Surfeit Is Hyperthyroid

I got mommy to write this arti­cle because one of my fursibs is hyper­thy­roid and I thought it was a good oppor­tu­nity to write about the hyper­thy­roidism and its treatment.



Surfeit at the food bowl

Surfeit is the senior cat we adopted recently. We were told he was eleven years old. At his first vet visit he checked out fine but the labs showed a bor­der­line T4. The vet ordered a free T4 and that was high, demon­strat­ing that Surfeit is hyper­thy­roid. We were sur­prised because he wasn’t what you think of as the rav­en­ous hyper­ac­tive cat. He’s actu­ally not a very good eater and we’ve had to give him Periactin (cypro­hep­ta­dine) to improve his appetite. He was started on Tapazole (methi­ma­zole) but blood tests done a month later showed that the med­ica­tion was affect­ing his liver and it had to be stopped. This means that radioac­tive Iodine, com­monly called I-​​131 (131I in proper sci­en­tific nota­tion) is the only prac­ti­cal option for him.


T3 or triiodothyronine

T3 or tri­iodothy­ro­nine. Note the three iodine atoms.

T4 or thyroxine

T4 or thy­rox­ine. Note the four iodine atoms.

The thy­roid gland is located in the neck. In humans it lies just over the bump below the Adam’s Apple. When your doc­tor puts a hand on your neck and tells you to swal­low, he or she is check­ing whether your thy­roid is enlarged. The thy­roid pro­duces and secretes thy­roid hor­mone, which is actu­ally a mix­ture of sev­eral hor­mones. The major thy­roid hor­mones are T3 and T4, con­tain­ing three and four iodine atoms, respec­tively. Thyroid hor­mones travel in the blood stream bound to spe­cial pro­teins. They are taken up by cells and help reg­u­late many dif­fer­ent cell func­tions includ­ing the body’s use of pro­tein, fat and car­bo­hy­drate. The usual blood test for T4 mea­sures total T4, includ­ing T4 that is bound to its trans­port pro­tein and the unbound (free) T4. The spe­cial free T4 test is more accu­rate because only the unbound T4 is active.

The thy­roid is reg­u­lated by the hypo­thal­a­mus and the  pitu­itary gland via TRH (thyrotropin-​​releasing hor­mone) and TSH (thyroid-​​stimulating hor­mone or thy­rotropin). When the hypo­thal­a­mus senses that there is not enough thy­roid hor­mone in the body, it secretes TRH, which stim­u­lates the pitu­itary to secrete TSH. TSH causes the thy­roid gland to pro­duce thy­roid hor­mone. When there is enough thy­roid hor­mone in the body, the hypo­thal­a­mus stops secret­ing TRH and the pitu­itary, in its turn, stops TSH secre­tion. This sys­tem of con­trol is called the hypo­thal­a­mic – pitu­itary – thy­roid axis.



The typ­i­cal hyper­thy­roid cat is under­weight in spite of a good appetite. It’s hyper­ac­tive and may have exces­sive uri­na­tion, vom­it­ing and diar­rhea as well as an unkempt appear­ance. The thy­roid may be pal­pa­bly enlarged. There may be a heart mur­mur, increased heart rate, abnor­mal heart rhythm and heart fail­ure. The heart fail­ure is gen­er­ally reversible once the hyper­thy­roidism is treated but the cat might require med­ica­tion in the mean­while. Blood flow to the kid­neys is increased, and this may mask pre-​​existing kid­ney dis­ease, which becomes appar­ent once the hyper­thy­roidism is con­trolled. Blood pres­sure may be increased and this may dam­age many organs, includ­ing the kid­neys, eyes, brain and heart. A few cats have what is called “apa­thetic hyper­thy­roidism,” with decreased activ­ity and appetite. This is the cat­e­gory Surfeit falls into. He’s actu­ally a poor eater and has required appetite-​​stimulating medication.


Hyperthyroidism most com­monly occurs in middle-​​aged cats and is typ­i­cally caused by a benign tumor (ade­noma) of the thy­roid gland. A minor­ity or hyper­thy­roidism in cats is caused by can­cer­ous (malig­nant) thy­roid tumors. Some cases must be caused by prob­lems with the pitu­itary or hypo­thal­a­mus but I haven’t come across a men­tion of that so it must be very rare indeed.

