Is [18F]-2-fluoro-2-deoxy-d-glucose (FDG) scintigraphy with non-dedicated positron emission tomography useful in the diagnostic management of suspected metastatic thyroid carcinoma in patients with no detectable radioiodine uptake?

Abstract

Objective: Dedifferentiation of thyroid cancer leads to an inability of thyroid cells to concentrate iodine. In these cases, imaging methods that allow an accurate detection of recurrence and/or metastases at an early stage are essential for an adequate management of patients. Positron emission tomography using [18F]-2-fluoro-2-deoxy-D-glucose and a dedicated (dPET-FDG) or non-dedicated (nPET-FDG) camera has been suggested as a potential tool for the detection of tumour foci. Design and methods: This prospective study was undertaken to evaluate nPET-FDG in 51 consecutive patients (18 men, 33 women) with differentiated thyroid cancer (33 papillary, 11 follicular, four insular and three oncocytic (Hü rthle-cell) thyroid carcinomas). Selection criteria were high thyroglobulin (Tg) levels (. 10 ng/ml off-levothyroxine treatment) and no detectable radioiodine uptake, on a whole body scan performed with a high dose, in the absence of iodine contamination. Results: Results were interpreted in terms of assumed presence of tumoral tissue. Sensitivity of nPET-FDG was similar to that of conventional imaging modalities (67%). False negative nPET-FDG (n ¼ 16) were observed mostly in cases of micro-lesions (lymph nodes or lung metastases). Conversely, nPET-FDG identified new tumoral sites in 11 cases. Better sensitivity was found for nPET-FDG in patients with Tg levels higher than 15 mg/l (P , 0.05). On a patient basis, results of nPET-FDG were equivalent to that of dPET-FDG. Finally, nPET-FDG changed treatment strategy in seven patients. Conclusions: nPET-FDG has a high sensitivity for the detection of tumour sites in patients when pathological iodine uptake cannot be demonstrated and appears to be a useful method in patients with elevated Tg levels, especially when dedicated PET is either unavailable or impractical.

Diagnostic management of suspected metastatic thyroid carcinoma: clinical value of octreotide scintigraphy in patients with negative high-dose radioiodine scans

“…SRS was positive in 22 patients (51%), and was the only positive test in three of them. PET-FDG was performed in 27 patients, belonging to a larger series of patients whose results have been previously reported (14). The examination was unequivocally positive in 16 patients, and was the only positive test in one patient.…”

Clinical Utility of 18F-FDG PET/CT Concurrent with 131I Therapy in Intermediate–to–High-Risk Patients with Differentiated Thyroid Cancer: Dual-Center Experience with 286 Patients

“…The early detection of iodinenegative DTC lesions is important, because it triggers an adjustment in the treatment strategy: surgical resection, external-beam radiation therapy (EBRT), or multikinase inhibitor therapy will be selected rather than 131 I treatment. 18 F-FDG PET/CT is useful for the detection of recurrent DTC lesions, especially in patients with iodine-negative tumors and elevated serum thyroglobulin levels (6)(7)(8)(9)(10). Furthermore, recent studies showed that 18 F-FDG PET can detect DTC lesions more accurately under thyroid-stimulating hormone (TSH) stimulation than under TSH suppression (11)(12)(13).…”

ENDOCRINE TUMOURS: Imaging in the follow-up of differentiated thyroid cancer: current evidence and future perspectives for a risk-adapted approach

“…Current guidelines recommend 18 FDG PET/CT when Tg levels exceed 10 ng/mL (9), and this threshold has been used in several studies. However, FDG PET positivity is also associated with lower thyroglobulin levels (101,109). For this reason, lower thresholds have been proposed.…”

“…Ultrasonography is still the best tool for detection of cervical lymph node metastases, but 18 FDG PET can be useful for identifying recurrence in areas that are difficult or impossible to explore sonographically, such as the upper mediastinum or the retropharyngeal region (101,112). As for distant metastases, 18 FDG PET can often detect small bone lesions that are missed on CT or MRI scans.…”

“…FDG PET findings lead to changes in patient management strategies (generally involving the surgical plan) in about 30% of the cases (101,102,103). As noted, however, false positivity related to inflammation is possible.…”