Objective: To retrospectively analyze the effect of plasma exchange (PLEX; yes = PLEX+, no = PLEX–) and steroids administration timing (prophylactically [proST] or therapeutically [therST]) on the longitudinal clinical course of patients with natalizumab-related progressive multifocal leukoencephalopathy (PML) and full-blown immune reconstitution inflammatory syndrome (PML-IRIS). Methods: Clinical and radiological data of 42 Italian patients with PML were analyzed. Patient's data are available until 12 months after PML diagnosis. PLEX and steroids treatment as time-dependent covariates were entered in: (1) a Cox model to investigate their impact on full-blown PML-IRIS latency; (2) an analysis of variance ANOVA to investigate their impact on IRIS duration; and (3) a linear mixed model to assess their impact on the longitudinal clinical course (measured by means of Expanded Disability Status Scale [EDSS]). Results: Treatment with PLEX was not associated to PML-IRIS latency (hazard ratio [HR] = 1.05; p = 0.92), but once IRIS emerged, its duration was significantly longer in patients who underwent PLEX (101 vs 54 days in PLEX+ and PLEX– patients; p = 0.028). Receiving proST versus therST was not associated to IRIS latency (HR = 0.67; p = 0.39) or duration (p = 0.95). Patients who underwent proST had a significantly higher EDSS increase during PML (0.09 EDSS points per month; p = 0.04) as compared to those who had therST. Interpretation: This study highlights that: (1) caution on the use of PLEX should be considered as the current data do not support a beneficial effect of PLEX and (2) caution on the early use of steroids is suggested because their prophylactic use to prevent full-blown PML-IRIS seems to negatively impact on the longitudinal disability course. Ann Neurol 2017;82:697–705.
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