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Hypothyroidism in dogs

Health & Wellbeing

Hypothyroidism is the most common endocrine disorder diagnosed in dogs. An endocrine disorder is a fancy name for a condition that affects your dog’s glands and hormone production.

Hypothyroidism in dogs

Because hormones are the chemical signals that trigger different bodily functions, a disorder like hypothyroidism in dogs can have a knock-on effect, causing dysfunction with other organs and areas of their body. In the case of hypothyroidism, your dog’s metabolism will be greatly affected which will lead to difficulty turning food into energy and problems maintaining a normal weight.

Let’s take a look at what hypothyroidism in dogs is, how it can be treated, and what the outlook is like if your four-legged friend has been diagnosed with this condition.

What is hypothyroidism in dogs?

Hypothyroidism is a condition affecting your dog’s thyroid gland. The thyroid can be found inside your dog’s neck near their voicebox. The gland is butterfly-shaped, and it has two lobes (which resemble the butterfly’s wings,) that sit on either side of your dog’s windpipe.

The thyroid creates hormones that control your dog’s metabolism, which is the process of turning food into energy. In a healthy pooch, the thyroid makes a hormone called “thyroxine” in the perfect amount so that their metabolism is not too fast and not too slow.

If your dog has hypothyroidism, then their body doesn’t make enough thyroxine which causes their metabolism to slow down.

Hypothyroidism itself is not life-threatening, however, it will have a significant impact on your dog’s health and wellbeing. It can lead to a lowered immune system, poor quality skin and fur, persistent skin problems and infections, weight gain, and low energy.

Hypothyroidism in dogs is a long-term condition and an affected dog will have the condition for the rest of their life.

The effects of hypothyroidism

One of the most common results of hypothyroidism is poor skin and fur. Their fur will become dry, dull, and brittle and your dog will probably suffer from excessive shedding. Their skin will also become thick, dry, scaly, and flaky.

This is uncomfortable for your poor pup but it also makes them vulnerable to chronic skin infections because the skin’s barrier, which is their body’s first line of defense, will be broken and let bacteria in.

Low energy and weight gain as a result of hypothyroidism will impact your dog’s activity level, and your pup might seem despondent and stop playing or enjoying walkies. Weight gain will also increase your dog’s risk of secondary conditions such as diabetes and cancer, in addition to increasing the pressure on their joints.

Dogs suffering from hypothyroidism often seem anxious or depressed, so their mood can suffer as well as their physical health.

If left untreated, your dog’s symptoms will become more serious, and they will be at greater risk of secondary illness or infection.

Having a hormone disease such as hypothyroidism means a dog is at higher risk of developing a rare but severe condition called megaesophagus, where a dog’s oesophagus loses the ability to move food down from the mouth and into the stomach. Hypothyroidism has also been linked with causing laryngeal paralysis, which is when the muscles in the larynx become weak and dysfunctional. Hypothyroidism also causes a lowered heart rate, and it has been investigated for links with dilated cardiomyopathy in dogs.

Primary hypothyroidism vs secondary hypothyroidism

The thyroid gland isn’t the only organ involved in the creation of hormones and controlling your dog’s metabolism. The thyroid works in conjunction with a dog’s pituitary gland in the brain. An abnormality or defect in either the thyroid or the pituitary gland could cause hypothyroidism.

Primary hypothyroidism is when a dog’s hypothyroidism is caused by a problem with the thyroid gland itself, and it’s the most common kind of hypothyroidism found in dogs.

Secondary hypothyroidism is caused by an underactive pituitary gland, which isn’t stimulating the thyroid into making hormones. In a healthy dog, the pituitary gland releases a hormone called thyrotropin which essentially tells the thyroid to make thyroxine.

An underactive pituitary gland will not release enough of this hormone, so the thyroid isn’t stimulated into working when it should. This will then lead to an underactive thyroid that doesn’t produce enough hormones for your dog’s metabolism to function correctly.

Regardless of whether your dog has primary or secondary hypothyroidism, the symptoms of their illness will look the same and the treatment and prognosis from your vet will be more or less identical.

Hypothyroidism vs hyperthyroidism

Hypothyroidism is a condition where a dog’s thyroid doesn’t produce enough hormones, which leads to slow metabolism and usually causes weight gain. On the other hand, hyperthyroidism is when the thyroid produces too many hormones, leading to increased metabolism which causes weight loss as well as multiple other symptoms. Out of the two conditions, hypothyroidism is much more common in dogs.

What causes hypothyroidism in dogs?

