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Authors’ Response: Pretreatment with a Single, Low Dose of Recombinant Human Thyrotropin Allows Dose Reduction of Radioiodine Therapy in Patients with Nodular Goiter

Department of Nuclear Medicine (W.-A.N., D.A.H.), Catharina Hospital, 5602 ZA Eindhoven, The Netherlands; and Department of Endocrinology (W.-A.N., A.R.H.), University Medical Center, 6500 HB Nijmegen, The Netherlands

Address correspondence to: W.-A. Nieuwlaat, M.D., Department of Endocrinology, University Medical Center Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands. E-mail: wanieuwl{at}knmg.nl.

To the editor:

We thank Dr. Bonnema and colleagues for their comments. Indeed, our study (1) is an observational study, not a randomized trial, comparing the safety and efficacy of ¹³¹I therapy after treatment with various doses of recombinant human TSH (rhTSH) with that of standard ¹³¹I therapy, i.e. without pretreatment with rhTSH. As Bonnema et al. emphasize, rhTSH administration in patients with nodular goiters might induce acute increases in serum thyroid hormone levels and thyroid size. At the start of our study, no data on this issue were available. Therefore, the principal aim of our study was to explore the short-term safety of the administration of a therapeutic dose of ¹³¹I after pretreatment with a single dose of rhTSH. For safety reasons, we used low doses of rhTSH (0.01 or 0.03 mg), and we adjusted the therapeutic dose of ¹³¹I to the rhTSH-induced increase in 24-h radioactive iodine uptake, as determined in a diagnostic study, using a tracer dose of ¹³¹I. We did not aim at doses higher than 100 µCi (3.7 MBq) ¹³¹I per gram of thyroid tissue retained at 24 h. We agree that thyroid volume measurements in the first few days after rhTSH administration would have been informative. However, because in our study a therapeutic dose of ¹³¹I was given 24 h after rhTSH administration, radiation safety regulations in our hospital precluded such early measurements. Anyhow, we did not observe symptoms and signs of (worsening of) tracheal compression in the first days after rhTSH administration.

We fully agree with Bonnema et al. that further studies are needed before rhTSH can be advised as an adjunct to ¹³¹I therapy in nodular goiter. First, it has to be determined in a formal dose-response study which dose of rhTSH is optimal for this purpose. This study is currently being performed in the United States. The optimal rhTSH dose should stimulate radioactive iodine uptake considerably, but should not cause unacceptable increases in serum thyroid hormone levels and thyroid volume. Then, radioiodine therapy with and without pretreatment with that particular dose of rhTSH should be investigated in randomized studies. Such studies should look carefully at dose-response relationships with respect to efficacy and adverse effects, especially when ¹³¹I treatment with rhTSH prestimulation is intended to reach higher radiation-absorbed doses in the thyroid than in our study, with the aim of achieving larger volume reductions.

Received September 11, 2003.

References

1. Nieuwlaat WA, Huysmans DA, Van Den Bosch HC, Sweep CG, Ross HA, Corstens FH, Hermus AR 2003 Pretreatment with a single, low dose of recombinant human thyrotropin allows dose reduction of radioiodine therapy in patients with nodular goiter. J Clin Endocrinol Metab 88:3121–3129[Abstract/Free Full Text]

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