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).
Purpose: To compare empiric and calculated I activities using 2013 EANM recommendations. To look for predictive factors of therapeutic response to an empiric activity of I. To assess clinical situations favoring calculated treatment modalities.
Patients and Methods: Prospective monocentric study of clinical outcomes at 1 year follow-up in 86 patients with GD and MNG who received empiric I therapeutic activities (348-939 MBq). Differences between empiric and calculated activities were confronted to clinical outcomes. Physicians were not aware of the calculated activity at the time of prescription.
Results: One 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 activities were higher than calculated ones (564±131 vs. 316±319 MBq, P<0.001) in 93% (53/57) of patients. Pretherapeutic thyroid volume (>26 ml for GD; >40 ml for MNG) was associated with persistent hyperthyroidism.
Conclusion: Empirically administered I 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 26 ml or patients with MNG and thyroid volumes higher than 40 ml. A selective approach based on pretherapeutic thyroid volume and radioiodine biokinetics might improve treatment success.