General Discussion. Autoimmune thyroiditis (AT), also known as Hashimoto's disease, is a chronic inflammatory disorder of the thyroid gland that is caused by abnormal blood antibodies and white blood cells that mistakenly attack and damage healthy thyroid cells.eneral Discussion. Autoimmune thyroiditis (AT), also known as Hashimoto's disease, is a chronic inflammatory disorder of the thyroid gland that is caused by abnormal blood antibodies and white blood cells that mistakenly attack and damage healthy thyroid cells.