Description

• A gastrointestinal (GI) disorder characterized by chronic and recurrent abdominal pain and altered bowel habits in the absence of an organic cause
• May be characterized as diarrhea-predominant (IBS-D), constipation-predominant (IBS-C), mixed (IBS-M), or unknown (IBS-U); may alternate between symptoms

Epidemiology

Irritable bowel syndrome (IBS) accounts for 25–50% of visits to gastroenterologists and ~2 million primary care visits annually in United States with estimated cost of $1.5 to 10 billion dollars a year.

Incidence
1–2% per year

Prevalence

• Pooled estimate of ~4% globally using Rome IV criteria or 10% globally using Rome III criteria
• Predominant age: 20 to 39 years; if age >50 years, consider other diagnoses. In the United States, it affects 10–15% of the population; in the United States, female > male (3:1); females are more likely to have IBS-C as compared to males.
• More common in low socioeconomic communities

Etiology and Pathophysiology

• The pathophysiology of IBS is unknown; it is associated with abnormalities of intestinal motility, intestinal inflammation, and enhanced sensitivity to visceral stimuli. The trigger may be luminal contractions, prolonged transit time, or environmental.
• PI-IBS (post-infectious) develops in roughly 10% with infectious enteritis. The odds of developing PI-IBS after acute GI infection is increased 6-fold. The cause of bowel symptoms following acute infection is uncertain, but several theories have been suggested such as malabsorption, increase in enteroendocrine cells/lymphocytes, and antibiotic use.
• Food sensitivity, microbiome dysbiosis, genetic, and psychosocial causes including early childhood stress are under investigation. Increase in mast cell and lymphocytic density and activity has been demonstrated on biopsy from terminal ileum, jejunum, colon in patients with IBS and may correlate with visceral hypersensitivity (1).
• Increase in proinflammatory cytokines have been observed and may correlate with intestinal inflammation.
• 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).
• There is an ongoing investigation of the role of colonic and small intestinal motility.

Genetics
Unknown; IBS tracks in some families; relatives of someone with IBS are 2 to 3 times more likely to have IBS.

Risk Factors

Female sex (odds ratio 1.67); other family members with similar GI disorder; psychological factors: stress, abuse history, anxiety, depression, or somatization; somatic factors: GI infection, pain syndromes, obesity, antibiotic use, and abdominal surgery; social factors: socioeconomic status in childhood

Pediatric Considerations
No risk to mother or fetus

General Prevention

See “Diet.”

Commonly Associated Conditions

• Other functional GI disorders (heartburn, dyspepsia, gastroesophageal reflux disease, nausea, diarrhea, incontinence, pelvic floor dyssynergia, and constipation)
• Chronic conditions including migraines, fibromyalgia, chronic pelvic pain, temporomandibular joint dysfunction, chronic fatigue syndrome, sleep disorders, noncardiac chest pain, and overactive bladder
• Psychiatric disorders: major depression, anxiety, somatoform disorders, and posttraumatic stress