Irritable Bowel Syndrome

Meet the patient

A 28-year-old teacher has spent four months with crampy lower-abdominal pain that eases when she opens her bowels, visible bloating by evening, and stools that swing between hard pellets and urgency. She has lost no weight, is not woken at night, her periods are unchanged, and her family history is a father on a statin — not a cancer story. Her GP has ordered three normal blood panels and a normal ultrasound.[1]

The fork that decides her next month is the fork that decides every IBS referral: are there alarm features? If the answer is no — and here it is no — this is a positive gut-brain diagnosis: confirm Rome IV, do a limited screen, name the subtype, and treat. Endlessly re-investigating a clearly positive case is the second-commonest mistake; the first is labelling her IBS without ever asking the alarm questions.[1]

Is this IBS, or organic disease? — the red-flag fork

One line splits the clinic: weight loss, nocturnal symptoms, anaemia, rectal bleeding, or a family history of colorectal cancer or IBD means this is NOT yet IBS. Those are alarm features — investigate first, diagnose later. Their absence, with a limited normal screen, is what licenses the Rome IV label.[1]

[1] [1]

The classic trap: labelling a chronic, fluctuating bowel story "IBS" without ever asking the alarm-feature questions. Nocturnal symptoms are the single best discriminator — the gut sleeps when the patient sleeps, so pain or stool that wakes them is organic until proven otherwise.[1]

Rome IV — pain, plus two of three

The criteria ARE the diagnosis. Reproduce them verbatim in the viva. Recurrent abdominal pain, on average at least one day per week during the last three months, associated with two or more of:[2]

1. Related to defaecation — better, worse, or just different.
2. Associated with a change in stool frequency.
3. Associated with a change in stool form (appearance).[2]

Onset must be at least six months before diagnosis. Rome IV is explicit that this is a symptom-based, positive diagnosis, not a label of exclusion — once alarm features are absent and a limited targeted work-up is unrevealing, the criteria make the call.[2]

The number rule: pain, plus two of three. Say it as one breath and you have the marks. The associations are deliberately broad — "related to" covers both relief and worsening, which is why pain eased by defaecation and pain triggered by defaecation both count.[2]

Etymology for viva gold: irritable here does not mean the patient is irritable — it means the bowel is, by analogy with a hyper-reactive organ. The 1849 coinage by Cummings predates every modern investigation; what changed is that Rome IV finally made the diagnosis positive rather than a confession of defeat.[2]

Subtype by the Bristol chart — four stool-pattern boxes

Subtype is decided by stool form on the Bristol Stool Form Scale, and it is a moving target — reclassify at every visit. Up to three in four patients switch subtype over a year, so the IBS-C you treated in March may be an IBS-D by October.[1]

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Severity is a separate axis: mild (symptoms come and go, life continues), moderate (intrusive, intermittent disruption, anxiety common), severe (symptoms dominate the day, frequent work absence, marked psychological comorbidity). Severity predicts who seeks care and who needs neuromodulators — set it from impact, not from the pain score alone.[2]

The gut-brain axis — why this is real, not "all in the head"

IBS is a Disorder of Gut-Brain Interaction (DGBI), and that framing is the whole point. The gut and the brain talk bidirectionally; in IBS that conversation is dysregulated, so a normal colon hurts and a mildly irregular bowel dominates a life. Calling it "stress" is not just unkind — it is mechanistically wrong, and it blocks the treatments that work.[2]

The DGBI family is large — IBS sits alongside functional dyspepsia, functional constipation, functional diarrhoea, globus, and centrally mediated abdominal pain syndrome — and they overlap heavily: up to half of IBS patients also meet criteria for functional dyspepsia. Recognising the family explains the reflux, the fatigue, the dyspareunia, and the urinary frequency that ride alongside the bowel complaint.[2]

[1]

This is the frame that earns the treatments examiners love to under-prescribe: gut-directed CBT, gut-focused hypnotherapy, and low-dose neuromodulators are not last resorts or admissions of failure — they target the dysregulated axis itself, which is why they work when yet another antispasmodic does not.[7]

