Hypothyroidism is a syndrome caused by a lack or insufficiency of thyroxine secretion. The causes of hypothyroidism include: 1) Substantial thyroid lesions, such as thyroiditis, excessive destruction of glandular tissue due to surgery or radioisotope therapy, and abnormal development; 2) Impaired thyroxine synthesis, such as chronic iodine deficiency, chronic antithyroid drug therapy, congenital hypothyroidism, or idiopathic hypothyroidism. congenital disorders of thyroxine synthesis, idiopathic hypothyroidism possibly due to an autoantibody (TSH receptor blocking antibody), etc.; 3. Pituitary or hypothalamic lesions. Depending on the age of onset, they can be classified as ketinopathy and mucinous edema. Clinical manifestations: (1) General manifestations: fear of cold, dry skin with little sweating, roughness, yellowing, coldness, thinning hair, dryness, brittle and cracked nails, fatigue, drowsiness, poor memory, mental retardation, unresponsiveness, mild anemia, weight gain. (2) Special manifestations: pale and waxy face, swollen face, dull gaze, puffy eyelids, indifferent expression, little speech, hoarse speech, slurred speech. (3) Cardiovascular system: slow heart rate, low heart sounds, generalized enlargement of the heart, often accompanied by pericardial effusion, swelling of myocardial fibers, deposition of mucus glycoproteins (PAS staining positive) and interstitial fibrosis after the disease, called hypothyroid cardiomyopathy. (4) Reproductive system: Men may have hypogonadism, delayed sexual maturation, delayed paraphilia, decreased libido, impotence and testicular atrophy. Women may have irregular menstruation, excessive menstrual bleeding or amenorrhea, and are generally infertile. There are effects on fertility in both male and female patients. (5) Muscle and joint system: muscle contraction and relaxation are slow and delayed, muscle pain and stiffness are often felt, bone metabolism is slow, bone formation and resorption are reduced, joints are dysfunctional, there is a feeling of tonicity, aggravated by cold, as in chronic arthritis, and joint cavity effusion is occasionally seen. (6) Digestive system: Patients have decreased appetite, constipation, abdominal distension, and even paralytic intestinal obstruction, and about half of the patients have complete gastric acid deficiency. (7) Endocrine system: impotence in men, excessive menstruation in women, amenorrhea in patients with prolonged illness, low adrenocortical function, and reduced blood and urine cortisol. (8) Psychoneurological system: memory loss, mental retardation, unresponsiveness, drowsiness, depression, and sometimes psychotic manifestations, and in severe cases, the development of suspicious schizophrenia, late dementia, ring hallucinations, or lethargy. (1) To understand the metabolic status of the body: basal metabolic rate (BMR) measurement; blood cholesterol, triglyceride and urinary creatine acid measurement. (2) To understand the level of serum thyroid hormone: serum total T3 (TT3), serum total T4 (TT4), serum free T3 (FT3), serum free T4 (FT4), serum reverse T3 (rT3). (3) Understand the pituitary-thyroid axis regulation: thyroid iodine uptake rate and thyroid suppression test (including T3 suppression test and thyroid tablet suppression test), serum supersensitivity thyroid stimulating hormone (S-TSH), thyrotropin-releasing hormone excitation test (TRH excitation test). (4) Items for understanding thyroid enlargement: B-mode ultrasonography of the thyroid gland and radionuclide imaging of the thyroid gland. (5) Thyroid immunological tests: measurement of thyroid receptor antibodies, such as thyroid-stimulating immunoglobulin assay (TRAb); thyroglobulin antibody assay (TGAb); thyroid microsomal antibody (TMAb) or anti-thyroid peroxide antibody (TPOAb). (6) Items to understand the nature of thyroid lesions (7) Check electrolyte status Classification (clinically classified into 3 types according to age of onset) It is called cretinism. Juvenile hypothyroidism Hypofunction begins in children before they develop is called juvenile hypothyroidism. In adults, hypothyroidism begins in adulthood and is referred to as adult hypothyroidism. In severe cases, the patient may develop non-sunken edema in the subcutaneous tissue, called mucinous edema, or in more severe cases, mucinous edema coma.