Iodine Avid Muscle Metastases Mimicking Skeletal Lesions on Whole-Body Iodine Scan in Poorly Differentiated Thyroid Carcinoma –SPECT/CT to the Rescue

Differentiated thyroid carcinoma (DTC) metastasizes frequently to lymph nodes, lungs, and bones; however, muscle metastasis is a very rare manifestation in DTC and has never been reported in poorly differentiated thyroid carcinomas (PDTCs). Whole-body iodine scans are done postsurgery for staging and iodine avidity at residual/metastatic sites in patients of thyroid cancer. Iodine-avid muscle deposits may mimic bone metastases on whole-body iodine-131 planar imaging. SPECT/CT plays an important role in the localisation of abnormal tracer activity. Moreover, the existing data on iodine avidity of PDTC is variable. We present a case with PDTC with multifocal radioiodine-avid muscle metastases mimicking as skeletal metastases.