Hyperthyroidism in Dogs: Causes, Symptoms & Treatment

Hyperthyroidism in Dogs: Causes, Symptoms & Treatment

Author WDF Staff


Like humans, dogs can have problems with the thyroid gland. The most common issue is hypothyroidism, but there is an opposite problem - hyperthyroidism. Hyperthyroidism is common in certain breeds, and if you noticed something off about your dog and you’re worried about their health, here’s what you should know about hyperthyroidism, its symptoms, and treatment.

What is hyperthyroidism?

Before we go into details about hyperthyroidism, we need to understand what the thyroid gland is and what it does. The thyroid gland produces thyroid hormones after the pituitary gland gets stimulated. Normally, the thyroid hormones will increase chemical processes within cells. These processes are connected to the dog’s metabolism.

When hyperthyroidism occurs, the dog’s thyroid gland goes into overdrive. It starts producing too many hormones and sends cells controlling the metabolism into hyperspeed. The dog’s metabolism increases, leading to different health complications that can have dire consequences if left untreated.

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How can I know if my dog has hyperthyroidism?

A few tell-tell signs might point dog owners toward the correct diagnosis. However, the best way to actually know your dog has hyperthyroidism is to get a diagnosis from your vet. Most dog owners will notice their dog is exhibiting symptoms of an unknown disease, which is when they’ll book a vet appointment. You could also learn hyperthyroidism symptoms and make an educated guess.

Hyperthyroidism symptoms in dogs

All health conditions come with specific sets of symptoms, and hyperthyroidism is no different. Your vet will ask you about what symptoms your dog is exhibiting, so you should remember as many of them as possible. Here are the most common symptoms of hyperthyroidism in dogs;

  • Diarrhea
  • Difficulty breathing (dyspnea)
  • Enlarged thyroid gland
  • Heart murmur; rapid heart rate
  • Hyperactivity
  • Increased appetite
  • Increased thirst (polydipsia)
  • Increased urination (polyuria)
  • Different organ systems are affected due to the overall increase in metabolism
  • Poor body condition
  • Rapid breathing (tachypnea)
  • Stray dog” appearance
  • Vomiting
  • Weight loss

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However, your dog can exhibit only a few of these symptoms, but that doesn’t mean they don’t have hyperthyroidism. It is a good idea to write them down, so you don’t forget any of them.

What causes hyperthyroidism in dogs?

Hyperthyroidism can be caused by different things. It is impossible to know until your vet runs some tests. One of the possible causes is the reaction to hypothyroidism medications. They are meant to boost thyroid hormone production, and in some cases, they send the gland into overdrive.

Tumors can interfere with normal thyroid functions. They can cause disruptions that result in the thyroid gland producing too much T3 (triiodothyronine) or T4 (tetraiodothyronine).

The third possible cause is the over-functioning of thyroid nodules. These nodules should produce hormones when the pituitary gland gets stimulated. The nodules can start producing these hormones completely independently of the pituitary gland.

How dangerous is hyperthyroidism in dogs?

Hyperthyroidism in dogs can become problematic. However, most cases are caught pretty early, and treatments are pretty effective in those cases. If this condition is left untreated for a long time, it can lead to health complications that can lead to the dog’s death.


How is hyperthyroidism in dogs diagnosed?

The first thing your vet will look at is the dog’s gland. The vet will try to see if the gland is enlarged by palpitation. Other tests will include urinalysis, blood count, and complete chemical blood profile. If the blood tests confirm elevated amounts of T4 hormone in the blood, the vet will confirm the diagnosis. However, some tests can come back as inconclusive. The levels of T4 in the blood will be normal, which is especially common in the early stages of hyperthyroidism in dogs.

If the vet still cannot get an accurate diagnosis based on what the blood tests show, they can ask for thyroid gland scintigraphy, which will show them “a two-dimensional picture of a body radiation source is obtained through the use of radioisotopes.” The vet will place the abnormal thyroid tissue more precisely. It is also possible the vet has to perform thoracic radiography and echocardiography to determine the severity of the myocardial disease. Chest x-rays can show them pulmonary metastasis. Don’t be surprised if your vet asks for these tests to confirm hyperthyroidism in your dog.

How can hyperthyroidism be treated?

The exact treatment will be determined by the cause. For example, if hyperthyroidism started as a reaction to hypothyroidism medication, your vet can adjust the dosage or switch drugs the dog’ is taking.

If the disease is connected to a thyroid tumor, there are several available options. If the cancer is close to the esophagus or major arteries, surgery might not be an option. In some cases, only a part of the tumor can be removed, and further treatment will be based on radioactive therapy. If the tumor can be removed, the vet will certainly suggest that as an option.


The third possible option is complete thyroid gland removal. If only one thyroid gland is affected, the vet might remove it. Removal of both can result in hypothyroidism.

Depending on where you live, treatment with radioactive iodine might be possible. However, that will require your dog to be hospitalized for a few weeks until the radioactivity clears. This treatment option should be discussed with your vet.

What is the prognosis?

The prognosis for dogs with hyperthyroidism is usually good, but it will depend on the exact cause. If your dog has a malignant tumor of the thyroid gland, the prognosis is bad. However, treatment options are available, and if hyperthyroidism is caught early, the dog can live a healthy and happy life with medications.

World Dog Finder team

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