Impact of (18)F-FDG PET/CT on treatment of patients with differentiated thyroid carcinoma, negative (131)I whole body scan and elevated serum thyroglobulin

OBJECTIVE(S): ( 18)F-FDG PET/CT is increasingly performed in patients with differen-tiated thyroid cancer. The aim of this study was to assess the clinical impact of (18)F-FDG PET/CT on the management of patients with differentiated thyroid carcinoma who had elevated serum thyroglobulin (Tg) and negative (131)I whole body scan (WBS). METHODS: 67 patients with differentiated thyroid carcinoma were included in this study. The findings of (18)F-FDG PET/CT imaging were compared with histo-pathology, follow up imaging, or clinical follow-up results. The diagnostic accuracy of (18)F-FDG PET/CT was evaluated for the entire patient group and for those patients with stimulated serum thyroglobulin levels of less than 5, 5–10, and more than 10 pmol/L as well as for local recurrences and metastases sites. The impact of (18)F-FDG PET/CT on therapeutic management was also evaluated. RESULTS: 30/67 patients had positive findings on (18)F-FDG PET/CT; 28 were true-positive and 2 were false-positive. (18)F-FDG PET/CT results were true-negative in 36 patients and false-negative in 1 patient. The overall sensitivity, specificity, accuracy, PPV and NPV of (18)F-FDG PET/CT were, 96.5%, 94.5%, 95.5%, 93.3%, and 97.2% respectively. Positive (18)F-FDG PET/CT findings were directly correlated with stimulated serum thyroglobulin levels, 7.1% had Tg between 5–10, and 92.9% had Tg greater than 10 pmol/L. (18)F-FDG PET/CT had a high or moderate impact on treatment management in 28 (41.8%) of patients. CONCLUSION: (18)F-FDG PET/CT is able to improve diagnostic accuracy and have management impact in a therapeutically relevant way in patients with differentiated thyroid carcinoma who present with rising thyroglobulin level, negative (131)I WBS, and clinical suspicion of recurrent disease.