title: Recurrent/metastatic thyroid carcinomas false negative for serum thyroglobulin but positive by posttherapy I-131 whole body scans.
abstract: OBJECTIVE
  Serum Tg and I-131 WBS have been used to detect recurrent and metastatic thyroid cancers postoperatively. Tg is known to be more sensitive than I-131 WBS, and therefore, false-negative WBS cases with elevated Tg levels are frequently found. However, the clinical characteristics of false-negative Tg cases with positive WBS have not been clarified.
  
  
  METHODS
  The authors evaluated 824 postoperative patients with differentiated thyroid carcinoma who underwent post-ablation/therapy I-131 WBS. Tg negativity was defined as a Tg level of < or = 2 ng/mL without TgAb under thyroid-stimulating hormone stimulation. Remission, recurrence, and metastasis were confirmed using pathologic or clinically findings.
  
  
  RESULTS
  Fifty-two patients (6.3%) with functioning metastasis and negativity for TgAb were Tg-negative and posttherapy I-131 WBS-positive (TgN group), and 128 patients with functioning metastases were Tg positive and WBS positive (TgP group). The TgN group consisted of 45 cases of cervical/mediastinal lymph node metastases (86.5%) and seven cases of distant metastasis to lung or bone by follow-up WBS. The TgN group demonstrated significantly higher profiles of regional involvement than the TgP group (P < 0.029). In 47 patients in the TgN group, metastatic uptake disappeared in 33, ameliorated in four, and persisted in ten during follow-up.
  
  
  CONCLUSIONS
  A significant number of differentiated thyroid cancer patients were Tg-/TgAb-negative despite a positive WBS finding. Cervical and mediastinal lymph nodes were predominant sites of metastasis in the TgN group. WBS should be undertaken routinely as a complementary modality to detect functioning recurrence and metastasis regardless of serum Tg results.
authors.affiliation: Department of Nuclear Medicine, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-Gu, Seoul, 110-744, Korea.
authors.forename: Eun-Kyung
authors.initials: EK
authors.lastname: Park
authors.forename: June-Key
authors.initials: JK
authors.lastname: Chung
authors.forename: Il Han
authors.initials: IH
authors.lastname: Lim
authors.forename: Do Joon
authors.initials: DJ
authors.lastname: Park
authors.forename: Dong Soo
authors.initials: DS
authors.lastname: Lee
authors.forename: Myung Chul
authors.initials: MC
authors.lastname: Lee
authors.forename: Bo Youn
authors.initials: BY
authors.lastname: Cho
mesh_terms: D000328:Adult; D005188:False Negative Reactions; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D012008:Recurrence; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000556:secondary* / Q000628:therapy; D051598:Whole Body Imaging
chemical_list: D007457:Iodine Radioisotopes; D013954:Thyroglobulin
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