.png)
Treatment Options
Radioiodine (I-131) Therapy
Radioiodine (I-131) therapy is regarded as the “gold standard” for treating hyperthyroid cats. This treatment provides many advantages, making it the most reliable option for a safe and lasting cure for your pet.
Unlike medications and diets, it is a one-time treatment.
Unlike surgery, it is non-invasive.
To discover more about the benefits of radioiodine treatment, please visit our page.
Medication
Medication may be prescribed for control of your cat’s hyperthyroidism. Felimazole™ (methimazole) is the most common drug used for hyperthyroidism in the United States. It is important to understand that this medication prevents the production of thyroid hormone; it does not cure the disease, nor does it prevent the thyroid nodule from continuing to grow or becoming cancerous.
In order to be effective, this medication must be administered regularly (almost always twice a day) for the rest of the cat’s life. As almost any cat parent knows, that is a substantial downside to the medication approach and frequently becomes more difficult over time. In some cases, a transdermal (through-the-skin) gel applied to the hairless portion of the cat’s ear may be an option. While frequently easier to administer, this route has a lower rate of response than oral medication, and risk of accidental transdermal exposure to the humans that share the house must be considered.
Cost must also be considered. Generally, the oral medication is relatively inexpensive, but frequent monitoring lab work and visits to the veterinarian will quickly add to the overall cost. Remember also, that this medication must be continued for the rest of your cat’s life; as the nodule continues to grow it is common for dose adjustments to be required over time, and in some cases the nodule can become so large and active that the medication will no longer be effective.
Side effects to methimazole are unfortunately not rare. Transient gastrointestinal issues (loss of appetite, vomiting and diarrhea) are common. More concerning but less common side effects include severe rash and itchiness around the face and ears, liver damage, and bone marrow (red and white blood cell) issues.
.png)
Surgery
Surgery to remove the abnormal portions of the cat’s thyroid gland(s) can be an option for a hyperthyroid patient, though this procedure has become much less common lately since radio-iodine treatment has been established as a safer and non-invasive cure. However, as surgery is a cure-oriented treatment, if it is successful no further medications may be required.
The drawbacks to surgery can be substantial and must be considered:
-
Anesthesia and associated risks: While anesthesia has gotten progressively safer and more advanced over the last few decades, there are some unavoidable risks associated with it. In addition, hyperthyroid cats are older and most often have at least some amount of cardiovascular (heart and blood pressure) compromise making them less-than-ideal candidates for anesthesia. Some cats may be deemed an unacceptable anesthetic candidate due to risks from systemic illness.
-
Identifying the affected side (or sides) of the butterfly-shaped thyroid gland can be challenging. Radioactive imaging (nuclear scan) is required to confidently identify the abnormal tissue and usually requires referral to a separate facility. In approximately 10-20% of cases, active thyroid tissue will be found in areas of the body not accessible to surgery (such as within the chest) and in these cases surgery will not be successful in resolving the hyperthyroidism. If any abnormal tissue is left behind after surgery, relapse of hyperthyroidism will occur, most often within six to twelve months.
-
If both sides of the thyroid gland are affected, the surgeon may elect to only remove one side during the first surgery. Whie this approach is potentially safer, it will necessitate two separate anesthetic episodes with the two separate surgeries.
-
Anatomy in the area of surgery can present its own challenges. As the name suggests, four parathyroid glands are located very close to the thyroid (two on each side). If these are damaged or inadvertently removed, life-threatening drops in calcium will occur and this must be carefully monitored for during the post-surgical period. In addition, important nerves (laryngeal nerve, sympathetic trunk, etc.) are located in the same area and may accidentally be damaged during surgery. Nerve damage can be temporary but is sometimes permanent.
-
Surgery is an invasive procedure with post-operative pain and recovery concerns. Cost of surgery (especially if nuclear imaging is done) may easily exceed the cost of I-131 (radio-iodine) treatment.
Special Low-iodine Diet
An ultra-low iodine content food (Hills y/d) can be considered as a treatment option for feline hyperthyroidism. Iodine is a necessary component for the body to make active thyroid hormone, so it makes sense that starving the body of iodine will impair the synthesis of the thyroid hormone.
However, iodine exists in nearly everything around your cat. From other pets’ food to kitty treats or pill wraps to the occasional insect or lizard “snack”, they all have plenty of iodine to allow the overproduction of thyroid hormone to continue. Therefore, for the iodine-deficient diet to work, it needs to be absolutely the only thing your hyperthyroid cat eats. There are NO acceptable treats that can be used, not even to tempt them into eating if they become ill and need appetite support. Only one brand (and one flavor, currently) is available on the market, so there can be no variety offered.
Even under perfect circumstances, 10-20% of cats will fail to respond to the special diet, and even more will only partially respond to the treatment. If successful, the special diet will need to be absolutely the only thing that your hyperthyroid cat eats for the rest of its life.
Also important to remember (similar to the medication approach with methimazole) the iodine-deficient diet is not a curative-goal treatment approach. The abnormal nodule will continue to grow and may become less responsive to treatment as time passes, as well as continued risk to become cancerous.
.png)
Steer Clear Of
Stable Iodine or Lugol’s Iodine:
Large doses of stable iodine can temporarily slow the rate of the excess thyroid hormone in hyperthyroid patients. However, this effect is inconsistent and unpredictable, and at best does not last for long (perhaps a couple weeks) before it ceases to be effective. Sometimes, it can even worsen the toxic effects of the excess thyroid hormone. As such, this is a treatment option to be avoided.
Herbal Supplements (Thyroid Gold, Bugleweed (Lycopus virginicus), etc.):
Herbal supplements have never been shown to lower the levels of excessive thyroid hormone in the body, nor to prevent any of the weight loss or damage to other organ systems associated with hyperthyroidism. These products are often advertised with words like “support the normal thyroid function” to try to fool the consumer into thinking that these herbs treat hyperthyroidism. While you may find various anecdotes and unsubstantiated stories of success on the internet, the reason the manufacturers advertise their products in this way is to allow them to sell the herbal concoctions with NO safety or efficacy studies, let alone any guarantee or oversight of the sourcing of ingredients. These should be avoided in any hyperthyroid cat.
Do Nothing:
Your cat may seem to feel fine! He or she is eating great, zooming around the house, and seems to have the energy of a kitten. They don’t seem sick. These are common thoughts for us to hear, and on the surface they seem understandable. However, as has been discussed, hyperthyroidism is causing damage to your cat’s internal organs (heart, blood pressure, kidneys) when it is not appropriately treated. We want to cure your cat before that damage becomes permanent.