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Autonomic Medicine

Irritable Bowel Syndrome (IBS)

IBS · K58

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by recurrent abdominal pain associated with defecation or changes in bowel habits, closely linked to gut-brain axis dysfunction.

2026-03-28

At a Glance

IBS affects 10-15% of the global population with a female predominance. Rome IV criteria require recurrent abdominal pain at least 1 day per week for 3 months associated with defecation changes. IBS is classified into diarrhea-predominant (IBS-D), constipation-predominant (IBS-C), mixed (IBS-M), and unsubtyped. Visceral hypersensitivity, altered gut motility, and dysregulated gut-brain communication are key mechanisms. Autonomic dysfunction with reduced vagal tone is commonly observed. Treatment includes low-FODMAP diet, antispasmodics, gut-brain neuromodulators, and autonomic rehabilitation.

Definition and Overview

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by recurrent abdominal pain associated with defecation or changes in bowel habits. Rome IV criteria require abdominal pain at least 1 day per week for 3 months associated with two or more of: related to defecation, associated with change in stool frequency, or change in stool form [1].

IBS affects 10-15% of the global population with a 2:1 female predominance. It accounts for 25-50% of gastroenterology referrals and significantly impacts quality of life and work productivity [1].

Classification

  • IBS-D (diarrhea-predominant): >25% loose stools, <25% hard stools
  • IBS-C (constipation-predominant): >25% hard stools, <25% loose stools
  • IBS-M (mixed): >25% loose and >25% hard stools
  • IBS-U (unsubtyped): insufficient abnormality to meet other criteria

Causes and Pathophysiology

Visceral hypersensitivity: IBS patients have lowered pain thresholds to intestinal distension, reflecting central and peripheral sensitization [2].

Altered gut motility: accelerated transit in IBS-D and delayed transit in IBS-C. Post-infectious IBS develops in 10-15% after gastroenteritis [3].

Gut-brain axis dysregulation: altered serotonin signaling (95% of body's serotonin is in the gut), dysbiosis, and increased intestinal permeability contribute to symptoms.

Autonomic dysfunction: reduced vagal tone (decreased HRV) is commonly observed, with sympathetic predominance correlating with symptom severity [4].

Diagnosis

IBS is a positive diagnosis based on Rome IV criteria, not merely an exclusion diagnosis. Limited testing is recommended for typical presentations: CBC, CRP, celiac serologies, and fecal calprotectin [1].

Red flags requiring further investigation: onset after age 50, rectal bleeding, unintentional weight loss, nocturnal symptoms, and family history of colorectal cancer or IBD.

Treatment

Dietary Modification

The low-FODMAP diet reduces symptoms in 50-80% of IBS patients. It involves eliminating fermentable oligosaccharides, disaccharides, monosaccharides, and polyols for 4-6 weeks, then systematic reintroduction [5].

Pharmacotherapy

IBS-D: antispasmodics (hyoscine, mebeverine), loperamide, rifaximin, eluxadoline. IBS-C: linaclotide, lubiprostone, plecanatide. Gut-brain neuromodulators (low-dose TCAs for IBS-D, SSRIs for IBS-C) address central sensitization.

Psychological Therapy

CBT and gut-directed hypnotherapy show significant symptom improvement in clinical trials.

Lifestyle Management

  • Regular meal times; avoid large meals
  • Adequate hydration and regular exercise
  • Stress management (key trigger for symptom flares)
  • Limit gas-producing foods, caffeine, and alcohol
  • Probiotics (strain-specific; Bifidobacterium infantis 35624)

Frequently Asked Questions

FAQ content is being prepared.

References

  1. [1] Longstreth GF, Thompson WG, Chey WD, Houghton LA, Mearin F, Spiller RC (2006). "Functional bowel disorders." Gastroenterology, 130: 1480-1491. DOI PubMed
  2. [2] Ford AC, Moayyedi P, Lacy BE, Lembo AJ, Saito YA, Schiller LR, Soffer EE, Spiegel BM, Quigley EM (2014). "American College of Gastroenterology monograph on the management of irritable bowel syndrome and chronic idiopathic constipation." American Journal of Gastroenterology, 109: S2-S26. DOI PubMed
  3. [3] Mayer EA, Tillisch K, Gupta A (2015). "Gut/brain axis and the microbiota." Journal of Clinical Investigation, 125: 926-938. DOI PubMed
  4. [4] Enck P, Aziz Q, Barbara G, Farmer AD, Fukudo S, Mayer EA, Niesler B, Quigley EM, Rajilić-Stojanović M, Schemann M, Schwille-Kiuntke J, Simren M, Zipfel S, Spiller RC (2016). "Irritable bowel syndrome." Nature Reviews Disease Primers, 2: 16014. DOI PubMed
  5. [5] Lacy BE, Mearin F, Chang L, Chey WD, Lembo AJ, Simren M, Spiller R (2016). "Bowel disorders." Gastroenterology, 150: 1393-1407. DOI PubMed

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Gut-Brain Axis Parasympathetic Nervous System
IBSirritable bowel syndromegut-brain axisFODMAPfunctional GI disorderautonomic dysfunction

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