Canine Hypothyroidism

Canine Hypothyroidism

By Sarah Beckman

            Many people aren’t aware that dogs, just like humans, can be diagnosed with having low thyroid or hypothyroidism. According to Tappin (2014), canine hypothyroidism is the most common endocrine disease seen in dogs and affects approximately 0.8% of patients. This article will enlighten owners of hypothyroidism, the clinical signs, diagnosis of the disease and how it can potentially be managed.

            Hypothyroidism occurs when the body is not producing sufficient amounts of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). These hormones come from the thyroid gland, which is a paired organ found on each side of the trachea in the neck (Ettinger, Edward, Feldman, 2010). Thyroid hormones have many different jobs throughout the body. One of the main functions of thyroid hormone is to increase the metabolic rate throughout the body. This means that thyroid hormone can have an affect on the dog’s heart contractility, red blood cell production, mental alertness, cholesterol, and body temperature (Lathan, 2016). Ettinger et al. (2010), describes a “decrease in metabolic rate” from low thyroid means that the speed at which cells function or “work” slows down. 

            When the metabolic rate inside the body slows down, different clinical signs will start to be seen in the dog. Affected dogs may present with signs that include:  lethargy, weight gain, heat-seeking, or mental dullness. Other major clinical signs seen in patients diagnosed with hypothyroidism are associated with the skin of the dog. The vast majority, about 80%, of hypothyroid dogs have dermatological issues that can vary in severity. One might see symmetric alopecia or failure of the hair to grow back. Some dogs show signs of a hair coat change, which could be classified as “puppy-like,” dry, or even brittle. Along with a hair coat change, an owner might recognize that the dog has increased pigmentation to the skin or dry flaky skin. Additional dermatological signs reported may be ear infections or superficial skin infections (pyoderma) (Lathan, 2016). Again, since thyroid hormones are needed for normal cellular function, clinical signs can vary depending on the stage of the disease and the particular breed of dog affected. Two common breeds that tend to be affected by hypothyroidism more than others are the Doberman Pinschers and the Golden Retrievers; however, any breed can be affected by this disease (Ettinger et al. 2010).

            Once a dog presents with signs of low thyroid, there are many different tests that can be performed to diagnose it. Routine bloodwork can sometimes indicate changes from a lack of thyroid hormone. Examples of this would be a low Packed Cell Volume (PCV), non-regenerative anemia, iron deficiency, and increased white blood cells. A chemistry panel may reveal increased cholesterol or hyperlipidaemia, since thyroid hormones control all aspects of lipid metabolism (Tappin, 2014). When diagnosing hypothyroidism, clinical signs are the number one thing that should be observed. Next, some simple bloodwork should be done to rule-out other conditions that could possibly be occurring systemically. If the signs still point to hypothyroid, a test that specifically measures the thyroid concentrations in the blood will render a definitive diagnosis. Another reason a dog could have low thyroid could come from what is called sick euthyroid syndrome. This means that there is another concurrent illness occurring in the dog that is causing a natural response in the body that leads to low thyroid (Lathan, 2016). According to Tappin (2014), ultra sounding the thyroid glands is a useful diagnostic tool used to distinguish between a hypothyroid animal versus an animal with sick euthyroid syndrome. However, Dr. Lathan (2016) stated that interpreting hypothyroid in a sick dog can be very difficult.

            Fortunately, hypothyroidism is a disease that can be easily managed once it is diagnosed. Treatment involves once or twice daily medications, depending specifically on the dog affected. Tappin (2014) does not recommend “natural” thyroid preparations given by owners due to inconsistent dosing. Initial treatment is usually done twice a day, until the symptoms in the dog resolve. Most commonly, it takes several weeks to months for the symptoms of hypothyroidism to completely resolve. Once signs have resolved, the treatment can usually be reduced to just a single dose per day in most dogs. However, life long treatment is usually required for dogs diagnosed with hypothyroidism. When giving thyroid supplementation, there are some very important potential side effects that one should monitor their pet for. Excessive supplementation, which can lead to nervousness; weight loss, and increased drinking/urination. Normally, thyroid medications do not cause these things; however, it is very possible for them to occur, and it is very important to contact the dog’s local veterinarian if any of these signs are observed (Tappin, 2014).

            The prognosis for returning to a normal life in a hypothyroid dog is excellent. The most common reasons for a dog to not respond to treatment are insufficient doses of medication, another concurrent disease, difficulty administering the medication, and poor absorption of medication from the gastrointestinal tract. Yearly rechecks of the thyroid are recommended to make sure that the hormone supplementation is appropriate (Tappin, 2014). Even though hypothyroidism can be difficult to diagnose, management of the disease if fairly easy and provides a full, happy life for the animal.




Ettinger, Stephen J., and Edward C. Feldman. Textbook of Veterinary Internal Medicine:         Diseases of the Dog and the Cat. 7th ed. Vol. 1. St. Louis, MO: Elsevier       Saunders, 2010.

Tappin, Simon. "Canine Hypothyroidism: Making a Definitive Diagnosis." Veterinary Ireland Journal 4.9 (2014): 483-88. Print.

Lathan, Patty. (2016). Canine Hypothyroidism [powerpoint slides]. Retrieved from Small         Animal Medicine and Surgery Class Lecture.