In a 13-year-old obese boy with persistent hypertension, acanthosis nigricans, and symptoms of headache, sweating, and palpitations, what is the next step to establish the diagnosis?

Measure Plasma or Urinary Metanephrines to Screen for Pheochromocytoma

The next step is to obtain catecholamine testing—specifically plasma free metanephrines or 24-hour urinary fractionated metanephrines—to screen for pheochromocytoma. The classic triad of headache, sweating, and palpitations in a hypertensive patient has 90% diagnostic specificity for pheochromocytoma 1.

Clinical Reasoning

This 13-year-old presents with two distinct clinical pictures that must be addressed:

The Pheochromocytoma Picture (Priority)

The combination of persistent hypertension with headache, sweating, and palpitations is pathognomonic for pheochromocytoma until proven otherwise 1. This triad carries 90% specificity for the diagnosis. While pheochromocytoma is rare (0.1-0.6% of hypertensives), it is a life-threatening condition that can cause malignant hypertension, cardiovascular morbidity, and mortality if missed 1.

• Plasma free metanephrines are the best screening test with 99% sensitivity and 89% specificity 1
• 24-hour urinary fractionated metanephrines are also acceptable with 95-100% sensitivity 2, 3
• Guidelines specifically recommend screening when patients present with hypertension plus multiple catecholamine excess symptoms 4, 2, 5, 6

The Metabolic Syndrome Picture (Secondary Consideration)

The obesity and acanthosis nigricans suggest insulin resistance and metabolic syndrome. However, this does not explain the paroxysmal symptoms (headache, sweating, palpitations). While Cushing's syndrome can cause hypertension in obese patients, it typically presents with weight gain, central obesity, striae, and proximal muscle weakness—not the acute paroxysmal symptoms described 1.

Why Not the Other Options?

B. Cortisone level and ACTH: While Cushing's syndrome causes hypertension in 70-90% of cases 1, the paroxysmal triad of symptoms points away from Cushing's and toward pheochromocytoma. Cushing's presents with gradual weight gain, moon facies, and striae—not episodic headaches, sweating, and palpitations.

C. Renal ultrasound: Renovascular disease is less likely in a 13-year-old without other risk factors. The paroxysmal symptoms are not explained by renal artery stenosis.

D. Ambulatory BP monitoring: While useful for confirming hypertension and detecting white coat hypertension, it does not establish the underlying diagnosis. The question asks for the next step to establish diagnosis, not to confirm blood pressure patterns. Moreover, pheochromocytoma characteristically causes marked BP variability 1, which ABPM might detect but wouldn't diagnose.

Critical Pitfall to Avoid

Do not be distracted by the obesity and acanthosis nigricans. These findings suggest metabolic syndrome but are red herrings in the context of the classic pheochromocytoma triad. Missing a pheochromocytoma has severe consequences—autopsy studies show these tumors contributed to 55% of deaths and were unsuspected in 75% of cases 1. The average time from symptoms to diagnosis is 3 years, during which patients face significant cardiovascular risk 1.

Diagnostic Algorithm

1. Obtain plasma free metanephrines (preferred) or 24-hour urinary fractionated metanephrines 1, 4, 3
2. If positive: Proceed to imaging (MRI preferred over CT) to localize the tumor 4, 5, 6
3. If negative: Consider other causes of secondary hypertension, including evaluation for insulin resistance and metabolic syndrome given the obesity and acanthosis nigricans

The answer is A. Catecholamine testing (specifically metanephrines).