Hypothyroidism refers to a condition caused by congenital or acquired factors leading to insufficient thyroid hormones and metabolic dysfunction in the body (particularly characterized by a reduced metabolic rate). When it occurs in infancy, it is called cretinism, while in older children or adults, it manifests as myxedema. Congenital causes may include:

1. thyroid agenesis or hypoplasia;
2. disorders in the synthesis, secretion, or utilization of thyroid hormones;
3. maternal factors (such as receiving radioactive iodine therapy during pregnancy);
4. secondary to hypothalamic or pituitary diseases, such as septo-optic dysplasia;
5. iodine deficiency. The first four categories are sporadic, while the fifth is often endemic. Acquired causes may include thyroid surgery, thyroiditis, or radioactive iodine therapy for hyperthyroidism.

bubble_chart Clinical Manifestations

The clinical manifestations vary depending on the timing and severity of thyroid hormone deficiency.

1. Neonatal period: Prolonged physiological jaundice, feeding difficulties, delayed passage of meconium, abdominal distension and fullness, constipation, umbilical hernia, low body temperature, cold extremities, and delayed closure of the posterior fontanel.
2. Infancy and early childhood: Characteristic facial features, including a large head, short and thick neck, flattened nasal bridge, broad nasal wings, and a large tongue often protruding from the mouth. Dry and rough skin, yellowish and sparse hair. Delayed growth and intellectual development, disproportionate body proportions, with a longer trunk and upper body. Low body temperature, slow pulse rate, abdominal distension and fullness, and constipation.
3. Older children: Lack of strength, cold intolerance, myxedema, sluggish reactions, decreased appetite, dry and rough skin, etc. In congenital cases, in addition to the above hypothyroidism symptoms, certain specific manifestations may include: goiter, deafness, pseudohypertrophy of muscles, precocious puberty, hypercalcemia, epileptic seizures, ataxia, Turner syndrome, Down syndrome, etc.

bubble_chart Diagnosis

1. X-ray imaging: Bone age is delayed. X-rays of the knee joint should be taken during the neonatal period, and wrist bone films should be taken for children over 1 year old.
2. Serum T3 and T4 levels are decreased. TSH is elevated in primary cases.
3. Thyroid uptake ¹³¹I curve is flat.
4. Serum cholesterol is increased.
5. Thyroid scan: Can detect congenital absence or ectopic thyroid.
6. Basal metabolic rate is low.

bubble_chart Treatment Measures

Thyroid hormone replacement therapy should be initiated as early as possible. For congenital cases, long-term or even lifelong treatment is required. Delayed treatment often leads to irreversible intellectual and physical developmental delays.

1. Desiccated thyroid tablets: Start with a small dose, then increase the dosage every 1-2 weeks until symptoms disappear and blood tests show normal T3, T4, and TSH levels. Then maintain this dosage long-term, adjusting every 1-2 years, and continue lifelong. The dosages are as shown in Table 9-1.

   Table 9-1 Desiccated Thyroid Tablets for Treating Congenital Hypothyroidism Dose

   Age	Initial Dose (mg/d)	Maintenance Dose (mg/d)
   Under 6 months	5～10	15～30
   ～1 year	10～30	30～60
   ～3 years	30	60～90
   ～7 years	60	90～150
   ～12 years	60	120～180

2. Synthetic levothyroxine sodium: Calculate based on 100μg being equivalent to 60mg of desiccated thyroid tablets.
3. Provide the child with ample protein, calcium, and vitamins B, C, and D to meet the needs of growth and development after treatment.

bubble_chart Differentiation

The neonatal period should be differentiated from pathological jaundice and congenital megacolon. Intellectual disability should be differentiated from cerebral hypoplasia and Down syndrome. Growth retardation should be differentiated from rickets and chondrodysplasia.