Hypothyroidism is common in mid to large sized dogs, especially Golden Retrievers. Hypothyroidism refers to a condition in which the thyroid gland does not produce a sufficient amount of thyroid hormone. This hormone plays an important part in regulated the metabolism of the dog, including controlling growth and development. The thyroid gland is made up of two small butterfly-shaped lobes located on the trachea (wind pipe), just below the voice box.
Most cases of hypothyroidism are caused by autoimmune thyroiditis (also known as Hashimoto's Disease). This means the dog's own immune system attacks the thyroid gland. The thyroid gland compensates and secretes more thyroid hormone. However, eventually the thyroid gland can't keep up, and the dog becomes hypothyroid and the symptoms of the condition appear.
Hypothyroidism occurs more often in the mid to large size dog breeds (ie. Golden Retrievers, Labrador Retrievers, Poodles, Miniature Schnauzers, Dobermans, Greyhounds, Irish Setters, Dachshunds, Cocker Spaniels, Airedales, Sheepdogs, Boxers, Akitas, Chows, Clumbers). Spayed females seem to be affected more than unspayed females, but generally affects female and males evenly. Hypothyroidism usually appears between the ages of 2 and 6.
Hypothyroidism is a serious condition and it requires hormonal supplementation prescribed by a vet. However, after the dog begins receiving hormonal supplementation, a full and normal life should be expected, and the dog will be mostly symptom free. Without hormonal supplement, death can result. Because the thyroid gland regulates metabolism, without it the heart rate and breathing will slow, blood flow to the brain is reduced, seizures can occur, leading to eventual death.
What are the signs and symptoms?
Signs of hypothyroidism may include:
- hair loss - rat tail, dry and brittle coat
- seborrea
- bacterial skin infecions
- excessive skin pigmentation
- lethargy
- obesity
- muscle and nerve weakness
- slow heart rate
- reproductive disorders - failure for females to go into heat, male infertility
- mental dullness
- lethargy
- cold intolerance
- seizures
- severe behavioural changes - unprovoked aggression, head tilt, seizures, anxiety, compulsivity
How is hypothyroidism diagnosed?
There are a selection of laboratory tests that can be conducted on a blood sample from your dog.
Full Thyroid Panel: T3, T4, free T3, free T4, T3 and T4 auto antibodies, plus thyroglobulin auto antibody and TSH - gives the absolute best picture of the condition of a dog's thyroid function.
T4 Test: the most commonly used test, gives a meaningful result of thyroid levels. A dog with hypothyroidism will have a lower level of the T4 hormone. Not all dogs with a low level of T4 will have hypothyroidism though. If a low level is reported, then the vet will probably run another test - either the T3 test or the TSH test.
Thyroid Stimulating Hormone (TSH): helps determine if the thyroid gland or the pituitary gland which controls the thyroid gland is the cause of the hypothyroidism. A blood sample will be taken to test the thyroid hormone amounts in the blood, and then a Thyroid Stimulating Hormone (TSH) will be injected into the dog's vein. Six hours later, another blood test is conducted to test the level of T4. If the dog has hypothyroidism, there will be no increase in thyroid hormone levels, even with the TSH injection. This test is expensive and is not used as commonly as it once was.
Thyroglobulin Autoantibodies (TgAA): tests for evidence of immune attack of the thyroid. This procedure is an indication of the presence of the autoimmune process in the dog's thyroid.
In my personal opinion, having a dog who was hypothyroid, I find the results of the tests as nothing more than a guideline. Surf required a higher dosage that her T4 results indicate. This resulted in much frustration between me and a vet. She was only doing what was natural- basing her dosage on the lab results, but living with Surf, I knew when her levels are too high or too low. When she wasn't receiving enough supplementation, she was extremely lethargic, the end of her tail went bald, and she gained weight on the most minimal diet. Once when the dosage was too high, she was hyper, awake at night, panted a lot, and had the coat of a husky. The vet wanted her on one .3 dose a day, but she did much better on a .8 dosage once a day with our new vet.
How is hypothyroidism treated?
After a hypothyroidism diagnosis is made, the dog must receive hormonal supplementation in pill form, once or twice a day. Within 4 to 6 weeks, the symptoms of hypothyroidism should begin to reverse. Hair and skin problems could take several months to return to a healthy condition.
Routine blood tests will need to be conducted over the life of the dog to make sure the level of hormonal supplementation is still adequate.
Is hypothyroidism a genetic disorder?
Thyroid conditions are serious. Although thyroid level pre-screening is not required by the Golden Retriever Club of Canada, or the Golden Retriever Club of America before breeding, many think strongly that it should be. John Cargill MA, MBA, MS and Susan Thorpe Vargas MS, Ph.D. are two such professionals who take a hard stance on the importance of thyroid prescreening:
"If you have not tested your dogs for proper thyroid function, you have no business breeding them. Taking the hard line one step further, to breed hypothyroid or untested dogs is unconscionable, unethical and just plain wrongdoing. Without evil intent to mess up the gene pool of your breed, to conduct such breeding is ignorant, or worse yet, stupid if you have already been informed. Yet, we venture to guess that most breedings are without benefit of screening for thyroid function or other genetically transmittable disease." (source)
The attack of the thyroid gland (autoimmune thyroiditis) is undoubtedly genetic, as hypothyroidism is more common in certain dog breeds and within certain lines with a breed. Not every case of hypothyroidism is genetic, however, as a low thyroid can also be caused by low iodine in the dog's food (usually avoidable by feeding a quality diet), surgical removal the thyroid gland due to cancer, or the cause may never be known.Links and Resources:
- Hypothyroidism
- Hypothyroidism Article - written by John Cargil lMA, MBA, MS and Susan Thorpe Vargas MS, Ph.D. - excellent info about Hypothyroidism
- Hypothyroidism or Under-production by the Thyroid Gland - from the Yankee Golden Retriever Rescue club
- Canine Hypothyroidism: Frequently Asked Questions - Diagnosing and Treating Underactive Thyroid Problems in Dogs
- Canine Hypothyroidism and the connection to seizures in dogs
- Thyroid Testing in Dogs - by Karen J. Wolfsheimer D.V.M. Ph.D.
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