Irritable bowel syndrome
Exam Tips
- For UK finals/OSCEs, make a positive diagnosis: recurrent abdominal pain with altered stool pattern for at least 6 months, then actively screen for red flags (weight loss, rectal bleeding, iron-deficiency anaemia, positive FIT, raised calprotectin, mass, family history).
- Subtype by stool pattern (IBS-D/IBS-C/IBS-M/IBS-U) because treatment is phenotype-directed.
- In station answers, always include baseline tests to exclude mimics: FBC, CRP/ESR, coeliac serology, and faecal calprotectin in younger diarrhoea presentations.
- State key safety points for prescribing: avoid lactulose in bloating-prone IBS, caution anticholinergics, and check contraindications before loperamide/linaclotide.
- Use the Bristol Stool Form Scale for communication and monitoring (See figure: Bristol Stool Form Scale).
Definition
Irritable bowel syndrome (IBS) is a chronic, relapsing disorder of gut-brain interaction characterised by recurrent abdominal pain associated with altered stool frequency and/or form, often with bloating. It is diagnosed clinically (positive symptom-based diagnosis) after excluding alarm features and likely organic disease, and is commonly subtyped as IBS-D, IBS-C, IBS-M, or IBS-U using Bristol stool pattern.
Pathophysiology
IBS is multifactorial and reflects dysregulation along the brain-gut axis rather than structural bowel damage. Key mechanisms include visceral hypersensitivity (lower pain threshold to gut distension), altered motility (faster transit in IBS-D, slower in IBS-C), abnormal central pain processing, autonomic dysfunction, low-grade mucosal immune activation, altered intestinal permeability, and microbiome changes. Post-infectious IBS can follow bacterial/viral/protozoal gastroenteritis (around 10% after acute enteric infection). Psychosocial stress, anxiety, and depression modulate symptom severity and illness behaviour via central-autonomic pathways.
Risk Factors
- Female sex
- Age 20-39 years
- First-degree relative with IBS (familial aggregation)
- Previous acute enteric infection (post-infectious IBS)
- Psychological comorbidity (anxiety, depression, stress)
- Dietary triggers (caffeine, alcohol, fatty/spicy foods)
- Recent or recurrent antibiotic exposure
- History of gastrointestinal inflammation
Clinical Features
Symptoms
- Recurrent abdominal pain for at least 6 months
- Pain related to defaecation (may improve, worsen, or be unchanged)
- Change in stool frequency (diarrhoea, constipation, or alternating pattern)
- Change in stool form (hard/lumpy or loose/watery)
- Bloating and visible abdominal distension
- Straining, urgency, or sensation of incomplete evacuation
- Passage of mucus
- Symptoms often exacerbated after meals
- Extra-intestinal symptoms: lethargy, nausea, back pain, headache, bladder or gynaecological symptoms
Signs
- Often normal physical examination
- Possible mild abdominal tenderness without peritonism
- No objective red-flag signs in uncomplicated IBS
Investigations
Management
Lifestyle Modifications
- Give a clear positive diagnosis and explain IBS as a disorder of gut-brain interaction to reduce health anxiety and repeated investigations
- Use Bristol Stool Form Scale to phenotype subtype and monitor response (See figure: Bristol Stool Form Scale, types 1-7)
- Dietary advice: regular meals, avoid missed/late meals, limit caffeine/alcohol/fizzy drinks, reduce high-fat/spicy trigger foods, maintain adequate fluid intake
- Adjust fibre: prefer soluble fibre (e. g, ispaghula husk); reduce insoluble bran if it worsens bloating/pain
- Consider structured low-FODMAP diet with trained dietitian if first-line dietary steps fail
- Encourage physical activity, sleep optimisation, stress management, and management of anxiety/depression comorbidity
Pharmacological Treatment
Antispasmodics for pain/cramping
- Mebeverine 135 mg three times daily, 20 minutes before meals
- Hyoscine butylbromide 10 mg up to four times daily
- Peppermint oil capsules (enteric-coated) 1-2 capsules three times daily
Use as needed or regularly during flares. Anticholinergic agents (e. g, hyoscine) can cause dry mouth, blurred vision, urinary retention; use caution in angle-closure glaucoma, prostatic enlargement, and myasthenia gravis. Peppermint oil may worsen reflux/heartburn.
Antidiarrhoeal therapy (IBS-D)
- Loperamide 2 mg after each loose stool (maximum 16 mg/day)
Titrate to stool consistency/frequency. Avoid if acute severe colitis is suspected (bloody diarrhoea, fever, systemic toxicity) or suspected bowel obstruction.
Laxatives for constipation (IBS-C)
- Ispaghula husk 1 sachet twice daily with fluid
- Macrogol 3350, 1-3 sachets daily adjusted to response
- Linaclotide 290 micrograms once daily, at least 30 minutes before food (specialist/second-line in persistent IBS-C)
Avoid lactulose if bloating is prominent. Linaclotide commonly causes diarrhoea and is contraindicated in known/suspected mechanical bowel obstruction; avoid in pregnancy unless specialist advice.
Neuromodulators for refractory pain
- Amitriptyline 10 mg at night initially; increase gradually (for example to 20-30 mg nocte) according to response/tolerability
Use low-dose tricyclics as gut-brain neuromodulators (off-label for IBS pain in many settings). Counsel on anticholinergic effects, sedation, QT-risk/drug interactions, and overdose toxicity; review mood and suicidality risk.
Complications
- Chronic symptom burden with reduced quality of life
- Work/school absenteeism and social impairment
- Comorbid anxiety/depression and health anxiety
- Polypharmacy adverse effects (constipation, anticholinergic burden, sedation)
- Potential over-investigation or unnecessary procedures if red flags are not assessed carefully
Prognosis
IBS usually fluctuates over years with relapse and remission. Over medium-term follow-up, many patients remain stable, some improve, and a smaller proportion worsen; after appropriate initial negative work-up, later discovery of an alternative organic GI diagnosis is uncommon (less than 5%). Post-infectious IBS often has a better trajectory, with around half improving spontaneously over 6-8 years. Poorer outcomes are associated with longer symptom duration, prior surgery, higher somatic symptom burden, and coexisting anxiety/depression.
Sources & References
🏥BMJ Best Practice(3)
💊BNF Drug References(5)
- Alverine with simeticone[management.pharmacological]
- Hyoscine butylbromide[management.pharmacological]
- Mebeverine hydrochloride[management.pharmacological]
- Mebeverine with ispaghula husk[management.pharmacological]
- Peppermint oil[management.pharmacological]
✅NICE Guidelines(1)
- Irritable bowel syndrome[overview]
📖Textbook References(20)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 684)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 829)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 254, 255)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 656)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 328, 329)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1520)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 693, 694)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 683)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 829)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 684, 685)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 642)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 670)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 400)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 355)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 354, 355)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 353, 354, 355)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 71)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 71)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 257)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 73, 74)[context]