Hypothyroidism in Dogs and the Side Effects of Hormone Treatment

by Lydia Janssen
    Hyperthyroidism can result in an increased appetite.

    Hyperthyroidism can result in an increased appetite.

    Digital Vision./Photodisc/Getty Images

    Hyperthyroidism is a hormonal condition that leads to an over-functioning of your dog's thyroid gland. This condition can result in serious symptoms including physical and behavioral changes. Treatment involves a hormone injection that can have negative side effects of its own. Knowing the facts will help you get the best treatment for your dog.

    In hyperthyroidism, the hormone thyroxine is produced excessively. This hormone naturally speeds up metabolism in the body; when it is in excess, it can cause severe symptoms. Thyroid nodules that are producing thyroxine independently of pituitary control may be to blame. Thyroid cancer can also cause increased hormone output. Occasionally, medications for an opposite condition -- hypothyroidism, whereby not enough of the hormone is produced -- may cause hyperthyroidism as well. It is most common in medium-size to large dogs of middle age, although it can affect any dog.

    The condition's common symptoms, caused by a speeding metabolism, include weight loss, increased appetite, increased thirst, vomiting and diarrhea. More serious symptoms you may notice are rapid breathing, a rapid heart rate and difficulty breathing. Your dog may also undergo behavioral changes like hyperactivity, irritability or restlessness. If a tumor is to blame, the thyroid gland may swell, making an enlarged area on the neck.

    If a reaction to hypothyroid medication is to blame, the treatment may be as simple as adjusting your dog's medication. Dogs with a hyperacitve thyroid gland can benefit from a daily anti-thyriod drug, generally either methimazole or carbimazole. In cases whereby only one of the two thyroid glands are affected, surgical removal of the overactive gland may solve the problem. If your dog's hyperthyroidism is due to a tumor, then surgery, chemotherapy or radioactive iodine therapy may be necessary, separately or in unison.

    Antithyroid medications slow the metabolism and at the wrong doses can trigger hypothyroidism, a condition where the metabolism is pathogenically slow. You may notice weight gain, lethargy, chills, fever, weakness, jaundice, blood in the urine and easy bruising or bleeding in your dog, any of which should be brought to the attention of your veterinarian. If radioiodine is used, your dog must remain at the hospital until most of the radioactive materials have left his body before he is safe to handle and take home. Surgery may also have side effects, including low blood-calcium levels and paralysis of the voice box.

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    About the Author

    Lydia Janssen began her career writing news articles for the SPCA to connect adoptable pets with their potential owners. She moved into professional writing in 2009 and uses her experience as a dog trainer, SPCA kennel worker and veterinary technician to bring quality information to responsible pet owners.

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