Interlesional 'flip-flop' between ⁶⁸Ga-DOTATATE and FDG-PET/CT in thyroglobulin-elevated negative iodine scintigraphy (TENIS) syndrome

Patients with elevated thyroglobulin and negative iodine scintigraphy (TENIS) are a challenging group among patients of thyroid carcinoma. Currently, multiple therapeutic options and approaches (such as tyrosine kinase inhibitors, PRRT) are being explored. We illustrate the case of an 81-year-old man with a diagnosis of TENIS with both pulmonary and skeletal metastases (serum thyroglobulin level >300 μg/dl), where an interesting ‘flip-flop’ phenomenon was observed between individual metastatic lesions: the skeletal lesions were mostly ⁶⁸Ga-DOTATATE-positive (SUVmax 15.27 and 8.52) but FDG-negative (SUVmax 1.5 and 2.8) whereas the pulmonary lesions were FDG-positive (SUVmax 10.44) with minimal or absent uptake on ⁶⁸Ga-DOTATATE-PET/CT (SUVmax 3.7; [Figure - 1]). A solitary left pulmonary lesion was negative on both tracers ([Figure - 1] coronal slices). Interestingly, the patient had a recent history of associated middle ear infection, which was manifested by uptake on FDG-PET/CT in the petrous bone ([Figure - 1] MIP). Biopsy of the prominent right lung nodule showed a focus of poorly differentiated thyroid carcinoma arising in a conventional papillary thyroid carcinoma. The patient had relatively stable disease compared to his previous FDG-PET/CT (⁶⁸Ga-DOTATATE was not done previously). In view of his skeletal symptoms and the vertebral lesions showing intense uptake on ⁶⁸Ga-DOTATATE PET/CT, he was considered for PRRT with ¹⁷⁷Lu-DOTATATE.

Figure 1: 1. MIP and fused coronal and transaxial slices of PET-CT with 68Ga-DOTATATE (left columns) and FDG (right columns) showing interlesional 'flip-flop' between the two PET tracers

Molecular imaging with multitracer PET can depict tumour biology and aid in devising management strategy.