What is Hyperthyroidism?
Hyperthyroidism occurs when too much thyroid hormone is produced, increasing your dog’s metabolic rate to dangerous levels. This disease is rare in dogs and much more common in cats, but when it is present in dogs, it is typically serious.
Causes
This is a very common disease of the middle aged to older cat. Although the direct cause is unknown, one likely cause may be a tumor (97% are benign) on the thyroid gland which starts producing too much thyroid hormone. Other possible causes include dietary factors (canned cat foods), signaling agents (thyroid adenomatous hyperplasia), or environmental exposure (flame retardants and cat litter). Siamese and Himalayan breeds tend to be at a decreased risk for hyperthyroidism. No risk has been associated with the use of flea products.
Symptoms
Symptoms are usually weight loss in spite of eating well and vomiting. Other signs you might see are diarrhea, weakness, a dull and flaky hair coat, hyperactivity, irritability, or aggression.
Diagnosis
This disease usually can be easily diagnosed with a blood test along with clinical signs. One may also palpate the thyroid to see if a nodule is present or order a serum thyroid testing. About 90% of cats with hyperthyroidism have an elevated total T4 based on equilibrium dialysis. Since T4 levels can fluctuate, a cat that is suspected to have this condition based on clinical signs or a thyroid nodule and a normal T4 should be retested another day.
Treatment
There are three basic methods of treatment: radioactive iodine, surgery, or an oral medication called methimazole (Tapazole). For most cats, the best treatment is radioactive iodine. In 95% 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 14 days. In the past, surgery was a common treatment, but it is performed less frequently as the problem seems to recur on the other gland. Methimazole treatment is also common, but has the disadvantage that it is lifelong and the cat needs blood tests to monitor the thyroid level and to check for adverse effects. Kidney tests are also monitored when a cat is being treated for hyperthyroidism.
Source:
Blue Pearl Veterinary Partners: https://bluepearlvet.com/medical-library-for-dvms/treating-feline-hyperthyroidism/