Radioiodine treatment of hyperthyroidism - Prognostic factors for outcome

regimen for radioiodine (I-131) in the treatment of hyperthyroidism. We aud ited 813 consecutive hyperthyroid patients treated with radioiodine to comp are the efficacy of 2 fixed-dose regimens used within our center (185 megab equerels, 370 megabequerels) and to explore factors that may predict outcom e. Patients were categorized into 3 diagnostic groups: Graves' disease, tox ic nodular goiter, and hyperthyroidism of indeterminate etiology. Cure afte r a single dose of I-131 was investigated and defined as euthyroid off all treatment for 6 months or T-4 replacement for biochemical hypothyroidism in all groups. As expected, patients given a single dose of 370 megabequerels had a higher cure rate than those given 185 megabequerels, (84.6% vs. 66.6 %, P < 0.0001) but an increase in hypothyroidism incidence at 1 yr (60.8% v s. 41.3%, P < 0.0001). There was no difference in cure rate between the gro ups with Graves' disease and those with toxic nodular goiter (69.5% vs. 71. 4%; P, not significant), but Graves' patients had a higher incidence of hyp othyroidism (54.5% vs. 31.7%, P < 0.0001). Males had a lower cure rate than females (67.6% vs. 76.7%, P = 0.02), whereas younger patients (< 40 yr) ha d a lower cure rate than patients over 40 yr old (68.9% vs. 79.3%, P < 0.00 1). Patients with more severe hyperthyroidism (P < 0.0001) and with goiters of medium or large size (P < 0.0001) were less likely to be cured after a single dose of I-131. The use of antithyroid drugs, during a period 2 wk be fore or after 13% resulted in a significant reduction in cure rate in patie nts given 185 megabequerels I-131 (P < 0.01) but not 370 megabequerels. Log istic regression analysis showed dose, gender, goiters of medium or large s ize, and severity of hyperthyroidism to be significant independent prognost ic factors for cure after a single dose of I-131. We have demonstrated that a single fixed dose of 370 megabequerels I-131 is highly effective in curi ng toxic nodular hyperthyroidism as well as Graves' hyperthyroidism. Becaus e male patients and those with more severe hyperthyroidism and medium or la rge-sized goiters are less likely to respond to a single dose of radioiodin e, we suggest that the value of higher fixed initial doses of radioiodine s hould be evaluated in these patient categories with lower cure rates.