Altered Brain Glymphatic Flow at Diffusion-Tensor MRI in Rapid Eye Movement Sleep Behavior Disorder

Altered default mode network and glymphatic function in insomnia with depression: A multimodal MRI study

OBJECTIVES

This study aims to evaluate functional changes in the default mode network (DMN) and glymphatic system in individuals of chronic insomnia disorder (CID) with comorbid major depression disorder (MDD).

METHODS

A total of 112 CID patients and 56 healthy controls with good sleep (GS) were enrolled. CID patients were divided into were further divided into a CID-only group and a group with CID and comorbid MDD. Resting-state functional magnetic resonance imaging (rs-fMRI) assessed DMN dysfunction and its connectivity with external networks. To determine whether comorbid MDD exacerbated the decline in glymphatic function in patients with CID, the diffusion tensor imaging along the perivascular space (DTI-ALPS) index was calculated. Binary logistic regression identified key imaging features for diagnostic modeling.

RESULTS

Patients with CID and comorbid MDD exhibited significantly weakened functional connectivity within the DMN. In contrast, the key node posterior cingulate cortex(PCC) of the default mode network showed enhanced functional connectivity with brain regions outside the DMN, including middle cingulate cortex and supplementary motor area. Regarding the glymphatic system, the lower ALPS index in CID patients with comorbid MDD was lower than in CID patients, indicating reduced glymphatic function compared to those without depression. HAMD scores were significantly associated with bilateral Dyproj values (P < 0.001) and the functional connectivity values of PCC_L-SMA_L and TempP_L-PHC_L (P < 0.01). The diagnostic model developed based on these findings demonstrated high diagnostic efficacy for CID with comorbid MDD.

CONCLUSION

The destabilization of subsystems within the DMN may represent the neurological mechanism through which depression contributes to insomnia. Comorbid depressive disorders may exacerbate glymphatic dysfunction in patients with CID, highlighting the importance of early clinical intervention for depressive symptoms in insomnia disorder.

Investigating glymphatic function and bed nucleus of the stria terminalis-based functional connectivity in Parkinson's disease with and without depression

Glymphatic activity and the bed nucleus of the stria terminalis (BNST) have been implicated in the pathogenesis of Parkinson's disease (PD) with depression (PDD). This study aimed to investigate glymphatic function and BNST-based functional connectivity (FC) and potential biomarkers in PDD. The diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) index combined with BNST-based FC and support vector machine were applied to 24 PDD, 24 PD with non-depression (PDND), and 25 healthy controls. We found that (1) the DTI-ALPS indices (p < 0.001), the right BNST-based FC values (p < 0.001, FWE small volume correction) were significantly different among three groups; (2) the FC features in the right mPFC (mPFC_R), right MTG (MTG_R), and right ITG (ITG_R) can distinguish PDD from PDND; (3) the right BNST-based FC values, DTI-ALPS indices, and HAMD scores were correlated with each other (r = -0.620, p = 0.004; r = 0.651, p = 0.002; r = -0.53, p = 0.016). Impaired glymphatic function and altered BNST-based FC values are strongly associated with PD, and brain regions with differences in the right BNST-based FC values may serve as potential biomarkers for classifying clinical subtypes of PD. These findings provide new insights into the pathogenesis of depression in PD. This study protocol was registered on the Chinese Clinical Trial Registry (ChiCTR2000038411, September 22, 2020, https://www.chictr.org.cn/showproj.html?proj=56715 ).

Assessment of the glymphatic dysfunction in amyotrophic lateral sclerosis using the diffusion tensor imaging along the perivascular spaces index: a pilot study

Background

The glymphatic system plays a critical role in clearing interstitial waste from the brain. Dysfunction of this system has been linked to various neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). The diffusion tensor imaging-along the perivascular space (DTI-ALPS) index has emerged as a potential neuroimaging biomarker for evaluating glymphatic function. This study investigates whether glymphatic function differs in individuals with ALS compared to those with Parkinson's disease (PD) and normal controls (NCs), using the DTI-ALPS index.

Methods

This study included 35 ALS patients, 35 age- and sex-matched PD patients, and 13 NCs. Diffusion tensor imaging (DTI) was conducted, and the DTI-ALPS index was calculated. Clinical assessments included demographic data, disease duration, cognitive status, and functional scales. Group comparisons and correlation analyses were performed to assess the relationship between the DTI-ALPS index and clinical parameters.

Results

The ALS group exhibited a significantly lower right-side DTI-ALPS index than the NC group (p = 0.037), while no differences were observed between the ALS and PD groups. The DTI-ALPS index was negatively correlated with age in ALS and PD groups but showed no correlation with clinical measures in the ALS group. Women in the ALS group had a significantly higher DTI-ALPS index than in men.

Conclusion

Glymphatic dysfunction may contribute to the pathogenesis of ALS, as evidenced by a reduced DTI-ALPS index compared to NCs. However, its clinical relevance and specificity for ALS remain uncertain. Further studies with larger cohorts are warranted to validate these findings.

Atrial fibrillation catheter ablation, brain glymphatic function, and cognitive performance

BACKGROUND AND AIMS

It remains unknown whether the brain glymphatic system, which is driven by the heartbeat-driven pulsation of arteries and is responsible for cerebral waste clearance, is impaired in atrial fibrillation (AF) and mediates cognitive dysfunction related to AF. The aim of this study was to assess brain glymphatic alterations in AF, their role in cognitive function, and whether catheter ablation can improve glymphatic activity.

METHODS

In this case-control and prospective before-and-after study, patients with AF and healthy controls (HCs) were enrolled. Participants underwent brain magnetic resonance imaging and a comprehensive neuropsychological battery. Glymphatic activity was quantified by diffusion tensor image analysis along the perivascular space (DTI-ALPS) index. Magnetic resonance imaging was repeated after surgery in patients who underwent ablation.

RESULTS

Overall, 87 patients with AF and 44 HCs were enrolled. Compared with HCs, patients with AF had a lower ALPS index (P = .016). Nonparoxysmal AF patients showed lower ALPS index than both HCs (P = .002) and paroxysmal AF patients (P = .044). A lower ALPS index was associated with worse scores of Trail Making Test, Digit Symbol Substitution Test, Digit Span Test, and Stroop Colour and Word Test (all P < .05). Mediation analyses revealed that glymphatic activity was a mediator between AF and cognitive decline. Among the 50 patients who underwent ablation therapy, DTI-ALPS index was improved after surgery (P = .015).

CONCLUSIONS

Brain glymphatic function measured by DTI-ALPS index was impaired in patients with AF, mediates the association between AF and cognitive decline, and was improved after ablation therapy.

Diffusion Tensor Imaging Along the Perivascular Space Is a Promising Imaging Method in Parkinson's Disease: A Systematic Review and Meta-Analysis Study

INTRODUCTION

Parkinson's disease (PD) is a chronic, progressive neurodegenerative disorder that primarily affects motor functions. Recently, a diffusion tensor imaging technique called DTI along the perivascular space (DTI-ALPS) has gained attention as a noninvasive biomarker for glymphatic function. This systematic review and meta-analysis aimed to evaluate the potential and implications of the DTI-ALPS index for diagnosing PD.

METHODS

This study followed the PRISMA 2020 statement. Eligible cohort and cross-sectional studies measured the ALPS index in PD patients versus non-PD participants. Web of Science, Medline, Scopus, Embase, Cochrane, PROSPERO, and ICTRP databases were explored until November 14, 2024. Two researchers independently screened studies, extracted data, and assessed the risk of bias using the Newcastle-Ottawa Scale (NOS). The meta-analysis used a random effects model (REM), assessing heterogeneity (I2, Q-test) and publication bias (Egger's test, trim&fill plot). The certainty of the evidence was evaluated using the GRADE approach.

