Hyperthyroidism in Dogs

Hyperthyroidism in Dogs - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Hyperthyroidism?

Dogs with thyroid issues typically suffer from hypothyroidism; this is why it is considered rare if your dog is experiencing hyperthyroidism. Hyperthyroidism can present itself in your dog by him losing weight despite a healthy appetite.  Or maybe you try to increase the amount you are feeding him, but he isn’t gaining any weight.  

In addition to these symptoms, more common than not, owners discover a lump on their dog’s neck around the same area of the thyroid glands.  This is when they find out the lump is actually a thyroid carcinoma that is causing your dog’s hyperthyroidism.  If this is the case with your dog, you will need to treat the tumor in order to get the thyroid levels back to normal.  The tumor size, the depth it extends and the growth rate will affect the treatment process as well as recovery.  Even with medical intervention, the prognosis of recovery from a thyroid carcinoma is very poor.

More commonly than not, dogs suffering from hyperthyroidism are also suffering from a thyroid carcinoma.  If you notice your dog has a healthy appetite but is still losing weight, or if you feel a lump in your dog’s throat area, take him to his veterinarian.

Symptoms of Hyperthyroidism in Dogs

Symptoms may include:

  • Weight loss
  • Increased appetite
  • Polydipsia
  • Polyuria
  • Hyperexcitability
  • Palpable enlarged thyroid glands
  • Increased fecal volume
  • Vomiting
  • Diarrhea 
  • Tachycardia
  • Systolic murmur
  • Cardiomegaly
  • Congestive heart failure 
  • Dyspnea 


Hyperthyroidism is caused by excessive secretion of thyroid hormones resulting in an increased metabolic rate.  Thyroid issues in dogs are common in middle aged and older dogs and more prevalent in certain breeds.  While it is common for you to be able to palpate the thyroid glands of a healthy dog, a thyroid mass is different.  Almost all palpable thyroid masses found upon physical exam are malignant.  Some masses are encapsulated but others are invasive and move into underlying structures.  The tumors that are invasive also tend to have a high rate of metastasis.

Causes of Hyperthyroidism in Dogs

In dogs, one of the main causes of hyperthyroidism is thyroid carcinoma.  If there is a tumor in your dog associated with the issue of hyperthyroidism, it is always assumed it is a carcinoma until proven otherwise.  Of course, there is always the chance it is simply your dog’s thyroid not working properly anymore with no associated tumor, but this is rare.

Diagnosis of Hyperthyroidism in Dogs

To confirm hyperthyroidism in your dog, the veterinarian will need to perform blood work.  A high basal serum total thyroid hormone level is indicative of this endocrine disease.  There is a specific blood test that checks the levels of the thyroid.  Level checks can include T4, T3, total T4, and free T4.  The specific test will be chosen by the veterinarian depending on which levels she wants to look at.  If the thyroid is malfunctioning, it is always beneficial to have general blood work as well.  Additional lab work such as a full chemistry panel, complete blood count (CBC), and urinalysis will also be recommended to check for other issues.  Thyroid issues can sometimes be secondary to other illnesses so the blood work will help rule out or confirm the possibility.

A fine needle aspirate (FNA) should be performed on the mass near your dog’s thyroid gland to see what type of cells it is made of.  Cytology results may vary but if there are neuroendocrine cells found within the mass, and taking into account its location, it can be associated with thyroid gland origin.  

Diagnostic imaging is a good idea to fully understand the extent of the tumor.  An ultrasound image of the area can show if there is a thickened area around the thyroid glands or if there is thickening in the area distal to the larynx.  It can verify the location and the depth the mass reaches as well as help the veterinarian with her treatment plan.  

If your dog is experiencing heart abnormalities as one or more of her symptoms, the veterinarian may recommend specific cardiac diagnostics.  An ECG would be beneficial to check the heart rate and wave lengths and at which wave the arrhythmia is occurring.  An ultrasound of the heart may also be beneficial to check the pumping efficacy and to check for thickening of the cardiac musculature.

Treatment of Hyperthyroidism in Dogs

The size of the thyroid tumor will be a large factor in the veterinarian’s treatment protocol.  She will also take into consideration the extent of tissue invasion in the area, and if there if detectable metastasis.  If there is a tumor causing the hyperthyroidism, there are several therapy options available to fight the tumor.  Radiation therapy and chemotherapy are two possible options that may be available for your dog.

If this is not something you are interested in and would like a more natural approach, there are some holistic practices you can employ. There are Chinese herbs, homeopathic remedies and other options you can pursue if you choose.  Each case of hyperthyroidism or presence of a tumor is different in each pet.  One treatment that may work for one may not work the same for another.

If your dog’s hyperthyroidism is not associated with a tumor and is simply a thyroid issue, there are medications your veterinarian will prescribe to get the thyroid under control and levels back to normal.

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Recovery of Hyperthyroidism in Dogs

Since a thyroid carcinoma is almost always associated with hyperthyroidism condition in dogs, the prognosis of recovery for your dog is poor to grave.  If caught early, your dog’s chance of recovery is better than if caught later when the mass is larger.  Even if you notice the smallest of lumps around your dog’s throat region, take him to his veterinarian for evaluation immediately.

Hyperthyroidism Questions and Advice from Veterinary Professionals


German Shepherd




3 Years


0 found this helpful


0 found this helpful

My pet has the following symptoms:
Weight Loss
Isabella (my dog) is three year old, female , mixed breed: german sheperd and Indie (Indian). recently she has been experiencing seizures. got her blood test and LFT done: which were normal. Also got thyroid tested which has T3 & T4 high levels [1.96 & 14.03 respectively] where as TSH is low with value 0.05. our doc has suggested hyperthyroid. wanted to check with you and if some other test needs to be conducted. Also she is always hungry , still lost weight. Any inputs will be appreciated

April 23, 2018

Answered by Dr. Michele K. DVM

0 Recommendations

Without examing Isabella or knowing more about her lab work, I can't really comment on what might be going on with her, but if your veterinarian has diagnosed her with a low thyroid, that can cause a wide variety of signs, and may be contributing to her various issues. it would make sense to treat that condition and monitor her for improvement, as well as treating her for her seizures if needed. I hope that everything goes well for her.

April 23, 2018

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