Low iodine diet does not improve the efficacy of radioiodine for the treatment of Graves’ disease

Vanessa A Santarosa,Ilda S Kunii,Rui M B Maciel,Teresa S Kasamatsu,Magnus R Dias-Da-Silva,Marília M S Marone,Mário L Castiglioni,Lia B Fiorin,Denise M Orlandi,João R M Martins,Rosália P Padovani,Gilberto K Furuzawa,José Gilberto H Vieira

doi:10.1590/2359-3997000000082

Abstract

Consuming a low-iodine diet (LID) is a widely accepted practice before administering radioiodine (131I) to evaluate and to treat thyroid disease. Although this procedure is well established for the management of patients with differentiated thyroid cancer, its use in patients with benign disease is unclear. So, we aimed to evaluate the influence of a LID on the outcome in patients with Graves' disease (GD) treated with 131I. We evaluated 67 patients with GD who were divided into 2 groups: one group (n = 31) consumed a LID for 1-2 weeks, and the second group (n = 36) was instructed to maintain a regular diet (RD). The LID group experienced a 23% decrease in urinary iodine after 1 week on the diet and a significant 42% decrease after 2 weeks on the diet. The majority (53%) of the patients in the LID group had urinary iodine levels that were consistent with deficient iodine intake. However, there was no difference in the rate of hyperthyroidism's cure between the LID and the RD groups 6 months after 131I therapy. Furthermore, the therapeutic efficacy did not differ in patients with varying degrees of sufficient iodine intake (corresponding urinary iodine levels: < 10 μg/dL is deficient; 10-29.9 μg/dL is sufficient; and > 30 μg/dL is excessive). In the present study, we demonstrated that although a LID decreased urinary iodine levels, those levels corresponding with sufficient or a mild excess in iodine intake did not compromise the therapeutic efficacy of 131I for the treatment of GD.

Highlights

Radioiodine (131I) represents one of the first-line therapies for Graves’ disease (GD) [1,2,3,4]
There were no significant differences between the low-iodine diet (LID) and the regular diet (RD) groups in terms of gender, age, duration of disease, thyroid volume or thyroid-stimulating hormone (TSH), FT4 or urinary iodine levels
We evaluated whether urinary iodine levels at the time of treatment, regardless of whether the patients adhered to a restrictive diet, affected the response to radioiodine

Summary

Introduction

Radioiodine (131I) represents one of the first-line therapies for Graves’ disease (GD) [1,2,3,4]. Patients were followed for 2 weeks before RAIT and were examined weekly to determine thyroid function and to measure urinary iodine levels. There were no significant differences between the LID and the RD groups in terms of gender, age, duration of disease, thyroid volume or TSH, FT4 or urinary iodine levels.

Results

Conclusion