What causes hypothyroidism in dogs?
Most cases of hypothyroidism in dogs are acquired in adulthood. Rare cases have been described to occur congenitally. Affected puppies do not grow normally. There are two causes of aquired hypothyroidism lymphocytic thyroiditis and idiopathic atrophy. Lymphocytic thyroiditis is believed to be immune-mediated, where the dog’s own immune system attacks the gland. After a rather prolonged course (up to 3 – 4 years) enough of the gland is destroyed such that it no longer works. There appears to be a genetic predisposition of lymphocytic thyroiditis in certain breeds including borzoi, beagle, doberman, Great Dane, Irish setter, and Old English sheepdog. Lymphocytic thyroiditis appears to be similar to Hashimoto’s thyroiditis in humans, although it’s rarely accompanied by other immune system diseases. Idiopathic thyroid atrophy is the cause of the other half of the cases of acquired hypothyroidism in dogs. Atrophy means that the thyroid cells die and are replaced by fat. Idiopathic means tha
