Hypothyroidism is a thyroid hormone deficiency common in dogs. It impacts a dog's metabolism and may cause weight gain, lethargy, and skin issues. Any dog can be affected, but some breeds are more likely to get it than others. Here, learn the signs and causes of hypothyroidism in dogs and what to expect during treatment.
What Is Hypothyroidism in Dogs?
Hypothyroidism is an endocrine condition that occurs when a dog's thyroid gland does not produce adequate thyroid hormones to support the body's metabolism. It is the opposite of hyperthyroidism (overproduction of thyroid hormones), which is very rare in dogs and more common in cats. Hypothyroidism is common in dogs as well as humans.
The thyroid gland is located in a dog's neck near the trachea (windpipe). It produces and secretes hormones that play important roles in many bodily functions, particularly metabolism. Without adequate amounts of thyroid hormones, a dog may be unable to absorb or metabolize nutrients from food. This leads to a decreased metabolic rate and several associated signs and symptoms.
Symptoms of Hypothyroidism in Dogs
Dogs with hypothyroidism may experience one or more of the following symptoms:
- Weight gain
- Lethargy
- Excessive hair loss or thin coat
- Dry and dull hair coat
- Increased skin pigmentation
- Cold intolerance
- Recurrent skin or ear infections
- Difficulty regrowing hair after being shaved
The signs of hypothyroidism in dogs may not be sudden or obvious at first. Dogs will often gain weight gradually and begin to act lethargic. They may develop bald patches or a thinning of the coat. The hair coat that remains may appear dry and not as glossy as normal, and the skin may become darker due to increased pigmentation. If the dog's hair is shaved, it may also not grow back or regrow extremely slowly. Some dogs with hypothyroidism are more sensitive to the cold and prone to skin or ear infections.
What Causes Hypothyroidism in Dogs?
The majority of hypothyroidism cases are considered 'primary hypothyroidism' and are caused by one of two things:
- Lymphocytic thyroiditis: This is thought to be an immune-mediated or degenerative disease that may also be genetic.
- Idiopathic thyroid gland atrophy: Fat tissue replaces thyroid tissue in this disease for unknown reasons.
Secondary hypothyroidism may occur due to cancer of the thyroid gland or other rare diseases.
Dogs of any age can develop hypothyroidism, but it's most often seen in dogs between 4 and 10 years of age. Both males and females can develop the disease, but it's more common in dogs who have been spayed or neutered.
At-Risk Dog Breeds
Since hypothyroidism may have a genetic component to it, some dog breeds are predisposed to developing hypothyroidism. These dog breeds may benefit from routine thyroid hormone level screening during their annual veterinary exam, even if you don't see any signs of the disease.
- English setter
- Rhodesian ridgeback
- Giant schnauzer
- Hovawart
- Old English sheepdog
- Boxer
- Doberman pinscher
- Gordon setter
- Beagle
How Vets Diagnose Hypothyroidism in Dogs
Contact your veterinarian if you suspect hypothyroidism or any other illness in your dog. The vet will conduct a full physical examination and recommend diagnostics tests. This typically begins with basic bloodwork to check organ functions and cell counts. Next, the vet may recommend specialized thyroid tests:
- Thyroxine (thyroid hormone, or T4) with a total T4 test or free T4 test
- Triiodothyronine (T3)
- Thyroid-stimulating hormone (TSH)
- Anti-thyroglobulin antibodies (TgAA)
The vet will analyze blood test results along with the clinical signs to make a diagnosis.
How to Treat Hypothyroidism in Dogs
There is no cure for hypothyroidism in dogs, but most cases can be managed with a medication called levothyroxine sodium. Levothyroxine is sold under many brand names, including Thyro-Tabs and Thyrosyn. The medication can be easily administered in a daily pill for the rest of your dog's life.
Your veterinarian will routinely check thyroid hormone blood levels to ensure the proper amount of levothyroxine is being administered. Fortunately, the treatment of hypothyroidism is fairly inexpensive and straightforward. If the disease can be controlled, most dogs go on to live normal lives and experience no other complications.
How to Prevent Hypothyroidism in Dogs
Because the underlying causes of primary hypothyroidism are not known, it cannot be prevented. The best thing prevention is to ensure that dogs with hypothyroidism are not used for breeding. This may help prevent the offspring from carrying a genetic predisposition to the disease.