A retrospective study with long term follow-up of Graves' disease patients treated with low activities of 131Iodine.

Background: Previous studies have shown that application of relatively low I-Iodine activities can successfully be used to treat patients with Graves' disease (GD). We assessed treatment outcome in the long-term follow-up of our GD patients and influencing factors.

Methods: We evaluated 521 GD patients in this retrospective clinical single-center study. In all patients we performed scintigraphy and thyroid uptake measurement after 4 and 24 hours using 10 MBq I and calculated administered activity using Marinellis' formula. Treatment was done according to national regulations. Minimal routine clinical evaluation of all patients was available after 6 weeks and after 3, 6 and 12 months. Success of treatment was defined as euthyroid state or hypothyroidism 6 months after therapy.

Results: We usually applied relatively low I activities. Three hundred seven patients (58.9%) became hypothyroid within 21 years of follow-up. One hundred thirty-nine patients (26.7%) became euthyroid and stayed euthyroid until the end of follow-up. We found a plateau after 7 years of initial therapy with only a few patients becoming hypothyroid after that time and identified 75 patients (14.4%) with persistent hyperthyroidism or recurrence.

Conclusions: Treatment with relatively low I activities produce favorable responses as shown in previous works. We found a high proportion of patients with long-term euthyroid state. Application of low activities reduces radiation burden of patients and, depending on radiation protection legislation, may lead to shortened hospital stay and reduced costs. Therefore, we feel that application of higher activities to treat GD patients as recommended in several current guidelines should be reconsidered.