Introduction: I therapy is a choice for Graves' hyperthyroidism. Several factors that affect the success of I treatment in Graves' disease (GD) patients have been put forward. The aim of this retrospective study was to evaluate the factors influencing the success of I therapy and the occurrence of hypothyroidism after I therapy.
Patients and methods: We reviewed 325 GD patients, who were well documented out of 779 cases, treated with I in the First Affiliated Hospital of Xi'an Jiaotong University between 2010 and 2016. We collected the potential influencing factors, including demographic data (age, sex, family history), iodine intake state, antithyroid drugs (ATD) taking, thyroid texture, complications of hyperthyroidism, physical and laboratory examinations [thyroid weight, effective I half-life time (Teff), 24-h iodine uptake rate, tri-iodothyronine, thyroxine, free tri-iodothyronine (FT3), free thyroxine, thyroid-stimulating hormone, thyroglobulin antibody, thyroid microsome antibody, thyrotropin receptor antibody], and final administered dosages according to Quimby formula. The correlations between the prognosis of GD patients and these factors were analyzed by logistic regression analysis.
Results: Out of 325 patients, 247 (76.00%) were treated successfully with radioiodine. GD patients who were cured by I therapy were more likely to have smaller thyroid [odds ratio (OR)=0.988, 95% confidence interval (CI)=0.980-0.996, P=0.002], lower FT4 levels (OR=0.993, 95% CI=0.988-0.997, P=0.002), and shorter time of ATD withdrawal before I treatment (OR=0.985, 95% CI=0.975-0.996, P=0.002). Hypothyroidism occurred in 132 (41.00%) out of 325 patients. There was an increased risk of early hypothyroidism in patients with lower 24-h iodine uptake (OR=0.964, 95% CI=0.941-0.988, P=0.004), and treated with a lower total dose of iodine (OR=0.892, 95% CI=0.824-0.965, P=0.005) and a higher iodine dose per garm of thyroid tissue (OR=5.414E+14, 95% CI=45.495-6.444E+27, P=0.027).
Conclusion: Our results showed that I treatment was more successful in patients with lower weight of the thyroid, lower free thyroxine level, and shorter ATD taking period. Furthermore, early hypothyroidism after radioiodine treatment was more likely to occur in patients with lower 24-h iodine uptake, lower total dose of iodine, and higher iodine dose per garm of thyroid tissue.