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

Background. Studies have been performed in order to assess a treatment with I-131 able to induce a consistent improvement in Graves' hyperthyroidism. Methods. Experimental design: For this purpose, four different protocols ba sed on four different doses of radioiodine have been tested in Graves' dise ase patients. Patients never submitted previously to antithyroid drug treat ment 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 ac count the rate of thyroid iodine uptake, i.e. I-131 dose = mu Ci/gm of the estimated thyroid weight x 100/24 hrs I-131 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 w as increased in order to overcome the possible resistance of this kind of p atients to the effect of I-131. One group (group III; n=24) received the ca lculated dose plus 1 mu Ci/gm of the estimated thyroid weight. Finally, gro up IV (n=27) received the calculated dose plus 0.25 mu Ci/gm of the estimat ed thyroid weight. Results. The analysis of the patients one year later demonstrated that grou ps 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 percen t of patients still exhibiting hyperthyroidism was 28% in group I, 26% in g roup IV: 12.5% in group III and 8.3% in group II. The highest number df hyp othyroid 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 Gra ves' hyperthyroidism in patients not submitted previously to antithyroid dr ug therapy. The most satisfactory therapy seems that utilized in protocol I I, 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 f igure. The high incidence of hyperthyroidism observed in groups III and IV submitted to a therapy with I-131 doses consistently higher than those util ized in groups I and II seems to confirm the hypothesis that hyperthyroid s ubjects submitted to a therapy with antithyroid drugs become rather resista nt to a radioiodine treatment.