The convergent mechanisms — VISPERMS

No single mechanism explains every patient, which is exactly why monotherapy disappoints. Eight themes converge: visceral hypersensitivity, immune activation, stress and psyche, permeability, dysmotility, receptor genetics, microbiome, and the sensory brain-gut axis.[1]

[1]

Visceral hypersensitivity is the headline. IBS patients perceive gut distension at lower thresholds than controls — the balloon hurts sooner. It is partly peripheral (sensitised mucosal afferents, mast-cell and serotonergic modulation) and partly central (augmented processing in the insula, anterior cingulate, and somatosensory cortex).[2]

Dysmotility runs the subtype. Accelerated colonic transit and an exaggerated post-prandial motor response in IBS-D; delayed transit and impaired rectal evacuation in IBS-C; dyscoordinated, fragmented motility in IBS-M. The 5-HT3 and 5-HT4 pathways this implicates are exactly what ondansetron, alosetron and tegaserod target.[1]

Brain-gut dysregulation shows on functional MRI. Altered connectivity in the default-mode, salience and emotional-arousal networks, with impaired top-down inhibition of visceral afferents. Early-life adversity, chronic stress, and psychiatric comorbidity all amplify this central sensitisation.[1]

The microbiome is shifted, not absent. Reduced diversity, fewer Bifidobacterium and Faecalibacterium prausnitzii, a higher Firmicutes-to-Bacteroidetes ratio — driving excess gas, altered fermentation, and bile-acid dysmetabolism. Small-intestinal bacterial overgrowth is over-diagnosed by flawed breath tests and contested in IBS; treat the patient, not the hydrogen curve.[1]

Low-grade immune activation — subtle rises in mast cells, T lymphocytes, and pro-inflammatory cytokines (TNF-alpha, IL-6, IL-1 beta), without the overt inflammation of IBD — sensitise afferents and feed symptoms. Sterile, TLR- and STING-driven innate signalling is increasingly implicated in setting this mucosal tone.[5]

Increased intestinal permeability ("leaky gut") closes the loop. Reduced claudin-1 and occludin, raised zonulin, and bacterial translocation drive the immune activation above — the same machinery post-infectious IBS hijacks.[1]

Genetics is modest. Heritability is only 1 to 20 percent; candidate polymorphisms in the serotonin transporter (SLC6A4), SCN5A, TRPV1, TLR4, and HPA-axis genes explain inter-individual variation but are not used clinically.[2]

Post-infectious IBS — the 1-in-10 aftermath

About one in ten patients develops IBS after an acute gastroenteritis. Campylobacter jejuni, Shigella, Salmonella, E. coli O157, norovirus, and Giardia have all been implicated — severity of the initial illness, female sex, younger age, smoking, and pre-existing anxiety all raise the risk. The mechanism is persistent mucosal inflammation (more enterochromaffin cells, T lymphocytes), increased permeability, altered microbiota, and persistent T-cell activation.[3]

Recovery is slow — up to half remain symptomatic at five years. Management is standard IBS stepped therapy, with rifaximin and low-dose TCAs particularly useful in the IBS-D variant. The take-home is the take-a-history: a clearly dated gastroenteritis before symptom onset changes your confidence in the positive diagnosis and your choice of drug.[3]

Limited work-up — five tests, not fifty

The work-up is deliberately small. Blind testing manufactures false positives and harm. The aim is to exclude clinically relevant organic disease, not to chase every borderline value.[1]

First-line, in every suspected IBS case (especially IBS-D and IBS-M):[1]

• Full blood count — iron-deficiency anaemia, macrocytosis (coeliac, B12), eosinophilia.
• C-reactive protein — a normal CRP has high negative predictive value for IBD; a raised CRP drives further work-up.
• Coeliac serology — anti-tissue transglutaminase IgA with a total IgA; EMA or deamidated gliadin IgG if IgA-deficient.
• Thyroid function tests — hyperthyroidism mimics IBS-D, hypothyroidism IBS-C.
• Faecal occult blood test (FOBT or FIT) — any positive mandates colonoscopy.[1]

