Irritable Bowel Syndrome
A disorder of gut-brain signalling and visceral hypersensitivity with no structural lesion at all, so the diagnosis is made positively from a symptom pattern rather than by exclusion, once red flags are absent.
In a nutshell
IBS is disordered gut-brain signalling and visceral hypersensitivity with no structural lesion. Normal gut distension is perceived as pain, motility changes drive the bowel habit subtype, and diagnosis is positive once red flags and a minimal screening panel are clear, not a diagnosis reached only by exhaustive exclusion.
Classic presentation
A young or middle-aged patient with recurrent abdominal pain relieved by defecation, bloating and an altered bowel habit, worsened by stress, with entirely normal screening bloods and faecal calprotectin.
Key points
- IBS is a functional disorder: no inflammation, ulceration or structural lesion is found on investigation.
- Visceral hypersensitivity means normal gut distension is perceived as pain, hence pain relieved by defecation.
- Diagnosis is positive (symptom-pattern based) once red flags and a minimal screening panel (FBC, CRP, coeliac serology, faecal calprotectin) are normal.
- Low-FODMAP diet works because fermentable carbohydrates provoke gas and distension in a gut primed to over-interpret those signals.
- Any red flag (bleeding, weight loss, nocturnal symptoms, onset after 50, cancer family history) should prompt reconsideration of organic disease.
First-line investigation
A minimal screening panel (FBC, CRP/ESR, coeliac serology and faecal calprotectin) with colonoscopy reserved for red flags or diagnostic uncertainty.
First-line management
Dietary and lifestyle advice (including a trial of a low-FODMAP diet), with symptom-targeted drug therapy matched to the dominant bowel habit.
Exam traps
- IBS is not a diagnosis of exclusion requiring every test to be normal. It is made positively from a recognised symptom pattern once red flags are absent.
- Nocturnal symptoms that wake the patient are not typical of IBS and should prompt investigation for organic disease.
- A raised faecal calprotectin points away from IBS and towards inflammatory bowel disease.
Educational content pending clinical review. Not medical advice.