Hypothyroidism, or having a low or under-performing thyroid gland, seems to be the one disease pet owners wish for. I can’t tell you haw many overweight/obese dogs I see that the owners want me to test them for low thyroid. It can’t be that he’s fed too much, or never exercises. No, we want to blame the thyroid, and then get an easy fix. The vast majority of these owners get the following report from me: “I regret to inform you that your dog is… perfectly healthy.” They are bummed because they were hoping a pill could cause weight loss, but it rarely is that simple. (Here’s my article on weight loss).
Yes, hypothyroidism does exist! There are many dogs with low thyroid out there, but not as many as people may think (or hope).
The thyroid hormone regulates the metabolism for the whole body. So when the gland is not producing enough thyroid hormone, the metabolism slows. This results in the symptom everyone thinks of: weight gain. It can also result in hair loss, or a thin, poor haircoat. Thee dogs often feel cold and can’t ever seem to get warm. They may seem to lack energy. Everything is just sslloooww. In severe cases, dogs with little to no thyroid hormone can actually go into a coma and require emergency intervention!
How do we diagnose it? That is somewhat simple – we check the blood for the levels of thyroid hormone in the body, called Total T4. If a dog is looking like the textbook hypothyroid dog (fat, bald, slow moving), and the T4 is low, we’ll have our diagnosis. Other times, it is not that simple.
There is another syndrome that can imitate hypothyroidism on bloodwork that can make life more complicated for veterinarians. This is called euthyroid sick. Basically, if an animal has something else going on (could range from an ear infection to cancer, and everything in between!) it can cause their thyroid level to look a little low on the bloodwork, when it actually is fine.
So how do we know if the thyroid is actually low or just faking? We can measure an additional hormone called TSH: Thyroid Stimulating Hormone. This is the hormone that goes from the brain to the thyroid gland, telling it to produce more thyroid hormone. When a dog is hypothyroid, the thyroid gland is asleep at the wheel. The brain sees this, and sends more TSH to the thyroid gland telling it to wake up and produce thyroid hormone! Thing is, the thyroid gland isn’t listening. So the TSH level in hypothyroid dogs will be high, because the brain is trying to do its part! If a dog is euthyroid sick, the TSH will be normal. This is because the brain knows the actual thyroid level circulating in the body is OK, so it can relax.
Some hypothyroid dogs have other changes appearing on their blood panels as well. Cholesterol may be elevated, and some severely obese and hypothyroid dogs can see an increase in liver enzymes. These typically go back down to normal once we start treatment. If they don’t, we might want to make sure nothing else is going on.
So your dog has a low thyroid. What now? Treatment is simple. Most dogs are treated with a small pill twice a day, for life. The medication is generally affordable, and the pills are very tiny, making it a breeze to get your dog to take it.
As your dog loses weight, your veterinarian may need to adjust the dose of the medication. We typically check the thyroid level mid-day, between the two doses, to make sure the medication dose is not too high, not too low. Once we get them on the right dose, we’ll check them every 6-12 months to make sure nothing changes.
Bottom line – hypothyroidism is readily diagnosable and treatable!
And no, the majority of obese dogs are not hypothyroid, much to their owner’s disappointment.