Objective: To determine the incidence and clinical predictors of hypothyroidism in one institution after radioiodine treatment of solitary toxic nodules.
Methods: We retrospectively analyzed the outcome of radioiodine therapy in 105 patients with solitary autonomous thyroid nodules treated at our institution during a 10-year period (January 1996 to December 2005; mean duration of follow-up, 53 +/- 34 months). Patients were monitored until the development of hypothyroidism, death, or the end of the study period. The cumulative incidence of hypothyroidism was determined by Kaplan-Meier life-table analysis, and predictors of hypothyroidism were determined by using a Cox regression model.
Results: The cumulative incidence of hypothyroidism was 11% at 1 year, 33% at 5 years, and 49% at 10 years. The development of hypothyroidism was not associated with age, sex, radioiodine dose, radioiodine uptake, or degree of suppression of extranodal tissue on scintiscans. The predictors of occurrence of hypothyroidism were pretreatment with antithyroid medications (P = .004; relative risk = 1.94) and positive thyroid antibody status (P = .008; relative risk = 1.84). Antibody-positive patients showed an earlier progression toward hypothyroidism than did antibody-negative patients.
Conclusion: Hypothyroidism is a common outcome of radioiodine treatment for autonomous thyroid nodules. In this study, coexistent thyroid autoimmunity and pretreatment with antithyroid medications were significant risk factors for the development of hypothyroidism.