NEFL and Primary lateral sclerosis: Levels of serum NfL were significantly elevated in ALS patients compared with those given an alternative diagnosis or diagnosed with PLS at the first visit (ALS median 218.1 pg/ml, IQR 130.7–311.9; PLS 65.6 pg/ml, 51.5–106.9; non-ALS 45.1 pg/ml, 13.5–71.9 pg/ml; ALS versus PLS P < 0.001; ALS versus non-ALS P < 0.001; Fig. 1A).