As mentioned above, withdrawal of L-T4 sup-pressive therapy in preparation for 131I therapy may expose patients with metastases in critical body structures, such as vertebrae or the brain, to severe complications which are mainly neu-
Total thyroidectomy and 131I ablation
Undetectable Tg No other abnormalities
Tg detectable but institutional cut-off
Detectable Tg and other abnormalities or Tg > institutional cut-off
Decrease LT4 dose Yearly evaluation TSH, Tg on LT4 + neck US
Repeat rhTSH-stimulated Tg at • yearly interval
Tg stable or increasing
Withdraw LT4 Treatment with large activity of 131I and/or surgery Post-therapy WBS
Figure 17.1 A diagnostic algorithm for use of rhTSH in papillary and follicular thyroid cancer.
rological. In addition, a small minority of patients may not be able to elicit a sufficient response of endogenous TSH after thyroid hormone withdrawal, due to older age, long-term suppressive therapy, a concomitant illness, or pituitary insufficiency which prevents adequate uptake of 131I in metastatic foci. Finally, thyroid hormone withdrawal may be contraindicated for medical reasons, such as a coexistent illness. rhTSH is not approved for treatment of patients with 131I uptake in metastatic lesions; however, since 1995, rhTSH has been administered for this purpose to several hundred patients around the world within the framework of a clinical protocol named "compassionate use program."
In publications to date, rhTSH has been applied to stimulate radioiodine treatment in a total of 116 patients from different centers for a total of 155 treatment courses. The large majority of these patients were individuals with bulky, widespread, end-stage cancer. The results of the treatment are reported in a detailed and comprehensive review  indicating that rhTSH appeared to promote radioiodine uptake by tumor tissue in nearly all patients and that 66% of 92 patents with adequate follow-up data achieved some clinical benefit. Due to the more rapid renal clearance of 131I in euthyroidism compared to hypothyroidism, a higher 131I dose should theoretically be administered to achieve an equivalent dose to the metastatic lesion, although results from quantitative dosimetric studies are not yet available.
In some patients, swelling and pain due to bone metastases were observed after rhTSH administration. However, the duration of such symptoms was much shorter than was expected when therapy is administered during hypothy-roidism. Caution should be exerted in case of potential neurological complications and corti-costeroids should be used to prevent complications. At this stage, it is not possible to report on the long-term benefits of this treatment modality in comparison with thyroid hormone withdrawal. The general impression is that rhTSH stimulation may become the modality of choice as preparation for radioiodine treatment of metastatic patients provided that additional investigation, particularly in patients with less advanced disease than those included in the "compassionate use program," confirms the preliminary observation now available.
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