Urinary vanillylmandelic acid:creatinine ratio in dogs with pheochromocytoma

https://doi.org/10.1016/j.domaniend.2020.106559Get rights and content

Highlights

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    Urinary vanillylmandelic acid (VMA) is the end product of catecholamine metabolism.

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    Vanillylmandelic acid was determined by HPLC in dogs.

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    Vanillylmandelic acid was expressed as the ratio with respect to urinary creatinine (VMA:C).

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    The VMA:C can differentiate pheochromocytoma from cortisol-secreting adrenal tumors in dogs.

Abstract

Pheochromocytoma diagnosis in dogs is challenging because biochemical tests are not always available. In humans, urinary vanillylmandelic acid (VMA) is part of a pheochromocytoma biochemical diagnostic profile, whereas its diagnostic accuracy is currently unknown in dogs with pheochromocytoma. Prospectively, VMA was determined by HPLC and expressed as the ratio with respect to urinary creatinine (VMA:C). The diagnostic accuracy of the VMA:C ratio was evaluated by analyzing the receiver operating characteristic (ROC) curve in 10 healthy dogs, 8 dogs with pituitary-dependent hypercortisolism, 8 dogs with adrenal-dependent hypercortisolism, and 7 dogs with pheochromocytoma. The pheochromocytoma diagnosis was confirmed by histology and immunohistochemistry in all tumors. The VMA:C ratio was significantly higher in dogs with pheochromocytoma (158 [53.4 to 230.8] × 10−3) than in dogs with adrenal-dependent hypercortisolism (48.1 [24.3 to 144.9] × 10−3; P < 0.05), dogs with pituitary-dependent hypercortisolism (37.5 [32 to 47.1] × 10−3; P < 0.001), and healthy dogs (33.8 [13.3 to 87.9] × 10−3; P < 0.001). When using a VMA:C ratio >58.2 × 10−3 for pheochromocytoma diagnosis, a sensitivity of 85.7% and a specificity of 88.4% were obtained. Nevertheless, when using a cut-off ratio of 4 times the median VMA:C ratio determined in healthy dogs, there was no overlap (100% specificity). The area under the ROC curve indicated that the VMA:C ratio test could be used to discriminate between dogs with and without pheochromocytoma, what leads to the conclusion that it is useful for pheochromocytoma diagnosis in dogs.

Introduction

Pheochromocytoma (PCC) is a catecholamine-producing neuroendocrine tumor originated in the chromaffin cells of the adrenal medulla [1]. Its excessive production of catecholamines, such as epinephrine or norepinephrine, is, in general, released episodically, causing unspecific but potentially fatal clinical signs [2]. Unfortunately, complete blood count, routine serum biochemistry, urinalysis, and imaging studies (eg, magnetic resonance imaging [MRI], computed tomography, and ultrasound) do not provide specific data in diagnosing this entity [[3], [4], [5], [6]]. Currently, plasma and urinary catecholamines (norepinephrine and epinephrine) and metanephrines (normetanephrine—norepinephrine metabolite—and metanephrine—epinephrine metabolite) are used in PCC diagnosis in dogs [[6], [7], [8], [9]]. Of these tests, the urinary normetanephrine to creatinine ratio has shown superiority in differentiating between PCC, hypercortisolism (HC), and nonadrenal disease [6]. However, because of the limited availability of these biochemical tests, it is not possible to reach a PCC diagnosis in dogs. The cortisol-secreting adrenal tumor (AT) (adrenal-dependent HC, A-HC) is the most frequently diagnosed AT in adult dogs [5]. Its clinical signs (polydipsia-polyuria, weakness, tachypnea, panting, hypertension) often overlap with those described in dogs with PCC, making these 2 neoplasms clinically difficult to differentiate [4,6,9]. In addition, the association between pituitary-dependent HC (P-HC) and PCC, or, what is even more exceptional, the association between P-HC, PCC, and AT, has also been described, which may lead to more confusion when interpreting imaging studies, if there is no diagnostic biochemical test for each of these entities [5]. Adrenalectomy is the most indicated treatment for both PCC and cortisol-secreting AT [1], but omission of PCC diagnosis and presurgery treatment (phenoxybenzamide) can lead to serious complications (eg, hypertensive crisis, cardiac arrhythmias, pulmonary edema, and cardiac ischemia) or even to intraoperative or postoperative death [1,10].

