Time course to hypothyroidism after fixed-dose radioablation therapy of Graves' disease in children

Presented in modified form at the poster session at the 2002 Annual Meeting of the Pediatric Academic Societies, May 5, 2002, Baltimore, Maryland.
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Abstract

Objective: To characterize the development of hypothyroidism in pediatric patients who receive a fixed dose of radioactive iodine (RAI). Study design: Medical records of children treated with fixed-dose RAI for Graves'disease between 1993 and 2001 were reviewed. Multiple variables including sex, age, thyroid hormone levels, thyroid-stimulating immunoglobulin titer, antithyroid medication use, and 24-hour radioiodine uptake were investigated as possible predictive factors for the development of hypothyroidism after treatment. All patients received RAI at a dose of between 13.8 and 15.6 mCi (average, 14.7 mCi; SD, 0.5). Results: Permanent hypothyroidism developed in all 40 patients, although a second dose of RAI was required in one case. The average time to hypothyroidism was 77 days (SD, 32), with a range of 28 to 194 days; 75% of the patients were diagnosed with hypothyroidism between 40 and 90 days. RAI treatment was ineffective in an additional patient, who required subtotal thyroidectomy. Conclusions: We conclude that a fixed dose of RAI is effective therapy in nearly all pediatric patients with Graves'disease. Factors predicting the time course to hypothyroidism were not identified. (J Pediatr 2002;140:99-103)

Section snippets

Methods

After institutional review board approval, medical records of patients who received RAI for Graves'disease at Riley Hospital for Children in Indianapolis, Indiana, between February 1993 and June 2001 were reviewed. Inclusion criteria included the use of RAI at a fixed dose of 15 mCi (range of delivered dose, 13.8-15.6 mCi) and availability of follow-up data. All patients were diagnosed by a pediatric endocrinologist, on the basis of clinical and laboratory data. The interval from RAI treatment

Results

Of 54 patients identified as candidates for the study, 40 were included. Of the 14 patients excluded, 11 received a nonfixed dose of RAI and 2 were lost to follow-up; RAI was ineffective in 1 patient, who never became hypothyroid and eventually required thyroidectomy.

The patients included 10 boys and 30 girls. All had biochemical evidence of hyperthyroidism at diagnosis. Twenty patients had a family history of thyroid disease and 4 patients were referred to an ophthalmologist for evaluation.

Discussion

Radioiodine therapy is becoming a more popular method of treating Graves'disease in children and adolescents and has been studied previously by several investigators.13, 18, 19, 20, 21, 22, 23, 24, 25 A lower limit of age for the use of RAI in children has not been established, and medical therapy is often used initially, particularly in very young children. However, available safety data regarding the use of RAI in pediatric patients has been extremely reassuring.16 One technique of RAI

Acknowledgements

We thank Linda A. DiMeglio, MD, and Jack Fuqua, MD, for reviewing the manuscript.

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    Reprint requests: Erica A. Eugster, MD, Pediatric Endocrinology, Riley Hospital for Children, Room 5960, 702 Barnhill Dr, Indianapolis, IN 46202.

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