RESULTS

This meta-analysis of 11 studies, involving 1462 patients (855 PD, 607 non-PD of both genders), yielded significant findings. The overall ALPS index differed substantially between PD and non-PD groups (SMD: -0.61, 95% CI: -0.72, -0.50, p < 0.001). Additionally, a significant negative correlation emerged between the ALPS index and Unified PD Rating Scale III (UPDRS III) (r = -0.40, (95% CI: -0.59, -0.18, I2: 89.81, p < 0.001)), indicating glymphatic dysfunction's impact on cognitive decline. However, a weak and statistically non-significant correlation was observed between the ALPS index and Montreal Cognitive Assessment (MoCA) (r = 0.24, 95% CI: -0.32 to 0.68), with high heterogeneity across studies (I2 = 87.37, p < 0.001 for heterogeneity). Publication bias risk was low for the overall ALPS index.

CONCLUSION

These findings highlight the potential of DTI-ALPS as a noninvasive biomarker for PD diagnosis and progression monitoring. Further studies are warranted to explore its applicability in differentiating PD from other neurodegenerative disorders.

Association between movement impairments and glymphatic system dysfunction in spastic diplegic cerebral palsy using DTI-ALPS

BACKGROUND

The role of the glymphatic system in occult cerebral palsy (CP) remains unclear. In this study, glymphatic system function and its association with motor impairment in occult CP patients was investigated using diffusion tensor image analysis along the perivascular space (DTI-ALPS).

METHODS

This retrospective study used DTI to calculate the diffusivity values along the x-, y-, and z-axes in 27 occult CP patients and 27 matched controls. A correlation analysis the ALPS index, derived from perivascular, projection, and association fibres, and with the Gross Motor Function Classification (GMFSC) grade was performed.

RESULTS

We found significant differences in the ALPS index between occult CP patients and healthy controls (HCs). The ALPS index of the lateral hemisphere was lower in occult CP patients than in HCs (left: 1.51 ± 0.20 vs. 1.68 ± 0.24, p = 0.011; right: 1.51 ± 0.20 vs. 1.65 ± 0.24, p = 0.019). Correlation analysis revealed a negative correlation between the ALPS index in the lateral hemisphere and the GMFSC grade (left: r = -0.61, p = 0.004; right: r = -0.48, p = 0.015).

CONCLUSION

Our findings show that occult CP patients have reduced ALPS indices, suggesting glymphatic system dysfunction. Lower ALPS indices were associated with higher motor function grades, indicating a potential link between glymphatic system dysfunction and motor impairment in CP patients.

Clinical and brain volumetric correlates of decreased DTI-ALPS, suggestive of local glymphatic dysfunction, in iRBD

Glymphatic alterations may underlie neurodegeneration in alpha-synucleinopathies. Reduced Diffusion-Tensor Imaging ALong the Perivascular Space (DTI-ALPS), a proxy of perivascular glymphatic activity, has been scarcely studied in isolated REM sleep behaviour disorder (iRBD), a prodromal synucleinopathy stage. Furthermore, its associations with clinical symptoms and brain structural abnormalities remain unexplored. We assessed the DTI-ALPS in sixty-two patients with iRBD and twenty-three healthy controls (HC), exploring its associations with clinical symptoms, cortical thickness and brain volumetric data. iRBD patients exhibited a lower DTI-ALPS and poorer odor identification, semantic fluency and processing speed relative to HC. The DTI-ALPS positively correlated with cognitive performance, olfactory function and amygdalar, hippocampal, brainstem and diencephalic volumes, and negatively with age in iRBD. Perivascular glymphatic activity is compromised in iRBD and is associated with brain atrophy and clinical risk factors of progression to alpha-synucleinopathies, supporting the potential of the DTI-ALPS index as an early imaging neurodegeneration marker.

Parkinson's disease with possible REM sleep behavior disorder correlated with more severe glymphatic system dysfunction

This study aimed to evaluate the glymphatic system activity in Parkinson's disease (PD) with and without rapid eye movement sleep behavior disorder (RBD) using the diffusion tensor image analysis along the perivascular space (DTI-ALPS) methods. Overall, 91 patients with PD and 33 healthy controls were recruited. PD patients were divided into PD-RBD (n = 55) and PD-nRBD (n = 36) groups according to RBD scales. The ALPS-index and enlarged perivascular spaces (EPVS) scores were calculated. PD-RBD group exhibited lower ALPS-index than PD-nRBD and controls after controlling for the effect of age (p = 0.018 and p = 0.001). PD-RBD group showed higher UPDRS part I and HAMD score than those in PD-nRBD group. RBD symptom was independently correlated with ALPS-index in PD (β = -0.259, p = 0.014). In conclusion, PD with possible RBD correlated with more severe glymphatic system dysfunction and non-motor symptoms than those in PD without RBD.

Exploring glymphatic system alterations in iRBD and Parkinson's disease using automated DTI-ALPS analysis

Diffusion tensor image analysis along the perivascular space (DTI-ALPS) is a potential non-invasive marker of glymphatic function that typically relies on manual region of interest (ROI) placement. This study compared ALPS indices in treatment-naïve, de novo diagnosed patients with Parkinson's disease (PD), patients with isolated REM behavior disorder (iRBD), and healthy controls using both manual and automatic approaches to the ROI selection used in ALPS-index calculation. ALPS indices were analyzed bilaterally and correlated with clinical severity (MDS-UPDRS) and nigrostriatal denervation (DAT-SPECT). ANCOVA revealed significant inter-group differences using both manual (p = 0.018) and automatic (p = 0.002) ROI selection methods. The automatic ROI selection approach showed significantly lower ALPS indices in PD compared to controls (p = 0.001) and iRBD (p = 0.009). ALPS indices correlated with symptom severity and nigrostriatal denervation. These findings underscore the reliability of the automatic ROI placement approach for ALPS index calculation and may indicate early glymphatic alterations in Parkinson's disease.

Glymphatic system dysfunction and cerebrospinal fluid retention in gliomas: evidence from perivascular space diffusion and volumetric analysis

BACKGROUND

Gliomas may impair glymphatic function and alter cerebrospinal fluid (CSF) dynamics through structural brain changes, potentially affecting peritumoral brain edema (PTBE) and fluid clearance. This study investigated the impact of gliomas on glymphatic system function and CSF volume via diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) and volumetric magnetic resonance imaging (MRI), which clarified the relationships between tumor characteristics and glymphatic system disruption.

METHODS

In this prospective study, 112 glioma patients and 56 healthy controls underwent MRI to calculate DTI-ALPS indices and perform volumetric analyses of CSF, tumor, and PTBE. Statistical analyses were used to assess the relationships between the DTI-ALPS index, tumor volume, PTBE volume, and clinical characteristics.

RESULTS

Glioma patients had significantly lower DTI-ALPS indices (1.266 ± 0.258 vs. 1.395 ± 0.174, p < 0.001) and greater CSF volumes (174.53 ± 34.89 cm³ vs. 154.25 ± 20.89 cm³, p < 0.001) than controls did. The DTI-ALPS index was inversely correlated with tumor volume (r = -0.353, p < 0.001) and PTBE volume (r = -0.266, p = 0.015). High-grade gliomas were associated with lower DTI-ALPS indices and larger PTBE volumes (all p < 0.001). Tumor grade emerged as an independent predictor of the DTI-ALPS index in multivariate analysis (β = -0.244, p = 0.011).