In addition to the urinary and plasma biochemical tests used in dogs, a high value of urinary vanillylmandelic acid (VMA) (3-methoxy-4-hydroxymandelic acid) is used in humans as part of the diagnostic profile of catecholamine-secreting neuroendocrine tumors, such as PCC, paraganglioma, and neuroblastoma [[11], [12], [13]]. The end product of catecholamine metabolism is VMA; it is produced, almost exclusively, in the liver, from catecholamines, metanephrines, and dihydroxyphenylglycol extracted from the circulation, and excreted in urine [2]. In humans, VMA has a sensitivity of 64% to 84% and a specificity of 86% to 99% in the PCC diagnosis [12,14], whereas in veterinary medicine, this test has not been used so far. This study aims to determine the VMA:C ratio in dogs with PCC, dogs with A-HC, dogs with P-HC, and in healthy dogs by HPLC. Moreover, it also has the purpose of determining the sensitivity and specificity of the VMA:C ratio as a diagnostic test for canine PCC.

Section snippets

Dogs

Dogs with P-HC and AT were prospectively recruited between January 2017 and January 2019, in the Endocrinology Unit of the Hospital-School of Veterinary Medicine of the University of Buenos Aires. Healthy dogs were recruited by the staff at our institution. The healthy dogs were considered as such based on the lack of both clinical signs of any disease and unremarkable findings after physical examination. Likewise, complete blood count, biochemistry, and urinalysis results were within reference

Dogs

Twenty-nine dogs with unilateral or bilateral ATs were prospectively recruited during the study period. However, only 15 of these dogs were included because of the absence of adrenal tissue for histological evaluation or available hormonal tests in the remaining dogs.

In accordance with clinical signs, hormonal tests (Table 1), such dogs were divided into a group of dogs with A-HC (8) and another group of dogs with suspected PCC (7). In addition, 10 healthy dogs and 8 dogs with P-HC were also

Discussion

The present study demonstrates that the VMA:C ratio can help differentiate PCCs from ATs in dogs. The VMA:C sensitivity (85.7%) was lower than the specificity (88.4%), similar to those reported in humans with PCCs (64% to 84% and 86% to 99%, respectively) [12,14]. With the cut-off value found in the ROC curve, 1 PCC (case 2) was false-negative, which expressed a test sensitivity of 85.7%. In humans, VMA had low (64%) to moderated (84%) sensitivity compared with urinary or plasmatic

CRediT authorship contribution statement

E.A.S. Arias: Conceptualization, Methodology, Acquisition of data, Analysis and interpretation of data, Writing - original draft, Writing - review & editing. R.H. Trigo: NA. D.D. Miceli: Writing - original draft, Writing - review & editing, Acquisition of data. P.N. Vidal: Acquisition of data, Writing - review & editing. M.F.H. Blanco: Acquisition of data, Writing - review & editing. V.A. Castillo: Acquisition of data, Analysis and interpretation of data, Writing - original draft, Writing -

Acknowledgments

The authors thank the veterinarians Graciela Esposto, Daniel Raggio, Marcelo Harris, Roberto Streuli (case contribution), and Fabiana Rey (Rapela Laboratory, veterinary division). To authors thank dog owners and Claudia Piedrafita for their constant collaboration. This work was supported by the University of Buenos Aires, UBACyT 2018–2021 (20720170100006BA). The authors declare that they have no potential conflicts of interest.

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