Immunogenic hyperthyroidism following iodine-131-therapy of non-imunogenic, autonomous thyroid nodules: Results of a multicenter evaluation

Background: There are case reports in the literature that patients occasion ally develop immunogenic hyperthyroidism 2 to 14 months following iodine-13 1-therapy of focal, non-immunogenic, autonomous thyroid nodules with a prev alence between 0.05 and 2.5%. Purpose of this multicenter evaluation was to assess the appearance of this phenomenon in a larger patient population. Patients and Methods: So far 2867 patients out of 4 university hospitals ar e included in our study focusing on the appearance of pathologically elevat ed levels of thyrotropin-receptor-antibodies (TRAb) combined with hyperthyr oidism following iodine-therapy. Records of the patients were screened for pre- and post-therapeutic biochemical tests, scintigraphic uptake patterns and ultrasound findings of the thyroid. Results Nineteen of 2867 patients with pretherapeutically scintigraphic "ho t nodules" developed recurrent hyperthyroidism suggestive for immunogenic g enesis 2 to 12 months following iodine-131-therapy (elevated TRAb-levels, h omogeneous uptake in Tc-99m-pertechnetate scans). Pretherapeutically, 9 of these patients presented with a strictly focal scintigraphic uptake-pattern , 10 cases with a mixed disseminated-focal pattern. Because of missing pret herapeutic TRAb-tests in 8/9 patients presenting with a strictly focal scin tigraphic uptake pattern, postradiogenic immunogenic hyperthyroidism could be reliably assessed in 1 case only. Conclusion: One could speculate that iodine-131-therapy may stimulate immun ogenic mechanisms finally leading to immunogenic hyperthyroidism. Post-ther apeutically observed hyperthyroidism following iodine-treatment might be ba sed on an exacerbation of a preexisting - clinically not relevant/detectabl e - immunothyropathia, Also pretherapeutic TRAb-negative immunogenic hypert hyroidism could not be definitely excluded. Our multicenter data collected in a large patient population show similar results to the case reports of i mmunogenic hyperthyroidism following iodine-131-treatment in smaller popula tions, Therfore, the occurrence of this phenomenon plays a minor role regar ding to its prevalence. Therapeutical consequences in treatment of function al thyroid autonomy are not recommended.