NEFL and frontotemporal dementia: Although most studies on longitudinal NFL levels in FTD have been conducted on blood because of the less invasive nature of blood sampling compared with CSF sampling, two investigations reported longitudinal data regarding CSF NFL: whereas in the 27 patients with a follow-up lumbar puncture in the cohort of Ljubenkov et al. (2018) no consistent longitudinal trend of NFL could be recognized, 11 of the 14 FTD patients with a longitudinal CSF sample studied by Skillbäck et al. (2017) showed higher levels of NFL compared with the first sample (Skillbäck et al., 2017; Ljubenkov et al., 2018).