Hypothyroidism in Dogs: Your Guide to Causes, Symptoms, Treatment, and More

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If your energetic pup starts showing less interest in exercising as they age, it may not be from simply getting older. It could be hypothyroidism.

You've probably heard of hypothyroidism, because it can affect people, too. In fact, some of the symptoms are similar between humans and dogs, like slowing down and gaining weight. But there are differences, too. For example, dogs don't develop goiters like people do.

For a better understanding of how hypothyroidism may impact your pet, we've gathered all the info you need on its symptoms, causes, and treatments.

What is hypothyroidism in dogs?

Hypothyroidism means the thyroid gland isn't making enough thyroid hormone to support the body's functions. When the thyroid doesn't work properly, it affects the adrenal system, the reproductive system, metabolism, and more. Thyroid hormones also impact nearly every cell in the body.

Hypothyroidism is a common, slow-progressing disease. You may not notice the early signs because they're often subtle and can be mistaken for other problems.

Signs and symptoms of hypothyroidism in dogs

Hypothyroidism can cause a wide range of symptoms in dogs, including:

• Fatigue

• Sleeping for long hours

• Dull attitude

• Lack of interest in exercise

• Weight gain without an increase in appetite

• Inability to tolerate the cold

• Dry hair and skin

• Excessive shedding

• Loss or thinning of hair

• Dark coloring in the skin

• Obesity

• Dry, dull coat

• Slower heart rate

• Skin and ear infections

• Slow regrowth of fur after clipping

What causes hypothyroidism in dogs?

A couple of different conditions can cause hypothyroidism.

A dog with a thyroid gland that's been destroyed is said to have primary hypothyroidism, an autoimmune condition.

Either lymphocytic thyroiditis or idiopathic atrophy of the thyroid gland can destroy a dog's thyroid and cause primary hypothyroidism. Lymphocytic thyroiditis occurs when the immune system attacks the thyroid. Idiopathic atrophy happens when fat tissue replaces thyroid tissue.

Secondary hypothyroidism is the inability to release thyroid stimulating hormone (TSH). This prevents the thyroid from providing enough hormones to support your dog's bodily functions.

Primary hypothyroidism is more common than secondary hypothyroidism. But they both cause the same symptoms. Birth defects or tumors can also cause hypothyroidism.

Are some dog breeds more at risk of hypothyroidism?

Hypothyroidism is more common in middle-aged and older dogs. It's also seen more often in middle-sized and large-sized dogs. And certain breeds are more likely to have hypothyroidism. They include:

• Great Danes

• Irish setters

• Boxers

• Doberman pinschers

• Dachshunds

• Golden retrievers

• Tibetan terriers

• English setters

• Dalmatians

• Basenjis

• Rhodesian ridgebacks

• Old English sheepdogs

• Maltese dogs

• Chesapeake Bay retrievers

• Beagles

• Cocker spaniels

• Shetland sheepdogs

• Siberian huskies

• Border collies

• Huskies

• Akitas

How is hypothyroidism in dogs diagnosed?

Your dog's veterinarian will perform a physical exam and thyroid blood testing to make a diagnosis. They'll take any other conditions and medications your dog is taking into consideration.

Diagnostic testing for thyroid hormones can be tricky. That's because the results don't always reflect the true health of the thyroid gland.

For example, a dog with hypothyroidism could have a blood test that shows a normal, functioning thyroid. Or a dog can have low thyroid hormone levels on their blood test, but they don't actually have hypothyroidism. Your vet may need to do more tests to confirm a diagnosis.

Certain medications can also cause low thyroid levels in dogs but not hypothyroidism. These medications include:

• Steroids like prednisone

• Anti-seizure medications like phenobarbital

• Nonsteroidal anti-inflammatory drugs (NSAIDs)

• Sulfa class antibiotics

• Propranolol

• Clomipramine

If thyroid testing is part of your veterinarian's routine blood tests, they may catch unusual thyroid levels during a regular checkup. Or your vet may notice it if you get your dog's blood test done for an unrelated issue, such as checking their liver or kidneys.

How is hypothyroidism in dogs treated?

Hypothyroidism is treated with oral thyroid hormone replacement therapy, a specific type of medication given daily. The most commonly prescribed medication is levothyroxine (Thyro-Tabs Canine, Synthroid).

It may take many months to get the correct dosage of medication. Your veterinarian will prescribe a dosage and have you come back in a few weeks to recheck your dog's blood work. This will tell your vet if the initial dosage is too high, too low, or just right.

If it's too high or your dog is sensitive to the medication, they could experience symptoms such as:

• Having a fast heart rate

• Drinking more water

• Urinating more often

• Losing weight

• Showing a change in attitude

Contact your veterinarian if this happens. Once your dog starts treatment, their energy levels could improve quickly. But other symptoms - like hair loss and dark skin coloring - could take more time to improve.

You should continue monitoring your dog's thyroid levels through blood tests once they start treatment. Your veterinarian will help determine how frequently you should have this done.

What happens if dog hypothyroidism is left untreated?

If left untreated, hypothyroidism can lead to worse symptoms and health complications. Severe hypothyroidism can cause:

• Skin infections

• Ear problems

• Thick skin around the head and face

• Heart problems, such as a slow heart rate

• Balance issues, such as lack of coordination or a head tilt

• High cholesterol

• Changes to the surface of a dog's eyes

• Myxedema coma, a rare complication that leads to life-threatening hypothyroidism symptoms

Consult your veterinarian if you notice any of these signs. Myxedema coma can be fatal. Lethargy could develop into listlessness quickly before the coma occurs.

How long do dogs with hypothyroidism live?

Once your dog starts treatment, the general prognosis for hypothyroidism is good. But there isn't a cure. A dog with the condition will need thyroid hormone medication for the rest of their life.

If your pup's symptoms don't improve with treatment, consult your veterinarian. Your dog could have the wrong diagnosis, or they could have another condition, too.

Frequently asked questions

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