Clinical outcomes 1 year after empiric 131I therapy for hyperthyroid disorders: real life experience and predictive factors of functional response

Radioiodine is a therapeutic option in Europe for Graves' disease (GD) and toxic multinodular goiter (MNG).PurposeTo compare empiric and calculated I-131 activities using 2013 EANM recommendations. To look for predictive factors of therapeutic response to an empiric activity of I-131. To assess clinical situations favoring calculated treatment modalities.Patients and methodsProspective monocentric study of clinical outcomes at 1 year follow-up in 86 patients with GD and MNG who received empiric I-131 therapeutic activities (348-939MBq). Differences between empiric and calculated activities were confronted to clinical outcomes. Physicians were not aware of the calculated activity at the time of prescription.ResultsOne year after treatment, 9% (5/57) of GD patients and 7% (2/29) of MNG patients were still in a hyperthyroid state. Thyroid volume was reduced by 67% for GD and by 50% for MNG. In GD, empiric I-131 activities were higher than calculated ones (564131 vs. 316 +/- 319MBq, P<0.001) in 93% (53/57) of patients. Pretherapeutic thyroid volume (>26ml for GD; >40ml for MNG) was associated with persistent hyperthyroidism.ConclusionEmpirically administered I-131 for GD and MNG was associated with very high efficacy in thyroid function control and no side effects. Thyroid volume reduction did not preclude treatment efficacy. Activity calculation could be a useful method for treating patients with GD and thyroid volumes higher than 26ml or patients with MNG and thyroid volumes higher than 40ml. A selective approach based on pretherapeutic thyroid volume and radioiodine biokinetics might improve treatment success.