Positron emission tomography as an aid in the diagnosis and follow-up of Riedel's thyroiditis.

We describe the usage of positron emission tomography (PET) as an aid in the initial diagnosis and follow-up of Riedel's thyroiditis. A 41-year-old patient was admitted for an enlarged and tender thyroid gland in association with severe systemic symptoms of inflammation. Imaging with fluorine-18 fluorodeoxyglucose (FDG) and PET demonstrated an intensive uptake of FDG in both lobes of the thyroid gland as an indication of severe inflammation. The diagnosis of Riedel's thyroiditis was confirmed by the histological findings of biopsy specimens taken during a palliative thyroid resection. The inflammatory symptoms and local pain dramatically disappeared after commencement of high-dose corticosteroid therapy. A follow-up PET scan after 2 weeks of corticosteroid treatment showed a 60% decrease in the uptake of FDG in the thyroid. This indicates that FDG metabolic activity can also be used to assess a patient's response to therapy in Riedel's thyroiditis.