Etiopathogenesis of canine hypothyroidism.

Hypothyroidism in dogs usually results from a progressive destruction of the thyroid, associated with either lymphocytic thyroiditis or idiopathic atrophy. Both syndromes seem to occur with approximately equal frequency. Lymphocytic thyroiditis, which resembles Hashimoto's thyroiditis in humans, is probably an autoimmune disease, and patients often show thyroid autoantibody titers in circulation. By contrast, the pathogenesis of idiopathic atrophy is unclear, and the thyroid seems simply replaced by adipose and connective tissue.