This week, Veterinary Surgeon Jo Whitaker continues on the subject of hyperthyroidism in cats looking at how to diagnose it and treatment available

Last week we discussed what hyperthyroidism is, its causes and symptoms.

• Hyperthyroidism is commonly a disease of middle aged/ older cats.

• The thyroid gland becomes overactive and produces too much thyroid hormone.

• Signs includes weight loss despite having a very good appetite; drinking more and sometimes it may cause vomiting and diarrhoea.

• It is linked in with other diseases such as heart and kidney disease.

Diagnosis Although the thyroid glands usually enlarge with hyperthyroidism, this is not usually visible. Detection of enlarged glands will usually require careful palpation (examination by touch) by your vet. However, in some cats there is no obvious enlargement, often because the overactive tissue is in an unusual site (such as the chest cavity). To confirm a diagnosis, a blood test is needed to measure the level of thyroid hormones in the blood. Usually, measuring the thyroxine (T4) concentration is all that is required to confirm a diagnosis, but sometimes additional tests may be needed (such as measurement of ‘free T4’ in the blood). Other laboratory tests may also be abnormal – for example liver enzymes are commonly increased with hyperthyroidism, and both blood and urine tests are usually advised to help rule out concurrent problems (such as kidney disease). Where possible, blood pressure should also be checked with hyperthyroid cats.

Complications of hyperthyroidism Uncontrolled hyperthyroidism has important consequences on the heart, causing increased heart rate and consequently thickening of the heart wall, which can result in heart failure.

Treatment Successfully treated cats, irrespective of what treatment is used, will usually have complete reversal of all the signs of hyperthyroidism. Further evaluation will usually be needed to check kidney function and ensure long-term goals of thyroid hormone concentrations are being achieved, but most cats do remarkably well when treatment is administered.

Next week we will discuss the four main options for treatment.

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