[Early changes in thyroid hormones following radioiodine therapy of hyperthyroidism with reference to etiology and accompanying medication].

Radioiodine therapy (RITh) is an effective mode of treatment of different types of hyperthyroidism (immunogenic, IH; nonimmunogenic, NIH). The aim of this study was to evaluate the risk of thyroid storm after RITh. For this purpose a systematic determination of thyroid hormones (TT3, TT4) 5 and if possible 12 days after RITh was performed in 416 patients with borderline or overt hyperthyroidism. Additional antithyroid medication after RITh was necessary in 20 patients. Among the remaining 396 patients 48% had been pretreated with antithyroid drugs because of more severe clinical symptoms. This medication was canceled 10 to 5 days before RITh in all cases. After RITh the mean TT3 and TT4 levels of the subgroups, with and without antithyroid premedication, decreased nearly in parallel course. The whole group of 396 patients presented a significant decrease in TT3 levels with a mean from 1.9 to 1.4 ng/ml. In 18 cases (5%) an increase in TT3 level (greater than or equal to 0.5 ng/ml) was detected without requiring antithyroid therapy. No case of thyroid storm was observed in the entire patient group. TT3 decrease appeared to be more pronounced in patients with higher pretreatment levels. TT4 showed a significant decrease only in case of elevated levels. Post-therapeutic hormone levels were not dependent on the etiology of hyperthyroidism (IH, NIH). The decrease of TT3 levels in the IH group was more pronounced after application of 150 Gy compared with 60 Gy. The additional medication with propranolol (greater than or equal to 60 mg/day) enforced the TT3 decrease. Accompanying glucocorticoid medication had no influence on the hormone levels.(ABSTRACT TRUNCATED AT 250 WORDS)