Idiopathic REM sleep behaviour disorder and neurodegeneration - an update

Periodic limb movements in REM sleep: A periodically concerning phenomenon

Periodic limb movements of sleep (PLMS) are involuntary, sleep-related phenomena characterized by periodic episodes of repetitive, stereotypical movements of the limbs. The presence PLMS increases with age but are frequently comorbid with other sleep disorders and other medical, neurologic, and psychiatric disorders, and can be triggered by medications and psychoactive substances. PLMS typically occur during non-rapid eye movement sleep and are generally absent during rapid eye movement (REM) sleep, with exception of patients with REM behavior disorder (RBD). However, even in the absence of RBD, PLMS are sometimes noted in REM sleep, without a clear explanation or etiology. This systematic review will focus on what is known about PLMS, as they relate to REM sleep phenomenon: PLMS in RBD, in REM sleep without atonia, and in various sleep and neurologic will be discussed.

Efficacy and Safety of Electroacupuncture on Insomnia in Parkinson's Disease: A Multicentre, Randomized, Controlled Trial

BACKGROUND

Sleep disturbances, particularly insomnia, are prevalent and debilitating non-motor symptoms of Parkinson's disease (PD), significantly impacting quality of life. Current treatment options are limited by side effects and accessibility. Electroacupuncture (EA), a non-pharmacological approach, has shown promise in insomnia, while its specific impact on insomnia in PD remains unexplored.

OBJECTIVES

To determine the efficacy and safety of EA vs sham electroacupuncture (SA) on insomnia associated with PD.

METHODS

We conducted a multicenter, participant-and assessor-blinded, randomized, sham-controlled clinical trial from March 1, 2024, to October 28, 2024, across eight sites in China. A total of 136 PD patients with insomnia were assigned to receive EA or SA (68 per arm) over an 8-week treatment period followed by a 12-week follow-up period. The primary outcome was the change in Parkinson's Disease Sleep Scale (PDSS) scores at week 8. A range of subjective sleep-related metrics and objective sleep assessments derived from polysomnography were utilized as secondary outcomes.

RESULTS

Both groups showed significant improvements in PDSS scores, with the EA group demonstrating a greater effect (between-group difference, 13.50 [95%CI, 12.68 to 14.32]). Secondary outcomes, including Insomnia Severity Index, Epworth Sleepiness Scale, and polysomnography-derived parameters, also showed greater improvements in EA group. The effects were maintained during the 12-week follow-up with no severe adverse events. The blinding assessment confirmed successful blinding.

CONCLUSIONS

EA was effective in improving insomnia and related sleep disturbances in PD. This study provided Class I evidence supporting the integration of EA into the treatment regimen for insomnia in PD.

The Future of Parasomnias

Parasomnias are abnormal behaviours or mental experiences during sleep or the sleep-wake transition. As disorders of arousal (DOA) or REM sleep behaviour disorder (RBD) can be difficult to capture in the sleep laboratory and may need to be diagnosed in large communities, new home diagnostic devices are being developed, including actigraphy, EEG headbands, as well as 2D infrared and 3D time of flight home cameras (often with automatic analysis). Traditional video-polysomnographic diagnostic criteria for RBD and DOA are becoming more accurate, and deep learning methods are beginning to accurately classify abnormal polysomnographic signals in these disorders. Big data from vast collections of clinical, cognitive, brain imaging, DNA and polysomnography data have provided new information on the factors that are associated with parasomnia and, in the case of RBD, may predict the individual risk of conversion to an overt neurodegenerative disease. Dream engineering, including targeted reactivation of memory during sleep, combined with image repetition therapy and lucid dreaming, is helping to alleviate nightmares in patients. On a political level, RBD has brought together specialists in abnormal movements and sleep neurologists, and research into nightmares and sleep-wake dissociations has brought together sleep and consciousness scientists.

Polysomnographic biomarkers for persisting (isolated) REM sleep without atonia in patients with obstructive sleep apnea

BACKGROUND

The relationship between obstructive sleep apnea (OSA) and REM sleep without atonia (RSWA) is complex and not fully understood. While RSWA may prevent upper airway collapse during REM sleep, it can also mimic REM sleep behavior disorder (RBD) and be a potential biomarker for neurodegeneration. This study aims to identify the prevalence, characteristics, and predictors of persistent isolated RSWA (iRSWA) following positive airway pressure (PAP) therapy in OSA patients.

METHODS

A retrospective analysis was conducted on 297 patients with both OSA and RSWA who underwent polysomnography (PSG) with PAP titration. RSWA was assessed using both visual and automated methods. Clinical and PSG parameters were compared between patients with and without persistent RSWA after PAP titration. Statistical analyses, including receiver operating characteristic (ROC) curve analysis, were performed to identify significant predictors of persistent RSWA.

RESULTS

Persistent RSWA was observed in 41.5 % of patients. Older age (p = 0.006), higher periodic limb movement index (PLMSI) (p = 0.034), and lower apnea-hypopnea index (AHI) (p = 0.048) were significantly associated with persistent RSWA. ROC analysis identified four key PSG biomarkers - RSWA duration/REM duration, RSWA duration/total apnea-hypopnea duration (tAHD) in REM sleep, tAHD in REM sleep/REM duration, and REM atonia index - that strongly predicted persistent RSWA (OR = 10.714, p = 0.024).

CONCLUSIONS

A substantial portion of RSWA observed in OSA patients (approximately 40 %) was not directly related to OSA and persisted despite PAP therapy. These findings suggest that persistent RSWA may indicate iRSWA, a potential prodromal biomarker for neurodegenerative disorders. The identified PSG biomarkers may improve differentiation between iRSWA and OSA-related RSWA, aiding in early diagnosis and prognostic evaluation.

Non-motor Symptoms and Treatments in Parkinson's Disease

SYNOPSIS

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms. The non-motor features may precede the onset of motor symptoms and occur throughout all stages of PD. The non-motor symptoms reflect multisystem involvement of the central and peripheral nervous systems, multiple neurotransmitters, and multiple pathologies. PD management necessitates a comprehensive approach to address non-motor symptoms, including pharmacologic and non-pharmacological interventions and often multiple different disciplines or specialists in the PD care team. This review article discusses symptoms and treatments for the non-motor symptoms of PD including those affecting mood, cognition, behavior, sleep, autonomic function, and sensory systems.

Prodromal Parkinson's Disease: A Snapshot of the Landscape

Early observations of specific nonmotor and subtle motor symptoms preceding clinical diagnosis of Parkinson's disease (PD) have paved the way for prodromal PD research, significantly propelling our understanding of early, subclinical stages of neurodegeneration. Prodromal PD has emerged as a complex concept with some researchers suggesting that the period before PD onset is divided into the "at-risk," "preclinical," and "prodromal" phases. Advances in genetic, imaging, laboratory, and digital technologies have enabled the identification of pathophysiological patterns and the potential development of diagnostic, progressive, and therapeutic biomarkers, which could lead to early PD detection and intervention.

Longitudinal associations of lipid profiles with sleep disorders in patients with Parkinson's disease

To examine the associations of apolipoprotein E (APOE) carrier status and lipid profiles with sleep disorders, including excessive daytime sleepiness (EDS) and probable rapid eye movement sleep behavior disorder (pRBD), among patients with early Parkinson's disease (PD) over 5-year follow-up periods. The Parkinson's Progression Markers Initiative is a multicenter cohort study based on an ongoing and open-ended registry. Data from baseline and 5-year follow-up visits from participants of de novo PD were analyzed. Longitudinal associations of APOE carrier status and lipid profiles with sleep disorders were estimated via linear mixed-effects models. A total of 657 participants with complete APOE genotypes were enrolled at baseline. Among them, 153 (25.3%) had available lipid profiles at baseline. In the linear mixed-effects models, baseline APOE ε2/ε3/ε4 carrier status did not exhibit significant associations with EDS and pRBD (all p > 0.05) in all models. However, reduced high-density lipoprotein (HDL) and elevated triglycerides (TG) were associated with developing EDS (β = -0.04, 95% CI: -0.07, -0.00) and pRBD (β = 0.01, 95% CI: 0.00, 0.02) in PD patients, respectively. In the APOE ε4+ subgroup, decreased HDL and increased TG displayed substantial associations with developing EDS and sleep disorders (all p < 0.05) in all models, respectively, whereas no significant differences were noted in the APOE ε4- subgroup (all p > 0.05). Our study did not demonstrate a clear association between APOE ε2/ε3/ε4 and sleep disorders in PD patients. However, the presence of APOE ε4 was associated with changes in lipid profiles, notably affecting TG and HDL levels.

Continuous REM sleep without atonia quantification improves prediction of phenoconversion to α-synucleinopathies in isolated REM sleep behavior disorder

STUDY OBJECTIVES

isolated REM sleep behavior disorder (iRBD), characterized by REM sleep without atonia (RWA), is considered a prodromal stage of α-synucleinopathies. This study aims to evaluate the predictive potential for phenoconversion of cumulative RWA percentage (CRWA%) as a continuous quantification of RWA compared to conventional epoch-based methods.

METHODS

Baseline video-polysomnograms from 92 iRBD patients were analyzed. Eleven patients converted to α-synucleinopathies during follow-up (iRBD-CV), while the remaining patients did not (iRBD-NC). RWA quantification was performed using a validated in-house algorithm in mentalis (MT) and bilateral flexor digitorum superficialis (FDS) muscles. Receiver operating characteristic curves, Kaplan-Meier survival analysis, and Cox proportional hazards models were used to assess predictive performance.

