Another cause of 'pseudophaeochromocytoma'--quetiapine associated with a false positive normetanephrine result

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.

Pheochromocytoma: pitfalls in the biochemical evaluation

The current work-up of a patient suspected to have a pheochromocytoma starts with the measurement of plasma or urine metanephrines. Notably, up to a quarter of these patients will have a false positive result. When the plasma or urine metanephrines are less than the 4-fold upper limit of normal, clinicians struggle between the fear of missing a potentially fatal condition and ordering costly follow up tests. In many cases, ordering unnecessary imaging studies may only increase the level of patient anxiety. This article will review various physiologic factors, pathologic conditions and medications that may influence the levels of catecholamines and their metabolites yielding false positive or false negative results. Acquiring familiarity with these conditions as well as interfering medications will equip clinicians with better interpretation skills of the biochemical tests.

Malignant catatonia mimicking pheochromocytoma

Malignant catatonia is an unusual and highly fatal neuropsychiatric condition which can present with clinical and biochemical manifestations similar to those of pheochromocytoma. Differentiating between the two diseases is essential as management options greatly diverge. We describe a case of malignant catatonia in a 20-year-old male who presented with concurrent psychotic symptoms and autonomic instability, with markedly increased 24-hour urinary levels of norepinephrine at 1752 nmol/day (normal, 89-470 nmol/day), epinephrine at 1045 nmol/day (normal, <160 nmol/day), and dopamine at 7.9  μ mol/day (normal, 0.4-3.3  μ mol/day). The patient was treated with multiple sessions of electroconvulsive therapy, which led to complete clinical resolution. Repeat urine collections within weeks of this presenting event revealed normalization or near normalization of his catecholamine and metanephrine levels. Malignant catatonia should be considered in the differential diagnosis of the hypercatecholamine state, particularly in a patient who also exhibits concurrent catatonic features.