Abstract
The preparation for radioiodine administration recommended by the current pediatric literature is a 6-wk withdrawal that typically includes the transient administration of T3. Compared with adults, T4 clearance rates and serum TSH to free T4 ratios are higher in children, implying that pediatric patients can achieve adequate hyperthyrotropinemia with shorter levothyroxine withdrawals. The objective of this study was to determine whether children with differentiated thyroid cancer achieve adequate hyperthyrotropinemia using an abbreviated levothyroxine withdrawal protocol. The study design was a retrospective analysis of 15 consecutive levothyroxine withdrawals performed without T3 at Children's Hospital Boston. Eleven children with differentiated thyroid cancer were included. The average age at the time of withdrawal was 12.5 +/- 0.8 yr. Serum TSH concentrations obtained after the discontinuation of levothyroxine were analyzed to determine the time interval required to achieve a serum TSH level greater than 25 microU/ml for each patient. Adequate hyperthyrotropinemia was documented in all children tested by d 14. The mean interval required to achieve a serum TSH level above 25 microU/ml from a suppressed serum TSH was 12.3 +/- 0.7 d. Shorter withdrawals minimize hypothyroid morbidity and the theoretical risk of decreased 131micro)I residence time from excessive hyperthyrotropinemia. These benefits are amplified in children due to their high incidence of distant metastases. We propose an abbreviated 2-wk withdrawal protocol to facilitate the adjunctive therapy and surveillance of children with follicular cell-derived cancers.
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