RESULTS

The iRBD-CV group had significantly higher CRWA%, REM atonia index, and any RWA (using SINBAR and AASM methods) compared with the iRBD-NC group (p < 0.035). Among these metrics, CRWA% demonstrated the highest predictive performance, with an area under the curve (AUC) of 0.89 in the combined MT and FDS channels. Survival analysis showed that patients with CRWA% > 32.54 % had significantly reduced disease-free rates (p = 0.004), with 3-year and 5-year rates of 51.4 % and 25.7 %, respectively. Additionally, higher CRWA% was significantly associated with a higher phenoconversion risk (Hazard ratio = 1.063, p = 0.006).

CONCLUSION

CRWA% provides a more precise and continuous approach to quantifying RWA, outperforming traditional methods in predicting phenoconversion to α-synucleinopathies in iRBD. These findings underscore the potential of CRWA% as a robust biomarker for early neurodegenerative progression.

Enhanced delta-gamma phase-amplitude coupling during phasic rapid eye movement sleep in isolated rapid eye movement sleep behavior disorder

STUDY OBJECTIVES

This study aims to analyze phase-amplitude coupling (PAC) patterns during rapid eye movement (REM) sleep in patients with isolated REM sleep behavior disorder (iRBD), compared with demography-matched healthy control (HC) participants.

METHODS

At baseline, electroencephalogram data from 13 iRBD patients and 10 HCs during REM sleep were analyzed. During follow-up, four patients (converters) later converted to alpha-synucleinopathies. Phasic and tonic REM states were determined by eye movement in 3 s epochs. PAC was compared between the groups, and correlations with clinical indicators were investigated. Additionally, the contribution of each electrode to PAC components was assessed.

RESULTS

Patients with iRBD exhibited increased delta (1-3 Hz)-gamma (30-50 Hz) PAC only during the phasic REM state, but not during the tonic state, compared to the HCs (p < .05). Elevated PAC in patients negatively correlated with the REM atonia index (p = 0.011) and olfactory function (p = 0.038). Increase PACs were predominent in the fronto-temporo-occipital regions (corrected p < .05). Furthermore, patients showed reduced gamma-amplitude contributions of the parietal region (corrected p < .05). This reduction exhibited a progressively decreasing trend from HC to nonconverters, and further to converters (p for trend = 0.044).

CONCLUSIONS

Our findings suggest PAC patterns during REM sleep could provide pathophysiological insights for iRBD. The widespread increase of PAC and reduced gamma-amplitude contribution in the parietal region suggest PAC during phasic REM sleep as potential biomarkers for disease progression in iRBD.

Predicting Phenoconversion in Isolated RBD: Machine Learning and Explainable AI Approach

Isolated rapid eye movement (REM) sleep behavior disorder (iRBD) is recognized as a precursor to neurodegenerative diseases. This study aimed to develop predictive models for the timing and subtype of phenoconversion in iRBD. We analyzed comprehensive clinical data from 178 individuals with iRBD over a median follow-up of 3.6 years and applied machine learning models to predict when phenoconversion would occur and whether progression would present with motor- or cognition-first symptoms. During follow-up, 30 patients developed a neurodegenerative disorder, and the extreme gradient boosting survival embeddings-Kaplan neighbors (XGBSE-KN) model demonstrated the best performance for timing (concordance index: 0.823; integrated Brier score: 0.123). Age, antidepressant use, and Movement Disorder Society-Unified Parkinson's Disease Rating Scale Part III scores correlated with higher phenoconversion risk, while coffee consumption was protective. For subtype classification, the RandomForestClassifier achieved the highest performance (Matthews correlation coefficient: 0.697), indicating that higher Montreal Cognitive Assessment scores and younger age predicted motor-first progression, whereas longer total sleep time was associated with cognition-first outcomes. These findings highlight the utility of machine learning in guiding prognosis and tailored interventions for iRBD. Future research should include additional biomarkers, extend follow-up, and validate these models in external cohorts to ensure generalizability.

Sleep Alterations and Cognitive Decline

Sleep disturbances and cognitive decline are intricately connected, and both are prevalent in aging populations and individuals with neurodegenerative disorders such as Alzheimer's disease (AD) and other dementias. Sleep is vital for cognitive functions including memory consolidation, executive function, and attention. Disruption in these processes is associated with cognitive decline, although causal evidence is mixed. This review delves into the bidirectional relationship between alterations in sleep and cognitive impairment, exploring key mechanisms such as amyloid-β accumulation, tau pathology, synaptic homeostasis, neurotransmitter dysregulation, oxidative stress, and vascular contributions. Evidence from both experimental research and population-based studies underscores the necessity of early interventions targeting sleep to mitigate risks of neurodegenerative diseases. A deeper understanding of the interplay between sleep and cognitive health may pave the way for innovative strategies to prevent or reduce cognitive decline through improved sleep management.

The Impact of Sleep Disorders on Glymphatic Function in Parkinson's Disease Using Diffusion Tensor MRI

RATIONALE AND OBJECTIVES

To investigate the impact of sleep disorders on glymphatic system in Parkinson's disease (PD) using a non-invasive imaging technique called diffusion tensor image analysis along perivascular space (DTI-ALPS).

MATERIALS AND METHODS

A total of 114 PD patients and 54 healthy controls (HCs) underwent sleep questionnaires and MRI examinations as part of data collection from the Parkinson's Progression Markers Initiative cohort. An automated pipeline was proposed for ALPS calculation to reduce biases from manually region delineation. ALPS indices were compared between PD and HCs, as well as between PD with and without sleep disorders. Correlation was assessed between ALPS index and clinical characteristics. Furthermore, a 2-year follow-up analysis was performed to explore longitudinal impact of sleep disorders on glymphatic function.

RESULTS

PD patients showed significantly decreased ALPS indices compared with HCs (P = 0.038). PD patients with sleep disorders showed slightly but not significantly decreased ALPS index compared with those with normal sleep (P = 0.058). However, PD patients who transitioned from normal sleep to sleep disorders showed significantly decreased ALPS index at follow-up compared to baseline (P = 0.047). In contrast, patients who maintained normal sleep showed no significant difference in ALPS index between follow-up and baseline (P = 0.934). In addition, PD patients who transitioned from normal sleep to sleep disorders showed significantly increased ΔMDS-UPDRS Part I score (P = 0.004), ΔMDS-UPDRS total score (P = 0.040) and ΔSCOPA-AUT (P = 0.048) compared with PD who remained normal sleep.

CONCLUSION

Sleep disorders accelerate dysfunction of glymphatic system as indicated by ALPS index in PD patients, which may be associated with symptom progression in follow-up analysis. Therefore, more attention should be devoted to prevent sleep disorders in early PD.

The Many Faces of REM Sleep Behavior Disorder. Providing Evidence for a New Lexicon

BACKGROUND

People with idiopathic/isolated REM sleep behavior disorder (iRBD) are highly heterogeneous, showing mild motor, cognitive, and dysautonomia symptoms. The aim of this study is to unveil the clinical heterogeneity of iRBD with a specific reference to overlapping features with prodromal Parkinson's disease (pPD) and prodromal dementia with Lewy bodies (pDLB) labels.

METHODS

People with a polysomnography-confirmed diagnosis of iRBD were enrolled and followed over time. At baseline, pPD and pDLB criteria were assessed.

RESULTS

Among the 285 iRBD people (68.2 ± 7.6 years, 81% males), due to additional signs or symptoms, 49.8% fulfilled pPD criteria only, 5.6% pDLB criteria only, and 14.4% subjects fulfilled both pPD and pDLB criteria. Conversely, about one third of iRBD people (30.2%) did not meet either pPD or pDLB criteria. At follow-up (40.6 ± 43.6 months), 28.8% subjects phenoconverted, developing PD (56.1%), DLB (39%), or multiple system atrophy (4.9%). Subjects with iRBD fulfilling either pPD or pDLB criteria, or both, have an increased risk of phenoconversion (adjusted hazard ratio, aHR 2.34, 95% confidence interval, CI 1.24-4.41). On the opposite, subjects not fulfilling prodromal criteria have a significantly reduced short-term phenoconversion likelihood (aHR 0.43, 95% CI 0.23-0.81). Notably, pPD and pDLB criteria did not predict PD and DLB diagnoses, respectively.

CONCLUSIONS

People with iRBD are highly heterogeneous, and the presence of other concomitant signs and symptoms is frequent, leading to faster phenoconversion. Thus, the terms idiopathic and isolated may be poorly appropriate and possibly even confounding. These results pave the way to a more appropriate new lexicon for people with RBD.

Validation of the neuropathological criteria of the fourth Consortium on dementia with Lewy Bodies in autopsy cases from psychiatric hospitals

AIM

The pathological criteria from the fourth Consortium on Dementia With Lewy bodies (DLB) in psychiatric cohorts has not been validated. Also, the pathological differences in prodromal DLB subtypes remain unclear. This study aimed to elucidate the clinicopathological features of patients with DLB in psychiatric hospitals.

METHODS

Of 165 autopsied cases, patients who developed psychiatric symptoms at 50 years or older were investigated based on the current criteria of DLB. Clinicopathological findings were compared among prodromal DLB subtypes.

RESULTS

Sixteen of 30 cases with DLB pathology had no parkinsonism, which represented diverse nigral neurodegeneration. Regarding the scheme to estimate the likelihood of DLB syndrome, the prevalence of core clinical features excluding rapid eye movement sleep behavior disorder and probable DLB diagnosis were significantly higher in the high-likelihood group than in the low-likelihood group. Regarding the prodromal DLB subtypes, mild cognitive impairment (MCI) onset was identified in 60%, psychiatric onset in 20%, delirium onset in 10%, and motor onset in 10% of cases, and the proportion of psychiatric onset or delirium onset was significantly higher compared with those without DLB pathology. Coexistence of MCI and psychiatric symptoms was observed in 41.6% of the MCI-onset cases. Patients with psychiatric-onset cases were significantly younger at the onset, with a longer disease duration than those with MCI-onset cases. No differences were observed in other clinicopathological variables among the subtypes.

