Description

• A gastrointestinal (GI) disorder characterized by
  • Chronic and/or recurrent abdominal pain or discomfort, bloating and distention, and alteration in bowel habits in the absence of an organic cause.
• May be characterized as diarrhea-predominant or constipation-predominant; may alternate between symptoms
• Synonym(s): spastic colon; irritable colon

Epidemiology

Irritable bowel syndrome (IBS) accounts for 30–50% of visits to gastroenterologists:

• Second only to upper respiratory infection as cause of lost workdays

Pooled estimate of 11% IBS prevalence internationally; ranges from South Asia (7%) to South America (21%); prevalence in North America is 12%.

• Predominant age: 20 to 39 years
• If age >50 years, consider other diagnoses.
• In the United States, female > male (3:1)
• More common in low socioeconomic communities

Etiology and Pathophysiology

• The etiology is unknown; associated with abnormalities of intestinal motility and enhanced sensitivity to visceral stimuli
• The trigger may be luminal or environmental.
• Evidence for the role of small intestinal bacterial overgrowth (SIBO) in IBS and association with antibiotic therapy is controversial; older age and female gender are predictors of SIBO in IBS patients.
• The role of food sensitivity, genetic, and psychosocial causes are also under active investigation.
• Increase in mast cell density and activity has been demonstrated on biopsy from terminal ileum, jejunum, colon in patients with IBS, and may correlate with visceral hypersensitivity (1).
• Current investigation is ongoing regarding low-grade mucosal and neuroinflammation, and the contribution of this inflammation in the dysregulation of the “brain-gut” axis (1).
• Four bowel patterns in the Rome IV classification:
  • IBS-D (diarrhea predominant), IBS-C (constipation predominant), IBS-M (mixed diarrhea and constipation, IBS-U (unclassified-symptoms cannot be categorized into one of the three subtypes)
• The utility of subtyping has been questioned. Many patients change categories/subtypes over time.

Genetics
Unknown. IBS tracks in some families. Twin studies do not, however, show a clear genetic component.

Risk Factors

• Other family members with similar GI disorder
• History of childhood sexual abuse
• Sexual/domestic abuse (primarily in women)
• Depression
• Anxiety
• GI infection

Pediatric Considerations
No risk to mother or fetus

General Prevention

See “Diet.”

Commonly Associated Conditions

• Chronic migraine
• Fibromyalgia
• Chronic fatigue syndrome
• Sleep disorders
• Psychiatric disorders: major depression, anxiety, somatoform disorders, and posttraumatic stress
• Chronic pelvic pain
• Temporomandibular joint dysfunction