A 19-year-old woman presents with a BMI of 14.5 kg/m2, intense fear of gaining weight, distorted body image (believes she is fat despite being severely underweight), and amenorrhoea for six months. She severely restricts her food intake and exercises excessively. Which electrolyte abnormality is most life-threatening in this condition and most commonly causes sudden cardiac death?
- A Hypokalaemia ✓
- B Hyponatraemia
- C Hypocalcaemia
- D Hypomagnesaemia
Correct answer: A. Hypokalaemia
Explanation
In anorexia nervosa, hypokalaemia (low serum potassium) is the most immediately life-threatening electrolyte disturbance and the most common cause of sudden cardiac death in these patients. Hypokalaemia causes fatal cardiac arrhythmias, particularly ventricular fibrillation and torsades de pointes, by altering cardiac membrane potential. Purging behaviours (self-induced vomiting, laxative misuse, diuretic misuse) that may co-occur worsen hypokalaemia. Anorexia nervosa has the highest mortality of any psychiatric disorder, primarily from cardiac arrhythmia and suicide.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.