Autori: Mariana Purice, Daniela Neamtu, Lavinia Vija, Gabriela Voicu, Maria Belgun, Andrei Goldstein

Editorial: 3rd BALKAN CONGRESS OF NUCLEAR MEDICINE together with ROMANIAN CONGRESS OF NUCLEAR MEDICINE, Bucharest/Romania, 2014.

Rezumat:

Background: After total thyroidectomy and radioiodine ablation therapy in patients with differentiated thyroid carcinoma (DTC), thyroglobulin (Tg), anti-thyroglobulin antibodies (Anti TgAb) and post-therapeutic 131I scan (whole body scan-WBS) are essential for the risk stratification and for further management. Stimulated serum Tg levels on thyroid hormone (T4) withdrawal are usually well correlated with 131I imaging results. Changes in thyroglobulin (Tg) and/or Tg antibody (TgAb) determination methods can disrupt the serial monitoring of DTC patients. Objectives: We present a one year monocentric retrospective study, underwent in the Nuclear Medicine Department of our institution on 890 DTC patients. We present the correlations between Tg, Anti TgAb levels and 131I WBS, as well as the incidence of the interferences between positive Anti TgAb on Tg interpretation. Methods: Serum Tg and Anti TgAb were performed with the same method, using 125I Tg-S IRMA-CT kits(analytical sensitivity-0.1 ng/ml) and 125I TgAb-one step IRMA-CT (analytical sensitivity-6 UI/ml), produced by RADIM-Italia. 131I WBS were performed with a Siemens e.cam Signature System γ camera, using a High Energy High Resolution collimator for 131I. All patients had TSH>30mUI/L on T4 withdrawal and other causes for inadequate preparation for the scan were ruled out. Results: For the majority of patients (79 %), Tg levels were below the cut-off limit for disease persistence or recurrence (<10 ng/ml) and was correlated with negative 131I PCI and 131I WBS, in accordance with a complete remission. A total of 120 patients (21%), were Tg+ve, with high (10-20 ng/ml) or very high (>20 ng/ml) serum Tg levels and negative Anti TgAb. In 75 patients (8.4% of patients or 63% of the Tg+ve subgroup), elevated Tg levels correlated well with positive 131I imaging. In 13 patients with positive correlation Tg/131I WBS, WBS revealed pulmonary (12 pts) or bone (1 pt) metastases, with no uptake in the cervical region. Moreover, 45 patients (5% of all patients or 37.5% of the Tg+ve group) presented discordant elevated Tg levels and negative Anti TgAb but negative WBS imaging. Using the same immune-radiometric method, with optimal sensitivity for Tg and without reported Hook effect for Anti TgAb, we found in 9% of patients the presence of strong positive Anti Tg, interfering with the Tg assay and underestimating serum Tg levels. From 890 patients sera, in 79 % Anti TgAb were < 35 mUI/ml (negative value), 8 % were equivocal (35-65%) and 12 % were strongly positive ( >65 mUI/ml). Conclusions: Detectable or elevated Tg concentrations most often correlate with 131I uptake, allowing identification of local or metastatic disease persistence/recurrence. However we identified 5% of DTC patients with discordant findings of high Tg measurement and negative 131I WBS, suggesting radioidine refractory remnant thyroid tissue. Interferences of positive Anti TgAb on Tg interpretation were significant even when using high sensitivity assays. Testing different Tg assays, as well as further investigating with different imaging modalities (CT, 131I SPECT/CT, 18F FDG PET/CT) are needed to exclude false negative/false positive Tg or WBS.

Cuvinte cheie: radioterapia cancerului diferentiat, markeri tumorali, imagistica, concordanta // Diferentiated cancer, 131 I therapy, Tg and anti Tg, scintigraphy