Understanding Thyroid Issues in Dogs: Symptoms, Diagnosis, and Treatment

This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed on July 4, 2024

If you have questions or concerns, call your vet, who is best equipped to ensure the health and well-being of your pet. This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. See additional information.

Lack energy? Weight gain? Tired all the time? (Your dog, not you.)

These symptoms are commonly linked to thyroid issues in dogs, specifically hypothyroidism, also known as “underactive thyroid glands.”

Happily, hypothyroidism is easily treated — and once a diagnosis is made, it’s not hard to give your dog their bounce back.

Clearing Up Thyroid Issues in Dogs

Right away, let’s be clear that dogs are different in many respects, especially when it comes to thyroid disease.

Dogs are more prone to thyroid issues in dogs like hypothyroidism (underactive thyroids). This condition is characterized by:

• Weight gain
• Lack of energy

Now that we’ve got that common stumbling block clear, let’s learn more about thyroid issues in dogs.

Understanding the Thyroid Glands in Dogs

Dogs have 2 thyroid glands, located on either side of the windpipe, just below the doggy equivalent of the Adam’s apple, which can lead to thyroid issues in dogs.

• Function:
  • These glands work under instruction from the pituitary gland in the brain, which affects thyroid issues in dogs.
  • The pituitary sends a hormone message to the thyroid glands when more thyroid hormone is needed, preventing thyroid issues in dogs.
• Thyroid Hormone:
  • Governs the body’s metabolic rate.
  • Acts like gasoline in a car engine—when you rev the engine, it runs harder and faster. When you take your foot off the gas pedal, not much happens.

Hypothyroid dogs lack thyroid hormone, leading to a slow metabolism, lack of energy, and weight gain.

This sounds straightforward enough, but making a correct diagnosis can be challenging. Hypothyroidism can be incorrectly diagnosed because thyroid hormone levels may drop if the dog is unwell for another reason. But we’ll get into that in more detail later.

Causes of Low Thyroid Levels in Dogs

True hypothyroidism in dogs is due to one of three thyroid issues in dogs:

1. Congenital:
   • This occurs when a puppy is born with underactive thyroids.
   • It is rare.
2. Lymphocytic (or Autoimmune) Thyroiditis:
   • This is inflammation in the thyroid due to an immune system attack.
   • It is the most common cause of hypothyroidism in dogs.
   • Explanation: “Lymphocytic thyroiditis” means lymphocytes (white cells found in the immune system) flood the thyroid and cause inflammation.
   • The immune system mistakenly attacks the thyroid tissue as if it were an invading bacteria or infection, leading to thyroid issues in dogs.
   • Over time, inflamed glandular tissue is replaced by scar tissue, which cannot produce thyroid hormone, leading to a drop in blood levels.
   • Once more than 75% of the thyroid gland is damaged, clinical signs of low thyroid hormone develop.
3. Idiopathic Atrophy:
   • Active thyroid tissue is replaced by fat for reasons that are not clearly understood.

However, some dogs may have artificially low levels of thyroid hormone as a side effect of being ill. This condition is known as “sick thyroid syndrome.” When the illness is treated, thyroid levels usually return to normal.

To avoid incorrect diagnosis, veterinarians choose tests carefully and may retest thyroid function when the dog is well again.

Environmental Factors Contributing to Hypothyroidism in Dogs

Environmental factors can play a role in the development of hypothyroidism in dogs. These factors include:

• Exposure to Toxins: Certain chemicals and pollutants can affect thyroid function.
• Diet: Nutrient deficiencies or imbalances can impact thyroid health.
• Stress: Chronic stress can disrupt the endocrine system, including the thyroid gland.
• Obesity: Excess weight can contribute to hormonal imbalances.

Understanding these factors can help in preventing and managing thyroid issues in dogs.

Dog Breeds Prone to Hypothyroidism

Certain dog breeds seem more at risk of developing thyroid issues in dogs like hypothyroidism, implying a potential genetic factor.