Tests added only when clinical suspicion points at them:[1]

• Faecal calprotectin — raised in IBD, normal in IBS; use in IBS-D or IBS-M where IBD is plausible. Under 50 to 100 mcg/g favours IBS; above favours IBD.
• Colonoscopy — recommended at age over 50 with new symptoms, or 45 with a colorectal-cancer family history, or with any alarm feature. Take random biopsies if microscopic colitis is in the frame.
• Stool microbiology — recent travel, suspected Giardia, persistent diarrhoea.
• SeHCAT scan or fasting serum C4 — bile acid diarrhoea in refractory IBS-D (about 25 to 30 percent).
• Lactose or fructose hydrogen breath test — or skip straight to an empirical FODMAP exclusion.
• Gastroscopy with duodenal biopsy — upper GI symptoms, positive coeliac serology, or iron-deficient anaemia with negative serology.[1]

[1]

The mimics you must exclude — coeliac first

The differential of chronic abdominal pain with altered bowel habit is broad, and coeliac disease is the one you must actively exclude by serology, not by guess. Coeliac prevalence in IBS-D is 1 to 3 percent — four to five times background — which is why anti-tTG IgA plus total IgA is a first-line test, not an afterthought.[1]

[1]

The classic trap: a woman labelled "IBS-D" for years who is actually coeliac, or who has microscopic colitis needing biopsy, or bile acid diarrhoea needing a binder. Each has a positive diagnostic test — use them before the third antispasmodic. Drug-induced and structural causes belong on the list too: opioids, metformin, PPIs, SSRIs, colchicine, radiation enteritis, and chronic intestinal ischaemia in the older patient with post-prandial pain and weight loss.[4]

Treatment ladder — match the drug to the stool

IBS management is chronic, stepwise, and subtype-directed — never a single prescription. Three pillars carry the whole ladder: a trusting therapeutic relationship, lifestyle and dietitian-led dietary change, and pharmacotherapy matched to the predominant bowel pattern with neuromodulators for pain.[1]

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The therapeutic relationship is the first drug. Naming the diagnosis, explaining the chronic-relapsing course, stating plainly that this is neither cancer nor IBD, and framing the brain-gut axis — hopeful, evidence-based education measurably reduces healthcare-seeking. Patients with IBS have often been dismissed before they reached you; do not be the next clinician to dismiss them.[7]

Lifestyle: regular meals, soluble fibre (psyllium, ispaghula — insoluble bran worsens bloating), adequate hydration, regular exercise (it improves bloating and bowel symptoms), sleep hygiene, and stress reduction. Smoking and excess alcohol worsen symptoms.[1]

The low-FODMAP diet is the headline dietary move. Eliminate fermentable oligosaccharides, disaccharides, monosaccharides and polyols for 4 to 6 weeks, then reintroduce the FODMAP groups one at a time to identify triggers. It improves bloating and pain in 50 to 80 percent — powerful, but not curative, and not a lifetime diet. Best delivered by a registered dietitian to avoid long-term restriction and nutritional inadequacy.[1]

The classic trap: a low-FODMAP diet started in primary care, never reintroduced, and the patient is still avoiding onions, wheat and apples three years later, malnourished and fearful. Elimination without reintroduction is malpractice-by-neglect; the diet only earns its place if a dietitian structures the challenge phase.[1]

Psychological therapies are not last-resort. Gut-directed CBT and gut-focused hypnotherapy have robust evidence for pain, bloating, and quality of life in moderate-to-severe IBS — offer them early, alongside pharmacotherapy, not after the fifth drug has failed.[7]

IBS-C — fibre, osmotics, then secretagogues

Treat the constipation first; the pain often follows.[1]

Step 1 — soluble fibre and hydration:[1]

