HYPOTHYROIDISM IN THE SIBERIAN HUSKY

Hypothyroidism is an endocrine disorder associated with low circulating thyroid hormone levels. It is common knowledge that low thyroid levels can cause reproductive failures, poor hair coats, lethargy, and weight gain in dogs. Other symptoms of this condition, which are being reported with increasing frequency include chronic ear infections, allergic dermatitis, pyoderma, seborrhea, cardiac arrhythmias, seizures, head tilts, instability of the limbs, laryngeal paralysis, prolonged false pregnancy, behavioral changes, and prolonged estrual bleeding. The following information will discuss hypothyroidism in more detail

How common is hypothyroidism in the Siberian Husky?
Michigan State University Animal Health Diagnostic Laboratory released a current study concerning thyroid disease in the Working Breeds of dogs. The results of this study are alarming. The Akita, Boxer, and Siberian Husky were over-represented for this disorder. The Siberian Husky had 13.5% of the blood samples positive for autoimmune thyroid disease which is higher than the all breed average and the numbers are statistically significant. A total of 1292 blood samples were collected from Siberians which included samples submitted to test for thyroid disease for breeding purposes and samples submitted by veterinarians to test for thyroid disease. Based upon the results of this and other studies, a recommendation was made by Michigan State University that all breeding Siberians be tested for thyroid disease.

What are the different types of thyroid disease in dogs?
There are three main classifications of hypothyroidism in the canine population. The first type is congenital or juvenile onset of hypothyroidism. Most dogs undiagnosed with this condition die before weaning. The puppies that survive will have dwarfism, subnormal mentality, impaired growth of the skeletal system, and a multitude of other medical problems. Treatment with thyroid supplementation must be started within the first few weeks of life to preserve normal intelligence and behavior.

The second type of hypothyroidism is secondary hypothyroidism, which is rare in dogs. This condition is caused by a deficiency of thyroid stimulating hormone (TSH) due to pituitary gland abnormalities. The third type of hypothyroidism, called primary hypothyroidism, is the most common type of thyroid disease in the dog. This will be the topic of discussion for the rest of this article.

What are the causes of primary hypothyroidism in the dog?
Primary hypothyroidism is the most common type of thyroid disease in the dog. The two primary causes of this disorder are autoimmune thyroiditis, a type of thyroid disease whereby antibodies made by the dog are attacking and destroying its own thyroid cells, and idiopathic thyroid disease (cause is unknown). Recent data from the Michigan State University has shown that idiopathic hypothyroidism may be the end result of autoimmune thyroiditis. New studies predict that up to 90% of adult hypothyroidism may be autoimmune in origin. A number of scientific publications have reported the genetic transmission of autoimmune thyroiditis. Blood screening tests have been developed to accurately determine if a bitch or sire is affected with autoimmune thyroid disease.

Blood testing breeding dogs for autoimmune thyroiditis and using only normal dogs in a breeding program should dramatically reduce the incidence of thyroid disease in dogs.

Why should I test my dog or bitch for thyroid disease?
As previously mentioned, over 11% of Siberian Huskies screened for autoimmune thyroiditis are positive. The clinical signs of hypothyroidism can vary, but the skin and reproductive abnormalities can be significant. The following is a listing of clinical signs noted:

• Reproductive (male) - Low libido, low or absent sperm counts, poor semen quality, small testicle size
• Reproductive (female) - Decreased libido, prolonged interestrous interval, silent heats, failure to cycle, small litters, low birth weights of new- borns, abortion, prolonged false pregnancies, inappropriate milk production
• Skin disorders - Dry scaly skin, symmetrical hair loss, changes in haircoat color, seborrhea, increased bacterial and yeast infections, allergies, chronic ear infections
• Neurological - Exercise intolerance, weakness, gait abnormalities, head tilt, myasthenia gravis, megaesophagus, laryngeal paralysis, seizures, altered mental status, behavioral changes
• Other - Anemia, high cholesterol, arrhythmias

At what age should I test my dog for thyroid disease?
Autoimmune thyroiditis has a variable onset, but is usually observed in the canine between 1 to 5 years of age. The blood test can detect the disease before the appearance of clinical signs. Dogs negative at two years of age can become positive at 6 years of age. Since the majority of dogs tested have a positive blood test by 4 years of age, annual testing for the disorder for the first four years is recommended followed by testing every other year until the age of 8 years. One single negative blood test will not guarantee that the animal will never develop thyroid disease.

What does the thyroid test analyze?
In 1997, guidelines were established concerning the thyroid testing of breeding dogs. It was agreed that the thyroid test panel should include the following tests: Total thyroxine (T4), Thyroid Stimulating Hormone (TSH), Free T4 by Dialysis, and Thyroglobulin Autoantibody (TgAA). The Orthopedic Foundation for Animals (OFA) started the database for the Canine Thyroid Registry and has certified certain laboratories in the country to perform thyroid testing. For pet Siberians, a thyroid panel including a Total T4 and a Free T4 by Dialysis can be done by any veterinarian through their reference lab. The veterinarian may or may not include a TSH test in the panel.

How does a dog obtain an OFA Thyroid Registry number?
The purpose of the registry is to identify breeding dogs that are phenotypically normal for thyroid function. Certification is possible for any dog over 1 year of age. A certificate and breed registry number will be issued to all dogs found to have normal thyroid results at 12 months of age. It is recommended that the thyroid tests be repeated at 2,4,6, and 8 years of age. Ages will be used in the certification process since the classification can change as the dog ages and the autoimmune disease progresses.

A dog under 12 months of age can be evaluated but certification will not be available at that age.

Each dog tested is to have a veterinarian ship the blood sample, the OFA application, and the OFA fee to an OFA approved laboratory. The OFA application and list of participating laboratories can be obtained through the OFA by calling 573-442-0418 or by contacting the website at http://www.offa.org

I wish to thank Dr. Ray Nachreiner of Michigan State University for providing me with the current scientific information and reviewing this article.

Kathleen Stryeski, DVM

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