Antithyroid drugs as a factor influencing the outcome of radioiodine therapy in Graves' disease and toxic nodular goitre?

There is controversy over the factors that may influence the outcome of rad ioiodine therapy for benign thyroid diseases. Antithyroid medication has be en claimed to negatively influence the effectiveness of radioiodine therapy in Graves' disease. In a longitudinal study, we assessed the influence of sex, age, antithyroid drugs, target radiation dose, target mass, applied ac tivity, delivered dose. interval between last meal and application, and TSH , FT3 and FT4 levels on the outcome of radioiodine therapy. One hundred and forty-four patients (111 female, 33 male) suffering from Graves' disease ( GD) and 563 patients (434 female, 129 male) with toxic nodular goitre (TNG) were entered in the study and followed up until 8 months after therapy. Tr eatment was defined as successful when the TSH level was found to be normal or elevated. Ninety-eight GD patients and 418 TNG patients were successful ly treated. Forward stepwise multiple regression analysis models retained o nly the target mass in GD and the applied activity in TNG as significantly associated with the outcome of therapy. The predictive value of all variabl es involved was extremely low in both disease groups. Whereas concomitant a ntithyroid medication had no influence in GD, it adversely influenced radio iodine therapy of TNG. This effect may be attributed to a radioiodine "stea l phenomenon" induced by TSH-stimulated normal thyroid tissue, which causes overestimation of the uptake in toxic nodules.