Discordant hypothyroxinemia and hypertriiodothyroninemia in treated patients with hyperthyroid Graves' disease and toxic multinodular goiter.

Hypothyroxinemia and hypertriiodothyroninemia may occur in the course of antithyroid drug or 131I treatment for hyperthyroid Graves' disease and toxic multinodular goiter. To determine the frequency of this discordance, we reviewed 62 patients with hyperthyroidism. Among 41 Graves' disease patients treated with antithyroid drugs and/or 131I, discordant serum triiodothyronine (T3) and thyroxine (T4) levels occurred in 26.8%. Of these patients 72.8% had a high serum T3 level associated with a normal serum T4 level, whereas in 27.2% a high serum T3 level was associated with a low serum T4 level. Among 21 toxic multinodular goiter patients, 14.3% had discordant T3 and T4 levels. We conclude that discordance of serum T4 and T3 concentrations is frequently encountered in patients with hyperthyroid Graves' disease and less frequently in toxic multinodular goiter during or after therapy.