Feline Hyperthyroidism

Hyperthyroidism is the most common endocrine disease of older cats. It occurs when the thyroid gland, located in the neck beside the trachea, produces and excretes an excess amount of thyroid hormone into the bloodstream. In some hyperthyroid cats the gland will be enlarged and can be detected during a physical exam.

Thyroid hormone regulates the metabolism of the whole body. When there is too much thyroid hormone in the body all the normal functions are sent into “overdrive.” This speeding metabolism is a physical drain on the cat. Signs you may see include a ravenous appetite, weight loss and an unkempt coat. Additional changes that can be seen are behavior changes, nervousness, vomiting/diarrhea, increased drinking/urinating, and the desire to rest in cool places. Hyperthyroid cats are easily stressed by anything unusual, (company, boarding, new pets...). Frequently these signs are interpreted as “just getting old” when in fact there may be a medical reason for these changes.

Diagnosis of hyperthyroidism is really quite simple. As mentioned above, sometimes an enlarged thyroid gland can be found in the cat’s neck. The true diagnosis of hyperthyroidism relies on a blood test to measure the level of hormone in the cat’s system. This should be done in combination with a complete blood chemistry and CBC as hyperthyroidism can mimic other diseases seen in older cats, (diabetes, kidney disease).

There are several treatment options: oral medication forever, radioactive Iodine or surgical removal of the hyperactive gland. There are advantages and disadvantages to each treatment option.

	Advantages	Disadvantages
Oral Medication	Easy access	Cat may resent daily medication
Surgery	Usually curative	Poor surgical patients
Radioactive Iodine	Usually curative	Requires 1-2 week isolation

A hyperthyroid cat that goes untreated may suffer on-going weight loss, weakness, debilitation, kidney disease and heart arrhythmias. These changes can eventually lead to premature death. If treated, cats can live happily for many years.