CONCLUSION

Gliomas are associated with significant glymphatic dysfunction, as evidenced by reduced DTI-ALPS indices and increased CSF and PTBE volumes. The DTI-ALPS index serves as a potential biomarker of glymphatic disruption in glioma patients, offering insights into tumor-related fluid changes and the pathophysiology of brain-tumor interactions.

Reduced DTI-ALPS in H-type hypertension: insights into perivascular space function

Recent studies suggest that glymphatic dysfunction plays a significant role in vascular cognitive impairment (VCI). Both hypertension and hyperhomocysteinemia are independent risk factors for VCI, and their combination is referred to as H-type hypertension (HHT). However, the impact of HHT on glymphatic function remains unclear. This study used the recently popular indirect marker, diffusion tensor imaging along the perivascular space (DTI-ALPS) to assess potential changes in glymphatic function in patients with HHT. We recruited 58 HHT patients and 50 healthy controls without hypertension, collecting clinical, cognitive, biochemical, and diffusion MRI data. Behaviorally, HHT patients scored lower on global cognitive tests compared to controls. DTI-ALPS analysis revealed a bilateral reduction in DTI-ALPS in HHT patients. Correlation analysis showed strong associations between lower DTI-ALPS values, reduced cognitive scores, and elevated homocysteine (Hcy) levels in HHT patients. Mediation analysis further indicated that DTI-ALPS largely mediates the relationship between Hcy levels and cognitive performance. These findings suggest that hypertension and elevated Hcy levels contribute to DTI-ALPS reduction, which may underlie the cognitive decline observed in HHT.

REM sleep and neurodegeneration

Several brainstem, subcortical and cortical areas are involved in the generation of rapid eye movement (REM) sleep. The alteration of these structures as a result of a neurodegenerative process may therefore lead to REM sleep anomalies. REM sleep behaviour disorder is associated with nightmares, dream-enacting behaviours and increased electromyographic activity in REM sleep. Its isolated form is a harbinger of synucleinopathies such as Parkinson's disease or dementia with Lewy bodies, and neuroprotective interventions are advocated. This link might also be present in patients taking antidepressants, with post-traumatic stress disorder, or with a history of repeated traumatic head injury. REM sleep likely contributes to normal memory processes. Its alteration has also been proposed to be part of the neuropathological changes occurring in Alzheimer's disease.

Test-retest reliability of coupling between cerebrospinal fluid flow and global brain activity after normal sleep and sleep deprivation

The glymphatic system (GS) plays a key role in maintaining brain homeostasis by clearing metabolic waste during sleep, with the coupling between global blood-oxygen-level-dependent (gBOLD) and cerebrospinal fluid (CSF) signals serving as a potential marker for glymphatic clearance function. However, the test-retest reliability and spatial heterogeneity of gBOLD-CSF coupling after different sleep conditions remain unclear. In this study, we assessed the test-retest reliability of gBOLD-CSF coupling following either normal sleep or total sleep deprivation (TSD) in 64 healthy adults under controlled laboratory conditions. The reliability was high after normal sleep (ICC = 0.763) but decreased following TSD (ICC = 0.581). Moreover, spatial heterogeneity was evident in participants with normal sleep, with lower-order networks (visual, somatomotor, and attention) showing higher ICC values compared to higher-order networks (default-mode, limbic, and frontoparietal). This spatial variation was less distinct in the TSD group. These results demonstrate the robustness of the gBOLD-CSF coupling method and emphasize the significance of considering sleep history in glymphatic function research.

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.

Diffusion Tensor Imaging Analysis Along the Perivascular Space (DTI-ALPS) in Normal Pressure Hydrocephalus: A Review of Recent Advances

Glymphatic dysfunction is linked to neurodegenerative diseases, and imaging markers of this dysfunction may aid in diagnosis and prognosis. Glymphatic dysfunction has been proposed as a key mechanism in the pathogenesis of normal pressure hydrocephalus (NPH). Advanced magnetic resonance techniques, especially diffusion tensor imaging, have been used to evaluate glymphatic function. Diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) is a noninvasive metric that correlates with glymphatic function and has been recently studied in a variety of neurodegenerative diseases. We aim to summarize studies evaluating the association between DTI-ALPS index values and NPH diagnosis and outcomes. Current studies suggest lower DTI-ALPS index values in NPH patients compared to healthy controls. The DTI-ALPS index correlated with other imaging-based markers of NPH and clinical endpoints. However, limitations of the current literature include small cohort sizes; future studies are needed in larger, heterogeneous cohorts to validate these trends. Thus, the DTI-ALPS index shows promise as a valuable tool for diagnosing NPH, predicting treatment response, and assessing disease progression.

Olfactory Dysfunction as a Clinical Marker of Early Glymphatic Failure in Neurodegenerative Diseases

An abnormal accumulation of misfolded proteins is a common feature shared by most neurodegenerative disorders. Olfactory dysfunction (OD) is common in the elderly population and is present in 90% of patients with Alzheimer's or Parkinson's disease, usually preceding the cognitive and motor symptoms onset by several years. Early Aβ, tau, and α-synuclein protein aggregates deposit in brain structures involved in odor processing (olfactory bulb and tract, piriform cortex, amygdala, entorhinal cortex, and hippocampus) and seem to underly OD. The glymphatic system is a glial-associated fluid transport system that facilitates the movement of brain fluids and removes brain waste during specific sleep stages. Notably, the glymphatic system became less functional in aging and it is impaired in several conditions, including neurodegenerative diseases. As the nasal pathway has been recently described as the main outflow exit of cerebrospinal fluid and solutes, we hypothesized that OD may indeed be a clinical marker of early glymphatic dysfunction through abnormal accumulation of pathological proteins in olfactory structures. This effect may be more pronounced in peri- and postmenopausal women due to the well-documented impact of estrogen loss on the locus coeruleus, which may disrupt multiple mechanisms involved in glymphatic clearance. If this hypothesis is confirmed, olfactory dysfunction might be considered as a clinical proxy of glymphatic failure in neurodegenerative diseases.

Glymphatic system impairment in normal tension glaucoma evaluated by diffusion tensor image analysis along the perivascular space

Disruption of the glymphatic system plays a vital role in pathogenesis of neurodegeneration in normal tension glaucoma (NTG). We evaluated the impairment of glymphatic system of NTG patients by diffusion tensor image analysis along the perivascular space (DTI-ALPS), and explored the correlation between the ALPS index and dysfunction of visual cortices in resting state. DTI-ALPS was applied to 37 normal controls (NCs) and 37 NTG patients. Multidirectional diffusivity maps and fractional anisotropy (FA) maps were reconstructed to calculate ALPS index. The Amplitude of low-frequency fluctuation (ALFF) in visual cortices (V1-V5) were calculated using resting-state fMRI. Clinical data and ALPS indexes were compared between the groups. Lateralization of ALPS indexes and differences in visual field of two eyes were analyzed. Subsequently, regression analyses between ALPS indexes and mean deviation (MD) values of bilateral eyes and ALFF of visual cortices were performed. The bilateral ALPS indexes of NTG patients decreased significantly. In NCs and NTG patients, ALPS indexes in right hemisphere were lower than that in left hemisphere. The right ALPS indexes of NTG patients were positively correlated with the MD values of the left eyes. In NTG patients, decreased ALFF was detected in right V1 and bilateral V2-5, and the left ALPS indexes were positively correlated with ALFF in bilateral V1, V2, V5, and right V3V area. The ALPS index decreased in NTG patients, correlated with visual defects and ALFF, indicating impairment of the glymphatic system and the potential to be a biomarker in the future.

