Hyperthyroidism is Increasingly Common Among Older Cats

If you have a kitty, you have probably heard of feline hyperthyroidism. Chances are even better if your Fluffy is a senior. That’s because feline hyperthyroidism is the No. 1 endocrine disorder of aging cats.

Hyperthyroidism is caused by an overactive thyroid gland. The opposite condition is an underactive thyroid gland, or hypothyroidism. People can be affected by either condition. Interestingly, for our four-legged family members, hyperthyroidism is virtually exclusive to senior cats, and hypothyroidism to dogs.

In fact, hyperthyroidism is so common in aging cats that standard wellness guidelines recommend screening for this disorder annually once a cat turns 7 years old.

The initial signs of an overactive thyroid gland can be subtle. As the disease progresses, your kitty may begin to show more obvious signs of a problem.

Early detection is key to successfully managing this disease and Fluffy’s overall health. Although some consequences of hyperthyroidism are reversible once treatment is established, others are not.

Excess thyroid hormone affects virtually every organ in the body. It increases metabolism, causing weight loss despite increased appetite. Fat and muscle are burned away. If left untreated, hyperthyroidism is a wasting disease.

Initially, you may not be aware that your cat has lost a few ounces. Or, you may erroneously think that Fluffy’s diet is finally taking effect.

Your veterinarian may examine Fluffy and feel an enlarged thyroid gland in his throat. This is usually due to a benign growth of thyroid cells. These abnormal cells don’t listen to the cat’s body’s signals to turn off hormone production.

Rarely, the enlarged thyroid gland may be due to cancer. This occurs in 1 to 2 percent of hyperthyroid cats. These cats initially have signs similar to other hyperthyroid cats, but the abnormal cells eventually metastasize, causing tumors elsewhere, such as in the lungs.

As metabolism increases, the heart works harder. This muscle pump changes in size and dimension due to the constant stimulation. Eventually, this leads to heart failure.

The kidneys take a toll as hyperthyroid blood is pounded into their delicate filters. Ironically, hyperthyroidism can initially mask the signs of kidney disease, but the damage is occurring nevertheless.

Blood pressure may climb and affect a variety of organs. For example, cats may become blind from retinal detachment.

Uncontrolled hyperthyroidism increases anesthetic risk. Safe anesthesia protocols include screening all senior cats for hyperthyroidism before performing elective anesthesia.

Fortunately, hyperthyroidism can be easily diagnosed with a simple, inexpensive blood test. Occasionally, thyroid levels can be in the “gray zone.” These cases warrant monitoring until their thyroid trend can be determined.

The good news is that most cases of hyperthyroidism can be successfully managed.

Daily, lifelong medicine controls hyperthyroidism in many cats. Most kitties tolerate this quite well. However, 10 to 15 percent become too ill from side effects of the drug to continue. Risks include severe nausea, liver disease and blood cell destruction. Cats need to be monitored closely for life-threatening risks, especially when starting or increasing this drug.

Unlike drug treatment, radioactive iodine therapy is a permanent remedy for hyperthyroidism. Certain government-approved centers provide this treatment by injecting affected cats with radioactive iodine. The sick thyroid cells attract this medicine, which in turn destroys them. Not all cats are good candidates for this procedure, but for those that are, the results can be marvelous.

Another option is to surgically remove the sick thyroid gland. This is also a permanent treatment, but involves placing a potentially unstable patient under anesthesia. Sometimes, the adjacent parathyroid gland is also damaged or removed, causing possibly severe calcium derangements.

In recent months, a novel therapeutic diet has been developed by a major pet food manufacturer to treat hyperthyroidism. The food is safe and effective, but cats must stay on it forever and cannot have treats or other nibbles of food. This can be especially challenging in households with multiple cats.

Research is ongoing to better understand what causes some cats to become hyperthyroid.  We know that the incidence of this disorder is increasing.

This is partly due to the increasing lifespan of cats over the past few decades. Since hyperthyroidism is a disorder of senior cats, we expect to see the incidence rise with a larger senior feline population.

But the incidence of hyperthyroidism is increasing faster than the senior cat population. And indoor cats have a higher risk than cats that go outside.

Various environmental factors, including canned cat food, flea products and cat litter have been studied as possible causes, but none has been found to be associated with hyperthyroidism.

A more recent theory suggests flame retardants in furniture and rugs as a possible culprit. More research is needed to determine whether there is actually a cause and effect relationship.

The bottom line: You can help Fluffy by having her thyroid checked every year after age 7.

• • •

Dr. Heidi Bassler practices at Bassler Veterinary Hospital

22 Responses to “Hyperthyroidism is Increasingly Common Among Older Cats”

  1. Sarah says:

    Thank you so much for this informative article. I needed this information for a veterinary technology course I’m taking (a case study on a hyperthyroid cat), and could not find the information on the symptoms of untreated hyperthyroidism! Thank you, thank you. I’ll be saving this article for future reference.

    • lauren weber says:

      feel free to contact me. my 17yr old cat Nick, is hyperthyroid and is not being treated as the medication makes him vomit.amazingly he is still with us.

      • Cheryl says:

        Hello,we too have a17 yr old hyperthyroid cat who does not tolerate either the meds for hyperthyroidism or high blood pressure. She caterwauls at night–sounds like real pain but vet says it’s from the hypertension associated with hyperthyroidism. Do you have that problem? I don’t think there’s a chance she will try that diet food as she’s a very picky eater. Any advice, suggestions??
        Thank you

        • lauren weber says:

          Hi Cheryl-
          No caterwauling-Nick had always been “silent bob” (from the movie, Clerks). But he just eats and eats… I have not tried the special diet because I cannot guarantee that he wont eat anything else.

