Hypothyroidism in Dogs

Written by Small Door's medical experts

Hypothyroidism (also referred to as underactive thyroid disease) is a common disorder in dogs. It occurs when the thyroid gland is not producing enough thyroid hormones, which disrupts the normal balance of chemical reactions in the body.

In This Article

Located in the neck near the trachea, the thyroid produces thyroxine (T4), liothyronine (T3), and other important hormones that are necessary to regulate metabolism. In both animals and humans, metabolism affects the body’s heart rate, temperature, and the rate at which calories are burned. When the thyroid is underactive (hypothyroidism), metabolism slows and the body is thrown off course.

Hypothyroidism is more common in dogs ages four to ten years old. Females are more frequently affected than are males. Mid-size to larger breeds have a greater chance of developing the disease than smaller breeds, although it can affect any dog.

Breeds genetically inclined to the condition include:

  • Doberman Pinscher

  • Irish Setter

  • Golden Retriever

  • Great Dane

  • Old English Sheepdog

  • Dachshund

  • Miniature Schnauzer

  • Boxer

  • Poodle

  • Cocker Spaniel

Hypothyroidism vs. Hyperthyroidism: When talking about thyroid conditions in dogs, it’s important to understand the difference between these two. Hypothyroidism is a lack of thyroid hormone production, while hyperthyroidism is caused by excess thyroid hormone production, which causes a constant state of metabolic hyperactivity. This condition, unlike
hypothyroidism, is relatively rare in dogs.

Signs & Symptoms of Hypothyroidism

The early signs of hypothyroidism are often non-specific and can be attributed to a handful of other common ailments, which means it can easily be misdiagnosed or go undetected.

Early signs include a change in behavior and personality. For example, an older, mild-natured dog may suddenly start displaying signs of aggression. Weight gain is another early sign: the dog will put on weight even though he isn’t being overfed.

Other signs to look out for include:

  • Lethargy

  • Overall body weakness

  • Changes in pigmentation of the skin

  • Intolerance to cold

  • Slowed heart rate

  • Dry skin and coat

  • Recurring skin infections

  • Extreme shedding

  • Hair loss in the back region, trunk, and tail

  • Lack of hair regrowth

Additional symptoms, although not as common, can include seizures, infertility, and hearing problems.

Unfortunately, the classic clinical symptoms of hypothyroidism don’t occur until 70% of the thyroid is already damaged. Once that happens, the thyroid doesn’t regenerate. This is why catching hypothyroidism early is so important.

How Did My Dog Get Hypothyroidism?

Thyroid conditions are not uncommon in dogs. There are a few main causes.

Autoimmune destruction of the thyroid gland (lymphocytic thyroiditis) is thought to cause up to 80% of cases. This occurs when the body mistakenly sees the thyroid gland and its hormones as foreign or abnormal; in order to get rid of the “threat,” the immune system creates antibodies that attack the thyroid, resulting in a loss of thyroid function.

The remaining 15–20% of hypothyroid conditions are the result of familial genetic patterns or idiopathic thyroid atrophy. Idiopathic atrophy means that the thyroid is gradually damaged by a cause that is not completely known. Biopsies have found that as the normal tissue diminishes, it’s replaced by fat tissue instead of new, healthy thyroid tissue.

Other contributing factors may include the following:

  • Medications: Certain medications can decrease the production of thyroid hormone.

  • Dog collars: Prong collars, or any tight collar, could theoretically cause extensive damage to the thyroid, and day-to-day high pressure around the neck can cause inflammation.

  • Excessive inbreeding: Selective breeding can result in hypothyroidism being passed down to offspring.

  • Lack of exercise: Inactivity lowers the production of thyroid hormone.

  • Secondary hypothyroidism: The hypothalamus, thyroid, and pituitary glands work in conjunction. When the hypothalamus or pituitary gland isn’t working properly, it can affect the function of the thyroid, which results in secondary hypothyroidism.

