Feline hyperthyroidism is one of the most common endocrine disorders of mature cats (middle-aged and elderly cats). The disease results from overproduction and secretion of thyroid hormones such as thyroxine and tri-iodothyronine by the multinodular adenomatous goiter (Feldman and Nelson 2004). The disorder is similar to Plummer’s disease observed in humans (Peterson 2014). Dietary and environmental factors play a role in the development of the disease. Increasing age, dominance of commercial wet food in the diet, and indoor housing are considered as the main risk factors for feline hyperthyroidism (Peterson 2014).
As the disease progresses, clinical signs such as weight loss with increased appetite (sometimes normal or decreased appetite), behavioural changes (excessive vocalization, restlessness, aggression), tachypnea (rapid breathing) or dyspnea (breathlessness), unkempt and dry hair coat, alopecia, weakness, polyuria and polydipsia, and gastrointestinal signs such as vomiting and diarrhoea may be observed by the owner of the cat (Gunn-Moore 2011; Mooney and Peterson 2004; Peterson 2013). Clinical examination may reveal enlargement of the thyroid gland, tachycardia (increased heart rate), cardiac arrhythmia, hypertension (increased blood pressure) and increased body temperature (Mooney and Peterson 2004; Peterson 2013).
Diagnosis of the disease is based on clinical history, results of clinical examination and results of laboratory measurements of thyroid hormone concentrations. It should be emphasized that owing to the early phase of hyperthyroidism, fluctuations of thyroid hormones in hyperthyroid cats, or concurrent systemic disease in affected animals, the concentration of thyroid hormones may remain within reference or non-diagnostic intervals. That’s why in some cases confirmation of the disease may require a retest of the thyroid hormone concentrations (Graves 2011; Gunn-Moore 2005; Mooney and Peterson 2004; Peterson 2013).
Hyperthyroidism in cats may be treated with: pharmacological therapy with anti-thyroid drugs, surgical thyroidectomy, nutritional therapy (iodine deficient diet), and radioactive iodine therapy (Peterson 2013).
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Peterson M.E. Animal Models of Disease: Feline hyperthyroidism: an animal model for toxic nodular goiter. Journal of Endocrinology, 2014, 223, T97-T114.
Peterson M.E. Hyperthyroidism in Cats. In: Rand J., Behrend E.N., Gunn-Moore D. and Campbell-Ward M.L. (eds.) Clinical Endocrinology of Companion Animals. Wiley-Blackwell, Ames, 2013, pp. 295-310.