Primary hyperparathyroidism in a domestic shorthair cat following <scp>I¹³¹</scp> radioiodine therapy

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.