Canine Hypothyroidism
Hypothyroidism is a common hormonal disorder seen in middle-aged to older dogs. This is due to failure of the thyroid gland to produce thyroid hormone. Usually there is immune-mediated destruction of the thyroid gland which leads to the decreased production of hormone. In this case, the disease is known as primary hypothyroidism. The cause of this immune-mediated destruction is usually not determined. Some breeds such as Golden retrievers, Doberman pinschers, Cocker spaniels, Irish setters, Great Danes and Labrador retrievers seem to be predisposed to this disease.
The thyroid glands are paired glands located in the neck which secrete thyroid hormone. Thyroid hormone is important in controlling the metabolic rate of an animal. Dogs with hypothyroidism have a decreased metabolic rate, so they often appear sluggish and have recently gained weight. Other common clinical signs include hair loss and a characteristic "tragic facial expression." Shivering has also been seen in dogs suffering from hypothyroidism.
The diagnosis is relatively straightforward. Your veterinarian will begin by evaluating the thyroid hormone level in your dog's blood. If it is low, and your dog demonstrates the appropriate clinical signs, he most likely suffers from hypothyroidism. There are other confirmatory tests that may be performed to be sure that your dog truly has hypothyroidism. In some cases, the presence of other diseases may lower the thyroid hormone levels in the dog. In this case, if the underlying disease is treated, the hypothyroidism will resolve on its own. This is called secondary hypothyroidism.
In the case of primary hypothyroidism, treatment is very simple - replacement therapy using a supplemental thyroid hormone. This drug is usually administered once or twice a day for the life of the dog. This is a very successful treatment and will usually resolve all clinical signs within a few weeks.