Biomarkers for REM sleep behavior disorder in idiopathic and narcoleptic patients

Secondary RBD: Not just neurodegeneration

Rapid eye movement sleep behavior disorder is a parasomnia characterized by excessive muscle activity during rapid eye movement sleep (rapid eye movement sleep without atonia), along with dream enactment behavior. Isolated rapid eye movement sleep behavior disorder tends to occur in older males and is of concern due to the known link to Parkinson's disease and other synucleinopathies. When rapid eye movement sleep behavior disorder occurs in association with other neurological or general medical conditions, or resulting from the use of various substances, it is called secondary rapid eye movement sleep behavior disorder; the most common cause is neurodegenerative illness, specifically the synucleinopathies. Here, the focus will be on the subset of secondary rapid eye movement sleep behavior disorder in which there is no neurodegenerative disease.

Narcolepsy and rapid eye movement sleep

Since the first description of narcolepsy at the end of the 19th Century, great progress has been made. The disease is nowadays distinguished as narcolepsy type 1 and type 2. In the 1960s, the discovery of rapid eye movement sleep at sleep onset led to improved understanding of core sleep-related disease symptoms of the disease (excessive daytime sleepiness with early occurrence of rapid eye movement sleep, sleep-related hallucinations, sleep paralysis, rapid eye movement parasomnia), as possible dysregulation of rapid eye movement sleep, and cataplexy resembling an intrusion of rapid eye movement atonia during wake. The relevance of non-sleep-related symptoms, such as obesity, precocious puberty, psychiatric and cardiovascular morbidities, has subsequently been recognized. The diagnostic tools have been improved, but sleep-onset rapid eye movement periods on polysomnography and Multiple Sleep Latency Test remain key criteria. The pathogenic mechanisms of narcolepsy type 1 have been partly elucidated after the discovery of strong HLA class II association and orexin/hypocretin deficiency, a neurotransmitter that is involved in altered rapid eye movement sleep regulation. Conversely, the causes of narcolepsy type 2, where cataplexy and orexin deficiency are absent, remain unknown. Symptomatic medications to treat patients with narcolepsy have been developed, and management has been codified with guidelines, until the recent promising orexin-receptor agonists. The present review retraces the steps of the research on narcolepsy that linked the features of the disease with rapid eye movement sleep abnormality, and those that do not appear associated with rapid eye movement sleep.

A pathophysiological biomarker combination separates Lewy body from non-Lewy body neurogenic orthostatic hypotension ​

PURPOSE

Neurogenic orthostatic hypotension (nOH) results from deficient reflexive delivery of norepinephrine to cardiovascular receptors in response to decreased cardiac venous return. Lewy body (LB) forms of nOH are characterized by low 18F-dopamine-derived radioactivity (a measure of cardiac noradrenergic deficiency), olfactory dysfunction by the University of Pennsylvania Smell Identification Test (UPSIT), and increased deposition of alpha-synuclein (α-syn) in dermal sympathetic noradrenergic nerves by the α-syn-tyrosine hydroxylase (TH) colocalization index. This observational, cross-sectional study explored whether combinations of these biomarkers specifically identify LB forms of nOH.

METHODS

Clinical laboratory data were reviewed from patients referred for evaluation at the National Institutes of Health for chronic autonomic failure between 2011 and 2023. The cutoff value for low myocardial 18F-dopamine-derived radioactivity was 6000 nCi-kg/cc-mCi, for olfactory dysfunction an UPSIT score ≤ 28, and for an increased α-syn-TH colocalization index ≥ 1.57.

RESULTS

A total of 44 patients (31 LB, 13 non-LB nOH) had data for all three biomarkers. Compared to the non-LB group, the LB nOH group had low myocardial 18F-dopamine-derived radioactivity, low UPSIT scores, and high α-syn-TH colocalization indexes (p < 0.0001 each). Combining the three biomarkers completely separated the groups. Cluster analysis identified two distinct groups (p < 0.0001) independently of the clinical diagnosis, with one cluster corresponding exactly to LB nOH.

CONCLUSION

LB forms of nOH feature cardiac noradrenergic deficiency, olfactory dysfunction, and increased α-syn-TH colocalization in skin biopsies. Combining the data for these variables efficiently separates LB from non-LB nOH. Independently of the clinical diagnosis, this biomarker triad identifies a pathophysiologically distinct cluster of nOH patients.

REM sleep behaviour disorder (RBD): Personal perspectives and research priorities

The formal identification and naming of rapid eye movement (REM) sleep behaviour disorder (RBD) in 1985-1987 is described; the historical background of RBD from 1966 to 1985 is briefly discussed; and RBD milestones are presented. Current knowledge on RBD is identified with reference to recent comprehensive reviews, allowing for a focus on research priorities for RBD: factors and predictors of neurodegenerative phenoconversion from isolated RBD and patient enrolment in neuroprotective trials; isolated RBD clinical research cohorts; epidemiology of RBD; traumatic brain injury, post-traumatic stress disorder, RBD and neurodegeneration; depression, RBD and synucleinopathy; evolution of prodromal RBD to neurodegeneration; gut microbiome dysbiosis and colonic synuclein histopathology in isolated RBD; other alpha-synuclein research in isolated RBD; narcolepsy-RBD; dreams and nightmares in RBD; phasic REM sleep in isolated RBD; RBD, periodic limb movements, periodic limb movement disorder pseudo-RBD; other neurophysiology research in RBD; cardiac scintigraphy (123I-MIBG) in isolated RBD; brain magnetic resonance imaging biomarkers in isolated RBD; microRNAs as biomarkers in isolated RBD; actigraphic, other automated digital monitoring and machine learning research in RBD; prognostic counselling and ethical considerations in isolated RBD; and REM sleep basic science research. RBD research is flourishing, and is strategically situated at an ever-expanding crossroads of clinical (sleep) medicine, neurology, psychiatry and neuroscience.

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.

