Plasma free and conjugated catecholamines in diagnosis and localisation of pheochromocytoma

In six patients urinary excretion of vanillylmandelic acid and catecholamines (CA) could establish the diagnosis of pheochromocytoma. Free norepinephrine (NE) in plasma was within the normal range in two patients and plasma free epinephrine (E) was only marginally elevated in one of them. The degree of CA conjugation was not altered and scattered as in controls and was therefore not complementary to the usual determination of plasma free CA. The intermittent nature of CA secretion by the tumour could be demonstrated by multiple blood samplings during a 48-h study period in two patients, e.g. normal plasma values might be associated with pheochromocytoma if measurements are made during a trough. Thus a single peripheral CA determination cannot be of discriminative value in the diagnosis of pheochromocytoma unless it shows marked elevation. Ten patients subjected to intracardial measurements and five patients suspected of having a pheochromocytoma underwent venous catheterisation to determine their free and conjugated plasma CA. In controls CA values near the orifices of adrenal veins differed enormously and partly overlapped with corresponding levels of patients with pheochromocytoma. In one patient with surgically proven left adrenal tumour highest concentrations of CA were measured in the vena cava superior. These high CA concentrations, caused by paroxysmal release of CA by the tumour arouse suspicion of an additional, ectopic tumour. Because venous catheterisation cannot be relied on implicitly we propose computed tomographic scanning as a first step in localisation of a pheochromocytoma.