Hyperthyroidism in Senior Cats: Symptoms, Diagnosis, and Treatment Options

By: Samantha Morin, Laboratory Assistant
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  Our pet cats are living longer than ever these days, but its a rare cat (or person for that matter) who reaches their senior years without developing at least a few health problems. In older cats, one of the most common of these is hyperthyroidism – an enlargement of the thyroid glands (located in the neck below the jaw) that results in excessive production of thyroid hormones. A cat can develop hyperthyroidism at any age, but it most commonly surfaces in senior cats, with the average age of diagnosis being about 12 years old.
 

Common Signs of Hyperthyroidism in Cats

Some classic symptoms include:

• Excessive thirst and urination
• Weight loss accompanied by a ravenous appetite
• Restlessness and excessive vocalization (especially at night)
• An unkempt or greasy-looking coat
• Intermittent vomiting and diarrhea
• Swelling/tenderness of the neck just below the jaw (where the glands are located.)

Why Hyperthyroidism in Cats Matters

  While not usually life-threatening on its own, if left untreated, hyperthyroidism can lead to heart problems, high blood pressure, kidney damage, and blindness. Fortunately, its easy to diagnose on a routine senior blood panel, and the prognosis is generally quite good with the appropriate treatment.
 

Treatment Options for Feline Hyperthyroidism
 

  If your cat is diagnosed, the most common treatment is methimazole – a medication that inhibits production of those extra thyroid hormones. Though your cat will likely need to stay on this med for the rest of their life, its affordable and easy to obtain. It is also available as a pill, liquid, or even a topical gel to make administering it easier both you and your kitty. Depending on how your cat responds to the medication, your vet may require further blood testing to ensure that the dosage remains appropriate and that the medication is still working as intended.
 

  Some cats may respond well to a prescription low-iodine diet in lieu of medication, but it isn't a viable option for all cases. Its also possible for a specialist to surgically remove the affected thyroid tissue. But this method is far more invasive, and may not even be effective due to the fact that its possible for some tissue to be left behind, no matter how thorough the surgeon is.
 

  By far, the most effective method is a dose of radioactive iodine . This iodine is readily absorbed by the overactive thyroid tissue and destroys it from within, providing a permanent cure without harming any other organs. It sounds scary, but is actually much safer (and far less invasive) than surgery, and has a 98-99% success rate. Its so safe and successful that its the preferred treatment for humans with hyperthyroidism too! But, like surgery, it can be quite expensive, and also requires unique care by specialists.
 

When to Talk to Your Veterinarian
 

  If your senior cat is showing changes in appetite, weight, behavior, or litter box habits, it’s always worth having them evaluated. Hyperthyroidism is one of the most common endocrine conditions in older cats, and early detection can make a meaningful difference in long-term health and comfort.
 

  A routine senior wellness exam and bloodwork can often identify changes before symptoms become severe, helping you and your veterinary team choose the most appropriate treatment plan for your cat’s individual needs.
 

  If you have questions about hyperthyroidism, diagnosis, or treatment options, our team at Bishop Ranch Veterinary Center & Urgent Care is here to help guide you through next steps with clarity and care.