CONCLUSION

The fourth Consortium pathological criteria for DLB were applicable in a psychiatric cohort. MCI-onset cases in conjunction with core clinical features is the main prodromal DLB subtype, and four cases exhibited isolated psychiatric symptoms for long-term duration.

Frequency and Longitudinal Course of Autonomic Reflex Testing Abnormalities in Isolated REM Sleep Behavior Disorder

STUDY OBJECTIVES

Autonomic dysfunction is common across the α-synucleinopathies including isolated RBD (iRBD), however the presence, severity and distribution of autonomic dysfunction as a risk factor for phenoconversion in iRBD remains unclear. We aimed to characterize autonomic reflex testing (ART) abnormalities in a cohort of participants with iRBD and assess them as phenoconversion biomarkers.

METHODS

We performed ART on 45 individuals with iRBD and evaluated the ability of ART components (sympathetic cholinergic, cardiovagal, sympathetic adrenergic) to predict phenoconversion using univariate and multivariate models combined with measures of olfaction, cognition, motor function, and skin biopsy assessment of dermal synuclein.

RESULTS

Forty-one individuals with iRBD were enrolled (age 66.7 ± 7.4 yrs, 27% female), and followed annually for an average of 2.9 ± 2.4 yrs, with four participants lost to follow-up. Eight participants with iRBD phenoconverted during their follow-up period (3 Parkinson's disease, 4 dementia with Lewy bodies and 1 multiple system atrophy), yielding a phenoconversion rate of 6.6% per year. Eighty-seven percent of iRBD participants had an abnormal baseline ART, and 100% had an abnormal follow-up ART. A combination of MDS-UPDRS III score and cardiovagal dysfunction (abnormal HRVdb) best predicted phenoconversion (AUC = 0.77), especially when combined with iRBD disease duration (AUC = 0.89).

CONCLUSIONS

ANS dysfunction was common and spanned all domains of autonomic function. Cardiovagal function was the most common domain affected and most predictive of phenoconversion, especially if combined with motor examination and disease duration. Longitudinal studies with larger sample sizes are needed to confirm these findings.

Speech and language biomarkers for Parkinson's disease prediction, early diagnosis and progression

Parkinson's disease (PD), a multifaceted neurodegenerative disorder, can manifest as an array of motor and non-motor symptoms. Among these, speech and language impairments are particularly prevalent, often preceding motor dysfunctions. Emerging research indicates that these impairments may serve as early disease indicators. In this narrative review, we synthesised current findings on the potential of speech and language symptoms in PD identification and progression monitoring. Our review highlights convergent, albeit preliminary, lines of evidence supporting the value of speech-related features in detecting early or prodromal PD, even across language groups, especially with sophisticated analytical techniques. Distinct speech patterns in PD subtypes and other neurological disorders may assist in differential diagnosis and inform targeted management efforts. These features also evolve over the disease course and could effectively be utilised for disease tracking and guide management plan modifications. Advances in digital voice processing allow cost-effective, remote and scalable monitoring for larger populations.

Brain Health in Sleep Disorders

Sleep is a critical determinant of brain health, influencing cognitive, emotional, and physiologic functions. The complex bidirectional relationship between sleep and brain health underscores the importance of sleep in maintaining cognitive function, regulating brain homeostasis, and facilitating the clearance of metabolic waste through the glymphatic system. Chronic sleep deprivation and sleep disorders such as insomnia and obstructive sleep apnea have been shown to negatively impact brain structures and functions. This review discusses the impact of sleep disorders on brain health. It also explores the implications of impaired sleep on cardiovascular health, immune function, and neuroplasticity.

Isolated Rem Sleep Behavior Disorder: A Model to Assess the Overnight Habituation of Emotional Reactivity

(1) Background: Phasic events in rapid eye movement (REM) sleep are a core feature of isolated REM behavior disorder (iRBD), which is often associated with emotion dysregulation. This study explores the relationship between sleep and the overnight habituation of emotional reactivity in healthy controls (HCs) and iRBD patients, focusing on the role of REM phasic events and a specific non-REM waveform, namely sleep spindles. (2) Methods: Participants underwent polysomnography and completed arousal rating tasks and mood scales before and after sleep. In total, eight HCs (4 M, mean age 60.62 ± 6.8) and eight iRBD patients (7 M, mean age 68.25 ± 5.12) were included in the analyses. (3) Results: In HCs, longer REM sleep duration correlated positively with overnight habituation. In the whole sample, overnight habituation negatively correlated with REM sleep latency and wake-after-sleep onset, and positively with N2 sleep. Higher overnight habituation was associated with fewer REM arousals and awakenings in the whole sample, and with greater N2 sleep spindle density in HCs. (4) Conclusions: Our preliminary results suggest that REM sleep and spindles in N2 play critical roles in emotional processing. The study confirms the relationship between emotion dysregulation and REM phasic events, enhancing our understanding of how sleep impacts emotional reactivity and also in the prodromal phase of neurodegenerative disease.

From mechanisms to future therapy: a synopsis of isolated REM sleep behavior disorder as early synuclein-related disease

Parkinson disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy are synucleinopathies, characterized by neuronal loss, gliosis and the abnormal deposition of α-synuclein in vulnerable areas of the nervous system. Neurodegeneration begins however several years before clinical onset of motor, cognitive or autonomic symptoms. The isolated form of REM sleep behavior disorder (RBD), a parasomnia with dream enactment behaviors and excessive muscle activity during REM sleep, is an early stage synucleinopathy. The neurophysiological hallmark of RBD is REM sleep without atonia (RWSA), i.e. the loss of physiological muscle atonia during REM sleep. RBD pathophysiology is not fully clarified yet, but clinical and basic science suggest that ɑ-syn pathology begins in the lower brainstem where REM atonia circuits are located, including the sublaterodorsal tegmental/subcoeruleus nucleus and the ventral medulla, then propagates rostrally to brain regions such as the substantia nigra, limbic system, cortex. Genetically, there is only a partial overlap between RBD, PD and DLB, and individuals with iRBD may represent a specific subpopulation. A genome-wide association study identified five loci, which all seem to revolve around the GBA1 pathway. iRBD patients often show subtle motor, cognitive, autonomic and/or sensory signs, neuroimaging alterations as well as biofluid and tissue markers of neurodegeneration (in particular pathologic α-synuclein aggregates), which can be useful for risk stratification. Patients with iRBD represent thus the ideal population for neuroprotective/neuromodulating trials. This review provides insights into these aspects, highlighting and substantiating the central role of iRBD in treatment development strategies for synucleinopathies.

Sleep related injury and its correlates in isolated rapid eye movement sleep behavior disorder

OBJECTIVES

To evaluate factors associated with sleep related injury (SRI) and persistent SRI (pSRI) in patients with isolated rapid eye movement sleep behavior disorder (iRBD).

METHODS

This is a retrospective cohort study. A total of 388 patients with iRBD were involved for a comprehensive review of sleep related injuries. SRI is defined as a lifetime history of injurious behaviors to self and/or bed partner, and pSRI is considered if injurious symptoms continued to occur frequently (≥1/month). Correlations of SRI/pSRI with clinical, lifestyle and polysomnographic characteristics were analyzed.

RESULTS

Lifetime SRI was reported in 322 (83 %) patients (66.3 ± 8.5 years old, male 77.0 %), with 19.3 % having severe injuries, including fractures (2.5 %) and subdural hemorrhage (1.2 %), while 7.5 % required medical attendance. SRI was related to more severe depressive features (Padj = 0.017), current alcohol drinking (Padj = 0.014) and higher mentalis phasic and tonic EMG activity (Padj = 0.042 and 0.048). After a mean follow-up of 5.1 years, 18.2 % of SRI patients (38/209) had pSRI despite intense treatment. Frequent nightmare at baseline (OR [95 % CI] = 1.43 [1.01, 2.03]), restless leg syndrome (OR [95 % CI] = 5.68 [1.42, 22.64]) and adult-onset sleepwalking (OR [95 % CI] = 2.52 [1.10, 5.76]) were associated with an increased risk of pSRI.

CONCLUSIONS

SRI is common in patients with iRBD and 18 % had pSRI despite intensive treatment, emphasizing the importance of bedside safety. The identification of risk factors for SRI and pSRI underscores the need for systematic clinical screening and targeted interventions for at-risk patients.

Wider and faster degeneration of white matter in Parkinson's disease with possible REM sleep behaviour disorder

BACKGROUND

In Parkinson's disease (PD), rapid eye movement (REM) sleep behaviour disorder (RBD) signifies a poorer prognosis, yet its impact on white matter (WM) degeneration remains unclear. The study examined the effect of RBD on WM alterations in PD progression.

METHODS

The study included 45 PD patients with possible RBD (PD-pRBD), 38 PD patients without possible RBD (PD-npRBD), and 79 healthy controls (HC). All patients underwent clinical assessments and diffusion MRI scans at least once a year for up to 4 visits. 79 HC underwent the same protocol at baseline. WM metrics, including fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD), were calculated using tract-based spatial statistics. Linear mixed-effects models were conducted to examine the changes in clinical features and WM fibers.

RESULTS

At baseline, PD-npRBD showed increased RD in several regions, predominantly in bilateral uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF), compared to HC (PFDR<0.05). During follow-up, PD-npRBD had further FA decrease in left UF and ILF (PFDR<0.05). PD-pRBD showed reduced FA in several regions relative to HC at baseline (PFDR<0.05), and faster FA decline in left UF and ILF than PD-npRBD during follow-up, with more extensive FA decrease in other regions such as anterior thalamic radiation and inferior fronto-occipital fasciculus (PFDR<0.05). Moreover, increased RD in the left corticospinal tract correlated with motor symptoms (p = 0.045) in PD-pRBD.

