Prompt detection and timely treatment of hypothyroidism in infancy are vital since hypothyroidism in this age group is one of the preventable causes of mental retardation. Intelligence quotient (IQ) decreases the later the condition is detected and treated. Early detection and timely treatment to prevent this devastating outcome have resulted in one of the great success stories of newborn screening program implementation. Conditions that can cause hypothyroidism in infants are listed in Table 520-1.
TABLE 520-1CAUSES OF HYPOTHYROIDISM IN INFANTS |Favorite Table|Download (.pdf) TABLE 520-1CAUSES OF HYPOTHYROIDISM IN INFANTS
|Thyroid dysgenesis |
| Thyroid aplasia |
| Thyroid hypoplasia |
| Thyroid ectopy |
|Thyroid dyshormonogenesis |
|Resistance to thyroid-stimulating hormone |
|Defect in thyroid hormone transport |
|Resistance to thyroid hormone action |
|Central hypothyroidism |
|Transient hypothyroidism |
|Thyroxine-binding globulin deficiency |
|Hypothyroxinemia of prematurity |
|Nonthyroidal illness |
NEWBORN SCREENING PROGRAMS
Congenital hypothyroidism occurs in 1:2000 to 1:4000 newborns. There are no specific clinical manifestations of hypothyroidism, which makes detection of hypothyroidism based on symptoms almost impossible. This need for early detection led to the development of newborn screening programs in the mid-1970s. Heel stick blood specimens are obtained routinely by all 50 states at 2 to 5 days after birth, and in some states, they are repeated at 2 to 6 weeks after birth. Newborn screening is also performed in Canada, Europe, Australia, New Zealand, Israel, and Japan. However, there are many areas in the world where newborn screening is nonexistent or underdeveloped.
Blood is collected onto filter paper and sent to a centralized laboratory for testing. The initial test performed varies among states:
Initial thyroid-stimulating hormone (TSH) assay
Initial thyroxine (T4) assay, with follow-up TSH if the T4 is < 10%
Simultaneous TSH and T4, which is the most optimal method
It is advisable that each practicing general pediatrician and pediatric subspecialist should know their own state’s method in order to be able take into account possible limitations. Regardless of method, the vast majority of infants with primary hypothyroidism are detected. However, each method has its disadvantages. Initial TSH assay tends to miss central hypothyroidism or infants with delayed primary hypothyroidism in whom TSH rises later. Initial TSH testing tends to detect subclinical hypothyroidism. The initial T4 method can detect central hypothyroidism but tends to have false-positive results for thyroxine-binding globulin (TBG) deficiency.
The incidence of congenital hypothyroidism varies worldwide, and it varies by ethnicity and geographic location. The incidence has been increasing in the United States, with the latest report as 1:2372 in 2002. Additionally Hispanic and Asian infants tend to be more affected than Caucasian and African American infants. The incidence is also higher when comparing twin or multiple births to singletons and also increases with maternal age. The female-to-male ratio is ...