Widespread Skeletal Metastases in Medullary Thyroid Carcinoma: Diagnostic Superiority of 68 Ga-FAPI PET/CT Over Somatostatin Receptor-Targeted Imaging.
Fatemeh Taheri, Amin Saber Tanha, Robabeh Beygom Aboutorabi et al.
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Case in brief
A 78-year-old woman with medullary thyroid carcinoma had persistently elevated serum calcitonin after surgery and radiotherapy. Although 99m Tc-octreotide imaging did not show skeletal metastases, 68 Ga-FAPI PET/CT demonstrated extensive skeletal involvement. Biochemical markers were disproportionately low relative to the disease burden, a pattern consistent with low-secretory MTC.
What made this case unusual
Extensive skeletal disease was detected by 68 Ga-FAPI PET/CT despite negative 99m Tc-octreotide imaging, with biochemical markers low relative to the metastatic burden.
Diagnostic / clinical pearl
In this case of MTC, 99m Tc-octreotide imaging missed extensive skeletal metastases that were visible on 68 Ga-FAPI PET/CT; low biochemical markers did not reflect the disease burden.