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Stem
A candidate is asked to manage a classic presentation of Irritable Bowel Syndrome in an exam setting. Use precise definitions, scores, doses, and decision thresholds.
Core knowledge (model answer backbone)
Irritable Bowel Syndrome (IBS) is a Disorder of Gut-Brain Interaction (DGBI) defined by the Rome IV criteria as recurrent abdominal pain at least one day per week in the last three months, associated with two or more of: (1) relation to defaecation, (2) associated change in stool frequency, (3) associated change in stool form (appearance) — in the absence of alarm features or structural disease. Prevalence is 10 to 15 percent of adults worldwide, with a female-to-male ratio of about 2:1 and peak onset before age 50. The four Rome IV subtypes are IBS-C (constipation), IBS-D (diarrhoea), IBS-M (mixed) and IBS-U (unclassified); severity is graded mild, moderate or severe by impact on daily activities. Post-infectious IBS (PI-IBS) develops in up to one in ten patients after acute bacterial or viral gastroenteritis. Pathophysiology is multifactorial: visceral hypersensitivity, abnormal motility, brain-gut axis dysregulation, intestinal dysbiosis, increased intestinal permeability, low-grade mucosal immune activation, and post-infectious, genetic and psychosocial contributors. First-line management is reassurance, lifestyle, the low-FODMAP diet delivered by a dietitian, and antispasmodic
Red flags
- Unintentional weight loss of more than 5 percent of body weight over 6 months - exclude GI malignancy, IBD, malabsorption
- Gastrointestinal bleeding (haematemesis, melaena, or fresh rectal bleeding) - exclude upper/lower GI source, colorectal cancer
- Iron-deficiency anaemia - exclude occult GI blood loss, coeliac disease, colorectal cancer
- New-onset symptoms in a patient over 50 years (or 45 with family history) - colonoscopy to exclude colorectal neoplasia
High-yield structure examiners expect
Cover: Overview & Definition, Classification, Epidemiology & Risk Factors, Pathophysiology, Clinical Presentation, Differential Diagnosis.
Key doses / thresholds (from topic teaching)
- mebeverine 135 mg TDS**, hyoscine butylbromide, **pepperm
- linaclotide 290 mcg daily** for IBS-C; **loperamide 2 to 4
- mg PRN to a max of 16 mg/day**, **rifaximin 550 mg TDS for 14 da
- amitriptyline 10 to 30 mg nocte** or SSRIs) for refractory pain
- under 50 to 100 mcg/g", label: "Faecal calprotectin", hint:
- especially above 100 mcg/g) but normal in IBS; use in IBS-D or I
Questions
a) Define the condition and give the most important classification or severity framework used in exams. (3 marks)
- Clear one-line definition matching standard teaching.
- Named classification / stages / types with discriminating features.
- One sentence on why classification changes management.
b) Outline pathophysiology in a mechanism chain that explains the main clinical features. (3 marks)
- Initiating insult → intermediate pathway → end-organ effect.
- Link at least two symptoms/signs to mechanism.
- Mention one complication pathway (e.g. shock, perforation, herniation, arrhythmia).
c) List discriminating clinical features and bedside assessment. (3 marks)
- Classic presentation plus one atypical group (elderly, pregnancy, child, immunocompromised).
- Named signs/manoeuvres if relevant.
- What must never be missed on exam/bedside (pregnancy test, airway, glucose, etc.).
d) Investigations with thresholds and one named score if applicable. (3 marks)
- First-line tests and what positive findings mean.
- Gold-standard or definitive investigation when needed.
- Score components reproduced exactly if a named score is standard for this topic.
e) Immediate resuscitation and definitive management with doses where standard. (3 marks)
- ABC / time-critical steps first.
- First-line drug(s) with agent + dose + route (or procedure steps).
- Escalation triggers (theatre, ICU, thrombolysis window, antidote, etc.).
- Disposition and safety-netting.
Marking tips
Full marks require specificity (numbers, names, doses) not generic "give antibiotics/fluids." Regional practice (ICMR / NICE / AHA) may be cited as alternative where relevant.