INTRODUCTION: Most individuals with isolated rapid eye movement 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 magnetic resonance imaging 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. HIGHLIGHTS: FW in the NBM specifically identifies conversion to DLB. Increased FW in the NBM is associated with lower global cognition in iRBD. FW in the SN in iRBD does not relate more to DLB than PD. FW in the NBM is a biomarker of differential phenoconversion in iRBD.

• Klíčová slova
• Parkinson's disease, REM sleep behavior disorder, biomarker, dementia with Lewy bodies, diffusion magnetic resonance imaging, free water, prognosis,
• MeSH
• biologické markery MeSH
• demence s Lewyho tělísky * diagnostické zobrazování   diagnóza   MeSH
• difuzní magnetická rezonance MeSH
• lidé středního věku MeSH
• lidé MeSH
• Parkinsonova nemoc diagnostické zobrazování   MeSH
• porucha chování v REM spánku * komplikace   diagnostické zobrazování   MeSH
• progrese nemoci MeSH
• senioři MeSH
• voda * MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• multicentrická studie MeSH
• Názvy látek
• biologické markery MeSH
• voda * MeSH

Isolated REM sleep behavior disorder (iRBD) is associated with impaired colour discrimination, cognitive deficits and morphological changes. This study evaluates whether colour discrimination deficits in iRBD are mediated by cognitive functions or related to dopaminergic denervation and brain morphology. A sample of 73 patients with iRBD and 77 controls underwent neuropsychological assessment, and colour discrimination assessment using the Farnsworth Munsell 100 Hue Test, DAT-SPECT, and MRI. The data were analyzed using multiple regression, mediation analysis, and voxel-based morphometry. Significant between-group differences were found in total colour discrimination as well as in the red-yellow spectrum. The association between iRBD and performance in the yellow-green spectrum was mediated by cognitive functions, as measured by the Montreal Cognitive Assessment. In controls, a positive correlation between the yellow-green spectrum and the left inferior frontal gyrus was observed compared to patients, however, this association was largely driven by a single data point. The performance in the green-blue spectrum was associated with the activity of dopamine transporters in the caudate nucleus. No interactions were found for total colour discrimination in any analysis. The present findings demonstrate a colour vision deficit in iRBD, which is not directly linked to any of the proposed potential explanatory mechanisms.

• Klíčová slova
• Cognitive functions, Farnsworth-Munsell 100-Hue Test, REM sleep behavior disorder, Synucleinopathy, Vision,
• MeSH
• dopamin * metabolismus   MeSH
• dospělí MeSH
• jednofotonová emisní výpočetní tomografie MeSH
• kognitivní dysfunkce * etiologie   patofyziologie   diagnostické zobrazování   MeSH
• lidé středního věku MeSH
• lidé MeSH
• magnetická rezonanční tomografie MeSH
• mozek * diagnostické zobrazování   patologie   MeSH
• porucha chování v REM spánku * diagnostické zobrazování   patologie   metabolismus   komplikace   patofyziologie   MeSH
• proteiny přenášející dopamin přes plazmatickou membránu metabolismus   MeSH
• senioři MeSH
• vnímání barev * fyziologie   MeSH
• Check Tag
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• dopamin * MeSH
• proteiny přenášející dopamin přes plazmatickou membránu MeSH