NEFL and Parkinson disease: In detail, NDEV Nf-L showed a significantly higher concentration in PD patients compared to both the other groups (PD vs. rET: p value = 0.001; PD vs. HC: p value < 0.0001), while NDEV Nf-L levels between ET and HC were largely overlapping (p value = 0.62) (Fig. 2).