Abstract


Introduction:Recombinant human thyroid-stimulating hormone (rhTSH) is commonly used in preparation for radioactive iodine (RAI) treatment in differentiated thyroid cancer (DTC).  We describe a patient with papillary thyroid cancer (PTC) with miliary pulmonary metastases not detected on  cross-sectional imaging studies or on the post-treatment I131 scan after rhTSH stimulation. They became apparent as diffuse lung uptake on the post-treatment I-131 scan after thyroid hormone withdrawal (THW). view more

Introduction:Recombinant human thyroid-stimulating hormone (rhTSH) is commonly used in preparation for radioactive iodine (RAI) treatment in differentiated thyroid cancer (DTC).  We describe a patient with papillary thyroid cancer (PTC) with miliary pulmonary metastases not detected on  cross-sectional imaging studies or on the post-treatment I131 scan after rhTSH stimulation. They became apparent as diffuse lung uptake on the post-treatment I-131 scan after thyroid hormone withdrawal (THW).
Clinical Case:A 30-year-old woman with a history of mesenchymal chondrosarcoma was found to have PTC on surveillance PET-CT. Cross-sectional imaging showed no clear evidence of distant metastases but did reveal a few nonspecific small lung nodules up to 4mm. She underwent total thyroidectomy and left central and lateral modified neck dissection in April 2014. Pathology revealed a 3 cm diffuse sclerosing variant of PTC in the left lobe with lymphovascular invasion and minimal extrathyroidal extension. 17 of 31 lymph nodes were positive for metastases, many with extranodal extension, TNM -T3N1bMx. Five weeks postoperatively, thyroglobulin (Tg) was 18.1 ug/L. In June 2014, she received 150mCi of I-131 after rhTSH. TSH was 103 mIU/L and Tg was 133.8 ug/L on the day of treatment. Post-treatment scan showed thyroid bed uptake and a few foci outside of the thyroid bed in the neck consistent with local metastatic disease. Neck ultrasound showed a few small lymph nodes. Two months after RAI treatment Tg was 18.6 ug/L. Subsequent Tg levels on thyroid hormone suppression were 23.1, 19.1, and 24.5 ug/L in January, March, and June 2015 respectively. Repeat CT and PET-CT for surveillance for mesenchymal chondrosarcoma were unremarkable. Evaluation for heterophile antibodies was negative. In August 2015 the patient received RAI treatment after THW due to concern for distant metastases given persistently elevated Tg. After THW, TSH was 92 mIU/L and Tg was 495.3 ug/L. Pre-treatment I-123 scan was negative. She received 100 mCi of I-131. Post-treatment scan showed diffuse pulmonary uptake in addition to a few foci of neck uptake. Both RAI treatments took place after 2 weeks of low-iodine diet and were at least 4 months from CT imaging studies.
Conclusion:rhTSH is currently approved by the FDA for use in preparation for RAI remnant ablation and for surveillance of DTC recurrence. Iodine kinetics have been shown to be different between THW and rhTSH. Our case demonstrates a failure of iodine uptake in the microscopic pulmonary metastatic foci after rhTSH stimulation despite a higher dose of RAI. rhTSH avoids hypothyroid symptoms and is equally effective as THW for remnant ablation, but its effectiveness in the treatment of residual disease and distant metastases remains to be established. rhTSH should not be used routinely in these situations.

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