Free water predicts dementia with Lewy bodies in isolated REM sleep behavior disorder
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INTRODUCTION
Most individuals with isolated REM sleep behavior disorder (iRBD) develop dementia with Lewy bodies (DLB) or Parkinson’s disease (PD). Brain biomarkers predicting specific phenoconversion trajectories are lacking.
METHODS
In this multicenter diffusion MRI study (261 iRBD, 177 controls), free water (FW) was measured in the nucleus basalis of Meynert (NBM) and posterior substantia nigra (SN). Among 230 iRBD patients with follow-up, 64 converted (16 DLB, 38 PD). Time-to-event analyses were performed to assess differential phenoconversion.
RESULTS
Phenoconverters had higher FW in the NBM and posterior SN. Only FW in the NBM predicted conversion to DLB over PD. NBM volume predicted DLB conversion, but only FW remained significant when both were modeled. FW in the NBM correlated with lower MoCA scores in iRBD.
DISCUSSION
FW in the NBM is a sensitive biomarker of cognitive decline and DLB progression in iRBD, outperforming volume and supporting its use in early stratification.
