Hyperthyroidism and its treatment

Hyperthyroidism is one of the most common diseases seen in older cats in clinical practice. This is due to the excessive secretion of thyroid hormone, from most commonly, benign nodular hyperplasia of the thyroid gland, which is located in the neck. 

Thyroid hormone is involved in many regulatory functions of the body including heat production and metabolism of carbohydrates, fats and proteins, and act to increase activity of the sympathetic nervous system which ultimately effects many organs in the body.

Clinical signs are varied but commonly involve 

• weight loss 
• an increase in appetite 
• behavioural changes such as increased agitation and aggression 
• vomiting more frequently.

Unlike in human medicine, the cause of hyperthyroidism in cats is still unknown but believed to be multifactorial.

Treatment options can involve 

• oral tablets or transdermal gel using methimazole or carbimazole, 
• iodine restricted diets.
• surgical thyroidectomy 
• radioactive iodine treatment

The first option, only controls the symptoms and the thyroid nodules can subsequently out-grow the medication.

Iodine restricted diets are extremely difficult to manage, as the cat must have no access to any other food source EVER. The lack of any iodine in the diet means the body cannot make thyroid hormone.

Surgical thyroidectomy can be a permanent solution, but needs a skilled, practiced surgeon and there is always the anaesthetic risk to consider

In most cases Radioactive Iodine Treatment is preferred, and considered the gold standard treatment, as it is 

• less invasive
• requires no general anaesthetic risk,
• is a (usually) one-off treatment. 

The down sides are 

• the initial, relative higher cost outlay 
• the treated cat needs to be hospitalised for at least one week. 

However, in many cases the cost ends up being the same if not less than the overall cost, owners pay to treat their affected cat and ongoing blood test monitoring over the course of their lifetime. There is also the significant reduction in stress, to owners and cats alike, of avoiding the need to tablet or treat their cats twice a day forever.

Radioactive iodine administration, however, is limited in most areas due to the required licencing and facilities required to conduct these treatments.

At The Hyperthyroid Cat Clinic, we can offer this mode of treatment. There is a 92-95% success rate of the cat becoming euthyroid (normal function) after the initial dose. Treating early in the course of the disease has the most successful outcome, with cats that have had the condition a long time, possibly requiring a second dose. A few of these chronic cases have a small risk of becoming a carcinoma (malignant tumour), and will become unresponsive to normal treatment levels.

Our Veterinarian, Dr Amanda Gross BVSc has over 30 years of small animal veterinary experience and is a highly skilled and sort after local veterinarian, servicing the Eastern suburbs of Melbourne for many years.

Amanda has been licensed to administer Radioactive Iodine treatment to Hyperthyroid cats for more than 17 years and has treated hundreds of cases successfully. 

For more information in regard to the treatment and current costs please contact Dr Gross at

The Hyperthyroid Cat Clinic 

Phone: 0452 532 287 or 

Email: thehyperthyroidcatclinic@gmail.com

If you are interested in treating your cat, you will need to talk to your regular vet about referral.