To be continued.…

Mommy will be post­ing about the treat­ment of hyper­thy­roidism in cats and the radioac­tive iodine treat­ment in the next few days.


Sources and Further reading

Wikipedia links above

Hyperthyroidism in Cats by Cornell Feline Health Center

The Merck Veterinary Manual, Merck & Co., Inc., 2005

Plumb, Donald, Plumb’s Veterinary Drug Handbook, Sixth Edition, Blackwell Publishing, 2008

Feline hyper­thy­roidism by Advanced Veterinary Medical Imaging

What Is Feline Hyperthyroidism? by Cat Thyroid Center

I-​​Cat website

Insights into Veterinary Endocrinology blog on iopanoic acid

Erick Mears, DVM, per­sonal communication

21 thoughts on “Surfeit Is Hyperthyroid

    • Yes, Surfeit got radioac­tive iodine on Friday and he’ll be com­ing home tomor­row. Thank you for the info on Viyo. We’ll def­i­nitely check it out if we are still hav­ing trou­ble get­ting Surfeit to eat.

  1. Great post and super infor­ma­tion about the Hyperthyriodism. I have had a cat with that and she lived for five years with it and was older. She could take the med­i­cine and was easy to give pills to. Great info.

    • I’m glad you liked the post. Surfeit is easy to pill but mommy was still going to inves­ti­gate the radioac­tive iodine treat­ment, she was just going to take her time about it. Him get­ting a liver prob­lem from the med­ica­tion made the deci­sion for her.

  2. Excellent post sweetie. The kitty before me was hypothy­roid, which I know is totally dif­fer­ent than hyper­thy­roid. But we know both are treat­able with proper med­ica­tion, so we hope Surfeit has many more years ahead of him yet. Thanks you for all the kit­ties you adopt that wouldn’t have had a chance with­out you. He’s a very hand­some orange boy and we’ll look for­ward to hear­ing about his progress.

    • Thank you, Mario. Grandma is hypothy­roid and she feels so much bet­ter on med­ica­tion. As to Surfeit. I’m happy to report he got the radioac­tive iodine treat­ment yes­ter­day and is doing very well. He’ll be com­ing home tomor­row. Purrrrrrrrrrrrrrs.

  3. We are all send­ing our best purrs to Surfeit and hope eat­ing will start soon. Thanks for all of the infor­ma­tion, we don’t know much about it either.

  4. I am really inter­ested to know how the radioac­tive iodine treat­ment goes — I haven’t know a cat who had to have one of those before! Purrs and paws crossed it works for Surfiet!

  5. Surfeit — first we LOVE your name! — your momma & ours must be in cahoots, cuz she blogged abotu hypothy­roidism today & is blog­ging about hyper­thy­roidism tomor­row. And if it were one of us, her choice would def­i­nitely be 131-​​I  — but then again, she’s com­fort­able around radioiso­topes. Have you sched­uled the injec­tion yet?

    • Yes, Surfeit got the I-​​131 on Friday. He’s doing well and is com­ing home tomor­row morn­ing. Glad you like his name. It was mommy’s apol­ogy to daddy, who thinks she takes in too many ani­mals. Of course he loves Surfeit now. Purrrrrrrrrrrrrrs.

      • Excellent! If you guys lived closer, we could come over wif daddy’s Geiger counter to check his lit­ter­box MOL! (He hasta do that wif some of his human patients some­times — brachytherapy)

        • If mommy were still work­ing in the lab, she’d def­i­nitely bor­row a Geiger counter just for kicks. As it is, any­thing that doesn’t get flushed will sit in a plas­tic bag for 3 months and then get tossed or go back onto cir­cu­la­tion. We fig­ure ten half-​​lives should be good enough so we don’t have to worry about it. Is your daddy a doc­tor? Ours is an oncol­o­gist. Purrrrrrrrrrrrrrs.

  6. Great infor­ma­tion guys! The radi­a­tion treat­ment can be expen­sive which is why I think a lot of cats don’t get it. I’ve met a cou­ple who have had it but not many. Most peo­ple just opt for the medication.

    • Actually, if you give the med­ica­tion for sev­eral years, it’s prob­a­bly just as expen­sive as the radioac­tive iodine. But you don’t have to lay out all the money up front and that can make a big difference.

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