Factors suggesting relapse of Grave's disease after first radioiodine therapy. Analysis of 607 cases.

Objective: Despite the effectiveness of radioiodine therapy (RIT), a few patients are refractory and show relapse, warranting repeated RIT (RRIT). The purpose of this study is to explore the risk factors for RRIT.

Subjects And Methods: We retrospectively analyzed 607 cases treated with iodine-131 (I) between January 2013 and June 2016. Patients were categorized into two groups: RRIT (n=76) or non-RRIT (n=531). Univariate analysis and a final multivariate model were used to determine the risk factors for RRIT. P<0.05 indicated significance. After a mean 314.5MBq dose of I, 76 patients underwent secondary therapy.

Results: In the univariate analysis, the differences in terms of age, gender, family history of hyperthyroidism, course of disease, 24-hour I uptake, curve shape of I uptake, dose of I, thyroid peroxidase antibody, and thyrotrophin receptor antibody were not statistically significant (P>0.05). Anti-thyroid drug (ATD) treatment history, thyroid mass and dose of I were statistically significant (P values: 0.001, <0.001 and <0.001, respectively). Binary logistic analysis of factors that lead to repeated RIT showed a higher probability of ATD treatment history [OR=2.919, 95%CI (1.424, 5.982), P=0.003] and thyroid mass [OR=1.042, 95%CI(1.031, 1.052), P<0.001] associated with RRIT.

Conclusion: Patients treated with ATD before radioiodine treatment and with larger thyroid mass are at a higher risk for repeated radioiodine treatment.