Breeds linked to hypothyroidism include:

• Golden Retriever
• Beagle
• Doberman Pinscher
• Dachshund
• Miniature Schnauzer
• Akita
• Cocker Spaniel
• Boxer
• Old English Sheepdog

In dogs, thyroid issues like hypothyroidism typically affect young to middle-aged dogs. Larger breeds tend to develop the condition younger than smaller breeds:

• An Old English Sheepdog or Golden Retriever may show signs from as young as 2–3 years old.
• Smaller dogs such as the Dachshund or Miniature Schnauzer develop symptoms from 6 years onward.

Signs and Symptoms of Hypothyroidism in Dogs

Without enough thyroid hormone to stimulate the metabolism, all body systems become sluggish, affecting the skin, digestion, reproductive cycle, and tear fluid production.

Many times it’s as if the dog is aging prematurely:

• The dog no longer wants to go for walks and prefers to sleep by the fire.
• They gain weight.
• Their coat becomes dull and starts to thin.

These changes appear gradually, making them harder to spot. The dog doesn’t go from being active to a couch potato overnight, and many people just accept this gradual change as part of their dog aging.

Outward signs of hypothyroidism include:

• A dull dry coat where the hairs pluck out easily.
• Heavy shedding leading to a thinning coat.
• Hair loss progresses with matching bald patches on either side of the body.
• Those bald patches become hyperpigmented, and the skin darkens a few shades.
• If the coat is clipped, the hair fails to grow back.
• Hair loss occurs on the tail, making it look like a “rat’s tail.”
• The skin feels greasy and is often flaky.
• The skin on the face is subtly swollen, giving the dog a “tragic” expression.

Other miscellaneous changes:

• Feeling cold and seeking heat.
• Harsh breathing due to laryngeal problems.
• Shrinking testicles.
• Enlarged nipples.
• Dry eye.

Unfortunately, none of these signs alone are enough to diagnose hypothyroidism. Diagnosis requires blood tests.

Making a Diagnosis of Hypothyroidism

What could be simpler? Simply measure how much thyroid hormone is in the bloodstream, right?

Wrong.

Remember “sick thyroid syndrome?” If the dog is sick for some other reason, then levels of thyroid hormone drop as a result. These dogs don’t need thyroid medication — they need their underlying problem sorted out. When this is corrected, those thyroid levels pop right back up.

When your vet is strongly suspicious of hypothyroidism, they check out both the levels of thyroid hormone and the levels of thyroid stimulating hormone (TSH). When TSH is high but thyroid is low, this indicates hypothyroidism.

Indeed, there are several blood tests that will reach an accurate diagnosis with the take-home message that measuring thyroid hormone is not reliable.

Potential Complications from Untreated Hypothyroidism

Untreated hypothyroidism can lead to several serious complications:

• Cardiovascular Issues: Low thyroid hormone levels can lead to heart problems, including bradycardia (slow heart rate) and potential heart failure.
• Neurological Problems: Dogs may develop peripheral neuropathy, affecting their nerves and causing weakness or lack of coordination.
• Reproductive Issues: Hypothyroidism can cause infertility or complications during pregnancy.
• Immune System Dysfunction: A weakened immune system makes dogs more susceptible to infections and other illnesses.

Timely diagnosis and treatment are crucial to prevent these complications and ensure a better quality of life for your dog.

What Happens If Hypothyroidism Is Not Treated?

Diagnosing hypothyroidism in dogs involves more than just measuring thyroid hormone levels in the bloodstream due to the complexities of the condition.

• Sick Thyroid Syndrome:
  • If the dog is sick for another reason, thyroid hormone levels may drop.
  • These dogs need their underlying problem treated, not thyroid medication.
  • Once the underlying issue is corrected, thyroid levels should return to normal.
• Diagnosis Process:
  • Vets check both thyroid hormone levels and thyroid stimulating hormone (TSH) levels.
  • High TSH and low thyroid hormone levels indicate hypothyroidism.
• Reliability of Blood Tests:
  • Several blood tests are required to reach an accurate diagnosis.
  • Measuring thyroid hormone alone is not reliable.

For more details on thyroid stimulating hormone testing in dogs, refer to this guide.

Treatment for Hypothyroidism in Dogs

Hypothyroidism, a form of thyroid issue in dogs, can be treated but not cured. The treatment involves a simple tablet that supplements artificial thyroid hormone.

