There are two main types of canine hypothyroidism, primary and secondary. There also some rarer forms of this condition. The neoplastic and congenital forms of hypothyroidism are frequently breed-specific. Primary hypothyroidism accounts for over 95 percent of all cases and usually occurs between the ages of four and six.
Located on either side of the windpipe in the dog's throat area, the thyroid gland produces hormones responsible for metabolic function. When this gland is not functioning properly, hormone production is disrupted.
Symptoms of Hypothyroidism
- Skin abnormalities, such as dark patches or dry skin
- Hair loss or poor hair coat
- Lethargy, excess sleep
- Weight gain
- Chills, poor cold tolerance
- Slow heart rate
Canine Breeds Most Prone to Hypothyroidism
Any dog-including mixed breeds-can suffer from primary hypothyroidism, but the 10 breeds most susceptible include:
- Golden Retrievers
- Labrador Retrievers
- Cocker Spaniels
- English Bulldogs
- Great Danes
- Doberman Pinschers
Other breeds notably at risk of hypothyroidism include:
- American Staffordshire Terrier
- Siberian Husky
- Border Collie
- Chinese Shar-Pei
- Bernese Mountain Dog
Types of Hypothyroidism
- Secondary hypothyroidism is caused by a tumor encroaching upon the thyroid gland. Fortunately, this form of dog cancer is a somewhat rare condition, but Beagles, Golden Retrievers and Boxers are more likely to develop tumors of this type.
- Neoplastic hypothyroidism causes an abnormal growth or destruction of thyroid tissue and is caused by iodine deficiency. This condition is seen in giant schnauzers and boxers.
- Congenital or juvenile onset hypothyroidism is an inherited condition that is seen in Giant Schnauzers and German Shepherd Dogs. Toy Fox Terriers also carry a gene for congenital hypothyroidism.
Canine Hypothyroid Diagnosis and Treatment
Most forms of hypothyroidism are diagnosed with a blood test. Samples are taken and tested for thyroid hormone concentrations in the blood. There are several tests available and the test results can be somewhat inconclusive. Your veterinarian may want to perform more than one test to obtain an accurate diagnosis.
Primary hypothyroidism is successfully treated with daily medications. Ongoing blood tests will be done to monitor hormone levels. As treatment progresses, the hormone dosages may change.
Treatment of secondary hypothyroidism is also treated with daily medications, combined with treatment of the underlying illness.
The most common form of thyroid hormone replacement is L-thyroxine. Depending upon the manufacturer, it is available in liquid, tablet or chewable form. Most dogs will show improvement within weeks of beginning hormone replacement therapy.