Endocrine Abstracts

Case history: We present the case of a 40-year-old man who was referred to a cardiologist with hypertension. He was initiated on bisoprolol and doxazosin. Investigations revealed elevated urinary metanephrines and catecholamines, with normetadrenaline 7.4 μmol/24 h (normal <2), noradrenaline 820 nmol/24 h (normal <500) but normal dopamine levels. He was referred to our clinic. Two further 24 h urine catecholamine assays were elevated. Dexamethasone suppression test and aldosterone:renin ratio were normal. CT scan revealed a 2.8 cm right adrenal mass and normal left adrenal gland. MIBG uptake was increased in the right adrenal gland.

As patient was already on doxazosin a decision was made to continue it as the α-blockade agent, rather than swapping to phenoxybenzamine. The maximum tolerable dose was 8 mg daily. The patient was referred for laparoscopic adrenalectomy. In the preoperative assessment clinic, blood pressure was 118/70 mmHg but, during induction of anaesthesia, systolic BP rose to 300 mmHg. The operation was cancelled and an endocrine opinion was sought.

Phenoxybenzamine was started in place of doxazosin and, over the next few weeks, the dose was titrated up to 40 mg twice daily. The patient subsequently underwent uneventful laparoscopic adrenalectomy in January 2013. His hypertension resolved off all medication. Histological findings were of phaeochromocytoma with no overt malignant features; genetic testing is awaited.

Discussion: Adequate α- and β-adrenoceptor blockade is essential to minimise morbidity and mortality during resection of catecholamine-secreting tumours. Phenoxybenzamine, a non-competitive α-adrenoceptor antagonist, has historically been the standard choice for perioperative management. However, recent publications have proposed that doxazosin could be a safe alternative.

Our unit has dealt with ten cases of phaechromocytoma over past year. Eight patients had a smooth pre-operative period and successful surgery on phenoxybenzamine. Two patients were α-blocked initially with doxazosin but, after similar difficulties, both were swapped to phenoxybenzamine.

We review the literature and evidence on use of doxazosin and discuss possible reasons for its failure. We are also keen to learn of experience in other centres.