          • Selina brady says:

            Hi Lauren,

            My cat ash has just been diagnosed with hyperthyroidism, hes 14yrs old and our vet has given us two options, medicate or radiation iron therapy,now we are trying to make a decision what we should do, we are seriously thinking of going with the iron therapy the only thing is its out of town for us and our cat just wouldnt handle being away from home for all that time. What i would like to know how is everything going with your cat as you have decided not to go ahead with treatment,we are also considering this option,sorry for the long question, but thank you

      • Evie burke says:

        have you tried the Science Diet Y/D food for hyperthroidysm? I had my 11 year old on the food and she threw up everyday several times a day. I now have her on the medicine and she no longer throws up and is starting to gain weight. I know you said the medication didn’t work, but maybe the food will.

        • Brooke says:

          our kitty now 16plus.. had been on prescription for hyperthyroidism for couple years now. she too was throwing up daily..multiple times a day 🙁 i was given cans of Royal Canin Recovery (prescription only, of course) eventually getting our own script. The pill w/ the food did work.she eventually stopped liking that food (canned) . she never really gained but wasn’t losing anymore. she stopped throwing up.. which made us both happy!.. however the pill is no longer working:( Dr. won’t renew prescription 🙁 w/o basically $250 visit for labs. Not sure we want to put her through that stress (strictly indoor Siamese) looking into alternative means. I don’t have 1400$ for R.I.Therapy
          I might try Recovery Diet or the Thyroid canned food.

  2. dave says:

    my elderly cat has this problem… what is the medicine she needs to fight this?

    • Elizabeth Ingram says:

      The medication you require is methimazole it can be either in tablet form , which must be given whole not broken up, or a liquid which is squirted directly into the mouth, and that one’s marketed under the name Thyronorm.
      If you cat is indoor only and you can ensure exclusivity of feeding Hills Science produce yd prescription diet, which restricts iodine and will bring thyroid hormones back to normal levels, but it must be fed to the exclusion of all other foods. Hope this helps

  3. Barbara Keys says:

    Is it part of the desease, for my cat has this problem. She drinks a lot of water, so pees a lot, & it is in huge clumps, like clay, then gets like cement, very hard to clean out of ,litter box. Is she in pain also?

  4. Vickie Davis says:

    My 16 yr old female cat was diagnosed hyperthyroid. She has lost a 5% of her body weight. She has been taking Methimazole 5 mg 1 tablet twice a day. Also, Science Diet yd prescription. I crush her tablet an put it in her food so she’ll take it without getting her upset. She shows no sign of getting better. Besides she has started urinating outside of her litter box. I have been considering having to put her to sleep. I can’t afford to take her to a specialist.

  5. AmberJennings says:

    I was given the option of pill or topical cream to rub on inside of the ear. He was treated for two years, pills first, topical, then back to pills before having to do what was right for him at 17. He did a great job. never heard about the food. But, had multiple cats anyway. Sorry for anyone having to go through the pain.

  6. Michelle Mitchell says:

    My cat is 19 years old and she was placed on thyroid tablets last November 2017 to increase her weight. She to this day has not gained any weight whilst been on this medication and to actually try to give her it is an absolute nightmare and really stresses her and myself out so much that is is worth carrying on with the medication as she’s eating and drinking well going to toilet as normal and even still plays with string and balls. There is no change in her whatsoever since taking this medication. I personally would not like to continue with the medication as i hate stressing her out and just to give her the best quality of life what she has got left. Am I wrong in saying that? As she is not going to live much longer.

  7. Michelle Mitchell says:

    Hi i left a message yesterday about my 19yr old cat whose on thyroid tablets since last November and there has not been any change whatsoever. All I’m doing is stressing her out and it’s upsetting me really bad i hate this so I’m really wanting to stop the medication for this reason as she is so old and delicate now all i want is to give her the best quality of life of what she has got left which won’t be too long now. She’s eating and drinking and using the toilet as normal also she still play’s with balls and string she is showing no signs of anything different from before the medication till now as taking it. Please can you give me some advice on this stressful situation its causing both of us. Thank you. Mrs Christine larner

  8. Meghan Bright says:

    My cat is about 16 and was just diagnosed with hyperthyroidism. He’s lost about a pound or 1/10th of his body weight. I just started him on the Methimazadole ear cream. He’s going in for the Radiation Treatment in Denver next month. He will be 4 days in the clinic and then home with limited human contact for 2 weeks. If the thyroid responds well, he’ll have a clean bill of health for the next few years. It costs $1300 but it’s cheaper and easier than medication administration in my opinion. This cat has been my companion for his entire life and there isn’t anything that I wouldn’t do to keep him healthy and happy.

  9. April Miller says:

    My 16 yr old male cat has been using transdermal meds for hyperthroidism for many years, very successfully. It eliminates the stomach issues that may occur with the oral meds.

  10. Fran Gilbane says:

    Hi. I’m in the UK and my cat has undergone the radioactive treatment today. He has been on the twice a day liquid drug treatment since April. We were told it was ok to put it in a little bit of food, a process which made it a lot less stressful for both him and us and definitely much easier than pills. A big deciding factor in going for the radioactive treatment was that the vet said the drugs can reduce lifespan by as much as half compared to the radioactive treatment and no treatment at all will eventually be fatal. In the UK the cost is £2200. We were lucky enough to have pet insurance, hence we have been able to do this. If we couldn’t though, I would definitely recommend the liquid and would suggest putting it on a little bit of sandwich meat, which always gets wolfed down. At one point we did try to increase the dose but that made him sick. A lower dose, as suggested by the vet, did get his levels down to an acceptable, albeit not great, level. Good luck.

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