A 17-year-old girl weighs 41 kg (height 165 cm, BMI 15.1 kg/m²). She fears becoming fat, restricts caloric intake to fewer than 500 calories/day, and has amenorrhea for 6 months. She believes her thighs are 'huge' despite being severely underweight. Her electrocardiogram shows a prolonged QTc interval. Which electrolyte abnormality and its associated complication should be MOST urgently addressed?
- A Hyponatremia causing cerebral oedema
- B Hypokalaemia causing cardiac arrhythmia ✓
- C Hypercalcaemia causing nephrolithiasis
- D Hyperphosphatemia causing renal failure
Explanation
Anorexia Nervosa carries the highest mortality of any psychiatric disorder. Severe caloric restriction causes hypokalaemia (low potassium), which causes QTc prolongation and potentially fatal ventricular arrhythmias (torsades de pointes, ventricular fibrillation). This is the most urgent life-threatening complication requiring immediate electrolyte correction. If refeeding is initiated too rapidly, refeeding syndrome (a shift of phosphate, magnesium, and potassium intracellularly) causes potentially fatal hypophosphataemia. DSM-5 removed amenorrhea as a diagnostic criterion for AN to allow diagnosis in males and pre-pubescent girls.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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