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| Hypothyroidism in Dogs |
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What Causes Hypothyroidism?Hypothyroidism occurs when the thyroid gland makes too little thyroid hormone. In the majority of cases, this results from 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 inhibit thyroid hormone levels, as can pituitary disorders. Congenital hypothyroidism or cretinism, in which the thyroid gland is underdeveloped at birth, occurs in dogs but is extremely rare. What Dogs are Most Commonly Affected?Hypothyroidsm generally occurs in middle-aged dogs. Medium- to large-sized breeds are overrepresented. Susceptible breeds include:
What are the Symptoms?Thyroid hormone affects the function of nearly every cell in the body, so the signs of low thyroid levels take on several forms 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 symptoms rather than a single “typical” one. These symptoms might include:
How is it Diagnosed?Your veterinarian will start with a full physical exam and basic lab tests to rule out other major problems. Next come blood tests specific for the thyroid. It sometimes takes a series or combination of tests for your vet to arrive at a diagnosis. Total T4 level. This is the most common screening test. If the thyroid gland is not working properly, this level will be low. However, other diseases and certain drugs can depress blood T4 levels. So if your dog’s Total T4 level is low, another test is often required to confirm the diagnosis. Free T4. Thyroid hormone exists in two forms in the body. The majority is actually bound to blood proteins and is subject to daily fluctuations. A tiny fraction, or Free T4, is the active form that can actually enter cells and affect their function. This blood test is more expensive, but is more accurate, particularly when concurrent illness or medications are likely to affect Total T4 level. TSH. TSH levels usually go very high when the thyroid gland stops working. This is the way hypothyroidism is diagnosed in people. In dogs TSH is somewhat less indicative; however if Total T4 or Free T4 levels are low while TSH levels are high, this is diagnostic for hypothyroidism. TSH Stimulation Test. If your veterinarian suspects hypothyroidism but is unable to confirm it with conventional tests, this is the next step. A veterinarian injects your dog with synthetic human TSH and then draws blood after 6 hours to measure Total T4. In a normal dog, TSH should cause Total T4 levels to rise. In a hypothyroid dog, there is no response. The TSH Stimulation test is the gold standard for diagnosing hypothyroidism, but is usually reserved for difficult cases due to the expense of TSH. Anti-Thyroglobulin Antibodies. This test checks for antibodies against the dog’s own thyroid tissue. When present, these may predict the onset of lymphocytic thyroiditis, the condition that causes most cases of hypothyroidism. 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 medications or 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 and see if symptoms improve. This is becoming a less favored practice as better and more affordable tests become available. What is the Treatment?Hypothyroidism in dogs is easily treated using 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. My Dog Was Diagnosed with Hypothyroidism. What is the Prognosis.The good news is that with proper treatment and monitoring, your dog’s symptoms should improve in days to weeks. She can live with this disorder to a ripe old age. Disclaimer: This website is not intended to replace professional consultation, diagnosis, or treatment by a licensed veterinarian. If you require any veterinary related advice, contact your veterinarian promptly. Information at DogHealth.com is exclusively of a general reference nature. Do not disregard veterinary advice or delay treatment as a result of accessing information at this site. |
Hypothyroidism is a common hormonal condition of dogs. The thyroid gland has two symmetrical lobes and is in your dog’s neck just below the voice box. It 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.