Glymphatic dysfunction exacerbates cognitive decline by triggering cortical degeneration in Parkinson's disease: evidence from diffusion-tensor MRI

The glymphatic system may play a central role in cognitive impairment associated with Parkinson's disease, but its relationship with regional cortical atrophy is not fully explored. To explore associations among glymphatic dysfunction, regional cortical degeneration and cognitive impairment in Parkinson's disease participants, we evaluated 51 participants with documented Parkinson's disease (28 men; age, 61.65 ± 8.27 years) and 30 age- and sex-matched normal controls (11 men; age, 59.2 ± 5.90 years) who underwent 3.0-T MRI of the brain, including high-resolution T1-weighted imaging and diffusion-tensor imaging along the perivascular space as a surrogate for glymphatic flow. Cortical grey matter volume was segmented automatically based on three-dimensional T1-weighted sequences. Cognitive function was assessed by Mini-Mental State Examination. The relationship between glymphatic dysfunction, cognitive decline and regional cortical degeneration was explored. The participants with Parkinson's disease revealed lower diffusion-tensor imaging along the perivascular space (1.45 ± 0.17 versus 1.64 ± 0.17, P < 0.0001) as compared with normal controls, indicating disturbed glymphatic flow. Glymphatic dysfunction was associated with cognitive scores (r = 0.54, P = 0.003). Diffusion-tensor imaging along the perivascular space values were positively associated with the volume of specific cortical regions (all P-values <0.05) including the temporal pole, posterior orbital gyrus, orbital part of the inferior frontal gyrus, frontal operculum, central operculum and anterior cingulate gyrus. Mediation analysis within the Parkinson's disease participants indicated that the relationship between glymphatic dysfunction and cognitive scores was partially mediated by the integrity of orbital part of the inferior frontal gyrus and anterior cingulate gyrus. Glymphatic dysfunction is associated with cognitive decline in Parkinson's disease, whereas the distribution of regional cortical degeneration may constitute the link between glymphatic dysfunction and cognitive impairment.

New perspectives on the glymphatic system and the relationship between glymphatic system and neurodegenerative diseases

Neurodegenerative diseases (ND) are characterized by the accumulation of aggregated proteins. The glymphatic system, through its rapid exchange mechanisms between cerebrospinal fluid (CSF) and interstitial fluid (ISF), facilitates the movement of metabolic substances within the brain, serving functions akin to those of the peripheral lymphatic system. This emerging waste clearance mechanism offers a novel perspective on the removal of pathological substances in ND. This article elucidates recent discoveries regarding the glymphatic system and updates relevant concepts within its model. It discusses the potential roles of the glymphatic system in ND, including Alzheimer's disease (AD), Parkinson's disease (PD), and multiple system atrophy (MSA), and proposes the glymphatic system as a novel therapeutic target for these conditions.

Diffusion Tensor Imaging Analysis Along the Perivascular Space (DTI-ALPS) Demonstrates That Sleep Disorders Exacerbate Glymphatic Circulatory Impairment and Cognitive Impairment in Patients with Alzheimer's Disease

Objective

Sleep disorders are common in Alzheimer's disease (AD) patients and can impair the glymphatic system, leading to cognitive decline. This study aimed to investigate whether AD patients with sleep disorders exhibit worse glymphatic function and more severe cognitive impairment compared to those without sleep disorders and to explore the underlying molecular imaging mechanisms.

Methods

This study included 40 AD patients with sleep disorders (ADSD), 39 cognitively matched AD patients without sleep disorders (ADNSD), and 25 healthy middle-aged and elderly controls (NC). Participants underwent functional magnetic resonance imaging (fMRI), and cognitive and sleep assessments. The ALPS (Along the Perivascular Space) index was calculated, followed by intergroup comparisons, correlation analyses, and mediation analyses. The diagnostic utility of the ALPS index was assessed using a receiver operating characteristic (ROC) curve.

Results

The ALPS index was lower in the ADNSD and ADSD groups compared to the NC group. In the ADSD group, PSQI scores were negatively correlated with MMSE scores. The ALPS index was positively correlated with MMSE scores and negatively with PSQI scores. Mediation analyses indicated that the ALPS index partially mediated the effect of sleep disturbances on cognitive impairment (indirect effect = -0.134; mediation effect = 30.505%). The area under the ROC curve (AUROC) for distinguishing ADSD from ADNSD was 0.86, with a cutoff ALPS index value 1.309.

Conclusion

Sleep disorders worsen glymphatic function and cognitive impairment in AD patients. The ALPS index partially mediates the impact of sleep disorders on cognitive function and shows moderate accuracy in distinguishing between patients with ADSD and ADNSD.

Alterations in the DTI-ALPS index and choroid plexus volume are associated with clinical symptoms in participants with narcolepsy type 1

BACKGROUND

Narcolepsy type 1 (NT1) is a sleep disorder characterized by excessive daytime sleepiness accompanied by cataplexy. Sleep disorders have been shown to affect the glymphatic system. This study aimed to evaluate changes in the diffusion tensor imaging along the perivascular space (DTI-ALPS) index and choroid plexus (CP) volume in NT1 participants, and to further explore their clinical significance.

METHODS

We prospectively enrolled participants diagnosed with NT1 based on cerebrospinal fluid hypocretin-1 concentration and multiple sleep latency tests at our hospital. All participants underwent MRI to allow analysis of the DTI-ALPS index and CP volume. We subsequently performed correlation analyses between the DTI-ALPS index, CP volume, and important clinical parameters, including the Epworth Sleepiness Scale (ESS) score, Narcolepsy Severity Scale (NSS) score, stage rapid eye movement sleep (REM) ratio, stage 1 non-REM (N1) ratio, stage 2 non-REM (N2) ratio, and stage 3 non-REM (N3) ratio, among the NT1 participants. Inter-group and correlation analyses of DTI-ALPS index and CP volume were performed using age, sex, body mass index, and lateral ventricle volume as covariates.

RESULTS

This study enrolled 41 NT1 participants and 42 healthy controls (HC). The DTI-ALPS index of NT1 participants was significantly lower than HC (1.444 ± 0.119 vs.1.661 ± 0.135, P < 0.001), while the CP volume of NT1 participants was significantly larger than those of HC (0.831 ± 0.146 vs. 0.645 ± 0.137, P < 0.001). The DTI-ALPS index was negatively correlated with both the ESS (PFDR-corrected<0.001) and NSS scores (PFDR-corrected = 0.010), but positively correlated with the Stage N3 ratio (PFDR-corrected = 0.033). The CP volume of NT1 participants was positively correlated with ESS (PFDR-corrected = 0.047) and NSS scores (PFDR-corrected = 0.047), but negatively correlated with the stage N3 ratio (PFDR-corrected = 0.047).

CONCLUSION

Our study suggests that the DTI-ALPS index was lower and CP volume was larger in NT1 participants. The DTI-ALPS index and CP volume in the NT1 participants were related to disease severity and sleep structure. These findings may provide new insights into the mechanisms underlying NT1.

Glymphatic system dysfunction and risk of clinical milestones in patients with Parkinson disease

BACKGROUND AND PURPOSE

Glymphatic dysfunction may play a significant role in the development of neurodegenerative diseases. We aimed to evaluate the association between glymphatic dysfunction and the risk of malignant event/clinical milestones in Parkinson disease (PD).

METHODS

This study included 236 patients from August 2014 to December 2020. Diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) index was calculated as an approximate measure of glymphatic function. The primary outcomes were four clinical milestones including recurrent falls, wheelchair dependence, dementia, and placement in residential or nursing home care. The associations of DTI-ALPS with the risk of clinical milestones were examined using multivariate Cox proportional hazards regression models. Then, logistic regression was repeated using clinical variables and DTI-ALPS index individually and in combination of the two to explore the ability to distinguish patients who reached clinical milestones within a 5-year period.

