PSG and MRI capture distinct but complementary, stage-dependent processes in iRBD, with PSG reflecting early functional alterations and MRI indexing progressive neurodegeneration, supporting a stage-aware multimodal approach to risk stratification for α-synucleinopathy.
Key Findings
Results
Phenoconverted iRBD showed PSG abnormalities compared to non-converters without accompanying structural MRI differences.
Phenoconverted iRBD demonstrated higher NREM arousal index and periodic limb movements compared to non-converters
Phenoconverted iRBD showed lower REM-apnea-hypopnea index (REM-AHI) compared to non-converters
No structural MRI differences were found between phenoconverted iRBD and non-converters
Study groups: non-converted iRBD (n=27), phenoconverted iRBD (n=25), established α-synucleinopathy (n=34)
Results
Established α-synucleinopathy was characterized by widespread cortical and limbic atrophy alongside PSG abnormalities not seen in earlier disease stages.
α-Synucleinopathy showed widespread cortical and limbic atrophy compared to non-converters
PSG abnormalities in α-synucleinopathy included reduced N2 sleep and elevated NREM arousal index
Elevated heart rate during NREM sleep was also identified in α-synucleinopathy
α-Synucleinopathy was distinguished from non-converters by left cingulate and hippocampal atrophy, reduced REM-AHI, and elevated NREM heart rate
Results
Higher NREM arousal index and lower REM-AHI independently predicted phenoconversion in multivariable logistic regression.
Higher NREM arousal index was associated with phenoconversion: odds ratio (OR) = 1.08, p = 0.005
Lower REM-AHI was associated with phenoconversion: OR = 0.94, p = 0.006
These two PSG markers were identified via multivariable logistic regression as discriminative features between non-converted and phenoconverted iRBD
Results
Lower left cingulate cortex volume and higher NREM arousal index predicted shorter time to phenoconversion in Cox proportional hazards models.
Lower left cingulate cortex volume predicted shorter time to phenoconversion: hazard ratio (HR) = 0.77 per IQR, p = 0.018
Higher NREM arousal index predicted shorter time to phenoconversion: HR = 1.03, p = 0.010
These findings support MRI as an index of progressive neurodegeneration predictive of conversion timing
Results
Trend analyses demonstrated progressive cortical and limbic atrophy across disease stages from non-converted iRBD through phenoconverted iRBD to established α-synucleinopathy.
A stepwise pattern of increasing cortical and limbic atrophy was observed across the three groups
The progression was observed from non-converted iRBD to phenoconverted iRBD and then to established α-synucleinopathy
This trend supports MRI-indexed neurodegeneration as a marker of advancing disease stage
Methods
The study used a retrospective design with video-polysomnography and MRI in 86 patients classified at baseline as iRBD or established α-synucleinopathy, with longitudinal follow-up to define conversion status.
Total sample: 86 patients who underwent both video-PSG and MRI
Groups were defined longitudinally: non-converted iRBD (n=27), phenoconverted iRBD (n=25), established α-synucleinopathy (n=34)
Pairwise comparisons assessed stage-specific differences, followed by multivariable logistic regression, trend analyses, and Cox models
Baseline classification was as iRBD or established α-synucleinopathy, with longitudinal follow-up determining conversion
What This Means
This research suggests that people with isolated REM sleep behavior disorder (iRBD) — a condition where people act out their dreams and which often precedes diseases like Parkinson's — show different patterns of brain and sleep abnormalities depending on how close they are to developing a full neurodegenerative disease. By studying 86 patients using sleep studies (polysomnography) and brain imaging (MRI), researchers found that those who eventually developed a neurodegenerative disease (called α-synucleinopathy) first showed sleep-related changes — such as more frequent brief awakenings during non-REM sleep and fewer breathing pauses during REM sleep — before any detectable brain shrinkage on MRI. Brain shrinkage in regions like the cingulate cortex and hippocampus appeared later, becoming prominent only in those with established disease.
Two specific markers were identified as predictors of who would convert to a neurodegenerative disease: a higher rate of brief awakenings during non-REM sleep (NREM arousal index) and a lower rate of breathing pauses during REM sleep (REM-AHI). Additionally, people with smaller left cingulate cortex volume and higher NREM arousal index converted to disease faster. These findings suggest that sleep study abnormalities appear early in the disease process, while brain atrophy accumulates progressively and becomes measurable later.
This research suggests that combining sleep studies and brain MRI offers a more complete picture of disease risk and stage than either test alone. Sleep studies may help detect early warning signs before structural brain changes appear, while MRI may reflect how far neurodegeneration has progressed. This 'stage-aware' approach could help clinicians better identify which iRBD patients are at highest risk and how quickly they may develop a neurodegenerative disease, which is important for future treatment trials and monitoring strategies.
Check Your Own Numbers
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Yum J, Kim E, Seo D, Kim J, Ha W, Chu M, et al.. (2026). Stage-specific polysomnographic and MRI markers across phenoconversion in isolated REM sleep behavior disorder.. Journal of neurology. https://doi.org/10.1007/s00415-026-13870-6