Joey became hypothyroid after receiving radioactive iodine therapy (I-131) for hyperthyroidism in June of 2011. He was our second cat to have this treatment, and his was done at the VCA veterinary Hospital in San Leandro, California. The treatment and hospital stay went well, and it was great to have Joey back home again. The only initial downside was the disposal of the litter waste. Cats' fecal output retains radioactivity for several weeks after the ¹³¹I treatment.

The State of California had passed a law strongly suggesting safe disposal of the litter box droppings of a treated cat for ninety days. Because it was difficult to separate all four cats' droppings, I devised a workable plan. Although it was not required by law, the purpose was to help the plight of the coastal sea otters, who were dying of toxoplasmosis. I'd gladly do everything necessary to save those happy, friendly sea mammals.

Hypertrophic Cardiomyopathy Raise its Ugly Head

The most serious downside occurred in October of 2012 when Joey was diagnosed with the beginning signs of Hypertrophic Cardiomyopathy (HCM), confirmed with an ultrasound. This was not unusual. According to one source, "Eighty-seven percent (87%) of hyperthyroid cats will have some degree of hypertrophic cardiomyopathy, although it is rare for a cat to present with overt heart failure."

I wish I had known these figures when our Bubba turned hypothyroid following his I-131 treatments in early June, 2004 at a clinic in Sacramento, California.

He was treated with thyroxine, a thyroid supplement. He was euthanized on December 6, 2005 at eighteen years old, after a blood clot paralyzed his hind legs. In retrospect, it is entirely possible that he had developed undiagnosed HCM following his I-131 treatment.

Assuming Bubba's condition had been diagnosed as I mentioned above,  our third cat to have Hyperthropic Cardiomyopathy is Billy, 11 years old as of this writing. Billy has never had hyperthyroidism. His HCM is most likely attributed to his background. Adopted at five months old, a scrawny, underweight kitten whom the vet thought was only eight to ten weeks old, Billy grew into a fat, fluffy cat of apparent Maine Coon or Norwegian Forest Cat heritage. Both of those cats are among the breeds whose congenital makeup makes them prone to HCM.

In April of 2013, Billy was found to be diabetic, and during the course of his blood tests and examinations, our veterinarian, Dr. Ladonna Bailey, heard a heart murmur. Her office took X-Rays, which showed  certain abnormalities in Billy's heart, indicative of possible HCM (hypertrophic cardiomyopathy), and he would be scheduled for a echocardiogram in their associate veterinary hospital in an adjoining city. The echocardiogram confirmed  "mild to moderate concentric left ventricular atrophy, with mild left atrial dilation."

 Hypothyroidism is Most Often Caused by Radioactive Iodine Therapy

I mentioned above that Joey was our second cat to have the radioactive iodine therapy. He was also our second cat after Bubba to become hypothyroid after the treatment.

At the time when Bubba received the I-131, it was thought that somewhere between two and five percent of cats receiving that treatment would turn hypothyroid. I have read since that it may be closer to thirty percent or more, although conventional thinking is that it is considered a rare condition on cats. .

Joey's Hypothyroidism Sneaks Up on Us

Joey had several bouts with asthma in 2012 and early 2013. In October of 2013 he had a bout of bronchitis, and during the course of his treatment, it was discovered that he was hypothyroid. He was lethargic, seemed depressed, although he had a good appetite and had gained some weight. Several of these were symptoms of hypothyroidism, according to this article by Pet MD.

Treatment for hypothyrodism is a balancing act. We are giving Joey 5 ml. of tuna-flavored liquid thyroxine from a compounding pharmacy twice daily until his blood tests show that he has the normal amount of thyroid hormone. Then he will be tested regularly, and go back on the medication as needed. Some cats with hypothyroidism will need to be medicated for life. With Joey, we will take it only one day at a time.