In most cases, hypothyroidism is caused by either autoimmune thyroiditis (which is also called lymphocytic thyroiditis,) or idiopathic atrophy.

Autoimmune thyroiditis is when a dog’s immune system mistakenly begins to attack the dog’s thyroid as if it were a harmful, foreign particle. This means that your dog’s own immune system will gradually damage or destroy your pooch’s thyroid, lowering its function and efficacy. Autoimmune thyroiditis is believed to cause at least 50% of all cases of hypothyroidism in dogs, and it seems to be an inherited condition that is common in Akitas, Golden Retrievers, and Dobermans.

Idiopathic atrophy of the thyroid simply means that the thyroid gland begins to shrink, decline in effectiveness, or the tissue breaks down without any apparent cause. “Idiopathic” simply means that the illness is spontaneous and the cause is unknown. Idiopathic atrophy is another major cause of hypothyroidism in dogs, but it is much less common than hypothyroidism caused by autoimmune thyroiditis.

In rare cases, trauma to the thyroid or tumours can cause hypothyroidism. If the thyroid is damaged by a severe injury, or your dog develops a tumour or cancer on the gland, then the damage to their thyroid can lead to hypothyroidism.

Are some dogs more at risk of hypothyroidism?

All dogs of any age, size, and breed can develop hypothyroidism. However, it is more common in dog breeds that are medium or larger in size. It’s also much more often found in middle-aged dogs - most dogs will start exhibiting symptoms of illness by the time they are about 4 to 5 years old.

As well as bigger dogs being at greater risk of developing hypothyroidism, there are also many breeds that seem to be more at risk of the condition. Two of the breeds at the highest risk are Golden Retrievers and Dobermans.

Dog breeds prone to hypothyroidism include:

Spaying and neutering seem to have a potential link to a slightly increased risk of hypothyroidism in dogs. However, more study is needed and the reason for this link is currently unknown.

There are some medications for other canine health conditions that can affect thyroid function if they are taken for a long period of time. These include some seizure medications, steroids, and sulfonamides. However the risks are quite low, and your vet will manage your dog’s dosage and duration of treatment to ensure their condition is treated with minimal risk of any further complications like hypothyroidism.

Symptoms of hypothyroidism in dogs

It can sometimes be hard to spot the signs of hypothyroidism in dogs because they often develop slowly over time. However, the most common symptoms include unexplained weight gain or difficulty maintaining a healthy weight, as well as excessive shedding and fur loss.

The symptoms of hypothyroidism in dogs include:

  • Lethargy
  • Weakness
  • Unexplained weight gain
  • Difficulty losing weight
  • Difficulty keeping up on walkies
  • Exercise aversion
  • Excessive shedding
  • Alopecia (fur loss - particularly on their neck, sides, and tail.)
  • Dry, flaky, or scaly skin
  • Patches of darker or black skin
  • Dull, dry fur
  • Recurring or chronic skin infections
  • Chronic ear infections
  • “Tragic” facial expression
  • Shivering
  • Cold intolerance
  • Slow heart rate
  • Coma

There are other signs of hypothyroidism that have been observed, but there is not enough evidence to reliably link them to the condition.

One of these symptoms is aggression, however, many dogs will display behavioural changes if they are suffering from a chronic condition. That’s why it’s important to get your dog checked over by a vet if they start behaving differently or their personality changes.

How can hypothyroidism be prevented?

Hypothyroidism cannot be prevented because most cases are caused by an auto-immune disease or are idiopathic and have no known cause. The only thing you can do to try and help your pooch is to prevent trauma to their neck and thyroid and to keep them in good overall health and fitness

If your pup is a puller on the lead, teaching loose lead walking or walking them on a harness will prevent excess pressure on their neck that could damage their thyroid. The chances of harming the thyroid and causing hypothyroidism through pulling on a collar are still incredibly rare.

Otherwise, making sure your dog gets plenty of exercise and eats a fresh, healthy diet will help them to maintain a normal weight, a strong immune system, and promote normal bodily functions and healthy growth.

Sometimes, your vet might find your dog’s thyroid isn’t working as well as it should but hypothyroidism has not yet occurred. In these cases, they can give your dog iodine and other medications to try and return the thyroid to normal function and prevent the onset of hypothyroidism.

How is hypothyroidism diagnosed in dogs?

Your vet will talk to you about any signs of illness your dog has, and if they suspect your pooch has hypothyroidism they will conduct a blood test to check the amount of thyroxine in their body.