Psychobehavioural profile in narcolepsy type 1 with and without REM sleep behaviour disorder

REM sleep behaviour disorder (RBD) is common in narcolepsy type 1 (NT1). Abnormalities in the reward system have been observed in NT1, possibly related to impaired orexin projections towards the mesolimbic reward system, but also in RBD when associated with Parkinson's disease. Our study aimed to explore the psychobehavioural profile of NT1 patients with and without RBD compared with healthy controls (HC). Forty patients with NT1 were compared with 20 sex- and age-matched HC. All patients with NT1 underwent a video-polysomnography including a measure of REM sleep without atonia (RSWA). The following neuropsychobehavioural variables were assessed: apathy, impulsivity, depression, cognition, subjective and objective attention, sensation-seeking, and behavioural addictions. The patient population included 22 patients with NT1-RBD and 18 patients with NT1-noRBD. Compared with the healthy controls, patients with NT1 had higher scores of apathy, impulsivity, and depression; a lower score on global cognition, and poorer self-perceived attention. No differences were found between patients with NT1 with and without RBD in all neuropsychological variables, except for impaired objective attention in patients with NT1-RBD. In patients with NT1, a positive correlation was observed between RSWA and both apathy and impulsivity subscale. Moreover, in patients with NT1-RBD, RSWA was positively correlated with depression. Patients with NT1 showed higher depression, apathy, and impulsivity compared with controls. These measures correlate with the severity of RSWA, suggesting a transdiagnostic association between RBD and abnormalities of the reward system at least for patients with NT1.

Opportunities and Pitfalls of REM Sleep Behavior Disorder and Olfactory Dysfunction as Early Markers in Parkinson's Disease

During its pre-motor stage, Parkinson's disease (PD) presents itself with a multitude of non-motor symptoms with different degrees of specificity and sensitivity. The most important among them are REM sleep behavior disorder (RBD) and olfactory dysfunction. RBD is a parasomnia characterized by the loss of REM sleep muscle atonia and dream-enacting behaviors. Olfactory dysfunction in individuals with prodromal PD is usually described as hyposmia (reduced sense of smell) or anosmia (complete loss of olfactory function). These symptoms can precede the full expression of motor symptoms by decades. A close comprehension of these symptoms and the underlying mechanisms may enable early screening as well as interventions to improve patients' quality of life. Therefore, these symptoms have unmatched potential for identifying PD patients in prodromal stages, not only allowing early diagnosis but potentially opening a window for early, possibly disease-modifying intervention. However, they come with certain challenges. This review addresses some of the key opportunities and pitfalls of both RBD and olfactory dysfunction as early markers of PD.

α-synuclein antibody 5G4 identifies idiopathic REM-sleep behavior disorder in abdominal skin biopsies

INTRODUCTION

Idiopathic REM-sleep behavior disorder (iRBD) is considered the most specific prodromal marker of Parkinson's disease (PD). With the need to improve early detection of prodromal α-synucleinopathies, several methods to identify peripheral α-synuclein (α-syn) pathology have been exploited in manifest and prodromal PD with varying diagnostic accuracy. Recently, a disease specific 5G4 antibody has been evaluated in skin biopsies of manifest PD patients. The aim of our study was to analyze the 5G4 α-syn immunoreactivity in skin biopsies of deeply phenotyped subjects with iRBD and controls.

METHODS

The study cohort consisted of 28 patients with PD, 24 subjects with iRBD and 27 healthy controls, recruited from the CEGEMOD, PDBIOM and PARCAS cohorts. All subjects were deeply phenotyped and assessed for prodromal PD (pPD) probability based on MDS research criteria. Abdominal skin punch biopsies were processed and stained using a conformation specific 5G4 α-syn antibody as well as axonal markers SMI-31 and S100.

RESULTS

5G4-positivity was identified in 23/28 PD patients, 20/24 iRBD subjects and 8/27 healthy controls. Compared to healthy controls, sensitivity and specificity reached 83.33 % and 70.37 % for iRBD; and 82.14 % and 70.37 % for PD, respectively. 5G4-positivity rate in our study was irrespective of the calculated pPD probability of iRBD subjects.

CONCLUSIONS

This work establishes the diagnostic yield of conformation specific 5G4 α-syn antibody testing in skin biopsies of subjects with pPD, specifically iRBD. The diagnostic accuracy for this method seems to be similar for both manifest and prodromal PD and is not dependent on the pPD probability ratios.

Intra-neuronal alpha-synuclein deposition is related to cardiac noradrenergic deficiency and olfactory dysfunction in neurogenic orthostatic hypotension

Purpose

Neurogenic orthostatic hypotension (nOH) results from deficient reflexive delivery of norepinephrine to cardiovascular receptors in response to decreased cardiac venous return. Lewy body (LB) forms of nOH entail low 18F-dopamine-derived radioactivity (a measure of cardiac noradrenergic deficiency), olfactory dysfunction by the University of Pennsylvania Smell Identification Test (UPSIT), and increased deposition of alpha-synuclein (ɑ-syn) in dermal sympathetic noradrenergic nerves by the ɑ-syn-tyrosine hydroxylase (TH) colocalization index. This observational, cross-sectional study explored whether combinations of these biomarkers specifically identify LB forms of nOH.

Methods

Clinical laboratory data were reviewed from patients referred for evaluation at the National Institutes of Health for chronic autonomic failure between 2011 and 2023. The cutoff value for low myocardial 18F-dopamine-derived radioactivity was 6,000 nCi-kg/cc-mCi, for olfactory dysfunction an UPSIT score ≤ 28, and for an increased ɑ-syn-TH colocalization index ≥ 1.57.

Results

A total of 44 patients (31 LB, 13 non-LB nOH) had data for all 3 biomarkers. Compared to the non-LB group, the LB nOH group had low myocardial 18F-dopamine-derived radioactivity, low UPSIT scores, and high ɑ-syn-TH colocalization indexes (p<0.0001 each). Combining the 3 biomarkers completely separated the groups. Cluster analysis identified 2 distinct groups (p<0.0001) independently of the clinical diagnosis, 1 cluster corresponding exactly to LB nOH.

