High-Dose Corticosteroids for Immune Reconstitution Inflammatory Syndrome in Patients Who Develop Progressive Multifocal Leukoencephalopathy on Natalizumab

The objectives of this study are to explore the effects of administering high-dose corticosteroids to participants who developed progressive multifocal leukoencephalopathy (PML) while on natalizumab as measured by time-course change in functional status based on Karnofsky Performance Status Index through 6 months following the completion of plasma exchange (PLEX; or equivalent), survival at 6 months following the completion of PLEX (or equivalent), and incidence and severity of adverse events (AEs) and serious adverse events (SAEs); to characterize the evolution of immune reconstitution inflammatory syndrome (IRIS) as measured by time course changes in Global Clinical Impression of Improvement (GCI-I), Symbol Digit Modalities Test (SDMT), brain magnetic resonance imaging (MRI), magnetoencephalography (MEG), chemokines, cytokines, C-reactive protein (CRP), John Cunningham virus (JCV) load and cell count in cerebrospinal fluid (CSF); and to characterize the time course elimination of serum natalizumab concentrations in the study population following the last PLEX (or equivalent) procedure.