Comparison of the Histamine and Tyramine Hydrochloride Tests in the Diagnosis of Pheochromocytoma

The tyramine hydrochloride test of Engelman and Sjoerdsma was compared with the standard cold pressorhistamine test in seven patients with pheochromocytoma, five with essential hypertension, and three with labile hypertension. Urinary and blood catecholamines and urinary vanilmandelic acid (VMA) and metanephrines were also determined. One nontumor patient had a systolic pressor response (20 mm Hg greater than cold pressor response) after histamine; none had a response greater than 15 mm Hg after tyramine injection. The blood and urine values were normal in nontumor patients. Among the tumor patients, five had a marked pressor response to histamine, five had a mild pressor response (> 20 mm Hg) to tyramine, and six had increased circulating pressor amine levels. All tumor patients had increased values for urinary metanephrines, six had increased catecholamine values, and five had increased VMA values.