Feline Hyperthyroidism

by K Marie Alto December 08, 2018 3 min read

Feline Hyperthyroidism

Today hyperthyroidism is the most frequent endocrine disease in cats and is reported to occur in 10% of cats older than ten years of age. I recently read an article about animal health by the NY Times that made me go hmmmm.  “The Mystery of the Wasting House Cats,” states:

Forty years ago, feline hyperthyroidism was virtually nonexistent. Now it’s an epidemic – and some scientists think a class of everyday chemicals might be to blame.

Emily Anthes, The NY Times

My cat Moosie (read more about him below) was diagnosed with hyperthyroidism less than a year ago so needless to say this tagline drew me in quickly. While the article does not discuss important topics for pet parents such as symptoms of hyperthyroidism in cats, observable signs your cat is dying of thyroid disease, or if / when to euthanize a cat with hyperthyroidism, I would encourage you to read the whole article, but if you don’t have time, here are some highlights that caught my attention.

Risk Factors

Here are a few key risk factors for cats: spending time indoors, using cat litter, eating canned food, eating fish-flavored canned food, eating liver-and-giblet-flavored canned food, drinking puddle water, sleeping on the floor, sleeping on bedding treated with flea-control products, and living in a home with a gas fireplace.

Toxicological Studies

Research shows a possible correlation between hyperthyroidism a class of flame retardants known as polybrominated diphenyl ethers (PBDEs). Beginning in the 1970s, large amounts of these chemicals were being added to household goods (carpet padding, sofa cushions, electronics, etc.).

Possible Causes

PDBEs leach from our household goods and attach to dust coating the insides of our homes. PBDEs have also been found in several types of cat food, especially seafood-flavored canned foods.

In a small study done by Birnbaum and Dye in 2007, of the 23 cats tested, their blood showed PBDE levels of 20 to 100 times the amount typically found in American adults.

Researchers at the California Department of Toxic Substances Control recently identified more than 70 different compounds that seem to be present in especially high concentrations in hyperthyroid cats.

Clinical Signs

Cats afflicted with hyperthyroidism usually develop a variety of signs that may be subtle at first but that become more severe as the disease progresses. The most common clinical signs of hyperthyroidism are weight loss, increased appetite, and increased thirst and urination. Hyperthyroidism may also cause vomiting, diarrhea, and hyperactivity. The coat of affected cats may appear unkempt, matted, or greasy.

The College of Veterinary Medicine at Cornell University

Our Experience with Feline Hyperthyroidism

Moosie had all the classic symptoms, the first of which I noticed was huge clumps of urine in the litterbox. I suspected him immediately because of his age (16) and because his two sisters are quite a bit smaller. As I began watching him more closely over the coming days, I began to see him visiting his water fountain more often. Moosie had always been a voracious eater, so really no obvious change there, but because I weigh him regularly, I was able to see he was slowly losing weight. I knew it was time for a vet visit.

His diagnosis was fast, a simple blood panel showed an elevated T4 and he was immediately started on methimazole. Overall I was pretty relieved that a simple pill a day treatment would be all that was needed.


While these findings are not definitive, and it’s entirely possible that other factors play a role in the increased prevalence of hyperthyroidism in cats, I think it’s worth keeping in mind. I often think about the cleaning products we use in our homes since our kitty’s walk and lay on these surfaces and then groom ultimately consuming these chemicals, but I never thought there could be harmful chemicals in my furniture, that would not only affect my cats, but also the humans in my home.

Is your cat at risk of developing this disease?  Or does your cat currently have any thyroid disease symptoms?

I have written extensively about cat care, click here for more cat related articles.

K Marie Alto
K Marie Alto

K. Marie is an animal lover, wife, kitty mom, dog auntie, writer, and co-founder of Toe Beans, a proud American family-owned online boutique pet supplies store focused on the improvement of the life of furry family members via pet parent education, better products, and advocacy. She has over 20 years of experience as a pet momma. She loves sharing her personal journey and experience as a pet parent via her blog and Facebook page where she currently has more than 22K followers (@furrytoebeans) and counting :-).

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