Conclusion

LB forms of nOH feature cardiac noradrenergic deficiency, olfactory dysfunction, and increased ɑ-syn-TH colocalization in skin biopsies. Combining the data for these variables efficiently separates LB from non-LB nOH. Independently of the clinical diagnosis, this biomarker triad identifies a pathophysiologically distinct cluster of nOH patients.

Clinical and dopaminergic imaging characteristics of the FARPRESTO cohort of trial-ready idiopathic rapid eye movement sleep behavior patients

INTRODUCTION

Idiopathic/isolated rapid eye movement (REM) sleep behavior disorder (iRBD) is considered the prodromal stage of alpha-synucleinopathies. Thus, iRBD patients are the ideal target for disease-modifying therapy. The risk FActoRs PREdictive of phenoconversion in iRBD Italian STudy (FARPRESTO) is an ongoing Italian database aimed at identifying risk factors of phenoconversion, and eventually to ease clinical trial enrollment of well-characterized subjects.

METHODS

Polysomnography-confirmed iRBD patients were retrospectively and prospectively enrolled. Baseline harmonized clinical and nigrostriatal functioning data were collected at baseline. Nigrostriatal functioning was evaluated by dopamine transporter-single-photon emission computed tomography (DaT-SPECT) and categorized with visual semi-quantification. Longitudinal data were evaluated to assess phenoconversion. Cox regressions were applied to calculate hazard ratios.

RESULTS

365 patients were enrolled, and 289 patients with follow-up (age 67.7 ± 7.3 years, 237 males, mean follow-up 40 ± 37 months) were included in this study. At follow-up, 97 iRBD patients (33.6%) phenoconverted to an overt synucleinopathy. Older age, motor and cognitive impairment, constipation, urinary and sexual dysfunction, depression, and visual semi-quantification of nigrostriatal functioning predicted phenoconversion. The remaining 268 patients are in follow-up within the FARPRESTO project.

CONCLUSIONS

Clinical data (older age, motor and cognitive impairment, constipation, urinary and sexual dysfunction, depression) predicted phenoconversion in this multicenter, longitudinal, observational study. A standardized visual approach for semi-quantification of DaT-SPECT is proposed as a practical risk factor for phenoconversion in iRBD patients. Of note, non-converted and newly diagnosed iRBD patients, who represent a trial-ready cohort for upcoming disease-modification trials, are currently being enrolled and followed in the FARPRESTO study. New data are expected to allow better risk characterization.

Skin Biopsy as a Diagnostic Tool for Synucleinopathies

Studies published in the last decade identified skin biopsies as a promising source of material for detecting alpha-synuclein (αSN). Alpha-synuclein gets deposited in the skin of patients with synucleinopathies, and therefore, a skin biopsy can be used to diagnose and confirm these diseases histopathologically. A skin biopsy can also be helpful for studies focusing on the nature of αSN deposits. The most important aspects of a biomarker are sensitivity, specificity, and technical feasibility. The potential for a skin biopsy to become the clinical tool of choice as a reliable biomarker for diagnosing synucleinopathies appears to be high, with consistently high sensitivity (>80%) and specificity approaching 100%. The review aims to provide an overview of the factors impacting skin biopsy's sensitivity, specificity, and feasibility in detecting dermal αSN deposits.

Narcolepsies, update in 2023

Narcolepsy type 1 (NT1) and type 2 (NT2), also known as narcolepsy with and without cataplexy, are sleep disorders that benefited from major scientific advances over the last two decades. NT1 is caused by the loss of hypothalamic neurons producing orexin/hypocretin, a neurotransmitter regulating sleep and wake, which can be measured in the cerebrospinal fluid (CSF). A low CSF level of hypocretin-1/orexin-A is a highly specific and sensitive biomarker, sufficient to diagnose NT1. Orexin-deficiency is responsible for the main NT1 symptoms: sleepiness, cataplexy, disrupted nocturnal sleep, sleep-related hallucinations, and sleep paralysis. In the absence of a lumbar puncture, the diagnosis is based on neurophysiological tests (nocturnal and diurnal) and the presence of the pathognomonic symptom cataplexy. In the revised version of the International Classification of sleep Disorders, 3rd edition (ICSD-3-TR), a sleep onset rapid eye movement sleep (REM) period (SOREMP) (i.e. rapid occurrence of REM sleep) during the previous polysomnography may replace the diurnal multiple sleep latency test, when clear-cut cataplexy is present. A nocturnal SOREMP is very specific but not sensitive enough, and the diagnosis of cataplexy is usually based on clinical interview. It is thus of crucial importance to define typical versus atypical cataplectic attacks, and a list of clinical features and related degrees of certainty is proposed in this paper (expert opinion). The time frame of at least three months of evolution of sleepiness to diagnose NT1 was removed in the ICSD-3-TR, when clear-cut cataplexy or orexin-deficiency are established. However, it was kept for NT2 diagnosis, a less well-characterized disorder with unknown clinical course and absence of biolo biomarkers; sleep deprivation, shift working and substances intake being major differential diagnoses. Treatment of narcolepsy is nowadays only symptomatic, but the upcoming arrival of non-peptide orexin receptor-2 agonists should be a revolution in the management of these rare sleep diseases.

REM Sleep Behavior Disorder and Other REM Parasomnias

OBJECTIVE

This article reviews rapid eye movement (REM) sleep behavior disorder (RBD) and other REM sleep parasomnias, particularly recurrent isolated sleep paralysis and nightmare disorder.

