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

Abstract

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.

Successful removal of a functional parathyroid adenoma using a radio‐guided parathyroidectomy technique with a hand‐held gamma detector and technetium Tc 99m sestamibi scintigraphy in a horse

“…Percutaneous ultrasound‐guided ethanol ablation has been described in humans, dogs and horses; however, it is regarded as a second‐choice treatment with limited advantages over surgery. Current recommendations for ethanol ablation are for use in cases with a solitary parathyroid tumour with major contraindications for surgical treatment, as there are increased risk of morbidities including recurrent laryngeal nerve damage secondary to extravasation of ethanol and difficulty of subsequent surgical dissection due to development of peritumoural fibrosis (Colmer et al, 2022; Gear et al, 2005; Karstrup et al, 1990). Surgical management is the only curative treatment; however, there are many factors which may contribute to surgical failure including the presence of multi‐gland disease, misidentification of abnormal tissue on ultrasonography or scintigraphy, and misidentification of adenomatous tissue at surgery (Goldstein et al, 2003; Gorenberg et al, 2020; Jangjoo et al, 2017; Norman & Chheda, 1997).…”

“…Percutaneous ultrasound-guided ethanol ablation has been described in humans, dogs and horses; however, it is regarded as a second-choice treatment with limited advantages over surgery. Current recommendations for ethanol ablation are for use in cases with a solitary parathyroid tumour with major contraindications for surgical treatment, as there are increased risk of morbidities including recurrent laryngeal nerve damage secondary to extravasation of ethanol and difficulty of subsequent surgical dissection due to development of peritumoural fibrosis (Colmer et al, 2022;Gear et al, 2005;Karstrup et al, 1990). Surgical management is the only curative treatment;…”

“…While there are currently no published case reports of contrast‐enhanced CT in equids, it has been performed at this institution on a Miniature Horse with PHPT. Three‐phase CT was used successfully to confirm the localisation of aberrant parathyroid gland tissue adjacent to the left thyroid lobe following ultrasonography and sestamibi nuclear scintigraphy (Colmer et al, 2022). With the exception of standing robotic and large gantry CT systems, CT and MRI have diagnostic limitations in large animals.…”

Primary hyperparathyroidism in horses: What can we learn from human medicine?

“…Although the sensitivity of Tc-99 m sestimibi nuclear medicine scans for detecting parathyroid adenomas in horses is unknown, it has been reported to be approximately 90% in humans (Hillyar et al, 2022) and 17% in dogs (Matwichuk et al, 2000). In addition to the report in this issue (Connard et al, 2023), Tc-99 m sestimibi scintigraphic scanning has been reported to be effective in 13 of 16 (81%) previously published cases (Colmer et al, 2022;Cottle et al, 2016;Gorenberg et al, 2020;Tomlinson et al, 2014;Wong et al, 2004). Three quarters of human patients are asymptomatic and do not exhibit symptoms that are explained by PHPT, the clinical course of which has been described as being rather benign (Miedlich et al, 2002).…”

“…Unless an abnormal hyperfunctioning parathyroid gland can be identified and its location defined, surgical removal (parathyroidectomy) or chemical ablation with ethanol may not be possible (Colmer et al, 2022). Whereas surgical treatment (parathyroidectomy) is recommended and curative for patients with both clinical disease and asymptomatic disease in the absence of comorbidities, medical treatment can be employed.…”