Correlation between anti-thyroid peroxidase antibody levels and diffuse thyroid uptake of 18 F-fluorodeoxyglucose in Hashimoto's thyroiditis: a retrospective study.

Background: On 18 F-fluorodeoxyglucose (FDG)-positron emission tomography (PET), diffuse uptake in the thyroid gland is often observed in patients with Hashimoto's thyroiditis. In this study, we evaluated the factors associated with diffuse uptake by comparing Hashimoto's thyroiditis patients with or without diffuse uptake in the thyroid.

Methods: A retrospective study was conducted of 18 patients with Hashimoto's thyroiditis who underwent blood tests, thyroid ultrasonography, and FDG-PET during the period from 2014 to 2015. The patients were divided into two groups: one with diffuse thyroid uptake (group 1, n  = 13) and one without diffuse thyroid uptake (group 2, n  = 5). Clinical and laboratory parameters, including maximum standardized uptake in the thyroid (SUVmax), which was defined as the higher value obtained in either the right or left thyroid lobe, were compared in the two groups.

Results: The frequency of abnormal findings, such as a rough or heterogeneous pattern, was significantly higher in group 1 ( p  <  0.01), as were anti-thyroid peroxidase (TPO) antibody titers, anti-thyroglobulin (Tg) antibody titers, and SUVmax ( p  <  0.01). The frequency of hypothyroidism did not differ significantly in the two groups. Anti-TPO and anti-Tg titers were positively correlated with SUVmax ( r  = 0.856, p  <  0.01 and r  = 0.821, p  <  0.01, respectively); in univariate analysis, anti-TPO titer was predictive of SUVmax ( p  <  0.01).

Conclusions: The results of the current study suggest that Hashimoto's thyroiditis patients with high titers of anti-thyroid antibodies are likely to exhibit intense diffuse FDG uptake in the thyroid, and that thyroid function may be clearly impaired, even in the presence of mild FDG uptake in the thyroid.