title: The role of 18F-Fluorodeoxyglucose Positron Emission Tomography in patients with suspected recurrence or metastatic differentiated thyroid carcinoma with elevated serum thyroglobulin and negative I-131 whole body scan.
abstract: BACKGROUND
  The aim of this study is to evaluate the role of ¹⁸F-FDG PET/CT in the detection of recurrence or distant metastasis in patients with differentiated thyroid carcinoma (DTC) with elevated serum thyroglobulin (Tg) and negative ¹³¹I whole-body scan.
  
  
  METHODS
  The study included 19 patients (13 female, 6 male, average age 64 years) with DTC after total thyroidectomy and ¹³¹I ablation therapy that had elevated stimulated Tg and negative whole-body radioiodine scan. In all patients, standard imaging methods showed no suspicious changes. ¹⁸F-FDG PET/CT was performed after TSH stimulation with rhTSH or withdrawal of thyroid hormone. An evaluation of the dependence of the result of ¹⁸F-FDG PET/CT on the stimulated Tg levels was made accordingly. The statistical analysis was performed using Kruskal-Wallis test and ROC curves.
  
  
  RESULTS
  Based on the results of the study ¹⁸F-FDG PET/CT in 6 patients, the suspicion of metastasis involved: the cervical lymph nodes (3 patients, ~16%) and lungs (3 patients, ~16%). The patients underwent surgery. The histopathology confirmed metastatic thyroid cancer in all cases. High levels of TSH-stimulated Tg (Tg from 32 to >300 ng/ml, median of 59.7 ng/ml) in patients were reported. The group of remaining 13 patients (~68%) with negative 18F-FDG PET/CT had low levels of TSH-stimulated Tg (Tg of from 1.76 to 10.2 ng/ml, median of 4.0 ng/ml). A particular correlation was observed between ¹⁸F-FDG PET positivity and stimulated Tg levels. The receiver operating characteristic curve (ROC) analysis demonstrated a stimulated Tg cut-off of 28.5 ng/ml with 100% sensitivity and specificity. Stimulated Tg has a large and statistically significant (p<0.0001) accuracy in the detection of recurrence/metastasis.
  
  
  CONCLUSIONS
  1. ¹⁸F-FDG PET/CT is useful in the diagnosis of radioiodine-negative DTC in patients with high levels of stimulated Tg. 2. The sensitivity of ¹⁸F-FDG PET/CT increases with stimulated Tg levels. At stimulated Tg > 28.5 ng/ml, the sensitivity of the study reaches 100%.
authors.affiliation: Department of Endocrinology and Nuclear Medicine, Holycross Cancer Center, Kielce, Poland. trytom1@tlen.pl.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Trybek
authors.forename: Aldona
authors.initials: A
authors.lastname: Kowalska
authors.forename: Jacek
authors.initials: J
authors.lastname: Lesiak
authors.forename: Jacek
authors.initials: J
authors.lastname: Młynarczyk
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D009362:Neoplasm Metastasis; D049268:Positron-Emission Tomography; D012008:Recurrence; D012680:Sensitivity and Specificity; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood* / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging
chemical_list: D007457:Iodine Radioisotopes; D019788:Fluorodeoxyglucose F18; D013954:Thyroglobulin