RESULTS

A total of 175 PD patients with baseline DTI-ALPS index and follow-up clinical assessments were included. A lower DTI-ALPS was independently associated with increased risk of recurrent falls, wheelchair dependence, and dementia. Additionally, in 103 patients monitored over 5 years, a logistic regression model combining clinical variables and DTI-ALPS index showed better performance for predicting wheelchair dependence within 5 years than a model using clinical variables or DTI-ALPS index alone.

CONCLUSIONS

Glymphatic dysfunction, as measured by the DTI-ALPS index, was associated with increased risk of clinical milestones in patients with PD. This finding implies that therapy targeting the glymphatic system may serve as a viable strategy for slowing down the progression of PD.

Evaluating the robustness of DTI-ALPS in clinical context: a meta-analytic parallel on Alzheimer's and Parkinson's diseases

In recent years, the glymphatic system has received increasing attention due to its possible implications in biological mechanisms associated with neurodegeneration. In the field of human brain mapping, this led to the development of diffusion tensor image analysis along the perivascular space (DTI-ALPS) index. While this index has been repeatedly used to investigate possible differences between neurodegenerative disorders and healthy controls, a comprehensive evaluation of its stability across multiple measurements and different disorders is still missing. In this study, we perform a Bayesian meta-analysis aiming to assess the consistency of the DTI-ALPS results previously reported for 12 studies on Parkinson's disease and 11 studies on Alzheimer's disease. We also evaluated if the measured value of the DTI-ALPS index can quantitatively inform the diagnostic process, allowing disambiguation between these two disorders. Our results, expressed in terms of Bayes' Factor values, confirmed that the DTI-ALPS index is consistent in measuring the different functioning of the glymphatic system between healthy subjects and patients for both Parkinson's disease (Log10(BF10) = 30) and Alzheimer's disease (Log10(BF10) = 10). Moreover, we showed that the DTI-ALPS can be used to compare these two disorders directly, therefore providing a first proof of concept supporting the reliability of taking into consideration this neuroimaging measurement in the diagnostic process. Our study underscores the potential of the DTI-ALPS index in advancing our understanding of neurodegenerative pathologies and enhancing clinical diagnostics.

A Histopathologic Correlation Study Evaluating Glymphatic Function in Brain Tumors by Multiparametric MRI

PURPOSE

This study aimed to elucidate the impact of brain tumors on cerebral edema and glymphatic drainage by leveraging advanced MRI techniques to explore the relationships among tumor characteristics, glymphatic function, and aquaporin-4 (AQP4) expression levels.

EXPERIMENTAL DESIGN

In a prospective cohort from March 2022 to April 2023, patients with glioblastoma, brain metastases, and aggressive meningiomas, alongside age- and sex-matched healthy controls, underwent 3.0T MRI, including diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) index and multiparametric MRI for quantitative brain mapping. Tumor and peritumor tissues were analyzed for AQP4 expression levels via immunofluorescence. Correlations among MRI parameters, glymphatic function (DTI-ALPS index), and AQP4 expression levels were statistically assessed.

RESULTS

Among 84 patients (mean age: 55 ± 12 years; 38 males) and 59 controls (mean age: 54 ± 8 years; 23 males), patients with brain tumor exhibited significantly reduced glymphatic function (DTI-ALPS index: 2.315 vs. 2.879; P = 0.001) and increased cerebrospinal fluid volume (201.376 cm³ vs. 115.957 cm³; P = 0.001). A negative correlation was observed between tumor volume and the DTI-ALPS index (r: -0.715, P < 0.001), whereas AQP4 expression levels correlated positively with peritumoral brain edema volume (r: 0.989, P < 0.001) and negatively with proton density in peritumoral brain edema areas (ρ: -0.506, P < 0.001).

CONCLUSIONS

Our findings highlight the interplay among tumor-induced compression, glymphatic dysfunction, and altered fluid dynamics, demonstrating the utility of DTI-ALPS and multiparametric MRI in understanding the pathophysiology of tumor-related cerebral edema. These insights provide a radiological foundation for further neuro-oncological investigations into the glymphatic system. See related commentary by Surov and Borggrefe, p. 4813.

Evaluation of Glymphatic System Development in Neonatal Brain via Diffusion Analysis along the Perivascular Space Index

OBJECTIVE

Glymphatic system is a recently discovered macroscopic waste clearance system associated with numerous neurological diseases. However, little is known about glymphatic system development in neonates. We sought to evaluate diffusion along the perivascular space (ALPS) index, a proxy for glymphatic system function, in neonates and investigate its potential associations with maturation, sex, and preterm birth.

METHODS

Diffusion magnetic resonance imaging (MRI) data in 418 neonates, including 92 preterm neonates (57 males) and 326 term neonates (175 males), from the Developing Human Connectome Project were used for evaluating ALPS index. Linear regression modeling was performed to assess group differences in the ALPS index according to preterm birth and sex. Pearson's and partial correlation analysis were performed to assess the association between the ALPS index and gestational age (GA) as well as postmenstrual age (PMA) at MRI. Moderation analysis was performed to assess the moderation effect of preterm birth on the relationship between the ALPS index and PMA.

RESULTS

Compared to term neonates, preterm neonates exhibited lower ALPS indices (p < 0.001). The ALPS index positively correlated with PMA (p = 0.004) and GA (p < 0.001). Preterm birth (p = 0.013) had a significant moderation effect on the relationship between the ALPS index and PMA. Sex had no significant direct effect (p = 0.639) or moderation effect (p = 0.333) on ALPS index.

INTERPRETATION

Glymphatic system development is a dynamic process in neonates, which can be moderated by preterm birth, the ALPS index could serve as a sensitive biomarker for monitoring this process. ANN NEUROL 2024;96:970-980.

Decreased DTI-ALPS index in delirium: a preliminary MRI study

PURPOSE

Delirium is linked to brain abnormalities, yet the role of the glymphatic system is not well understood. This study aims to examine alterations in brain physiology in delirium by using diffusion-tensor imaging (DTI) to assess water diffusion along the perivascular space (ALPS) and to explore its correlation with clinical symptoms.

METHODS

We examined 15 patients with delirium and 15 healthy controls, measuring water diffusion metrics along the x-, y-, and z-axes in both projection and association fibers to determine the DTI-ALPS index. We used a general linear model, adjusted for age and sex, to compare the DTI-ALPS index between groups. We also investigated the relationship between the DTI-ALPS index and clinical symptoms using partial correlations.

RESULTS

Patients with delirium exhibited significantly lower DTI-ALPS indices compared to healthy controls (1.25 ± 0.15 vs. 1.38 ± 0.10, t = 2.903, p = 0.007; 1.27 ± 0.16 vs. 1.39 ± 0.08, 1.22 ± 0.16 vs. 1.37 ± 0.14, t = 2.617, p = 0.014; t = 2.719, p = 0.011; respectively). However, there was no significant correlation between the DTI-ALPS index and clinical symptoms.

CONCLUSION

Our findings indicate a decreased DTI-ALPS index in patients with delirium, suggesting potential alterations in brain physiology that may contribute to the pathophysiology of delirium. This study provides new insights into the mechanisms underlying delirium.