• Soluble fibre — psyllium (ispaghula husk) one to two sachets daily with water. Insoluble bran worsens bloating.
• Adequate hydration — 1.5 to 2 L per day.[1]

Step 2 — osmotic and stimulant laxatives after fibre fails:[1]

• Macrogol (polyethylene glycol) 3350 — 1 to 3 sachets daily; lactulose 15 to 30 mL BD if macrogol unavailable (expect flatulence).
• Stimulants — bisacodyl 5 to 10 mg nocte or senna 7.5 to 15 mg nocte as rescue; short bursts only.[1]

Step 3 — secretagogues for refractory IBS-C:[1]

• Linaclotide 290 mcg daily (145 mcg in the frail elderly) — a guanylate cyclase-C agonist; accelerates transit and reduces visceral pain; ACG- and NICE-recommended for moderate-severe IBS-C.
• Plecanatide 3 mg daily — alternative guanylate cyclase-C agonist.
• Lubiprostone 24 mcg BD — a chloride channel type 2 activator; third-line.
• Tegaserod 6 mg BD — a 5-HT4 agonist; limited availability on cardiac safety grounds.[1]

IBS-D — loperamide, rifaximin, eluxadoline

Treat the diarrhoea and the urgency; exclude coeliac and bile acid diarrhoea first.[1]

Step 1 — diet and loperamide:[1]

• Low-FODMAP trial, with systematic reintroduction.
• Loperamide 2 to 4 mg PRN, max 16 mg per day; regular 4 mg TDS may help chronic symptoms — titrate to a formed stool.[1]

Step 2 — rifaximin and antispasmodics after first-line failure:[1]

• Rifaximin 550 mg TDS for 14 days — a non-absorbable antibiotic targeting dysbiosis; benefits a subset and can be repeated. The TARGET 3 trial showed a 9 percent response over placebo, with relief of bloating, pain and loose stool.
• Antispasmodics — mebeverine, hyoscine, peppermint oil, as needed for pain.[1]

Step 3 — refractory IBS-D:[1]

• Eluxadoline 100 mg BD (75 mg BD in patients without a gallbladder or with hepatic impairment) — a mixed opioid receptor agonist/antagonist; contraindicated in patients without a gallbladder, with sphincter of Oddi dysfunction, or with severe liver disease.
• Bile acid binders — cholestyramine 4 g orally or colesevelam 625 mg when bile acid diarrhoea is suspected or confirmed (SeHCAT retention under 10 percent).
• Ondansetron 4 to 8 mg TDS — a 5-HT3 antagonist; useful in IBS-D with urgency and loose stool (off-label).
• Alosetron 0.5 to 1 mg BD — only in women with severe refractory IBS-D; restricted on ischaemic-colitis risk.[1]

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Pain-predominant and IBS-M — antispasmodics then neuromodulators

Pain is the symptom patients remember; treat it directly.[1]

• Antispasmodics for pain — mebeverine 135 mg TDS; hyoscine butylbromide 10 mg TDS; peppermint oil 0.2 to 0.4 mL TDS.
• Low-dose neuromodulators — analgesics at these doses, not antidepressants:
  • Amitriptyline 10 to 30 mg nocte — anticholinergic effect slows transit (helpful in IBS-D) and central analgesia improves pain and sleep.
  • Nortriptyline 10 to 30 mg nocte — similar profile, fewer anticholinergic effects.
  • Fluoxetine 20 mg daily — for IBS-C and IBS-M; SSRIs slightly speed transit.
  • Citalopram 20 mg daily — alternative; may help bloating and pain.
• Refractory pain — gastroenterology referral; consider low-dose gabapentin or pregabalin, or gut-directed CBT or gut-focused hypnotherapy.[1]

The classic trap: refusing a TCA because "the patient is not depressed." At 10 to 30 mg nocte the drug is acting on visceral afferent sensitisation and sleep — explain it that way and adherence follows.[7]

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Special populations — the thresholds that change

