Irritable bowel syndrome

Overview

•Abdominal pain - cramping, lower abdominal, present ≥6 months; relieved by defecation or associated with change in bowel frequency/stool form
•Altered stool passage - straining, urgency, incomplete evacuation
•Bloating/distension, mucus PR (no blood), symptoms worsened by eating
•Examination normal - no weight loss, no organomegaly, no systemic signs

Investigations

•First-line (to exclude organic disease): FBC, CRP/ESR, coeliac serology (anti-tTG IgA + total IgA), faecal calprotectin
•Faecal calprotectin - normal in IBS; raised in IBD - key test to distinguish IBS-D from IBD before colonoscopy
•NOT routinely indicated: colonoscopy, abdominal ultrasound, TFTs, faecal occult blood, stool microscopy, hydrogen breath testing

Differential diagnosis

IBS vs key differentials
FeatureIBSIBD (Crohn's/UC)Coeliac disease
Rectal bleedingNeverCommon (esp. UC)Absent
Weight lossAbsentPresentMay be present
CRP/calprotectinNormalRaisedNormal
DiagnosisClinical + exclusionEndoscopy + biopsyAnti-tTG IgA + biopsy

Management

First-line
  1. 1Patient education - explain gut-brain axis; reassure no progression to cancer or IBD
  2. 2Dietary advice - regular meals; adequate fluids; soluble fibre (ispaghula husk) for IBS-C; reduce insoluble fibre (bran) for bloating/diarrhoea
  3. 3Regular physical activity
  4. 4Address psychological comorbidity (anxiety, depression)
  5. 5Probiotics - 12-week trial if patient wishes; discontinue if no benefit
Second-line
  1. 1Dietician referral - low FODMAP diet (50-70% response rate)
  2. 2Mebeverine 135 mg TDS or hyoscine butylbromide 10 mg TDS - antispasmodics for pain/cramping
  3. 3Loperamide - for IBS-D (reduces motility, increases water reabsorption)
  4. 4Macrogol or ispaghula husk - for IBS-C; avoid lactulose (fermented by bacteria, worsens bloating)
Third-line (refractory)
  1. 1Amitriptyline 10 mg nocte - TCA neuromodulator; reduces visceral hypersensitivity; dose subtherapeutic for depression
  2. 2Citalopram (SSRI) - if TCA contraindicated or not tolerated
  3. 3CBT / gut-directed hypnotherapy / mindfulness - strong evidence base
  4. 4Referral to gastroenterology - diagnostic uncertainty or refractory symptoms
⚠️
Avoid lactulose in IBS-C - it is fermented by colonic bacteria, producing gas and worsening bloating. Use macrogol instead.

Red flag features (exclude IBS - investigate urgently)

Red flags
Rectal bleeding or melaena
Unintentional weight loss
Fever or night sweats
Onset after age 60
Family history of bowel/ovarian cancer
Iron-deficiency anaemia
Palpable abdominal/rectal mass
Symptoms waking from sleep
🎯
The exam question tests differentiating IBS from IBD. Red flags (weight loss, fever, mouth ulcers, rectal bleeding, raised CRP, raised faecal calprotectin) point to IBD - not IBS. IBS has no red flags and normal investigations.

Diagnostic criteria (NICE)

•Abdominal pain/discomfort ≥6 months PLUS pain relieved by defecation OR associated with altered bowel frequency/stool form
•Plus ≥2 of: altered stool passage; bloating/distension/hardness; symptoms worsened by eating; mucus PR
•Alternative conditions excluded