Also known as hypothyroidism, it is a syndrome caused by insufficient synthesis, secretion, or biological effects of thyroid hormones. Its characteristic feature is a reduced metabolic rate in the body, with severe cases potentially leading to myxedema. Depending on age, it is classified into cretinism (occurring during the fetal or neonatal period with intellectual and physical developmental disorders), adult hypothyroidism (primarily characterized by myxedema), and juvenile hypothyroidism (intermediate between cretinism and adult hypothyroidism). Based on the site of onset, it is categorized into primary hypothyroidism, pituitary hypothyroidism, hypothalamic hypothyroidism, and thyroid hormone resistance. Primary hypothyroidism accounts for approximately 90–95% of cases, and this section focuses on adult hypothyroidism.

bubble_chart Diagnosis

1. Medical History and Symptoms:

The onset is slow, with early symptoms including lack of strength, fatigue, weight gain, and cold intolerance. Later, drowsiness, sluggish reactions, a low and hoarse voice, facial puffiness, dry and rough skin, hair loss, abdominal distension and fullness, constipation, a sallow complexion, decreased libido, infertility/infertility, and menstrual disorders may occur.

2. Physical Examination Findings:

Rough skin, varying degrees of generalized mucinous edema (most noticeable in the lower limbs), an anemic appearance, a swollen tongue, hoarseness, and in some cases, goiter. Bradycardia, cardiomegaly, and in severe cases, pericardial effusion or even pleural and peritoneal effusions may be present.

3. Auxiliary Examinations:

(1) Serum TT3, TT4, FT3, FT4, and rT3 levels are all decreased, with T4 dropping more significantly than T3. Thyroid-specific antibodies such as TmAb and TGAb may be elevated. In primary hypothyroidism, TSH is elevated, whereas in pituitary or hypothalamic hypothyroidism, TSH does not rise. The TSH and TRH stimulation tests help differentiate primary, pituitary, and hypothalamic hypothyroidism. Blood cholesterol and triglyceride levels are often elevated.

(3) ECG shows sinus bradycardia.

(4) Chest X-ray may reveal cardiomegaly, and some patients may have pleural effusions.

4. Differential Diagnosis:

Should be distinguished from renal edema, anemia, and congestive heart failure. Based on rT3 and the patient’s primary disease presentation, differentiate from low T3 syndrome. Hypothyroid symptoms and milk regurgitation symptoms should be distinguished from prolactinoma.

bubble_chart Treatment Measures

Hypothyroidism in adults is treated with thyroid hormone replacement therapy. Start with a small dose, and the minimal dose required to bring TSH back to normal should be taken long-term as the maintenance dose. For older patients, those with severe conditions, or those with heart disease, the initial dose should be smaller, and the dose increase should be slower. The treatment for secondary hypothyroidism is discussed in the section on hypopituitarism.