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"irritable bowel syndrome"[MeSH Terms] AND treatment

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I now have comprehensive textbook content and the diagnostic/treatment algorithms. Here is a full, structured overview of IBS:

Irritable Bowel Syndrome (IBS)

Definition

IBS is a functional bowel disorder characterized by chronic or recurrent abdominal pain associated with alterations in stool form and/or frequency (diarrhea, constipation, or both), without a structural or biochemical cause to explain the symptoms. It belongs to the spectrum of functional GI disorders that can transition between each other over time.

Goldman-Cecil Medicine, p. 1413

Epidemiology

Global prevalence: ~4.1% using Rome IV criteria (33 countries, 6 continents)
More common in women (5.2%) than men (2.9%)
US/UK/Canada prevalence: ~4.6% by Rome IV
Incidence: ~38 per 10,000 person-years
Up to 50% of sufferers never seek care, yet IBS generates ~4.4 million physician visits annually
Associated with significant work absenteeism, comorbid somatic and psychiatric disorders, and higher rates of unnecessary diagnostic testing and surgery

IBS Subtypes (Rome IV)

Subtype	Abbreviation	Proportion
Predominant diarrhea	IBS-D	35-40%
Mixed bowel habits	IBS-M	35-40%
Predominant constipation	IBS-C	~25%
Unclassified	IBS-U	<5%

Note: Subtypes can transition in the same patient over time.

Pathobiology

IBS is a multifactorial disorder resulting from dysregulation of gut-brain interactions, causing:

Altered intestinal motility
Visceral hypersensitivity (heightened pain perception from normal gut stimuli)
Autonomic nervous system dysfunction
Impaired stress responsiveness
Mucosal immune activation
Gut microbiota alterations
Abnormal CNS modulation of viscerosensory input

Risk factors include:

Genetic predisposition (family clustering)
Adverse childhood experiences
Post-infectious IBS - developing after acute gastroenteritis (one of the strongest risk factors)
Psychological stress
Dietary triggers (especially FODMAPs - fermentable oligosaccharides, disaccharides, monosaccharides, polyols)

Diagnosis (Rome IV Criteria)

Core requirement: Recurrent abdominal pain at least 1 day/week on average over the last 3 months, with symptom onset ≥6 months ago, AND associated with ≥2 of the following:

Related to defecation
Change in stool frequency
Change in stool form/appearance

Supportive symptoms:

Abnormal stool frequency (≤3/week or >3/day)
Abnormal stool form (hard/lumpy or loose/watery)
Straining or urgency
Incomplete evacuation
Mucus in stool
Bloating or abdominal distension

Diagnostic Algorithm

Alarm Features (require further investigation)

New symptoms at age ≥50 years
Unintentional weight loss
Hematochezia or melena (not hemorrhoidal)
Nocturnal diarrhea
Anemia
Palpable abdominal mass or lymphadenopathy
Family history of colorectal cancer, IBD, or celiac disease

Limited Screening Tests Recommended

Test	Population
Celiac serologies	IBS-D
CBC, CRP, fecal calprotectin	All IBS
Routine colonoscopy	NOT recommended if <45 years without alarm features

Treatment

Treatment is symptom-driven and subtype-based. The IBS-C treatment algorithm:

1. General / Lifestyle

Patient education and reassurance
Dietary modification: low-FODMAP diet is the most evidence-based dietary approach
Soluble fiber supplementation (psyllium) for IBS-C; insoluble fiber (bran) may worsen symptoms
Regular exercise, stress management

2. Pain and Spasm

Drug	Dose	Notes
Peppermint oil	1-2 capsules 3x daily	First-line antispasmodic
Hyoscyamine	0.125 mg 3-4x daily	Anticholinergic; dry mouth, constipation
Dicyclomine	10 mg 3-4x daily	Anticholinergic
Amitriptyline (TCA)	10-25 mg at bedtime (up to 100 mg)	Best for IBS-D and pain
Desipramine/Nortriptyline (TCA)	10-25 mg at bedtime	Pain modulation
SSRIs (citalopram, fluoxetine, sertraline)	Standard doses	Better for IBS-C with anxiety/depression

3. IBS-C (Constipation-predominant)

Osmotic laxatives: polyethylene glycol 17 g/day, lactulose 10-40 g/day
Prosecretory agents:
- Linaclotide 290 mcg daily (guanylate cyclase-C agonist)
- Lubiprostone 8 mcg twice daily (chloride channel activator)
- Plecanatide 3 mg daily
Tenapanor (NHE3 inhibitor)

4. IBS-D (Diarrhea-predominant)

Drug	Class	Notes
Loperamide	Opioid receptor agonist	Reduces stool frequency; no effect on pain
Rifaximin	Non-absorbable antibiotic	550 mg 3x daily x 14 days; targets gut microbiota
Eluxadoline	Mixed opioid agonist/antagonist	100 mg twice daily; contraindicated post-cholecystectomy
Alosetron	5-HT3 antagonist	Women with severe refractory IBS-D only; risk of ischemic colitis
Bile acid sequestrants (cholestyramine)	For bile acid malabsorption variant

5. Psychological / Behavioral Interventions

A 2025 network meta-analysis (PMID 41077057) confirms efficacy of behavioral therapies including:

Cognitive-behavioral therapy (CBT) - most evidence-based
Gut-directed hypnotherapy
Relaxation training, mindfulness meditation
Psychodynamic psychotherapy

These are particularly effective for patients with prominent psychological comorbidities or inadequate response to medications.

6. Gut-Brain Neuromodulators

A 2025 meta-analysis (PMID 40258375) updated the evidence on TCAs, SSRIs, and SNRIs as "gut-brain neuromodulators" showing significant benefit for global IBS symptoms and abdominal pain, particularly TCAs.

Prognosis

IBS is a chronic, relapsing condition. Life expectancy is normal. Roughly one-third of patients experience sustained remission. Subtype can change over time. Comorbid psychological disorders (anxiety, depression, somatic symptom disorder) are common and worsen outcomes if untreated.

Sources: Goldman-Cecil Medicine 27e, p. 1413-1420; Katzung's Basic and Clinical Pharmacology 16e; Sleisenger and Fordtran's GI and Liver Disease

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