Congenital primary hypothyroidism in children

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

[1], [2], [3], [4], [5], [6], [7]

Causes of congenital hypothyroidism

In 75-90% of cases, congenital hypothyroidism occurs as a result of a defect of the thyroid gland - hypo- or aplasia. Often, hypoplasia is combined with the ectopic thyroid gland in the root of the tongue or trachea. The developmental defect of the thyroid gland is formed on the 4-9th 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 pregnant women in medical research), toxic effects of drugs and chemicals.

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

I. Primary hypothyroidism.

• Dysgenesis of the thyroid gland.
• Aplasia of the thyroid gland.
• Hypoplasia of the thyroid gland.
• Ectopic thyroid.
• Violation of the synthesis, secretion or peripheral metabolism of thyroid hormones.
• Treating the mother with radioactive iodine.
• Nephrotic syndrome.

II. Transitional primary hypothyroidism.

• The use of antithyroid drugs for the treatment of thyrotoxicosis in the mother.
• Iodine deficiency in the mother.
• The effect of excess iodine on the fetus or newborn.
• Transplacental transfer of maternal thyreblocking antibodies.

III. Secondary hypothyroidism.

• Malformations of the brain and skull.
• A rupture of the pituitary pedicle with birth trauma or asphyxia.
• Congenital aplasia of the pituitary gland.

IV. Transient secondary hypothyroidism.

[8], [9], [10], [11]

Pathogenesis of congenital hypothyroidism

Reducing the thyroid hormone content 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 disorders concern the nervous system: the number of neurons decreases, the myelination of nerve fibers and the differentiation of brain cells are disturbed. The slowing down of anabolic processes, the formation of energy are manifested in the violation of the endochondral ossification, the differentiation of the skeleton, and the decrease in the activity of hematopoiesis. The activity of certain enzymes of the liver, kidneys, and gastrointestinal tract also decreases. Slow down lipolysis, 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 child's physical and intellectual development, since changes in organs and tissues are almost irreversible with late treatment.

Symptoms of congenital hypothyroidism

The earliest symptoms of congenital hypothyroidism are not pathognomonic for this disease, only a combination of gradually emerging symptoms creates a complete clinical picture. Children are more often born with a large body weight, asphyxiation is possible. Expressed a protracted (longer than 10 days) jaundice. Reduced motor activity, sometimes note the difficulty in feeding. There are respiratory disorders in the form of apnea, noisy breathing. Children are diagnosed with difficulty nasal breathing, associated with the appearance of mucinous edema, constipation, bloating, bradycardia, a decrease in body temperature. Perhaps the development of anemia, resistant to treatment with iron.

Expressed symptoms of congenital hypothyroidism develops to 3-6 months. The growth of the child and his neuropsychological development are significantly slowed down. A disproportionate physique is formed - limbs become relatively short due to the lack of bone growth in length, hands broad with short fingers. The fontanelles remain open for a long time. Appear mucinous edema on the eyelids, thicken the lips, nostrils, tongue. The skin becomes dry, pale, there is a slight jaundice caused by caroteneemia. Due to the decrease in lipolysis and mucinous edema in children with very poor appetite, hypotrophy does not develop. The borders of the heart are moderately enlarged, the deaf tones, the bradycardia. The abdomen is swollen, umbilical hernia, constipation is not uncommon. The thyroid gland is not determined in most cases (developmental defect) or, conversely, may be increased (with hereditary disorders of the synthesis of thyroid hormones).

Screening for congenital hypothyroidism

Screening of newborns for congenital hypothyroidism is based on the determination of the TSH content in the child's blood. On the 4th-5th day of life in the maternity hospital, and in preterm infants on the 7-14th day, the level of ill is determined in a drop of blood applied to a special paper followed by extraction of serum. At a concentration of TSH above 20 mC / ml, a study of the serum levels of TSH in venous blood is necessary.

Diagnosis of congenital hypothyroidism

The criterion of congenital hypothyroidism is the serum TSH level above 20 mC / ml. Patient examination plan should include:

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

Ultrasound is used to verify the developmental defect of the thyroid gland.

[12], [13], [14], [15]

Differential diagnosis

In early childhood, differential diagnosis should be conducted with rickets, Down syndrome, birth trauma, jaundice of various genesis, anemia. In older children, it is necessary to exclude diseases accompanied by growth retardation (chondrodysplasia, hypophyseal nanism), mucopolis-charidosis, Hirschsprung disease, congenital dysplasia of the hip joints, and heart defects.

[16], [17], [18], [19], [20]

Treatment of congenital hypothyroidism

The main method of treatment is lifelong replacement therapy with thyroid medications with regular dose control. The drug of choice - synthetic levothyroxine sodium (deposited and converted to active T3). After a single morning intake of levothyroxine sodium, the physiological level of it persists for a day. The choice of the optimal dose is strictly individual and depends on the degree of thyroid insufficiency. The initial dose is 10-15 μg per day. In the subsequent dose weekly increase to the required. The indicators of the adequacy of the dose are absence of symptoms of hypo- or hyperthyroidism, normal TSH level. In a complex of therapeutic measures, vitamins can be included.

Prognosis of congenital hypothyroidism

With the timely begun (1st month of life) and subsequent adequate replacement therapy under the control of serum TSH levels, the prognosis for congenital hypothyroidism is favorable for physical and mental development. At belated diagnosis - after 4-6 months of life - the forecast is doubtful, with the full replacement therapy physiological rates of physical development are reached, but the lag in the formation of intelligence remains.