Extensive white matter lesions after 2 years of fingolimod: progressive multifocal leukoencephalopathy or MS relapse?

International audienceFingolimod is a widely used treatment for highly active relapsing multiple sclerosis (RR MS).Here we report the case of a 27-year-old MS patient treated for more than two years byfingolimod, who presented severe hemiplegia and speech disturbances associated withextensive white matter lesions on brain MRI. Although initial presentation questioned thepossibility of progressive multifocal leukoencephalopathy, final diagnosis was MS relapseand appropriate treatment resulted in clinical and radiological improvement. Severe MSrelapses under fingolimod have been reported, but late onset after treatment initiation andextensive subcortical topography are unusual, and represent a diagnostic challenge