Hyperthyroidism is one of the most common diseases diagnosed in older cats.  It is caused by a growth of the thyroid gland, which is completely benign in the vast majority of cases, but causes the thyroid gland to produce more thyroid hormone than usual.  Thyroid hormone has effects all over the body, and causes a general increase in metabolism. The clinical signs of hyperthyroidism are therefore many and varied, and can include effects on the heart, gut and urinary tract.

The most common signs an owner will see in an affected cat are weight loss, increased appetite, drinking and urinating more, diarrhoea and vomiting.  Not all cats will necessarily show any of these signs, however, and a definitive diagnosis is important.  Diagnosis is usually with a simple blood test, but occasionally more thorough testing may be required.

Hyperthyroidism is the most treatable disease of older cats, and most cats have an excellent response to therapy.  The three main treatment options are medication, surgery and radioactive Iodine therapy.

1.Oral medications: Most cats will start treatment with tablets (usually twice daily), and some cats will continue these for life.  Whilst on tablets, cats should be checked regularly to ensure that they are on the correct dose.

Very rarely, a cat may have an adverse reaction to these tablets, which is reversible when the medication is stopped.

2. Radioactive Iodine treatment: Radioactive iodine (I-131) is a simple, effective, safe and permanent treatment for cats with hyperthyroidism. An appropriate dose of radioactive iodine is injected (or given orally), and destroys the abnormal tissue in the thyroid gland. Your cat must remain in a referral hospital for about a week after the dose is given and you should minimise contact with your cat for a few weeks after coming home (as there is often still some minimal radioactivity). No further medication is required after the treatment is performed.

A recheck 2 weeks after your cat goes home is recommended to check body weight, heart rate and general condition, then a blood test to check thyroid levels is performed 6 weeks after treatment.

3. Surgery:  This is a permanent treatment, which involves the surgical removal of the thyroid gland.  If both thyroid glands need removal, then it is recommended to perform this operation in two stages, 6 weeks apart.  Again, rechecks at 2 and 6 weeks are recommended.  If only one gland is involved, there is a chance the other thyroid gland may require removal in the future.

There are many factors involved in choosing the right treatment option in each case, and close consultation with your vet is vital for the best decision for you and your cat.


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