Thyroid Conditions Part 1: Hypothyroidism

Pet terrier asleep between bedding at home

The thyroids are small but important glands located in the neck that produce hormones affecting all aspects of metabolism and many other vital body functions. Dogs or cats experiencing problems with the thyroid can have a variety of physical symptoms and behavioral changes.

The majority of thyroid problems in pets are because of an underproduction of thyroid hormones, known as hypothyroidism, or an overproduction of thyroid hormones, known as hyperthyroidism.

In the first part of a two-part series on thyroid conditions, Dr. Kathleen Aicher, a clinical assistant professor at the Texas A&M School of Veterinary Medicine & Biomedical Sciences, discusses hypothyroidism and how it can impact our canine and feline friends.

“Thyroid problems are encountered commonly in veterinary medicine, but they tend to affect dogs and cats differently,” Aicher said. “Cats commonly develop hyperthyroidism and very uncommonly develop hypothyroidism, while dogs commonly develop hypothyroidism and rarely develop hyperthyroidism.”

A pet with hypothyroidism will often be less active than usual and may have changes to its skin and hair, such as dull/brittle fur, hair thinning, symmetrical hair loss, and scaling of the skin. They may also be intolerant of cold, have inappropriate weight gain, demonstrate neurological abnormalities, have reproductive abnormalities, and, in rare cases, become critically ill.

Hypothyroidism most often occurs in dogs when an autoimmune disease affects the thyroid glands or the thyroid tissue atrophies (shrinks in size); it also can sometimes occur if a drug is disrupting the synthesis of thyroid hormones.

“When cats develop hypothyroidism, it is most often caused by over management of their hyperthyroidism,” Aicher said. “Rarely, cats can have congenital hypothyroidism or can develop it spontaneously as adults.”

When a pet is tested for thyroid problems, their veterinarian will take into account any illnesses the animal is experiencing or medications it is taking.

“There are some patients who may appear hypothyroid on their lab results but do not actually have hypothyroidism (known as ‘sick euthyroid syndrome’),” Aicher said. “Therefore, a veterinarian will evaluate drug history, clinical signs, other lab work abnormalities, and maybe even additional thyroid testing to make the diagnosis with confidence.”

Fortunately, treating hypothyroidism is usually relatively simple.

“If there is a drug, dietary, or environmental exposure that could be causing a thyroid problem in a patient, it should be taken away first,” Aicher said. “However, the majority of thyroid problems are not created this way and there are well-established medical treatment options for spontaneous hypothyroidism.”

The most common treatment is a daily dose of a thyroid hormone replacement medication, which will bring the hormones back up to normal levels.

A diagnosis of hypothyroidism may seem scary, but with help from a veterinarian, treatment can be easy and effective and will allow the pet to get back to normal in no time.

Pet Talk is a service of the School of Veterinary Medicine & Biomedical Sciences, Texas A&M University. Stories can be viewed on the web at Suggestions for future topics may be directed to

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