Radiometabolic treatment of hyperthyroidism with a calculated dose of 131-iodine: results of one-year follow-up.

Oral administration of radioactive iodine (131I) is a well-known and effective procedure for the treatment of hyperthyroidism. However, the optimal dose is still a matter of debate, as is the frequency of recurrence and hypothyroidism. The aim of our study was to evaluate the 1-yr outcome of a calculated dose of 131I activity in the treatment of hyperthyroidism, following the guidelines published jointly by the Italian Society of Endocrinology and the Italian Society of Nuclear Medicine.We studied 84 patients affected with hyperthyroidism (55 with Graves' disease and 29 with toxic adenoma), who were treated with a dose of 131I activity obtained by using the formula from the guidelines. In all patients serum free T4, free T3, and TSH were measured before, and 2, 6, and 12 months after radiometabolic therapy. A thyroid scan and thyroid uptake with 131I were also performed before treatment, and a thyroid ultrasound scan was obtained before and 1 yr after treatment. One year after treatment, 22 out of 55 patients with Graves' diseases (40.0%) had persistence/ recurrence of hyperthyroidism, whereas only 1 patient of the 29 with toxic adenoma (3.4%) was still in a hyperthyroid state. The frequency of hypothyroidism in patients responsive to therapy was higher in subjects with Graves' disease (45.5%), than in those with toxic adenoma (17.3%, p=0.02). Overall size reduction of the target lesion was 56.2+/-23.1%. In conclusion, the dose calculation suggested by the guidelines represents an effective method for treating thyroid toxic adenoma. In subjects with Graves' disease, we propose using a pre-determined 131I activity, which is higher than that derived from the guidelines. Such an approach would reduce the incidence of recurrent/persistent hyperthyroidism. On the other hand, an increase in post-131I hypothyroidism should not be regarded as a negative effect in these patients, since hypothyroidism is easily corrected, and the risk of worsening ophthalmopathy is reduced.