Pregnancy — first-line is reassurance, dietary advice, soluble fibre, and osmotic laxatives (macrogol, lactulose). Loperamide is used cautiously in IBS-D. Anticholinergic antispasmodics are generally avoided, especially in the first trimester; TCAs and SSRIs only when benefit clearly outweighs risk, with obstetric-psychiatry input.[1]

Elderly — new-onset bowel symptoms over age 50 mandate colorectal-cancer exclusion (FIT, then colonoscopy). Secondary causes — medication, hypothyroidism, diverticular disease, ischaemia — overtake primary IBS in this group. Do not label new symptoms IBS until the screen is clean.[1]

Post-cholecystectomy — cholecystectomy can unmask or worsen IBS-D through the altered bile-acid pool; bile acid diarrhoea is commoner, and a SeHCAT test with bile-acid binders (cholestyramine) is often rewarded.[1]

Severe and refractory IBS — symptoms dominate daily life, often with marked anxiety, depression, somatic comorbidity, a history of abuse, or central sensitisation. This is a multidisciplinary problem: gastroenterologist, dietitian, psychologist or hypnotherapist, and primary care, combining neuromodulators with rational antispasmodic, laxative, and antidiarrhoeal use. Never escalate to opioids — they worsen pain centrally and cause narcotic bowel syndrome; centres that manage the most complex chronic disease recognise that opioid-sparing, multidisciplinary care outperforms escalation every time.[6]

Paediatric IBS — common, about 10 percent of school-age children, using Rome IV with developmentally appropriate language. Treat with family education, school liaison, a cautious FODMAP trial (growth matters), polyethylene glycol, and psychological therapies.[1]

What IBS does — and does not — do to a life

IBS does not kill, does not cause cancer, and does not progress to IBD. The harm is functional and psychosocial, and it is substantial.[1]

• Quality of life impaired on par with rheumatoid arthritis or major depression on validated instruments.
• Anxiety and depression coexist in 30 to 50 percent of severe IBS — bidirectional.
• Sleep disturbance — chronic non-restorative sleep, pain disrupting sleep onset.
• Work and economic impact — IBS is a top-ten reason for primary-care absenteeism; lost productivity runs into the billions.
• Surgical harm — patients with IBS-D undergo more unnecessary cholecystectomy, appendicectomy and hysterectomy; meticulous differential diagnosis before any elective operation.
• Healthcare over-use — repeated visits, ED attendances, endoscopies, polypharmacy.[7]

Prognosis: chronic and relapsing, with a stable medium-term burden; about a third improve durably after first presentation. Lifestyle, diet and drugs reduce severity; CBT and hypnotherapy have the most durable effect. Mortality is not increased.[7]

The classic trap: dismissing the patient as "just IBS." The patient in front of you has a real, biopsychosocial, treatable disorder that is limiting their life. The diagnosis is not a brush-off — it is the start of a plan.[7]

Five ways to fail an IBS patient

• Labelling IBS without excluding red flags — weight loss, nocturnal symptoms, anaemia, bleeding, family history must be asked, every time.[1]
• Over-investigating a clearly positive-diagnosis patient — three normal panels and a normal ultrasound are not an indication for a second colonoscopy; they are an indication to start treating.[1]
• A low-FODMAP diet started without dietetic support or reintroduction — a lifetime elimination diet is the iatrogenic harm, not the cure.[1]
• Missing coeliac disease — test serology (anti-tTG IgA plus total IgA); it runs at 1 to 3 percent in IBS-D and it is treatable.[1]
• Dismissing the patient — IBS is real, biopsychosocial, and treatable; the dismissal is the failure, not the diagnosis.[7]

The mantra

Red flags out, criteria in; match the drug to the stool.[1]

Diagnose IBS positively by Rome IV once the alarm features are gone and a limited screen is clean — then choose therapy by subtype: fibre, osmotics and secretagogues for the constipated gut; loperamide, rifaximin and eluxadoline for the loose one; antispasmodics and low-dose TCAs for pain. Offer CBT and hypnotherapy early, never opioids, and never a brush-off.[1]

[1]