LATEST DEVELOPMENTS

People with RBD have dream enactment behaviors that can be distressing and cause injuries to themselves or a bed partner. Diagnosis of RBD still requires video polysomnography but new evaluative techniques are emerging. Automatic scoring of REM sleep without atonia, the polysomnographic RBD feature, has led to clearer diagnostic cutoff values. Isolated RBD is strongly linked with neurodegenerative disorders, particularly α-synucleinopathies, with a median latency to neurodegenerative disease diagnosis of 8 years. Mounting imaging, electrophysiologic, and pathologic evidence supports neurodegenerative changes in patients with isolated RBD. Safety precautions should be reviewed with patients to reduce the risk of injury. Clonazepam and melatonin are first-line agents for RBD symptoms, and rivastigmine appears to be beneficial for RBD in people with mild cognitive impairment. For nightmare disorder, image rehearsal therapy is effective and can be delivered through online platforms.

ESSENTIAL POINTS

While RBD symptoms can often be managed, patients with isolated RBD should be monitored for signs and symptoms of impending neurodegenerative disease. Individuals who wish to know about the associated risk should be counseled accordingly to allow planning and involvement in research if they choose. Exercise may have some neuroprotective effects, although no treatment has been shown to modify the neurodegenerative risk.

Considering REM Sleep Behavior Disorder in the Management of Parkinson's Disease

Rapid eye movement (REM) sleep behavior disorder (RBD) is the result of the loss of physiological inhibition of muscle tone during REM sleep, characterized by dream-enacting behavior and widely recognized as a prodromal manifestation of alpha-synucleinopathies. Indeed, patients with isolated RBD (iRBD) have an extremely high estimated risk to develop a neurodegenerative disease after a long follow up. Nevertheless, in comparison with PD patients without RBD (PDnoRBD), the occurrence of RBD in the context of PD (PDRBD) seems to identify a unique, more malignant phenotype, characterized by a more severe burden of disease in terms of both motor and non-motor symptoms and increased risk for cognitive decline. However, while some medications (eg, melatonin, clonazepam, etc.) and non-pharmacological options have been found to have some therapeutic benefits on RBD there is no available treatment able to modify the disease course or, at least, slow down the neurodegenerative process underlying phenoconversion. In this scenario, the long prodromal phase may allow an early therapeutic window and, therefore, the identification of multimodal biomarkers of disease onset and progression is becoming increasingly crucial. To date, several clinical (motor, cognitive, olfactory, visual, and autonomic features) neurophysiological, neuroimaging, biological (biofluids or tissue biopsy), and genetic biomarkers have been identified and proposed, also in combination, as possible diagnostic or prognostic markers, along with a potential role for some of them as outcome measures and index of treatment response. In this review, we provide an insight into the present knowledge on both existing and future biomarkers of iRBD and highlight the difference with PDRBD and PDnoRBD, including currently available treatment options.

Cutaneous α-Synuclein Signatures in Patients With Multiple System Atrophy and Parkinson Disease

BACKGROUND AND OBJECTIVES

Multiple system atrophy (MSA) is a progressive neurodegenerative disorder caused by the abnormal accumulation of α-synuclein in the nervous system. Clinical features include autonomic and motor dysfunction, which overlap with those of Parkinson disease (PD), particularly at early disease stages. There is an unmet need for accurate diagnostic and prognostic biomarkers for MSA and, specifically, a critical need to distinguish MSA from other synucleinopathies, particularly PD. The purpose of the study was to develop a unique cutaneous pathologic signature of phosphorylated α-synuclein that could distinguish patients with MSA from patients with PD and healthy controls.

METHODS

We studied 31 patients with MSA and 54 patients with PD diagnosed according to current clinical consensus criteria. We also included 24 matched controls. All participants underwent neurologic examinations, autonomic testing, and skin biopsies at 3 locations. The density of intraepidermal, sudomotor, and pilomotor nerve fibers was measured. The deposition of phosphorylated α-synuclein was quantified. Results were compared with clinical rating assessments and autonomic function test results.

RESULTS

Patients with PD had reduced nerve fiber densities compared with patients with MSA (p < 0.05, all fiber types). All patients with MSA and 51/54 with PD had evidence of phosphorylated α-synuclein in at least one skin biopsy. No phosphorylated α-synuclein was detected in controls. Patients with MSA had greater phosphorylated α-synuclein deposition (p < 0.0001) and more widespread peripheral distribution (p < 0.0001) than patients with PD. These results provided >90% sensitivity and specificity in distinguishing between the 2 disorders.

DISCUSSION

α-synuclein is present in the peripheral autonomic nerves of patients with MSA and when combined with synuclein distribution accurately distinguishes MSA from PD.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that measurement of phosphorylated α-synuclein in skin biopsies can differentiate patients with MSA from those with PD.

A comparative blind study between skin biopsy and seed amplification assay to disclose pathological α-synuclein in RBD

To compare the diagnostic accuracy of the immunofluorescence (IF) technique and aSyn-seed amplification assay (aSyn-SAA) of skin and cerebrospinal fluid (CSF) in disclosing pathological α-syn in idiopathic idiopathic REM sleep behavior disorder (iRBD) as early phase of a synucleinopathy. We prospectively recruited 41 patients with iRBD and 40 matched clinical controls including RBD associated with type 1 Narcolepsy (RBD-NT1, 21 patients), iatrogenic causes (2 pt) or OSAS (6 pt) and 11 patients with peripheral neuropathies. IF from samples taken by skin biopsy and aSyn-SAA from skin and CSF samples were analysed blinded to the clinical diagnosis. IF showed a good diagnostic accuracy (89%) that was lower in the case of skin and CSF-based aSyn-SAA (70% and 69%, respectively) because of a lower sensitivity and specificity. However, IF showed a significant agreement with CSF aSyn-SAA. In conclusion, our data may favor the use of skin biopsy and aSyn-SAA as diagnostic tools for a synucleinopathy in iRBD.

Derivation and Validation of a Phenoconversion-Related Pattern in Idiopathic Rapid Eye Movement Behavior Disorder

BACKGROUND

Idiopathic rapid eye movement sleep behavior disorder (iRBD) represents the prodromal stage of α-synucleinopathies. Reliable biomarkers are needed to predict phenoconversion.

