Congenital Hypothyroidism

Congenital Hypothyroidism
Tests Used to Diagnose Hypothyroidism
Treatment
Who has Congenital Hypothyroidism?
Long-Term Follow-Up
A Word to Parents

Hypothyroidism is a condition in which not enough thyroid hormone is produced. Thyroid hormone, or thyroxine (T4), is made by the thyroid gland which is located in the front of the neck just beneath the Adam's apple. In most cases of hypothyroidism, the problem arises from an underfunctioning thyroid gland. In rare instances there can be a normally functioning gland which does not make enough thyroid hormone because of insufficient thyroid stimulating hormone (TSH) from the pituitary.

Thyroxine affects the function and development of many body systems and is essential for normal growth and development. Thyroid hormone is especially necessary in the first three years of life when it plays an important role in ensuring normal brain growth and nervous system development. By measuring thyroid hormone levels in all babies shortly after birth, newborn screening programs are able to identify infants with low thyroid hormone levels who may have congenital hypothyroidism even before there are any signs or symptoms of hypothyroidism. Prompt and appropriate treatment of infants with congenital hypothyroidism with thyroxine allows normal growth and intellectual development.

Tests Used to Diagnose Hypothyroidism

At about 2 days of life, a small sample of blood is collected from the newborn and sent for testing to the New England Newborn Screening Program. One of the screening tests performed is a measurement of T4. If the T4 is low it could be a sign of hypothyroidism and further testing is done. The next test is measurement of Thyroid Stimulating Hormone (TSH) in the filter paper specimen. In most cases of congenital hypothyroidism the TSH is elevated indicating that the thyroid gland is not functioning properly. If an elevation of TSH is detected by the New England Newborn Screening Program, the health care provider caring for the infant is contacted immediately so that the baby can be further evaluated to determine if the baby has hypothyroidism (this generally requires an additional blood sample and an examination by the health care provider). As soon as a diagnosis of hypothyroidism is confirmed, the baby is started on thyroxine treatment. Appropriate thyroxine replacement should restore an optimal pattern of growth and development in the child.

Additional tests may include a "thyroid scan" to estimate how much thyroid tissue is present and its exact location. This test can be performed at the time of diagnosis of hypothyroidism or when the child is older.

Because hypothyroidism can become manifest or acquired after a specimen has been collected for newborn screening, children who show signs or symptoms of hypothyroidism warrant repeat thyroid testing, regardless of results of the initial screening specimen.

Treatment

Treatment for hypothyroidism is straightforward. The synthetic form of thyroxine (levothyroxine) is prescribed in a tablet form. A typical starting dose of thyroxine for a newborn is between 25-50 micrograms per day.* This amount may increase to 150 micrograms, or more, as the child grows.

Sometimes, establishing and maintaining the correct dose takes some effort. Typically, the need for T4 increases during periods of rapid growth. During times of rapid growth (such as the newborn period, infancy and puberty) it is essential to monitor blood levels of T4 and TSH frequently so that the proper dosage of thyroxine can be determined.

Most children diagnosed with hypothyroidism by newborn screening will need thyroxine treatment lifelong. Rarely, a child may be found to no longer need thyroxine treatment. In these cases of transient hypothyroidism the child does not require increased doses during the growth spurts, and has normal levels of T4 and TSH when thyroxine is discontinued.

*WARNING Replacement thyroxine should not be mixed with soy based formula because soy binds the medication and prevents absorption.

Who has Congenital Hypothyroidism?

In North America approximately one child in 4,000 is found to be hypothyroid at birth. The majority of these cases are "sporadic" due to abnormal or incomplete thyroid gland development. It is unknown why the thyroid gland does not develop normally in these cases. In a minority of cases (approximately 12%), the child lacks or has a non-functional enzyme which is necessary to make thyroid hormone. This type of hypothyroidism (thyroid dyshormonogenesis) is often inherited and when this type is found there is a 1:4 chance that a sibling will also be born with congenital hypothyroidism. Thyroid dyshormonogenesis is often associated with an enlarged thyroid gland (goiter) if not treated. There are other, rarer causes of congenital hypothyroidism, including transient hypothyroidism and hypothalamic- pituitary hypothyroidism.

Long-Term Follow-Up

Frequent clinical examinations will be necessary to assess the growth and development of children diagnosed with hypothyroidism. Also, routine laboratory evaluations of thyroid function must be performed every few months during the first 3 years of life.

The New England Congenital Hypothyroid Collaborative recommends that serum T4 and TSH measurements should be carried out as follows for growing children:

  1. At 2 weeks following any change in therapy
  2. Every 1 to 2 months during the first year of life
  3. Every 2 to 3 months from 1 to 3 years of age
  4. Every 3 months until the child's growth is complete

Once growth is complete, we recommend thyroid tests as follows:

  1. When signs and/or symptoms of hypothyroidism or hyperthyroidism exist
  2. Annually if dose, weight and clinical condition are stable
  3. 6 weeks after a change in dose
  4. Frequently during pregnancy (ideally, as soon as a pregnancy is detected as the dose of thyroxine may need to be increased during pregnancy)

The concentration of T4 should be above 10mcg/dl within two weeks of starting therapy and be maintained in the mid-upper half of the normal range (approximately 12.5 mcg/dl). TSH levels should be below 20 microU/ml within 2-4 weeks of starting treatment, and should remain in the normal range thereafter.

These guidelines are in agreement with the American Academy of Pediatrics guidelines (see PEDIATRICS 1993, 91(6): 1203-9 and PEDIATRICS 1996, 98:473-501).

A Word to Parents

Screening for congenital hypothyroidism has been carried out in New England since January, 1976. At the outset of screening little was known about the eventual outcome of children identified and treated shortly after birth. Therefore, children who were diagnosed in the early years of thyroid newborn screening were given periodic neuropsychological and physical examinations to assess their development. Those children are now young adults and adolescents. The results of these studies of outcome of children treated for hypothyroidism identified by newborn screening demonstrate that treatment is safe and effective. Parents can be assured that the future of a hypothyroid infant is the same as any other infant as long as treatment with thyroxine is maintained at a satisfactory level.
This information has been prepared by the New England Newborn Screening Program.

New England Newborn Screening Program
State Laboratory Institute
305 South Street
Jamaica Plain, MA 02130
(617) 983-6300