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Learning more about what happens if dog hypothyroidism is left untreated may be of interest to owners of dogs recently diagnosed with this condition. 

Hypothyroidism is a condition that develops due to low thyroid hormone levels and manifests with lack of energy, weight gain, and patchy fur loss. 

With proper management, dogs with hypothyroidism can live normally. However, if left untreated, hypothyroidism can be fatal.

In this article, we will talk about hypothyroidism and the risks of leaving the condition untreated. 

We will cover the consequences of low thyroid levels in dogs and what happens if the dog is not treated in a timely manner. We will also discuss the importance of early diagnosis and treatment.

Discovering the Dog's Thyroid Gland 

Located in the neck area (close to the windpipe), the thyroid gland is one of the most important glands in the dog's body. 

The thyroid gland consists of two lobes (one on each side of the windpipe), and its function is regulated by the pituitary gland.

The thyroid gland produces hormones with various functions, from growth control to managing metabolic rates to thermoregulation. In general, there are two main disorders associated with the thyroid gland:

Hypothyroidism – underactive thyroid gland (produces low levels of thyroid hormones), which slows down the metabolism. Hypothyroidism is very common in dogs and rare in cats.

Hyperthyroidism – overactive thyroid gland (produces excess levels of thyroid hormones), which speeds up the metabolism. Hyperthyroidism is rare in dogs, but widespread among cats.

Your dog's thyroid gland plays many important roles. 

Your dog's thyroid gland plays many important roles. 

Causes of Low Thyroid Levels in Dogs 

When it comes to hypothyroidism causes, there are many suspected culprits and factors such as poor dietary choices (raw diets and commercial low-quality dog foods), exposure to chemicals and environmental toxins (pesticides, PCBs, phthalates in dog toys, antibacterial agents), vaccines, choke collars, etc.

However, these suspicions are anecdotal and not scientifically backed up. As for scientific evidence, so far, there are two confirmed and common causes of hypothyroidism in dogs:

Lymphocytic thyroiditis. Lymphocytic thyroiditis is considered to be an immune-mediated disease and probably the most common cause of canine hypothyroidism.

 It develops when the dog's immune system misidentifies the thyroid gland as a threat and starts attacking. The exact mechanism is not very clear, but a congenital component is suspected.

Idiopathic thyroid gland atrophy. As the name suggests, idiopathic thyroid gland atrophy is a poorly understood condition. 

In dogs with this issue, the normal and functional thyroid tissue is gradually replaced by fat tissue. Obviously, the new fat tissue cannot secrete thyroid hormones.

Together lymphocytic thyroiditis and idiopathic thyroid gland atrophy are responsible for 95 percent of hypothyroidism cases. The remaining 5 percent of the cases are due to rare disorders and conditions such as thyroid gland cancer (which is more likely to cause hyper instead of hypothyroidism).

Dogs Predisposed to Hypothyroidism 

Hypothyroidism can develop in all dogs. However, there are some important risk factors. 

For example, hypothyroidism is more common in middle-aged dogs (usually between four and ten years old). Interestingly, the hormonal disorder is more common in spayed females and neutered males than in intact dogs.

The breed is also a predisposing factor. Namely, medium to large breeds is at a higher than average risk of developing hypothyroidism. Commonly affected breeds are:

  • Great Danes
  • Boxers
  • Dachshunds
  • Irish Setters
  • Cocker Spaniels
  • Doberman Pinschers
  • Golden Retrievers
  • Old English Sheepdogs
  • Airedale Terrier
  • Miniature Schnauzer

Once again, these are predisposing factors and statistics. Just because your dog is on the list does not mean it will develop hypothyroidism and vice versa – in the same way, not being on this list does not rule out the possibility of low thyroid hormone levels.

Signs of Hypothyroidism in Dogs 

The main clinical signs and symptoms of hypothyroidism in dogs are due to the reduced metabolic rates. Namely, when the metabolism slows down, all organs and body systems suffer the consequences.

