Hyperthyroidism: A Common Diagnosis in Cats

Learn all about hyperthyroidism in cats.

Hyperthyroidism in cats is a condition in which the body is producing too many thyroid hormones.

What Is Feline Hyperthyroidism?

Hyperthyroidism in cats was first recognized in the 1970s. Since then, its diagnosis has increased steadily over time. Unfortunately, the exact reason this has occurred isn't known by scientists with certainty yet. Two major avenues of research into the cause of feline hyperthyroidism include:

You can learn more here: "Flame Retardants and Hyperthyroidism in Cats" and here: "Fishy Food and Feline Hyperthyroidism."

Regardless of its cause, hyperthyroidism is now the most commonly diagnosed endocrine disease of cats that are middle-age and older. It's found in both sexes and all breeds of cats. Most cats diagnosed with hyperthyroidism have benign (non-cancerous) growths on their thyroid gland and are producing levels of the thyroid hormones T3 and T4 that are too high. Some cats have malignant thyroid cancer, but that's much rarer.

Signs of Hyperthyroidism in Cats

Cats with hyperthyroidism often show some or all of the following signs:

Hyperthyroidism increases the metabolism and creates stimulant-like effects in the body. Signs of the condition are related to those effects.

A veterinarian may notice the following signs of hyperthyroidism:

Diagnosis of Feline Hyperthyroidism

The first step toward diagnosing feline hyperthyroidism is going to the veterinarian and sharing the signs you have noticed at home. Then, the doctor will do a thorough examination. If he or she suspects hyperthyroidism at that point, the next step is doing some lab work. Increased thyroid levels in the blood along with clinical signs of hyperthyroidism can confirm the diagnosis.

Sometimes thyroid levels need to be retested a few weeks after they're first checked because the levels might be high normal or low abnormal in early stages of the condition. Rising levels over time indicate hyperthyroidism.

A specially executed test called a free T4 by equilibrium dialysis can be done if the results of regular T3 and T4 testing are ambiguous.

Treatment of Hyperthyroidism in Cats

There are three main ways of treating feline hyperthyroidism:

Prognosis of Feline Hyperthyroidism

Most cats with hyperthyroidism respond well to treatment and the signs improve. Depending on which treatment method is used, there may be complications or adjustments down the road.

Hyperthyroidism must be treated or serious side effects like heart disease will result.

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