Cats suffer in silence–hyperthyroidism

Increased thirst is one symptom of feline hyperthyroidism

Last week I started to sing the praises of cats because they “don’t constantly complain” like some of us humans do. As previously stated however, this “suffering in silence” sometimes allows a small matter to become much more serious before getting the proper treatment. Hyperthyroidism  is one of the most common of all the cat diseases and one of the most commonly missed conditions. Many times until the cat becomes seriously ill,  cat owners keep making “excuses” for why the cat is acting or doing certain things. If a middle-aged cat  has decreased appetite or shows a little weight loss it’s easy to say to ourselves that it could be due to old age. Vomiting – “Oh that’s from hairballs,”  poor looking coat – “He’s not getting enough vitamins.”  Many of the conditions that could be clear signs of hyperthyroidism could be easily missed.

One of the veterinarians that I was recently having this discussion with actually  told me how often it is not until the cat begins having extreme muscle weakness, severe vomiting or diarrhea, or very profound weight loss, will the owner even suspect anything could be seriously wrong.  Hyperthyroidism is easily treatable and there is no reason that a cat should suffer for years before getting the proper treatment.

The thyroid gland has the role of converting iodine into thyroxine (T4) and triiodothyronine (T3). The T4 and T3 circulate throughout the body and affect almost every single organ. Thyroxine regulates growth, metabolism, immune function and heart function. Thyroid stimulating hormone (TSH) from the pituitary gland is what signals the thyroid gland to secrete thyroxine. Hyperthyroidism is the most common endocrine disorder diagnosed in cats. It usually occurs because of a tumor of the thyroid gland that ends up increasing the secretion of the thyroid hormones.

Hyperthyroidism is more common in middle-aged to older cats and is an extremely common condition. There are many suspected causes for this condition but none have been identified with certainty. Some health care professionals have blamed it on a possible environmental pollutant but the no official cause has been officially determined. However, even though the causes have not be conclusively identified, cats suffering from this condition show  very similar symptoms.

Signs and Symptoms of Hyperthyroidism:

  • High heart rate
  • Vomiting
  • Weight loss and a decrease in appetite
  • Poor hair coat
  • Increased thirst, and increased urination
  • Diarrhea
  • Nervousness
  • Irritability
  • Muscle weakness
  • Irregular or slowed weak breathing (dyspnea)

If not detected early, hyperthyroidism in cats can proceed to something called the “Thyroid Storm,” an emergency condition that needs immediate treatment. Signs and symptoms of Thyroid Storm are extremely elevated heart rate, open-mouthed breathing, appearance of a panic attack, possible aggression and/or other hysterical behavior when handling.

Since feline hyperthyroidism can also look like other diseases such as chronic renal failure, diabetes, inflammatory bowel disease, and other intestinal disorders only a trained veterinarian is able to differentiate and come up with the proper treatment plan. The veterinarian may do a complete blood count (CBC), run a serum biochemistry to detect for possible presence of increased liver enzymes, a baseline T4 test to get an estimate of the thyroid levels, and something called a T3 Suppression test. In the T3 Suppression test, T3 is administered and if it causes a decrease in T4 then the cat is normal; if the cat has hyperthyroidism then administering T3 will cause no decrease or a slight decrease in T4. The veterinarian may also want to do a scan of the thyroid gland to get a better idea of what is going on.

The goal of treatment is to lower and normalize circulating levels of thyroid hormone. There are three treatment options available for hyperthyroidism in cats:

  1. Drug Therapy: The antithyroid drug of choice methimazole is  administered as a long term maintenance treatment for hyperthyroidism. It may also be administered temporarily until treatment through surgery or radioiodine is completed. The usual dose is 5mg by mouth every 8 to 12 hours. Blood tests are usually completed every 3 to 4 weeks until the proper maintenance dose is reached. A transdermal gel formulation may also be compounded by the pharmacist and can be administered to the hairless skin of the inner ear flap. Propylthiouracil (PTU) can also be used, but has higher incidences of side effects and is therefore no longer recommended in use for cats.
  2. Surgery: The thyroid gland can be removed. This is relatively safe if performed by an experienced surgeon. As with any surgery, there are certain risks involved with the anesthetics or from the procedure itself.
  3. Radioiodine: In radioiodine treatment, the cat is given a one-time injection of radioactive iodine. The radioactive particles concentrate in the thyroid and selectively irradiate and destroy only the thyroid tissue that is malfunctioning.

There are other treatment options that your veterinarian may discuss with you during the exam. There is no known way to prevent hyperthyroidism in cats since the cause is not known. Monitoring weight loss and having regular blood work done in older cats may help in early detection. The best way to keep our cats healthy and safe is by developing a good relationship with your veterinarian and by asking questions when something is not clear.

It is important to note that keeping medications separate and understanding these conditions and the reason for each medication that is used could actually save your pet’s life. If you have any questions about your pet’s medication you may give one of the 1800PetMeds pharmacists a  call for assistance. Under no circumstance is it a good idea to give a medication that you are not understanding and fully clear about.

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  1. I have a 13 yr old cat diagnosed with hyperthyroidism quite a while back and is on methimazole…the only way we can administer it is in food and he has lost his appetite and will NOT eat ANYTHING. We tried the transdermal previously and it was not effective…what should we do to assure he receives his daily meds dose??

  2. Dr. Michael Dym, VMD veterinarianOctober 22, 2014 at 10:59 am

    You could ask vet to refer you to a compounding pharmacy in your area to make the medication into a feline friendly favored liquid suspension. 1800petmeds may offer this service as well, but you would have to ask a pharmacist. There are also some cats that cant tolerate this medication, as it causes lethargy and loss of appetite in some, so you may need to discuss other treatment options like radioactive iodine with your vet

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