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.

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

BACKGROUND

Primary hyperparathyroidism is uncommon in equids.

OBJECTIVES

To describe the diagnostic findings and efficacy of treatment in equids with primary hyperparathyroidism.

STUDY DESIGN

Retrospective case series describing 16 horses and one mule.

METHODS

Cases were identified by retrospective review of records at Cornell University and via an ACVIM listserv query. Inclusion criteria were an equid with hypercalcemia, normal renal function and high parathyroid hormone (PTH) or histopathological diagnosis of a parathyroid adenoma. Equids with normal PTH and PTH-related protein (PTHrP) in the face of hypercalcemia were included as suspect cases.

RESULTS

The most common presenting complaints were weight loss (12/17) and hypercalcemia (10/17). PTH was above reference range in 12/17 cases. Suspected parathyroid tumours were localised in 12/14 equids imaged using ultrasonography alone (2/3), technetium 99m Tc sestamibi scintigraphy alone (1/1) or both modalities (9/10). Three horses did not have imaging performed. Surgical exploration successfully excised tumours in six of 10 cases. Five were located at the thoracic inlet, and surgery resulted in complete cure. One tumour was excised from the thyroid lobe, and the horse remained hypercalcemic. Four other cases explored surgically, four treated medically and three that were not treated also remained hypercalcemic.

MAIN LIMITATIONS

The small study size prohibited statistical analysis.

CONCLUSIONS

Parathyroid adenomas in equids can be successfully localised with ultrasonography and scintigraphy. Surgical excision appears more likely to be successful for single gland disease at the thoracic inlet.