A lot of people don't know about hypothyroidism in dogs and the various symptoms that it can cause. Dogs with hypothyroidism may have a lower tolerance for exercise and be more prone to developing other infectious diseases. The most common symptom of hypothyroidism is unexplained weight gain, but there are many others. This is why it's important to be aware of the signs and get your dog checked if you think it might have hypothyroidism.

Hypothyroidism is a common endocrine disease that affects many dogs in different age groups and breeds. It is caused by an underactive thyroid gland and we will discuss the causes in more detail in this article. When the thyroid gland doesn’t produce enough thyroid hormone to meet the needs of the body, it can lead to a variety of symptoms such as weight gain, lethargy, hair loss, and hyperpigmentation of the skin. Dogs with hypothyroidism may also have a lower tolerance for exercise. It should be noted that hypothyroidism is very rare in cats.

What is the normal function of the thyroid gland in dogs?

The thyroid gland produces two hormones, thyroxine (T4) and triiodothyronine (T3). These hormones are under regulation from the hypothalamus (TRH) and pituitary (TSH) glands in the brain. Thyroid hormones are involved in metabolism, growth, central nervous system (CNS) development, and tissue healing. They also promote heart function, facilitate cholesterol synthesis and metabolism, and stimulate red blood cell production.

What are the causes of hypothyroidism in dogs?

The majority of hypothyroidism cases are caused by autoimmune thyroiditis. Autoimmune destruction of the thyroid gland occurs when circulating antibodies target the cells of the thyroid gland, reducing the production of the thyroid hormones, T3 and T4. Over time, the amounts of T3 and T4 are depleted and the dog starts to show signs of hypothyroidism. Most commonly, it is dogs greater than 6 years of age that are most commonly affected and a wide range of breeds are unaffected, but most commonly seen in Golden Retrievers, Dobermans, Boxers, Daschunds, Huskys, and others.

Less commonly, a congenital defect can be noticed whereas puppies are born with a dysfunctional pituitary gland. This will result in lower levels of circulating thyroid-stimulating hormone (TSH) from the pituitary gland, and therefore less T3 and T4 production from the thyroid gland.

What are the symptoms of hypothyroidism in dogs?

The most common symptoms of hypothyroidism are:

  • Unexplained weight gain
  • Lethargy
  • Mental dullness
  • Decreased appetite
  • Hair loss

Dogs with hypothyroidism may also have a lower tolerance for exercise and can be more prone to developing other infectious diseases such as recurring bladder or skin infections such as pyoderma. As the thyroid hormones also play a role in thermoregulation, hypothyroid dogs will also have intolerances to cold. In rare cases, hypothyroidism can also cause seizures in dogs.

How is hypothyroidism diagnosed?

There are several blood tests that can be performed to diagnose hypothyroidism. These include thyroid-stimulating hormone (TSH), total thyroxine (T-total), and free T4 (fT4). A high TSH with low or inappropriately normal levels of T4 indicates hypothyroidism. If your veterinarian suspects autoimmune hypothyroidism, they may recommend testing your dog for elevated levels of thyroid antibodies.

Hypothyroidism treatment for dogs

Hypothyroidism is treated with thyroid hormone replacement medication. This can be given orally as it is in tablet form. The treatment must be continued for life since hypothyroid dogs cannot produce their own thyroid hormones anymore.

The prognosis following hypothyroidism therapy is very good. Most dogs respond very well to treatment and show marked improvement in their clinical signs. There is no cure for hypothyroidism, however regular monitoring with blood tests will ensure that your dog remains on the correct dose of thyroid medication and therefore symptom-free.

Dogs of all ages and breeds are susceptible to hypothyroidism, a very common endocrine condition that is caused by an underactive thyroid gland. Symptoms of hypothyroidism include weight gain, lethargy, and hair loss. The disease is treated with an oral medication that must be taken indefinitely. Most dogs respond very well to treatment and show marked improvement in their clinical signs. There is no cure for hypothyroidism; however, most cases can be easily managed.