Diagnosing Hypothyroidism in Dogs

Diagnosing hypothyroidism can be very difficult because other diseases mimic the symptoms.

For a complete look at the levels of thyroid hormone in your dog’s blood, the most common baseline tests are the T4 and T3. While some veterinarians may perform only a T4 count, in some cases it may be necessary to obtain a full thyroid antibody profile for best results.

But in order to accurately diagnose a thyroid condition, your vet may also need to perform a number of other tests:

  • Evaluation: A complete blood count (CBC), chemistry profile, and urinalysis may be required to rule out other conditions.

  • Thyroid screening: In order to see how much of the thyroid is affected, additional diagnostic tests may be given. (Imaging of the thyroid is usually performed only if cancer is suspected—and dogs with thyroid cancer typically have a palpable mass in their necks.)

  • Biopsy: If a tumor is detected, a biopsy may be necessary. (Fortunately, thyroid cancer is quite uncommon in dogs, so this test is rarely needed.)

Treating Your Dog for Hypothyroidism

Hypothyroidism is easily treatable and not life-threatening as long as it’s taken care of. But if left untreated, the disease will negatively affect your dog’s quality of life.

The clinical way to treat hypothyroidism is with synthetic thyroid replacement medication to offset low thyroid function. Given once or twice daily, the dosage varies depending on the severity of the disease and the individual response to the medication.

Once the medication has been in the dog’s system for a month or two, the symptoms should begin to resolve. Most dogs can eventually resume living a normal, healthy life with continued medication.

Finally, keep in mind that a balanced, high-quality diet can help your dog maintain overall good health—of which thyroid health is a part. Ask your veterinarian about the best food you can get for your dog’s particular needs.

Is There a Cure for Hypothyroidism?

Hypothyroidism is not curable, but it is treatable.

Is Hypothyroidism Contagious for Humans or Other Animals?

No. Hypothyroidism is a clinical condition, not a contagious disease.

What Is the Cost for Treating Hypothyroidism?

After a definitive diagnosis, which comes with costs that depend on your particular vet clinic and geographic location, hypothyroidism is a condition that must be treated for the rest of your dog’s life. Daily medication is required. While the cost may be relatively inexpensive (depending on the dose and brand), the cost over the span of the dog’s lifetime adds up. Additional costs to factor in are periodic blood tests to monitor the disease, along with office visit charges.

Recovery and Management of Hypothyroidism

Once your dog is diagnosed with hypothyroidism, regular blood work may be required to monitor thyroid hormone levels. In the beginning, these tests may be carried out more frequently; once the disease is regulated, these tests are usually needed only once or twice a year.

Be sure to keep track of any changes in your dog’s health, appearance, and behavior, and alert your vet to those changes.

Preventing Hypothyroidism

Hypothyroidism is not a disease that can be prevented per se, especially because the triggers aren’t fully understood. However, you can try to minimize the risk in the following ways:

  • Use a front-clipping harness to prevent strain or pressure on your dog’s neck area, especially if he’s a leash-puller.

  • Feed your dog a healthy, balanced diet, and minimize his consumption of processed foods and treats.

  • Avoid using household and outdoor products that contain harmful chemicals.

  • Beginning around the age of five, consider having your dog’s thyroid checked on a yearly basis.

Is There a Vaccine for Hypothyroidism?

There is no vaccine that prevents hypothyroidism.

Summary of Hypothyroidism in Dogs

Hypothyroidism in dogs is a common disorder, which occurs when the thyroid gland is not producing enough thyroid hormones, so the dog is unable to regulate their metabolism correctly. Although it can be tricky to diagnose, it’s easily manageable and not life-threatening if treated.

A lifelong disease, hypothyroidism requires continuous medication and care. In order to maximize your dog’s quality of life, know the clinical signs of hypothyroidism and stay on top of everyday healthcare—from administering medications to feeding your dog a nutritious diet and booking veterinary check-ups as needed.

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