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Nursing the feline hyperthyroid patient

02 April 2014
14 mins read
Volume 5 · Issue 3

Abstract

Hyperthyroidism is the most common endocrinopathy in middle aged to older cats. Dogs and cats are affected very differently by this disease. This article will focus on feline hyperthyroidism.

The disorder is characterised by excess production and circulation of active thyroid hormones in almost all cats. These hormones induce a hypermetabolic state, with clinical signs such as weight loss despite increased appetite, and muscle wasting. Other common signs include palpable thyroid gland, diarrhoea, vomiting, tachycardia, hyperthermia, restlessness, and behavioural changes.

Thyroxine (total T4 (TT4) ) is the hormone test used to diagnose feline hyperthyroidism. However, since a high metabolic rate can mask other diseases a range of diagnostic tests are necessary for a thorough assessment of the patient.

The recommended treatment approach is to first establish euthyroidism by the use of oral anti-thyroid drugs, such as methimazole. Surgery or radioiodine therapy can be considered for definitive, long-term control if renal function remains adequate following re-establishment of euthyroidism.

Hyperthyroidism is a common endocrine disorder of the cat where there is an excessive production of thyroid hormones (thyroxine (T4) and triiodothyronine (T3)), from the thyroid gland that circulate in the body resulting in clinical signs related to hyperthyroidism. Hyperthyroidism is the most common endocrinopathy in cats with a reported median age of 12-13 years at time of diagnosis (Peterson, 2012) (Table 1).

Feline hyperthyroidism is usually the result of a functional adenomatous hyperplasia of thyroid tissue involving in approximately 70% of hyperthyroid cats both thyroid lobes (Lucke, 1964; Leav et al, 1976; Wakeling et al, 2005).

Functional adenomatous hyperplasia is present in approximately 95% of the cases (Peterson, 1981; Peterson, 2007; Mooney and Peterson, 2012; Baral and Peterson, 2012). By contrast thyroid carcinoma is affecting less than 5% of the feline hyperthyroid population (Turrel et al, 1988; Hibbert et al, 2009; Peterson, 2011a; Peterson and Broome, 2012). Biopsies obtained from thyroid lobes of hyperthyroid cats, have revealed the presence of mixed adenomatous and carcinoma tissues (Hibbert et al, 2009).

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