The Cerebrovascular Side of Plasticity: Microvascular Architecture across Health and Neurodegenerative and Vascular Diseases

The delivery of nutrients to the brain is provided by a 600 km network of capillaries and microvessels. Indeed, the brain is highly energy demanding and, among a total amount of 100 billion neurons, each neuron is located just 10-20 μm from a capillary. This vascular network also forms part of the blood-brain barrier (BBB), which maintains the brain's stable environment by regulating chemical balance, immune cell transport, and blocking toxins. Typically, brain microvascular endothelial cells (BMECs) have low turnover, indicating a stable cerebrovascular structure. However, this structure can adapt significantly due to development, aging, injury, or disease. Temporary neural activity changes are managed by the expansion or contraction of arterioles and capillaries. Hypoxia leads to significant remodeling of the cerebrovascular architecture and pathological changes have been documented in aging and in vascular and neurodegenerative conditions. These changes often involve BMEC proliferation and the remodeling of capillary segments, often linked with local neuronal changes and cognitive function. Cerebrovascular plasticity, especially in arterioles, capillaries, and venules, varies over different time scales in development, health, aging, and diseases. Rapid changes in cerebral blood flow (CBF) occur within seconds due to increased neural activity. Prolonged changes in vascular structure, influenced by consistent environmental factors, take weeks. Development and aging bring changes over months to years, with aging-associated plasticity often improved by exercise. Injuries cause rapid damage but can be repaired over weeks to months, while neurodegenerative diseases cause slow, varied changes over months to years. In addition, if animal models may provide useful and dynamic in vivo information about vascular plasticity, humans are more complex to investigate and the hypothesis of glymphatic system together with Magnetic Resonance Imaging (MRI) techniques could provide useful clues in the future.

Research Progress on the Relationship between Parkinson's Disease and REM Sleep Behavior Disorder

An individual's quality of life is greatly affected by Parkinson's disease (PD), a prevalent neurological degenerative condition. Rapid eye movement (REM) sleep behavior disorder (RBD) is a prominent non-motor symptom commonly associated with PD. Previous studies have shown a close relationship between PD and RBD. In addition to being a prodromal symptom of PD, RBD has a major negative impact on the prognosis of PD patients. This intrinsic connection indicates that there is a bidirectional relationship between PD and RBD. This paper provides a comprehensive review of the pathological mechanism related to PD and RBD, including the α-synuclein pathological deposition, abnormal iron metabolism, neuroinflammation, glymphatic system dysfunction and dysbiosis of the gut microbiota. Increasing evidence has shown that RBD patients have the same pathogenic mechanisms that underlie PD, but relatively little research has been done on how RBD contributes to PD progression. Therefore, a more thorough investigation is warranted to characterise how RBD affects the course of PD, in order to prepare for future therapeutic trials.

Diffusion magnetic resonance imaging of cerebrospinal fluid dynamics: Current techniques and future advancements

Cerebrospinal fluid (CSF) plays a critical role in metabolic waste clearance from the brain, requiring its circulation throughout various brain pathways, including the ventricular system, subarachnoid spaces, para-arterial spaces, interstitial spaces, and para-venous spaces. The complexity of CSF circulation has posed a challenge in obtaining noninvasive measurements of CSF dynamics. The assessment of CSF dynamics throughout its various circulatory pathways is possible using diffusion magnetic resonance imaging (MRI) with optimized sensitivity to incoherent water movement across the brain. This review presents an overview of both established and emerging diffusion MRI techniques designed to measure CSF dynamics and their potential clinical applications. The discussion offers insights into the optimization of diffusion MRI acquisition parameters to enhance the sensitivity and specificity of diffusion metrics on underlying CSF dynamics. Lastly, we emphasize the importance of cautious interpretations of diffusion-based imaging, especially when differentiating between tissue- and fluid-related changes or elucidating structural versus functional alterations.

Glymphatic function from diffusion-tensor MRI to predict conversion from mild cognitive impairment to dementia in Parkinson's disease

BACKGROUND

Although brain glymphatic dysfunction is a contributing factor to the cognitive deficits in Parkinson's disease (PD), its role in the longitudinal progression of cognitive dysfunction remains unknown.

OBJECTIVE

To investigate the glymphatic function in PD with mild cognitive impairment (MCI) that progresses to dementia (PDD) and to determine its predictive value in identifying individuals at high risk for developing dementia.

METHODS

We included 64 patients with PD meeting criteria for MCI and categorized them as either progressed to PDD (converters) (n = 29) or did not progress to PDD (nonconverters) (n = 35), depending on whether they developed dementia during follow-up. Meanwhile, 35 age- and gender-matched healthy controls (HC) were included. Bilateral diffusion-tensor imaging analysis along the perivascular space (DTI-ALPS) indices and enlarged perivascular spaces (EPVS) volume fraction in bilateral centrum semiovale, basal ganglia (BG), and midbrain were compared among the three groups. Correlations among the DTI-ALPS index and EPVS, as well as cognitive performance were analyzed. Additionally, we investigated the mediation effect of EPVS on DTI-ALPS and cognitive function.

RESULTS

PDD converters had lower cognitive composites scores in the executive domains than did nonconverters (P < 0.001). Besides, PDD converters had a significantly lower DTI-ALPS index in the left hemisphere (P < 0.001) and a larger volume fraction of BG-PVS (P = 0.03) compared to HC and PDD nonconverters. Lower DTI-ALPS index and increased BG-PVS volume fraction were associated with worse performance in the global cognitive performance and executive function. However, there was no significant mediating effect. Receiver operating characteristic analysis revealed that the DTI-ALPS could effectively identify PDD converters with an area under the curve (AUC) of 0.850.

CONCLUSION

The reduction of glymphatic activity, measured by the DTI-ALPS, could potentially be used as a non-invasive indicator in forecasting high risk of dementia conversion before the onset of dementia in PD patients.

Clinical magnetic resonance imaging evaluation of glymphatic function

The glymphatic system is a system of specialized perivascular spaces in the brain that facilitates removal of toxic waste solutes from the brain. Evaluation of glymphatic system function by means of magnetic resonance imaging (MRI) has thus far been largely focused on rodents because of the limitations of intrathecal delivery of gadolinium-based contrast agents to humans. This review discusses MRI methods that can be employed clinically for glymphatic-related measurements intended for early diagnosis, prevention, and the treatment of various neurological conditions. Although glymphatic system-based MRI research is in its early stages, recent studies have identified promising noninvasive MRI markers associated with glymphatic system alterations in neurological diseases. However, further optimization in data acquisition, validation, and modeling are needed to investigate the glymphatic system within the clinical setting.

Glymphatic function and its influencing factors in different glucose metabolism states

BACKGROUND

Dysfunction of the glymphatic system in the brain in different stages of altered glucose metabolism and its influencing factors are not well characterized.

AIM

To investigate the function of the glymphatic system and its clinical correlates in patients with different glucose metabolism states, the present study employed diffusion tensor imaging along the perivascular space (DTI-ALPS) index.

METHODS

Sample size was calculated using the pwr package in R software. This cross-sectional study enrolled 22 patients with normal glucose metabolism (NGM), 20 patients with prediabetes, and 22 patients with type 2 diabetes mellitus (T2DM). A 3.0T magnetic resonance imaging was used to evaluate the function of the glymphatic system. The mini-mental state examination (MMSE) was used to assess general cognitive function. The DTI-ALPS index of bilateral basal ganglia and the mean DTI-ALPS index was calculated. Further, the correlation between DTI-ALPS and clinical features was assessed.

RESULTS

The left-side, right-side, and mean DTI-ALPS index in the T2DM group were significantly lower than that in the NGM group. The right-side DTI-ALPS and mean DTI-ALPS index in the T2DM group were significantly lower than those in the prediabetes group. DTI-ALPS index lateralization was not observed. The MMSE score in the T2DM group was significantly lower than that in the NGM and prediabetes group. After controlling for sex, the left-side DTI-ALPS and mean DTI-ALPS index in the prediabetes group were positively correlated with 2-hour postprandial blood glucose level; the left-side DTI-ALPS index was negatively correlated with total cholesterol and low-density lipoprotein level. The right-side DTI-ALPS and mean DTI-ALPS index were negatively correlated with the glycosylated hemoglobin level and waist-to-hip ratio in the prediabetes group. The left-side, right-side, and mean DTI-ALPS index in the T2DM group were positively correlated with height. The left-side and mean DTI-ALPS index in the T2DM group were negatively correlated with high-density lipoprotein levels.

