Recently, methotrexate-associated lymphoproliferative disorders (MTX-LPDs) in rheumatoid arthritis (RA) have been found to commonly occur in association with iatrogenic immunodeficiency. Several factors have been reported to be related to the prognosis. We herein investigate the efficacy of 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in predicting the prognosis of MTX-LPD. We performed a retrospective analysis of the clinical features, characteristics, and outcomes of 18 patients with MTX-LPDs who were treated from 2004 to 2015. All of the patients were diagnosed with MTX-LPD based on the histological examination of biopsy specimens. Spontaneous regression was detected after the cessation of MTX in 5 of 18 cases (28%). The maximum standardized uptake value (SUVmax) of the FDG uptake on PET/CT was significantly lower, and the maximum size of the LPD-associated tumor was significantly smaller among the patients who showed spontaneous regression (p = 0.01, p = 0.04, respectively). Both the SUVmax and the maximum tumor size were related to better overall survival (p = 0.02, p = 0.04, respectively). Thus, PET/CT can be used to predict spontaneous regression and the prognosis at the diagnosis of MTX/LPD. Cases that showed spontaneous regression never relapsed during the follow-up period, despite the usage of several anti-rheumatoid arthritis drugs, including biological agents. The early detection of LPDs and the early cessation of MTX are important for the management of RA patients. An evaluation by F-FDG-PET/CT can be useful for predicting spontaneous regression and the prognosis.
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