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I wrote last week that Thomas has kidney disease and hyperthyroidism. This week I’m going to talk about the hyperthyroidism part of the equation. It’s one of the more common diseases seen in senior cats, and the risk of developing hyperthyroidism increases with age.

What causes hyperthyroidism?

Nobody knows for sure if there’s any one thing that can be blamed for the disease, although some research has shown a possible connection between certain canned foods and hyperthyroidism.

What are the symptoms?

Hyperthyroid cats typically eat and drink a lot but they still lose weight. They may be anxious, which can result in increased vocalization, especially at night. Thomas certainly does his share of vocalizing at night, even though his disease is well-controlled. Cats may also experience nausea and vomiting, and their fur coat starts looking greasy and unkempt. A tiny minority of cats will experience atypical symptoms like lethargy.

How is hyperthyroidism treated?

There are several methods of treatment for the disease: I-131 therapy, medication, surgery to remove the thyroid glands, and dietary treatment.

Dietary treatment involves feeding a prescription food formulated with a low iodine level, since the thyroid glands need iodine to do their job. I don’t know how this treatment plan works in the long run, but I know plenty of cats who utterly refuse to eat any kind of prescription food. I have issues with prescription foods in general, so this is not a treatment I would undertake even if I could do so in my home. (I have a diabetic cat in remission, so no kibble is allowed in my house. I’ll write a post on feline diabetes sometime in the future.)

Surgery to remove the thyroid glands will result in a cat that becomes hypothyroid–that is, the hormones excreted by the thyroid gland aren’t there anymore–if both glands are removed. The cat will be on medication to treat that condition after the surgery is completed. Because medication and I-131 therapy are so much less invasive, surgery is rarely done these days.

I-131, or radioactive iodine, therapy is considered the gold standard of treatment, because it cures the disease without destroying the normal tissue in the thyroid glands. It involves a hospital stay that can extend up to a week, depending on when your cat’s radiation level goes down to a safe level, and then some “safe handling techniques,” so to speak, for several weeks after the treatment is done. I-131 therapy is very expensive, but it is curative.

Medication is the most common treatment for hyperthyroidism. A medicine called methimazole (brand name Felimazole or Tapazole) helps to calm the thyroid glands down and reduces the amount of thyroid hormones circulating in the blood. Medication can be administered as a pill or as an ointment that is rubbed on the inside of the ear flaps. Oftentimes, a hyperthyroid cat will be started on medication and his blood work will be monitored to ensure that the treatment is doing its job.

Another reason for monitoring hyperthyroid cats’ blood work is because hyperthyroidism and kidney disease have a relationship that can’t be ignored.

The relationship between hyperthyroidism and kidney disease

Because hyperthyroidism improves the blood flow to the kidneys, it can “mask” kidney disease. That is, it helps a cat compensate for kidney disease and artificially lowers creatinine and BUN. One of the reasons cats with hyperthyroidism are monitored before proceeding with I-131 therapy is so the vet can determine whether or not your cat has kidney disease as well.

If your cat does have kidney disease and hyperthyroidism at the same time, treatment for the hyperthyroidism can reveal new or more severe kidney disease. For example, Thomas has been on methimazole for about three months, and prior to that, his creatinine hovered around 3.4, Now that his hyperthyroidism is being well managed, his creatinine went up as the hyperactive thyroid glands were no longer increasing that blood flow to the kidneys.

A delicate dance

Treating both conditions is a delicate dance that requires a close partnership between you and your vet. Although Thomas’s thyroid values are still a little high, we don’t want to overtreat his thyroid and cause his kidney function to crash. Thomas is going back to the vet in three months for an exam and more blood work so we can see how his kidney disease is progressing or staying stable as we treat his hyperthyroidism.

I’m a really lucky cat mom, because Thomas is really good about taking his pill every day. I give it to him in a Pill Pocket (his favorite flavor is chicken), and he eats it right up. I decided not to do the ointment because my cats like to groom one another, and I didn’t want the other cats suffering from thyroid gland damage if they licked it off his ears.

I’m also lucky that Thomas is still pretty healthy, all things considered. His fur coat looks good, he’s bright-eyed and content, and he loves his food–even though he eats it more slowly than he used to because he’s had 14 teeth extracted, most of those being molars and premolars.

The last word

It’s very rare for cats to die from hyperthyroidism, as long as the condition is treated. If left untreated, a cat could more or less starve to death because the thyroid glands are running so hot that no matter how much he eats, he’ll continue to lose weight.

It’s also not “just part of getting old” for a cat to get really skinny. If your cat is losing weight in spite of eating a lot, drinking and peeing a lot, and meowing late at night, take him to the vet for a checkup and blood work. A lot of endocrine disorders like hyperthyroidism and diabetes have very similar symptoms. Both those conditions can be successfully managed with help from your veterinarian.

Do you have a cat with hyperthyroidism? How are you managing it? Please sound off in the comments.