Quick Overview
Irritable Bowel Syndrome (IBS) is a functional gastrointestinal disorder characterized by recurrent abdominal pain related to defecation, with altered bowel habits. Diagnosis is clinical using NICE CG61 criteria, after excluding red flags. Management is symptom-subtype specific (constipation vs diarrhoea-predominant), with dietary modification (low FODMAP) as first-line alongside pharmacological and psychological interventions.
Core Facts & Concepts
NICE CG61 Diagnostic Criteria (all must be present):
- Abdominal pain/discomfort ≥6 months duration
- Pain relieved by defecation OR associated with altered stool frequency/form
- At least 2 of the following: altered stool passage (straining/urgency/incomplete evacuation), abdominal bloating/distension, symptoms worsened by eating, passage of mucus
IBS Subtypes (Rome IV):
- IBS-C (Constipation-predominant): >25% hard stools, <25% loose stools
- IBS-D (Diarrhoea-predominant): >25% loose stools, <25% hard stools
- IBS-M (Mixed): >25% hard AND >25% loose stools
- IBS-U (Unclassified): Insufficient abnormality to meet other subtypes
Key Numbers:
- Prevalence: 10-20% of UK population
- Female:male ratio 2:1
- Mean age at diagnosis: 30-50 years
- 50-60% respond to low FODMAP diet
First-Line Dietary Advice (NICE CG61):
- Regular meals, adequate fluid intake (8 cups/day)
- Limit caffeine to ≤3 cups/day
- Reduce alcohol and fizzy drinks
- Limit fresh fruit to 3 portions/day
- Trial low FODMAP diet for 6-8 weeks (specialist dietitian supervision)
Problem-Solving Approach
Step-by-Step Diagnostic Pathway:
- Confirm positive criteria (abdominal pain + altered bowel habit ≥6 months)
- Screen for red flags 🚩 (see below) - if present, investigate before diagnosing IBS
- Perform baseline tests: FBC, ESR/CRP, coeliac serology (anti-tTG), faecal calprotectin if diarrhoea-predominant
- Classify subtype (IBS-C/D/M/U) to guide pharmacological management
- Initiate dietary modification (first-line: general advice → low FODMAP if inadequate response)
🚩 Red Flags Requiring Investigation (NOT IBS):
- Unintentional weight loss
- Rectal bleeding (unless anal fissure/haemorrhoids)
- Family history of colorectal/ovarian cancer
- Age >60 years at symptom onset
- Anaemia, raised inflammatory markers
- Abdominal/rectal mass on examination
- Change in bowel habit to looser/more frequent stools >6 weeks in >60 years
Pharmacological Management by Subtype:
| Symptom | First-Line | Second-Line |
|---|---|---|
| IBS-C | Laxatives (avoid lactulose) | Linaclotide (if inadequate response after 12 months) |
| IBS-D | Loperamide (as needed) | Tricyclic antidepressant (low-dose amitriptyline 5-10mg) |
| Abdominal Pain | Antispasmodics (hyoscine, mebeverine, peppermint oil) | TCA if antispasmodics fail |
| Bloating | Probiotics (trial 12 weeks) | Review diet |
💊 Tricyclics for IBS-D/pain: Start amitriptyline 5-10mg nocte, titrate up to 30mg. If inadequate/not tolerated, consider SSRI (e.g., citalopram).
⚠️ Warning: Avoid lactulose in IBS-C (increases bloating/gas). Use ispaghula, macrogols, or linaclotide.
Analysis Framework
Differential Diagnosis of Chronic Abdominal Pain + Altered Bowel Habit:
| Condition | Discriminating Features | Key Investigation |
|---|---|---|
| IBS | Normal inflammatory markers, faecal calprotectin <50 μg/g, no red flags | Clinical diagnosis |
| IBD (Crohn's/UC) | Blood/mucus PR, weight loss, raised CRP/calprotectin >250 μg/g | Colonoscopy + biopsy |
| Coeliac Disease | Positive anti-tTG, anaemia, dermatitis herpetiformis | Duodenal biopsy |
| Colorectal Cancer | Age >60, rectal bleeding, weight loss, anaemia, mass | Colonoscopy |
| Bile Acid Malabsorption | Watery diarrhoea, responds to cholestyramine | SeHCAT scan |
| Microscopic Colitis | Watery diarrhoea, normal colonoscopy appearance | Colonic biopsy |
| Ovarian Cancer (♀) | Pelvic mass, ascites, early satiety, CA-125 elevated | Pelvic USS, CA-125 |
⭐ Clinical Pearl: Faecal calprotectin <50 μg/g has >90% negative predictive value for excluding IBD in patients with suspected IBS-D.
Visual Aid
Psychological Interventions (NICE CG61):
| Intervention | Indication | Evidence Level |
|---|---|---|
| Cognitive Behavioural Therapy (CBT) | Refractory IBS after 12 months pharmacological treatment | Strong evidence |
| Gut-Directed Hypnotherapy | Refractory IBS | Moderate evidence |
| Psychological Therapy | Consider if patient requests OR poor response to pharmacological treatment | NICE recommendation |
📌 Remember: FODMAP - Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. Restrict for 6-8 weeks, then systematic reintroduction.
Key Points Summary
✓ Diagnosis: Clinical (NICE CG61) - abdominal pain ≥6 months relieved by defecation, plus altered stool frequency/form. Exclude red flags first.
✓ Baseline tests: FBC, CRP, coeliac serology (anti-tTG), faecal calprotectin if diarrhoea-predominant. Faecal calprotectin <50 μg/g excludes IBD.
✓ First-line management: General dietary advice (regular meals, limit caffeine to ≤3 cups/day, fresh fruit ≤3 portions/day) → low FODMAP diet (6-8 weeks) if inadequate response.
✓ IBS-C: Laxatives (avoid lactulose) → linaclotide if refractory after 12 months. IBS-D: Loperamide → low-dose TCA (amitriptyline 5-10mg).
✓ Abdominal pain/bloating: Antispasmodics (hyoscine, mebeverine, peppermint oil) first-line. Consider TCA if inadequate response.
✓ Psychological therapy: CBT or gut-directed hypnotherapy for refractory IBS after 12 months of pharmacological treatment (NICE CG61 recommendation).
✓ Common pitfall: Diagnosing IBS without excluding red flags or performing baseline investigations (coeliac serology mandatory).
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