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We read with interest the excellent case report of von Hippel-Lindau disease complicated by pheochromocytoma.1 However, the authors proceeded directly to imaging and radionuclide scintiscan with 131I-metaiodobenzylguanidine or preoperative localisation of pheochromocytoma, without biochemical confirmation of the diagnosis. The diagnosis of pheochromocytoma is established by demonstrating increased concentrations of catecholamines or catecholamine metabolites, typically in urine but also sometimes in plasma samples. The most reliable tests are measurements of free catecholamines, metanephrines, or vanillylmandelic acid in a 24 hour urine specimen. The last measurement is less sensitive than the other two. Diagnostic accuracy is improved by measuring at least two of the three substances.2 Plasma catecholamine measurements have a sensitivity of more than 90% and a specificity of 95% for the diagnosis of pheochromocytoma.3 However, plasma normetanephrine and metanephrine estimation has been found to be a more sensitive (97% sensitivity) and specific (96% specificity) test for detection of phaeochromocytoma in von Hippel-Lindau disease and multiple endocrine neoplasia type 2 compared with plasma concentrations of catecholamines (norepinephrine and epinephrine), urinary excretion of norepinephrine, epinephrine, metanephrines (normetanephrine and metanephrine combined), and vanillylmandelic acid.4,5 The biochemical diagnosis is also relevant for follow up for recurrence of pheochromocytoma on the same or the other side, particularly in von Hippel-Lindau disease, where multifocal disease is more common than in non-familial cases.6
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