Pseudohyperparathyroidism in a mare associated with squamous cell carcinoma of the vulva.

This research article explores the case of an 18-year-old mare with a squamous cell carcinoma of the vulva, which also showed signs of anorexia, weight loss, and hypercalcemia. The researchers concluded that the hypercalcemia was likely due to the mare’s malignancy, a scenario termed pseudohyperparathyroidism.

Case Overview

• The research article introduces an 18-year-old Appaloosa mare that showed symptoms such as pronounced weight loss, anorexia, and hypercalcemia, and was identified to have squamous cell carcinoma of the vulva.
• This tumor had rapidly developed over three months, extending to the perineum and dorsal aspect of the udder.

Post Mortem Findings

• Upon necropsy, a large primary squamous cell carcinoma was found involving the mare’s vulva, perineum, and mammary gland. Metastases were present in the supramammary, sublumbar, deep inguinal, and mediastinal lymph nodes.
• Despite the hypercalcemia, an examination of the kidneys revealed no significant issues. Only mild vacuolation of the renal tubular epithelium was noted.

Diagnosis

• With the lack of vitamin D overdose evidence, normal kidney function, and regular serum parathyroid hormone concentration, the researchers concluded that the mare’s hypercalcemia resulted from her malignancy – a condition known as pseudohyperparathyroidism.
• The mechanism leading to hypercalcemia was not definitively established in the research. Still, the cancer’s type and the clinical course suggested it might be due to a humoral hypercalcemic factor produced by the neoplasm. This phenomenon has previously been noted in particular types of human squamous cell carcinoma.