Biochemical Assessment of Pheochromocytoma and Paraganglioma

Pheochromocytoma and paraganglioma (PPGL) require prompt consideration and efficient diagnosis and treatment to minimize associated morbidity and mortality. Once considered, appropriate biochemical testing is key to diagnosis. Advances in understanding catecholamine metabolism have clarified why measurements of the O-methylated catecholamine metabolites rather than the catecholamines themselves are important for effective diagnosis. These metabolites, normetanephrine and metanephrine, produced respectively from norepinephrine and epinephrine, can be measured in plasma or urine, with choice according to available methods or presentation of patients. For patients with signs and symptoms of catecholamine excess, either test will invariably establish the diagnosis, whereas the plasma test provides higher sensitivity than urinary metanephrines for patients screened due to an incidentaloma or genetic predisposition, particularly for small tumors or in patients with an asymptomatic presentation. Additional measurements of plasma methoxytyramine can be important for some tumors, such as paragangliomas, and for surveillance of patients at risk of metastatic disease. Avoidance of false-positive test results is best achieved by plasma measurements with appropriate reference intervals and preanalytical precautions, including sampling blood in the fully supine position. Follow-up of positive results, including optimization of preanalytics for repeat tests or whether to proceed directly to anatomic imaging or confirmatory clonidine tests, depends on the test results, which can also suggest likely size, adrenal vs extra-adrenal location, underlying biology, or even metastatic involvement of a suspected tumor. Modern biochemical testing now makes diagnosis of PPGL relatively simple. Integration of artificial intelligence into the process should make it possible to fine-tune these advances.

Diagnostic Accuracy of Computed Tomography to Exclude Pheochromocytoma: A Systematic Review, Meta-analysis, and Cost Analysis

OBJECTIVES

To assess the diagnostic accuracy of unenhanced computed tomography (CT) attenuation values to exclude a pheochromocytoma in the diagnostic work-up of patients with an adrenal incidentaloma and to model the associated difference in diagnostic costs.

METHODS

The MEDLINE and Embase databases were searched from indexing to September 27, 2018, and studies reporting the proportion of pheochromocytomas on either side of the 10-Hounsfield unit (HU) threshold on unenhanced CT were included. The pooled proportion of pheochromocytomas with an attenuation value greater than 10 HU was determined, as were the modeled financial costs of the current and alternative diagnostic approaches.

RESULTS

Of 2957 studies identified, 31 were included (N=1167 pheochromocytomas). Overall risk of bias was low. Heterogeneity was not observed between studies (Q=11.5, P=.99, I²=0%). The pooled proportion of patients with attenuation values greater than 10 HU was 0.990 (95% CI, 0.984-0.995). The modeled financial costs using the new diagnostic approach were €55 (∼$63) lower per patient.

CONCLUSION

Pheochromocytomas can be reliably ruled out in the case of an adrenal lesion with an unenhanced CT attenuation value of 10 HU or less. Therefore, determination of metanephrine levels can be restricted to adrenal tumors with an unenhanced CT attenuation value greater than 10 HU. Implementing this novel diagnostic strategy is cost-saving.

Biochemical Diagnosis of Chromaffin Cell Tumors in Patients at High and Low Risk of Disease: Plasma versus Urinary Free or Deconjugated O-Methylated Catecholamine Metabolites

BACKGROUND

Measurements of plasma or urinary metanephrines are recommended for diagnosis of pheochromocytoma and paraganglioma (PPGL). What test offers optimal diagnostic accuracy for patients at high and low risk of disease, whether urinary free metanephrines offer advantages over deconjugated metanephrines, and what advantages are offered by including methoxytyramine in panels all remain unclear.

METHODS

A population of 2056 patients with suspected PPGLs underwent prospective screening for disease using mass spectrometric-based measurements of plasma free, urinary deconjugated, and urinary free metanephrines and methoxytyramine. PPGLs were confirmed in 236 patients and were excluded in others on follow-up evaluation.

RESULTS

Measurements of plasma free metabolites offered higher (P < 0.01) diagnostic sensitivity (97.9%) than urinary free (93.4%) and deconjugated (92.9%) metabolites at identical specificities for plasma and urinary free metabolites (94.2%) but at a lower (P < 0.005) specificity for deconjugated metabolites (92.1%). The addition of methoxytyramine offered little value for urinary panels but provided higher (P < 0.005) diagnostic performance for plasma measurements than either urinary panel according to areas under ROC curves (0.991 vs 0.972 and 0.964). Diagnostic performance of urinary and plasma tests was similar for patients at low risk of disease, whereas plasma measurements were superior to both urinary panels for high-risk patients.

CONCLUSIONS

Diagnosis of PPGLs using plasma or urinary free metabolites provides advantages of fewer false-positive results compared with commonly measured deconjugated metabolites. The plasma panel offers better diagnostic performance than either urinary panel for patients at high risk of disease and, with appropriate preanalytics, provides the test of choice. Measurements of methoxytyramine in urine show limited diagnostic utility compared with plasma.