J Nucl Med 2000 Dec;41(12):1989-95
Influence of thyroid-stimulating hormone levels on uptake of FDG in recurrent
and metastatic differentiated thyroid carcinoma.
Moog F, Linke R, Manthey N, Tiling R, Knesewitsch P, Tatsch K, Hahn K.
The objective of this prospective study was to determine the extent to which the
levels of thyroid-stimulating hormone (TSH) influence the uptake of FDG by
thyroid carcinoma tumors METHODS: Ten patients with follicular (n = 7) or
papillary (n = 3) thyroid carcinoma underwent FDG PET during TSH suppression
(<0.05 microU/mL) and TSH stimulation (>22 microU/mL) within an average
interval of 42 d (range, 28-73 d). The findings were evaluated by visual
criteria. In addition, a tumor-to-background ratio (TBR) was determined for 17
lesions that were visualized. RESULTS: In 15 of 17 lesions with positive FDG
uptake, TSH stimulation was associated with an increase in the TBR from 3.85 +/-
2.53 (mean +/- SD) to 5.84 +/- 4.84, corresponding to an average increase of
63.1% (P < 0.001). Determination of absolute counting rates indicated that
this increase was the result of a decrease in FDG metabolism in the background
together with an increase in the tumor tissue. No relationship was found between
the presence or absence of iodine storage capacity (5 versus 12/17 lesions) and
increase in FDG accumulation. Seven of 10 patients had additional
iodine-positive metastases that showed no accumulation of FDG. CONCLUSION: Most
locally recurrent and metastatic follicular and papillary thyroid carcinomas
exhibited a significant increase in FDG uptake on TSH stimulation. In 3 of 10
patients, TSH stimulation resulted in either detection of new lesions or
classification of the FDG uptake pattern as typical for malignancy. These
findings suggest that FDG uptake in recurrent and metastatic thyroid carcinoma
depends on the TSH level. Therefore, we recommend that PET examinations be
performed in patients with thyroid carcinoma under TSH stimulation and follow-up
examinations be performed under identical TSH conditions to prevent erroneous
interpretation.
