CHI3L1 and multiple system atrophy: Lower CSF levels of NFL (SMD = −3.609, 95% CI: −4.545 to −1.594), t-tau (SMD = −0.977, 95% CI: −1.520 to −0.434), YKL-40 (SMD = −0.973, 95% CI: −1.292 to −0.655), and CRP (SMD = −0.556, 95% CI: −0.871 to −0.242) were observed in PD patients compared with MSA patients.