Hyperthyroidism

Dear Dr Jody:  Our twelve year old calico cat “Brooklyn” has recently started displaying some unusual symptoms.  She has lost quite a bit of weight and always seems hungry.  She also seems agitated and even hyperactive at times.   We have recently dewormed her, so why is she so thin?

Senior cats are prone to a variety of metabolic changes, including hyperthyroidism.  Although a diagnosis cannot be confirmed without detailed investigation, cats with overactive thyroid glands can often experience the symptoms you are seeing in Brooklyn. 

The thyroid gland, which produces thyroid hormone, is a tiny gland in the neck right next to the larynx.  Because these chemicals are involved in controlling a pet’s metabolic rate, pets with excessive amounts of thyroid hormone can experience elevations in heart rate, blood pressure, and metabolism.  Thyroid hormone has a stimulatory effect on many body systems, and so hyperthyroid cats are often agitated, aggressive, hyperactive, restless, hungry, and extraordinarily vocal. 

In order to make an accurate diagnosis of hyperthyroidism in Brooklyn, your veterinarian will perform a thorough physical exam and run blood and urine tests.  Additional tests such as chest x-rays and blood pressure measurements are also recommended.  Because excessive levels of thyroid hormone can be heavily taxing on your cat’s heart, your veterinarian will want to rule out any secondary changes that might be occurring such as hypertrophic cardiomyopathy (HCM) or hypertension. 

Once a diagnosis is made, your veterinarian will begin medical therapy immediately.  Methimazole is a relatively inexpensive medication that can be administered orally or, less reliably, through a transdermal gel applied to the ear.   If your veterinarian has diagnosed secondary HCM or hypertension, additional medications may be useful to help control these side effects of hyperthyroidism. 

The frustrating thing with methimazole is that it must be given twice a day for the rest of the cat’s life.  Because easy-to-medicate cats are few and far between, lifelong oral medications can be a daunting task for the average cat owner.  For clients who do not like the idea of medicating their cat daily for the rest of eternity, there is I-131 therapy. 

I-131 therapy is a highly effective, but expensive, treatment whereby your cat is given a single, painless injection of radioactive iodine.  Radioactive iodine is scooped up by your cat’s thyroid gland where it significantly minimizes production of thyroid hormone.  Your cat will be happily euthyroid (have acceptable thyroid levels) within a few weeks, and will likely never require thyroid medication again.  Because your cat will be essentially radioactive for a short period after her injection is given, she will need to remain in the treatment facility until her radioactivity level has subsided.  You will not be permitted to visit her during this short hospital stay since even brief contact with your temporarily-radioactive cat could adversely affect your own thyroid hormone levels.  Rest assured that the veterinary specialists caring for her will not only give her daily love and affection but will also measure her radioactivity levels frequently, and will send her home as soon as the radioactivity has disappeared.

Early diagnosis and treatment is crucial in order to minimize the life-threatening effects of the illness.  Regardless of which treatment you choose, Brooklyn will thank you for relieving her of this uncomfortable condition!