Usefulness of basal catecholamine plasma levels and clonidine suppression test in the diagnosis of pheochromocytoma

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.

The association between systolic blood pressure reduction during clonidine suppression testing and the decrease in plasma catecholamines and metanephrines

Borderline isolated norepinephrine (NE) and normetanephrine (NMT) elevation is common among patients with suspected pheochromocytoma and paraganglioma (PPGL). The clonidine suppression test (CST) may help establish the etiology in these cases. Prolonged laboratory processing and/or paucity of reliable biochemical assays may limit the utility of CST. The aim of this study was to evaluate whether blood pressure (BP) reduction during CST is associated with alterations in plasma NMT/NE, thereby potentially providing an immediate indication of CST results. In this cross-sectional study, the authors included all consecutive patients with suspected PPGL who underwent CST from January 1, 2014, to December 31, 2019. Linear regression models were conducted to evaluate the association between BP reduction and decrease in plasma NMT/NE. The final analysis included 36 patients (17 males). The decrease in systolic BP (SBP) 90 minutes postclonidine was associated with a decrease in plasma NMT (R = 0.668, P = .025) and NE (R = 0.562, P = .005). A 40% decrease in NMT and NE correlated with a 9.74% and 7.16% decrease in SBP, respectively. Subgroup analyses demonstrated that the association between SBP reduction and the decrease in plasma NMT (R = 0.764, P = .046) and NE (R = 0.714, P = .003) strengthens among patients with hypertension and among those with diabetes mellitus (R = 0.974, P = .026 for NMT). In conclusion, SBP reduction during CST is associated with plasma NMT and NE decrease. Therefore, the decrease in SBP 90 minutes postclonidine may serve as an immediate complementary clinical tool for PPGL diagnosis.

Unusual association of adrenal pheochromocytoma and para-aortic neurofibroma in pregnancy

The association of pheochromocytoma (PHEO) and pregnancy is uncommon and life threatening for both the fetus and the mother. Early diagnosis and treatment is essential to decrease maternal and fetal mortality and to differentiate the disease from the more common pre-eclampsia. While medical treatment should be started immediately after diagnosis, the timing of surgical treatment is still debated. We describe the case of a 27-yr-old woman in the 18th week of pregnancy who showed a biochemical pattern typical of PHEO and, by imaging studies, 2 tumors with the same characteristics: the first localized on the right adrenal gland, the second at the right renal hilum. The patient underwent surgery because of suspicion of malignant PHEO with local metastasis, while histology revealed a rare association of a solitary PHEO and para-aortic neurofibroma, both tumors embryologically deriving from a common cell precursor.

New advances in the biochemical diagnosis of pheochromocytoma: moving beyond catecholamines

Pheochromocytomas are dangerous tumors that, although a rare cause of hypertension, require consideration among large numbers of patients. The resulting low prevalence of the tumor among tested populations and the inadequacies of commonly used biochemical tests make excluding or confirming the tumor an often difficult and time-consuming task. Recognition that catecholamines are metabolized to free metanephrines within pheochromocytoma tumor cells, and that this process is independent of catecholamine release, provides a rationale for use of these metabolites in the biochemical diagnosis of pheochromocytoma. Here we briefly review the history of biochemical diagnosis of pheochromocytoma in relation to recent data about the diagnostic utility of plasma free metanephrines for detection of these tumors. Measurements of urinary or plasma catecholamines have reasonable sensitivity for detection of most pheochromocytomas, particularly those in patients with sustained hypertension. False-negative test results can, however, occur in asymptomatic patients tested because of an adrenal incidentaloma or a familial predisposition for pheochromocytoma, or when sampling is carried out between episodes of paroxysmal hypertension. Measurements of urinary total metanephrines or vanillylmandelic acid are less reliable and are of little value as initial screening tests. In contrast, measurements of plasma concentrations or free metanephrines or 24-hour urinary outputs of fractionated normetanephrine and metanephrine almost always reveal the tumor. Although, both tests have similarly high sensitivity, the relatively low specificity of urinary fractionated metanephrines means that pheochromocytomas can be more efficiently excluded or confirmed using measurements of plasma free metanephrines.

Diagnosis and management of pheochromocytoma during pregnancy

Although the presence of pheochromocytoma in pregnancy is extremely rare, this association deserves much attention as the tumor constitutes a very high risk for both mother and fetus. Any pregnant woman with hypertension, especially if paroxysmal or labile, or with so far unexplained "spells", should induce the clinician to consider the possibility of a pheochromocytoma. Maternal and fetal survival depend a lot on an early diagnosis, a correct medical therapy and a correct timing of delivery and surgery. In this respect, a strict collaboration between obstetricians, endocrinologists, anesthesiologists and surgeons is pivotal.

Clonidine suppression test revisited

BACKGROUND

The diagnosis of pheochromocytoma may be difficult because the clinical picture is variable.

