Feline Hyperthyroidism

Overview

Your pet has been diagnosed with hyperthyroidism, a condition where the thyroid gland becomes overactive. In most cats, it is a benign change to the thyroid gland, but in some cases it is malignant, may develop into thyroid cancer over time. If left untreated, it can lead to serious health problems, including heart disease, blindness, weight loss, vomiting, and diarrhoea.

The thyroid gland produces hormones that regulate various bodily functions. However, when too much thyroid hormone is released, it can cause a range of symptoms, such as weight loss, increased appetite, vomiting, diarrhoea, excessive thirst and urination, and hyperactivity or nervousness. It also affects the heart, leading to a rapid heart rate, heart murmurs, irregular heart rhythms, and high blood pressure.

While hyperthyroidism is a serious condition, it can be effectively managed. Many cats respond well to medication, which helps regulate hormone levels and improve their quality of life. Alternatively, radioactive iodine therapy is a long term treatment option that eliminates the need for lifelong medication.

Medication

Medical management requires ongoing treatment for the lifetime of your pet. Methimazole remains the most commonly used medication in veterinary medicine due to its reasonable cost and overall efficacy. This medication is given twice a day and can be effective in controlling the disease, but it does not cure hyperthyroidism. It can take 2-4 weeks before you notice a change in your cat's symptoms.

This medication can have adverse effects on humans, so use caution when dosing or applying it to your pet.

Please tell your vet about any medications, vitamins, supplements, or herbal therapies that you're pet is on. Some medications may interact with methimazole.

Potential medication side effects

Please notify your Veterinary Team if you notice:

• Vomiting or nausea
• Loss of appetite
• Lethargy
• Pawing or scratching at the face
• Jaundice
• Anaemia

How to handle methimazole

• Store in a tight, light-resistant, childproof container.
• Keep out of reach of children and pets.
• Wear gloves when administering the medication or handling faeces, urine or vomit.
• Wash your hands well with soap and water if you come into contact with the medication or feaces, urine or vomit.
• Never break or crush tablets.
• Extra care - Pregnant and nursing women, or women who may become pregnant, MUST wear gloves when handling the medication, cat litter, or body fluids from treated pets.

estimated cost of methimazole therapy

Depending on your preference of administration, the estimated costs of various forms of Methimazole are listed below (prices are approximate only and may change according to the manufacturers without notice):

• Tablets eg Felimazole 2.5mg 100 tablets (~$85) usually lasts 50 days
• Liquid eg Thyronorm Liquid 30ml (~$85) usually lasts 30 days or 100ml (~$160) usually lasts 100 days
• Transdermal cream - this formulation needs a script from your Veterinarian (~$33 script fee) to get it compounded for your pet. The dosing and costs depend on your cat's specific doses (please check with your compounding chemist).

Your cat will be required to come in for regular T4 bloodwork, initially monthly (during the stabilisation period), then between 3 to 6 monthly when stable. Estimated cost of blood tests range between $80-160 depending on the number of abnormal parameters your pet has. A physical checkup and consultation with your Veterinarian is normally scheduled every 6 months to monitor your pet's overall health.

radioactive iodine therapy

Radioiodine treatment is considered the gold standard treatment for hyperthyroidism.

The goal of radioiodine (I-131) treatment is to destroy the abnormal thyroid tissue that is producing too much thyroid hormones. The thyroid gland naturally takes up iodine from the blood to produce thyroid hormones. Treatment with I-131 takes advantage of this natural iodine uptake mechanism as it is actively taken up into the thyroid gland, preferentially by the abnormal thyroid tissue. The accumulated I-131 then causes destruction of the abnormal thyroid cells resulting in a decrease in thyroid hormone production.

The dose is calculated for each cat individually based on severity of clinical signs and elevation of thyroid hormones. Unlike medication or a low-iodine diet, administration of radioiodine can provide a permanent cure for feline hyperthyroidism. It is also almost always a one-off treatment; less than 5% of the cats needing a second dose. Most cats will have normal hormone levels within 1 or 2 weeks of I-131 treatment although it can take up to 6 months to take full effect. A follow-up blood test (ranging between $80-160) is recommended 6-8 weeks post treatment to assess progress.

The cost of this treatment is approximately $3000-3500.

This treatment is done at a specially licensed facility registered to handle I-131. Please speak with your Veterinarian to find out more about how to get your pet referred.