Residual FDG uptake of primary thyroid lymphoma after treatment may overestimate residual lymphoma

Objective

To assess ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) images in primary thyroid lymphoma (PTL) patients before and after treatment.

Methods

We conducted a retrospective review of data for ten patients (four men, six women) of mean age 65 (range 48–88) years, with histopathologically confirmed malignant thyroid lymphoma who underwent pre-treatment and post-treatment ¹⁸F-FDG PET between January 2005 and December 2014. Thyroid uptake was assessed by the 5-point scale score based on maximum intensity projection images.

Results

Four of the ten patients were judged to have a complete metabolic response (scores 1–3) and four to have a partial metabolic response (PMR; scores 4–5). Three of the four PMR patients had a good outcome with a treatment-free interval and overall survival of at least 53.0 months, although two of these three patients showed residual FDG uptake in the thyroid for more than 2 years after completion of treatment. Two of the ten patients were considered to have progressive metabolic disease.

Conclusions

In patients with PTL, residual FDG uptake in the thyroid after treatment that corresponds to a PMR may not always indicate a poor outcome.