CSF Biomarkers for Early Diagnosis of Synucleinopathies: Focus on Idiopathic RBD

Idiopathic REM sleep behavior disorder (iRBD) is one of the most significant prodromal manifestations of synucleinopathies. Different predictive biomarkers for iRBD conversion have been investigated, but scarce data are present in literature about the predictive role of cerebrospinal fluid (CSF) biomarkers. In this review, we focus on CSF biomarkers in patients with both iRBD and RBD associated with synucleinopathies to explore their potential predictive power.

Recent studies revealed that CSF α-synuclein levels are higher in Parkinson's disease (PD) patients with RBD compared to those without RBD, even if α-synuclein does not seem to predict conversion of iRBD into PD. In the Parkinson Progression Marker Initiative (PPMI) cohort, early PD patients with RBD show lower CSF Aβ₄₂ levels, which predict faster cognitive decline. CSF prion protein and inflammatory biomarkers have been also investigated in RBD and synucleinopathies with controversial results. A variety of CSF biomarkers are promising candidate for predicting iRBD conversion into synucleinopathies. Further studies are needed in iRBD patients followed for several years in order to observe the phenoconversion in synucleinopathies and to elucidate the possible role of CSF biomarkers as predictive biomarkers of conversion.