Unexpected symptoms after rhTSH administration due to occult thyroid carcinoma metastasis

¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸FDG-PET) scintigraphy is a useful imaging technique in the evaluation of metastasised thyroid carcinoma. Administration of recombinant human thyrotropin (rhTSH, Thyrogen®) increases the diagnostic yield of this procedure. Here we present a 64-year-old male who was followed for Hürthle cell carcinoma of the thyroid with several intrapulmonary metastases. He developed sudden complaints of neck pain following rhTSH administration as part of the routine preparation for a diagnostic ¹⁸FDG-PET÷CT procedure. This investigation subsequently revealed a previously undetected metastatic lesion in the first cervical vertebra, with no signs of spinal cord compression. Treatment with a nonsteroidal anti-inflammatory drug reduced the symptoms sufficiently, and a few weeks later the neurosurgeon performed a complete resection of the metastasis. It is likely that the symptoms were caused by oedema and÷or increased blood flow to the lesion. Physicians should be aware that rhTSH administration to patients with disseminated thyroid carcinoma may lead to sudden onset of symptoms caused by previously occult metastases.