Hypothyroidism in Dogs


Hypothyroidism is a common hormonal condition of dogs. The thyroid gland has two symmetrical lobes, and it is in your dog's neck just below his voice box. This important gland produces thyroid hormone, which is like a volume control for your dog's metabolism. Thyroid hormone regulates the energy level in almost every cell in the body. What happens in the thyroid affects your dog's entire system.

What Causes Canine Hypothyroidism?

Hypothyroidism occurs when the thyroid gland doesn't make enough thyroid hormone. In the majority of cases, this is the result of the destruction of thyroid cells by the dog's own immune system, a condition called lymphocytic thyroiditis. Other causes of hypothyroidism include thyroid atrophy or, less commonly, thyroid cancer. Certain drugs or other diseases can also inhibit thyroid hormone levels.

Thyroid hormone levels are regulated by the pituitary gland in the brain, so disorders affecting this gland can also result in hypothyroidism. Congenital hypothyroidism, or cretinism, in which the thyroid gland is underdeveloped at birth, occurs in dogs but is extremely rare.

Which Dogs Are Most Commonly Affected by Hypothyroidism?

Hypothyroidism generally occurs in middle-aged dogs. Medium- to large-sized breeds seem to be affected more often. Breeds in which hypothyroidism occurs commonly include:

What Are the Signs of Hypothyroidism in Dogs?

Thyroid hormone affects the function of nearly every cell in the body, so the signs of low thyroid levels can be vague and mimic many different diseases. You may simply notice that your dog is "aging" or "slowing down." Your veterinarian looks at the overall pattern of signs rather than a single "typical" one. These signs might include:

How Is Hypothyroidism in Dogs Diagnosed?

Your veterinarian will start with a full physical examination and basic lab tests to rule out other major problems that may be causing your dog's signs. Next come blood tests specific for thyroid function. It sometimes takes a series or combination of tests for your vet to arrive at a diagnosis of hypothyroidism. Some tests that your veterinarian may order include:

My Dog's Thyroid Results Were "Equivocal." What Happens Now?

Equivocal results are common, either because the disease is in an early phase, or because of the use of medications or the presence of concurrent illness. When this happens, your veterinarian may choose to monitor your dog every 3-6 months until the disease is more easily detected. Some veterinarians choose to treat for hypothyroidism and see if the signs improve. This is becoming a less favored practice as better and more affordable tests become available.

What Is the Treatment for Canine Hypothyroidism?

Hypothyroidism in dogs is easily treated using a synthetic thyroid hormone called levothyroxine. This is administered as a once- or twice-daily pill. Your vet starts with a standard dose based on your dog's weight. Regular blood tests and occasional dose adjustments are required to keep thyroid levels in control. Levothyroxine is safe and very effective. Hypothyroid dogs must be treated for life.

What Is the Prognosis for a Dog Diagnosed with Hypothyroidism?

The good news is that, with proper treatment and monitoring, your dog's signs should improve in days to weeks. She can live with this disorder to a ripe old age.

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