Wednesday, June 12, 2024
HomePediatrics: General MedicineCongenital Hypothyroidism

Congenital Hypothyroidism

Practice Essentials

Congenital hypothyroidism (CH) is inadequate thyroid hormone production in newborn infants. It can occur because of an anatomic defect in the gland, an inborn error of thyroid metabolism, or iodine deficiency. (See the image below.) CH is the most common neonatal endocrine disorder, and historically, thyroid dysgenesis was thought to account for approximately 80% of cases. However, studies have reported a change in the epidemiology, with a doubling in incidence to around 1 in 1500 live newborns.​
  This is thought to be due in part to an increase in congenital hypothyroidism with thyroid gland-in-situ (GIS).
 Lower TSH screening cutoffs may also be driving this increase in diagnosis, although altered ethnicities of the screened population, increased multiple and premature births, and iodine status are contributing factors. Some infants identified as having primary congenital hypothyroidism may have transient disease and not permanent congenital hypothyroidism.

An infant with cretinism. Note the hypotonic postu

An infant with cretinism. Note the hypotonic posture, coarse facial features, and umbilical hernia.

View Media Gallery

The term endemic cretinism is used to describe clusters of infants with goiter and hypothyroidism in a defined geographic area. Such areas were discovered to be low in iodine, and the cause of endemic cretinism was determined to be iodine deficiency. In the 1920s, adequate dietary intake of iodine was found to prevent endemic goiter and cretinism.
Endemic goiter and cretinism are still observed in some areas, such as regions of Bangladesh, Chad, China, Indonesia, Nepal, Peru, and Zaire.

The term sporadic cretinism was initially used to describe the random occurrence of cretinism in nonendemic areas. The cause of these abnormalities was identified as nonfunctioning or absent thyroid glands. This led to replacement of the descriptive term sporadic cretinism with the etiologic term congenital hypothyroidism. Treatment with thyroid replacement therapy was found to elicit some improvement in these infants (see the images below), although many remained impaired.

An infant shown a few months after starting thyroi

An infant shown a few months after starting thyroid hormone replacement.

View Media Gallery

Infant a few months after starting thyroid hormone

Infant a few months after starting thyroid hormone replacement.

View Media Gallery

The morbidity from congenital hypothyroidism can be reduced to a minimum by early diagnosis and treatment.
Although initial preliminary studies were performed using thyroid-stimulating hormone (TSH) levels in cord blood,
mass screening was made feasible by the development of radioimmunoassay for TSH and thyroxine (T4) from blood spots on filter paper, obtained for neonatal screening tests.

Signs and symptoms

Infants with congenital hypothyroidism are usually born at term or after term. Symptoms and signs include the following:

Decreased activity

Large anterior fontanelle

Poor feeding and weight gain

Small stature or poor growth

Jaundice

Decreased stooling or constipation

Hypotonia

Hoarse cry

Often, affected infants are described as “good babies” because they rarely cry and they sleep most of the time.

The physical findings of hypothyroidism may or may not be present at birth. Signs include the following:

Coarse facial features

Macroglossia

Large fontanelles

Umbilical hernia

Mottled, cool, and dry skin

Developmental delay

Pallor

Myxedema

Goiter

Anemia may occur, due to decreased oxygen carrying requirement. A small but significant number (3-7%) of infants with congenital hypothyroidism have other birth defects, mainly atrial and ventricular septal defects.

See Clinical Presentation for more detail.

Diagnosis

Diagnosis of primary hypothyroidism is confirmed by demonstrating decreased levels of serum thyroid hormone (total or free T4) and elevated levels of thyroid-stimulating hormone (TSH). If maternal antibody–mediated hypothyroidism is suspected, maternal and neonatal antithyroid antibodies may confirm the diagnosis.
Such antibodies are an uncommon cause of congenital hypothyroidism.

The combination of low or low-normal serum total T4 levels and a serum TSH within the reference range suggests thyroid-binding globulin (TBG) deficiency. This congenital disorder causes no pathologic consequence but should be recognized to avoid unnecessary thyroid hormone administration.

Thyroid scanning

Thyroid scanning is not required to make or confirm the diagnosis of congenital hypothyroidism, but it can provide important information about the etiology.

On thyroid scanning (using technetium-99m or iodine-123), the absence of radionuclide uptake suggests sporadic athyreotic hypothyroidism but can also occur when uptake is blocked by excess iodide or thyroid receptor–blocking antibodies. If no uptake is found on isotope scanning, thyroid ultrasonography may demonstrate thyroid tissue.

Thyroid scans can also demonstrate the presence of an ectopic thyroid, such as a lingual or sublingual gland, which is also sporadic. The presence of a bilobed thyroid in the appropriate position or a goiter would suggest either an inborn error of thyroid hormone production or transient hypothyroidism or hyperthyrotropinemia

Other imaging studies

Ultrasonography may be a reasonable alternative or addition to scintigraphy but may fail to reveal some ectopic glands.

A lateral radiograph of the knee may be obtained to look for the distal femoral epiphysis; this ossification center appears at about 36 weeks’ gestation, and its absence in a term or postterm infant indicates prenatal effects of hypothyroidism.

See Workup for more detail.

Management

The mainstay in the treatment of congenital hypothyroidism is early diagnosis and thyroid hormone replacement. Optimal care may include diagnosis before age 10-13 days and normalization of thyroid hormone blood levels by age 3 weeks.

Only levothyroxine is recommended for treatment.
Parents should be provided the hormone in pill form and taught proper administration, as follows:

The pills can be crushed in a spoon; dissolved with a small amount of breast milk, water, or other liquid immediately before administration; and administered to the child with a syringe or dropper

The pills should not be mixed in a full bottle of formula

Toddlers typically chew the tablets without problems or complaints.

Initial dosages of 10-15 mcg/kg/day, equivalent to a starting dose of 50 mcg in many newborns, have been recommended.
Equally good developmental results, but with higher thyroid-stimulating hormone (TSH) levels, have been reported with half this starting dose (25 mcg/day).

See Treatment and Medication for more detail.

Previous articlePrematurity
Next articleKnee Examination
RELATED ARTICLES
- Advertisment -

Most Popular