CONCLUSIONS

PD patients with pRBD demonstrated more extensive WM degeneration and accelerated degeneration in the left ILF and UF during the disease course. However, due to the lack of PSG verification, these results should be interpreted cautiously while directly relating to RBD. These findings provide new insights into the neural structural basis associated with the potential impact of RBD on PD progression.

Managing sleep issues in Parkinson's disease: an up-to-date review

INTRODUCTION

In Parkinson's disease (PD), sleep-wake problems are disease-related symptoms that occur throughout the day and have a negative impact on patients' quality of life to an extent that is equal to or greater than that of typical motor symptoms.

AREAS COVERED

Insomnia due to fragmented sleep and excessive daytime sleepiness (EDS) worsen as PD progresses. Nighttime wearing-off and early morning-off should be considered first when fragmented sleep is reported in PD patients. If the main complaint of patients with insomnia is difficulty falling asleep, restless legs syndrome should be differentiated first. Obstructive sleep apnea causes sleep quality deterioration and fragmented sleep. For rapid eye movement sleep behavior disorder (RBD), preventative measures against sleep-related trauma are necessary. RBD has also attracted attention as a PD precursor state and as a disease progression marker that is associated with specific PD clinical subtypes. In PD patients, the sleep-wake phase may advance/delay or become irregular due to circadian dysfunction.

EXPERT OPINION

Importantly, sleep-wake problems are core symptoms related to the pathogenesis and progression of PD, and addressing a wide range of these symptoms will improve patients' quality of life.

Parkinson's disease subtypes and their association with probable rapid eye movement sleep behavior disorder severity: a brainstem tractography and machine learning investigation

Rapid Eye Movement (REM) sleep behavior disorder (RBD) affects nearly half of Parkinson's disease (PD) patients. However, the structural heterogeneity within the brainstem, which regulates REM sleep, remains largely unexplored in PD. Our objective was to identify distinct PD subtypes based on microstructural characteristics in the brainstem and examine their associations with the severity of RBD. Data, including diffusion tensor imaging and REM sleep behavior disorder screening questionnaire (RBDSQ) responses, were obtained from 124 PD patients and 61 healthy controls through the Parkinson's Progression Marker Initiative database. Mean Quantitative Anisotropy (QA) values, representing axonal density, were extracted from 14 brainstem tracts and input into the semi-supervised machine learning algorithm, Heterogeneity through Discriminative Analysis (HYDRA), to cluster subtypes. Applying HYDRA, we identified two distinct PD subtypes (Subtype 1: n = 66, Subtype 2: n = 58). Subtype 2 exhibited reduced QA across assessed brainstem tracts and significantly higher RBDSQ scores than Subtype 1 and healthy controls (p < 0.001). Conversely, Subtype 1, characterized by lower RBDSQ scores, exhibited increased QA, notably in the right medial longitudinal fasciculus, when compared to Subtype 2 and controls (p < 0.001). These findings suggest that heterogeneous axonal damage in brainstem circuits correlates with variations in RBD severity, providing insights into the neurobiological underpinnings of early PD.

From Night to Light: A Bibliometric Analysis of the Global Research Trajectory of Sleep Disorders in Parkinson's Disease

Purpose

Sleep disorders are prevalent non-motor symptoms in patients with Parkinson's disease (PD), significantly diminishing the overall quality of life for patients and potentially accelerating the deterioration of motor and cognitive functions, accelerating disease progression. Despite increasing research on sleep disorders in PD, a comprehensive analysis of the knowledge structure and key issues in this field are still lacking. This study aims to identify research hotspots and emerging trends related to sleep disorders in PD through a detailed bibliometric analysis.

Patients and Methods

On October 1, 2024, an extensive search was conducted in the Web of Science Core Collection (WOSCC) database to gather relevant literature on sleep disorders in PD. Bibliometric and knowledge mapping analyses were performed using CiteSpace, VOSviewer, and bibliometrix.

Results

Between January 1, 2004, and October 1, 2024, a total of 3,655 publications on sleep disorders in PD were published by 3,387 institutions across 87 countries. The volume of publications has shown a steady increase, a trend projected to continue. Current research is primarily centered on Neurosciences, Pharmacology, and Clinical Neurology. Emerging trends involve comprehensive evaluations of sleep, early diagnosis and prevention of various sleep disorder subtypes in PD, and advancing research through animal models to develop effective therapies. Emerging keywords include machine learning, sleep quality, biomarkers, covid-19, and mouse model.

Conclusion

This bibliometric analysis sheds light on the global landscape of PD-related sleep disorder research over the past two decades, highlighting key countries, institutions, authors, and journals driving advancements in the field. Moreover, it uncovers pivotal research hotspots and emerging trends, offering valuable insights and guidance for scholars engaged in this area.

Substantia nigra and locus coeruleus microstructural abnormalities in isolated rapid eye movement sleep behaviour disorder and Parkinson's disease

Substantia nigra (SN) and locus coeruleus (LC) are two catecholaminergic, neuromelanin-rich nuclei that are affected in Parkinson's disease (PD) and may show neuroimaging abnormalities before the onset of motor manifestations. The simultaneous, multimodal investigation of their microstructural abnormalities may provide useful insights on the spatial diffusion and tissue characteristics of neurodegeneration, and this may in turn help develop markers for disease-modifying clinical trials. Therefore, through neuromelanin-sensitive and diffusion MRI, we aimed to investigate microstructural abnormalities in those nuclei in isolated REM sleep behaviour disorder (iRBD) and PD. Fourteen participants with polysomnography-confirmed iRBD, 18 with PD and 18 healthy controls were scanned with structural, neuromelanin-sensitive and neurite orientation dispersion and density imaging (NODDI) MRI. iRBD participants also underwent dopamine transporter imaging. SN neuromelanin and NODDI diffusion parameters and LC neuromelanin signals were extracted. Motor and global cognitive assessments were also collected. iRBD and PD participants showed significantly reduced neuromelanin contrast in the LC middle section compared with healthy controls. PD also showed significantly reduced caudal LC and posterior SN neuromelanin signal. No differences in SN NODDI parameters were detected between iRBD and healthy controls. Five iRBD participants showed reduced striatal dopamine transporter. In the combined disease groups (iRBD and PD), significant associations were shown between SN neuromelanin signal and neurite density index (r = -0.610, corr-p = 0.001) and between SN neurite density index and free water fraction (r = 0.417, corr-p = 0.042). In the same group, motor scores were negatively associated with nigral neuromelanin signal (r = -0.404, corr-p = 0.044) and free water fraction (r = 0.486, corr-p = 0.018). In conclusion, iRBD participants showed significant neuromelanin loss in the LC, with a minority showing initial nigrostriatal dopaminergic abnormalities. Across the entire iRBD-PD spectrum, the association between SN neuromelanin signal loss, diffusion parameters and motor scores has the potential to capture different yet related aspects of SN degeneration.

Audiovisual analysis of the diagnostic video polysomnography in patients with isolated REM sleep behavior disorder

BACKGROUND

The diagnosis of isolated REM sleep behavior disorder (IRBD) requires video polysomnography (V-PSG) showing increased muscle activity and abnormal behaviors in REM sleep.

OBJECTIVE

To describe in IRBD the behavioral manifestations occurring during REM sleep in the diagnostic V-PSG.

METHODS

This is a systematic audiovisual V-PSG analysis of consecutive IRBD patients. According to the International RBD Study Group recommendations, REM sleep movements and vocalizations were classified into categories and severity.

RESULTS

We analyzed the V-PSG of 62 IRBD patients with a mean age of 67.6 ± 8.1 years. Of 6,330 30-s epochs of REM sleep, 55.1% epochs exhibited motor events, 5.5% contained vocalizations and 39.4% were silent. Among the epochs with motor manifestations, 66.1% contained simple minor movements, 25.0% simple major and 8.9% complex movements. Motor severity of the epochs was mild in 82.2%, moderate in 13.2% and severe in 4.6%. Most movements were bilateral (62.4%) and located in the upper limbs (42.5%). Of the epochs with vocalizations, 61.5% were simple minor, 20.7% complex and 17.8% simple major of mild (72.7%), moderate (23.0%) and severe (4.3%) severity. Complex movements occurred in 87.1% of the patients and complex vocalizations in 38.7%.

CONCLUSIONS

In IRBD, the most common manifestations in REM sleep are simple minor movements and vocalizations of mild intensity. Complex movements are observed during REM sleep in most patients but are much less frequent than simple minor and major motor events. These findings should be considered for the routine diagnosis of IRBD when reviewing the V-PSG studies.

Sleep and circadian dysfunction in Parkinson disease: New perspective and opportunities for treatment

Sleep and circadian dysfunction are common nonmotor symptoms in patients with Parkinson disease (PD). Sleep and circadian dysfunction usually have a significant negative impact on quality of life and may also serve as markers to identify patients in the preclinical stage of PD. Sleep disturbances have different types in PD such as insomnia, excessive daytime sleepiness, rapid eye movement sleep behavior disorders, restless legs syndrome, and sleep-disordered breathing. Because PD has a variety of clinical manifestations, sleep disorders and circadian dysfunction are most easy to be overlooked. The management of sleep and circadian dysfunction in patients with PD is complex as these conditions are heterogeneous; therefore, treatment plans must be individualized and directed at the underlying cause(s). Therefore, screening for and managing sleep and circadian dysfunction are important in clinical practice, and looking for new perspective and opportunities for treatment of them may improve the quality of life of PD patients. Therefore, screening for and managing sleep and circadian dysfunction are important in clinical practice. Looking for new perspective and opportunities for treatment will likely improve the quality of life of PD patients.

