Failure of metyrosine therapy for preoperative management of pheochromocytoma: a case report.

PURPOSE: Pheochromocytomas (PHEOS) are rare catecholamine-secreting adrenal tumours requiring surgical resection. Preoperative alpha-adrenergic receptor blockade to prevent intraoperative hypertension has traditionally been achieved with phenoxybenzamine. Due to changes in the availability of phenoxybenzamine in Canada, alternate therapies are needed for patients. We report our first experience using metyrosine, a tyrosine hydroxylase inhibitor, for preoperative management in a symptomatic patient with a unilateral PHEO.

CLINICAL FEATURES: A 50-yr-old male was referred to our centre with a history of symptoms suggestive of a catecholamine-secreting PHEO, including tachycardia, diaphoresis, nervousness, and tremor. Computerized tomography revealed a right adrenal mass, and additional positive imaging and elevated urine epinephrine levels supported a diagnosis of PHEO. The patient was admitted to hospital five days prior to surgery, and metyrosine therapy was initiated and titrated to 4 g daily over four days. Despite adequate blood pressure (BP) control leading up to the resection, the initial BP reading in the operating room was 191/106 mmHg, but it subsequently declined and was well controlled during induction (100-110 mmHg systolic BP). Significant hypertension (up to 201/110 mmHg) developed upon tumour manipulation and resolved with phentolamine administration and surgical isolation of the tumour. The patient's BP remained stable throughout the residual part of the procedure and in the recovery room and step-down unit.

CONCLUSION: In the case of this patient's PHEO, the use of metyrosine was unsatisfactory in achieving sufficient inhibition of catecholamine synthesis as evidenced by significant intraoperative hypertension. Metyrosine could have a role in preoperative management of these patients, but it may not be optimal as monotherapy for some patients with actively secreting tumours.