MRI phenotyping of progressive multifocal leukoencepahlopathy

Background Progressive multifocal leukoencephalopathy (PML) is an opportunistic infection of the brain caused by JC polyomavirus. Brain magnetic resonance imaging (MRI) is the most sensitive tool for the in vivo detection of PML. However, comprehensive data on imaging findings using multisequence image acquisition are limited. Objective To investigate MRI findings of active PML in a large, prospectively collected cohort using a comprehensive and standardized MRI protocol. Methods Eighty patients with active PML underwent standardized 3T brain MRI including 3D-T2w-fluid-attenuated inversion recovery, 3D-T1-weighted, T2-weighted, diffusion-weighted (DWI), susceptibility-weighted (SWI) and contrast-enhanced T1-weighted sequences. Lesions were analysed regarding dissemination, location, morphology, borders, and signal characteristics. Results Eighty patients showed widespread involvement affecting the frontal (91%) and parieto-occipital (93%) lobes, typically involving juxtacortical (95%) and deep white matter (99%), but also cortical grey matter (94%) and deep grey matter (71%). Most patients showed large (> 3 cm, 89%), focal (99%), T2-hyperintense (100%) and T1-hypointense (99%) lesions with ill-defined borders (79%). DWI hyperintensity was present in 90%, while SWI hypointense rims were detected in 61% of the patients. Contrast enhancement was observed in 55%. Certain imaging features included the punctate pattern (76%) and the shrimp sign (20%). Conclusions PML exhibits characteristic but heterogeneous MRI findings on a patient level predominantely showing widespread white matter and frequent cortical grey matter involvement. Sequences such as DWI and SWI show frequently additional imaging findings potentially improving the diagnostic certainty. Our data stress the need of standardized imaging protocols for reliable detection and phenotyping of PML across diverse immunosuppressive conditions.