• Dosage:
  • The dose is usually between 10–20 mg for each kg of the dog’s body weight.
  • This is given twice a day by mouth.
  • Example: A 30 kg Labrador Retriever would take 300–600 mcg twice a day.
• Monitoring and Adjustment:
  • Vets may start with the lowest dose and then recheck blood levels.
  • This ensures the dog isn’t given too much, which can cause other problems.
• Improvement Timeline:
  • Mood improvement is often seen within 1 week of starting therapy.
  • It takes 4–6 weeks for hair to start growing back.
  • Full benefits can take up to 6 months to be realized.

Proper treatment helps manage the symptoms and improve the quality of life for dogs with hypothyroidism.

In the video below, Dr. Patrick McHale, DVM, talks more about the symptoms and treatment of hypothyroidism in dogs:

Long-term Management of Hypothyroidism in Dogs

Managing hypothyroidism in dogs is a lifelong commitment that involves:

• Regular Medication: Consistently administering thyroid hormone supplements as prescribed by your vet.
• Routine Blood Tests: Regularly monitoring thyroid hormone levels to adjust medication dosage as needed.
• Balanced Diet: Providing a nutritionally balanced diet to support overall health and thyroid function.
• Regular Exercise: Keeping your dog active to help manage weight and support metabolic health.
• Veterinary Check-ups: Scheduling regular vet visits to monitor your dog’s condition and address any emerging issues promptly.

With proper management, dogs with hypothyroidism can lead happy, healthy lives.

Hyperthyroidism in Dogs

Hyperthyroidism in dogs is rare and usually results from a tumor of the thyroid gland. Another scenario is when dogs are misdiagnosed with hypothyroidism and given unnecessary thyroid supplements. This can lead to hyperthyroidism.

Symptoms of Hyperthyroidism in Dogs:

• Increased thirst and peeing
• Weight loss
• Agitation and restlessness
• Racing heart
• Diarrhea

Hypothyroidism in Dogs in a Nutshell

Thyroid issues in dogs like hypothyroidism can be tricky to diagnose, but it’s easy to treat once identified. Simply taking a daily pill will help your dog regain their energy, managing thyroid issues in dogs.

Key Points:

• Be patient with the vet, as the signs are vague, and different tests may be necessary.
• Proper diagnosis and treatment will be worth it in the end, as your pet will go from an “aging” dog back to their puppyish ways.

For information on thyroid issues in cats, you can read our detailed article on thyroid problems in cats.

Frequently Asked Questions (FAQ)

References

• Peterson, Mark E., DVM, DACVIM. “Hypothyroidism.” Merck Veterinary Manual. https://www.msdvetmanual.com/endocrine-system/the-thyroid-gland/hypothyroidism.
• Williams, Krista, DVM, and Ernest Ward, DVM. “Hypothyroidism in Dogs.” VCA Hospitals. 2019. https://vcahospitals.com/know-your-pet/hypothyroidism-in-dogs.
• Scott-Moncrieff, J. Catharine, VetMB, MRCVS, DACVIM, DECVIM, DSAM. “Diagnosis and Treatment of Canine Hypothyroidism and Thyroiditis (Proceedings).” dvm360. Aug. 1, 2011. http://veterinarycalendar.dvm360.com/diagnosis-and-treatment-canine-hypothyroidism-and-thyroiditis-proceedings.
• Huisinga, Elke, DVM. “Diagnostic Update: Hypothyroidism in Dogs.” Idexx Laboratories. 2016. https://www.idexx.eu/globalassets/documents/country-specific/nordic/1509042-0216-uk-du-hypothyroidism-dog.pdf.
• “Hypothyroidism in Dogs.” WebMD. https://www.webmd.com/pets/dogs/hypothyroidism-in-dogs
• “Hypothyroidism in Dogs.” VCA Hospitals. https://vcahospitals.com/know-your-pet/hypothyroidism-in-dogs
• “Disorders of the Thyroid Gland in Dogs.” Merck Veterinary Manual. https://www.merckvetmanual.com/dog-owners/hormonal-disorders-of-dogs/disorders-of-the-thyroid-gland-in-dogs