Hypothyroidism

Classification of hypothyroidism

Depending on the level of the lesion, two main forms of the syndrome are distinguished:

• Primary hypothyroidism. The problem lies directly in the thyroid gland, which is unable to produce a sufficient amount of hormones.
• Secondary hypothyroidism. The pathology affects the pituitary gland. In this case, the synthesis of thyroid-stimulating hormone (TSH) decreases, as a result of which the thyroid gland does not receive the necessary stimulation to function.

According to the time of onset, the disease is divided into:

• Congenital. Develops due to anomalies of intrauterine development of the thyroid gland. This form poses the greatest danger to the child's development.
• Acquired. Can manifest at any age. One of the most common causes of the acquired form is chronic autoimmune thyroiditis.

Congenital hypothyroidism: clinical presentation

The main difficulty in diagnosing in the early neonatal period is that the symptoms are nonspecific.

Nevertheless, a number of early manifestations can be distinguished:

• Skin: pallor, dryness, peeling, presence of edema.
• Digestive system: prolonged course of neonatal jaundice, pronounced tendency to constipation.
• Neuromuscular apparatus: decreased muscle tone (hypotonia), hypothermia.
• Specific symptom: macroglossia — abnormal enlargement of the tongue.

It is extremely important to understand the prognosis: if treatment is not started on time, late diagnosis will inevitably lead to severe and irreversible delay in both physical and psychomotor development.

Neonatal Screening

To prevent irreversible central nervous system damage, neonatal screening has been universally introduced in Russia since 1992.

Examination algorithm:

1. Blood sampling: in full-term newborns, it is performed on days 3–4 of life, in premature infants — on days 7–14.
2. Methodology: blood is taken from the heel, applied to filter paper, and the dried spot is sent to the laboratory.
3. Marker evaluation: the primary indicator is the TSH level. For this age, the reference value is TSH $\le$ 20 mIU/L.

Actions in case of deviations (TSH > 20 mIU/L):

• The laboratory notifies the local outpatient clinic.
• The child is called back for a repeat blood draw.
• Confirmatory diagnostics are performed: TSH levels are determined along with free thyroxine (free T4).
• The diagnosis is confirmed if elevated TSH is detected against the background of a decreased free T4 level.

Principles of therapy

The basis of treatment for any variant of hypothyroidism is hormone replacement therapy (HRT). Levothyroxine sodium preparations (a synthetic analog of the T4 hormone) are used.

• The dose of the drug is selected strictly individually to fully compensate for the deficiency of endogenous hormones.
• In congenital hypothyroidism, therapy must be started urgently to prevent irreversible psychomotor development disorders.
• Parents must be explained that taking the medication will be continuous and lifelong.

Treatment monitoring: laboratory monitoring of TSH and free T4 levels is carried out at least once every 6 months. Clinically, the adequacy of the dose is confirmed by normal rates of growth and physical development of the child.

Class and exam questions

What else to study on this topic

• Clinical features of chronic autoimmune thyroiditis
• Mechanism of action and pharmacokinetics of levothyroxine sodium
• Differential diagnosis of prolonged neonatal jaundice
• Rules for hormone dose titration in early childhood
• Interpretation of TSH and free T4 results in different age groups

Other topics in the section «Chapter 11. Endocrine Diseases in Children»

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.