ContextMeasurements of plasma methoxytyramine, the O-methylated dopamine metabolite, are useful for detecting rare dopamine-producing pheochromocytomas and paragangliomas (PPGLs) and head and neck paragangliomas (HNPGLs), but utility for screening beyond that achieved using standard measurements of normetanephrine and metanephrine is unclear.ObjectiveEvaluation of the additional utility of methoxytyramine compared to plasma normetanephrine and metanephrine for diagnosis of PPGLs and HNPGLs.DesignComparative prospective study.MethodsComparison of mass spectrometric-based measurements of plasma methoxytyramine, normetanephrine and metanephrine in 1963 patients tested for PPGLs at six tertiary medical centers according to reference intervals verified in 423 normotensive and hypertensive volunteers.ResultsOf the screened patients, 213 had PPGLs and 38 HNPGLs. Using an upper cut-off of 0.10 nmol/L for methoxytyramine, 0.45 nmol/L for metanephrine and age-specific upper cut-offs for normetanephrine, diagnostic sensitivity with the addition of methoxytyramine increased from 97.2% to 98.6% for patients with PPGLs and from 22.1% to 50.0% for patients with HNPGLs, with a small decrease in specificity from 95.9% to 95.1%. Addition of methoxytyramine did not significantly alter areas under receiver operating characteristic curves for patients with PPGLs (0.984 vs 0.991), but did increase (P < 0.05) areas for patients with HNPGLs (0.627 vs 0.801). Addition of methoxytyramine also increased the proportion of patients with PPGLs who showed highly positive predictive elevations of multiple metabolites (70.9% vs 49.3%).ConclusionsWhile the benefit of additional measurements of plasma methoxytyramine for the detection of PPGLs is modest, the measurements do assist with positive confirmation of disease and are useful for the detection of HNPGLs.

Context Cross-sectional imaging with CT or MRI is regarded as a first-choice modality for tumor localization in patients with pheochromocytoma and paraganglioma (PPGL). 123I-labeled metaiodobenzylguanidine (123I-MIBG) is widely used for functional imaging but the added diagnostic value is controversial. Objective To establish the virtual impact of adding 123I-MIBG scintigraphy to CT or MRI on diagnosis and treatment of PPGL. Design International multicenter retrospective study. Intervention None. Patients Two hundred thirty-six unilateral adrenal, 18 bilateral adrenal, 48 unifocal extra-adrenal, 12 multifocal, and 26 metastatic PPGL. Main Outcome Measures Patients underwent both anatomical imaging (CT and/or MRI) and 123I-MIBG scintigraphy. Local imaging reports were analyzed centrally by two independent observers who were blinded to the diagnosis. Imaging-based diagnoses determined by CT/MRI only, 123I-MIBG only, and CT/MRI combined with 123I-MIBG scintigraphy were compared with the correct diagnoses. Results The rates of correct imaging-based diagnoses determined by CT/MRI only versus CT/MRI plus 123I-MIBG scintigraphy were similar: 89.4 versus 88.8%, respectively (P = 0.50). Adding 123I-MIBG scintigraphy to CT/MRI resulted in a correct change in the imaging-based diagnosis and ensuing virtual treatment in four cases (1.2%: two metastatic instead of nonmetastatic, one multifocal instead of single, one unilateral instead of bilateral adrenal) at the cost of an incorrect change in seven cases (2.1%: four metastatic instead of nonmetastatic, two multifocal instead of unifocal and one bilateral instead of unilateral adrenal). Conclusions For the initial localization of PPGL, the addition of 123I-MIBG scintigraphy to CT/MRI rarely improves the diagnostic accuracy at the cost of incorrect interpretation in others, even when 123I-MIBG scintigraphy is restricted to patients who are at risk for metastatic disease. In this setting, the impact of 123I-MIBG scintigraphy on clinical decision-making appears very limited.