CONCLUSION

Cerebral glymphatic system dysfunction may mainly occur in the T2DM stage. Various clinical variables were found to affect the DTI-ALPS index in different glucose metabolism states. This study enhances our understanding of the pathophysiology of diabetic brain damage and provides some potential biological evidence for its early diagnosis.

Association of Extent of Transverse Sinus Stenosis With Cerebral Glymphatic Clearance in Patients With Idiopathic Intracranial Hypertension

BACKGROUND AND OBJECTIVES

Idiopathic intracranial hypertension (IIH) is a neurologic disorder characterized by symptoms of elevated intracranial pressure in the absence of a clear cause. There is a developing theory that IIH may, in part, be related to abnormal cerebral glymphatic clearance. In addition, transverse sinus stenosis (TSS) is a common finding in IIH of unclear pathophysiologic significance. Similarly, whether or not TSS is associated with glymphatic outflow in IIH is unknown. The aim of this investigation was to explore the possible association between glymphatic outflow and extent of TSS in patients with IIH.

METHODS

The study cohort consisted of patients with IIH and healthy controls who were retrospectively identified from our tertiary care institution located in upstate New York from 2016 to 2023. Patients with IIH were included if they had brain MRIs completed with sufficient sequences for analysis. Brain MRIs were computationally analyzed using diffusion tensor imaging analysis along the perivascular space technique to quantify the glymphatic function in patients with IIH. Glymphatic clearance, the primary outcome, was then correlated with the degree of TSS on MR venography using 2 different scoring systems, the 'Farb score' and 'Carvalho score.'

RESULTS

Overall, 81 patients with IIH (70 [86%] female, mean age 29.8 years [SD: 8.2 years], mean BMI 41 [SD: 8.4]) and 10 normal controls were identified with sufficient imaging. Based on the Carvalho TSS score, IIH patients without TSS had significantly lower glymphatic clearance than healthy controls (mean ALPS index: 1.196 [SD: 0.05] vs 1.238 [SD: 0.04], respectively; p = 0.018). Furthermore, IIH patients with TSS had significantly lower glymphatic outflow than healthy controls (1.129 [SD: 0.07] vs 1.238 [SD: 0.04], respectively; p < 0.0001) and IIH patients without TSS (1.129 [SD: 0.07] vs 1.196 [SD: 0.05], respectively; p < 0.0001). In addition, there was a significant association between increasing extent of TSS and declining glymphatic clearance (p < 0.0001, R = 0.62). Finally, IIH patients with severe TSS had significantly lower glymphatic flow than IIH patients with mild stenosis (1.121 [SD: 0.07] vs 1.178 [SD: 0.05], respectively; p < 0.0001). These findings were similarly recapitulated using the Farb TSS scoring system.

DISCUSSION

These preliminary findings suggest that the extent of TSS is associated with the degree of glymphatic clearance in IIH, providing novel insights into IIH pathophysiology. Further research is required to clarify the possible causal relationship between TSS and impaired glymphatic clearance in IIH.

Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS): Revisiting the Meaning and Significance of the Method

More than 5 years have passed since the Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS) method was proposed with the intention of evaluating the glymphatic system. This method is handy due to its noninvasiveness, provision of a simple index in a straightforward formula, and the possibility of retrospective analysis. Therefore, the ALPS method was adopted to evaluate the glymphatic system for many disorders in many studies. The purpose of this review is to look back and discuss the ALPS method at this moment.The ALPS-index was found to be an indicator of a number of conditions related to the glymphatic system. Thus, although this was expected in the original report, the results of the ALPS method are often interpreted as uniquely corresponding to the function of the glymphatic system. However, a number of subsequent studies have pointed out the problems on the data interpretation. As they rightly point out, a higher ALPS-index indicates predominant Brownian motion of water molecules in the radial direction at the lateral ventricular body level, no more and no less. Fortunately, the term "ALPS-index" has become common and is now known as a common term by many researchers. Therefore, the ALPS-index should simply be expressed as high or low, and whether it reflects a glymphatic system is better to be discussed carefully. In other words, when a decreased ALPS-index is observed, it should be expressed as "decreased ALPS-index" and not directly as "glymphatic dysfunction". Recently, various methods have been proposed to evaluate the glymphatic system. It has become clear that these methods also do not seem to reflect the entirety of the extremely complex glymphatic system. This means that it would be desirable to use various methods in combination to evaluate the glymphatic system in a comprehensive manner.

Imaging Interstitial Fluid With MRI: A Narrative Review on the Associations of Altered Interstitial Fluid With Vascular and Neurodegenerative Abnormalities

Interstitial fluid (ISF) refers to the fluid between the parenchymal cells and along the perivascular spaces (PVS). ISF plays a crucial role in delivering nutrients and clearing waste products from the brain. This narrative review focuses on the use of MRI techniques to measure various ISF characteristics in humans. The complementary value of contrast-enhanced and noncontrast-enhanced techniques is highlighted. While contrast-enhanced MRI methods allow measurement of ISF transport and flow, they lack quantitative assessment of ISF properties. Noninvasive MRI techniques, including multi-b-value diffusion imaging, free-water-imaging, T2-decay imaging, and DTI along the PVS, offer promising alternatives to derive ISF measures, such as ISF volume and diffusivity. The emerging role of these MRI techniques in investigating ISF alterations in neurodegenerative diseases (eg, Alzheimer's disease and Parkinson's disease) and cerebrovascular diseases (eg, cerebral small vessel disease and stroke) is discussed. This review also emphasizes current challenges of ISF imaging, such as the microscopic scale at which ISF has to be measured, and discusses potential focus points for future research to overcome these challenges, for example, the use of high-resolution imaging techniques. Noninvasive MRI methods for measuring ISF characteristics hold significant potential and may have a high clinical impact in understanding the pathophysiology of neurodegenerative and cerebrovascular disorders, as well as in evaluating the efficacy of ISF-targeted therapies in clinical trials. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2.

Multimodal neuroimaging exploration of the mechanisms of sleep quality deterioration after SARS-CoV-2 Omicron infection

BACKGROUND

To evaluate the neurological alterations induced by Omicron infection, to compare brain changes in chronic insomnia with those in exacerbated chronic insomnia in Omicron patients, and to examine individuals without insomnia alongside those with new-onset insomnia.

METHODS

In this study, a total of 135 participants were recruited between January 11 and May 4, 2023, including 26 patients with chronic insomnia without exacerbation, 24 patients with chronic insomnia with exacerbation, 40 patients with no sleep disorder, and 30 patients with new-onset insomnia after infection with Omicron (a total of 120 participants with different sleep statuses after infection), as well as 15 healthy controls who were never infected with Omicron. Neuropsychiatric data, clinical symptoms, and multimodal magnetic resonance imaging data were collected. The gray matter thickness and T1, T2, proton density, and perivascular space values were analyzed. Associations between changes in multimodal magnetic resonance imaging findings and neuropsychiatric data were evaluated with correlation analyses.

