Hyperthyroidism, overactive thyroid, is the most common hormone imbalance in cats. Cats have two thyroid glands, one on either side of the trachea in the neck, and these play an instrumental role in the body’s metabolic rate. Hyperthyroidism is characterized by overproduction of the thyroid hormone, which then results in increasing the body’s metabolic rate. The disease can affect cats of any age, however it is predominantly noted in older cats. As time progresses the thyroid gland enlarges and can often be felt when your cat’s neck is stretched back. In fewer than 2% of cases, the enlargement of the thyroid gland involves a malignant cancer; therefore in most cases the overall enlargement is not of major concern. However the results of the increase in circulating thyroid hormone are of concern, particularly for the heart and the kidneys.

The primary cause for hyperthyroidism is not known, but there are some studies that indicate increases in iodine in the diet may play a role in its prevalence. There is not a particular breed predisposed to hyperthyroidism, although Siamese cats appear to be among some of the most common patients.

The symptoms of hyperthyroidism include weight loss, despite a healthy appetite and often an increased appetite. Cats affected by the disease are often restless and may have increased cranky or aggressive behaviors. In the later stages of the disease some cats even stop eating altogether.

Secondary complications of the disease include high blood pressure, which has detrimental effects on the heart and the kidneys. The heart condition is known as thyrotoxic cardiomyopathy, in which elevated blood pressure causes increased work for the heart, ending in over-use of the muscle and thickening of the chambers. In the long term, increased blood pressure causes similar destruction of the kidneys, resulting in kidney failure.

Hyperthyroidism can be diagnosed by complete blood testing that many veterinarians may be able to perform right in the office, or by sending samples to an outside laboratory. It is strongly recommended to get all baseline blood work first, in addition to a T4 level and urinalysis. Occasionally, a cat suspected of having hyperthyroidism has a T4 level within the upper range of normal. When this occurs, a second test, usually either an FT4 by Equilibrium Dialysis or a T3 Suppression Test is performed.

There are four treatment options for hyperthyroid patients:

(1) Surgery: This is where a portion of the thyroid, or one of the pairs, is removed. Prior to having the procedure done, a cat is placed on an oral medication called Methimazole to determine if there are any secondary diseases (liver or kidney disease).

(2) Oral medication: Long-term management can also be achieved by administering an oral medication once to twice daily for the rest of the patient’s life. This is often the preferred choice for many pet parents given that the initial costs are a lot less, however in the long run, it may be a more expensive treatment option.

(3) Radioactive iodine: This treatment is a very effective plan in which radioactive material is injected that subsequently destroys the thyroid gland. The treatment does however require a one- to two-week hospitalization stay at a center certified in the treatment and handling of patients. Some of the negatives would include over-destruction of the thyroid gland that would require the patient to go on supplementation for the rest of its life.

(4) Dietary management: In recent years, a prescription food has been introduced to manage hyperthyroidism. This food is made by Hill’s Science Diet and called “y/d diet.” The food is not considered a drug but has the precise amount of iodine in the food so as not to permit overactive thyroid function. In order for the food to work, it must be the only food fed, thus no treats or special snacks. Hyperthyroidism can be easily managed and monitored under the watchful eye of your family veterinarian. Early detection is key, and therefore it is strongly encouraged that cats over the age of six years old have annual blood work performed. Do talk to your veterinarian if you have concerns that your feline companion has thyroid disease.

[Contact Dr. D’Abbraccio at jdabbracciodvm@icloud.com or follow at www.facebook.com/CatskillVeterinaryServices.]