I’ve been opining on feline hyperthyroidism a LOT in the past 18 months or so. It all started with Latifah. Something seemed amiss with her back in January/February 2007, as although her diabetes was well controlled, even went into sporadic remissions, she had a ravenous hunger and her fur/coat wasn’t as smooth and glossy as I’d expect in a cat on an all-wet diet. Bloodwork looked pretty good, but I had this nagging feeling – and she just “felt” hyperthyroid, I’d tell the veterinarians. They’d usually dismiss the idea, saying her T4 values (in her bloodwork) were well within the reference range.
In a conversation with Dr. Hogkins, I noted my misgivings and I got quite the education. T4 values in an older cat (over age ten) should not *just* be in the reference range, but in the lower half to third of the reference range and decreasing over time. Other ailments, such as CRF (kidney disease), IBD (inflammatory bowel disease), etc. deflate T4 values as well as age.
Latifah’s T4 in January 2007 was 2.2, well within the lab’s range of 1 to 4, but it was up from 1.2 in January of 2006. I decided to get her in to a nearby specialty center for a technitium (or scintrigraphic) scan, which enables the imaging veterinarian to see the thyroid glands and any potential tumor causing hyperthyroidism.
I’ll admit, I was fully prepared to be told she was not hyperthyroid and I was off my rocker – but the day of the scan came and I got the call there was significant hyperthyroidism. I opted have her treated via radioactive iodine therapy immediately – and she stayed there five days until the radioactivity reached levels deemed “safe” by the government.
It was only about a month later, in February of 2007, that Omaha had routine bloodwork which showed his T4 value of 3.7. Again, within the lab’s range of 1 to 4, but up significantly from his last test and near the top of the range. We had him scanned, and he was hyperthyroid as well, which we treated with radioactive iodine. The only symptom I can recall was some excessive thirst – I rarely see most of my cats drink water, due to their all-wet diet, but I recall seeing Omaha at the water dish several times.
A year later, March 2008, and I noticed Afer’s T4 was up in her bloodwork. It was only 2.6, within range of 0.5 to 5.8, but up from 1.8 the prior September, and 1.0 the year before that. Afer’s about 20 years old, and has CRF (renal or kidney insufficiency) and a history of IBD (currently controlled by diet). These three factors should result in decreased T4 levels. Again, we got a scan and again it showed significant hyperthyroidism. After a consult with a nephrologist (kidney specialist) we got her radioactive iodine treatment in July of 2008. Her kidney values per bloodwork did worsen a bit post-treatment (as expected) but she looks great overall. (Hyperthyroidism can “mask” some kidney insufficiency.)
The story doesn’t quite end there – Ralphie also had T4 values increased in his last bloodwork and I had him scanned. This time the scan showed only slight hyperthyroidism and we opted to wait and retest in four to six months. I could have opted for a trial of methimazole (Tapazole), the oral or transdermal medication, but with Ralph’s history of anemia and IBD I was not willing to chance the side effects.
The reason I have such a ‘bug in my bonnet’ about hyperthyroidism isn’t just my personal experiences (which so far all had very happy endings). I’ve met some caregivers whose cats show EVERY symptoms of hyperthyroidism, but when I ask if they’ve considered whether their cat may be hyperthyroid they declare that their veterinarian “ruled it out”. When I inquire further, I find out “the T4 values were in range”. T4 VALUES WITHIN REFERENCE RANGE DOES NOT RULE OUT HYPERTHYROIDISM! Cats with untreated hyperthyroidism can suffer hypertension (high blood pressure, which can lead to blindess or stroke) or heart failure. A hyperthyroid cat’s system is in overdrive, causing pressure to all the organs. In one case, the caregiver opted to drive the cat five hours to another imaging center that would do the scan (after a nearby vet school refused to do the scan as T4 values were in range, and suggested she put the cat to sleep) and the cat had significant hyperthryoidism and was treated and is now fine. Another case had a sadder ending where the caregiver consulted specialist after specialist looking for one to help her cat – it was *finally* diagnosed with hyperthyroidism despite it’s bloodwork values – but too late, and the cat lost its life.
I know I’ll be watching my cats’ T4 values like a HAWK.
Discussion of possible causes of hyperthyroidism (including discussion of the pop-top can research and more recent research indicating fire retardants) here
More information on hyperthyroidism available at Feline Outreach: