Disorder of gut-brain interaction with recurrent abdominal pain and altered bowel habits without structural disease.
Also known as: IBS, irritable bowel syndrome, IBS-D, IBS-C, IBS-M, functional bowel disorder
Overview
A disorder of gut-brain interaction characterized by recurrent abdominal pain associated with defecation or change in bowel habits, in the absence of identifiable structural, biochemical, or inflammatory abnormalities. Diagnosed by Rome IV criteria.
Epidemiology
Prevalence 5-15% in Western countries; 2:1 female-to-male predominance; typical onset under age 50. Major contributor to outpatient GI visits and loss of work productivity.
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Ovarian cancer — Bloating in women >50; pelvic exam, CA-125, ultrasound
Diagnostic workup
Diagnostic criteria
Rome IV: Recurrent abdominal pain on average ≥1 day/week in the last 3 months, associated with ≥2 of: (1) related to defecation, (2) change in stool frequency, (3) change in stool form. Symptom onset ≥6 months prior to diagnosis. Subtypes by predominant stool form using Bristol Stool Scale: IBS-C, IBS-D, IBS-M, IBS-U.
Labs
CBC (exclude anemia)
CRP (exclude inflammation)
Fecal calprotectin (helpful to exclude IBD if borderline)
TTG IgA + total IgA (exclude celiac)
TSH (exclude thyroid disease)
Stool studies (Giardia antigen, C. diff, ova/parasites) if recent infection or travel
Imaging
Colonoscopy — NOT routinely required for typical IBS without alarm features; perform if age ≥45 (CRC screening), alarm features, family history of IBD/CRC, or refractory symptoms
Random colonic biopsies if chronic watery diarrhea (microscopic colitis)
Diagnostic algorithm
IBS Subtype
Bristol Stool Scale Pattern
Preferred Pharmacotherapy
IBS-C
>25% type 1-2, <25% type 6-7
Linaclotide, plecanatide, lubiprostone, PEG
IBS-D
>25% type 6-7, <25% type 1-2
Rifaximin, loperamide, eluxadoline, alosetron
IBS-M
>25% both ends of spectrum
Tailor by predominant symptom; TCAs for pain
IBS-U
Insufficient abnormality to classify
Symptom-targeted
Rome IV IBS subtypes by Bristol Stool Scale and first-line pharmacotherapy.
Treatment
First-line
Establish therapeutic relationship; educate that IBS is a real, chronic, manageable condition
Dietary modification: regular meals, adequate fiber (soluble — psyllium); trial of low-FODMAP diet under dietitian guidance
Exercise, sleep hygiene, stress management
Cognitive behavioral therapy and gut-directed hypnotherapy (strong evidence)
IBS-C (constipation predominant)
Soluble fiber (psyllium)
PEG 3350
Linaclotide, plecanatide, or lubiprostone (prosecretory)
Tenapanor (NHE3 inhibitor)
Avoid stimulant laxatives long-term
IBS-D (diarrhea predominant)
Loperamide PRN
Rifaximin 550 mg TID × 14 days (can repeat up to twice for recurrence)
Bile acid sequestrants — cholestyramine, colesevelam — if bile acid diarrhea suspected
Eluxadoline (mu/kappa-opioid agonist, delta antagonist) — avoid post-cholecystectomy and in heavy drinkers (sphincter of Oddi spasm)
Alosetron — 5-HT3 antagonist; restricted use in women with severe refractory IBS-D
IBS-M (mixed)
Tailor to predominant symptom at the time
TCAs particularly useful for pain-predominant phenotypes
Second-line / adjunct
Symptom-based pharmacotherapy (see by_subtype)
Tricyclic antidepressants (amitriptyline, nortriptyline, desipramine) — pain and IBS-D; low dose 10-50 mg at bedtime
SSRIs (citalopram, sertraline, paroxetine) — global symptoms with comorbid mood disorder
Diagnostic uncertainty leading to missed structural disease (if alarm features ignored)
PANCE pearls
Diagnose IBS POSITIVELY using Rome IV criteria — avoid diagnosis of exclusion approach with exhaustive testing.
Alarm features mandating colonoscopy: age ≥45 (CRC screening), GI bleeding, unexplained anemia, weight loss, nocturnal symptoms, family history of IBD or CRC, palpable mass.
Low-FODMAP diet has strong evidence but should be supervised by a dietitian — strict phase ≤6 weeks, followed by reintroduction.
Rifaximin is non-absorbable and effective for IBS-D bloating; up to 3 courses approved for recurrence.
Linaclotide and plecanatide are guanylate cyclase-C agonists — improve both constipation and IBS-related pain.
Avoid chronic opioid use — opioid-induced constipation and narcotic bowel syndrome amplify IBS symptoms.
CBT and gut-directed hypnotherapy have effect sizes rivaling pharmacotherapy for refractory IBS.
References
ACG 2021 — Lacy BE et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol 2021;116:17-44
AGA 2022 — Chang L et al. AGA Clinical Practice Guideline on the Pharmacological Management of IBS with Constipation and Diarrhea. Gastroenterology 2022;163:118-160
Rome IV — Lacy BE et al. Bowel Disorders. Gastroenterology 2016;150:1393-1407
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