Which of the following statements is true with respect to pheochromocytoma?

b. Clonidine fails to suppress basal plasma-catecholamine levels in patients with pheochromocytoma

d. The ratio of plasma 3,4-dihydroxyphenoglycol (DHPG) to norepinephrine is generally elevated in patients with pheochromocytoma compared to patients with essential hypertension

Pheochromocytoma associated with the MEN IIa syndrome is more often bilateral and more often malignant, therefore, abdominal exploration through an anterior approach is indicated. The ability to measure catecholamines in the plasma has made possible the clonidine suppression test. In patients without pheochromocytoma, clonidine suppresses high basal plasma concentrations into the normal range, whereas concentrations in patients with pheochromocytoma are not suppressed. Another use of plasma catecholamine measurements is in examining the ratio of 3,4-dihydroxyphenoglycol (DHPG) to norepinephrine in plasma. DHPG is released from the chromaffin cells and adrenergic neurons to a much greater extent than norepinephrine in pheochromocytoma patients compared with patients who have essential hypertension, i.e. the ratio of DHPG to norepinephrine is higher in patients with pheochromocytomas.

NP-59 (131I-6 b-iodomethyl-19-norcholesterol) is taken up as cholesterol by the adrenal cortex and is incorporated in the adrenocortical steroidogenic pathway. This is a useful agent for imaging adrenocorticol lesions. 131I-methaiodobenzylguanidine (MIBG) is a norepinephrine analogue that is useful in localizing pheochromocytomas throughout the body, especially when the tumors are multiple, extraadrenal, recurrent, or metastatic.