Radioiodine therapy with individualized dose protocol in a feline patient with hyperthyroidism

Abstract

Hyperthyroidism is the most prevalent endocrinopathy in felines, especially in elderly cats. It consists of a multisystemic condition resulting from increased production of T3 and T4 by the thyroid gland. The etiology of the disease is due, in most cases, to adenomatous hyperplasia or glandular adenoma that leads to increased hormone production. The pathogenesis and risk factors of the disease are not yet well defined. Factors such as the consumption of endocrine disruptors have already been associated with the disease. The most common clinical manifestations are polyphagia associated with weight loss, vomiting and diarrhea, polyuria, polydipsia, hyperactivity and palpable nodules in the thyroid’s topography. Diagnosis is made based on anamnesis, clinical signs, results of laboratory and imaging tests, and measurement of thyroid and pituitary hormones. There are several therapeutic protocols such as the use of oral drugs, surgery, iodine-restricted diets and radioiodine therapy. This report aimed to describe the case of a feline, female, mixed breed, 11 years old, with a history of slight weight loss and sporadic episodes of emesis. Based on history and anamnesis, physical evaluation and findings from laboratory and imaging tests, including thyroid scintigraphy, the diagnosis of hyperthyroidism was made. The treatment carried out was the application of radioactive iodine with an individual dose based on the protocol proposed by Peterson and Rishniw (2021). Three months after the procedure, the values found for the hormonal tests (total T4 and TSH) were within the reference range and, currently, the patient is in a state of euthyroidism.