Hyperthyroidism in Dogs

Hyperthyroidism in dogs is a relatively rare but serious condition that can impact your pet’s overall health. Pet owners must understand the symptoms and get their dogs diagnosed early to ensure the best outcomes. In this blog, we’ll dive deep into hyperthyroidism, how it affects dogs, and what treatment options are available.

written by

Barbara Perez

Source: PetMD

What Does the Thyroid Do in Dogs?

The thyroid is a butterfly-shaped gland located on either side of a dog’s windpipe (trachea). It produces thyroid hormones that help regulate metabolism and calcium levels. In cases of hyperthyroidism, the thyroid becomes overstimulated, producing and releasing excess thyroid hormones into the body. This leads to an increased metabolism and elevated calcium levels in the dog.

What is Hyperthyroidism in Dogs?

Hyperthyroidism in dogs occurs when the thyroid glands, located in the neck, produce too much thyroid hormone. This hormone helps regulate metabolism, but when overproduced, it can lead to weight loss, excessive thirst, and other symptoms. While hyperthyroidism is common in humans, it is much less common in dogs, with hypothyroidism being the more frequently diagnosed thyroid disorder.

Causes of Hyperthyroidism in Dogs

The primary cause of hyperthyroidism in dogs is typically benign tumors, known as adenomas, that develop on the thyroid glands. These tumors increase the production of thyroid hormone, leading to the symptoms of hyperthyroidism.

Other common causes of hyperthyroidism include:

Genetics: Certain dog breeds, like Boxer and Beagle, Golden Retriever, and Siberian Husky. are more predisposed to developing hyperthyroidism.
Tumors: Rare malignant tumors can also lead to hyperthyroidism.
Thyroid Gland Overstimulation: In some cases, the thyroid glands can be overstimulated due to underlying conditions.

Symptoms of Hyperthyroidism in Dogs

Recognizing the symptoms of hyperthyroidism is essential for early diagnosis and treatment. Common signs include:

Weight loss despite increased appetite: Your dog may seem hungrier than usual, but still lose weight.
Hyperactivity and restlessness: Dogs with hyperthyroidism may become unusually active and find it hard to calm down.
Increased thirst and urination: This is a key indicator that the thyroid may be overactive.
Coat changes: You may notice thinning or hair loss, particularly around the back.
Other symptoms: Vomiting, diarrhea, and irregular heart rate may also occur.

How is Hyperthyroidism Diagnosed in Dogs?

There are several treatment options available for managing hyperthyroidism in dogs, depending on the severity of the condition:

Surgery: If a thyroid tumor is detected and not attached to surrounding tissue, a thyroidectomy (tumor removal) is recommended. For tumors under the tongue or at the heart base, surgery can also be performed. If surgery is delayed, methimazole may be prescribed to manage thyroid levels until the procedure.
Radiation Therapy: Used for metastatic thyroid carcinoma or when surgery to remove a tumor is too risky due to the tumor’s size or location. This treatment can also be effective when radioactive iodine therapy is performed to target thyroid cancerous cells.
High-Dose Radioactive Iodine (I-131) Therapy: This treatment is highly effective for thyroid carcinoma that cannot be surgically removed or has spread. It’s also used to treat residual cancer cells after a thyroidectomy.
Chemotherapy: Drugs like toceranib phosphate (Palladia), doxorubicin, and cisplatin are used for hyperthyroidism caused by thyroid carcinoma.
Diet Change or Discontinuing Seaweed/Kelp Supplements: For dogs with hyperthyroidism caused by consuming thyroid tissue in raw meat diets or seaweed/kelp supplements, eliminating these sources is the best treatment.
Adjusting Thyroid Supplement Dose: Dogs on thyroid medication for hypothyroidism may need a dose adjustment if they develop hyperthyroidism symptoms.
Palliative Care for Cancerous Tumors: If surgery, chemotherapy, or radiation are not options, Methimazole medication and Hill’s y/d diet can help manage hyperthyroidism symptoms. This palliative care does not address the tumor, allowing it to continue growing or spreading.
Additional testing: In some cases, a T3 suppression test may be used to help diagnose thyroid disorders, including hyperthyroidism caused by thyroid carcinoma.