OBJECTIVE

The aim was to derive and validate a brain glucose metabolism pattern related to phenoconversion in iRBD (iRBDconvRP) using spatial covariance analysis (Scaled Subprofile Model and Principal Component Analysis [SSM-PCA]).

METHODS

Seventy-six consecutive iRBD patients (70 ± 6 years, 15 women) were enrolled in two centers and prospectively evaluated to assess phenoconversion (30 converters, 73 ± 6 years, 14 Parkinson's disease and 16 dementia with Lewy bodies, follow-up time: 21 ± 14 months; 46 nonconverters, 69 ± 6 years, follow-up time: 33 ± 19 months). All patients underwent [¹⁸ F]FDG-PET (¹⁸ F-fluorodeoxyglucose positron emitting tomography) to investigate brain glucose metabolism at baseline. SSM-PCA was applied to obtain the iRBDconvRP; nonconverter patients were considered as the reference group. Survival analysis and Cox regression were applied to explore prediction power.

RESULTS

First, we derived and validated two distinct center-specific iRBDconvRP that were comparable and significantly able to predict phenoconversion. Then, SSM-PCA was applied to the whole set, identifying the iRBDconvRP. The iRBDconvRP included positive voxel weights in cerebellum; brainstem; anterior cingulate cortex; lentiform nucleus; and middle, mesial temporal, and postcentral areas. Negative voxel weights were found in posterior cingulate, precuneus, middle frontal gyrus, and parietal areas. Receiver operating characteristic analysis showed an area under the curve of 0.85 (sensitivity: 87%, specificity: 72%), discriminating converters from nonconverters. The iRBDconvRP significantly predicted phenoconversion (hazard ratio: 7.42, 95% confidence interval: 2.6-21.4).

CONCLUSIONS

We derived and validated an iRBDconvRP to efficiently discriminate converter from nonconverter iRBD patients. [¹⁸ F]FDG-PET pattern analysis has potential as a phenoconversion biomarker in iRBD patients. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Assessment of glymphatic function in narcolepsy using DTI-ALPS index

INTRODUCTION

Sleep is a modulator of glymphatic activity which is altered in various sleep disorders. Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness (EDS), rapid onset of rapid eye movement (REM) sleep, cataplexy, disturbed night sleep with fragmentation. It is categorized into two types, type 1 (NT1) and type 2 (NT2) depending on the presence of cataplexy and/or absence of orexin. We sought for alterations in glymphatic activity in narcoleptic patients using diffusion tensor imaging (DTI) along perivascular space (ALPS) index on magnetic resonance imaging (MRI).

MATERIAL AND METHODS

Adult patients diagnosed with NT1 or NT2 who had polysomnography (PSG) and MRI with DTI were included in the study. Sleep recording included Epworth Sleepiness Scale (ESS) score, sleep latency during multiple sleep latency test (MSLT), sleep efficiency during night PSG, wake after sleep onset (WASO), REM sleep latency during PSG, percentage of non-REM (NREM), REM sleep and wakefulness during night PSG. DTI-ALPS index was calculated for each patient and age-sex matched healthy control(HC)s.

RESULTS

The study group was composed of 25 patients [F/M = 15/10, median age = 34 (29.5-44.5)], 14 with NT1 and 11 with NT2 disease. ESS, WASO and percentage of wakefulness were significantly higher in NT1 patients (p < 0.05). Mean DTI-ALPS was not significantly different neither between narcoleptic patients and HCs, nor between NT1 and NT2 patients (all, p > 0.05). However, DTI-ALPS was negatively correlated with WASO (r = -0.745, p = 0.013) and percentage of wakefulness (r = -0.837, p = 0.005) in NT1 patients. DTI-ALPS correlated negatively with percentage of N1 sleep (r = -0.781, p = 0.005) but positively with REM percentage (r = 0.618, p = 0.043) in NT2 patients.

CONCLUSION

In this study, DTI-ALPS was not significantly different in narcoleptic patients than the HCs. However, the glymphatic index as assessed by DTI-ALPS correlated with PSG parameters; negatively with WASO, percentage of wakefulness in NT1, percentage of N1 sleep in NT2, and positively with REM sleep in NT2. A tendency for a reduction in DTI-ALPS in NT1 patients compared to both NT2 patients and HCs was also found. These findings might show the first evidence of an alteration of glymphatic activity, especially in NT1 patients, thus warrant further prospective studies in larger size of narcoleptic patient cohorts.

Decreased cerebrospinal fluid orexin levels not associated with clinical sleep disturbance in Parkinson's disease: A retrospective study

Patients with Parkinson's disease (PD) often suffer from sleep disturbances, including excessive daytime sleepiness (EDS) and rapid eye movement sleep behavior disorder (RBD). These symptoms are also experienced by patients with narcolepsy, which is characterized by orexin neuronal loss. In PD, a decrease in orexin neurons is observed pathologically, but the association between sleep disturbance in PD and cerebrospinal fluid (CSF) orexin levels is still unclear. This study aimed to clarify the role of orexin as a biomarker in patients with PD. CSF samples were obtained from a previous cohort study conducted between 2015 and 2020. We cross-sectionally and longitudinally examined the association between CSF orexin levels, sleep, and clinical characteristics. We analyzed 78 CSF samples from 58 patients with PD and 21 samples from controls. CSF orexin levels in patients with PD (median = 272.0 [interquartile range = 221.7-334.5] pg/mL) were lower than those in controls (352.2 [296.2-399.5] pg/mL, p = 0.007). There were no significant differences in CSF orexin levels according to EDS, RBD, or the use of dopamine agonists. Moreover, no significant correlation was observed between CSF orexin levels and clinical characteristics by multiple linear regression analysis. Furthermore, the longitudinal changes in orexin levels were also not correlated with clinical characteristics. This study showed decreased CSF orexin levels in patients with PD, but these levels did not show any correlation with any clinical characteristics. Our results suggest the limited efficacy of CSF orexin levels as a biomarker for PD, and that sleep disturbances may also be affected by dysfunction of the nervous system other than orexin, or by dopaminergic treatments in PD. Understanding the reciprocal role of orexin among other neurotransmitters may provide a better treatment strategy for sleep disturbance in patients with PD.

