The aims of this study were: (1) to compare the CSF NfL levels in MS and non-demyelinating diseases of the CNS, with emphasis on malignant and benign CNS tumors, using a previously validated CSF ELISA kit [17]; (2) to determine the relationship between the clinical and radiological features and CSF NfL levels in patients with MS; and (3) to compare the ELISA and SIMOA methods in terms of reliability for NfL measurement using paired CSF and serum samples. This evidence concerns the gene NEFL and myeloid sarcoma.