One of the most common conditions resulting in weight loss despite a good appetite is hyperthyroidism.  Hyperthyroidism is usually thought of as a disease in senior cats but can be diagnosed as early as 6 years, with an average patient age of 13 years old.  Symptoms can include increased thirst, restlessness, begging for food and attention, periodic vomiting and diarrhea, or even urination in inappropriate places.  Owners of cats with hyperthyroidism often don’t even realize their pet is sick – they assume that they are losing weight due to aging.  Another reason for regular physical examinations, a veterinarian can often feel that the thyroid (usually not palpable) is enlarged, but the true diagnosis of hyperthyroidism will come with results of blood panels taken at the appointment.

Hyperthyroidism is a condition most often caused by a benign tumor on the thyroid gland that is essentially goiter.  This tumor causes the overproduction of thyroid hormones leading to the signs listed above.  The increased amount of thyroid hormone increases metabolism greatly, in turn increasing the heart rate and blood pressure as well.  I often describe to owners that hyperthyroidism is a similar feeling to the cats as drinking several energy drinks at a time.  The kitties cannot eat enough calories to meet their increased metabolism and they often feel “wired” all the time.  These cats are essentially in a state of starvation despite eating, so increased food alone will not solve the problem.  Also, many patients have secondary hypertension (high blood pressure) and heart disease that must be controlled to reduce the likelihood of blindness, heart failure, stroke and sudden death.

There are 3 main types of treatment for hyperthyroidism – medication, surgery, and radiotherapy.   It is recommended that all patients start with medication first, in order to see how they respond to suppression of the thyroid hormone and also to see if any underlying kidney disease has been masked by the rapidly circulating blood of the hyperthyroid patient. If the kidneys are in good health, the patient will then be eligible for other treatment options.

The medication, methimazole, is an oral drug with relatively few side effects.  Methimazole blocks the production of thyroid hormones from the tumor so that the symptoms related to overproduction of the hormone subsides.  However, this medication does not cure, only manages – so it must be given for the life of the cat.  Methimazole is relatively inexpensive and most side effects (most commonly facial itching) are fairly rare and reversible by stopping the medication.  Some cats are difficult to pill and for those patients, a compounded version of the medication such as a flavored liquid or ear gel can be ordered.  While on methimazole, the veterinarian will recommend periodic blood testing, initially to be sure your cat is on the proper dose for their tumor, and then to be sure that other diseases have not occurred that would dictate the need to change the dose.

The other treatment options are surgery or radiotherapy.  The goal of surgery is to remove the tumor tissue from the thyroid without removing the thyroid or its very small neighbor, the parathyroid.  Proper removal will provide a cure without the need for further medication unless the parathyroid is disrupted.  However, this surgery is very difficult and, depending on the patients’ status, can be risky.  Therefore, out of the three types of treatment, radiotherapy is considered the treatment of choice.

Radiotherapy is known to be the safest and most effective of the three treatments.  The therapy must be done by a certified provider (you can find one listed at and after 3-7 days’ hospitalization, 97-98% of patients will be completely cured!  No anesthesia is required for this procedure so it is not stressful for these senior patients who often have heart disease as well and treatment is a one-time event (2-4% of cats need a second treatment).  Radiotherapy has minimal risks, side effects, or discomfort. It is an awesome way to cure your kitty without having to manage a disease through twice daily pills for life.

If you think your cat is losing weight, or have concerns about any other changes you may be noticing at home, please call your veterinarian to schedule a thorough physical exam today!

Have questions?

We’re here to help! Don’t hesitate to contact us today!