Brain network analysis reveals hemispheric aberrant topology in patients with idiopathic REM sleep behavior disorder

Idiopathic REM sleep behavior disorder (iRBD) is recognized as a prodromal stage of neuro-degenerative disease. While brain network analysis is a well-documented approach for characterizing disease-related dysfunctions, the specific patterns in iRBD, particularly those related to hemispheric aberrations remain largely unexplored. To address this gap, this study investigated the topological abnormalities of multi-band EEG networks in patients with iRBD. Specifically, eyes-open resting-state EEG signals were collected from 30 iRBD patients and 30 matched health control (HC) participants. Graph theoretical analysis was then employed to explore network properties at the whole-brain and the hemispheric level. At the whole-brain level, we found aberrant increased local and global efficiency along with a distinct pattern of increased frontal and decreased parietal nodal efficiency in alpha band of iRBD patients. At the hemispheric level, iRBD networks displayed more efficient topological properties in the left hemisphere. Additionally, significant hemispheric asymmetry was observed in alpha-band iRBD network compared to that of HC. In sum, these findings provide novel insights into the disrupted network reorganization in iRBD and suggest aberrant hemispheric asymmetry as a potential neural biomarker for early diagnosis and monitoring of the disease.

Alpha-synuclein pathology in isolated rapid eye movement sleep behaviour disorder: a meta-analysis

Accumulating evidence indicates that patients with isolated rapid eye movement sleep behaviour disorder (iRBD), a prodromal stage of synucleinopathies, show abnormal deposition of misfolded alpha-synuclein (a-Syn) in peripheral tissues. The clinical utility of testing for a-Syn in iRBD is unclear. This meta-analysis focused on the utility of testing for the abnormal a-Syn phosphorylated at Ser129 (p-syn) and a-Syn seeding activity (a-Syn seed amplification assays [aSyn-SAA]). Following an electronic database search, 15 studies were included that provided at a minimum data on test positivity in participants with iRBD. Test positivity from cerebrospinal fluid (CSF) was 80% (95% confidence interval [CI] 68-88%, I2 = 71%) and for skin was 74.8% (95% CI 53.2-88.5%, I2 = 64%) for aSyn-SAA and 78.5% (95% CI 70.4-84.9%, I2 = 14%) for p-syn. The phenoconversion rate ratio of biopsy-positive versus biopsy-negative iRBD was 1.28 (95% CI 0.68-2.41, I2 = 0%). Skin as a source had a specificity of 99% (95% CI 95-100%, I2 = 0%; p = 0.01 compared to CSF). As a test, p-syn, had a specificity of 100% (95% CI 93-100%, I2 = 0%; p < 0.001) compared to aSyn-SAA. The odds ratio of a-Syn test positivity in iRBD versus other RBDs was 112 (95% CI 20-629, I2 = 0%). These results demonstrate clinically significant test positivity in iRBD and favour skin over CSF as the source of a-Syn pathological analysis, and p-syn over aSyn-SAA as the testing method. Overall, these findings indicate that testing for a-Syn could help in differentiating iRBD from RBD secondary to other conditions.

Cholinergic dysfunction in isolated rapid eye movement sleep behaviour disorder links to impending phenoconversion

BACKGROUND AND PURPOSE

Most patients with isolated rapid eye movement sleep behaviour disorder (iRBD) progress to a parkinsonian alpha-synucleinopathy. However, time to phenoconversion shows great variation. The aim of this study was to investigate whether cholinergic and dopaminergic dysfunction in iRBD patients was associated with impending phenoconversion.

METHODS

Twenty-one polysomnography-confirmed iRBD patients underwent baseline 11C-donepezil and 6-Fluoro-(18F)-l-3,4-dihydroxyphenylalanine (18F-DOPA) positron emission tomography (PET). Potential phenoconversion was monitored for up to 8 years. PET images were analysed according to patients' diagnoses after 3 and 8 years using linear regression. Time-to-event analysis was made with Cox regression, dividing patients into low and high tracer uptake groups.

RESULTS

Follow-up was accomplished in 17 patients. Eight patients progressed to either Parkinson's disease (n = 4) or dementia with Lewy bodies (n = 4), while nine remained non-phenoconverters. Compared with non-phenoconverters, 8-year phenoconverters had lower mean 11C-donepezil uptake in the parietal (p = 0.032) and frontal cortex (p = 0.042), whereas mean 11C-donepezil uptake in 3-year phenoconverters was lower in the parietal cortex (p = 0.005), frontal cortex (p = 0.025), thalamus (p = 0.043) and putamen (p = 0.049). Phenoconverters within 3 years and 8 years had lower 18F-DOPA uptake in the putamen (p < 0.001). iRBD patients with low parietal 11C-donepezil uptake had a 13.46 (95% confidence interval 1.42;127.21) times higher rate of phenoconversion compared with those with higher uptake (p = 0.023). iRBD patients with low 18F-DOPA uptake in the most affected putamen were all phenoconverters with higher rate of phenoconversion (p = 0.0002).

CONCLUSIONS

These findings suggest that cortical cholinergic dysfunction, particularly within the parietal cortex, could be a biomarker candidate for predicting short-term phenoconversion in iRBD patients. This study aligns with previous reports suggesting dopaminergic dysfunction is associated with forthcoming phenoconversion.

Major alteration of motor control during rapid eye movements sleep in mice models of sleep disorders

Alteration of motor control during rapid eye movements (REM) sleep has been extensively described in sleep disorders, in particular in isolated REM sleep behavior disorder (iRBD) and narcolepsy type 1 (NT1). NT1 is caused by the loss of orexin/hypocretin (ORX) neurons. Unlike in iRBD, the RBD comorbid symptoms of NT1 are not associated with alpha-synucleinopathies. To determine whether the chronic absence of ORX neuropeptides is sufficient to induce RBD symptoms, we analyzed during REM sleep the EMG signal of the prepro-hypocretin knockout mice (ORX-/-), a recognized mouse model of NT1. Then, we evaluated the severity of motor alterations by comparing the EMG data of ORX-/- mice to those of mice with a targeted suppression of the sublaterodorsal glutamatergic neurotransmission, a recognized rodent model of iRBD. We found a significant alteration of tonic and phasic components of EMG during REM sleep in ORX-/- mice, with more phasic events and more REM sleep episodes without atonia compared to the control wild-type mice. However, these phasic events were fewer, shorter, and less complex in ORX-/- mice compared to the RBD-like ORX-/- mice. We thus show that ORX deficiency, as seen in NT1, is sufficient to impair muscle atonia during REM sleep with a moderate severity of alteration as compared to isolated RBD mice. As described in NT1 patients, we report a major interindividual variability in the severity and frequency of RBD symptoms in ORX-deficient mice.

Circadian rhythm disruption: a potential trigger in Parkinson's disease pathogenesis

Parkinson's disease (PD) is a neurodegenerative disease characterized by the gradual loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc), abnormal accumulation of α-synuclein (α-syn), and activation of microglia leading to neuroinflammation. Disturbances in circadian rhythm play a significant role in PD, with most non-motor symptoms associated with disruptions in circadian rhythm. These disturbances can be observed years before motor symptoms appear and are marked by the emergence of non-motor symptoms related to PD, such as rapid eye movement sleep behavior disorder (RBD), restless leg syndrome (RLS), excessive daytime sleepiness (EDS), depression and anxiety, changes in blood pressure, gastrointestinal dysfunction, and urinary problems. Circadian rhythm disruption precedes the onset of motor symptoms and contributes to the progression of PD. In brief, this article outlines the role of circadian rhythm disruption in triggering PD at cellular and molecular levels, as well as its clinical manifestations. It also explores how circadian rhythm research can contribute to preventing the onset and progression of PD from current and future perspectives.

Sleep disorders and Parkinson's disease: is there a right direction?

In the last years, the hypothesis of a close relationship between sleep disorders (SDs) and Parkinson's disease (PD) has significantly strengthened. Whether this association is causal has been also highlighted by recent evidence demonstrating a neurobiological link between SDs and PD. Thus, the question is not whether these two chronic conditions are mutually connected, but rather how and when this relationship is expressed. Supporting this, not all SDs manifest with the same temporal sequence in PD patients. Indeed, SDs can precede or occur concomitantly with the onset of the clinical manifestation of PD. This review discusses the existing literature, putting under a magnifying glass the timing of occurrence of SDs in PD-neurodegeneration. Based on this, here, we propose two possible directions for studying the SDs-PD relationship: the first direction, from SDs to PD, considers SDs as potential biomarker/precursor of future PD-neurodegeneration; the second direction, from PD to SDs, considers SDs as concomitant symptoms in manifest PD, mainly related to primary PD-neuropathology and/or parkinsonian drugs. Furthermore, for each direction, we questioned SDs-PD relationship in terms of risk factors, neuronal circuits/mechanisms, and impact on the clinical phenotype and disease progression. Future research is needed to investigate whether targeting sleep may be the winning strategy to treat PD, in the context of a personalized precision medicine.

Smartphone Voice Calls Provide Early Biomarkers of Parkinsonism in Rapid Eye Movement Sleep Behavior Disorder

BACKGROUND

Speech dysfunction represents one of the initial motor manifestations to develop in Parkinson's disease (PD) and is measurable through smartphone.

OBJECTIVE

The aim was to develop a fully automated and noise-resistant smartphone-based system that can unobtrusively screen for prodromal parkinsonian speech disorder in subjects with isolated rapid eye movement sleep behavior disorder (iRBD) in a real-world scenario.

