Congenital primary hypothyroidism in children

Congenital primary hypothyroidism occurs with a frequency of 1 in 3500-4000 newborns.

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Causes of congenital hypothyroidism

In 75-90% of cases, congenital hypothyroidism occurs as a result of a malformation of the thyroid gland - hypo- or aplasia. Hypoplasia is often combined with ectopia of the thyroid gland in the root of the tongue or trachea. Malformation of the thyroid gland is formed in the 4th-9th week of intrauterine development due to: viral diseases of the mother, autoimmune diseases of the thyroid gland in the mother, radiation (for example, the introduction of radioactive iodine to a pregnant woman during medical research), toxic effects of drugs and chemicals.

In 10-25% of cases, congenital hypothyroidism is caused by genetically determined disorders of hormone synthesis, as well as hereditary defects of receptors for triiodothyronine (T3), thyroxine (T4) or TSH.

I. Primary hypothyroidism.

• Thyroid dysgenesis.
• Thyroid aplasia.
• Thyroid hypoplasia.
• Ectopic thyroid gland.
• Disorders of the synthesis, secretion or peripheral metabolism of thyroid hormones.
• Treatment of the mother with radioactive iodine.
• Nephrotic syndrome.

II. Transient primary hypothyroidism.

• Use of antithyroid drugs for the treatment of thyrotoxicosis in the mother.
• Iodine deficiency in the mother.
• Effects of excess iodine on the fetus or newborn.
• Transplacental transfer of maternal thyroid-blocking antibodies.

III. Secondary hypothyroidism.

• Malformations of the brain and skull.
• Rupture of the pituitary stalk due to birth trauma or asphyxia.
• Congenital pituitary aplasia.

IV. Transient secondary hypothyroidism.

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Pathogenesis of congenital hypothyroidism

A decrease in the content of thyroid hormones in the body leads to a weakening of their biological effects, which is manifested by a violation of the growth and differentiation of cells and tissues. First of all, these violations concern the nervous system: the number of neurons decreases, myelination of nerve fibers and differentiation of brain cells are disrupted. Slowing down of anabolic processes, energy formation are manifested in a violation of enchondral ossification, differentiation of the skeleton, a decrease in the activity of hematopoiesis. The activity of some enzymes of the liver, kidneys, and gastrointestinal tract also decreases. Lipolysis slows down, the metabolism of mucopolysaccharides is disrupted, mucin accumulates, which leads to the appearance of edema.

Early diagnosis of the disease is the main factor determining the prognosis for the physical and intellectual development of the child, since with late initiation of treatment, changes in organs and tissues are almost irreversible.

Symptoms of congenital hypothyroidism

The earliest symptoms of congenital hypothyroidism are not pathognomonic for this disease, only a combination of gradually appearing signs creates a complete clinical picture. Children are often born with a large body weight, asphyxia is possible. Prolonged (longer than 10 days) jaundice is expressed. Motor activity is reduced, sometimes difficulties with feeding are noted. Respiratory disorders occur in the form of apnea, noisy breathing. Children have difficulty breathing through the nose, associated with the appearance of mucinous edema, constipation, bloating, bradycardia, decreased body temperature. Anemia resistant to treatment with iron preparations may develop.

Expressed symptoms of congenital hypothyroidism develop by 3-6 months. The child's growth and neuropsychic development are significantly slowed down. A disproportionate body build is formed - the limbs become relatively short due to the lack of bone growth in length, the hands are wide with short fingers. The fontanelles remain open for a long time. Mucinous edema appears on the eyelids, the lips, nostrils, and tongue thicken. The skin becomes dry, pale, and mild jaundice appears due to carotenemia. Due to decreased lipolysis and mucinous edema, children with very poor appetite do not develop hypotrophy. The borders of the heart are moderately dilated, the tones are muffled, and there is bradycardia. The abdomen is bloated, umbilical hernia and constipation are common. The thyroid gland is not determined in most cases (developmental defect) or, conversely, can be enlarged (with hereditary disorders of thyroid hormone synthesis).

Screening for congenital hypothyroidism

Screening of newborns for congenital hypothyroidism is based on determining the TSH content in the child's blood. On the 4th-5th day of life in the maternity hospital, and in premature babies on the 7th-14th day, the ill level is determined in a drop of blood applied to special paper with subsequent serum extraction. If the TSH concentration is higher than 20 μU/ml, it is necessary to study the TSH content in the venous blood serum.

Diagnosis of congenital hypothyroidism

The criterion for congenital hypothyroidism is a serum TSH level above 20 μU/ml. The patient's examination plan should include:

• determination of free thyroxine content in blood serum;
• clinical blood test - in hypothyroidism, normochromic anemia is detected;
• biochemical blood test - hypercholesterolemia and elevated blood lipoprotein levels are typical for children over 3 months of age;
• ECG - changes in the form of bradycardia and decreased voltage of the teeth;
• X-ray examination of the wrist joints - a delay in the rate of ossification is revealed only after 3-4 months.

To verify a developmental defect of the thyroid gland, an ultrasound scan is performed.

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Differential diagnosis

In early childhood, differential diagnostics should be carried out with rickets, Down syndrome, birth trauma, jaundice of various origins, and anemia. In older children, it is necessary to exclude diseases accompanied by growth retardation (chondrodysplasia, pituitary dwarfism), mucopolysaccharidosis, Hirschsprung's disease, congenital hip dysplasia, and heart defects.

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Treatment of congenital hypothyroidism

The main method of treatment is lifelong replacement therapy with thyroid drugs with regular dose monitoring. The drug of choice is synthetic sodium levothyroxine (it is deposited and converted into active T3). After a single morning dose of sodium levothyroxine, its physiological level is maintained for 24 hours. The selection of the optimal dose is strictly individual and depends on the degree of thyroid insufficiency. The initial dose is 10-15 mcg per day. Subsequently, the dose is increased weekly to the required level. The indicators of the adequacy of the dose are the absence of symptoms of hypo- or hyperthyroidism, normal TSH level. Vitamins can be included in the complex of therapeutic measures.

Prognosis of congenital hypothyroidism

With timely initiation (1st month of life) and subsequent adequate replacement therapy under control of the TSH level in the blood serum, the prognosis for physical and mental development in congenital hypothyroidism is favorable. With late diagnosis - after 4-6 months of life - the prognosis is questionable, with full replacement therapy, physiological rates of physical development are achieved, but a lag in the formation of intelligence remains.