title: Selectively false-positive radionuclide scan in a patient with sarcoidosis and papillary thyroid cancer: a case report and review of the literature.
abstract: BACKGROUND
  Radioiodine and Tc-99 m pertechnetate scans are routinely relied upon to detect metastasis in papillary thyroid cancer; false-positive scans are relatively rare. To our knowledge, no published reports exist of sarcoidosis causing such selectively false-positive scans.
  
  
  METHODS
  We present a case of a 41-year-old woman with known metastatic papillary thyroid cancer (T1bN1aMx) in whom sarcoidosis-affected cervical and mediastinal lymph nodes demonstrated uptake of thyroid-targeting radionuclides. Only the minority of these nodes demonstrated radionuclide uptake, raising the suspicion of adjacent or coexisting sarcoid and metastatic involvement. Selective uptake of thyroid-targeted radionuclides by isolated sarcoidosis is, to our knowledge, a previously undocumented occurrence.
  
  
  RESULTS
  Biopsies of uptake-negative mediastinal nodes revealed sarcoidosis. Pathology from a subsequent neck dissection excising uptake-positive cervical nodes also showed sarcoidosis, with no coinciding malignancy.
  
  
  CONCLUSIONS
  We document a case of sarcoidosis causing a selectively false-positive thyroid scintigraphy scan. It is useful for clinicians to be aware of potential false-positives and deceptive patterns on radionuclide scans when managing patients with both well-differentiated thyroid cancer and a co-existing disease affecting the nodal basins draining the thyroid gland.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, The Ottawa Hospital, University of Ottawa, 501 Smyth Rd., Box 216, Ottawa, ON, K1H 8L6, Canada. nlebo045@uottawa.ca.
authors.forename: Nicole L
authors.initials: NL
authors.lastname: Lebo
authors.affiliation: Department of Medicine, Division of Nuclear Medicine, University of Ottawa, Ottawa, Canada. fraymond@ottawahospital.on.ca.
authors.forename: Francois
authors.initials: F
authors.lastname: Raymond
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, The Ottawa Hospital, University of Ottawa, 501 Smyth Rd., Box 216, Ottawa, ON, K1H 8L6, Canada. modell@toh.on.ca.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Odell
mesh_terms: D000231:Adenocarcinoma, Papillary / Q000000981:diagnostic imaging* / Q000473:pathology; D000328:Adult; D044963:Biopsy, Fine-Needle; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008198:Lymph Nodes / Q000473:pathology; D008207:Lymphatic Metastasis / Q000000981:diagnostic imaging / Q000473:pathology; D009367:Neoplasm Staging; D011877:Radionuclide Imaging; D012507:Sarcoidosis / Q000000981:diagnostic imaging*; D013670:Sodium Pertechnetate Tc 99m; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology
chemical_list: D007457:Iodine Radioisotopes; D013670:Sodium Pertechnetate Tc 99m