NEFL and amyotrophic lateral sclerosis: In studies differentiating FTD cases according to definite (pathologically proven or carrying a gene mutation) or probable (inferred from phenotype) pathological subtype, there is no agreement as to whether FTLD-TDP cases with ALS have higher CSF NFL levels than FTLD-TDP cases without ALS (Pijnenburg et al., 2015; Abu-Rumeileh et al., 2018).