Hyperthyroidism in cats, also known as thyrotoxicosis, occurs
when a cat’s thyroid produces too much of the T3 and T4
hormone, due most often to benign or sometimes malignant tumors
on the thyroid. Hyperthyroidism is primarily found in
middle-aged to older cats, typically 8-13 years and older, but
not exclusively. Because thyroid health is an important aspect
of overall good health, testing is important.
The thyroid is responsible for doling out the appropriate
hormones the cat needs in order to maintain healthy organ
function throughout the entire body. When there is a tumor on
the thyroid, and the hormones are irregular, it results in
serious organ function decline. Some of the tumors found to
cause hyperthyroidism, are benign tumors called adenomas, while
malignant tumors, which are far less common, are called
adenocarcinomas. These tumors interfere with the thyroid’s
ability to determine the appropriate amount of hormone to
How to Prevent Hyperthyroidism in Cats
As there is no known way to effectively prevent hyperthyroidism
in cats, it is crucial to perform diagnostic tests early enough
to prevent further damage. As cats get older, more frequent
visits to the veterinarian for blood tests may become
necessary. Be diligent at notifying your veterinarian about any
new behaviors or physical changes. This may help your vet in
determining whether or not to test for hyperthyroidism.
Hyperthyroidism in Cats Tests Explained
To test for hyperthyroidism, your veterinarian will check the
thickness of the cat’s neck, where the thyroid is located. If
there is any additional tissue, such as a tumor or enlarged
glands, the veterinarian will sometimes be able to feel the
lump. If this is indicative of hyperthyroidism, a
blood-chemistry test may be ordered. This test breaks down the
blood chemistry into hormone levels. Usually hyperthyroidism is
obvious, based on elevated levels of T4 hormone; however, T4
may be normal while hyperthyroidism exists. Additional testing
of the heart and kidneys using urinalysis, can further
determine the presents of hyperthyroidism.
Because hyperthyroidism causes the body damage very slowly at
first, the symptoms are often overlooked, and categorized as
normal aging, such as a dull matted coat. However, a few
symptoms may be more obvious, such as weight loss, increased
appetite, thirst and urination. Symptoms may also include
diarrhea, vomiting, and
Three options are available when considering treatment for
hyperthyroidism in cats. They are medication (Methimazole
tablets such as Tapazole is commonly prescribed for cats),
surgery, or radioactive-iodine therapy. Consult with your
veterinarian about the positives and negatives of each
treatment, and which is best for the circumstances of your
cat’s progress in the disease.
5 Facts on Hyperthyroidism in Cats
Cats between the ages of 8 and 13 are in the age range most
commonly associated with the diagnosis of hyperthyroidism, which is the most common
cause of hormone imbalance in cats. With that in mind, it is
crucial to the future health of your cat, that you can identify
the signs and take your cat in for testing before serious
damage is done. These five facts may help you understand
hyperthyroidism and how to proceed.
1. Can Hyperthyroidism in Cats be Cured?
Yes. If the thyroid is successfully removed, or the radioactive
iodine therapy is successful, hyperthyroidism can be cured.
Medication, however, does not cure, and requires
lifelong treatment. When
determining a course of action, it is important to keep in mind
that there are risks to every option, and no guarantees.
2. Is Hyperthyroidism Preventable?
No. While some researchers believe that there are chemical
causes which can be avoided, there is no real way to prevent
hyperthyroidism. It is similar to trying to prevent cancer,
just do the best you can in regards to keeping your cat
healthy, by maintaining a balanced diet and frequent checkups
to the vet, especially as they get older.
3. It Does Not Always Mean Cancer
Tumors on the thyroid, which cause hyperthyroidism, are rarely
cancerous. Often when a cat has a visible mass on the thyroid,
the immediate fear is cancer. And while cancer is a possibility
in the cases of adenocarcinomas, the tumors are usually benign
and do not spread.
4. Pay Attention to the Signs
Because hyperthyroidism can progressively do some serious
damage to organ function, getting your cat tested is crucial.
If you see any behavior that is unlike previous typical
behavior, take note and make sure you tell your vet.
The symptoms are what
lead the veterinarian to perform tests, so accurately
identifying them may speed up the process of figuring out what
is wrong. If you notice a change such as hyperactivity, when
previously the cat was consistently laid back, let your vet
5. The Thyroid Determines Metabolic Rate
Good thyroid health is important to the overall health of your
cat, because it determines at what rate calories are
metabolized into energy. This affects every cell in the body,
and how they perform. While having a high metabolism may seem
like a positive thing, especially to humans, hyperthyroidism is
destructive to organ function.
This information is for informational
purposes only and is not meant as a substitute for the
professional advice of, or diagnosis or treatment by, your
veterinarian with respect to your pet. It has, however, been
verified by a licensed veterinarian for accuracy.