According to the severity of clinical manifestations, the following 4 stages are described, which can also be understood as the continuous development process of the disease. The main diagnostic basis of this stage is a mild increase in TSH. 2.Clinical hypothyroidism stage The severity of clinical manifestations and the degree of obviousness and invisibility depend on the slow and rapid onset of the disease, the speed and degree of hormone deficiency, and are related to the variability of individual response to thyroid hormone reduction. Therefore, the diagnosis of clinical hypothyroidism should be based on different degrees of clinical manifestations and increased serum TSH and decreased T4. Clinical hypothyroidism can be divided into mild and severe. The former has mild or atypical symptoms, showing only non-specific symptoms such as weakness, drowsiness, loss of appetite and a feeling of peripheral swelling; while the latter has a light mucinous edema-like presentation. The manifestation is closely related to the cause of the disease. Primary hypothyroidism is insidious and develops slowly, and the symptoms of mucinous edema may appear only after more than 10 years. Secondary hypothyroidism depends on the cause of the disease. For example, in the case of hyperthyroidism with overdose of thyroid medication, the cause is clear, the symptoms are mild, and the patient recovers quickly after treatment. If the disease is caused by surgery or 131I treatment, the onset is not very insidious. Early symptoms start from the 4th week and typical symptoms are common after the 8th week. (1) General manifestations: The earliest symptoms of mucinous edema are lethargy, chilliness, slow speech and movement, low sweating, mental depression, poor appetite, weight gain, body swelling and constipation. Subsequently, there is a systemic “mucus edema-like” typical manifestations: facial performance “indifference”, “dull” and even “idiocy”. Cheeks and eyelids are vainly swollen, the lower eyes are baggy and droopy, and the face is pale and slightly waxy (due to increased carotenoids in the blood). The nose and lips are thickened, the tongue is large and slurred and low, the hair is thin, dry and easy to fall out, and the eyelashes and eyebrows fall out. The skin is rough, dry and thick, with non-depressible mucinous edema and weight gain. Mucinous edema can involve a variety of organs and systems. (2) Psychoneurological manifestations: memory loss, decreased intelligence. Reactivity, drowsiness, depression, and sometimes neurotic manifestations due to anxiety, and severe cases develop into suspicious schizophrenia. In severe cases, dementia, delusions, mydriasis, lethargy or convulsions are associated. When mucin deposition causes cerebellar dysfunction, ataxia, nystagmus, etc. occur. (3) Muscle and joint manifestations: muscle weakness, but also temporary muscle ankylosis, spasm, pain, etc. Occasionally, severe muscle weakness is seen. Chewing muscles, sternocleidomastoid muscles, quadriceps and hand muscles may show progressive muscle atrophy. In a few cases, there is muscle hypertrophy, and pseudohypertrophy occurs in the distal extremities of the limbs. Percussion of the muscles can cause local swelling (“myxomatosis” or “mound” phenomenon). The muscle contraction is followed by delayed relaxation and slow release after clenching the fist. The systolic period of the tendon reflex is normal or prolonged, but the relaxation period is characteristically prolonged, often exceeding 350 ms (normal 240-320 ms), in which the prolonged semi-relaxation time of the Achilles tendon reflex is more pronounced and has important diagnostic value for this disease. Patients with mucinous edema may have associated arthropathy and occasionally joint effusion. Carpal tunnel syndrome occurs due to the accumulation of mucin outside the nerve in the carpal tunnel, with numbness and pain in the fingers and abnormal sensation. (4) Cardiovascular system manifestations: reduced cardiac output, bradycardia, often sinus. The cardiac turbinate is enlarged and the heart sounds are low. Ultrasonography may reveal pericardial effusion, which is usually a high specific gravity plasma exudate. There may also be a pleural or abdominal effusion. In patients with prolonged disease, due to increased blood cholesterol, coronary artery disease is easily complicated, but due to low metabolic rate, myocardial oxygen consumption is reduced, and angina pectoris and heart failure are rare. The diagnosis of hypothyroid heart disease is based on hypothyroidism with one of the following abnormalities: ① large heart; ② arrhythmia; ③ heart failure; ④ extensive ST-T changes on ECG or atrioventricular block of degree 1 or more, which is reduced or recovered after hypothyroidism treatment. Digestive system manifestations. Slow gastrointestinal motility, impaired gastric emptying, atrophy of gastric mucosa, lack of gastric acid, and positive anti-mural cell antibodies in half of the patients. There is often anorexia, bloating, constipation, and in severe cases, paralytic intestinal obstruction or mucinous edematous megacolon. Iron-deficiency anemia or pernicious anemia may result due to gastric acid deficiency or vitamin B12 malabsorption. ⑤ Endocrine system manifestations. Decreased libido, impotence in men, excessive menstruation, prolonged menstruation and infertility are often seen in women. About 1/3 of patients may have breast overflow and even enlarged butterfly saddle, which affects vision. Primary hypothyroidism with autoimmune hypoadrenocorticism and type I diabetes mellitus is called Schmidt syndrome. (6) Mucinous edema coma, seen in severe cases. Triggers are severe physical illness, interruption of TH replacement therapy, cold, infection, surgery and the use of anesthetic and sedative drugs. Clinical manifestations are drowsiness, hypothermia (<35°C), brady respiration, bradycardia, decreased blood pressure, hypoglycemia, hyponatremia, muscle relaxation in the extremities, diminished or absent reflexes, and even coma, shock, and life-threatening cardiac and renal insufficiency.