Lack energy? Weight gain? Tired all the time? (Your dog, not you.)
These symptoms are commonly linked to a condition called hypothyroidism in dogs, also known as “underactive thyroid glands.”
Happily, hypothyroidism is easily treated — and once a diagnosis is made, it’s not hard to give your dog their bounce back.
In this article, we’ll get to grips with thyroid problems in dogs and cover:
- Dogs vs. Cats: Dogs have underactive thyroids, while those of cats are overactive
- Thyroid Hormone: What happens when there isn’t enough
- The Causes: Why some dogs develop hypothyroidism
- Diagnosis: Pitfalls to avoid
- Treatment: What, how much and when
- Very Rare Indeed: Hyperthyroidism in dogs
Clearing Up Some Confusion
Right away, let’s be clear that cats and dogs are different in many respects — but especially thyroid disease.
Older cats tend to get hyperthyroidism (overactive thyroid glands) leading to weight loss and strangely kitten-like behavior. But their canine cousins err toward hypothyroidism (underactive thyroids) with weight gain and lack of energy.
Now that we’ve got that common stumbling block clear, let’s learn more about the thyroids and thyroid problems in dogs.
The Thyroid Glands
Dogs have 2 thyroid glands. They sit either side of the windpipe, just below the doggy equivalent of the Adam’s apple.
These glands work under instruction from the pituitary gland in the brain. The pituitary gets busy when more thyroid hormone is required and sends a message, via a hormone, to the thyroid glands to increase production.
Thyroid hormone governs the body’s metabolic rate and is like gasoline in a car engine. When you rev the engine, it runs harder and faster. Take your foot off the gas pedal, and not a lot happens.
- So our hyperthyroid cats have oodles of thyroid hormone sloshing around. This is a stimulant that makes the body burn calories much more quickly than is healthy.
- And hypothyroid dogs lack thyroid hormone, so their metabolism runs slow, leading to lack of energy and weight gain.
This sounds straightforward enough, but making a correct diagnosis can be a problem.
As you’ll read, hypothyroidism can be incorrectly diagnosed because thyroid hormone takes a hit if the dog is unwell for some other reason. But I’m getting ahead of myself.
What Can Cause Low Thyroid Levels in Dogs?
This is a great question. True hypothyroidism is due to 1 of 3 reasons:
This is when the puppy is born with underactive thyroids. This, however, is rare.
2. Lymphocytic (or Autoimmune) Thyroiditis
This is inflammation in the thyroid due to attack by the immune system. This is the most common cause of hypothyroidism in dogs.
Don’t be intimidated by the name. “Lymphocytic thyroiditis” is simply a description of what’s happening within the thyroid and translates as “lymphocytes flooding the thyroid and causing inflammation.”
Lymphocytes are white cells found in the immune system. In a case of mistaken identity, the immune system turns against the body’s own thyroid tissue and attacks as if it’s an invading bacteria or infection. This causes inflammation.
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Over time, the inflamed glandular tissue is replaced by scar tissue. Unfortunately, scar tissue is nonfunctional and can’t produce thyroid hormone, so blood levels drop.
Once more than 75% of the thyroid gland is damaged, levels of thyroid hormone become so low that clinical signs develop.
3. Idiopathic Atrophy
Fat replaces active thyroid tissue for reasons that aren’t clearly understood.
However, some dogs often have artificially low levels of thyroid hormone. This doesn’t mean they have underactive thyroids — rather, it is merely a side effect of being ill. When the patient gets better, thyroid levels bounce back up again.
This makes it unsafe to diagnose hypothyroidism in sick patients or when only the levels of thyroid hormone are used to make the call.
This syndrome has a name: “sick thyroid syndrome.”
To avoid making an incorrect diagnosis, the veterinarian chooses the tests carefully and, if necessary, retests thyroid function when the dog is well again.
Dog Breeds Prone to Hypothyroidism
Certain dog breeds seem more at risk of developing hypothyroidism than others. This is interesting, as it implies there may be a genetic factor at play.
Breeds linked to this condition include:
- Golden Retriever
- Doberman Pinscher
- Miniature Schnauzer
- Cocker Spaniel
- Old English Sheepdog
In dogs, hypothyroidism is a disease of young to middle age.
An interesting quirk is that larger breeds tend to develop the condition younger than smaller breeds:
- For example, an Old English Sheepdog or Golden Retriever may show signs from as young as 2–3 years old.
- But smaller dogs such as the Dachshund or Miniature Schnauzer develop symptoms from 6 years onward.
Signs and Symptoms of Hypothyroidism in Dogs
Without enough thyroid hormone to pep up the metabolism, things run slow — very slow. From skin to digestion, the reproductive cycle to tear fluid production, all body systems get sluggish.
Many times it’s as if the dog is aging prematurely: The dog no longer wants to go for walks and prefers to sleep by the fire. They gain weight, and their coat becomes dull and starts to thin.
Part of the problem is that these changes appear gradually, which makes them harder to spot. The dog doesn’t go from bouncing around to a couch potato overnight, and many people just accept this gradual change as part of their dog aging.
