Positron emission tomography with F-18-deoxyglucose in patients with differentiated thyroid carcinoma, elevated thyroglobulin levels, and negative iodine scans

Abstract

Introduction: In patients with differentiated thyroid carcinoma, elevated serum levels of thyroglobulin (hTg) may occur in spite of otherwise negative diagnostic procedures and in particular in spite of a negative iodine-131 scan. Positron emission tomography with F-18-deoxyglucose (FDG-PET) is a potentially useful method for the detection of metastatic lesions or the recurrence of thyroid cancer. We aimed to investigate whether FDG-PET is capable of detecting metastastic lesions or recurrence in patients with differentiated thyroid carcinoma, elevated serum levels of thyroglobulin, and otherwise negative diagnostic procedures, including the iodine-131 scan. Methods: From a group of 500 patients with differentiated thyroid carcinoma, a subgroup of 32 patients had elevated serum hTg-levels, negative iodine-131 scans, negative cervical and abdominal ultrasound, and negative X-ray of the chest. In 12 of these patients (hTg 77.8±94.3 ng/ml, range 1.5 -277 ng/ml, median 20 ng/ml), FDG-PET was performed. All but one FDG-PET study was performed in a state of hypothyroidism (TSH 75.8±32.2 µIU/ml, range 31 -116 µIU/ml, median 74.6 µIU/ml). Results: In 6 of the 12 patients investigated, the FDG-PET was positive. In three of the patients, the diagnosis was confirmed by computed tomography or magnetic resonance imaging. In patients with a positive FDG-PET finding, the hTg level was 146.7±90.1 ng/ml (23 -277 ng/ml, median 144.5 ng/ml). In contrast, in patients with a negative finding the hTg level was only 9.0±7.6 ng/ml (range 1.5 -17 ng/ml, median 8.1 ng/ml), P = 0.01. Conclusion: These preliminary results show that in patients with differentiated thyroid carcinoma, elevated hTg levels, and otherwise negative "conventional" diagnostic procedures, FDG-PET is helpful in detecting metastatic lesions.A total of 500 patients treated for differentiated thyroid carcinoma were investigated retrospectively. Of these patients, 301 (60.2%) suffered from papillary carcinoma (48.0% pure papillary, 12.2% follicular variant), 199 (39.8%) from follicular carcinoma. The mean age of the 380 female (76.0%) and 120 male (24.0%) patients was 46.8±16.4 years at time of presentation.

The role of FDG-PET in localization of recurrent lesions of differentiated thyroid cancer (DTC) in patients with asymptomatic hyperthyroglobulinemia in a real clinical practice

“…We rather focused on the clinical usefulness of a widely accepted method in the real clinical practice. According to the published data and our own analysis, a positive FDG-PET result was achieved in DTC patients with higher serum Tg level (18,22). When Tg cut-off level that constitutes an indication for FDG-PET is lower, the sensitivity of FDG-PET decreases as a larger tumor volume is related to the higher Tg level and simultaneously the larger tumor is easier to detect.…”

“…PET combined with computed tomography (PET/ CT hybrid scanner Philips GEMINI GXL) was performed 60 min after intravenous administration of 7.4 mCi of 18 flourodeoxyglucose ( 18 FDG). The scanning volume covered the area from the top of the skull to the middle of the thighs.…”

Should high hTG levels in the absence of iodine uptake be treated?

“…We regard whole-body fluorine-18 fluorodeoxyglucose positron emission tomography (FDG PET) as essential in the diagnostic work-up of patients with elevated hTG and/or suspicious lesions without demonstrable 131 I uptake [6]. Using FDG PET, Alnafisi et al were able to identify metastatic lesions in the neck or upper mediastinum in 11/11 asymptomatic patients with positive hTG (median 61 ng/dl; range 25-12,000 under TSH stimulation), negative 131 I whole-body scans (3.7-7.4 GBq) and negative morphological imaging (cervical ultrasound and computed tomography of the neck and chest).…”

Relevance of Positron Emission Tomography (PET) in Oncology

“…Thyroid cancers with remaining functional differentiation for hormone synthesis and iodine uptake appear to have low glucose metabolism whereas undifferentiated tumors show high glucose utilization [45]. Accordingly, FDG-PET studies have been found to allow detection of metastases in patients with rising thyreoglobulin levels and normal iodine-131 scintigraphy [7,55]. Medullary thyroid carcinoma has also been found to show increased FDG uptake.…”