Pheochromocytoma with Normal Urinary and Plasma Catecholamines but Elevated Plasma Free Metanephrines in a Patient with Adrenal Incidentaloma

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Abstract
: We present an asymptomatic 75-year-old patient (normal renal function, no hypertension) with adrenal incidentaloma (5 cm) who repetitively had had negative screening tests for pheochromocytoma by determination of urinary and plasma catecholamines. The attempt then to exclude malignant disease by fine needle aspiration biopsy caused the patient's one and only hypertensive crisis. A high performance liquid chromatography (HPLC) method for measurement of plasma metanephrines, however, showed raised levels consistent with the diagnosis of pheochromocytoma, later confirmed by histology. Finally, open transperitoneal surgery caused the tumor to release large quantities of the parent amines norepinephrine and epinephrine in addition to normetanephrine and metanephrine. This case is to demonstrate the difficulties and possible serious consequences often encountered in the diagnostic work-up of pheochromocytoma. In addition, it suggests that the measurement of plasma metanephrines by means of the presented HPLC method may contribute to the diagnosis of this condition to minimize interventional risks and to raise diagnostic sensitivity. Intratumor metabolism of catecholamines to metanephrines is well known, especially in large tumors, leading to complete absence of symptoms. As in this patient, however, there are certain clinical situations (such as fine-needle biopsy of the lesion or abdominal surgery) that have to be kept in mind for their ability to dramatically raise plasma catecholamines even in "catecholamine-negative" pheochromocytomas. The Endocrinologist 2000; 10: 65-68 (C) 2000 Lippincott Williams & Wilkins, Inc.

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