MBBS viva · Endocrinology / General Medicine
Phaeochromocytoma — the adrenal incidentaloma, metanephrines and alpha-before-beta viva
A final-prof viva on interpreting an adrenal incidentaloma with raised metanephrines, the biochemical rationale for choosing metanephrines over catecholamines, the alpha-before-beta preoperative rule, the receptor pharmacology that explains unopposed alpha crisis, and the intra-operative catecholamine-crisis response. Examiner expects the metanephrine principle, phenoxybenzamine dosing and goals, IV phentolamine for crisis, and genetic testing for all.
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Interpretation
The examiner hands you a panel from a 45-year-old woman with a year of episodic headaches and sweating, found to have a 4.5 cm right adrenal mass: plasma normetanephrine 3.2 nmol/L (reference under 0.9), metanephrine 0.4 nmol/L, 24-hour urine normetanephrine markedly raised, CT unenhanced 44 Hounsfield units with slow washout, blood pressure 168/104 with an orthostatic drop, haemoglobin 145, glucose 7.2 mmol/L, and a note she is on amitriptyline for insomnia. The examiner asks: "Interpret these results, give the diagnosis, and outline the preparation for surgery."
- Interpretation: the markedly raised plasma normetanephrine (with a high-attenuation, slow-washout adrenal mass) confirms a noradrenaline-secreting phaeochromocytoma. The biochemistry — metanephrines — is the correct first-line test (more sensitive than catecholamines); the CT pattern is the radiological correlate. The mild hyperglycaemia reflects catecholamine effect.[1]
- The decisive discriminator the examiner will probe: a unenhanced attenuation over 10 HU (here 44) with slow washout distinguishes a phaeo from a lipid-rich adenoma (which is <10 HU and washes out rapidly); and the pallor/orthostatic drop localises the physiology to alpha-1 vasoconstriction with volume depletion.[1]
- The pitfall in the data — she is on amitriptyline (a tricyclic), which can falsely elevate metanephrines; if borderline, stop it (with supervision) and re-test, or use the clonidine suppression test. Here the level is high enough and the imaging characteristic, so the diagnosis stands.[1]
Key points
The examiner will probe each; be ready to defend them at viva depth:
- The metanephrine principle — metanephrine and normetanephrine are produced continuously inside the tumour by catechol-O-methyltransferase, independent of the episodic catecholamine release, so they are far more sensitive than the parent catecholamines or VMA. This is why they are first-line (Endocrine Society 2014).[1]
- Biochemistry before imaging, before biopsy — confirm with metanephrines first; never biopsy an unblocked adrenal mass with raised metanephrines (fatal crisis).[1]
- The cardinal rule — alpha before beta — phenoxybenzamine (non-competitive alpha-blocker) 10 mg twice daily, titrate over 10 to 14 days to about 1 mg/kg/day, aiming for seated BP ~130/80 with a mild orthostatic drop and nasal congestion (a sign of adequate blockade); volume expansion; only then add a beta-blocker for tachycardia; then operate.[1][2]
- Why beta-first kills — a beta-blocker given alone leaves alpha-1 vasoconstriction unopposed, producing a catastrophic hypertensive crisis (stroke, MI, arrhythmia).[2]
- Intra-operative crisis — on tumour handling, treat surges with IV phentolamine or sodium nitroprusside/nicardipine; treat arrhythmia with esmolol only after alpha-blockade; anticipate post-clamping hypotension (fluids + vasopressors) and hypoglycaemia (monitor glucose).[2]
- Heritability and genetics — over 30 percent carry a germline mutation (the old 'rule of 10' is outdated for heritability); SDHB carries the highest risk of malignant, extra-adrenal, recurrent disease. Offer genetic testing to all patients.[1]
- Functional imaging — use MIBG scintigraphy, 18F-DOPA or 68Ga-DOTATATE PET for extra-adrenal, metastatic, hereditary or large tumours, and to plan radioligand therapy.[1]
- Hereditary syndromes to volunteer — MEN 2 (RET: bilateral adrenal phaeos, medullary thyroid carcinoma, hyperparathyroidism), VHL (adrenal phaeos, RCC, CNS/retinal haemangioblastomas), NF1 (neurofibromas, cafe-au-lait), and SDHx paraganglioma.[1]
- Special situations — pregnancy (high maternal/fetal mortality if missed; alpha-blockade is safe, plan multidisciplinary delivery and resection); adrenal incidentaloma (always screen biochemistry); children (more often bilateral, extra-adrenal, hereditary).[1]
- Long-term follow-up — lifelong biochemical surveillance (plasma metanephrines 6-12 monthly) for recurrence, metastasis and new primaries, even after complete resection.[1]
References
- Lenders JW, Duh QY, Eisenhofer G, et al. Pheochromocytoma and paraganglioma: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2014.[1]
- Nazari MA, Hasan R, Haigney M, et al. Catecholamine-induced hypertensive crises: current insights and management. Lancet Diabetes Endocrinol 2023.[2]
References2ShowHide
- [1]Lenders JW, Duh QY, Eisenhofer G, et al. Pheochromocytoma and paraganglioma: an endocrine society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism, 2014.PMID 24893135
- [2]Nazari MA, Hasan R, Haigney M, et al. Catecholamine-induced hypertensive crises: current insights and management. Lancet Diabetes and Endocrinology, 2023.PMID 37944546