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A case of stunning of lung and bone metastases of papillary thyroid cancer after a therapeutic dose (3.7 GBq) of ¹³¹I and review of the literature: implications for sequential treatments

Department of Nuclear Medicine, Hôpital Necker–Enfants Malades, 149 rue de Sèvres, 75743 Paris Cedex 15, France

Thyroid stunning is usually defined as the inhibition or suppression of iodide trapping by remnant thyroid tissue or by functioning metastases following a diagnostic dose of ¹³¹I. The risk of stunning increases progressively with larger doses. Because the threshold above which this effect occurs in thyroid remnants seems to be between 37 MBq and 111 MBq of ¹³¹I, therapeutic ¹³¹I doses of 3.7 GBq may cause stunning. We describe stunning of papillary thyroid cancer lung and bone metastases after a therapeutic dose of ¹³¹I (3.7 GBq). A T1 bone metastasis and bilateral lung metastases were diagnosed by post-therapeutic dose whole-body scan. Nuclear MRI detected another lesion at T4, whose ¹³¹I fixation was not obvious. An additional 0.7 GBq were given after recombinant TSH, 37 days after the therapeutic dose; 24 h later, uptake by the lung and T1 metastases had disappeared, but trapping was again seen 6 months later on the post-therapeutic scan. This re-appearance is evidence in favour of the transitory and reversible character of stunning, and confirms its correspondence to the decreased ability of viable thyroid cells to trap iodine and not to their destruction. A better understanding of stunning would make it possible, in the event of rapidly progressing disease and in conjunction with recombinant thyroid stimulating hormone (TSH), to give several therapeutic doses of ¹³¹I in close succession without each dose hampering the effectiveness of the subsequent one.