Primary hyperparathyroidism with osteodystrophia fibrosa of the facial bones in a pony.

This study examines a case of a 17-year-old pony mare with progressive enlargement of facial bones, ultimately diagnosed with primary hyperparathyroidism, an uncommon disease in ponies. Despite diagnosing the condition, no physical lesion of the parathyroid gland could be identified, highlighting the intrinsic challenges in diagnosing and treating parathyroid conditions in horses.

Introduction to the Case

• The research focuses on a case involving a 17-year-old pony mare which was experiencing a progressive enlargement of its facial bones over nine months.
• This unusual presentation, alongside symptoms such as hypercalcemia (high level of calcium in the blood), hypophosphatemia (low phosphate levels in the blood), and high urinary fractional excretion of phosphorus, indicated that the pony was suffering from a severe health condition.

Diagnosis Process

• Subsequent lab tests revealed a high serum concentration of intact parathyroid hormone (185.1 pmol/L, compared to the reference range of 0.25 to 2.0 pmol/L).
• Given these findings, the veterinary team diagnosed the pony with primary hyperparathyroidism by eliminating other possibilities such as nutritional secondary hyperparathyroidism, chronic renal disease, and pseudohyperparathyroidism which could result from neoplasia (abnormal tissue growth).

Attempted Treatment and Outcome

• Usually, primary hyperparathyroidism is best treated by surgically removing the affected parathyroid gland. In this case, however, the pony’s owners declined surgical exploration of the neck for their animal.
• Given the severity of the illness and the lack of viable treatment options, the pony had to be euthanized due to its poor prognosis.

Postmortem Examination

• A follow-up autopsy and histologic analysis did not locate a functional lesion of the parathyroid tissue, even though the test results had strongly suggested a parathyroid issue.
• This discrepancy underlines the inherent challenges in identifying parathyroid tissue anomalies in horses and in creating a definitive diagnosis of primary hyperparathyroidism in these animals.