# Primary hyperparathyroidism in a domestic shorthair cat following I131 radioiodine therapy

## TL;DR

A cat developed primary hyperparathyroidism after undergoing I131 radioiodine therapy for hyperthyroidism, a condition not previously reported in cats.

## Contribution

This is the first documented case of primary hyperparathyroidism in a cat following radioiodine therapy.

## Key findings

- The cat's hyperparathyroidism and hypercalcaemia resolved after surgical removal of the parathyroid tumor.
- Primary hyperparathyroidism in cats following radioiodine therapy has not been previously reported.
- The case highlights a potential long-term risk of radioiodine therapy in cats.

## Abstract

A 12‐year‐old male neutered domestic shorthaired cat presented for further assessment of a cervical mass, having undergone radioiodine therapy for treatment of hyperthyroidism 2 years prior to presentation. Initial cytological diagnosis of the mass was supportive of a carcinoma and laboratory results were consistent with primary hyperparathyroidism. Thoracic radiographs and magnetic resonance imaging were performed of the neck prior to surgical removal of the mass. Histopathology and immunohistochemical characteristics were supportive of a parathyroid tumour. Primary hyperparathyroidism and the associated hypercalcaemia fully resolved following surgery. In human medicine, there is awareness of an association between radioactive iodine therapy and development of primary hyperparathyroidism. Based on our literature search, this sequence of pathologies has not been reported in cats. This report documents primary hyperparathyroidism in a cat following radioiodine therapy.