Feline Hyperthyroidism

Feline Hyperthyroidism is a commonly seen disease. By definition, Hyperthyroidism is when the thyroid glands are overactive and producing an excessive amount of thyroid hormone. Most affected cats are brought in when they are eating ravenously but seem to be losing weight.

Some owners will also notice their cat being more vocal. Other clinical signs can include a dull/flaky coat, hyperactivity, and intermittent vomiting/diarrhea. When a cat is brought in with one or more of the above concerns and the vet is doing a physical exam, they may feel the thyroid gland (which is located on the underside of their neck) for any abnormalities. Their heart may have an increased rate as thyroid hormones stimulate a faster rate.

The only way to definitively diagnose Hyperthyroidism is by running bloodwork.  When the Veterinarian recommends bloodwork, they will likely want to run a panel that will show more than just the T4 to rule out any other conditions. An animal with Hyperthyroidism will usually have an elevated T4 on their bloodwork. Once the veterinarian has this diagnostic information, they will discuss treatment options.

The gold standard treatment option for Feline Hyperthyroidism is iodine therapy given by injection. The cat is given a dose of radioactive iodine and kept quarantined in the hospital for a short period of time afterwards. Radioactive iodine treatment cures ~90% of cats. There is a thorough screening process for a cat to ensure that they are an ideal candidate for iodine therapy. If there are other underlying health concerns, medical management may be an ideal option.

One of the easiest options is a diet made by Hills called Y/D. The thyroid needs iodine to function, so this diet helps decrease T4 production by having a limited amount of iodine. To work effectively, Y/D must be the only thing that the pet consumes- no additional treats, water additives, food scraps, etc. Y/D may not be an option in a multi-cat/pet household. Improvement can be seen as soon as 3 weeks after a strict diet. If the Y/D is not a suitable option, owners may opt to use medication. The medication we use is typically in pill form and given twice per day. For picky cats, the medication can be compounded into a liquid or chewable tablet.

Follow up appointments are a crucial component of managing a cat’s Hyperthyroidism. After starting medication, the vet will need to know if the T4 level has come down. Typically this follow-up bloodwork is done 4 weeks after getting medication consistently. Although a cat’s symptoms may seem to be resolved, it is not definitive without the bloodwork. A pet’s symptoms may resolve yet their T4 may still be elevated, or could be overcorrected by the medication and a dose may need to be adjusted. Once Feline Hyperthyroidism is under management, other health concerns that were hidden may be unmasked. Annual exams will need to be done as they are required to continue prescribing any medication. Bloodwork is also recommended to be done every 6-12 months to monitor any changes and ensure that we are always in the therapeutic range with the medication.

Of course, each pet is unique in their own way and individual treatment plans are made to suit each pet’s needs. If your cat is behaving abnormally, be sure to book an appointment with your veterinarian so that if there are any underlying concerns, they can be addressed and treated as soon as possible.

For more information please visit: www.usask.ca

Written by Liz Espejo, RAHT

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Last updated: May 25, 2020

Dear Clients,

With recent changes to restrictions on businesses, we are pleased to advise that effective May 25, 2020 the restrictions on veterinary practices have been lifted. Based on these changes, below are some important updates to our operating policies.


This includes vaccines, wellness exams, blood work, heartworm testing, spays and neuters, dental services, and more!



If you wish to connect with a veterinarian via message, phone or video, visit our website and follow the "Online Consultation" link.


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- Your dedicated team at Mill Creek Animal Hospital