Psychological development at 7 years of age in children with congenital hypothyroidism. Timing and dosage of initial treatment.

Sixty of 68 consecutive patients detected during the first two years of the Swedish screening programme for congenital hypothyroidism were Griffiths tested at the age 6.5-7.5 years. The test quotients of the patients could not be distinguished from those of a reference population. Replacement therapy with 8.7 +/- 2.8 micrograms of L-thyroxine (mean +/- SD)/kg/d had been started at 15.0 +/- 7.1 days of life. Furthermore, normal results on Griffiths tests were also found in 13 patients with delayed normalization of serum TSH, i.e. greater than 19 mU/l at the age of six weeks, as well as in patients with retarded skeletal maturity and/or very low neonatal serum levels of thyroxine, i.e. less than 18 nmol/l and tri-iodothyronine, i.e. less than 0.92 nmol/l. Our findings indicate that a replacement dose of 6-11 micrograms L-thyroxine/kg/d is adequate and allows normal psychological development if treatment is started early.