NEFL and Parkinson disease: After conducting Bonferroni post-hoc analysis, it was found that both PD-CN patients and NC at follow-up time (PD-CN patients: 16.26 ± 7.92 pg/mL; NC: 13.04 ± 6.48 pg/mL) exhibited higher serum NfL levels compared to those at baseline (Figure 2).