REM sleep behavior disorder as a complex condition with heterogeneous underlying disorders: clinical management and prognostic implications [Commentary]

PURPOSE

To review how REM sleep behavior disorder (RBD) is a complex condition with heterogeneous underlying disorders; and to review clinical management issues and prognostic implications.

METHODS

PubMed literature search and contents from the first textbook of RBD (2018).

RESULTS

RBD, with its core objective diagnostic feature of REM-without-atonia (RWA) documented by video-polysomnography, can emerge during the entire lifespan, and can initially present as an idiopathic (isolated) condition (iRBD), or can be associated with a broad spectrum of disorders including narcolepsy, alpha-synuclein neurodegenerative disorders (esp. Parkinson's disease [PD] and dementia with Lewy bodies [DLB]), paraneoplastic neurological syndromes and autoimmune disorders, CNS lesions (e.g., tumors, stroke), other neurological disorders, psychiatric disorders (PTSD, mood disorders), can be triggered by antidepressant/other medications, and can emerge acutely with drug withdrawal states, toxic-metabolic states, etc. Important clinical issues include the evolution of iRBD to PD/DLB in most middle-aged and older patients over a period of years to several decades, with compelling prognostic implications, along with the hope of enrolling these patients in future clinical trials to test promising disease-modifying therapies. Also, the strong link of RBD with narcolepsy needs further investigation. Parasomnia overlap disorder involves RBD and NREM parasomnias that can be idiopathic or linked with a broad range of clinical disorders. RBD usually responds to therapy consisting mainly of melatonin and/or clonazepam at bedtime. The complex associations of RBD with OSA are being increasingly investigated. RBD mimics with dream-enactment need to be recognized for diagnostic and management purposes, including severe OSA, NREM parasomnias, PLMD, nocturnal seizures, and other conditions.

CONCLUSIONS

The clinical and research RBD fields span across the disciplines of neurology, pulmonary, psychiatry, psychology, and pediatric sleep medicine, along with physical medicine and rehabilitation medicine, other allied disciplines, and the basic and clinical neurosciences.

What Is the Prognostic Significance of Rapid Eye Movement Sleep Without Atonia in a Polysomnogram?

SUMMARY

Freud said we are lucky to be paralyzed during sleep, so we cannot act out our dreams. Atonia of skeletal muscles normally present during rapid eye movement sleep prevents us from acting out our dreams. Observing rapid eye movement sleep without atonia in a polysomnogram in older adults first and foremost warrants consideration of rapid eye movement behavior disorder. Seventy-five to 90% of older adults with isolated rapid eye movement behavior disorder will develop a neurodegenerative disease within 15 years, most often a synucleinopathy. Rapid eye movement sleep without atonia in those younger than 50 years is commonly found in individuals with narcolepsy and those taking antidepressant medications.

Fluid and Tissue Biomarkers of Lewy Body Dementia: Report of an LBDA Symposium

The Lewy Body Dementia Association (LBDA) held a virtual event, the LBDA Biofluid/Tissue Biomarker Symposium, on January 25, 2021, to present advances in biomarkers for Lewy body dementia (LBD), which includes dementia with Lewy bodies (DLBs) and Parkinson's disease dementia (PDD). The meeting featured eight internationally known scientists from Europe and the United States and attracted over 200 scientists and physicians from academic centers, the National Institutes of Health, and the pharmaceutical industry. Methods for confirming and quantifying the presence of Lewy body and Alzheimer's pathology and novel biomarkers were discussed.

Neurophysiological Aspects of REM Sleep Behavior Disorder (RBD): A Narrative Review

REM sleep without atonia (RSWA) is the polysomnographic (PSG) hallmark of rapid eye movement (REM) sleep behavior disorder (RBD), a feature essential for the diagnosis of this condition. Several additional neurophysiological aspects of this complex disorder have also recently been investigated in depth, which constitute the focus of this narrative review, together with RSWA. First, we describe the complex neural network underlying REM sleep and its muscle atonia, focusing on the disordered mechanisms leading to RSWA. RSWA is then described in terms of its polysomnographic features, and the methods (visual and automatic) currently available for its scoring and quantification are exposed and discussed. Subsequently, more recent and advanced neurophysiological features of RBD are described, such as electroencephalography during wakefulness and sleep, transcranial magnetic stimulation, and vestibular evoked myogenic potentials. The role of the assessment of neurophysiological features in the study of RBD is then carefully discussed, highlighting their usefulness and sensitivity in detecting neurodegeneration in the early or prodromal stages of RBD, as well as their relationship with other proposed biomarkers for the diagnosis, prognosis, and monitoring of this condition. Finally, a future research agenda is proposed to help clarify the many still unclear aspects of RBD.

Neurophysiological Aspects of REM Sleep Behavior Disorder (RBD): A Narrative Review

REM sleep without atonia (RSWA) is the polysomnographic (PSG) hallmark of rapid eye movement (REM) sleep behavior disorder (RBD), a feature essential for the diagnosis of this condition. Several additional neurophysiological aspects of this complex disorder have also recently been investigated in depth, which constitute the focus of this narrative review, together with RSWA. First, we describe the complex neural network underlying REM sleep and its muscle atonia, focusing on the disordered mechanisms leading to RSWA. RSWA is then described in terms of its polysomnographic features, and the methods (visual and automatic) currently available for its scoring and quantification are exposed and discussed. Subsequently, more recent and advanced neurophysiological features of RBD are described, such as electroencephalography during wakefulness and sleep, transcranial magnetic stimulation, and vestibular evoked myogenic potentials. The role of the assessment of neurophysiological features in the study of RBD is then carefully discussed, highlighting their usefulness and sensitivity in detecting neurodegeneration in the early or prodromal stages of RBD, as well as their relationship with other proposed biomarkers for the diagnosis, prognosis, and monitoring of this condition. Finally, a future research agenda is proposed to help clarify the many still unclear aspects of RBD.

