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Dogs, Cats and Hypothyroidism

Hypothyroidism is a hormonal condition that can affect both dogs and cats.

How the Thyroid Can Affect your Dog or Cat’s Health

Hypothyroidism is a hormonal condition that can affect both dogs and cats. This occurs when thyroid hormones are impaired and the secretion of thyroid hormones gradually decreases an animal’s metabolism. It is more common in dogs, but it has the ability to affect cats as well.

The thyroid is an important gland that creates hormones that help regulate an animal’s metabolism and development. It works to manage heart, digestive and muscle function, in addition to bone management and development of the brain.

The gland is located in the neck, close to the trachea. It has two lobes, with each one situated around the trachea. It is managed by the pituitary gland, located at the base of the brain.

What Causes Hypothyroidism

For dogs, more than 95% of hypothyroidism cases are caused by the gradual deterioration of the thyroid gland itself. The thyroid over time becomes unable to produce and secrete enough thyroid hormones.

Another cause may be a tumor of the pituitary gland, which would cause deficiencies of other pituitary hormones. It’s considered very rare for a dog to be born with a thyroid gland that doesn’t develop normally. Puppies with disorders such as pituitary dwarfism can also develop hypothyroidism.

Hypothyroidism often affects mid to large sized breed dogs between the ages of four to ten. Golden Retrievers, Doberman Pinschers, Irish Setters, Miniature Schnauzers, Dachshunds, Cocker Spaniels, and Airedale Terriers are the breeds that are often affected.

It can affect both males and females. In non-neutered male dogs, hypothyroidism may cause various reproductive disturbances, such as a limited libido, shrunken testicles, a low sperm count, and even infertility. Spayed females tend to be at a higher risk of developing hypothyroidism compared to non-spayed females. Non-spayed females may have irregular or nonexistent heat cycles and eventually become infertile. Any litters they have may not fully survive.

Two Specific Causes of Hypothyroidism in Dogs and Cats

There are two diseases which cause the majority of cases of hypothyroidism in dogs and cats. One is lymphocytic thyroiditis. The other is idiopathic thyroid gland atrophy. The remaining five percent of hypothyroidism cases are usually caused by rare diseases, such cancer of the thyroid gland.

Lymphocytic Thyroiditis (aka Autoimmune Thyroiditis)

Lymphocytic thyroiditis is a common immune mediated disease that is the most common cause of hypothyroidism. It’s similar to auto-immune thyroiditis and is associated with more than 50% of cases of canine hypothyroidism. When the immune system believes that the thyroid is showing abnormalities, it goes on the attack. Healthy thyroid tissue gradually deteriorates due to the dog’s own immune system causing inflammation within the glands. The can happen over the course of months or years; it’s often genetic in origin. There is no clear definition as to why this actually happens, but it’s believed that genetics play a major role.

Idiopathic thyroid gland atrophy

There is no definitive information as to the cause of idiopathic thyroid gland atrophy. It’s a condition that is not fully understood, but, it often occurs when fat and connective tissue replaces normal thyroid tissue. This may also be a final stage of autoimmune thyroiditis, which occurs when the immune system attacks the thyroid gland.

How Hypothyroidism Affects Cats

Symptoms in Cats

Hypothyroidism is rarely seen in cats, but, should it occur it can cause a variety of issues including noticeable weight gain. In adult cats, clinical signs associated with advanced or severe hypothyroidism may include:

There is a chance for obesity to develop, as may slight cases of alopecia, but this is rare.

Treating Cats with Hypothyroidism

In most cases, cats that are diagnosed with hypothyroidism will not require any kind of treatment. However, if your cat is showing severe signs, then synthetic hormone supplements may need to be prescribed by your Austin vet. Blood tests may also be required to manage the cat’s hormone levels.

If your cat is suffering from hypothyroidism, they may need a change in diet with limited fat while they recover. Cats normally make a full recovery from this disease.

How Hypothyroidism Affects Dogs

Symptoms in Dogs

Hypothyroidism is most common in dogs between 4 to 10 years old. When a dog’s metabolic rate decreases, it can affect every organ in their body. Most dogs with hypothyroidism will have one or more of these symptoms:

  • weight gain with little change in their appetite
  • lethargy, with no urge to exercise
  • susceptible to cold
  • dry hair with shedding
  • thinning hair
  • dark pigmentations in the skin
  • prevalence of skin and ear infections
  • unable to re-grow hair after clipping
  • high blood cholesterol
  • slow heart rate

These additional abnormalities may also appear:

  • facial skin thickening, which gives them a sad expression
  • nerve issues leading to lameness, foot dragging, coordination issues and head tilting
  • libido loss and infertility in non-neutered males
  • lack of heat periods and infertility in females
  • increased fat deposits in the corneas
  • dry eye, known as keratoconjunctivitis sicca (KCS) based on lack of normal tear production

Diagnosing Hypothyroidism in Dogs

Based on your dog’s symptoms, your Austin veterinarian may perform several blood tests to determine your dog’s thyroid function.

The most common test is a total thyroxin (TT4) level, which is a measurement of the main thyroid hormone in a blood sample. A low level of total thyroxin is suggestive of hypothyroidism. A definitive diagnosis can be made made by conducting a free T4 by equilibrium dialysis (free T4 by ED) or a thyroid panel to help determine the levels of multiple forms of thyroxin. If this test has a low result, then the dog will have hypothyroidism.

Some dogs will have a low TT4 and normal free T4 by ED, which means they do not have hypothyroidism. However, additional tests may be needed based on your pet’s condition.

Dogs with illnesses in addition to thyroid disease that are on specific medications may have low thyroid hormone levels but not hypothyroidism. There are certain drugs that can help to reduce thyroid hormone levels, but be sure to discuiss this with your vet to avoid any potential contraindications:

  • Anti-seizure meds, such as phenobarbital
  • Prednisone and other related steroids
  • non-steroidal anti-inflammatory drugs (NSAIDs)
  • propranolol (a heart medication)
  • clomipramine (a behavior medication)
  • sulfonamide antibiotics

Your vet will evaluate the results of the blood tests. It’s important to note that hypothyroidism in dogs and cats can be difficult to confirm and may require additional testing.

Treating Dogs with Hypothyroidism

What’s positive is that hypothyroidism can be treated with a synthetic hormone called levothyroxine or L-thyroxine. The negative aspect is that the dog will need to take this medication for the rest of his/her life. Levothyroxine is available in a variety of doses, which the vet will determine based on the weight of the dog. Frequent bloodwork will most likely be required to determine if a change in dose is necessary.

If untreated, hypothyroidism can shorten a dog’s life span. Every organ in the body will be affected by the thyroid hormone and its metabolism. Untreated hypothyroidism can lead to high cholesterol, decreased immunity, reduced heart rate, and neuromuscular issues including balance problems, head tilting, and seizures.

As the thyroid gland plays an important role in your pet’s health, it’s important that hypothyroidism be properly treated and controlled. If you have any questions, or if you notice any of these symptoms with your dog or cat, please contact us right away.