Etiology and classifcation Primary(thyroid failure) t Hashimoto's thyroiditis t lodide deficiency or excessive Radioactive iodine therapy for gD Subtotal thyroidectomy t Subacute thyroiditis Secondary: pituitary deficit Tertiary: hypothalamic dysfunction Peripheral resistance to thyroid hormoneEtiology and Classifcation Primary(thyroid failure)  Hashimoto’s thyroiditis  Iodide deficiency or excessive  Radioactive iodine therapy for GD  Subtotal thyroidectomy  Subacute thyroiditis Secondary: pituitary deficit Tertiary: hypothalamic dysfunction Peripheral resistance to thyroid hormone