Radioiodine therapy compared in patients with toxic nodular or Graves' hyperthyroidism

In view of uncertainty regarding the most appropriate radioiodine dose for patients with hyperthyroidism due to toxic nodular disease or Graves' disease, we prospectively studied outcome in patients with these disorders given a single 5 mCi (185 MBq) dose of radioiodine. We studied 103 patients receiving their first radioiodine dose; 44 with toxic nodular hyperthyroidism and 59 with Graves' hyperthyroidism. Thyroid status (off anti-thyroid drug therapy) at 6 and 12 months after radioiodine was related to diagnosis, use of carbimazole before or after radioiodine, and physical and biochemical findings. At 6 months, persistent hyperthyroidism was less frequent in toxic nodular disease than in Graves' 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 hyperthyroidism at 6 months were given a second (10 mCi, 370 MBq) dose of radioiodine. 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 rate of hypothyroidism again being less in toxic nodular disease (19.4% vs. 58.8%, p < 0.05). Logistic regression and stepwise discriminant analysis demonstrated that 'cure' (euthyroidism or hypothyroidism) at 6 months was related to serum free T4 at presentation (p < 0.001) and administration of carbimazole before or after radioiodine (p < 0.001) (severe hyperthyroidism and carbimazole increasing the likelihood of persistent hyperthyroidism) but was not related to the diagnosis of toxic nodular or Graves' hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)