OBJECTIVE

The purpose of this paper is to report our experience and to review the published data on the diagnostic significance and risks of the clonidine suppression test in the diagnosis of pheochromocytoma.

PATIENTS AND METHODS

114 patients were evaluated for pheochromocytoma using the clonidine suppression test.

RESULTS

The diagnosis was established in four patients. Overall accuracy of the test in our own series was 98% when the normal response to clonidine was defined as total plasma catecholamines of less than 500 ng/L, or less than 70% of the baseline value. No serious complication was noted.

CONCLUSION

Our data and the published series demonstrate that the clonidine suppression test is accurate and safe in patients with suspected pheochromocytoma.

The mechanism responsible for hypertension in a patient with Guillain-Barré syndrome

We report a case of hypertension associated with Guillain-Barré syndrome. In this case, the circadian variation of blood pressure was interrupted. Examination of neurohumoral factors revealed a hyperactive sympathetic nervous system and an increase in plasma renin activity. Clonidine, which acts centrally to inhibit sympathetic outflow, did not suppress serum norepinephrine or epinephrine. These observations suggest that autonomous hyperactivity of the efferent pathway of the sympathetic nervous system may cause the sustained hypertension throughout the day in this case.

A nonsecreting pheochromocytoma presenting as an incidental adrenal mass. Report on a case

A 25 year old women presented an incidental adrenal mass which was diagnosed to be a pheochromocytoma before surgery by means of a positive 131-I-MIBG scintigraphy. Urinary vanilmandelic acid resulted repeatedly normal as well as basal plasma norepinephrine (NE), epinephrine (E) and dopamine (DA). Urinary homovannilic acid resulted in the normal range. Stimulation tests with iv glucagone, tyramine and metoclopramide evoked normal NE and E responses while a slight increase in plasma DA was observed after metoclopramide. Oral clonidine suppressed plasma catecholamines (CA) normally. Histologic and immunohistochemical studies confirmed that the tumor was a pheochromocytoma showing positivity for tyrosine hydroxylase but not for dopamine-beta-hydroxylase activity. This case is the first report on a completely asymptomatic pheochromocytoma presenting as an incidental adrenal mass which was investigated with repeated biochemical tests before surgery and demonstrates that, among the extremely variable functional attitudes of pheochromocytomas, a defect in CA synthesis and secretion is also to be included.

Acute mercury poisoning (acrodynia) mimicking pheochromocytoma in an adolescent

A 14-year-old boy was seen because of irritability, insomnia, lethargy, and profuse sweating, together with hypertension (blood pressure: 160/120 mm Hg), tachycardia, and a diffuse erythematous rash with desquamation of the palms and soles. Initial biochemical investigation suggested a diagnosis of pheochromocytoma, but subsequently a history of exposure to mercury vapor was obtained. This case emphasizes the clinical and biochemical similarities between mercury poisoning (acrodynia) and pheochromocytoma.

Glucagon and clonidine testing in the diagnosis of pheochromocytoma

We assessed the sensitivity and specificity of glucagon stimulation and clonidine suppression tests in the diagnosis of pheochromocytoma in 113 hypertensive patients, 39 with and 74 without the tumor. In the glucagon stimulation test, blood was sampled 2 minutes after intravenous injection of 0.28 mumol (1 mg) glucagon, and in the clonidine suppression test, blood was sampled 3 hours after administration of oral clonidine, 1.30 mumol (0.3 mg)/70 kg body wt. Baseline levels of catechols in antecubital venous blood were abnormal, with norepinephrine greater than 7.10 nmol/l (1,200 pg/m), epinephrine greater than 1.51 nmol/l (276 pg/ml), norepinephrine/dihydroxyphenylglycol (DHPG) ratio greater than 1.09, or dopa greater than 35.53 nmol/l (7,000 pg/ml), in 30 of 39 patients with pheochromocytoma (sensitivity 77%) and 1 of 74 patients without pheochromocytoma (specificity 99%). Results of the glucagon test were abnormal (norepinephrine greater than 11.83 nmol/l [2,000 pg/ml] or more than threefold increase from baseline) in 25 of 31 patients with pheochromocytoma (sensitivity 81%) and 0 of 72 patients without pheochromocytoma (specificity 100%). Results of the clonidine test were abnormal (after clonidine norepinephrine greater than 2.96 nmol/l [500 pg/ml] or less than 50% decrease from baseline) in 29 of 30 patients with pheochromocytoma (sensitivity 97%) and in 7 of 30 patients without pheochromocytoma (specificity 67%). Very high baseline levels of catechols therefore indicated the presence of pheochromocytoma, but there were several false-negative results when normal levels were obtained. The glucagon test alone was highly specific but not sensitive, and the clonidine test was highly sensitive but less specific.(ABSTRACT TRUNCATED AT 250 WORDS)