Kuijt WJ and Huang SA (2005) Children with differentiated thyroid cancer achieve adequate hyperthyrotropinemia within 14 days of levothyroxine withdrawal. J Clin Endocrinol Metab [10.1210/jc.2005-1085]

Current literature recommends that levothyroxine be withdrawn for 6 weeks prior to radioiodine treatment for thyroid cancer, to increase serum TSH levels and consequently increase the iodine-concentrating ability of malignant thyroid tissue. Recent studies have shown that a shortened withdrawal time is beneficial, because it lessens hypothyroid morbidity. Kuijt and Huang investigated whether adequate hyperthyrotropinemia (serum TSH >25 μU/ml) could be achieved using a simplified 2-week withdrawal program in children with differentiated thyroid cancer.

This retrospective study took place between May 2000 and February 2005 at the Children's Hospital Boston, MA, and included data on 15 withdrawals from 11 children (mean age at withdrawal 12.5 years). Most patients underwent radioiodine whole-body scanning before and after radioiodine therapy. Serum TSH was measured anytime between 19 days before levothyroxine withdrawal to 2 days afterwards, and then regularly from approximately 7 days after withdrawal.

Levothyroxine withdrawal was followed by a rapid rise in serum TSH levels. The mean length of time needed to achieve hyperthyrotropinemia was 12.3 ± 0.7 days. All children tested achieved adequate hyperthyrotropinemia by day 14. The children showed a more rapid rise in serum TSH levels following levothyroxine withdrawal than was expected, compared with previous studies in adults.

The authors suggest that a treatment algorithm should be constructed and recommend that, in children with thyroid cancer, the 6-week levothyroxine withdrawal protocol should be replaced with one of 2 weeks.