Standardized radioiodine therapy in Graves' disease: the persistent effect of thyroid weight and radioiodine uptake on outcome.

Abstract

OBJECTIVE: To assess the incidence of hypothyroidism, euthyroidism, and recurrent hyperthyroidism following a standard dose of Na131I (3.7 MBq or 100 microCi) per g thyroid tissue, adjusted for radioiodine tracer uptake. DESIGN: A single-centre prospective follow-up study from January 1990 to December 1992. SETTING: Academic Hospital in Utrecht, the Netherlands. SUBJECTS: Newly diagnosed patients with Graves' disease (n = 148). INTERVENTIONS: Radioiodine treatment at a standard dose of 3.7 MBq or 100 microCi per g thyroid tissue. MAIN OUTCOME MEASURES: Confidence interval testing of resulting thyroid status, defined by biochemical criteria. RESULTS: The overall cure rate was 70% (103 of 148 subjects), confidence interval (CI) 62-77%. A 90% incidence of hypothyroidism was found in patients with a small thyroid (less than 20 g). Recurrent hyperthyroidism was found significantly more often in subjects with a thyroid weight exceeding 60 g compared to those who had a thyroid of 9-59 g. More recurrences were found in subjects in the highest tertile of a 24-h radioiodine uptake test (> 80% uptake) compared to those in the lowest tertile (< 60% uptake). CONCLUSIONS: No uniform treatment results expressed per thyroid weight category were obtained, in spite of standardizing the treatment Na131I dose (3.7 MBq per g thyroid). Graves' patients with a thyroid smaller than 20 g and those with less than 60% 24-h radioiodine uptake have a 50-90% chance of hypothyroidism at the 12-month follow-up.