The use of chemical ablation to treat a parathyroid problem in a 15-year-old miniature horse was described in a recently published case report.
Clinicians from the New Bolton Center, part of the University of Pennsylvania, entered the mare’s skin to perform ultrasound-guided ethanol ablation of the mare’s parathyroid mass.
The method, not previously described in horses, was performed under general anesthesia.
This resulted in a rapid return to normal of the mare’s plasma concentrations of ionized calcium and parathyroid hormone.
Sarah Colmer and her colleagues, writing in the Journal of Veterinary Internal Medicinesaid the 102kg, 15-year-old miniature was referred for evaluation after six months of weight loss.
An on-farm evaluation one month prior to hospital admission identified multiple abnormalities in his serum biochemical profile.
The mare had a history of pituitary gland intermediate dysfunction (PPID), or equine Cushing’s disease, and was being treated with a daily dose of pergolide. The mare also had a previous episode of mild laminitis.
Ultrasound imaging of the thyroid region identified an enlarged mass on the right side suggesting an enlarged parathyroid gland. It was confirmed by sestamibi nuclear scintigraphy and CT imaging.
For the treatment, the horse was anesthetized and placed on its left side. Approximately 1.4 milliliters of sterile 100% ethanol was injected into the mass using a 2.5-inch 25-gauge spinal needle under ultrasound guidance.
Only 35 minutes after ablation, serum parathyroid hormone levels had fallen to normal and plasma ionized calcium concentration had decreased.
About three hours after the procedure, a further decrease in plasma concentrations of ionized calcium occurred. They were at normal levels 21 hours after the operation.
No clinical abnormality was identified overnight. No obvious warmth or swelling was observed in the area where the injection was performed.
Ultrasound imaging 72 hours after the procedure was consistent with successful removal of the mass.
The mare was released and six months later was doing well, with a more comfortable gait and ionized plasma and total calcium concentrations within normal limits.
Mild increases in serum parathyroid hormone concentrations were observed eight to 15 months after the procedure, but repeated ethanol ablation was not continued.
The elevated levels may have been caused by the presence of additional active ectopic parathyroid tissue that was not identified by imaging, or by the incomplete success of the ablation procedure, they said.
However, 30 months postoperatively, serum parathyroid hormone and calcium levels were normal. The mare was examined and found to be comfortable with no abnormalities on physical examination.
Discussing the case, the case report team said that primary hyperparathyroidism is considered rare in horses and can be suspected with a combination of weight loss, facial swelling, lack of appetite and changing lameness.
Achieving a decrease in circulating serum parathyroid hormone concentration is imperative in treatment.
Removal of the parathyroid glands – parathyroidectomy – is considered the only curative procedure in humans and is recommended for symptomatic patients. The procedure has been described in the horse, with one case study involving the removal of a mass resulting in an immediate 95% decrease in serum parathyroid hormone concentrations.
Alternatives to surgery to remove the parathyroid glands include ultrasound-guided heat ablation and alcohol ablation, both of which have been successful in dogs.
The advantages of ablation include lower cost, less invasiveness, and less anesthesia time compared to parathyroidectomy.
The authors described their removal as successful, with no adverse effects observed.
A case series or prospective controlled study may provide confirmation of its efficacy in other equines with primary hyperparathyroidism, as well as discrete mass identification.
The New Bolton case report team included Colmer, Kathryn Wulster, Amy Johnson, David Levine, Claire Underwood, Trevor Watkins and Andrew Van Eps.
Colmer, SF, Wulster, K, Johnson, AL, et al. Treatment of primary hyperparathyroidism in a miniature horse by chemical ablation of abnormal parathyroid tissue localized by three-phase computed tomography. J Vet Intern Med. 2022; 36(2): 798-804. doi:10.1111/jvim.16390