Predictive factors of repeat therapy in patients receiving iodine-131 for Graves’ disease

Objectives To explore the factors predicting repeat 131I therapy in patients with Graves' disease (GD).

Methods We collected clinical data on 1707 patients with GD (1174 females and 533 males, mean age 40.4±12.2 yrs) presenting consecutively between Jan 2002 and Nov 2010 who were treated with 131I. 131I dose (MBq)= 131I dose for per gram of thyroid tissue (MBq/g) × thyroid weight (g) / 24h radioactive iodine uptake (24h-RAIU). The influence of factors including patient’s gender, age, course of hyperthyroidism (mons), whether taking ATD before 131I therapy, thyroid weight(g), the texture(soft, moderate or stiff), with complications or not, 24h-RAIU(%), whether peak RAIU moving forward or not, the first dose of 131I and giving 131I dose per gram thyroid tissue was determined. Logistic Regression was used to determine which factors contributed to the prediction of repeat 131I therapy.

Results Overall, 1540 patients (90.2%) received a single dose of 131I. The remaining 167 cases were given a further dose of 131I (range: 2-4 doses). In the univariate analysis, subjects receiving more than one dose of 131I had a longer course of hyperthyroidism, heavier weight, higher 24h-RAIU, larger initial 131I dose and 131I dose per gram thyroid tissue when compared with those underwent a single dose, and patients taking ATD before 131I therapy and those whose peak RAIU moving forward were more likely retreated (P<0.05). Multivariate logistic regression analysis identified longer course of hyperthyroidism (OR:1.004, 95%CI:1.001-1.007, P=0.01), heavier weight (OR:1.011,95%CI:1.005-1.016, P<0.001) and peak RAIU moving forward (OR:1.787, 95%CI:1.183-2.697, P=0.006) to be independent factors predicting repeat treatment.

Conclusions A single dose 131I therapy for the majority of GD patients can exert good therapeutic effects. Subjects with longer course of hyperthyroidism, heavier weight and peak RAIU moving forward should be treated with a relatively high dose of 131I in order to achieve cure.