Hyperthyroidism is a common - but very serious - condition that usually occurs in older cats. PDSA vet Emma Fisher explains all you need to know
What is hyperthyroidism in cats?
Cats have two thyroid glands in their neck that control metabolism. Hyperthyroidism is when one or both of the thyroid glands become enlarged and overactive, giving rise to too much thyroid hormone in the body.
What causes hyperthyroidism in cats?
The majority of cases are caused by benign swellings, but some rare cases are caused by cancer.
Hyperthyroidism causes a high metabolism, which has many negative effects on the body. Weight loss, a high heart rate and high blood pressure are just a few of the common problems encountered in hyperthyroid cats.
What are the symptoms of hyperthyroidism?
Symptoms appear slowly, so you may not notice a problem at first but left untreated over a long period, hyperthyroidism can be fatal.
Symptoms of hyperthyroidism include:
- An increased appetite
- Weight loss, despite eating more
- Hyperactivity, noisy and demanding behaviour
- Drinking and peeing more
- Sickness and diarrhoea
- A dry, untidy coat
- Low energy (lethargy)
- One or two small lumps/swellings in the neck under the skin
- A very fast heartbeat (you may feel this when your cat is sat on you)
- Hair loss (alopecia)
Hyperthyroidism is most common in middle aged to older cats. Your vet may suspect hyperthyroidism based on your cat’s symptoms and clinical exam, and usually it is confirmed with a blood test which measures the level of circulating thyroid hormone.
How is hyperthyroidism in cats treated?
Many treatment options are available and well managed hyperthyroid cats can live for many years. Some of the ways to treat hyperthyroidism include:
- Daily or twice daily medication to slow the overactive thyroid gland(s) - this treatment is lifelong.
- Surgery to remove the gland(s) - cats are first stabilised with medication for about a month prior to surgery. There is a risk your cat may develop low calcium levels (hypocalcaemia) after surgery and require short-term or long-term medication.
The risk is higher if both thyroid glands are removed (though the risk can be reduced by staging the surgeries i.e. removing one gland during one procedure, and the other gland three to four weeks later). It is a good option for owners who would prefer not to have to give medication to their cats every day.
- Radioactive iodine injection – a one-off injection offered by some specialist practices. It is expensive and cats are required to stay hospitalised for about 1-2 weeks after the injection, however it is very effective and a good option for owners who would rather avoid surgery for their cats or for the rare cases caused by cancer.
- Prescription food – feeding a specialised diet can help to control the disease and its symptoms. In order for the diet to be effective cats must only be fed this food (no treats!) which can be difficult if they go outdoors.
The majority of hyperthyroid cats can be treated successfully. However, it’s important to remember hyperthyroidism is sometimes caused by thyroid cancer. It’s very rare, but if your cat is unlucky enough to have one of these rare thyroid cancers their condition may not improve.
Sometimes, treating hyperthyroidism uncovers hidden kidney disease. You may not see any signs of kidney disease in a cat with hyperthyroidism and sometimes by treating the hyperthyroidism we can unmask the kidney disease. This is because overactive thyroid glands cause increased blood flow to the kidneys, which supports them.
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However, treating hyperthyroidism in cats with kidney disease is still essential. This is because if left untreated, hyperthyroidism causes a lot of harm to many body systems, including the kidneys. Your vet may start your cat on thyroid medication (instead of surgery or radioactive iodine) if they also have kidney disease, as the dosage is adjustable and the effects are reversible, thereby making it easier to see the effect of treating the hyperthyroidism on your cat’s kidneys.
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