title: 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.
  
  
  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 (Hurthle-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=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 microg/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.
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D018249:Adenoma, Oxyphilic / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002291:Carcinoma, Papillary / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis / Q000000981:diagnostic imaging*; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013954:Thyroglobulin / Q000097:blood; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D013965:Thyroidectomy; D014055:Tomography, Emission-Computed
chemical_list: D007457:Iodine Radioisotopes; D019788:Fluorodeoxyglucose F18; D013954:Thyroglobulin