One-year follow-up of Graves' disease treatment by four different protocols of radioiodine administration

Abstract

Background: Studies have been performed in order to assess a treatment with 131I able to induce a consistent improvement in Graves' hyperthyroidism.

Experimental design: For this purpose, four different protocols based on four different doses of radioiodine have been tested in Graves' disease patients. Patients never submitted previously to antithyroid drug treatment were given 1 mCi/10 gm of the estimated thyroid weight (group I; n = 50). Group II (n = 48) included patients not previously treated with antithyroid drugs and who were given doses of iodine based on a formula taking into account the rate of thyroid iodine uptake, i.e. 131I dose = microCi/gm of the estimated thyroid weight x 100/24 hrs 131I uptake (%). Patients previously submitted to antithyroid drug therapy were treated with radioiodine whose dose was calculated according to the formula reported above, but the dose was increased in order to overcome the possible resistance of this kind of patients to the effect of 131I. One group (group III; n = 24) received the calculated dose plus 1 microCi/gm of the estimated thyroid weight. Finally, group IV (n = 27) received the calculated dose plus 0.25 microCi/gm of the estimated thyroid weight.

Results: The analysis of the patients one year later demonstrated that groups I and II presented the higher percent of euthyroid patients (60% and 58%, respectively) followed by group IV (37%) and group III (29.2%). The percent of patients still exhibiting hyperthyroidism was 28% in group I, 26% in group IV, 12.5% in group III and 8.3% in group II. The highest number of hypothyroid patients was present in group III (58.3%) followed by group IV (37%), group II (33.3%) and group I (12%).

Conclusions: The data here presented suggest that protocols I and II based on relatively low doses of radioiodine are rather effective in reducing Graves' hyperthyroidism in patients not submitted previously to antithyroid drug therapy. The most satisfactory therapy seems that utilized in protocol II, that in front of a fair amount of euthyroid patients (58.3%) presents a very low number of subjects still hyperthyroid (8.3%). However, the number of patients who became hypothyroid (33.3%) as a consequence of the therapy was too high. Hopefully, a better design of the protocol will reduce this figure. The high incidence of hyperthyroidism observed in groups III and IV submitted to a therapy with 131I doses consistently higher than those utilized in groups I and II seems to confirm the hypothesis that hyperthyroid subjects submitted to a therapy with antithyroid drugs become rather resistant to a radioiodine treatment.