Hyperthyroidism in Dogs

Written by Small Door's medical experts

Dogs with thyroid issues usually suffer from hypothyroidism, which is when the glands are not producing enough thyroid hormones. Hyperthyroidism, on the other hand, is rather rare in dogs and more commonly affects older cats. However, dogs are not immune to developing this thyroid condition. If left untreated, hyperthyroidism can cause heart and kidney failure.

In This Article

What is hyperthyroidism in dogs?

Hyperthyroidism is an endocrine (hormonal) condition in which the thyroid glands produce an excess of thyroid hormones, causing a constant state of metabolic hyperactivity. In essence, the thyroid glands are working overtime.

Thyroid hormones are important, because they help control the body’s metabolic rate — the rate at which calories are burned and turned into fuel for the dog’s organs and bodily functions. Your dog’s body temperature, heart rate, food utilization, and more are affected by the level of thyroid hormone in their bloodstream.

Signs & symptoms of hyperthyroidism in dogs

The symptoms of hyperthyroidism include:

  • Weight loss despite no change (or even an increase) in appetite

  • Excessive water consumption

  • Increased heart rate

  • Vomiting

  • Diarrhea

  • Heart murmur

  • Congestive heart failure

  • Increased amount of stool

  • Tachycardia (fast heart rate)

  • Dyspnea (shortness of breath)

  • Cardiomyology (enlarged heart)

If you notice any of these signs, it’s important to contact your veterinarian immediately. Hyperthyroidism in dogs, although rare, can cause heart and kidney failure if left untreated.

Hyperthyroidism is rare in dogs, but if you notice any of the symptoms, contact your vet immediately.

What causes hyperthyroidism in dogs?

Hyperthyroidism in dogs is usually caused by a thyroid carcinoma, which triggers an excessive production of the hormone thyroxine (T4). The tumor, found on the neck close to the thyroid gland, interferes with the normal functions of the thyroid.

But in some cases of hyperthyroidism, the overproduction of thyroid hormones does not originate in the thyroid itself. Medication taken for hypothyroidism, a much more common condition in dogs, contains a synthetic form of thyroxine, and an overcorrection of hormone levels can sometimes lead to hyperthyroidism.

Another possible culprit? A raw food diet. Certain raw foods naturally contain higher levels of thyroid hormones, so you should always consult your vet before switching your dog to a raw food diet.

Thyroid cancer is the most common cause of hyperthyroidism in dogs, although medication for hypothyroidism and certain raw foods can also trigger this condition.

Diagnosing hyperthyroidism in dogs

Hyperthyroidism can be diagnosed easily with a specialized blood test that measures thyroid hormones. However, your vet may order general blood work because thyroid issues can be secondary to other illnesses, which a more comprehensive blood test can help detect.

If the vet finds a lump in your dog’s neck area, a tissue biopsy may be taken and studied under a microscope to determine whether it is cancerous. Additional testing such as diagnostic imaging may be required to get a better understanding of the extent of the tumor. This will help determine the best course of treatment.

Hyperthyroidism is diagnosed via blood tests that measure the levels of thyroid hormones. Your vet may order additional testing if there’s evidence of a thyroid tumor.

Treatment for hyperthyroidism in dogs

Various options are available for treating hyperthyroidism in dogs. If a tumor is the cause, there are several options to treat it, such as surgery, radiation, and chemotherapy. Your vet will determine the best course of action.

If the hyperthyroidism is not the result of thyroid carcinoma and is strictly a thyroid issue, there are medications that will help get the thyroid under control and bring the levels back down to normal. Nutritional management can also help.

Is there a cure for hyperthyroidism in dogs?

With the help of medication, hyperthyroidism can be controlled. But if it is the result of thyroid carcinoma, then a cure depends on a few factors, such as the stage in which it’s caught. If caught early, the chance of recovery is better. If it is discovered when the mass is much larger, the prognosis for recovery is poor.

Is hyperthyroidism in dogs contagious for humans or other pets?

Hyperthyroidism is not contagious.

What is the cost of treating hyperthyroidism in dogs?

The cost for treating hyperthyroidism varies. A simple thyroid test and general exam will depend on your individual veterinary clinic’s fees, but in general they will run between $100 and $250. If needed, biopsies and imaging diagnostics will be more expensive, potentially costing upwards of $1000.

Treatment options for hyperthyroidism caused by cancer will run into the thousands of dollars. For instance, a standard dose of chemotherapy can cost anywhere between $3000 and $5000. If medication is necessary, it’s fairly affordable, but keep in mind that your dog will need to take the medication for the rest of his life.

Diagnosing hyperthyroidism with simple blood tests and physical exams shouldn’t cost too much, but other diagnostic exams can be more expensive. As for treatment, options range from medication and nutritional management to surgery and cancer treatment, the latter two being especially expensive.

Recovery and management of hyperthyroidism in dogs

If hyperthyroidism is the result of a tumor, recovery depends on the stage at which the cancer is first discovered, along with whether it has spread to other organs. Unfortunately, if the cancer is in an advanced stage, the prognosis for recovery will be poor to grave.

If your dog’s hyperthyroidism is the result of a thyroid condition, medication and nutritional management, along with consistent check-ups of your dog’s hormone levels, will be important.

Recovery and management of hyperthyroidism depends on the root of the condition.

Preventing hyperthyroidism in dogs

To help prevent hyperthyroidism in dogs, a healthy diet is important. If you feed your dog a raw diet, be aware that certain ingredients such as gullets, animal necks, and head meat contain higher amounts of thyroid hormones, which can trigger hyperthyroidism.

If your dog has been diagnosed with hypothyroidism, keep in mind that administering a high dose of hypothryopid medication can have the same effect on a dog’s body as an overactive thyroid gland. Be aware of any symptoms related to hyperthyroidism, and consult your vet immediately if you notice any of them. Your vet will help you correct the medication dosage.

Is there a vaccine for hyperthyroidism in dogs?

There is no vaccine that prevents hyperthyroidism in dogs.

Summary of hyperthyroidism in dogs

Hyperthyroidism in dogs is very uncommon, but if you are seeing signs and symptoms, get your dog checked out right away. If your dog suffers from hypothyroidism, make sure the medication that treats it doesn’t lead to an overcorrection in thyroid hormones, which could trigger hyperthyroidism. When in doubt, always consult your vet, because any thyroid condition that is left untreated can lead to bigger health problems.

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