Your vet may need to undertake several tests to check your dog’s thyroid function and to ensure an accurate diagnosis. They might also conduct an overall blood test to see if there is another underlying problem that might be causing your dog’s illness instead of hypothyroidism.

Hypothyroidism is clinically overdiagnosed. This is because there are many conditions that cause similar symptoms that can impact a dog’s thyroid function. It can be difficult to diagnose other conditions reliably, and many other illnesses can still be effectively treated using hypothyroidism medication.

Your vet will continue to take regular blood tests to monitor your dog’s hormone levels and to ensure the dosage of medication is effective. This monitoring will also help to rule out any other issues which might have been causing your dog’s illness.

Treatment for hypothyroidism in dogs

There is no cure for hypothyroidism and your dog will need daily medication to manage their symptoms. The condition is very easy to treat and the medication available is very safe and effective, allowing your pup to live a full and normal life without symptoms or any compromise to their wellbeing.

The treatment for hypothyroidism in dogs will involve your pooch taking a daily pill that contains a man-made version of the thyroid hormone, which will replace the hormones that your dog’s body is missing. These hormones are usually called levothyroxine or sometimes L-thyroxine.

Generally, dogs respond very well to this drug and your dog’s energy levels will improve. Most of their symptoms can disappear in as little as 4-6 weeks from starting treatment. If your pooch has suffered from hair loss as a result of hypothyroidism, it can take a few months for it to grow back. Treatment with levothyroxine on its own is normally enough for a dog to lose weight and return to a more normal body mass, and it has also been shown to improve their kidney function.

Typically, a dog will show no symptoms once they are being treated, and within 6 months they are usually back to being a perfectly happy, healthy dog.

When your pup begins treatment, they’ll need frequent blood tests for a few weeks. This is to monitor the levels of thyroid hormone in their body to make sure they are perfect, as well as to check that the dosage of their medication is effective and working as expected.

Once your vet is happy with the dosage and your dog’s condition seems to be stable, your pooch will only need a blood test every 6 months or once a year, just to keep an eye on their hormone levels. Your dog might need an adjustment to the medication after a while, and these regular tests help your vet to spot any changes to their hormone level and adjust their medication before your dog becomes ill.

Natural treatment for hypothyroidism in dogs

Just as there is no way to prevent hypothyroidism, there are no effective home remedies or natural treatments that can help your dog to recover. There is no natural supplement that can replace the hormones your dog’s body is lacking, which makes medication the only effective treatment for your pooch.

Lifestyle changes won’t fix your dog’s hypothyroidism either, but they can keep your dog healthier overall. Providing plenty of exercise will help to improve your dog’s muscle tone and prevent weight gain. Meanwhile, a healthy diet will help to provide the nourishment your dog needs to maintain a strong immune system and normal bodily functions, such as healthy skin and fur growth.

No amount of exercise or healthy food will treat hypothyroidism, so you must still undertake any medication and treatment as advised by your vet. But by keeping your pup well-fed and active, you can help to support their body and improve their overall health and wellbeing to give them a healthier, longer life.

What happens if I do not treat hypothyroidism?

If you do not treat your dog’s hypothyroidism, they simply won’t get better. Hypothyroidism does not go away and the longer it’s left untreated, the more severe your dog’s symptoms will become and the sicker they will be.

What is the outlook like for a dog with hypothyroidism?

Provided your dog begins treatment for hypothyroidism promptly and keeps up with their daily medication, their outlook is very good. With medication to manage the condition, most dogs will show little to no signs of illness and will live to a normal life expectancy.

Their fur will grow back, their skin will improve, and their energy levels will return to normal. Your dog will usually lose any weight that they gained too and return to a normal body mass once they have started treatment.

Sources
  1. Laryngeal Paralysis in Dogs and Cats MSD, Veterinary Manual, July 2020
  2. Lymphocytic thyroiditis The Veterinary Clinics of North America, Small Animal Practices, 31, (5), 915-933, Sept 2001, doi: 10.1016/s0195-5616(01)50005-4.
  3. Influence of Drugs on Thyroid Function in Dogs Journal of Veterinary Internal Medicine, 17, 2003, 463-473
  4. Four cases of aggression and hypothyroidism in dogs Veterinary Record, Nov 2002, 547-548
  5. Effect of Thyroxine Supplementation on Glomerular Filtration Rate in Hypothyroid Dogs Journal of Veterinary Internal Medicine, 23, (4), June 2009, 844-849, doi.org/10.1111/j.1939-1676.2009.0331.x