Plasma norepinephrine response to standing in patients with pheochromocytoma or medullary carcinoma of the thyroid.

We determined the effect of a lying/standing test on 22 patients with medullary carcinoma of the thyroid (MCT), seven patients with pheochromocytoma (six of whom also had MCT), six healthy first-degree family members of patients with MCT, and nine normal subjects who did not have a family history of MCT. The purpose of the study was to determine if the patients with MCT had an altered noradrenergic response to standing and to determine if this test would be useful in screening MCT patients for the presence of pheochromocytoma. All of the patients with MCT, as well as all of the healthy family members, had normal urinary excretion of catecholamines and their metabolites. Plasma norepinephrine (NE) concentrations, plasma cortisol levels, and blood pressure (BP) were determined during the lying/standing test. The plasma NE concentration showed the expected increase with a change in posture; the plasma cortisol concentration did not change. There was no significant difference in the plasma NE, plasma cortisol, and BP response in the four study groups. Only one of the seven patients with pheochromocytoma had a hypertensive episode in response to standing. We conclude that there is probably a normal noradrenergic response to standing in patients with MCT, and the standing/lying test, as performed in this study, is of limited value in screening for the presence of pheochromocytoma.