Erector spinae metastases from differentiated thyroid cancer identified by I-131 SPECT/CT.

Metastatic lesions from differentiated thyroid cancer (DTC) are usually seen in the cervical lymph nodes, lungs, or bones. Skeletal muscle, especially erector spinae metastasis from DTC, is extremely rare. In this report, 2 cases of DTC metastasizing to the erector spinae incidentally found by I-131 whole-body scanning and low-dose I-131 SPECT/CT scan are described. One is a PTC and the other is the follicular variant of PTC. I-131 whole-body scan is indispensable for the management of patients with DTC. However, precise localization of the foci of I-131 uptake is formidable because of the lack of anatomic landmarks. Low-dose integrated SPECT/CT allows for better location and definition of I-131 whole-body scan findings for residual or metastases in DTC. Metastases to skeletal muscle in DTC may be incidental findings and are more common on I-131 whole-body scans combined with SPECT/CT scans.