Positron Emission Tomography/Computed Tomography is useful in the follow-up of well-differentiated thyroid carcinoma with elevated anti thyroglobulin antibodies

Aim: Assessment of the clinical impact of a PET/CT with F.D.G. for the follow-up of differentiated thyroid cancer (D.T.C.) with rising or positive thyroglobulin autoantibodies (AbTg) level and negative or inconclusive conventional imaging work-up. Methodology:This retrospective study involves 15 patients seen in follow-up with confirmed D.T.C. primarily treated with total thyroidectomy and Iodine-131. Patients presenting increased AbTg and a negative or non informative conventional workout were included. The results of the PET/CT were correlated with histology and/or clinical follow-up. The clinical impact was determined on a change of intention to treat, which was decided upon in multidisciplinary meetings, based on the PET/CT result. Results: We observed 10 true positive exams confirmed via histology in seven patients and via clinical follow-up in three on the average 33 months (20-53 months), three real negative exams with negative follow up of on the average 39.5 months (30-47 months), one false positive and one false negative. The intention to treat was modified in 73.3 % (11/15 patients). PET/CT showed sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 91, 75, 90, 75, 86.6% respectively. There was a large and comparable dispersion of the AbTg values in both the true positive and the true negative groups, the kinetic of AbTg evolution could have a predictive value of a positive PET. Discussion/Conclusion: PET/CT with F.D.G. seems to be very useful in the therapeutic management of D.T.C. in the case of AbTg increased or positive, in particular for the patients with N1 in the initial staging. Further studies are suggested to confirm the very promising negative predictive value and specificity of this exam in a larger number of patients. (authors)