T3 toxicosis in children.

Triiodothyronine (T3) toxicity has been well documented in adults, but only isolated cases have been reported in children. Two girls presented with firm goitres and overt hyperthyroidism. In each patient, total serum thyroxine (T4) values by competitive protein binding were normal, however total T3 values by radioimmunoassay were elevated. One patient had Graves' disease, the second patient had Hashimoto's disease which has been only infrequently associated with T3 toxicity in adults. Both patients responded to therapy with propylthiouracil. The mechanisms by which T3 is preferentially secreted in thyrotoxic states in man are poorly understood, but iodine deficiency and poor iodination of thyroglobulin may be important factors.