Cerebrospinal fluid NFL in the differential diagnosis of parkinsonian disorders: a meta-analysis.

•The CSF NFL levels in APD were significantly elevated relative to PD and healthy controls.•The CSF NFL levels can differentiate APD from PD with high sensitivity, specificity and diagnostic accuracy.•Prospective study design, and duration and severity of the disease may affect test performance.•Large and longitudinal studies are still needed on individuals who are suspected to have APD.