1.Primary hypothyroidism (1) Hypothyroidism caused by chronic lymphatic thyroiditis, accounting for the majority of primary hypothyroidism. (2) Medical hypothyroidism (anti-thyroid drugs, radioactive iodine, thyroid surgery). (3) Hypothyroidism caused by postpartum thyroiditis or painless thyroiditis. (4) Endemic iodine deficiency causing hypothyroidism. (5) Hypothyroidism due to hormone synthesis disorder. (6) Congenital thyroid dysplasia. 2.Secondary hypothyroidism Secondary hypothyroidism is caused by a decrease in thyrotropin (TSH) and/or thyrotropin-releasing hormone (TRH) due to pituitary and/or hypothalamic lesions, including Sheehan’s disease, autoimmune pituitary inflammation, pituitary tumors, radiation pituitary inflammation, and tumors, inflammation, degeneration and hemorrhage in the hypothalamus and surrounding tissues. 3. Peripheral hypothyroidism Peripheral hypothyroidism includes thyroid hormone receptor and post-receptor defects.