Hypothyroidism is a common health condition in dogs that causes weight gain, behavioral changes, skin and coat problems. The condition occurs when a dog’s thyroid gland isn’t creating enough thyroid hormones to regulate their body’s metabolism. 

The thyroid gland is located in their neck, close to the windpipe. The gland is responsible for regulating the metabolism. When the thyroid becomes underactive their metabolism slows down and hypothyroidism occurs.

Hypothyroidism is caused by two diseases. One is lymphocytic thyroiditis, an immune-mediated disease where the dog’s immune system mistakes the thyroid as foreign and starts attacking it. We don’t know why this happens but lymphocytic thyroiditis is the most common reason for hypothyroidism in dogs. 

The other disease that causes hypothyroidism is idiopathic thyroid gland atrophy where thefat tissue replaces the normal thyroid tissue. The cause of this disease is also unclear.

95% of hypothyroidism is caused by these two diseases, and the other 5% by rare diseases like thyroid gland cancer. Whatever the cause, the symptoms and treatments of hypothyroidism are usually the same.

While all dogs can get hypothyroidism, breeds like Labrador Retrievers, Golden Retrievers, Boxers, Cocker Spaniels, Dachshunds and Doberman Pinschers are more likely to get it. Hypothyroidism usually occurs in middle-aged dogs between the age of 4 and 10, in medium and large dog breeds. 

Symptoms of Hypothyroidism

The slow metabolic rate impacts all the organs in the dog’s body. Common symptoms of hypothyroidism are:

  • Unexpected weight gain without an increased appetite
  • Lethargy and no interest in exercise
  • Excessive shedding
  • Muscle loss
  • Dry and dull hair
  • Thin or balding fur
  • Black patches on their skin
  • Hair doesn’t regrow after clipping
  • Slow heart rate
  • High cholesterol
  • Low tolerance to cold

Diagnosis of Hypothyroidism

Hypothyroidism is diagnosed by a screening test called total thyroxine (TT4) level that measures the level of thyroid hormones in the blood. If the level of thyroid hormone is low and your dog has symptoms then it indicates hypothyroidism. For confirmation another test is performed to check multiple forms of thyroxin levels. A low result in the test confirms hypothyroidism. 

Dogs that have low TT4 and normal free T4 don’t have hypothyroidism. Your vet may conduct additional tests based on your dog’s condition.

Treatment of Hypothyroidism

Hypothyroidism is not life-threatening and easy to treat. If your dog is diagnosed with hypothyroidism and is not treated, they will have a lower quality life. 

While there is a treatment for hypothyroidism, there is no cure for it. Dogs with hypothyroidism need to be given thyroid replacement hormones for the rest of their life. The thyroid replacement hormone is given orally and the most common one is called levothyroxine.  

The dosage of the thyroid replacement hormone varies based on your dog’s weight. A blood sample is taken to calculate how much medication they need. This is because their thyroid hormone can fluctuate. 

Initially dogs are given the thyroid hormone twice a day, and then the dose is reduced. Dogs are tested every 6 months to make adjustments to their dose. 

Always consult your vet regarding the dose because a high or low dose can cause problems. Talk with your vet if there are symptoms of hypothyroidism in your dog.