NEFL and myeloid sarcoma: This group of biomarkers consist of polypeptides found in the cytoplasm ofneurons, which are released into the cerebrospinal fluid (CSF) and blood in numerousCNS diseases, including MS.10 We and others have previously shown that neurofilament light chainmeasurements in CSF (CSF-NfL) correlate well with clinical worsening ofdisability.11–13 In addition, both cross-sectional and longitudinal studiesreport associations of CSF-NfL with MRI activity in MS, but the number of studiesare limited, with relatively short follow-up.14–17