Adjuvant effect of hydrochlorothiazide on radioiodine treatment in low-iodine uptake Graves’ disease patients

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Maythinee Chantadisai
Supatporn Tepmongkol


Background: The outcome of radioiodine (RAI) treatment in Graves’ disease patients depends mostly on
the percentage of RAI uptake in the thyroid gland. Most Graves’ disease patients have a high percentage of RAI uptake while some have low uptake even after continuation of a low-iodine diet before RAI treatment.
Hydrochlorothiazide has been proven to increase the percentage of uptake in low-iodine diet low-uptake Graves’ disease patients. However, the effect on the patient’s outcome has never been demonstrated.

Objective: The aim of this study was to investigate the outcome of RAI treatment in low-iodine uptake Graves’
disease patients who were pre-treated with hydrochlorothiazide (HCTZ). The results were then compared with
those who continued the low-iodine diet alone.

Methods: All patients had Graves’ disease and had low iodine uptake at baseline (1st RAI uptake). This retrospective study aimed to compare the treatment outcomes between two groups. The control group consisted of patients who discontinued an iodine-containing diet for 2 weeks before the 2nd RAI uptake. The HCTZ group consisted of patients who discontinued an iodine-containing diet for 2 weeks together with 50 mg of HCTZ in two divided doses for 5 days before the 2nd RAI uptake. 131 I treatment doses were calculated based on the size of the thyroid gland, and the second 24-hr RAI uptake. The outcomes of treatment were then compared between the two groups at 3, 6, 9 and 12 months after treatment.

Results: There were 13 subjects in each group. At baseline, there was significantly higher 24-hr RAI uptake in the control group than the HCTZ group. However, in the second RAI uptake, the HCTZ group had significantly higher 3-hr and 24-hr uptake than the control group. Regarding the thyroid size, the HCTZ group had a larger mean of thyroid size than the control group. There was no significant difference in the percentage of remission at each time point between the two groups. However, after adjustment of the thyroid size and baseline 24-hr uptake, patients in the HCTZ group were 3.06 (adjusted OR = 3.06, 95%CI: 0.45, 20.68) times more likely to have disease remission than those in the control group, but this was not statistically significant.

Conclusions: Pre-treatment with HCTZ together with a low-iodine diet in low-uptake Graves’ disease patients are more likely to have a higher remission rate than using a low-iodine diet alone.

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