Primary Hyperparathyroidism Associated With Atypical Headshaking Behavior in a Warmblood Gelding

Area of Science:

• Veterinary Internal Medicine
• Equine Endocrinology
• Comparative Pathology

Background:

• Hypercalcemia is an uncommon finding in horses and requires thorough investigation.
• Differential diagnoses for hypercalcemia include renal failure, malignancy, and nutritional imbalances.

Observation:

• A 14-year-old horse presented with lethargy, headshaking, and a history of lameness, back problems, and colic.
• Persistent hypercalcemia, hypophosphatemia, and mild hypermagnesemia were detected over 1.5 years.
• Parathyroid hormone (PTH) levels were within the reference interval, ruling out nutritional secondary hyperparathyroidism.

Findings:

• Despite normal PTH, the diagnosis of primary hyperparathyroidism was established based on persistent hypercalcemia, hypophosphatemia, and altered fractional excretions of calcium and phosphorus.
• PTH secretion was found to be refractory to high calcium levels, further supporting primary hyperparathyroidism.
• Other potential causes of hypercalcemia, including renal failure, vitamin D toxicosis, granulomatous disease, and neoplasia, were excluded.

Implications:

• This case highlights primary hyperparathyroidism as a rare but critical differential diagnosis in horses with persistent hypercalcemia.
• The condition carried a poor prognosis, leading to euthanasia, underscoring the importance of early and accurate diagnosis.
• Further research into equine endocrinopathies like primary hyperparathyroidism is warranted for improved diagnostic and therapeutic strategies.