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.
First principles
IBS is a functional disorder of gut-brain signalling, not a structural disease
In IBS, the bowel wall, mucosa and blood supply are all structurally normal: there is no inflammation, ulceration or lesion to find on investigation. Instead, the problem lies in disordered communication along the gut-brain axis: altered gut motility, visceral hypersensitivity (normal levels of gut distension or contraction are perceived as painful) and dysregulated central processing of visceral signals, often influenced by stress, prior gut infection (post-infectious IBS) and gut microbiome composition. Because there is no lesion to biopsy or image, IBS is a diagnosis made from a characteristic symptom pattern, not a diagnosis of exclusion requiring every test to be normal first.
Educational content pending clinical review. Not medical advice.