Progressive multifocal leukoencephalopathy (PML) mimicking high-grade glioma on delayed F-18 FDG PET imaging.

The purpose of our study was to determine the increase in F-18 fluorodeoxyglucose (FDG) uptake in a patient with progressive multifocal leukoencephalopathy (PML) between early and late scan times using positron emission tomography (PET) imaging with F-18 FDG at conventional (60 minutes [min] after injection, PET(60)) and delayed (300 min after injection, PET(300)) intervals. PET(60) and PET(300) imaging was performed on a pathologically proven PML lesion. The PML lesion in the posterior fossa exhibited an increase in F-18 FDG uptake of 52% between early and late times, which was in the range of that in high-grade gliomas. Thus, dual-time-point PET with F-18 FDG may not be able to differentiate between infectious and malignant brain lesions.