Everything You Need to Know About Pheochromocytoma for Step 1

Pheochromocytoma is one of those “don’t-miss” endocrine diagnoses because it turns vague symptoms (headaches, anxiety, sweating) into a potentially lethal hypertensive emergency—yet it’s also one of the most testable adrenal tumors on Step 1. If you can recognize the classic triad, understand why catecholamines cause the symptoms, and know the correct diagnostic and pre-op treatment sequence, you’ll pick up easy points.

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Where It Fits (Big Picture)

• System: Endocrine
• Topic: Adrenal disorders
• Core concept: Catecholamine-secreting tumor arising from chromaffin cells (neural crest–derived) in the adrenal medulla or extra-adrenal paraganglia.

First Aid cross-reference (conceptual): Endocrine → Adrenal medulla tumors → Pheochromocytoma; MEN syndromes; catecholamine metabolism.

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Definition & Pathophysiology

What it is

Pheochromocytoma = a tumor of chromaffin cells that secretes catecholamines (usually norepinephrine > epinephrine, sometimes dopamine).

• Most common location: adrenal medulla
• Extra-adrenal version: paraganglioma (classically organ of Zuckerkandl near the aortic bifurcation)

Why it causes symptoms

Catecholamines stimulate adrenergic receptors:

Classic catecholamine metabolism (Step 1 favorite)

Catecholamines are metabolized by COMT and MAO → end products include:

• Metanephrines (metanephrine, normetanephrine)
• VMA (vanillylmandelic acid) in urine

High-yield line: Pheochromocytoma → ↑ plasma free metanephrines and/or ↑ urinary fractionated metanephrines.

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Clinical Presentation (How It Shows Up on Questions)

Classic episodic symptoms (the “triad” + HTN)

The board-style presentation is often paroxysmal (spells):

• Episodic headaches
• Sweating
• Tachycardia/palpitations
• Hypertension (sustained or episodic)

Bonus symptoms they love to add:

• Tremor, anxiety/panic-like symptoms
• Pallor
• Weight loss
• Hyperglycemia (catecholamine-induced insulin resistance + glycogenolysis)

Triggers (often in stems)

Episodes can be triggered by:

• Surgery/anesthesia
• Exercise
• Stress
• Certain drugs (can precipitate catecholamine surge)

Complications (why you treat aggressively)

• Hypertensive emergency
• Arrhythmias
• MI, stroke
• Catecholamine-induced cardiomyopathy (takotsubo-like picture can appear in real life and occasionally shows up conceptually)

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High-Yield Associations (Step 1 Gold)

MEN syndromes

Pheochromocytoma is strongly associated with:

• MEN 2A: medullary thyroid carcinoma + pheo + parathyroid hyperplasia
• MEN 2B: medullary thyroid carcinoma + pheo + mucosal neuromas/marfanoid habitus

Exam pearl: If MEN2 is suspected, screen for pheochromocytoma before thyroid surgery to prevent intraoperative hypertensive crisis.

Other inherited associations to recognize

• VHL (von Hippel–Lindau)
• NF1 (neurofibromatosis type 1)
• RET mutations (MEN2)
• SDHx mutations (succinate dehydrogenase) → paragangliomas/pheos

High-yield pattern: young patient, bilateral tumors, or extra-adrenal tumor → think genetic syndrome.

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Diagnosis: The Right Test, Done the Right Way

Best initial tests (what Step 1 expects)

Most sensitive screening:

• Plasma free metanephrines
  or
• 24-hour urinary fractionated metanephrines

Why metanephrines? Tumors continuously metabolize catecholamines to metanephrines, so metanephrines stay elevated even if catecholamine secretion is episodic.

Classic but less preferred “old school” clue: ↑ urinary VMA.

Confirm and localize (after biochemical confirmation)

Once biochemical tests are positive:

• CT or MRI of abdomen/pelvis to find adrenal lesion
• If needed (e.g., extra-adrenal suspicion): functional imaging (classically MIBG scan)

Histology (Step 1 pathology favorite)

• Tumor shows zellballen (“cell ball”) nests of chromaffin cells.
• Chromaffin reaction: turns brown with chromium salts (historical pearl).

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Treatment: The Sequence Matters (Most Tested Management Point)

Definitive treatment

• Surgical resection (adrenalectomy or removal of paraganglioma)

Pre-op medical optimization (must know)

You must block alpha before beta:

1. Alpha blockade first

   • Classic: phenoxybenzamine (irreversible, nonselective $\alpha$ blocker)
   • Alternative: selective $\alpha_1$ blockers (e.g., doxazosin; more Step 2/clinical nuance)

2. Then beta blockade (only after adequate alpha blockade)

   • To control tachycardia (e.g., propranolol)

Why the order matters (testable mechanism):
If you give a beta blocker first, you remove $\beta_2$-mediated vasodilation and leave unopposed $\alpha_1$ vasoconstriction → dangerous hypertensive crisis.

Acute hypertensive crisis (conceptual management)

In suspected pheo crisis:

• Rapid-acting alpha blockade and BP control (institution-dependent agents); the board-relevant concept is alpha blockade is key.

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Classic USMLE-Style Vignettes (What to Recognize Fast)

Vignette 1: “Panic attacks” with HTN

A patient with episodic headache + sweating + palpitations, high BP during episodes, and elevated plasma metanephrines → pheochromocytoma.

Vignette 2: MEN2 clue

Patient with medullary thyroid carcinoma (calcitonin, amyloid stroma) + episodic hypertension → MEN2-associated pheochromocytoma.
Do pheo workup first if surgery is planned.

Vignette 3: Medication error

A patient with suspected pheo is given propranolol before alpha blockade → sudden severe hypertension → unopposed alpha effect.

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Rapid Review Table (High-Yield Summary)

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First Aid “Anchor Facts” to Memorize

• Triad: headache + sweating + tachycardia (often with paroxysmal HTN)
• Dx: plasma free metanephrines (high sensitivity); urine metanephrines also common
• Tx: phenoxybenzamine first, then beta blocker, then resection
• MEN2: screen/treat pheo before thyroid surgery