Perioperative characteristics, histological diagnosis, and outcome in cats undergoing surgical treatment of primary hyperparathyroidism

Primary hyperparathyroidism in a domestic shorthair cat following I131 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.

Primary hyperparathyroidism caused by bilateral parathyroid cystic carcinoma in a cat

Case summary

A 16-year-old neutered female Korat cat presented with chronic vomiting, mild azotaemia and mild hypercalcaemia. Physical examination revealed bilateral palpable masses on each side of the trachea. Laboratory results were consistent with primary hyperparathyroidism, diagnostic imaging findings with cystic thyroid or parathyroid masses, and fine-needle aspiration cytology with thyroid hyperplasia or adenoma. In order to confirm whether one or two of the masses were the cause of the hyperparathyroidism, cystic fluid was aspirated from both for parathyroid hormone concentration measurement. The concentration was shown to exceed that of the serum manyfold in both samples, confirming both masses to be functional and of parathyroid origin. A total parathyroidectomy and thyroidectomy were performed on the right side, and a subtotal thyroidectomy and a subtotal to total parathyroidectomy on the left, without any major postoperative complications. Histopathology was consistent with bilateral parathyroid carcinoma.

Relevance and novel information

To our knowledge, this report is the first to describe a rare case of bilateral parathyroid cystic carcinoma in a cat. It highlights the usefulness of determining parathyroid hormone concentration in the cystic fluid of a suspected neoplastic parathyroid mass preoperatively. It also demonstrates that it may be possible to remove most of the cervical parathyroid and thyroid tissue of a cat without causing any clinically relevant hypocalcaemia or iatrogenic hypothyroidism. However, serum concentrations of ionised calcium, thyroxine and creatinine should be closely monitored in the postoperative period in order to detect and control possible complications.