Thyroid Disease in Dogs: HYPOthyroidism

A good friend asked me to expound on this topic. 

It’s a good one too because it can be a bit of a murky diagnosis.  There are many things that need to be taken into account and it's NOT based simply on a blood test.

Most pet owners would love for their dog to have a thyroid issue. Why? Because, unfortunately, the majority of pets are overweight. 

A low thyroid is GENERALLY not the reason however.  Remember, our pets don’t make their own meals, buy or give their own treats or open the refrigerator door and find a midnight snack (for the MOST part !).  

It takes a good 80-90% of the gland to be destroyed to see TRUE dysfunction. 

What do we see in dogs with TRUE thyroid dysfunction?

Most of the signs are generally dermatologic (skin) and a decreased metabolic rate (weight gain, lethargy, etc). There are some less common signs that include neurologic diseases (seizures, etc).  

What blood test do we use?

A good baseline is the T4 level. However, this is more of a screening tool.  There are a lot of other things that can cause this level to be low, even though the dog’s thyroid gland is functioning perfectly normally. We must take this number as part of the BIG PICTURE - what is going on with this dog? - other illnesses? is the dog truly showing any signs of hypothyroidism?, is the animal on any medications that might cause this to be lower than normal (phenobarbital, certain antibiotics in the sulfa class, steroids) ?  

A dog that has an illness that is suppressing it’s thyroid level is termed “euthyroid (normal thyroid) sick syndrome.”  Once that issue is dealt with and the dog is fine, we can recheck the thyroid level. Experts think this is some sort of protective mechanism for the dog. If they are ill with some disease process, their metabolism slowing down may help NOT drain their resources as quickly.

If we do indeed STILL suspect hypothyroidisim, we will want to run a few further tests including a FREE T4 and maybe a TSH (thyroid stimulating hormone level). 

The Free T4 measure what most people think of as the “active” form of the thyroid molecule.   But we must remember that this molecule can also be affected by other illnesses going on in the dog too. 

What if the dog IS hypothyroid?

Then we need to start on a thyorid hormone supplement available through your veterinarian. This is not an expensive drug but it is LIFELONG. Most vets will want a recheck of that T4 or FreeT4 level in 1-2 months, usually at 4-6 hours post pill (this is when peak blood levels are reached).   We can adjust the dosage from there - based on the level and how the dog is doing.

What if it's NOT hypothyroid?

...and your dog is still gaining weight ?  (then very likely he is being overfed - remember if  he is eating 2 pieces of kibble a day and is gaining weight, he's NOT burning those calories off)  ...so back it down, limit treats, and increase exercise or...you may end up needing more info on Wednesday's topic - diabetes.  

... and your dog has skin issues? Well, that could and will likely be a whole week or more in itself.