Radioiodine treatment for hyperthyroid cats: frequently asked questions from vets and clients
Abstract
Feline hyperthyroidism is the most common endocrinopathy affecting senior and geriatric cats. Radioactive iodine treatment is widely considered the gold-standard treatment because of its curative effect, associated high success rates, the lack of requirement for anaesthesia, preservation of parathyroid tissue and the ability to treat ectopic tissue and thyroid carcinoma. Until recently, access to radioactive iodine in the UK was limited to a few centres; however, more clinics are starting to offer the treatment, increasing the potential number of cats that can receive radioactive iodine. This review will cover topics including the pros and cons of treatment, the mechanism of radioactive iodine action and management of the feline patient during and after radioactive iodine, to enable veterinary surgeons to discuss the therapy in detail with their clients.
Hyperthyroidism is the most common endocrinopathy diagnosed in senior and geriatric cats. The prevalence in English cats >10 years of age has been reported to be 8.7% (Stephens et al, 2014). Hyperthyroidism is most commonly caused by hyperplastic or adenomatous thyroid goitre development, resulting in high levels of circulating thyroid hormones (T3 and T4). Thyroid carcinomas are rare, accounting for <1–3% of all cases of hyperthyroidism (Naan et al, 2006).
Hyperthyroidism can be managed long-term with either anti-thyroid medications (methimazole or carbimazole) or dietary restriction of iodine, with the aim of controlling excessive thyroid hormone concentrations.
Alternatively, thyroidectomy or radioactive iodine (radioiodine, RAI) treatment can be used to remove the hyperfunctional thyroid tissue and source of excessive thyroid hormone production, curing the cat of hyperthyroidism.
Radioactive iodine has been used to treat hyperthyroidism for over 30 years. It is widely considered to be the gold standard treatment for feline hyperthyroidism and is becoming increasingly available across the UK, as more centres are now able to provide this option.
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