Hypothyroidism, also known as hypothyroidism, is a group of endocrine disorders caused by insufficient synthesis, secretion or biological effects of thyroid hormones. Symptoms include fatigue, drowsiness, fear of cold, constipation, memory loss, difficulty concentrating, rough skin, abnormal weight gain, etc. Women also have symptoms of excessive menstruation and prolonged menstrual periods. Clinical classification: cretinism, juvenile hypothyroidism, adult hypothyroidism three categories. Common causes: 1. Abnormal thyroid development: Commonly seen in thyroid deficiency or thyroid hypoplasia, ectopic thyroid gland. Most have a family tendency. 2. Thyroid lesions: Insufficient secretion of thyroid hormones due to thyroid lesions, mainly: ① Chronic lymphocytic thyroiditis as the main cause, producing thyroid antibodies, causing destruction of thyroid follicles, and finally mechanized atrophy, called idiopathic hypothyroidism. (2) Endemic goiter: Impaired synthesis of thyroid hormones due to iodine deficiency, which can eventually develop into hypothyroidism. ③Nodular disease. About 10% of nodules involve the thyroid gland, which can also lead to insufficient synthesis and secretion of thyroid hormones and cause hypothyroidism. ④Spontaneous hypothyroidism in hyperthyroidism: it may be caused by combined autoimmune thyroiditis. 3. Hypothalamic lesions: Hypothalamic hypofunction caused by some reasons may lead to a decrease in thyrotropin-releasing hormone and finally to a decrease in thyrotropin and thyroid hormone. 4, hypopituitary anterior lobe function: due to some reasons such as postpartum pituitary necrosis and atrophy, tumor compression, surgery or radiation injury, various infections and intracranial vascular lesions caused by hypopituitary anterior lobe function, resulting in the reduction of thyrotropin and thyroid hormone secretion.