What is the next step to establish a diagnosis for an obese boy with persistent hypertension, acanthosis nigricans, headache, sweating, and palpitations?

Diagnostic Approach for Obese Boy with Hypertension and Catecholaminergic Symptoms

The next step is to measure plasma free metanephrines or 24-hour urinary fractionated metanephrines (Option D) to screen for pheochromocytoma, as the combination of headache, sweating, and palpitations in a hypertensive patient has 93.8% specificity and 90.9% sensitivity for this diagnosis. 1, 2

Clinical Reasoning

While this patient presents with obesity, acanthosis nigricans, and hypertension—features strongly associated with insulin resistance and metabolic syndrome 3—the presence of the classic catecholaminergic triad (headache, sweating, palpitations) dramatically shifts the diagnostic priority toward pheochromocytoma. This triad has an exclusion value of 99.9% when absent, making it a critical red flag that cannot be ignored. 1, 2

Why Metanephrines First

• Plasma free metanephrines have the highest sensitivity (96-100%) and specificity (89-98%) for diagnosing pheochromocytoma, making them the screening test of choice. 1, 2, 4

• 24-hour urinary fractionated metanephrines are an acceptable alternative with sensitivity of 86-97% and specificity of 86-95%, particularly useful in pediatric patients. 1, 2

• Pheochromocytoma, though rare (0.01-0.2% of hypertensive patients), reaches up to 4% prevalence in resistant hypertension and can cause life-threatening complications including cardiac arrest, myocardial infarction, stroke, or sudden death if unrecognized. 1, 2

• The American Heart Association specifically recommends measuring catecholamines in patients with hypertension and episodic palpitations and headache, as this represents a classic presentation warranting immediate biochemical testing. 1

Critical Safety Considerations

• Never initiate beta-blockade alone before excluding pheochromocytoma, as this can precipitate severe hypertensive crisis due to unopposed alpha-adrenergic stimulation. 1, 2, 4

• Avoid contrast-enhanced CT, fine needle biopsy of adrenal masses, or any invasive procedures until pheochromocytoma is definitively excluded, as these can trigger fatal catecholamine crisis. 1, 4

• If pheochromocytoma is confirmed, alpha-adrenergic blockade must be started 7-14 days before any surgical intervention. 1, 2, 4

Why Not the Other Options

Option A (Catecholamine): While catecholamines can be measured, metanephrines (the metabolites) are superior because they have higher sensitivity and are not affected by episodic catecholamine release. 1, 2

Option B (Cortisone level and ACTH): While Cushing's syndrome can present with obesity, hypertension, and acanthosis nigricans 3, the episodic catecholaminergic symptoms (headache, sweating, palpitations) are not characteristic of Cushing's and point specifically toward pheochromocytoma. This would be a secondary consideration after excluding pheochromocytoma.

Option C (Renal US): While renovascular hypertension is a consideration in pediatric hypertension, it does not explain the episodic catecholaminergic symptoms. Renal evaluation would be part of the standard hypertension workup but is not the immediate priority given the clinical presentation. 3

Concurrent Evaluation

• The acanthosis nigricans and obesity still warrant evaluation for insulin resistance, including fasting plasma glucose testing, as recommended for obese children with hypertension and acanthosis nigricans. 3

• However, this metabolic evaluation should proceed in parallel with—not instead of—the pheochromocytoma workup, given the potentially life-threatening nature of undiagnosed pheochromocytoma. 1, 2

Testing Technique

• For plasma free metanephrines, ideally collect from an indwelling venous catheter after the patient has been lying supine for 30 minutes to minimize false positive results. 1, 2

• Confirm that interfering medications (tricyclic antidepressants, sympathomimetics, decongestants) were avoided prior to testing. 1, 2

• If levels are ≥4 times the upper limit of normal, proceed immediately to imaging (preferably MRI) to localize the lesion. 1, 2

• If levels are 1-4 times upper limit, repeat testing under ideal conditions or consider clonidine suppression test (100% specificity, 96% sensitivity). 1, 2