Physiology · Year 1 · from Physiology
Case 3: Pheochromocytoma - Catecholamine Excess
Clinical Image
Source: Radiopaedia - Pheochromocytoma - Used for educational purposes
Patient Presentation
A 38-year-old man is brought to the emergency department after experiencing an episode of severe headache, profuse sweating, palpitations, and anxiety that lasted about 30 minutes. He describes similar episodes occurring 2-3 times per week over the past 3 months. During these episodes, his wife notes that he becomes pale and tremulous. Between episodes, he feels relatively normal.
Demographics
- Age: 38 years
- Sex: Male
- Past Medical History: Hypertension (diagnosed 1 year ago, difficult to control)
- Medications: Three antihypertensive medications
Chief Complaint
Episodic headaches, palpitations, sweating, and anxiety
Physical Examination (during episode)
- Blood pressure: 228/124 mmHg
- Heart rate: 118 bpm
- Temperature: 37.8°C
- General: Anxious, diaphoretic, pallor
- Cardiovascular: Tachycardic, regular rhythm, no murmurs
- Pupils: Dilated
Workup
- 24-hour urine metanephrines: Markedly elevated
- 24-hour urine catecholamines: Epinephrine and norepinephrine elevated
- Plasma free metanephrines: Elevated
- CT abdomen: 4 cm heterogeneous mass in the right adrenal gland
- MIBG scan: Intense uptake in right adrenal mass
Diagnosis
Pheochromocytoma (catecholamine-secreting adrenal tumor)
Treatment
- Alpha-blockade (phenoxybenzamine) initiated first - 10-14 days preoperatively
- Beta-blockade added only AFTER adequate alpha-blockade
- Liberal salt and fluid intake to expand volume
- Surgical adrenalectomy (laparoscopic)
- Intraoperative monitoring for hemodynamic instability
- Genetic testing for hereditary syndromes (MEN2, VHL, SDH mutations)
Physiological Principles Demonstrated
- Catecholamine receptor mechanisms: Episodic release of catecholamines produces classic symptoms through alpha and beta receptor activation: vasoconstriction (hypertension, pallor), cardiac stimulation (tachycardia, palpitations), sweating, and metabolic effects.
- G-protein coupled receptor signaling: Catecholamines act through GPCRs to activate adenylyl cyclase (beta receptors) or phospholipase C (alpha-1 receptors), producing rapid physiological effects.
- Treatment sequence rationale: Alpha-blockade must precede beta-blockade because blocking beta-mediated vasodilation without first blocking alpha-mediated vasoconstriction can cause unopposed alpha effects and hypertensive crisis.
- Hormone measurement: Metabolites (metanephrines) are more stable than catecholamines themselves and provide better diagnostic sensitivity.