Irritable Bowel Syndrome (IBS)

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Irritable Bowel Syndrome (IBS) is a functional gastrointestinal disorder characterised by recurrent abdominal pain associated with changes in bowel habits, without an underlying organic cause.

Aetiology

  • Altered gut brain interaction: abnormal communication between the gut and central nervous system.
  • Visceral hypersensitivity: increased pain perception in response to normal gut activity.
  • Gut dysmotility: altered intestinal contractions leading to diarrhoea or constipation.
  • Post infectious IBS: occurs after bacterial, viral, or parasitic gastroenteritis.
  • Changes in gut microbiota: imbalances in gut bacteria may contribute.
  • Psychological factors: stress, anxiety, and depression are associated with IBS symptoms.
  • Dietary triggers: certain foods (e.g., dairy, high-FODMAP foods) can exacerbate symptoms.

Pathophysiology

  • Disruptions in gut motility lead to either increased or decreased transit time.
  • Increased gut permeability can lead to immune activation and inflammation.
  • Altered serotonin signalling affects bowel function and pain perception.
  • Psychological stressors can exacerbate symptoms through the gut brain axis.

Risk factors

  • Female sex (twice as common as in males).
  • Age (typically presents before 50 years).
  • Family history of IBS.
  • Psychological conditions (anxiety, depression, somatisation disorders).
  • History of gut infections.
  • Dietary factors (high fat or high FODMAP diets).

Signs and symptoms

  • Recurrent abdominal pain: often relieved by defecation.
  • Altered bowel habits: diarrhoea, constipation, or mixed pattern.
  • Bloating and excessive gas.
  • Mucus in stools: without blood.
  • Symptoms worsened by stress or certain foods.
  • Fatigue and difficulty concentrating.

Investigations

  • Clinical diagnosis: based on symptom and examination findings.
  • Blood tests:
    • FBC (rule out anaemia or infection).
    • CRP and faecal calprotectin (exclude inflammatory bowel disease).
    • Coeliac serology (rule out coeliac disease).
  • Stool sample: if infectious or inflammatory cause suspected.
  • Colonoscopy: only if red flag symptoms are present (e.g., weight loss, rectal bleeding, nocturnal diarrhoea).

Management

1. Lifestyle and Dietary Advice:

  • Regular meals: avoid skipping meals or eating too quickly.
  • Increase fibre intake: soluble fibre (e.g., oats).
  • Low FODMAP diet: avoid fermentable carbohydrates like onions, garlic, legumes.
  • Reduce caffeine, alcohol, and carbonated drinks.
  • Increase physical activity: beneficial for symptom control.

2. Pharmacological Management:

For diarrhoea predominant:

  • Loperamide: Reduces stool frequency.
  • Amitriptyline (low dose): Helps with visceral pain and diarrhoea.

For constipation predominant:

  • Bulk forming laxatives: ispaghula husk preferred.

For mixed type:

  • Tailored approach depending on predominant symptoms.

3. Psychological Therapies:

  • Cognitive Behavioural Therapy (CBT): helps manage stress related symptoms.
  • Gut directed hypnotherapy: may improve symptom control.

4. Probiotics:

  • May benefit some patients by restoring gut microbiota balance.
  • Trial for 4 weeks before assessing effectiveness.
GastroenterologymypanotesIrritable Bowel Syndrome (IBS)