METHODS

This cross-sectional study assessed regular, everyday voice call data from individuals with iRBD compared to early PD patients and healthy controls via a developed smartphone application. The participants also performed an active, regular reading of a short passage on their smartphone. Smartphone data were continuously collected for up to 3 months after the standard in-person assessments at the clinic.

RESULTS

A total of 3525 calls that led to 5990 minutes of preprocessed speech were extracted from 72 participants, comprising 21 iRBD patients, 26 PD patients, and 25 controls. With a high area under the curve of 0.85 between iRBD patients and controls, the combination of passive and active smartphone data provided a comparable or even more sensitive evaluation than laboratory examination using a high-quality microphone. The most sensitive features to induce prodromal neurodegeneration in iRBD included imprecise vowel articulation during phone calls (P = 0.03) and monopitch in reading (P = 0.05). Eighteen minutes of speech corresponding to approximately nine calls was sufficient to obtain the best sensitivity for the screening.

CONCLUSION

We consider the developed tool widely applicable to deep longitudinal digital phenotyping data with future applications in neuroprotective trials, deep brain stimulation optimization, neuropsychiatry, speech therapy, population screening, and beyond. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Orexin and Sleep Disturbances in Alpha-Synucleinopathies: a Systematic Review

PURPOSE OF REVIEW

Sleep disturbances are amongst most frequent non-motor symptoms of Parkinson's Disease (PD), and they are similarly frequently reported in other alpha-syncleinopathies, such as Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA). More recently, the orexin system has been implicated in control of arousal based on salient environmental set points, and its dysregulation in sleep issues in alpha-synucleinopathies suggested by the findings from the translational animal models. However, its role in the patients with alpha-synucleinopathies remains unclear. We thus set to systematically review, and to critically assess, contemporary evidence on the association of the orexinergic system and sleep disturbances in alpha-synucleinopathies. In this systematic review, studies investigating orexin and sleep in alpha-synucleinopathies (Rapid Eye Movement (REM) Behaviour Disorder (RBD), Parkinson's Disease (PD), Dementia with Lewy Bodies (DLB), Multiple System Atrophy (MSA)) were identified using electronic database searches of PubMed, Web of Science and PsychINFO using MeSH terms, keywords, and title words such as "Alpha-synucleinopathies" AND "Orexin" AND "Sleep Disturbances".

RECENT FINDINGS

17 studies were included in this systemic review, of which 2 studies on RBD, 10 on PD, 4 on DLB, and 1 on MSA patients. Taken together, RBD and PD studies suggest a potential adaptive increase in orexin levels in early stages of the neurodegenerative process, with reduced levels more often reported for later, more advanced stages of illness. To date, no differences in orexin levels were demonstrated between MSA patients and healthy controls. There is a dearth of studies on the role of orexin levels in alpha-synucleinopathies. Moreover, significant methodologic limitations in the current body of work, including use of non-standardised research protocols and lack of prospective, multi-centre studies, disallow for any finite conclusion in regards to underlying pathomechanisms. Nonetheless, a picture of a complex, multifaceted relationship between the dysregulation of the orexinergic pathway and sleep disturbances in alpha-synucleinopathies is emerging. Hence, future studies disentangling orexinergic pathomechanisms of alpha-syncleinopathies are urgently needed to obtain a more comprehensive account of the role of orexinergic pathway in alpha-synucleinopathies. Pharmacological manipulations of orexins may have multiple therapeutic applications in treatment strategies, disease diagnosis, and might be effective for treating both motor and non-motor symptoms.

Inflammation and heterogeneity in synucleinopathies

Neurodegenerative diseases represent a huge healthcare challenge which is predicted to increase with an aging population. Synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), present complex challenges in understanding their onset and progression. They are characterized by the abnormal aggregation of α-synuclein in the brain leading to neurodegeneration. Accumulating evidence supports the existence of distinct subtypes based on the site of α-synuclein aggregation initiation, genetics, and, more recently, neuroinflammation. Mediated by both central nervous system-resident cells, peripheral immune cells, and gut dysbiosis, neuroinflammation appears as a key process in the onset and progression of neuronal loss. Sex-based differences add another layer of complexity to synucleinopathies, influencing disease prevalence - with a known higher incidence of PD in males compared to females - as well as phenotype and immune responses. Biological sex affects neuroinflammatory pathways and the immune response, suggesting the need for sex-specific therapeutic strategies and biomarker identification. Here, we review the heterogeneity of synucleinopathies, describing the etiology, the mechanisms by which the inflammatory processes contribute to the pathology, and the consideration of sex-based differences to highlight the need for personalized therapeutics.

Machine Learning Predicts Phenoconversion from Polysomnography in Isolated REM Sleep Behavior Disorder

Isolated rapid eye movement (REM) sleep behavior disorder (iRBD) is a prodromal stage of alpha-synucleinopathies. This study aimed at developing a fully-automated machine learning framework for the prediction of phenoconversion in patients with iRBD by using data recorded during polysomnography (PSG). A total of 66 patients with iRBD were included, of whom 18 converted to an overt alpha-synucleinopathy within 2.7 ± 1.0 years. For each patient, a baseline PSG was available. Sleep stages were scored automatically, and time and frequency domain features were derived from electromyography (EMG) and electroencephalography (EEG) signals in REM and non-REM sleep. Random survival forest was employed to predict the time to phenoconversion, using a four-fold cross-validation scheme and by testing several combinations of features. The best test performances were obtained when considering EEG features in REM sleep only (Harrel's C-index: 0.723 ± 0.113; Uno's C-index: 0.741 ± 0.11; integrated Brier score: 0.174 ± 0.06). Features describing EEG slowing had high importance for the machine learning model. This is the first study employing machine learning applied to PSG to predict phenoconversion in patients with iRBD. If confirmed in larger cohorts, these findings might contribute to improving the design of clinical trials for neuroprotective treatments.

Network disruption based on multi-modal EEG-MRI in α-synucleinopathies

Background

Brain network dysfunction has been characterized by resting-state electroencephalography (EEG) and magnetic resonance imaging (MRI) in the prodromal stage. This study aimed to identify multi-modal electrophysiological and neuroimaging biomarkers for differential diagnosis in synucleinopathies and phenoconversion in isolated rapid eye movement sleep behavior disorder (iRBD).

Methods

We enrolled 35 patients with multiple system atrophy (MSA), 32 with Parkinson's disease (PD), 30 with iRBD and 30 matched healthy controls (HC). Power spectral density (PSD) was calculated in different frequency bands. EEG functional connectivity (FC) was calculated using the weighted Phase Lag Index (wPLI) after source localization. Significant network disruptions were further confirmed by MRI FC analysis.

Results

Quantitative EEG analysis demonstrated that delta and theta power spectral density significantly differed among MSA, PD and HC. The increased PSD was correlated with cognitive decline and olfactory dysfunction in PD. Band-specific FC profiles were observed in theta, alpha, and gamma bands. The hypoconnected alpha network significantly correlated with motor dysfunction, while the gamma FC distinguished PD from MSA. By integrating EEG and MRI network analyses, we found that FC between the olfactory cortex and dorsolateral prefrontal cortex was significantly different between MSA and PD. A multimodal discriminative model for MSA and PD, integrating spectral and FC attributes of EEG and MRI, yielded an area under the receiver operating characteristic curve of 0.900. Simultaneously, we found the FC abnormalities were more prominent than spectral features in iRBD indicating prodromal dysfunction. The decreased FC between the angular gyrus and striatum was identified in α-synucleinopathies. This hypoconnectivity was associated with dopaminergic degeneration in iRBD examined by dopamine transporter imaging.

Discussion

Our study demonstrated EEG spectral and functional profiles in prodromal and clinical-defined synucleinopathies. Multimodal EEG and MRI provided a novel approach to discriminate MSA and PD, and monitor neurodegenerative progression in the preclinical phase.

PET-based brain molecular connectivity in neurodegenerative disease

PURPOSE OF REVIEW

Molecular imaging has traditionally been used and interpreted primarily in the context of localized and relatively static neurochemical processes. New understanding of brain function and development of novel molecular imaging protocols and analysis methods highlights the relevance of molecular networks that co-exist and interact with functional and structural networks. Although the concept and evidence of disease-specific metabolic brain patterns has existed for some time, only recently has such an approach been applied in the neurotransmitter domain and in the context of multitracer and multimodal studies. This review briefly summarizes initial findings and highlights emerging applications enabled by this new approach.

RECENT FINDINGS

Connectivity based approaches applied to molecular and multimodal imaging have uncovered molecular networks with neurodegeneration-related alterations to metabolism and neurotransmission that uniquely relate to clinical findings; better disease stratification paradigms; an improved understanding of the relationships between neurochemical and functional networks and their related alterations, although the directionality of these relationships are still unresolved; and a new understanding of the molecular underpinning of disease-related alteration in resting-state brain activity.

SUMMARY

Connectivity approaches are poised to greatly enhance the information that can be extracted from molecular imaging. While currently mostly contributing to enhancing understanding of brain function, they are highly likely to contribute to the identification of specific biomarkers that will improve disease management and clinical care.

Detection of α-Synuclein in Oral Mucosa by Seed Amplification Assay in Synucleinopathies and Isolated REM Sleep Behavior Disorder

OBJECTIVE

Evidence of abnormal α-synuclein (α-Syn) deposition in the brain is required for definitive diagnosis of synucleinopathies, which remains challenging. The seed amplification assay (SAA) is an innovative technique that can detect the seeding activity of misfolded α-Syn, enabling the amplification and detection of minute quantities of pathogenic α-Syn aggregates. This study aimed to evaluate oral mucosa α-Syn SAA as possible diagnostic and prodromal biomarkers for synucleinopathies.

