Irritable Bowel Syndrome (IBS)

Rome IV diagnosis, positive diagnostic strategy, low-FODMAP diet, and GRADE-based pharmacologic management — ACG 2021 first-ever IBS guideline.

📖 4 Sections⏱ ~35 min✅ 4-question quiz

Overview & Rome IV

Definition, prevalence, subtypes

IBS: A Disorder of Gut-Brain Interaction

IBS is a chronic, highly prevalent disorder of gut-brain interaction (DGBI) affecting ~4.4–4.8% of Americans. It significantly impairs quality of life and generates up to $10 billion/year in direct US healthcare costs. Characterized by recurrent abdominal pain and disordered defecation — not a diagnosis of exclusion.

Rome IV Diagnostic Criteria

Recurrent abdominal pain, on average ≥1 day/week in the last 3 months, associated with ≥2 of:

Related to defecation (better or worse)

Associated with a change in stool frequency

Associated with a change in stool form/appearance

Criteria fulfilled for last 3 months; symptom onset ≥6 months before diagnosis. Bloating is common but NOT required.

IBS Subtypes (Bristol Stool Form Scale)

IBS-C

Constipation

>25% BSF types 1–2, <25% types 6–7

Linaclotide, Lubiprostone, Tenapanor, Plecanatide

IBS-D

Diarrhea

>25% BSF types 6–7, <25% types 1–2

Rifaximin, Alosetron, Eluxadoline, Loperamide

IBS-M

Mixed

>25% BSF types 1–2 AND >25% types 6–7

Symptom-directed therapy

IBS-U

Unclassified

Does not fit C, D, or M criteria

Individualized approach

Pathophysiology: Gut-Brain Axis

IBS results from dysregulated gut-brain interaction, not purely structural or motility disorder. Key mechanisms include visceral hypersensitivity, altered intestinal microbiome (post-infectious IBS, SIBO), abnormal gut motility, increased intestinal permeability, and central sensitization. This multifactorial model justifies both gut-targeted and centrally-acting therapies.

Lacy BE et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021;116:17–44.