Chromatic Pupillometry in Isolated Rapid Eye Movement Sleep Behavior Disorder

Background

Melanopsin retinal ganglion cell (mRGC)‐mediated pupillary light reflex (PLR) abnormalities have been documented in several neurodegenerative disorders including Parkinson's disease. Overall, isolated rapid eye movement (REM) sleep behavior disorder (iRBD) represents the strongest prodromal risk factor for impending α‐synucleinopathies.

Objectives

To quantitatively compare PLR and mRGC‐mediated contribution to PLR in 16 iRBD patients and 16 healthy controls.

Methods

iRBD and controls underwent extensive neuro‐ophthalmological evaluation and chromatic pupillometry. In iRBD, PLR metrics were correlated with clinical variables and with additional biomarkers including REM atonia index (RAI), DaTscan, and presence of phosphorylated‐α‐synuclein (p‐α‐syn) deposition in skin biopsy.

Results

We documented higher baseline pupil diameter and decreased rod‐transient PLR amplitude in iRBD patients compared to controls. PLR rod‐contribution correlated with RAI. Moreover, only iRBD patients with evidence of p‐α‐syn deposition at skin biopsy showed reduced PLR amplitude compared to controls.

Conclusion

The observed PLR abnormalities in iRBD might be considered as potential biomarkers for the risk stratification of phenoconversion of the disease. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Metabolomics in Parkinson's disease

Parkinson's disease (PD) is a multifactorial neurodegenerative disorder in which environmental (lifestyle, dietary, infectious disease) factors as well as genetic make-up play a role. Metabolomics, an evolving research field combining biomarker discovery and pathogenetics, is particularly useful in studying complex pathophysiology in general and Parkinson's disease (PD) specifically. PD, the second most frequent neurodegenerative disorder, is characterized by the loss of dopaminergic neurons in the substantia nigra and the presence of intraneural inclusions of α-synuclein aggregates. Although considered a predominantly movement disorder, PD is also associated with number of non-motor features. Metabolomics has provided useful information regarding this neurodegenerative process with the aim of identifying a disease-specific fingerprint. Unfortunately, many disease variables such as clinical presentation, motor system involvement, disease stage and duration substantially affect biomarker relevance. As such, metabolomics provides a unique approach to studying this multifactorial neurodegenerative disorder.

Neurochemical Features of Rem Sleep Behaviour Disorder

Dopaminergic deficiency, shown by many studies using functional neuroimaging with Single Photon Emission Computerized Tomography (SPECT) and Positron Emission Tomography (PET), is the most consistent neurochemical feature of rapid eye movement (REM) sleep behaviour disorder (RBD) and, together with transcranial ultrasonography, and determination of alpha-synuclein in certain tissues, should be considered as a reliable marker for the phenoconversion of idiopathic RBD (iRBD) to a synucleopathy (Parkinson’s disease –PD- or Lewy body dementia -LBD). The possible role in the pathogenesis of RBD of other neurotransmitters such as noradrenaline, acetylcholine, and excitatory and inhibitory neurotransmitters; hormones such as melatonin, and proinflammatory factors have also been suggested by recent reports. In general, brain perfusion and brain glucose metabolism studies have shown patterns resembling partially those of PD and LBD. Finally, the results of structural and functional MRI suggest the presence of structural changes in deep gray matter nuclei, cortical gray matter atrophy, and alterations in the functional connectivity within the basal ganglia, the cortico-striatal, and the cortico-cortical networks, but they should be considered as preliminary.

Biomarkers of conversion to α-synucleinopathy in isolated rapid-eye-movement sleep behaviour disorder

Patients with isolated rapid-eye-movement sleep behaviour disorder (RBD) are commonly regarded as being in the early stages of a progressive neurodegenerative disease involving α-synuclein pathology, such as Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy. Abnormal α-synuclein deposition occurs early in the neurodegenerative process across the central and peripheral nervous systems and might precede the appearance of motor symptoms and cognitive decline by several decades. These findings provide the rationale to develop reliable biomarkers that can better predict conversion to clinically manifest α-synucleinopathies. In addition, biomarkers of disease progression will be essential to monitor treatment response once disease-modifying therapies become available, and biomarkers of disease subtype will be essential to enable prediction of which subtype of α-synucleinopathy patients with isolated RBD might develop.

Detection of Dermal Alpha-Synuclein Deposits as a Biomarker for Parkinson's Disease

Alpha-synuclein deposits are detectable in skin biopsies of patients with Parkinson’s disease and other synucleinopathies like multiple system atrophy by immunohistochemical staining. As they are easily to obtain, they appear a promising tool for the pre-mortem histopathological confirmation of the disease and as a potential outcome measure in studies targeting alpha-synuclein aggregates. Good sensitivity, specificity, and practicability are the most important requirements of a biomarker. The review gives an overview on all three aspects, addresses methodological problems and the lack of standardized procedures as a major problem and gives an outlook on the future of skin biopsy as a potential diagnostic tool in synucleinopathies.

Cutaneous Alpha-Synuclein is Correlated with Autonomic Impairment in Isolated REM Sleep Behavior Disorder

STUDY OBJECTIVES

To define the clinical implications of cutaneous phosphorylated α-synuclein (p-syn) and its association with subjective and objective measures of autonomic impairment and clinical features including antidepressant use in isolated REM sleep behavior disorder (iRBD).