METHODS

A total of 107 Parkinson's disease (PD) patients, 99 multiple system atrophy (MSA) patients, 33 patients with isolated rapid eye movement sleep behavior disorder (iRBD) and 103 healthy controls (HC) were included. The SAA was applied to detect the seeding activity of α-Syn from oral mucosa. A combination of morphological, biochemical, and biophysical methods was also used to analyze the fibrils generated from the oral mucosa α-Syn SAA.

RESULTS

Structured illumination microscopy images revealed the increased α-Syn species in oral mucosa of PD, MSA, and iRBD patients than in HCs. Oral mucosa α-Syn SAA distinguished patients with PD from HC with 67.3% sensitivity and 90.3% specificity. Oral mucosa was α-Syn SAA positive in 53.5% MSA patients and 63.6% iRBD patients. Furthermore, the α-Syn fibrils generated from MSA demonstrated greater resistance to proteinase K digestion and exhibited stronger cytotoxicity compared to those from PD patients.

CONCLUSION

Oral mucosa α-Syn seeding activity may serve as novel non-invasive diagnostic and prodromal biomarkers for synucleinopathies. The α-Syn aggregates amplified from the oral mucosa of PD and MSA exhibited distinct biochemical and biophysical properties. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Clinical presentations and diagnostic application of proposed biomarkers in psychiatric-onset prodromal dementia with Lewy bodies

Research criteria for the diagnosis of prodromal dementia with Lewy bodies (DLB) include three clinical subtypes: mild cognitive impairment with Lewy bodies (MCI-LB), delirium-onset prodromal DLB, and psychiatric-onset prodromal DLB. Late-onset psychiatric manifestations are at a higher risk of developing dementia, but its relation to prodromal DLB remains unclear. In addition to the risk of severe antipsychotic hypersensitivity reactions, accurate discrimination from non-DLB cases is important due to the potential differences in management and prognosis. This article aims to review a rapidly evolving psychiatric topic and outline clinical pictures of psychiatric-onset prodromal DLB, including the proposed biomarker findings of MCI-LB: polysomnography-confirmed rapid eye movement sleep behaviour disorder, cardiac [123I]metaiodobenzylguanidine scintigraphy, and striatal dopamine transporter imaging. We first reviewed clinical pictures of patients with autopsy-confirmed DLB. Regarding clinical reports, we focused on the patients who predominantly presented with psychiatric manifestations and subsequently developed DLB. Thereafter, we reviewed clinical studies regarding the diagnostic applications of the proposed biomarkers to patients with late-onset psychiatric disorders. Clinical presentations were mainly late-onset depression and psychosis; however, other clinical manifestations were also reported. Psychotropic medications before a DLB diagnosis may cause extrapyramidal signs, and potentially influences the proposed biomarker findings. These risks complicate clinical manifestation interpretation during the management of psychiatric symptoms. Longitudinal follow-up studies with standardised evaluations until conversion to DLB are needed to investigate the temporal trajectories of core features and proposed biomarker findings. In patients with late-onset psychiatric disorders, identification of patients with psychiatric-onset prodromal DLB provides the opportunity to better understanding the distinct prognostic subgroup that is at great risk of incident dementia. Advances in the establishment of direct biomarkers for the detection of pathological α-synuclein may encourage reorganising the phenotypic variability of prodromal DLB.

Alterations of Peripheral Lymphocyte Subsets in Isolated Rapid Eye Movement Sleep Behavior Disorder

BACKGROUND

Adaptive immune dysfunction may play a crucial role in Parkinson's disease (PD) development. Isolated rapid eye movement sleep behavior disorder (iRBD) represents the prodromal stage of synucleinopathies, including PD. Elucidating the peripheral adaptive immune system is crucial in iRBD, but current knowledge remains limited.

OBJECTIVE

This study aimed to characterize peripheral lymphocyte profiles in iRBD patients compared with healthy control subjects (HCs).

METHODS

This cross-sectional study recruited polysomnography-confirmed iRBD patients and age- and sex-matched HCs. Venous blood was collected from each participant. Flow cytometry was used to evaluate surface markers and intracellular cytokine production in peripheral blood mononuclear cells.

RESULTS

Forty-four iRBD patients and 36 HCs were included. Compared with HCs, patients with iRBD exhibited significant decreases in absolute counts of total lymphocytes and CD3+ T cells. In terms of T cell subsets, iRBD patients showed higher frequencies and counts of proinflammatory T helper 1 cells and INF-γ+ CD8+ T cells, along with lower frequencies and counts of anti-inflammatory T helper 2 cells. A significant increase in the frequency of central memory T cells in CD8+ T cells was also observed in iRBD. Regarding B cells, iRBD patients demonstrated reduced frequencies and counts of double-negative memory B cells compared with control subjects.

CONCLUSIONS

This study demonstrated alterations in the peripheral adaptive immune system in iRBD, specifically in CD4+ and INF-γ+ CD8+ T cell subsets. An overall shift toward a proinflammatory state of adaptive immunity was already evident in iRBD. These observations might provide insights into the optimal timing for initiating immune interventions in PD. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Sleep structure discriminates patients with isolated REM sleep behavior disorder: a deep learning approach

Rapid eye movement (REM) sleep behavior disorder (RBD) is a disorder characterized by increased muscle tone and dream-enactment behaviors in REM sleep. In its isolated form (iRBD), it is a prodromal stage of neurodegenerative diseases. Currently, diagnosis of RBD requires time-consuming and subjective visual inspection of polysomnography (PSG). We propose a novel fast and objective deep learning model to identify patients with iRBD based on their sleep structure. A total of 86 iRBD and 81 controls, who underwent PSG, were included in the study. A validated algorithm was used to generate hypnodensity graphs (i.e., probabilistic representations of sleep structure). A ResNet-18 model was trained on five datasets consisting of whole night hypnodensities (with and without augmentation), and shorter segments (4 hours, 2 hours, and 30 minutes) to discriminate iRBD from controls. Using entire-night hypnodensity had notable benefits in terms of performance compared to shorter length segments, leading to a mean macro F1 score of 0.717 (per-segment), and of 0.784 (per-subject). Our findings show that sleep structure is important for iRBD classification and could potentially help clinicians.

Alteration of circadian sleep-wake rhythm and salivary melatonin secretion in idiopathic/isolated REM sleep behavior disorder: Preliminary evidence

OBJECTIVE/BACKGROUND

Idiopathic/isolated REM sleep behavior disorder (iRBD) is widely regarded as an early sign of neurodegeneration leading to synucleinopathies. While circadian rhythm alterations in iRBD have been preliminarily demonstrated, evidence on melatonin secretion patterns in this clinical condition is limited. To address this knowledge gap, this exploratory study aimed to integrate salivary melatonin measurement with actigraphic monitoring in individuals with iRBD and age-matched healthy controls (HC) under real-life conditions.

METHODS

Participants diagnosed with iRBD and HC underwent clinical evaluation and wore an actigraph for seven days and nights. Salivary melatonin concentrations were measured at five time points during the last night of recording. Comparative analyses were conducted on clinical data, actigraphic parameters, and melatonin levels between the two groups.

RESULTS

iRBD participants (n = 18) showed greater motor (p < 0.01) and non-motor symptoms (p < 0.001), alongside disruptions in circadian sleep-wake rhythm compared to HC (n = 10). Specifically, actigraphy revealed a delayed central phase measurement (p < 0.05), reduced activity during the most active hours (p < 0.001), and decreased relative amplitude (p < 0.05). Total salivary melatonin concentration was significantly lower in iRBD (p < 0.05), with a slight but non-significant phase delay in dim light melatonin onset.

CONCLUSIONS

This exploratory study highlights a dysregulation of circadian sleep-wake rhythm coupled with reduced melatonin secretion in iRBD. Future research could add to these preliminary findings to evaluate novel treatment approaches to regulate the sleep-wake cycle and elucidate the implications of circadian dysregulation in the conversion from iRBD to neurodegeneration.

The new science of sleep: From cells to large-scale societies

In the past 20 years, more remarkable revelations about sleep and its varied functions have arguably been made than in the previous 200. Building on this swell of recent findings, this essay provides a broad sampling of selected research highlights across genetic, molecular, cellular, and physiological systems within the body, networks within the brain, and large-scale social dynamics. Based on this raft of exciting new discoveries, we have come to realize that sleep, in this moment of its evolution, is very much polyfunctional (rather than monofunctional), yet polyfunctional for reasons we had never previously considered. Moreover, these new polyfunctional insights powerfully reaffirm sleep as a critical biological, and thus health-sustaining, requisite. Indeed, perhaps the only thing more impressive than the unanticipated nature of these newly emerging sleep functions is their striking divergence, from operations of molecular mechanisms inside cells to entire group societal dynamics.

Minimal effect of long-term clonazepam on cognitive function in patients with isolated rapid eye movement sleep behavior disorder

STUDY OBJECTIVES

Despite its widespread use in patients with isolated rapid eye movement sleep behavior disorder (iRBD), the cognitive effect of clonazepam is uncertain. This study aimed to investigate the effect of cumulative clonazepam on cognitive function in patients with iRBD.

METHODS

Demographic characteristics, baseline cognitive test, and most recent cognitive test information were collected retrospectively. Based on cumulative clonazepam doses, patients were classified into 4 subgroups: group 1, < 365 mg (1 mg × 1 year); group 2, 365 mg to < 1,095 mg (1 mg × 3 years); group 3, 1,095 mg to < 2,190 mg (1 mg × 6 years); and group 4, 2,190 mg or more. Cognitive test scores were calculated as z scores adjusted for age, education, and sex.

