Extreme Hyperthyroidism in a Cat

Your vet can help manage your kitty's extreme hyperthyroidism.
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Hyperthyroidism, excessive production of thyroid hormone, is common in aging cats. If yours has an extreme case of hyperthyroidism, she probably suffers from considerable symptoms that require careful management to keep her feeling well. If you suspect a thyroid imbalance, discuss your concerns with your vet.


Extreme hyperthyroidism in your cat produces noticeable symptoms. She'll probably start eating more but paradoxically lose weight, and she's likely to drink and urinate more. Your kitty may also vomit or have diarrhea with some frequency. Hyperactivity and increased aggression are to be expected, as is poor coat condition. Extreme hyperthyroidism affects the heart, as well, causing an accelerated heart rate and symptoms such as murmurs, arrhythmia and labored breathing.


Feline hyperthyroidism results from one or two enlarged thyroid glands; in extreme cases, both of the glands in the neck are probably overgrown. The most common cause of enlargement is a benign tumor called an adenoma. In rare instances, a malignant tumor is to blame. Thyroid enlargement -- especially extreme cases -- is prevalent in elderly cats; the average age of onset is 13 years, and 95 percent of affected cats are at least 10 years old, cites the Washington State University College of Veterinary Medicine.


See your vet promptly if you notice symptoms of hyperthyroidism in your cat. Explain your causes for concern with as much detail as possible, and give a thorough history of your cat's health. Your vet relies on this information, along with a physical examination, to decide what tests to run. In an extreme case, the enlarged thyroid glands may be palpable, but definitive diagnosis requires a blood test that measures your kitty's level of thyroid hormone. Levels will be very high with extreme feline hyperthyroidism. Further blood testing and urinalysis will check for kidney impairment and other possible complications.


Treating your kitty's extreme hyperthyroidism is essential, as the condition can turn fatal without management. There are three approaches to treatment, and extreme cases may require more than one. Your cat may have her affected thyroid glands surgically removed. This doesn't always solve the problem, though, because some cats with extreme conditions have abnormal thyroid cells elsewhere in their bodies. Methimazole, a drug that suppresses the production of thyroid hormone, is another treatment possibility; your cat will have to take it for the rest of your kitty's life. Injection of radioactive iodine, which kills overactive thyroid tissue, is the third treatment. Your kitty probably has kidney damage from her extreme hyperthyroidism, so she'll need supportive therapy for this condition, too.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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