METHODS

Twenty-five iRBD patients had quantified neurological and cognitive examinations, olfactory testing, questionnaires, autonomic function testing, and 3 punch skin biopsies (distal thigh, proximal thigh, neck). Skin biopsies were stained for the pan-axonal marker PGP 9.5 and co-stained with p-syn, and results were compared to 28 patients with Parkinson's disease (PD) and 18 healthy controls. Equal numbers of iRBD patients on and off antidepressants were recruited. The composite autonomic severity scale (CASS) was calculated for all patients.

RESULTS

P-syn was detected in 16/25 (64%) of iRBD patients, compared to 27/28 (96%) of PD and 0/18 controls. The presence of p-syn at any biopsy site was correlated with both sympathetic (CASS adrenergic r = 0.6, p < 0.05) and total autonomic impairment (CASS total r = 0.6, p < 0.05) on autonomic reflex testing in iRBD patients. These results were independent of the density of p-syn at each site. There was no correlation between p-syn and antidepressant use.

CONCLUSIONS

In patients with iRBD, the presence of cutaneous p-syn was detected in most patients and was associated with greater autonomic dysfunction on testing. Longitudinal follow-up will aid in defining the predictive role of both skin biopsy and autonomic testing in determining phenoconversion rates and future disease status.

Dream enactment behavior: review for the clinician

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Dream enactment behavior commonly occurs on occasion in normal children and adults. Disruptive and frequent dream enactment behavior may come to the attention of the clinician either as the primary reason for consultation or as a prominent characteristic of a patient with other sleep disorders. Questioning patients with chronic neurologic and psychiatric disorders may also reveal previously unrecognized behavior. In the absence of sleep pathology, process of dream enactment likely begins with active, often emotionally charged dream content that may occasionally break through the normal REM sleep motor suppressive activity. Disrupted sleep resulting from many possible causes, such as circadian disruption, sleep apnea, or medications, may also disrupt at least temporarily the motor-suppressive activity in REM sleep, allowing dream enactment to occur. Finally, pathological neurological damage in the context of degenerative, autoimmune, and infectious neurological disorders may lead to chronic recurrent and severe dream enactment behavior. Evaluating the context, frequency, and severity of dream enactment behavior is guided first and foremost by a structured approach to the sleep history. Physical exam and selected testing support the clinical diagnosis. Understanding the context and the likely cause is essential to effective therapy.

Phosphorylated Alpha-Synuclein Within Cutaneous Autonomic Nerves of Patients With Parkinson's Disease: The Implications of Sample Thickness on Results

The detection of cutaneous phosphorylated alpha-synuclein (P-syn) in patients with Parkinson's disease (PD) has ranged from 30% to 100% across different studies. We hypothesize that part of the variability in P-syn detection is due to methodological differences using sections of different tissue thickness. Three skin biopsies were obtained from 29 individuals with PD and 21 controls. Tissues were cut into 10-, 20-, and 50-µm-thick sections and double-stained with protein gene product (PGP) 9.5 and P-syn. We quantified the deposition of P-syn with and without PGP 9.5 in sweat glands, pilomotor muscle, and blood vessels using confocal digital images of autonomic structures. Overall, the P-syn-positive rates with PGP 9.5 colocalization in subjects with PD were 100% using 50 µm sections, 90% using 20 µm sections, and 73% using 10 µm sections with 100% specificity. (No P-syn was detected within control subjects.) Without PGP 9.5, colocalization of the P-syn-positive rates was 100% for all samples, but specificity dropped below 70%. In this study, double-immunostained 50 µm skin biopsy tissue sections are superior to 20 and 10 µm tissue sections at detecting P-syn in subjects with PD. The increased sensitivity is likely secondary to a combination of greater volume of tissue analyzed and improved visualization of nerve fiber architecture.

The role of tissue biopsy as a biomarker in REM sleep behavior disorder

Patients with idiopathic REM-sleep behavior disorder (iRBD) are at substantial risk of progressive neurodegenerative disease of α-synuclein pathology. Longitudinal studies have demonstrated that abnormal α-synuclein deposition occurs early in the course of disease and may precede the appearance of motor symptoms by several decades. This provides rationale for the use of a reliable biomarker to both follow disease progression and to assess treatment response, once disease-modifying treatments become available. Tissue α-synuclein has emerged as a promising candidate, however the utility of α-synuclein detection in tissues accessible to biopsy in iRBD remains unclear. This article summarizes the current literature on the role of tissue biopsy in iRBD, with specific focus on its potential role as a biomarker of disease progression and its role in future clinical trials.

REM sleep behavior disorder in narcolepsy: A secondary form or an intrinsic feature?

Disrupted nighttime sleep is one of the pentad of symptoms defining Narcolepsy. REM sleep behavior disorder (RBD) largely contributes to night sleep disruption and narcolepsy is the most common cause of secondary RBD. However, RBD linked to narcolepsy (N-RBD) has been insufficiently characterized, leaving unsolved a number of issues. Indeed, it is still debated whether N-RBD is an intrinsic feature of narcolepsy, as indubitable for cataplexy, and therefore strictly linked to the cerebrospinal fluid hypocretin-1 (CSF hcrt-1) deficiency, or an associated feature, with a still unclear pathophysiology. The current review aims at rendering a comprehensive state-of-the-art of N-RBD, highlighting the open and unsettled topics. RBD reportedly affects 30-60% of patients with Narcolepsy type 1 (NT1), but it may be seen also in Narcolepsy type 2 (NT2). When compared to idiopathic/isolated RBD (iRBD), N-RBD has been reported to be characterized by less energetic and quieter episode, which however occur with the same probability in the first and the second part of the night and sometime even subcontinuously. N-RBD patients are generally younger than those with iRBD. N-RBD has been putatively linked to wake-sleep instability due to CSF hcrt-1 deficiency, but this latter by itself cannot explain completely the phenomenon as N-RBD has not been universally linked to low CSF hcrt-1 levels and it may be observed also in NT2. Therefore, other factors may probably play a role and further studies are needed to clarify this issue. In addition, therapeutic options have been poorly investigated.