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Treatment Options for Feline Hyperthyroidism



Hyperthyroidism is one of the most common diseases in cats. It is a type of hormone imbalance that first emerged in the 1980s, and it happens when a benign growth in a cat’s thyroid gland leads to an imbalance in the cat’s metabolism.

While often not directly fatal, hyperthyroidism can lead to a greatly reduced quality of life, with hyperthyroid cats experiencing severe muscle deterioration, weight loss, and chronic diarrhea and vomiting. Hyperthyroidism can also lead to high blood pressure and heart disease, which can in turn lead to blindness and fatal heart failure.

The good news is that all of these things can be avoided if hyperthyroidism is detected and treated in its early stages. Modern medical veterinary equipment makes it possible to cure hyperthyroidism relatively quickly and with minimum damage to the cat’s health.

Signs and Symptoms of Hyperthyroidism

The most common sign of hyperthyroidism is when your cat appears to be losing weight despite having a healthy appetite. This happens because the cat’s overactive thyroid gland causes its metabolic rate to increase abnormally.

Other symptoms include abnormally high thirst. Hyperthyroid cats also tend to be especially restless and demanding. Chronic vomiting and diarrhea, as well as inappropriate urinating, are also symptoms. Note also that hyperthyroidism tends to afflict older cats, with the average diagnosis age being 13.


Radiotherapy is the safest and most effective treatment method for feline hyperthyroidism. The procedure requires the use of advanced medical machines available at a limited number of radiotherapy facilities. The first step is to conduct a nuclear medicine scan.

The cat is injected with a radioactive compound that allows the scan to show the size and location of the animal’s thyroid gland. The scan serves to confirm the disease and to help determine what dose of therapeutic iodine 131 should be used in the treatment. The scan also helps identify the rare cases when a thyroid tumor is malignant.

Once the appropriate dose has been determined, iodine 131 is injected and goes directly to the thyroid gland. It emits radioactive electrons that kill the thyroid growth without harming surrounding healthy tissue. Usually, only one treatment is required, and after about three days of post-procedure recovery, the cat can return home.


The surgical removal of abnormal thyroid growths in cats is a more risky procedure. This is in part because cats have more fragile hearts. If used, EKG machines would reveal a cat’s heart beating more than twice as fast as a human heart.

Additionally, most cats are naturally prone to high blood pressure, so a lot of preparation is required in order to reduce the risks of heart failure that could be incurred by anesthesia. In about 30% of hyperthyroid surgeries, only one gland is removed—when there is an obviously normal gland and an obviously abnormal one.

But in most cases, it is hard to tell if a gland is unaffected or not, and so both glands must be removed in order to guarantee the complete removal of abnormal tissue. Special care must be taken to not damage the parathyroid glands that rest above the thyroid glands. Hyperthyroid surgery generally results in permanent recovery with no further treatments needed.

Oral Medication

The third treatment option available for feline hyperthyroidism is an oral medication called methimazole. The pill blocks T4 and T3 production, thus slowing down abnormal metabolic rate to normal levels. It takes about 2 to 4 weeks to start seeing the effects of this oral treatment. The medication has a few side effects, and it won’t reduce the size of the cat’s thyroid nodule. Furthermore, medication intake must be ongoing. This treatment option, however, has the advantage of being inexpensive and requiring no hospitalization or high-risk procedures.