Clinical Significance of Diffusely Increased 18F-FDG Uptake in the Thyroid Gland

Abstract

Our purpose was to determine the clinical significance of diffusely increased 18 F-FDG uptake in the thyroid gland as an incidental finding on PET/CT. Methods: All patients who were found to have diffuse thyroid uptake on 18 F-FDG PET/CT in our institution between November 2004 and June 2006 were investigated and compared with an age-and sex-matched control group. The 18 F-FDG uptake in the thyroid was semiquantified using maximum standardized uptake value and correlated to the available serum thyroid-stimulating hormone (TSH) and thyroid peroxidase (TPO) antibody levels using regression analysis. Results: Of the 4,732 patients, 138 (2.9%) had diffuse thyroid uptake. Clinical information was available for 133 of the 138 patients. Sixty-three (47.4%) had a prior diagnosis of hypothyroidism or autoimmune thyroiditis, of whom 56 were receiving thyroxine therapy. In the control group, consisting of 133 patients with no thyroid uptake, there were 13 (9.8%) with a prior diagnosis of hypothyroidism, 11 of whom were receiving thyroxine therapy. In the study group, 38 (28.6%) of 133 patients did not undergo any further investigation for thyroid disease, whereas 32 (24.1%) of 133 patients were examined for thyroid disease after PET. Nineteen were found with autoimmune thyroiditis or hypothyroidism, and replacement therapy was initiated in 12. No significant correlation was found between maximum standardized uptake value and TSH (P 5 0.09) or TPO antibody (P 5 0.68) levels. Conclusion: The incidental finding of increased 18 F-FDG uptake in the thyroid gland is associated with chronic lymphocytic (Hashimoto's) thyroiditis and does not seem to be affected by thyroid hormone therapy. SUV correlated neither with the degree of hypothyroidism nor with the titer of TPO antibodies.

Clinical Significance of Diffuse 18F-FDG Uptake in Residual Thyroid Gland after Unilateral Thyroid Lobectomy

“…Diffuse thyroid uptake does not seem to be affected by hormone replacement therapy and thyroid function state. Karantanis et al found that patients receiving thyroxine therapy for primary hypothyroidism could demonstrate diffusely increased 18 F-FDG uptake in their thyroid gland [11]. In agreement, most (95.8%) of our study population had already started thyroid hormone replacement therapy after unilateral thyroid lobectomy, and the thyroid function status was not significantly different between the two groups.…”

“…Interestingly, Tateish et al recently found that 20% of breast cancer patients in their study population showed diffuse thyroid uptake in PET/CT, which was significantly greater compared to the results of previous studies [14]. Although the precise mechanism for diffuse thyroid uptake is still unknown, the possibility of lymphocytic infiltration or active fibrosis formation related to chronic thyroiditis has been suggested [10,11]. 18 F-FDG PET is a noninvasive whole body imaging technique used to evaluate many kinds of malignant tumors.…”

“…The relationship between SUVmax and serum TSH level was evaluated by Karantanis et al in 138 patients with diffuse thyroid uptake [11]. They suggested that diffuse thyroid uptake might be associated with chronic thyroiditis, but no significant correlation between SUVmax and serum TSH level was found.…”

“…A thyroid lesion with focal 18 F-FDG uptake is likely to be malignant [5][6][7][8][9], whereas diffusely increased uptake in the thyroid gland is associated with several thyroid disorders including chronic thyroiditis, Graves' disease, and diffuse goiter [9][10][11][12][13]. Several studies have reported that incidence of diffusely increased 18 F-FDG uptake in the thyroid gland was 0.6-3.3%.…”

Clinical Correlation between the Autoimmune Thyroid Disease for the Thyroid Autoimmune Antibodies and the Maximum Standardized Uptake Value: Base on the Hashimoto's Thyroiditis and the Graves' Disease

“…검사 환자의 0.6-3.3% 정도로 보고되었으며 [8]- [11] 자가 면역 갑상선 질환(autoimmune thyroid disease)과 관련 있음을 보고하였다 [12]- [15] .…”