RESULTS

This study included 101 patients with iRBD (63 males). Groups 1, 2, 3, and 4 had 14, 20, 32, and 35 patients, respectively. In within-group comparisons, follow-up Digit Span Backward test and the Trail Making Test A scores decreased in group 3, and follow-up Trail Making Test A and the Trail Making Test B scores decreased significantly in group 4. In the multiple regression analysis to determine influential factors on cognitive decline, cumulative clonazepam dose did not show a significant correlation with any cognitive domain. Follow-up cognitive function showed significant correlation only with baseline cognitive function.

CONCLUSIONS

Memory and executive functions tended to decline in patients with iRBD. However, there was no significant effect of cumulative clonazepam. There was no evidence that long-term use of clonazepam was related to cognitive decline in patients with iRBD.

CITATION

Lee M, Kim TK, Hong JK, Yoon I-Y. Minimal effect of long-term clonazepam on cognitive function in patients with isolated rapid eye movement sleep behavior disorder. J Clin Sleep Med. 2024;20(7):1173-1182.

Reading the mind in the eyes in patients with idiopathic REM sleep behavior disorder

OBJECTIVES

Idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD) is characterized by vocalizations, jerks, and motor behaviors during REM sleep, often associated with REM-related dream content, which is considered a prodromal stage of α-synucleinopathy. The results of the Reading the Mind in the Eyes (RME) reflecting affective Theory of Mind (ToM) are inconsistent in α-synucleinopathy. The present study tried to investigate the RME in patients with iRBD.

METHODS

A total of 35 patients with iRBD and 26 healthy controls were included in the study. All participants were administered the RME and the cognitive assessments according to a standard procedure. The patients with iRBD were further divided into two groups (high or low RME) according to the scores of the RME (> 21, or ≤ 20).

RESULTS

The patients with iRBD had worse scores on cognitive tests compared with healthy controls involving global cognitive screening, memory, and visuospatial abilities (p < 0.05), but the scores of the RME were similar between the two groups (20.83 ± 3.38, 20.58 ± 3.43) (p ˃ 0.05). Patients with low RME had more obvious cognitive impairments than healthy controls. After applying Bonferroni correction for multiple tests, the low REM group only performed worse on the Sum of trials 1 to 5 and delayed recall of the RAVLT compared with the healthy control group (p < 0.001, = 0.002). The RME correlated with the scores of cognitive tests involving executive function, attention, memory, and visuospatial function.

CONCLUSIONS

The changes in RME had a relationship with cognitive impairments, especially memory, in patients with iRBD.

Olfactory Dysfunction and Long-Term Trajectories of Sleep Disorders among early Parkinson's Disease: Findings from a Longitudinal Cohort

BACKGROUND

Previous studies have suggested a connection between impaired olfactory function and an increased risk of rapid eye movement sleep behavior disorder (RBD) in individuals diagnosed with Parkinson's disease (PD). However, there is a gap in knowledge regarding the potential impact of olfactory dysfunction on the long-term patterns of sleep disorders among early PD patients.

METHODS

Data from the Parkinson's Progression Markers Initiative program included 589 participants with assessments of sleep disorders using the Epworth Sleepiness Scale (ESS) and RBD Screening Questionnaire (RBDSQ). Olfactory dysfunction at baseline was measured using the University of Pennsylvania Smell Identification Test. Trajectories of sleep disorders over a 5-year follow-up were identified using group-based trajectory modeling, and the relationship between olfactory dysfunction and sleep disorder trajectories was examined through binomial logistic regression.

RESULTS

Two distinct trajectories of sleep disorders over the 5-year follow-up period were identified, characterized by maintaining a low or high ESS score and a low or high RBDSQ score. An inversion association was observed between olfactory function measures and trajectories of excessive daytime sleepiness (odds ratio [OR] = 0.97, 95% confidence interval [CI] 0.95, 1.00, p = 0.038), after controlling for potential covariates. Similarly, olfactory function showed a significant association with lower trajectories of probable RBD (OR = 0.96, 95% CI 0.94, 0.98, p = 0.001) among early PD individuals. Consistent findings were replicated across alternative analytical models.

CONCLUSIONS

Our findings indicated that olfactory dysfunction was associated with unfavorable long-term trajectories of sleep disorders among early PD.

BACKGROUND

Previous studies have suggested a connection between impaired olfactory function and an increased risk of rapid eye movement sleep behavior disorder (RBD) in individuals diagnosed with Parkinson's disease (PD). However, there is a gap in knowledge regarding the potential impact of olfactory dysfunction on the long-term patterns of sleep disorders among early PD patients.

METHODS

Data from the Parkinson's Progression Markers Initiative program included 589 participants with assessments of sleep disorders using the Epworth Sleepiness Scale (ESS) and RBD Screening Questionnaire (RBDSQ). Olfactory dysfunction at baseline was measured using the University of Pennsylvania Smell Identification Test. Trajectories of sleep disorders over a 5-year follow-up were identified using group-based trajectory modeling, and the relationship between olfactory dysfunction and sleep disorder trajectories was examined through binomial logistic regression.

RESULTS

Two distinct trajectories of sleep disorders over the 5-year follow-up period were identified, characterized by maintaining a low or high ESS score and a low or high RBDSQ score. An inversion association was observed between olfactory function measures and trajectories of excessive daytime sleepiness (odds ratio [OR] = 0.97, 95% confidence interval [CI] 0.95, 1.00, p = 0.038), after controlling for potential covariates. Similarly, olfactory function showed a significant association with lower trajectories of probable RBD (OR = 0.96, 95% CI 0.94, 0.98, p = 0.001) among early PD individuals. Consistent findings were replicated across alternative analytical models.

CONCLUSIONS

Our findings indicated that olfactory dysfunction was associated with unfavorable long-term trajectories of sleep disorders among early PD.

Lysosomal and synaptic dysfunction markers in longitudinal cerebrospinal fluid of de novo Parkinson's disease

Lysosomal and synaptic dysfunctions are hallmarks in neurodegeneration and potentially relevant as biomarkers, but data on early Parkinson's disease (PD) is lacking. We performed targeted mass spectrometry with an established protein panel, assessing autophagy and synaptic function in cerebrospinal fluid (CSF) of drug-naïve de novo PD, and sex-/age-matched healthy controls (HC) cross-sectionally (88 PD, 46 HC) and longitudinally (104 PD, 58 HC) over 10 years. Multiple markers of autophagy, synaptic plasticity, and secretory pathways were reduced in PD. We added samples from prodromal subjects (9 cross-sectional, 12 longitudinal) with isolated REM sleep behavior disorder, revealing secretogranin-2 already decreased compared to controls. Machine learning identified neuronal pentraxin receptor and neurosecretory protein VGF as most relevant for discriminating between groups. CSF levels of LAMP2, neuronal pentraxins, and syntaxins in PD correlated with clinical progression, showing predictive potential for motor- and non-motor symptoms as a valid basis for future drug trials.

Reduced cardiac 123I-MIBG uptake is a robust biomarker of Lewy body disease in isolated rapid eye movement sleep behaviour disorder

Cardiac 123I-MIBG scintigraphy is used to assess the function of postganglionic presynaptic cardiac sympathetic nerve endings. 123I-MIBG cardiac uptake is markedly reduced in patients with isolated rapid eye movement sleep behaviour disorder, similar to Parkinson's disease and dementia with Lewy bodies. As a result, it can be used as an early biomarker of isolated rapid eye movement sleep behaviour disorder. Most patients with isolated rapid eye movement sleep behaviour disorder develop synucleinopathies: Parkinson's disease, dementia with Lewy bodies or multiple system atrophy. We aimed to investigate whether cardiac postganglionic denervation is present in patients with isolated rapid eye movement sleep behaviour disorder, as well as its possible usefulness as a marker for Lewy body disease status. This retrospective cohort study examined 306 patients (236 men and 70 women; mean age: 68.2 years; age range: 43-87 years) with polysomnography-confirmed isolated rapid eye movement sleep behaviour disorder who were followed for 1-3 months and underwent 123I-MIBG scintigraphy. We retrospectively analysed data from 306 patients with polysomnography-confirmed isolated rapid eye movement sleep behaviour disorder, and their longitudinal outcomes were documented at two centres. Among isolated rapid eye movement sleep behaviour disorder patients, reduced 123I-MIBG uptake was observed in the early and delayed images in 84.4 and 93.4% of patients, respectively, whereas 88.6% of the patients had a high washout rate. This large Japanese two-cohort study (n = 306) found that 91 patients (29.7%) developed an overt synucleinopathy (51 Parkinson's disease, 35 dementia with Lewy bodies, 4 multiple system atrophy, and 1 cerebellar ataxia) during a mean follow-up duration of 4.72 ± 3.94 years, with a conversion risk of 14.5% at 3 years, 25.4% at 5 years, 41.4% at 8 years and 52.5% at 10 years. On the other hand, among patients with heart-to-mediastinum ratio < 2.2 in the delayed images (n = 286), 85 (29.7%) developed Parkinson's disease or dementia with Lewy bodies during a mean follow-up duration of 4.71 ± 3.94 years, with a conversion risk of 14.5% at 3 years, 25.6% at 5 years, 42.0% at 8 years and 51.0% at 10 years. Among the 33 patients who underwent repeat 123I-MIBG scintigraphy, there was a progressive decline in uptake over the next 4.2 years, with patients exhibiting reduced uptake progressing to Parkinson's disease or dementia with Lewy bodies. In contrast, patients without decreased 123I-MIBG uptake progressed to multiple system atrophy. Reduced cardiac 123I-MIBG uptake was detected in over 90% of isolated rapid eye movement sleep behaviour disorder patients, with progression to Parkinson's disease or dementia with Lewy bodies, rather than multiple system atrophy, over time. Reduced 123I-MIBG uptake is a robust maker for Lewy body disease among isolated rapid eye movement sleep behaviour disorder patients.