This
Hypertension Grand Rounds shows how applying new clinical laboratory techniques helped to diagnose
pheochromocytoma in a difficult case. In the setting of long-standing, sustained
hypertension, the patient had a hypertensive paroxysm during
anesthesia induction for surgery, leading to suspicion of a
pheochromocytoma. Conventional testing, including CT scanning and fractionated urinary
metanephrine test, was not diagnostic. The patient had another hypertensive paroxysm during subsequent
anesthesia induction, requiring
intensive care. Consistently elevated plasma levels of free
normetanephrine provided the first and only biochemical evidence for a
pheochromocytoma in this case. 6-[18F]Fluorodopamine positron emission tomography and 123I-metaiodobenzylguanidine scintigraphy subsequently agreed on the existence of a small left adrenal mass, which when removed surgically proved to be a
pheochromocytoma. Postoperatively, plasma levels of
normetanephrine normalized, and there were no further hypertensive paroxysms, although the patient remained hypertensive. This case illustrates the superiority of plasma levels of free (unconjugated) metanephrines, compared with other biochemical tests, to detect
pheochromocytoma. It also confirms that functional imaging by 6-[18F]fluorodopamine or 123I-metaiodobenzylguanidine scanning can localize
pheochromocytoma in difficult cases in which other imaging tests are not diagnostic.