Phaeochromocytoma and endocrine hypertension — formative SAQs

SAQ 1 — The hypertensive adolescent with spells (20 marks, ~15 minutes)

A 14-year-old boy presents with a six-month history of episodes of severe headache, generalised sweating, palpitations and anxiety lasting minutes, with pallor noted by his mother. Between episodes he feels well. His blood pressure is 160/100, sustained on repeat measurement, and his heart rate is 96. A catecholamine-secreting tumour is suspected. [4]

Questions

1. State the best first-line biochemical test and explain why it is preferred over a random catecholamine level. (4 marks) [3]
2. Outline the imaging strategy once biochemistry is positive, including functional imaging. (5 marks) [1]
3. Describe the mandatory preoperative pharmacological preparation, stating the sequence and the consequence of getting it wrong. (6 marks) [1]
4. Explain why every child with this diagnosis needs a hereditary gene panel, and name the gene that flags metastatic extra-adrenal disease. (5 marks) [2]

Model answer (must-hit)

1. Measure plasma free metanephrines or a twenty-four-hour urine fractionated metanephrines collection. These are preferred because the tumour cell continually converts catecholamines to metanephrines (noradrenaline to normetanephrine, adrenaline to metanephrine), which leak into the bloodstream continuously, whereas catecholamine release is episodic from stored vesicles. A random catecholamine level drawn between spells reads normal and misses the tumour; metanephrines do not. [3]
2. Start with CT or MRI of the abdomen and pelvis (MRI preferred in children to avoid radiation) because most tumours lie in the adrenal gland or the organ of Zückerkandl. Then characterise and stage with functional imaging — iodine-123 MIBG scintigraphy or, increasingly, gallium-68 DOTATATE PET, which is more sensitive for metastatic and hereditary disease. [1]
3. Alpha-blockade first, then beta-blockade. Start phenoxybenzamine at around 0.5 mg per kilogram per day in divided doses and titrate over ten to fourteen days until the child is normotensive or mildly hypotensive with an orthostatic drop and nasal stuffiness — the block-and-fill end-point. Add a beta-blocker only once the child is fully alpha-blocked, to control reflex tachycardia. Giving a beta-blocker first removes beta-two vasodilator tone and leaves unopposed alpha-one vasoconstriction, precipitating a fatal hypertensive crisis. [1]
4. Around forty percent of paediatric phaeochromocytomas and paragangliomas carry a pathogenic germline mutation, far above adults, so every child earns a gene panel covering SDHx, VHL, RET, NF1, TMEM127, MAX and FH. Identifying the mutation predicts tumour behaviour, sets the surveillance schedule and enables cascade testing of relatives. An SDHB mutation flags extra-adrenal paraganglioma with metastatic potential. [2]