Abstract
A relatively uncommon occurrence of multiple unusual distant metastasis in a patient
with thyroglobulin-elevated negative iodine scintigraphy (TENIS) (subcutis, skeletal
muscle, kidney, and pericardium) is presented. A 65-year-old man with papillary thyroid
carcinoma post two cycles of radioactive iodine therapy on subsequent follow-up showed
elevated serum thyroglobulin (>300 ng/mL) and negative iodine scintigraphy (TENIS).
[18F]-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography
(CT) for disease restaging revealed extensive metastatic disease involving cervical
and mediastinal nodes, bones, liver, subcutis, skeletal muscle, kidney, and pericardium.
[68Ga]-fibroblast activation protein inhibitor (FAPI)-04 PET/CT was done to evaluate
for fibroblast activation protein (FAP) expression, and the feasibility of targeted
radionuclide therapy showed nil to very low FAP expression at the metastatic sites,
except for the few cervical and mediastinal nodes, subcutaneous nodule in the left
arm, and L3 vertebral lesion. In addition to illustrate the rare presentation in TENIS,
this case demonstrates the superiority of [18F]-FDG PET/CT over FAPI PET/CT in this
patient. However, FAPI-PET/CT may be used as a theranostic tool for assessing radionuclide
therapy prospects in selected cases.
Keywords
thyroid cancer - TENIS - unusual distant metastasis -
18F-FDG PET/CT - [
68Ga]-FAPI-04 PET/CT
