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Hyperthyroidism in Cats

You noticed that your senior cat’s fur has been looking scruffy lately. He’s been eating like crazy, but he’s still losing weight. He’s suddenly acting hyper and crying in the night, and when you go to clean the litter box, it’s flooded with urine.  A visit to the vet and a blood test reveals that he has feline hyperthyroidism. So, what do you do about hyperthyroidism in cats?

While having only been identified in the past 30 years or so, hyperthyroidism has become the most common endocrine disease diagnosed in cats.

The disease is a result of a benign growth on the thyroid glands that produces an excessive amount of thyroid hormone (or T4).  In a small percentage of cats, this growth is cancerous.

Hyperthyroidism is due to overactive thyroid glands. The thyroid hormone is responsible for the metabolic rate in the body.  Cats with hyperthyroidism tend to burn energy too rapidly and typically suffer weight loss despite having an increased food intake. No breeds are particularly affected, with many of the cats diagnosed being the common domestic short-haired mixed breed cats.

The cause of this condition is yet to be identified.  Iodine levels in the diet have been thought to play a role, cats eating diets of mostly fish based canned food, soy proteins in food and environmental factors such as being exposed to (PBDE) chemicals used to fire-protect materials and products.

The disease affects older cats, with most cats being diagnosed with the condition at around 13 years of age or over.  Due to the advanced age of the cats, the pets usually suffer other health problems as well as hyperthyroidism. The top 5 disorders that usually co-exist with hyperthyroidism are: renal failure, arthritis, hypertension (high blood pressure), inflammatory bowel disease and hepatopathy (liver disorder).

Common signs of hyperthyroidism in cats include: weight loss - despite have an excellent appetite, increased water intake, on/off vomiting & diarrhoea, behavioural changes including aggression. 

Treatment options for this condition include medical therapy, surgery or radioactive iodine therapy. Most cats are treated medically with anti-thyroid drugs which can give excellent results over the long-term.  Hyperthyroidism can be treated and is not a death sentence that the name may suggest.  We are always available to give advice on these questions.