Of the outward signs of hypothyroidism, the skin is perhaps the easiest to spot. The effect of thyroid hormone is so widespread, and here are just some examples of what you might see:
- A dull dry coat where the hairs pluck out easily
- Heavy shedding leading to a thinning coat
- The hair loss progresses with matching bald patches on either side of the body
- Those bald patches become hyperpigmented, and the skin darkens a few shades
- If the coat is clipped, the hair fails to grow back
- Hair loss occurs on the tail, so it starts to look like a “rat’s tail”
- The skin feels greasy and is often flaky
- The skin on the face is subtly swollen, giving the dog a “tragic” expression
Other miscellaneous and seemingly random changes can occur, including:
- Feeling cold and seeking heat
- Harsh breathing due to laryngeal problems
- Shrinking testicles
- Enlarged nipples
- Dry eye
Unfortunately, none of these signs in themselves are enough to diagnose hypothyroidism. To do so requires blood tests.
Making a Diagnosis of Hypothyroidism
What could be simpler? Simply measure how much thyroid hormone is in the bloodstream, right?
Remember “sick thyroid syndrome?” If the dog is sick for some other reason, then levels of thyroid hormone drop as a result. These dogs don’t need thyroid medication — they need their underlying problem sorted out. When this is corrected, those thyroid levels pop right back up.
When your vet is strongly suspicious of hypothyroidism, they check out both the levels of thyroid hormone and the levels of thyroid stimulating hormone (TSH). When TSH is high but thyroid is low, this indicates hypothyroidism.
Indeed, there are several blood tests that will reach an accurate diagnosis with the take-home message that measuring thyroid hormone is not reliable.
What Happens If Hypothyroidism Is Not Treated?
Is hypothyroidism in dogs fatal? No, but it has a big impact on quality of life.
The dog lacks energy, which means they aren’t interested in playing or going for walks. They don’t take part in family life, which is sad to see, and everything seems an effort.
In addition, they often have bad skin, which is sore or itchy, and the dog doesn’t look great. They may also suffer from uncomfortable conditions such as constipation, and their immune system is more sluggish, so they pick up infection easily.
In a few rare cases, hypothyroidism can interfere with heart function. This can be more dangerous as it paves the way for heart failure or a heart attack.
Hypothyroidism in dogs can be treated but not cured.
Once a diagnosis is made, a simple tablet, which is a supplement of artificial thyroid hormone, gets them back on an even keel.
The dose is usually between 10–20 mg for each kg of the dog’s body weight. This is given twice a day by mouth. For example, a 30 kg Labrador Retriever would take 300–600 mcg twice a day.
The vet may well start on the lowest dose and then recheck blood levels. This is to be sure the dog isn’t given too much, which causes a whole new set of problems (think of hyperthyroidism in cats).
Many people report seeing an improvement in their dog’s mood within as little as 1 week of starting therapy, while it takes a little longer, 4–6 weeks, for hair to start growing back.
And these improvements carry on, with it taking as much as 6 months before all the benefits are seen.
In the video below, Dr. Patrick McHale, DVM, talks more about the symptoms and treatment of hypothyroidism in dogs:
Very Rare: Hyperthyroidism in Dogs
I briefly mentioned hyperthyroidism as being rare in dogs.
Sadly, when it does happen, it’s usually the result of a tumor of the thyroid gland.
Another circumstance is those dogs who are misdiagnosed with hypothyroidism and given a thyroid supplement they don’t need. This can also result in hyperthyroidism, the symptoms of which are:
- Increased thirst and peeing
- Weight loss
- Agitation and restlessness
- Racing heart
Hypothyroidism in Dogs in a Nutshell
Hypothyroidism is a tantalizing condition. It can be tricky to diagnose, but, once identified, it’s easy to treat.
Simply taking a daily pill will give your dog their bounce back.
Just be patient with the vet, because the signs are vague and different tests may be necessary to avoid jumping to the wrong conclusion. But it will be worth it in the end, as your pet goes from an “aging” dog back to their puppyish ways.
- Peterson, Mark E., DVM, DACVIM. “Hypothyroidism.” Merck Veterinary Manual. https://www.msdvetmanual.com/endocrine-system/the-thyroid-gland/hypothyroidism.
- Williams, Krista, DVM, and Ernest Ward, DVM. “Hypothyroidism in Dogs.” VCA Hospitals. 2019. https://vcahospitals.com/know-your-pet/hypothyroidism-in-dogs.
- Scott-Moncrieff, J. Catharine, VetMB, MRCVS, DACVIM, DECVIM, DSAM. “Diagnosis and Treatment of Canine Hypothyroidism and Thyroiditis (Proceedings).” dvm360. Aug. 1, 2011. http://veterinarycalendar.dvm360.com/diagnosis-and-treatment-canine-hypothyroidism-and-thyroiditis-proceedings.
- Huisinga, Elke, DVM. “Diagnostic Update: Hypothyroidism in Dogs.” Idexx Laboratories. 2016. https://www.idexx.eu/globalassets/documents/country-specific/nordic/1509042-0216-uk-du-hypothyroidism-dog.pdf.