SPMS patients showed higher NfL levels than observed in PPMS patients, confirming previous results derived from larger cohorts [SPMS n = 1452 and PPMS n = 378; retrospective analysis of INFORMS and EXPAND trials presented by Kuhle et al. (26) ECTRIMS 2018] and CSF levels were highly correlated with serum concentration (Spearman rho = 0.684; p = 0.007). Here, NEFL is linked to primary progressive multiple sclerosis.