Fluoride Action Network

Clarifying Hyperactive Thyroid Disease In Cats

Source: DrFoxVet.com | December 11th, 2014

DEAR DR. FOX: I recently read your article in which you said that after radiation for hyperthyroidism in cats, the cat would need continuing medication.

In 2010, my 14-year-old cat developed hyperthyroidism. Our vet said that she could either take medication for the rest of her life or go to Radiocat for a one-time treatment (at a cost of $1,300), after which she would never need treatment for that disease. We opted to do that at Radiocat in Baltimore. She spent four days there. She has been fine for five years, and has never taken medication for that problem again.

I feel that you misled the person who wrote to you. Her cat could have many more years of good health with no need for additional medication. I understand that Radiocat is available in many parts of the country.


Dear C.L.: Thank you for comments and confirmation of the effectiveness of radioactive iodine (RI) treatment for thyroid cancer and hyperthyroidism in cats, giving me the opportunity to clarify my earlier response.

It is actually very rare for cats to need supplemental thyroid hormone medication after the mutated cells in the thyroid gland are selectively destroyed by RI. (That is not the case when put on anti-thyroid drug medication such as methimazole, which is also not without some potentially harmful side effects.) Periodic monitoring of blood thyroid hormone levels following RI treatment is advisable. This treatment is costly, and in all diagnosed cases of hyperthyroidism-associated heart disease, hypertension and age-related kidney disease must also be considered.

Signs of thyroid disease include increased appetite and thirst, weight loss, hyperactivity or apathy (depends on the case), irritability/aggression, excessive grooming, loss of fur on flanks, vomiting and/or diarrhea, panting, heat avoidance and seeking a cool place.

Mixed-breed cats seem more susceptible to the disease; there is a lower incidence in Burmese, Siamese and Persian purebred cats. The risk of this disease increases with age, thus reflecting possible accumulating environmental factors and chronic exposure to goitrogens (thyroid-inhibiting foods). Suspected factors that may disrupt thyroid activity and cause cellular damage and genetic mutation include soy products in many cat foods; erythrosine (red dye No. 3), especially in some canned pet foods; high iodine content; high concentrations of heavy metals and biphenyls in foods containing fish; bisphenol A (BPA) lining in canned foods; external anti-flea medications; and flame-retardant chemicals (polybrominated diphenyl ethers, or PBDEs) in carpets and other in-home materials. PBDEs are found in household dust. It gets into cats’ fur, which they swallow in the process of grooming. Contaminants and additives in municipal tap water, fluoride in particular, given to cats to drink may also be contributory factors to this now-common endocrine disease in older cats.