Plasma neurofilament light for early differentiation of multiple system atrophy from Parkinson disease.

backgroundEarly differentiation of multiple system atrophy (MSA) from Parkinson's disease (PD) remains difficult, particularly within two years of symptom onset, when diagnostic uncertainty has major implications for prognosis, referral, and trial enrolment. Because MSA is rare, previous biomarker studies have often been limited by relatively small samples and restricted multicentre validation. We aimed to determine the diagnostic performance of plasma neurofilament light chain (NfL) for differentiating MSA from PD and to assess the incremental value of glial fibrillary acidic protein (GFAP), total tau (t-tau), and phosphorylated tau at threonine 217 (p-tau217).

methodsIn this multicentre cross-sectional diagnostic study, participants were enrolled from five movement-disorder referral centres in China between Jan 1, 2018, and June 30, 2024, and were divided by enrolment period into discovery and temporally separated validation datasets. Plasma NfL, GFAP, t-tau, and p-tau217 were measured using light-initiated chemiluminescence assays. Group comparisons used age- and sex-adjusted models, and discrimination was assessed using receiver-operating-characteristic analysis with sensitivity, specificity, predictive values, and robustness analyses.

findingsThe analysis included 2408 participants: 782 (32.5%) with PD, 796 (33.1%) with MSA, and 830 (34.5%) healthy controls. NfL was the best single biomarker for differentiating MSA from PD in the discovery dataset (AUC 0.920, 95% CI 0.903-0.936). The discovery-derived cutoff of 41.3 pg/mL yielded sensitivity of 90.5% and specificity of 83.4% in the discovery dataset, and sensitivity of 86.7% and specificity of 85.5% in the validation dataset (AUC 0.924, 95% CI 0.898-0.948). In the early-stage subgroup, NfL retained strong performance (AUC 0.943, 95% CI 0.915-0.966). Integrated multimarker models provided limited incremental discrimination over NfL alone.

interpretationPlasma NfL may support the differentiation between clinically diagnosed MSA and PD, including early in the disease course. The limited added value of multimarker panels supports a simpler and more immediately translatable NfL-first strategy for diagnostically uncertain parkinsonism.

fundingNational Natural Science Foundation of China; the Capital's Fund for Health Improvement and Research; Beijing Natural Science Foundation; Beijing Municipal Science and Technology Commission; Beijing Neurosurgical Institute; Beijing Traditional Chinese Medicine Science and Technology Development Fund.