Question: Hyperthyroidism in Cats

Dr. Schaeberle,

My cat was diagnosed with hyperthyroidism, what treatments are available? Which is the best?

Susan

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Hi Susan,

Feline hyperthyroidism, or overactive thyroid gland, is a common condition in older cats. It is generally caused by a benign tumor in the thyroid gland located in the neck. The gland produces hormones which help control metabolism.

Symptoms include increased appetite with concurrent weight loss, vomiting and/or diarrhea, increased thirst and urination, agitation and increased vocalization. Cats may have one or more of the symptoms listed above.

Complications of hyperthyroid disease, particularly if left untreated, include high blood pressure, retinal detachment and heart disease. Diagnosis is made by testing thyroid levels in the blood. Hyperthyroid disease is relatively easy to treat, especially if caught early. Treatment options include radioactive iodine therapy, medication, and surgical removal of the thyroid gland.

Radioactive iodine therapy involves visiting a special treatment facility to receive an injection of a radioactive substance into the bloodstream targeting the abnormal thyroid tissue. This treatment is curative. The cat must board at the facility for about a week after treatment so that radioactive waste material can be properly disposed of.

The most common treatment is in the form of a daily medication called methimazole. Methimazole does not cure hyperthyroidism but does help to control the symptoms. As mentioned above, the medication must be given every day for the duration of the cat’s life. As many cats are not easy to medicate, this can be a frustrating prospect. The medication does come in several formulations including a tablet, an oral liquid that may be flavored to make it more palatable, and a transdermal gel applied to the cat’s ear flap where it is absorbed into the bloodstream. Side effects such as vomiting, loss of appetite or an allergic reaction causing itching around the face can occur with methimazole use. A small number of patients do not respond to medication.

The third option is surgical removal of the thyroid gland. Dr. Hoffman and myself are both trained to perform this type of surgery. At Shiloh Veterinary Hospital we have been successful with this type of treatment with little to no complications. Thyroidectomies are a great alternative when radioactive iodine therapy or medications have not shown improvement in your pet’s condition.

Hyperthyroidism is a common but treatable disease of older cats. If your cat is showing any symptoms listed above, please make an appointment with your veterinarian today.

Thanks,
Thomas Schaeberle, V.M.D.