Chronic thyroiditis: diffuse uptake of FDG at PET

To determine the frequency and clinical importance of diffuse 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake in the thyroid gland.

A total of 1,102 healthy subjects underwent whole-body positron emission tomography (PET). PET images were evaluated for increased diffuse FDG uptake in the thyroid gland. Serum free thyroxine and thyrotropin levels were measured in 36 subjects with increased uptake and in 36 matched control subjects without uptake. Antithyroid antibodies were also measured. Morphologic abnormalities were examined by using ultrasonography (US).

Diffuse FDG uptake was found in three men and 33 women; the prevalence was significantly higher in women (P < .01). Thirty-five subjects were euthyroid; one had hypothyroidism. Antithyroid antibodies were positive in 27 subjects. In most subjects, US findings facilitated the diagnosis of chronic thyroiditis. In control subjects, the positive rates for antithyroid antibodies and US abnormalities were significantly lower than those of the study group (P < .01).

Diffuse thyroidal FDG uptake may be an indicator of chronic thyroiditis. The actual prevalence of the disorder was not low in this series, and such lesions may be found incidentally at FDG PET.