Selectively false-positive radionuclide scan in a patient with sarcoidosis and papillary thyroid cancer: a case report and review of the literature

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.