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Radioiodine Treatment of Hyperthyroidism—Prognostic Factors for Outcome

Division of Medical Sciences, University of Birmingham, Queen Elizabeth Hospital, Edgbaston, Birmingham, B15 2TH, United Kingdom

Address all correspondence and requests for reprints to: Professor J. A. Franklyn, Division of Medical Sciences, University of Birmingham, Queen Elizabeth Hospital, Birmingham, B15 2TH, United Kingdom. E-mail: j.a.franklyn{at}bham.ac.uk

Abstract

There is little consensus regarding the most appropriate dose regimen for radioiodine (¹³¹I) in the treatment of hyperthyroidism. We audited 813 consecutive hyperthyroid patients treated with radioiodine to compare the efficacy of 2 fixed-dose regimens used within our center (185 megabequerels, 370 megabequerels) and to explore factors that may predict outcome. Patients were categorized into 3 diagnostic groups: Graves’ disease, toxic nodular goiter, and hyperthyroidism of indeterminate etiology. Cure after a single dose of ¹³¹I was investigated and defined as euthyroid off all treatment for 6 months or T₄ 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% vs. 41.3%, P < 0.0001). There was no difference in cure rate between the groups 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 hypothyroidism (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) had a lower cure rate than patients over 40 yr old (68.9% vs. 79.3%, P < 0.001). 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 ¹³¹I. The use of antithyroid drugs, during a period 2 wk before or after ¹³¹I, resulted in a significant reduction in cure rate in patients given 185 megabequerels ¹³¹I (P < 0.01) but not 370 megabequerels. Logistic regression analysis showed dose, gender, goiters of medium or large size, and severity of hyperthyroidism to be significant independent prognostic factors for cure after a single dose of ¹³¹I. We have demonstrated that a single fixed dose of 370 megabequerels ¹³¹I is highly effective in curing toxic nodular hyperthyroidism as well as Graves’ hyperthyroidism. Because male patients and those with more severe hyperthyroidism and medium or large-sized goiters are less likely to respond to a single dose of radioiodine, we suggest that the value of higher fixed initial doses of radioiodine should be evaluated in these patient categories with lower cure rates.

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