A 17-year-old girl presents with secondary amenorrhoea for 8 months, lanugo on the back, bradycardia (48 bpm), hypotension, and a BMI of 14. She exercises 2 hours daily and believes she is overweight. Which electrolyte abnormality is the MOST life-threatening acute risk?
- A Hyponatraemia due to water loading
- B Hypocalcaemia due to malabsorption
- C Hypokalaemia due to purging behaviour ✓
- D Hyperphosphataemia due to starvation
Correct answer: C. Hypokalaemia due to purging behaviour
Explanation
Anorexia nervosa with purging behaviours (self-induced vomiting, laxative/diuretic misuse) leads to hypokalaemia, which is the most immediately life-threatening electrolyte abnormality due to risk of potentially fatal cardiac arrhythmias, including ventricular tachycardia and torsades de pointes. The QTc interval may also be prolonged in anorexia. Hypocalcaemia and hyponatraemia may occur but are less immediate risks. Refeeding syndrome causing hypophosphataemia (not hyperphosphataemia) is a serious risk during nutritional rehabilitation.
Reference: Ghai Essential Pediatrics, 10th ed.
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