Value of serum thyroxine measurements for the management of congenital hypothyroidism in children.

Fourteen cases of primary congenital hypothyroidism were studied and separated for the analysis purpose into two groups. Group A consisted of 7 children whose hypothyroidism was diagnosed after 1971 and the therapy by thyroid gland extracts evaluated by regular serum thyroid hormone determinations. Group B was made of 7 children whose disease was diagnosed and treated before 1971. Two periods were therefore studied in group B: first period, before any hormonal determinations (as a growth control period for group A), and second period, during which hormonal determinations were made and taken into consideration for the dosage. Although growth patterns were similar in both groups, mean thyroid extracts dose was 63 +/- 25 mg/m2/day (mean +/- SD) during follow-up with hormonal determinations, while it was markedly higher during the first period of group B (125 +/- 76, range 46.1 to 219.9 mg/m2/day). The mean dose of 63 +/- 25 mg/m2 induces a mean level of plasma thyroxine of 82 +/- 32 microgram/1 (mean +/- 1SD), a normal growth (with catch-up growth in the patients who had a retarded growth), and a good psychomotor development. Regular measurements of serum thyroxine during therapy seems to be a valid parameter for determining the dose of thyroid gland extracts necessary for adequate substitution. Serum=1-triiodo-thyronine levels have more fluctuations than thyroxine. Serum TSH mainly prevents the underdose of patients but cannot help in case of overdose. The suggested dose for treatment of such patients is 88 mg/m2/day (= 63 + 1SD).