Objective: To quantify cortical and subcortical brain volumes using structural MRI analysis in idiopathic REM sleep behavior disorder (iRBD) subjects at risk for Parkinson`s disease (PD), as compared to healthy individuals.

Background: iRBD represents an early prodomal phase for PD.  Structural brain volume abnormalities have been reported in iRBD, suggesting they might represent markers to phenoconversion to PD.

Method: 12 iRBD subjects (10 M; age 62.3±12.1) with at least one other pre-motor PD symptom (hyposmia, constipation, depression) and 11 healthy controls (6M; age 40.8±14.1) were tested with a 3-Tesla magnetic resonance imaging (MRI) scanner. Dopamine transporter scan (DaTscan) was used to exclude PD. Whole brain, regional and subregional brain analysis (average left and right hemispheres) used volumetric segmentation (mm³) of brain structures extracted with FreeSurfer software. Unpaired t-test was used for statistical analyses between iRBD and control subjects.

Results: Subcortical measures showed a significant volume loss in the caudate nucleus of iRBD subjects (3296.9±380.8 vs 3634.2±339.7; p<0.05), while volume loss in the nucleus accumbens (474.3±101.1 vs 544.7±81.3; p=0.09) and globus pallidus (1866.9±203.3 vs 2042.8±310.6; p=0.1) approached significance. Non-significant volume decrease was observed in the amygdala (1680.0±177.3 vs 1731.3±196.1), hippocampus (4059.9±361.6 vs 4326.0±511.4), putamen (4673.5±560.3 vs 4980.1±618.0) and thalamus (6940.2±470.7 vs 6947.8±754.2). Subregional analyses showed in iRBD subjects significant cortical thinning in the caudal anterior cingulate (2.28±0.13 vs 2.43±0.15; p=0.03) and superior frontal areas (2.50±0.13 vs 2.63±0.10; p=0.02), with an increased cortical volume in inferior temporal (2.82±0.11 vs 2.64±0.07; p=0.0003). Significantly increased volumes were also detected in the hippocampal fissure (174.6±32.8 vs 145.1±23.1; p=0.03) and thalamic central lateral nucleus (43.1±5.2 vs 34.2±7.3; p=0.004).

Conclusion: We found a pattern of brain volume loss iRBD, including reduced cortical thickness and subcortical volume loss in the basal ganglia and limbic system. Increased volumes in some areas may be related to compensatory mechanisms. Our findings suggest that brain structural MRI measures might represent a neuroimaging biomarker of iRBD phenoconversion to PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cortical-and-subcortical-brain-volume-changes-in-idiopathic-rem-sleep-disorder-subjects-at-risk-for-parkinsons-disease/