Thyroid Problems in Dogs

Clare Deming
Fat Beagle

Canine thyroid problems are common, with acquired hypothyroidism being the most common endocrine disease. However, other thyroid problems can occur, including thyroid cancer or congenital hypothyroidism.

The Thyroid Gland

The thyroid glands are a pair of tiny organs located near the larynx in the neck of your dog. In all mammals, the thyroid plays a vital job in regulating the basal metabolic rate by producing a hormone called thyroxine.

In dogs, several thyroid diseases can occur. These include:

  • Acquired hypothyroidism
  • Congenital hypothyroidism
  • Cancer of the thyroid glands

Thyroid function can also be affected by other illness, certain medications or a few other rare disorders.

Acquired Hypothyroidism

The most common thyroid problem in dogs is acquired hypothyroidism. It comprises more than 95% of thyroid diseases in dogs. There are several things that can cause this disease, but ultimately, acquired hypothyroidism results in decreased thyroid hormone production. Symptoms of acquired hypothyroidism include:

  • Mental dullness
  • Lethargy
  • Exercise intolerance
  • Weight gain
  • Heat-seeking behavior
  • Hair loss or thinning
  • Dry hair coat
  • Skin infections

Less commonly, some dogs can develop neurologic symptoms secondary to hypothyroidism. These can include:

  • Neuropathy
  • Vertigo
  • Laryngeal paralysis
  • Facial nerve paralysis

Acquired hypothyroidism is most commonly diagnosed in middle-aged and older dogs, from four to ten years of age. It is usually diagnosed in medium and large-breed dogs, including the following breeds:

  • Golden retriever
  • Doberman pinscher
  • Irish setter
  • Miniature schnauzer
  • Dachshund
  • Cocker spaniel
  • Airedale terrier

Diagnosis and Treatment

Your veterinarian can diagnose acquired hypothyroidism by using a combination of blood tests. The total T4 level is usually assessed first. If your vet suspects hypothyroidism, additional levels may be measured. These can include:

  • Free T4
  • Thyroid stimulating hormone (TSH)
  • Anti-thyroglobulin antibodies

Interpretation of thyroid levels is not always easy because these blood tests are affected by other medical conditions. If your veterinarian diagnoses acquired hypothyroidism in your dog, treatment is straightforward and consists of an oral thyroid supplement. Your dog will have to take the supplement for the rest of his life. In addition, your dog will need an occasional follow-up blood test to make sure that adequate levels are achieved.

Rarely, a severe state in untreated hypothyroidism can occur, called a myxedema coma. This causes swelling of the face, stupor, coma, low body temperature, low heart rate, and low blood pressure. Immediate treatment in the hospital is required.

Congenital Hypothyroidism

Congenital hypothyroidism occurs when a dog is born without a functional thyroid gland. Two forms exist - one in which the thyroid gland is atrophied, and another in which a goiter is present. (A goiter is a swelling in the neck that can become quite large.) Congenital hypothyroidism is found in puppies, usually evident by three to eight weeks of age. Symptoms include:

  • Slow growth
  • Abnormal body proportions
  • Mental dullness
  • Weak suckling reflex
  • Low heart rate
  • Low body temperature
  • Delayed tooth eruption
  • Dry skin and poor hair growth

Diagnosis and Treatment

The diagnosis of congenital hypothyroidism in dogs is similar to that for acquired hypothyroidism. Your vet may order blood tests to measure the levels of thyroid hormones. Treatment requires oral supplementation with a thyroid hormone supplement. This should be started quickly to try to prevent ongoing delays in mental development.

Thyroid Tumors

Overweight inactive dog

In older dogs, usually those between 9 and 11 years of age, thyroid tumors can develop. While thyroid tumors are almost always cancerous, overall thyroid cancer is rare in dogs. One-third of thyroid cancers in dogs will have already spread to other parts of the body by the time they are diagnosed. Occasionally, thyroid tumors in dogs can produce excessive thyroid hormones. Symptoms of a thyroid tumor include:

  • A lump in the neck
  • Change in voice or bark
  • Difficulty breathing
  • Difficulty swallowing
  • Coughing
  • Facial swelling

In dogs where excessive thyroid hormones are produced, additional symptoms can include:

  • Increased appetite
  • Increased thirst
  • Muscle wasting and weight loss

Diagnosis and Treatment

If your veterinarian suspects that your dog may have a thyroid tumor, a surgical biopsy is usually required to confirm the diagnosis. Often, preliminary tests will be done before this. These can include:

  • An aspirate (or needle biopsy)
  • Blood tests
  • Chest x-rays
  • Ultrasound of the neck

A CT scan or MRI can be performed to help assess the extent of the tumor and to identify involvement of adjacent structures in the neck.

The treatment options for thyroid cancer will vary depending on the size and extent of the tumor, and on whether it has spread through the body at the time of diagnosis. Some of the treatments can include:

  • Surgery
  • Radiation therapy
  • Chemotherapy
  • High-dose radioactive iodine therapy

If the thyroid tumor is small and can be surgically removed, some dogs can live an average of three years after diagnosis. Survival times for those dogs with larger tumors or those that have spread through the body can range from three months to one or two years.

Home Treatment Options

Unfortunately, there are no proven ways to identify canine thyroid problems at home. Many dogs may show symptoms that mimic hypothyroidism as they age, but this is often part of the normal aging process. Blood tests are necessary to determine if your dog truly has acquired hypothyroidism.

Treatment of hypothyroidism is most likely to succeed by using a well-known brand of a thyroid supplement as prescribed by your vet. In a few special cases, natural thyroid supplements for people can be used, but make sure to work with your vet if considering these treatments as doses for dogs are vastly different from those for people. Over-the-counter thyroid support products are available for dogs, but these do not contain thyroid hormones and there is no evidence that they help correct low thyroid function in dogs.

For any dog in which congenital hypothyroidism or a thyroid tumor are suspected, prompt diagnosis and treatment by your vet are required for the best outcome.

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Thyroid Problems in Dogs