Diagnosis and treatment of confirmed and suspected primary hyperparathyroidism in equids: 17 cases (1999-2016)

Paraneoplastic Syndromes in Horses

This article discusses the reported paraneoplastic syndromes (PNSs) in horses, including the possible pathogenesis, diagnostic methods, and any treatment options. The more commonly reported PNSs in horses include cancer anorexia and cachexia, fever and increased acute phase protein concentrations, and hypercalcemia and monoclonal gammopathy. As these conditions can often be more commonly diagnosed in non-neoplastic conditions, the diagnosis of a PNS and the accompanying neoplasia can be challenging. As signs of a PNS may precede signs of the underlying neoplasia, it is important that the clinician be aware of the possible presence of a PNS.

SERUM VITAMIN D AND SELECTED BIOMARKERS OF CALCIUM HOMEOSTASIS IN ASIAN ELEPHANTS (ELEPHAS MAXIMUS) MANAGED AT A LOW LATITUDE

An understanding of species-specific vitamin D metabolism and its role in calcium homeostasis is essential for correct diet formulation and development of husbandry protocols for managed nondomestic species. This study documented serum vitamin D metabolites and other analytes involved in calcium homeostasis in Asian elephants (Elephas maximus) managed at a latitude similar to their wild natural habitat. Serum values for 33 elephants managed at a low latitude were measured in the peak of summer, revealing low vitamin D2 (25(OH)D2 2.3 ± 0.6 ng/ ml and 24,25(OH)2D2 2.17 ± 0.52 ng/ml) and nondetectable vitamin D3. Serum minerals (calcium, phosphorus, magnesium), ionized calcium, and parathyroid hormone were within normal reported ranges. In comparison with previously reported values in elephants managed at a high latitude, 25(OH)D2 (P < 0.001), 24,25(OH)2D2 (P = 0.001), and magnesium (P = 0.013) were significantly lower, and parathyroid hormone was significantly higher (P < 0.001). The lack of D3 production during ample sun exposure at a low latitude suggests that Asian elephants are incapable of cutaneous photobiosynthesis of vitamin D, and that low serum D2 is normal for this species.

Treatment of primary hyperparathyroidism in a Miniature Horse using chemical ablation of abnormal parathyroid tissue localized by 3-phase computed tomography

A 15‐year‐old Miniature Horse mare with persistently increased plasma calcium (total and ionized) and serum parathyroid hormone concentrations was presented for suspected primary hyperparathyroidism. Ultrasonography of the thyroid region identified an enlarged heterogeneous mass axial to the right thyroid lobe suggestive of an enlarged parathyroid gland, which was further confirmed using sestamibi nuclear scintigraphy and 3‐phase computed tomography. Percutaneous ultrasound‐guided ethanol ablation of the mass, a method not previously described in the horse, was performed under general anesthesia resulting in rapid normalization of plasma ionized calcium and serum parathyroid hormone concentrations. Ablation of abnormal parathyroid gland tissue may be a suitable alternative to surgical resection in certain cases of primary hyperparathyroidism in the horse.

Primary Hyperparathyroidism in a Quarter Horse Mare Associated With a Chief Cell Adenoma

Primary hyperparathyroidism is rare in large animal species, and little is known regarding its pathophysiology, endocrine and electrolyte derangements, diagnosis, medical management, and prognosis. This report describes the clinicopathologic diagnosis of a parathyroid (PT) gland chief cell adenoma in a 12-year-old Quarter Horse mare, including PT hormone (PTH) and electrolyte disarrangements associated with the neoplasia, the surgical removal of the adenoma, and medical management of the case. This report also describes for the first time the use PTH immunohistochemistry to confirm the nature of this neoplasia in a horse.

Primary Hyperparathyroidism Associated With Atypical Headshaking Behavior in a Warmblood Gelding

A 14-year-old Zweibrücker Warmblood gelding was presented for evaluation of lethargy and headshaking. The horse had a history of bouts of lameness in different limbs and back problems. It also had many mild colic episodes in the past. Results of repeat laboratory tests had shown persistent hypercalcemia (4.8 mmol/L; reference interval [RI]: 2.0-3.2 mmol/L) for 1.5 years and later on hypophosphatemia (0.4 mmol/L; RI: 0.5-1.3 mmol/L) and mild hypermagnesemia (1.0 mmol/L; RI: 0.5-0.9 mmol/L). Parathyroid hormone (PTH) concentration was within the RI. Other causes of hypercalcemia, such as renal failure, vitamin D toxicosis, and granulomatous disease, and nutritional secondary hyperparathyroidism were ruled out. Furthermore, there was no evidence of neoplastic disease. Parathyroid hormone-related protein was measured but inconclusive. A diagnosis of primary hyperparathyroidism was established on the basis of hypercalcemia, hypophosphatemia, low fractional excretion of calcium, and high fractional excretion of phosphorus in combination with a PTH secretion refractory to high calcium levels. Because of the bad prognosis, the owner decided to euthanize the horse. Results of postmortem examination were unremarkable. Hypercalcemia should always be considered abnormal, and further examinations need to be performed to proof hypercalcemia and subsequently find the cause. The main differential diagnoses are renal insufficiency and humoral hypercalcemia of malignancy, but also rare diseases, such as hyperparathyroidism, have to be taken into account.