In two other blogs, we talked about the adrenal gland, and the two diseases that arise from the overproduction or underproduction of cortisol, Addison’s disease, and Cushing’s disease. Let’s bring the focus today to a different gland: the thyroid gland. As is the case with the adrenal gland, the thyroid can also produce too much or too little hormone, which has ramifications to the health of our beloved pets.


Hypothyroidism is a condition which results from the underproduction of thyroid hormone. This is largely a disease of dogs, though rarely it can occur in our feline friends.

You may know someone that has hypothyroidism, as it is a common condition in humans. It also happens to be the most common hormone imbalance in dogs, where most cases of hypothyroidism are due to immune-mediated destruction of the thyroid gland. Occasionally hypothyroidism occurs congenitally in very young dogs, but for the most part, it is a disease of middle-aged to older dogs.

Classic signs of hypothyroidism:

1. Patchy hair coat or hair loss

2. Skin infection

3. Lethargy

4. Heat seeking behavior, and

5. Weight gain

Your veterinarian can find low thyroid levels on routine blood work, but will likely need to run an additional blood test to confirm the disease. If your pet develops this condition, having comprehensive dog insurance (which not only covers treatment but also diagnostics and exam fees for ill or injured pets) can help you deal with the costs that come with additional testing.

Luckily, hypothyroidism is usually easily controlled by giving an oral thyroid supplement daily. Once your dog is diagnosed with hypothyroidism, he will need to be treated for life.

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Hyperthyroidism is, as you probably guessed, the overproduction of thyroid hormone. This is almost exclusively a disease of cats, and the average age at diagnosis is about 13 years old.

Hyperthyroidism in cats is usually caused by a benign (non-cancerous) thyroid tumor, though about three percent of cases are due to malignant tumors. The classic sign of hyperthyroidism is a cat with weight loss despite a normal to increased appetite. In fact, most owners tell me that their cat is ravenous and constantly bugging them for food!

Hyperthyroidism can be easily detected with routine blood work, but treatment is a bit trickier.

Treatment options:

Surgery: In this case, the affected thyroid gland is surgically removed. Treatment is generally permanent, but there are a few potential complications.

Medication: Oral medication can block the production of thyroid hormone, but will need to be given daily for the life of the cat. Luckily, the medication is inexpensive. Periodic blood work will need to be performed to ensure proper thyroid levels are being maintained.

Radiotherapy: In this treatment modality, an injection of a radioactive isotope of iodine 131 is injected into the bloodstream, where it travels to the thyroid to destroy the overactive tissue. Generally, this is a one-time treatment and achieves a cure.

There are advantages and disadvantages associated with each treatment option. If your cat is diagnosed with hyperthyroidism, you and your veterinarian will discuss the best treatment option for your family.

Oct 11, 2011
Pet Health

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