The value of FDG-PET in the follow-up of differentiated thyroid cancer: a review of the literature.

Well differentiated (follicular and papillary) thyroid cancer (DTC) is characterized by rare occurrence and a good prognosis. However, up to 20% of patients with DTC develop locoregional recurrences, whereas even 8% of patients with such recurrences will eventually die from disease. In some of these patients it is related to incomplete initial treatment, whereas in others it indicates the presence of an aggressive tumor. In this latter case, dedifferentiation may occur with negative I-131 whole body scintigraphy (WBS) results and unreliable Tg measurements. In patients with thyroid cancer metastases that lost the capability of I-131 uptake, other imaging techniques are required to depict the non-functioning metastases, irrespective of the Tg-levels and irrespective of the site of recurrent disease. In this respect, some reports have discussed the value of ultrasonography of the head and neck region with good results for the detection of locoregional disease. We have assessed the role of FDG-PET in patients with I-131 negative WBS and its relation with Tg values and TSH-stimulation based on data that have appeared in the literature. In this review article, a discussion is given on the results published so far.