Most cases of canine hypothyroidism are caused by an immune system mediated inflammation of the thyroid gland. We do not know what causes this inflammation to occur in a particular dog, only that it decreases thyroid hormone production. This disease can occur in any age or breed of dog, but is most commonly seen in middle-aged and older dogs. Most of the clinical signs of hypothyroidism involve the skin, haircoat, and overall body condition. Hair loss is common, and often occurs in a symmetric pattern over the animal's trunk.
Hypothyroid animals are often overweight, sometimes markedly so.
In addition, most owners report that the dog seems less active, or listless at home. In our practice, we see canine hypothyroidism most frequently in Dachshunds, Cocker Spaniels, Pomeranians, and Golden Retrievers. Diagnosis of hypothyroidism relies on clinical signs and measuring blood levels of thyroxine and thyroid-stimulating hormone. The treatment of canine hypothyroidism is straightforward. Supplemental thyroxine is administered orally to the dog, usually twice daily.