NEFL and frontotemporal dementia: Few fluid biomarkers have been investigated in FTD, although there have now been a number of studies of neurofilament concentration in the CSF.3, –, 11 Higher neurofilament light chain (NfL) levels are believed to represent axonal degeneration,12,13 and while early studies showed variability in CSF concentrations in FTD,4, –, 10 a more recent study has suggested that CSF NfL levels correlate with disease severity.11