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Hyperthyroidism in Cats

Hyperthyroidism is a very common disease of the middle aged to older cat; it is the most common hormone imbalance of cats.  A tumor (97% are benign) on the thyroid gland starts producing too much thyroid hormone.  Symptoms are usually weight loss in spite of eating well and vomiting.  Other signs you might see are diarrhea, a dull and flaky hair coat, and personality changes.  This disease usually can be easily diagnosed with a blood test.

There are three basic methods of treatment:  an oral medication called methimazole (Tapazole), radioactive iodine, or surgery. A new medical diet is showing some promise of being able to control the disease with a diet change alone. For most cats, the best treatment is radioactive iodine. In 97% of the cases, it is a one -time treatment. The biggest disadvantage is that the treatment needs to be done at a special facility, and the cat needs to be hospitalized for usually 5 to 10 days in bio hazard isolation. In the past, surgery was a common treatment, but it is performed less frequently as the problem seems to recur on the other gland. Treating with Tapazole is also common, but has the disadvantage that it is life long and the cat needs blood tests to monitor the thyroid level and to check for adverse effects.

The disease of hyperthyroidism can mask signs of early kidney disease.  If the cat has both kidney disease and hyperthyroidism, it is not a candidate for radioactive iodine and the dose of Tapazole may need to be adjusted.  Kidney tests are also monitored when a cat is being treated for hyperthyroidism.

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