Bulimia Physical Complications — MRCPsych Paper B MCQ

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ModerateEating DisordersBulimia Physical ComplicationsMRCPsych Paper B

A 30-year-old woman with bulimia nervosa has severe dental erosion, bilateral parotid enlargement and calluses over the dorsum of her hand. Her predominant compensatory behaviour is frequent self-induced vomiting; she does not misuse laxatives or diuretics. Which serum biochemical pattern is most likely?

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Correct answer: E — Hypokalaemia with metabolic alkalosis

Explanation lettering: D = shown as A · A = shown as B · E = shown as C · C = shown as D · B = shown as E

The correct answer is B. Dental erosion, parotid enlargement and Russell's sign indicate recurrent self-induced vomiting. Loss of gastric hydrochloric acid produces a hypochloraemic metabolic alkalosis. Associated extracellular volume depletion activates the renin–angiotensin–aldosterone system, increasing renal potassium excretion and causing hypokalaemia. Severe hypokalaemia is clinically important because it can precipitate cardiac arrhythmias. Hypokalaemia with hyperchloraemic metabolic acidosis (D) is more characteristic of bicarbonate loss through diarrhoea, including stimulant-laxative misuse. Hyperkalaemia with acidosis (C) suggests impaired renal potassium excretion or cellular potassium redistribution rather than uncomplicated vomiting. Hypernatraemia (A) and hyponatraemia (E) can occur in particular fluid disturbances but are not the characteristic biochemical pattern produced by recurrent vomiting.

Reference: Royal College of Psychiatrists. Medical Emergencies in Eating Disorders: Guidance on Recognition and Management (CR233), section 2: Self-induced vomiting. 2022. https://www.rcpsych.ac.uk/docs/default-source/improving-care/better-mh-policy/college-reports/college-report-cr233-medical-emergencies-in-eating-disorders-%28meed%29-guidance.pdf