RADIOIODINE THERAPY COMPARED IN PATIENTS WITH TOXIC NODULAR OR GRAVESHYPERTHYROIDISM

In view of uncertainty regarding the most appropriate radioiodine dose for patients with hyperthyroidism due to toxic nodular disease or Gra ves' disease, we prospectively studied outcome in patients with these disorders given a single 5 mCi (185 MBq) dose of radioiodine. We studi ed 103 patients receiving their first radioiodine dose; 44 with toxic nodular hyperthyroidism and 59 with Graves' hyperthyroidism. Thyroid s tatus (off antithyroid drug therapy) at 6 and 12 months after radioiod ine was related to diagnosis, use of carbimazole before or after radio iodine, and physical and biochemical findings. At 6 months, persistent hyperthyroidism was less frequent in toxic nodular disease than in Gr aves' disease (34.1% vs. 55.9%, p<0.05); hypothyroidism was also less frequent (11.4% vs. 27.1%, p<0.05). Those with persistent hyperthyroid ism at 6 months were given a second (10 mCi, 370 MBq) dose of radioiod ine. At 12 months after the first dose, 80.6% of the group with toxic nodular hyperthyroidism were either euthyroid or hypothyroid, and 74.5 % of those with Graves' disease were euthyroid or hypothyroid, the rat e of hypothyroidism again being less in toxic nodular disease (19.4% v s, 58.8%, p<0.05). Logistic regression and stepwise discriminant analy sis demonstrated that 'cure' (euthyroidism or hypothyroidism) at 6 mon ths was related to serum free T4 at presentation (p<0.001) and adminis tration of carbimazole before or after radioiodine (p<0.001) (severe h yperthyroidism and carbimazole increasing the likelihood of persistent hyperthyroidism) but was not related to the diagnosis of toxic nodula r or Graves' hyperthyroidism, These results argue in favour of a 'low dose' rather than a 'high dose' radioiodine regimen in patients with t oxic nodular hyperthyroidism, at least in those with mild disease and without complications. The marked influence upon outcome of both carbi mazole treatment before or after radioiodine, and the degree of hypert hyroidism at presentation, suggests that doses of radioiodine of >5 mC i should be administered to hyperthyroid patients requiring adjunctive antithyroid drugs and those with marked biochemical hyperthyroidism.