Managing Hyperthyroidism in Dogs

Managing hyperthyroidism in dogs involves ongoing treatment and monitoring. Regular veterinary checkups will be necessary to ensure that hormone levels are in check. You may need to adjust your dog’s diet, manage stress levels, and monitor for any changes in their behavior.

Prognosis and Lifespan for Dogs with Hyperthyroidism

With proper treatment, many dogs with hyperthyroidism can live normal, healthy lives. The prognosis depends on how early the condition is diagnosed and how effectively it is treated. Some dogs may require lifelong medication or occasional checkups, but the quality of life remains high with consistent care.

Hyperthyroidism in dogs is a treatable condition, but it requires careful attention and timely intervention. Recognizing the symptoms early and seeking veterinary care can make all the difference in your dog’s health and longevity. If your dog shows any signs of hyperthyroidism, schedule an appointment with your vet as soon as possible.

Key Takeaways

Thyroid carcinoma is the most common cause of hyperthyroidism in dogs, often requiring surgical removal (thyroidectomy) if feasible.

Radioactive iodine therapy is a highly effective treatment for inoperable or metastatic thyroid tumors.

Radiation therapy and chemotherapy (e.g., Palladia, doxorubicin, cisplatin) can help manage thyroid carcinoma when surgery isn’t an option.

A T3 suppression test may be used to diagnose thyroid disorders, including hyperthyroidism.

If hyperthyroidism is caused by diet (raw meat with thyroid tissue or seaweed/kelp supplements), eliminating these sources can resolve the issue.

Overmedication of hypothyroid dogs can lead to hyperthyroidism, requiring a thyroid supplement dose adjustment.

Palliative care (Methimazole and Hill’s y/d diet) can manage symptoms but does not stop tumor progression.

What is the prognosis for dogs with hyperthyroidism?

The prognosis depends on the underlying cause and treatment approach. If hyperthyroidism is caused by benign factors, such as diet or overmedication, adjusting the diet or medication leads to a good prognosis. For thyroid carcinoma, the outlook varies. If the tumor is small and surgically removed, or if radioactive iodine therapy is performed early, survival rates are promising. However, if the cancer has spread (metastasized), the prognosis is more guarded, with survival times depending on the effectiveness of radiation or chemotherapy.

At what age are dogs most commonly diagnosed with hyperthyroidism?

Hyperthyroidism is rare in dogs but is most often diagnosed in middle-aged to senior dogs, typically over 9 years old. Thyroid carcinoma, the leading cause of hyperthyroidism in dogs, is also more common in older dogs.

What is the life expectancy of a dog with hyperthyroidism?

Life expectancy depends on the cause and treatment:

If hyperthyroidism is diet-related or medication-induced, correcting the issue results in a normal lifespan.
With successful surgical removal of a thyroid tumor, dogs may live for several years.
Radioactive iodine therapy can extend survival for 1–3+ years, especially if the cancer hasn’t spread.
For metastatic thyroid carcinoma, life expectancy varies, but with chemotherapy and radiation, some dogs live 6–24 months or longer.

What are the first signs of hyperthyroidism in dogs?

Early symptoms of hyperthyroidism can be subtle but may include:

Weight loss despite a normal or increased appetite
Increased thirst and urination
Restlessness, hyperactivity, or irritability
Increased heart rate (tachycardia)
Vomiting or diarrhea
Poor coat quality or excessive shedding

If you notice these signs, a vet visit and T3 suppression test or thyroid function test can help diagnose the condition.

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Barbara Perez

Barbara Perez is the Lead Pet Expert and an avid animal advocate at ThePetWorld.org, bringing over a decade of experience in pet care, training, and animal welfare. With a deep passion for improving the lives of pets and their owners, Barbara combines expert knowledge with a heartfelt commitment to educating and empowering pet lovers everywhere. Whether it's through her insightful articles or hands-on advice, she is dedicated to fostering a stronger bond between humans and their furry companions, one wagging tail at a time.