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Is Your Older Cat Losing Weight? Hyperthyroidism Explained

Mar 21, 2024 | Cats, Pet Health

Karyn Falconer, Veterinarian, Anexa Vets Raglan

Is your cat looking a bit rough? Are they always hungry but still losing weight? Has it become more vocal lately, demanding food? Are they not quite themselves? Some may just write this off as expected behaviour from an older cat, but these symptoms could actually be indicating a very treatable disease.


What is hyperthyroidism in cats?

Hyperthyroidism is a condition caused by a hormone imbalance in cats. It occurs when the thyroid gland in the neck produces too much thyroid hormone, which has affects all over the body by causing an increased metabolic rate. It is typically a condition of older cats, with the average age at diagnosis being around 13 years.

Old sad senior calico cat lying down on wooden deck terrace patio in outdoor garden of house on floor with eyes closed


What are the symptoms of hyperthyroidism in cats?

The most common signs of hyperthyroidism include weight loss despite a normal and often increased appetite. It can cause energy levels to be elevated, coat to be rough and unkempt, and drinking and urinating to be increased. As the disease progresses, cats often lose a considerable amount of condition and muscle mass, and their appetite can be reduced. Occasional vomiting can also be seen.

Untreated hyperthyroidism can lead to other secondary problems including heart disease and hypertension. Persistently high blood pressure leads to an increased risk of life-threatening blood clots and blindness, as well as putting extra strain on body organs including the heart and kidneys. This is important as chronic kidney disease is another common condition affecting geriatric cats. Early diagnosis and treatment can help prevent development of these serious complications.

Veterinary nurse feeding a cat at veterinary clinic .


How is hyperthyroidism diagnosed?

Your veterinarian may suspect this condition based on history as well as findings on clinical exam. Affected cats often have a rapid heart rate, with or without a murmur. They tend to be agitated and stressed in the exam room. Many cases will have a palpably enlarged thyroid gland, felt by feeling between muscles in the neck. If we suspect disease, we will recommend blood and urine tests, as well as a blood pressure measurement. All these tests can be performed in clinic and are recommended for all geriatric cats as part of a thorough wellness examination.


What is the treatment for hyperthyroidism?

There are a few different treatment options for hyperthyroidism. Initial treatment often includes medication to suppress production of thyroid hormone, either in tablet form or as a special transdermal gel applied to the surface of the ear. Most cats tolerate medication well, and thyroid hormone can be quickly reduced to normal levels. They do require regular monitoring, and when starting treatment, monthly blood tests will be required until the correct dosage is found. If the decision is made to stay on medication, then treatment will be life-long as thyroid hormone will rapidly elevate again if medication is discontinued.

Cat getting transdermal ear medication administered by owner. Woman with finger cot rubbing ointment in cat ear. Super senior tabby cat with hyperthyroidism. 18 years old, female cat. Selective focus.

Radioactive iodine is a more permanent treatment option available. This will require the cat staying at a referral clinic where it will be given a subcutaneous injection of radioactive iodine (I-131). This is a safe and effective treatment, but the cat will need to be kept in isolation at the referral clinic for one to two weeks, as they will excrete low levels of radiation following treatment. I-131 treatment is relatively noninvasive and has huge benefits of being a single treatment and cure for the condition, with thyroid levels normalizing within 3 months in 95% of cases.

Other treatment options less commonly used include surgical thyroid removal, and dietary restriction with a special prescription diet. The pros and cons of all the different treatment options can be discussed with your veterinarian upon diagnosis of the condition.

Hyperthyroidism of cats is a common but treatable disease. If you think you cat might be showing some of the above signs, we recommend bringing them in for a full check-up, as diagnosing illness early can increase the longevity and quality of life of your precious pet.


Other resources you may find helpful:

A cats battle with hyperthyroidism

Do you have an older cat that seems to be eating a lot and not gaining weight?


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