Graves' disease (GD) may coexist with
papillary thyroid microcarcinoma (PTMC). The main purpose of this study was to evaluate whether treatment with radioactive
iodine (RAI) may cause acute exacerbation of PTMC concurrent with GD or not. From the medical records of 10,257 GD patients who underwent RAI
therapy between 2000-2017, 12 subjects with concurrent PTMC were retrieved. Further, 49 patients with concurrent GD and PTMC who underwent no RAI administration throughout their
clinical course were enrolled as controls. Size of the PTMC nodules was evaluated based on maximal diameter and
tumor volume-doubling rate (TV-DR). Among the 12 subjects who underwent RAI
therapy (median dose, 13 mCi), 2 showed
tumors >10 mm in maximal diameter with slow growth for more than 10 years, while the other 10 showed
tumors with maximal diameter ≤10 mm. No subject showed any clinical findings of nodal or distant
metastasis during the follow-up periods (0.4-11.5 years) before surgery or during active surveillance. No significant differences were observed in the TV-DR values (median, 0.044/year; range, -0.81-1.40) between the study subjects and controls (median, 0.025/year; range, -0.70-1.29; p = 0.69). When comparing the TV-DR before and after RAI administration in 3 individuals in particular, in whom PTMC were cytologically confirmed before RAI administration and whose prospective follow-up data were available,
tumor progression was observed to be stable or decreased after RAI administration. There were no acute exacerbations or unfavorable outcomes of concurrent PTMC and GD after low-dose RAI administration.