for irritable bowel syndrome symptoms. It is a major cause of absenteeism at the workplace and at school. Abdominal pain in patients with irritable bowel syndrome is responsible for significant school absences in 4-5% of middle and high-school students.

Race

Irritable bowel syndrome is not well characterized outside Western countries. According to reported studies, the disease prevalence is lower in Hispanic and Asian populations than in Caucasian populations, and whites are more likely to have irritable bowel syndrome than blacks.

Sex

Women are 2-3 times more likely than men to have irritable bowel syndrome. In pediatric patients, both sexes are equally affected.

Age

Irritable bowel syndrome is a disorder of young people. One half of patients experience symptom onset when younger than 35 years, and 40% of patients are aged 35-50 years when symptoms begin. Irritable bowel syndrome is recognized in children. Symptoms consistent with irritable bowel syndrome are reported in 16% of students aged 11-17 years. Irritable bowel syndrome is not described in preschool-aged and younger children because the diagnosis depends on the child's ability to report detailed symptoms.

Clinical

History

Irritable bowel syndrome (IBS) has a broad range of symptoms; the most common are abdominal pain and altered bowel movements. Although symptoms may vary among patients, a pattern usually develops for each patient. The presence of characteristic symptoms in an otherwise healthy individual is sufficient to make a diagnosis of irritable bowel syndrome in most individuals.

• The characteristics of abdominal pain vary between patients and even within an individual patient.
  • The pain can be dull, achy, colicky, or sharp.
  • Pain can occur anywhere in the abdomen but is commonly located in the hypogastric or periumbilical regions.
  • The pain has no specific pattern but may be aggravated by stress and food and partially relieved after defecation.
• Altered bowel habits include constipation, diarrhea, or alternating constipation with diarrhea.
  • Stools are usually of small volume and pasty. Constipation is associated with small, hard, pelletlike stools. Diarrhea characteristically occurs during waking hours and often is precipitated by meals.
  • Mucus can be a component of the stool in as many as 50% of patients with irritable bowel syndrome.
  • In some patients, defecation is associated with a sense of incomplete evacuation that can lead to repeated trips to the bathroom and prolonged straining.
• Symptoms of abdominal distension (ie, bloating, increased belching, flatulence) are frequently reported by patients with irritable bowel syndrome. They are less common in children than adults.
• Other GI symptoms (ie, heartburn, dyspepsia, nausea, vomiting) are reported in 25-50% of adult patients with irritable bowel syndrome. Dyspeptic symptoms are present in as many as 30% of pediatric patients with irritable bowel syndrome.
• Extraintestinal symptoms are also reported. Patients with irritable bowel syndrome frequently report dysmenorrhea, urinary frequency, incomplete bladder emptying, back pain, and headache. These complaints are common in adults but rare in children.
• Patients may relate a history of inciting events.
  • Exacerbation of irritable bowel syndrome symptoms is sometimes reported to follow stressful experiences, ingestion of specific foods, or consumption of alcohol or caffeine.
  • Menses may exacerbate irritable bowel syndrome symptoms in women.
  • In children, symptom precipitants include school-related problems, overeating, or eating problems.
• The following clinical features should alert the physician to the possibility of a disorder other than irritable bowel syndrome:
  • Frequent awakening by symptoms
  • Steady progressive course
  • Fever
  • Weight loss
  • Arthritis
  • Rectal bleeding
  • Persistent vomiting
• The diagnosis of irritable bowel syndrome requires the identification of the symptoms characteristic of irritable bowel syndrome and the exclusion of other medical conditions with similar clinical presentations. Symptom-based criteria have been established for the diagnosis of irritable bowel syndrome, which includes the Manning or, more recently, the Rome criteria. The pediatric working team adopted the Rome II criteria in the adult population because these criteria seemed to apply equally well to children. Rome II criteria apply to children old enough to provide an accurate pain history of at least 12 weeks, which need not to be consecutive, in the preceding 12 months. The history can include the following:
  • The abdominal discomfort or pain has 2 out of the following 3 features: (1) relief with defecation, (2) onset associated with a change in frequency of stool, and (3) onset associated with a change in the form of stool.
  • No structural or metabolic abnormalities exist to explain the symptoms.

Physical

• Physical examination findings generally are unremarkable. The patient may appear tense and anxious with sweaty palms. Abdominal tenderness may be present. Tender and palpable sigmoid is found in some patients.
• Findings against the diagnosis of irritable bowel syndrome include the following:
  • Abdominal rigidity
  • Rebound tenderness
  • Lymphadenopathy
  • Hepatosplenomegaly
  • Positive fecal bleeding test result

Causes

• Irritable bowel syndrome has no identifiable cause (see Pathophysiology).

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