Dogs with hypothyroidism will manifest one or more of these issues:

  • Unexpected weight gain (not associated with increased appetite and food intake)
  • Low energy levels (disinterest in everyday activities and reluctance to move)
  • Cold sensitivity (seeking warm spots, shaking, and shivering)
  • Skin changes (decreased coat quality, excess shedding or patchy hair loss, dark skin pigmentation, stunt hair growth after clipping and shaving)
  • Recurrent ear infections (reddening, discharge, and unpleasant odor)
  • Mental dullness (overall apathy, decreased sensitivity to stimuli, mood swings)
  • Slow heart rate and increased blood cholesterol levels.
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Not every dog with hypothyroidism will show all of the above signs and symptoms. Each dog is different, and variations are possible. Rarely, some dogs may exhibit unusual issues, such as:

  • Tragic facial expression due to thickening of the facial skin
  • Thickening of the skin in high-friction places (armpits, groins)
  • Unusual fat deposits in the eye corneas (small white spots)
  • Dry eyes and irritation due to inadequate tear production
  • Nerve and muscle issues resulting in lack of coordination, head tilts, weight shifting, and non-painful, intermittent lameness
  • Megaesophagus (dilated esophagus) followed by regurgitation
  • Reproductive abnormalities (infertility and loss of libido in males and absent heats and abortions in females).

The telltale signs of hypothyroidism in dogs are sudden weight gain, hair loss, and cold intolerance. However, some dogs may exhibit other rarer signs and symptoms (lameness, regurgitation, eye problems).

If your dog is showing some of these signs and symptoms, you need to call the vet and schedule an appointment. The sooner you spot something is wrong and seek help, the better the outcome.

Diagnosis of Hypothyroidism in Dogs 

Hypothyroidism is diagnosed by measuring the total thyroxin levels (TT4). When suspecting hypothyroidism, the vet will start with a full physical exam and then evaluate TT4 levels.

To reach a definitive diagnosis, the vet will perform a thyroid panel that measures the different thyroxin forms.

 The test results combined with the clinical manifestation are usually enough for the vet to diagnose hypothyroidism.

However, if necessary, based on the dog’s condition and potentially co-existing diseases, the veterinarian may order additional tests and diagnostic procedures.


Treatment of Hypothyroidism in Dogs 

Hypothyroidism is not a curable condition, but it is manageable. 

Dogs with hypothyroidism need thyroid replacement hormones for the rest of their lives. The most popular synthetic replacement comes in the form of oral tablets and is called levothyroxine.

At first, the vet will prescribe a standard levothyroxine dose based on the dog’s body weight. Then, after one month of supplementation, the vet will take a blood sample to check the thyroid hormone levels.

Over time, the dog's sensitivity to hormone replacement can change. Therefore, the thyroid hormone levels should be checked on a regular basis, usually at least every six months. Based on the results, dosage modifications can be made.

It is paramount that you stick to the vet's dosing instructions and use the levothyroxine tablets as instructed. 

This is because giving too much can result in an overdose. Giving your dog too much levothyroxine can cause an inability to sleep, hyperactivity, and increased thirst (and consequently water intake and urination). If giving your dog too much levothyroxine over a prolonged timeframe, significant weight loss is likely to occur.

Levothyroxine is relatively fast-acting and will make your dog visibly better after several weeks of use. At first, the dog's fur loss may worsen, but it will normalize and even start growing after four to six weeks. Weight loss is expected within three months and complete stabilization within six months.

Proper nutrition is important for dogs with hypothyroidism. Dogs with low thyroid levels benefit from nutritionally balanced diets rich in proteins, amino acids, probiotics, antioxidants, fats, carbs, vitamins, and minerals (iodine in particular).

What Happens if Dog Hypothyroidism is Left Untreated?

The expectations depend on how the situation is managed. Dogs with hypothyroidism can lead long and high-quality lives as long as the low thyroid levels are corrected with synthetic supplements. 

While the condition is not reversible, its management is relatively straightforward and ensures an excellent prognosis.

On the other hand, if left untreated, hypothyroidism progresses. The dog will keep on feeling poorly, and its symptoms will worsen. 

Untreated hypothyroidism results in both physical and mental issues. Severe and even fatal complications (heart diseases and nerve damages) are possible.

If your dog is diagnosed with hypothyroidism and prescribed synthetic hormone replacements, you need to be prepared for ongoing costs. The medication itself does not cost much, but the expenses add considering their long-term need.

Life Span of Dogs With Hypothyroidism 

A dog with hypothyroidism can live a long, happy, and symptom-free life as long as the condition is appropriate and timely managed (using synthetic thyroid hormone replacements).

Hypothyroidism is a relatively common hormonal disorder, especially among dogs of certain breeds. Hypothyroidism is a progressive and irreversible condition which if left untreated, can be fatal.

On the bright side, with early diagnosis and a proper management approach, dogs with hypothyroidism can have long and normal lives.

If you suspect your dog has hypothyroidism, it is highly advisable to seek veterinary help as soon as possible. Sometimes, even minor changes in your dog's behavior can indicate underlying issues.

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