Irritable Bowel Syndrome (IBS)
Summary
Irritable Bowel Syndrome (IBS) is a chronic Functional Gastrointestinal Disorder (Disorder of Gut-Brain Interaction). It is characterized by recurrent abdominal pain associated with a change in stool form or frequency. It affects 10-20% of the population. Diagnosis is based on satisfying positive diagnostic criteria (Rome IV) while excluding organic disease (Cancer, IBD, Coeliac). [1,2]
Clinical Pearls
Nocturnal Diarrhoea: The bowel sleeps when you sleep. If a patient wakes up at 3am to open their bowels, this is ORGANIC pathology (e.g., Colitis, Bile Acid Malabsorption) until proven otherwise. IBS does not wake patients from sleep.
Rectal Bleeding: NEVER ascribe rectal bleeding to IBS. Even if they have IBS, they might also have piles, but you must exclude cancer/colitis first.
The "Diagnosis of Exclusion" Trap: Do not just run a million tests and if all negative say "It's IBS". Make a Positive Diagnosis using the criteria early. This validates the patient's symptoms and prevents "doctor shopping".
Demographics
- Prevalence: Very common (15% of population).
- Gender: Female > Male (2:1).
- Age: Diagnosis usually < 50 years. New symptoms in elderly require cancer referral (2WW).
Risk Factors
- Post-Infectious: 10% develop IBS after gastroenteritis (Campylobacter/Salmonella).
- Psychological: Anxiety/Depression strongly associated (Gut-Brain Axis).
- Antibiotics: Dysbiosis.
Mechanism (Gut-Brain Axis)
- Visceral Hypersensitivity: Nerves in the gut are "tuned up" (Central Sensitization). Normal gas/peristalsis feels like severe pain.
- Dysmotility: Spasm (Pain) or rapid transit (Diarrhoea).
- Dysbiosis: Altered microbiome (SIBO - Small Intestinal Bacterial Overgrowth).
| Condition | Distinguishing Feature | Test |
|---|---|---|
| IBS | Pain relieved by defecation. Bloating. | Rome IV Criteria |
| Coeliac Disease | Anaemia, fatigue. Gluten link. | TTG Antibodies |
| Inflammatory Bowel Disease | Blood/Mucus. Nocturnal. Weight loss. | Faecal Calprotectin |
| Bile Acid Malabsorption | Post-cholecystectomy. Watery diarrhoea. | SeHCAT Scan |
| Colorectal Cancer | Age >50. Bleeding. Weight loss. | Colonoscopy (FIT) |
| Ovarian Cancer | Bloating in older women. | CA-125 |
Symptoms (Rome IV)
Recurrent abdominal pain (on average >1 day/week in last 3 months) associated with 2 or more of:
- Related to defecation.
- Associated with a change in frequency of stool.
- Associated with a change in form (appearance) of stool.
Associated Features
Subtypes (Bristol Stool Chart)
The "IBS Screen" (NICE)
Do NOT arrange Ultrasound or Colonoscopy if simple IBS features.
- FBC: Anaemia?
- CRP/ESR: Inflammation?
- Coeliac Screen (TTG): Mandatory.
- Faecal Calprotectin: To exclude IBD (Crohn's/UC).
- Ca-125: In women over 50 with bloating (Ovarian Cancer).
Management Algorithm
DIAGNOSIS CONFIRMED
(Positive Criteria + Normal Screen)
↓
EXPLAIN & REASSURE
- Explain "Visceral Hypersensitivity"
- Explain Brain-Gut connection
- Validate symptoms
↓
LIFESTYLE
- Regular meals
- Reduce Caffeine / Alcohol / Spice
- Exercise
↓
DIETETICS
- First Line: General advice (fibre/fluid)
- Second Line: Low FODMAP Diet (Dietitian led)
- Probiotics (Try for 12 weeks)
↓
PHARMACOLOGY (By Symptom)
┌──────────────┼──────────────┐
PAIN DIARRHOEA CONSTIPATION
↓ ↓ ↓
Antispasmodic Loperamide Laxatives
(Buscopan) (Imodium) (Polyethylene Glycol)
(Mebeverine) (Linaclotide)
(Peppermint)
↓
SECOND LINE (Central)
- TCAs (Amitriptyline 10mg)
- SSRIs (Citalopram 10-20mg)
1. Diet
- Low FODMAP: Excludes Fermentable Oligo-, Di-, Mono-saccharides And Polyols.
- Foods like Onion, Garlic, Wheat, Lactose, Stone fruits create gas/osmotic load.
- Highly effective (70%) but hard to maintain. Reintroduction phase essential.
2. Pharmacological Pearls
- Amitriptyline: Low dose (5-10mg) works as a "pain modulator" for visceral hypersensitivity, NOT as an antidepressant.
- Linaclotide: Guanylate cyclase-C agonist. Increases fluid secretion and transit. For severe IBS-C.
- Rifaximin: Non-absorbed antibiotic. Used in US (and privately in UK) for IBS-D (treats SIBO).
3. Psychological Therapies
- CBT: Cognitive Behavioural Therapy tuned for IBS.
- Hypnotherapy: Gut-directed hypnotherapy is remarkably effective (NNT 4).
- Quality of Life: Significant impact (school/work absence).
- Mental Health: Anxiety/Depression.
- Nutritional: Avoidant eating disorders (ARFID) from exclusion diets.
- Chronic, fluctuating course.
- Does NOT increase mortality.
- Does NOT progress to cancer or colitis. (Reassure patient!).
- Symptoms usually improve with age.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| IBS in Adults | NICE CG61 (2015) | Positive diagnosis over exclusion. TCA use. |
| IBS Management | BSG (2021) | Updated advice on Probiotics and Rifaximin. |
Landmark Evidence
1. Low FODMAP Diet (Monash University)
- The pivotal research defining the dietary triggers of functional bowel disease.
What is IBS?
It is a condition where the gut is "oversensitive". The nerves in your bowel wall are too reactive. Normal things like gas bubbles or food moving along, which most people ignore, are felt by your brain as pain or cramping.
Is it all in my head?
No. The pain is real. However, because the gut and brain are connected (by the Vagus nerve), stress and anxiety can turn the volume up on these pain signals, making symptoms worse.
Is it something I ate?
Often yes. Certain foods (like onions, garlic, wheat, or milk) ferment in the gut, producing gas that stretches the sensitive bowel wall.
Will it turn into cancer?
No. IBS never turns into cancer or colitis. It is a functional problem (how it works), not a structural one (damage).
How do I treat it?
We start with diet and lifestyle. Medications can help calm the spasms (buscopan) or settle the diarrhoea (imodium). Low dose amitriptyline can help "turn down the volume" on the nerve signals.
Primary Sources
- Vasant DH, et al. British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut. 2021.
- Ford AC, et al. Irritable bowel syndrome. N Engl J Med. 2017.
- NICE. Irritable bowel syndrome in adults: diagnosis and management (CG61). 2008.
Common Exam Questions
- Diagnosis: "Rome IV Criteria?"
- Answer: Pain linked to stool frequency/form.
- Investigation: "Test for IBD?"
- Answer: Faecal Calprotectin.
- Management: "Drug for pain?"
- Answer: Antispasmodic (Mebeverine) or TCA (Amitriptyline).
- Diet: "Dietary advice?"
- Answer: Low FODMAP.
Viva Points
- Serotonin: 95% of the body's serotonin is in the gut (enterochromaffin cells). This is why SSRIs affect the bowel (can cause diarrhoea).
- Post-Infectious IBS: The link between acute gastroenteritis and subsequent IBS.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.