Thyroid Disorders in Pets: Hyperthyroidism


While dogs are more likely to develop hypothyroidism, caused by an underproduction of thyroid hormones, cats are more likely to develop hyperthyroidism, caused by an overproduction of thyroid hormones.

Hyperthyroidism is the opposite of hypothyroidism in many ways and has very different symptoms. Dr. Kathleen Aicher, assistant clinical professor at the Texas A&M School of Veterinary Medicine & Biomedical Sciences, discusses these symptoms and more in part two of this two-part series on thyroid conditions.

“Thyroid disorders occur frequently in middle-aged to older dogs and cats and, therefore, should be on the radar of pet parents as well as their primary care veterinarians,” Aicher said. “Both disorders can have a significant impact on the health and well-being of patients, particularly untreated hyperthyroidism.”

Hyperthyroidism often develops in cats when excess thyroid hormone is released either by benign enlargement of the thyroid glands or, much less commonly, by a cancerous growth. This is rare in dogs, however, who generally only develop hyperthyroidism if their hypothyroidism is mismanaged, if they develop a tumor that produces thyroid hormones, or if they eat meat containing neck tissue with glands. thyroid.

“Patients with hyperthyroidism experience weight loss despite eating a good diet or even more than usual,” Aicher said. “These patients may also have increased thirst and urination, be restless or vocal, and may have gastrointestinal symptoms such as vomiting or diarrhea. Internally, patients with hyperthyroidism may have increases in their heart rate, structural changes in their heart, and hypertension.

Cats with hyperthyroidism may also appear to have sloppy coats and changes with their body condition, which may be mistaken by their families as expected changes with advancing age. For this reason, annual blood tests for hyperthyroidism are beneficial for all cats once they reach middle age, around 7 years old.

“Cats can be treated for hyperthyroidism in four main ways: daily medication to reduce thyroid hormone synthesis, radioactive iodine which destroys thyroid tissue, surgery to remove overactive thyroid tissue (thyroidectomy), or exclusive diet with a diet low in iodine”. Asher said.

“It’s really important to get hyperthyroid cats to a euthyroid (normal) state to stop the systemic effects that excess thyroid hormone has on their bodies,” she said. “Therefore, definitive treatments, such as radioactive iodine, are preferred, as they have a very high probability of curing the cat without the need for long-term medication or a change in diet. The disadvantages of Radioiodine treatment includes a higher initial cost and the fact that treated cats must stay in the hospital for a few days after treatment.

Since canine hyperthyroidism is usually caused by the dog’s diet or hypothyroidism over management, treatment is usually as simple as adjusting or stopping the dog’s medications or food.

“In the rare event that a dog has developed hyperthyroidism due to a thyroid hormone-producing tumor, they should be evaluated by a veterinary oncologist to learn more about treatment options for the tumor,” Aicher said.

“Most of the time, treatments for thyroid disorders can significantly improve the quality of life of affected dogs and cats,” she said.

If your pet is diagnosed with hyperthyroidism, don’t worry; once a treatment plan is established and in place, most pets will recover from hyperthyroidism and go on to live long and wonderful lives.

Pet Talk is a service of the School of Veterinary Medicine & Biomedical Sciences, Texas A&M University. The stories can be viewed on the web at vetmed.tamu.edu/news/pet-talk. Suggestions for future topics can be directed to [email protected]

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