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

Objectives: ¹⁸F-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 ¹⁸F-FDG PET/CT on the management of patients with differentiated thyroid carcinoma who had elevated serum thyroglobulin (Tg) and negative ¹³¹I whole body scan (WBS).

Methods: 67 patients with differentiated thyroid carcinoma were included in this study. The findings of ¹⁸F-FDG PET/CT imaging were compared with histo-pathology, follow up imaging, or clinical follow-up results. The diagnostic accuracy of ¹⁸F-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 ¹⁸F-FDG PET/CT on therapeutic management was also evaluated.

Results: 30/67 patients had positive findings on ¹⁸F-FDG PET/CT; 28 were true-positive and 2 were false-positive. ¹⁸F-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 ¹⁸F-FDG PET/CT were, 96.5%, 94.5%, 95.5%, 93.3%, and 97.2% respectively. Positive ¹⁸F-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. ¹⁸F-FDG PET/CT had a high or moderate impact on treatment management in 28 (41.8%) of patients.

Conclusion: ¹⁸F-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 ¹³¹I WBS, and clinical suspicion of recurrent disease.