Use of quantitative susceptibility mapping (QSM) in progressive multifocal leukoencephalopathy

Summary Background Progressive multifocal leukoencephalopathy (PML) is an opportunistic demyelinating encephalopathy related to JC virus. Its characteristics on conventional brain MRI are well known and are important for the diagnosis. Objective To analyze SWI hypointensities recently described in U-fibers and cortex adjacent to the white matter lesions of PML. Methods Prospective study including four patients with an history of definite diagnosis of PML. Clinical data were collected retrospectively. Brain MRI exams were done on a 3 T magnet, including FLAIR, T2 GRE sequences and SWI. Results Four males were included (mean age: 47 years, mean PML duration: 24.2 months). Immunosuppression was related to AIDS (n = 2), natalizumab for multiple sclerosis (n = 1), B-cell lymphoma treated by chemotherapeutic agents and rituximab (n = 1). All patients had SWI hypointensities in cortex and/or U-fibers adjacent to the white matter lesions. QSM always suggested a paramagnetic effect. Conclusion SWI and T2 GRE hypointensities in cortex and U-fibers adjacent to the white matter lesions seem highly prevalent in PML, irrespective of the delay between PML onset and the MRI. QSM data suggest a paramagnetic effect.