Evoked potentials show early and delayed abnormalities in children with congenital hypothyroidism.

To evaluate the effect of congenital hypothyroidism (CH) on nervous system development, we performed evoked potential studies on 7 CH infants at 3-8 weeks of age before treatment and at four months or more after treatment began. All infants were screened using filter paper determination of T4 and TSH, confirmed by serum specimen determinations. These infants had serum TSH concentrations greater than 100 microU/ml (normal less than 7), and the serum T4 range was 4.1-8.5 micrograms/dl. All had thyroid tissue on 99Tc scan; five had ectopic thyroid tissue, and two had a thyroid gland in the normal location. Four older CH children were tested after 3-6 years of treatment. Brainstem auditory evoked potentials (BAEP) were abnormal in three of the 7 infants and showed bilateral conduction delays in caudal brainstem regions. The BAEP became normal after 6 months of thyroxine treatment. Visual evoked potentials (VEP) were abnormally delayed and had an immature pattern in the four patients tested at four weeks of age. At age 8 weeks, even in untreated patients, the VEP was normal and remained so. Somatosensory evoked potentials (SSEP) were normal at the time of diagnosis. However, seven patients tested after at least five months of therapy had prolonged central conduction times. We conclude that infants with relatively mild CH (serum T4 values greater than 4 micrograms/dl at 3-8 weeks of age) have evidence of delayed visual system maturation that becomes normal even without treatment and of abnormal caudal brainstem development that resolves slowly with replacement therapy.(ABSTRACT TRUNCATED AT 250 WORDS)