A 45-year-old man is referred for panic disorder. He describes discrete episodes of palpitations, throbbing headache, drenching sweating, tremor, and a sensation of impending doom. During an episode his blood pressure is recorded at 220/125 mmHg; between episodes examination is entirely normal. Which investigation should be done before confirming a psychiatric diagnosis?
- A Serum morning cortisol
- B Overnight polysomnography
- C 24-hour urinary metanephrines and catecholamines ✓
- D Serum vitamin B12 level
Correct answer: C. 24-hour urinary metanephrines and catecholamines
Explanation
Paroxysmal hypertension with headache, sweating, and palpitations is the classic triad of pheochromocytoma, and such patients are frequently misdiagnosed as having panic disorder. Measurement of fractionated metanephrines in a 24-hour urine sample, or plasma free metanephrines, screens for catecholamine excess. Normal blood pressure between episodes argues against chronic hypertension but not against a secreting tumour. Cortisol testing addresses Cushing syndrome, which does not produce episodic attacks.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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