Ward-round test — three stems

Stem 1 — the IBS-D that is not IBS (answer)

A 34-year-old with two years of loose stools, bloating and urgency, labelled IBS-D in primary care, now has iron-deficiency anaemia with a ferritin of 8. Three antispasmodics have not helped. What changed the diagnosis, and what do you do? Model: The anaemia is an alarm feature and the IBS label is now unsafe. The two missed diagnoses are coeliac disease (test anti-tissue transglutaminase IgA with a total IgA — coeliac runs at 1 to 3 percent in IBS-D, four to five times background) and microscopic colitis (colonoscopy with random colonic biopsies — normal mucosa, abnormal histology). Add faecal calprotectin to split IBD from IBS-D, and a SeHCAT for bile acid diarrhoea if the coeliac and colitis screens are negative. The lesson: a new alarm feature in a "known IBS" patient revokes the diagnosis.[1]

Stem 2 — the over-investigated young woman (answer)

A 26-year-old teacher has had four months of crampy lower-abdominal pain eased by defaecation, evening bloating, and stools swinging between Bristol 1 and Bristol 6. She has had three normal blood panels, a normal abdominal ultrasound, a normal CT abdomen, and is booked for a second colonoscopy. She has lost no weight, sleeps through the night, and has no family history of colorectal cancer or IBD. What is the right next step? Model: Stop investigating and start treating. She meets Rome IV — pain at least one day a week for over three months, related to defaecation, with change in stool form and frequency — onset over six months ago, no alarm features, and a limited screen already normal. This is a positive gut-brain diagnosis. Confirm subtype (likely IBS-M), start a dietitian-led low-FODMAP trial with planned reintroduction, an antispasmodic (mebeverine 135 mg TDS) for pain, and a low-dose TCA (amitriptyline 10 to 30 mg nocte) if pain dominates. Cancel the second colonoscopy.[2]

Stem 3 — first-line therapy for IBS-C versus IBS-D (answer)

Two patients, both positive Rome IV, both asking "what do I actually take?" Pick the first drug for each. Model: IBS-C — start soluble fibre (psyllium one to two sachets daily with water) and hydration; if insufficient, add an osmotic laxative (macrogol 3350 one to three sachets daily); for refractory moderate-severe disease, linaclotide 290 mcg daily. IBS-D — start a low-FODMAP trial with planned reintroduction and loperamide 2 to 4 mg PRN, max 16 mg per day; if that fails, rifaximin 550 mg TDS for 14 days; for refractory disease, eluxadoline 100 mg BD or a bile-acid binder if SeHCAT is positive. Both get reassurance, lifestyle advice, and — if pain dominates — an antispasmodic and a low-dose TCA. The unifying rule: match the drug to the stool.[1]

References

1. [1]Lacy BE, Pimentel M, Brenner DM, et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome Am J Gastroenterol, 2021.PMID 33315591
2. [2]Drossman DA Functional Gastrointestinal Disorders: History, Pathophysiology, Clinical Features and Rome IV Gastroenterology, 2016.PMID 27144617
3. [3]Freisling H, Haas K, Elmadfa I Mass media nutrition information sources and associations with fruit and vegetable consumption among adolescents Public Health Nutr, 2010.PMID 19706216
4. [4]Drenckhan A, Grob T, Dupree A, et al. Esophageal carcinoma cell line with high EGFR polysomy is responsive to gefitinib Langenbecks Arch Surg, 2014.PMID 25070024
5. [5]Ahn J, Son S, Oliveira SC, et al. STING-Dependent Signaling Underlies IL-10 Controlled Inflammatory Colitis Cell Rep, 2017.PMID 29281834
6. [6]Gooley TA, Chien JW, Pergam SA, et al. Reduced mortality after allogeneic hematopoietic-cell transplantation N Engl J Med, 2010.PMID 21105791
7. [7]McGinty EE, Webster DW The Roles of Alcohol and Drugs in Firearm Violence JAMA Intern Med, 2017.PMID 28055044