RESULTS

Compared with healthy controls, gray matter thickness changes were similar in the patients who have and do not have a history of chronic insomnia groups after infection, including an increase in cortical thickness near the parietal lobe and a reduction in cortical thickness in the frontal, occipital, and medial brain regions. Analyses showed a reduced gray matter thickness in patients with chronic insomnia compared with those with an aggravation of chronic insomnia post-Omicron infection, and a reduction was found in the right medial orbitofrontal region (mean [SD], 2.38 [0.17] vs. 2.67 [0.29] mm; P < 0.001). In the subgroups of Omicron patients experiencing sleep deterioration, patients with a history of chronic insomnia whose insomnia symptoms worsened after infection displayed heightened medial orbitofrontal cortical thickness and increased proton density values in various brain regions. Conversely, patients with good sleep quality who experienced a new onset of insomnia after infection exhibited reduced cortical thickness in pericalcarine regions and decreased proton density values. In new-onset insomnia patients post-Omicron infection, the thickness in the right pericalcarine was negatively correlated with the Self-rating Anxiety Scale (r =  - 0.538, P = 0.002, PFDR = 0.004) and Self-rating Depression Scale (r =  - 0.406, P = 0.026, PFDR = 0.026) scores.

CONCLUSIONS

These findings help us understand the pathophysiological mechanisms involved when Omicron invades the nervous system and induces various forms of insomnia after infection. In the future, we will continue to pay attention to the dynamic changes in the brain related to insomnia caused by Omicron infection.

Regional Burden of Enlarged Perivascular Spaces and Cognition and Neuropsychiatric Symptoms in Drug-Naive Patients With Parkinson Disease

BACKGROUND AND OBJECTIVES

Although the potential role of enlarged perivascular spaces (EPVSs) in Parkinson disease (PD) is increasingly recognized, whether EPVSs located in different anatomical regions exert differential effects on clinical manifestation remains uncertain. We investigated the regional EPVS burden and its association with cognition and neuropsychiatric symptoms (NPSs) in newly diagnosed PD population.

METHODS

In this retrospective, cross-sectional study, EPVS in the temporal lobe (T-EPVS), centrum semiovale (CS-EPVS), and basal ganglia (BG-EPVS) were visually rated in drug-naive patients with PD who underwent magnetic resonance imaging, dopamine transporter (DAT) scans, neuropsychological assessments, and Neuropsychiatric Inventory Questionnaire at baseline. Cognitive performance, NPS burden, vascular risk factors, small vessel disease (SVD) imaging markers, and DAT availability were compared across groups dichotomized by their regional EPVS burden (cutoff for high-degree vs low-degree: >10 for T-EPVS/BG-EPVS and >20 for CS-EPVS).

RESULTS

A total of 480 patients with PD (123 without cognitive impairment, 291 with mild cognitive impairment, and 66 with dementia) were included. The proportion of high-degree T-EPVS (p for trend <0.001) and BG-EPVS (p for trend = 0.001) exhibited an increasing trend across the cognitive spectrum, corresponding to worsening cognition. Compared with the low-degree group, the high-degree BG-EPVS group showed higher SVD burden (moderate-to-severe white matter hyperintensity [14.8% vs 40.5%, p < 0.001], lacune [10.3% vs 30.7%, p < 0.001], and cerebral microbleeds [8.1% vs 22.2%, p < 0.001]), greater atrophy in cortical gray matter (40.73% ± 1.09% vs 39.96% ± 1.20% of intracranial volume, p < 0.001), and lower cognitive performance (in language [-0.22 ± 1.18 vs -0.53 ± 1.29, p = 0.013], and visual memory domains [-0.24 ± 0.97 vs -0.61 ± 0.96, p = 0.009]). The high-degree T-EPVS group presented with greater NPS burden in decreased motivation (0.61 ± 1.78 vs 1.35 ± 2.36, p = 0.007), affective dysregulation (0.88 ± 2.13 vs 2.36 ± 3.53, p < 0.001), and impulse dyscontrol (0.43 ± 1.67 vs 1.74 ± 4.29, p < 0.001), compared with the low-degree T-EPVS group. Meanwhile, the burden of CS-EPVS did not reveal any differences in cognition or NPS.

DISCUSSION

BG-EPVS and T-EPVS seem to exert differential effects on cognition and NPS in patients with PD. Investigating the EPVS profile in distinct anatomical regions may be useful in disentangling the heterogeneity within PD.

Dominance of Tau Burden in Cortical Over Subcortical Regions Mediates Glymphatic Activity and Clinical Severity in PSP

BACKGROUND

Progressive supranuclear palsy (PSP) is a tauopathy that involves subcortical regions but also extends to cortical areas. The clinical impact of different tau protein sites and their influence on glymphatic dysfunction have not been investigated.

PATIENTS AND METHODS

Participants (n = 55; 65.6 ± 7.1 years; 29 women) with PSP (n = 32) and age-matched normal controls (NCs; n = 23) underwent 18 F-Florzolotau tau PET, MRI, PSP Rating Scale (PSPRS), and Mini-Mental State Examination. Cerebellar gray matter (GM) and parametric estimation of reference signal intensity were used as references for tau burden measured by SUV ratios. Glymphatic activity was measured by diffusion tensor image analysis along the perivascular space (DTI-ALPS).

RESULTS

Parametric estimation of reference signal intensity is a better reference than cerebellar GM to distinguish tau burden between PSP and NCs. PSP patients showed higher cortical and subcortical tau SUV ratios than NCs ( P < 0.001 and <0.001). Cortical and subcortical tau deposition correlated with PSPRS, UPDRS, and Mini-Mental State Examination scores (all P 's < 0.05). Cortical tau deposition was further associated with the DTI-ALPS index and frontal-temporal-parietal GM atrophy. The DTI-ALPS indexes showed a significantly negative correlation with the PSPRS total scores ( P < 0.01). Finally, parietal and occipital lobe tau depositions showed mediating effects between the DTI-ALPS index and PSPRS score.

CONCLUSIONS

Cortical tau deposition is associated with glymphatic dysfunction and plays a role in mediating glymphatic dysfunction and clinical severity. Our results provide a possible explanation for the worsening of clinical severity in patients with PSP.

Noninvasive Magnetic Resonance Imaging Measures of Glymphatic System Activity

The comprehension of the glymphatic system, a postulated mechanism responsible for the removal of interstitial solutes within the central nervous system (CNS), has witnessed substantial progress recently. While direct measurement techniques involving fluorescence and contrast agent tracers have demonstrated success in animal studies, their application in humans is invasive and presents challenges. Hence, exploring alternative noninvasive approaches that enable glymphatic research in humans is imperative. This review primarily focuses on several noninvasive magnetic resonance imaging (MRI) techniques, encompassing perivascular space (PVS) imaging, diffusion tensor image analysis along the PVS, arterial spin labeling, chemical exchange saturation transfer, and intravoxel incoherent motion. These methodologies provide valuable insights into the dynamics of interstitial fluid, water permeability across the blood-brain barrier, and cerebrospinal fluid flow within the cerebral parenchyma. Furthermore, the review elucidates the underlying concept and clinical applications of these noninvasive MRI techniques, highlighting their strengths and limitations. It addresses concerns about the relationship between glymphatic system activity and pathological alterations, emphasizing the necessity for further studies to establish correlations between noninvasive MRI measurements and pathological findings. Additionally, the challenges associated with conducting multisite studies, such as variability in MRI systems and acquisition parameters, are addressed, with a suggestion for the use of harmonization methods, such as the combined association test (COMBAT), to enhance standardization and statistical power. Current research gaps and future directions in noninvasive MRI techniques for assessing the glymphatic system are discussed, emphasizing the need for larger sample sizes, harmonization studies, and combined approaches. In conclusion, this review provides invaluable insights into the application of noninvasive MRI methods for monitoring glymphatic system activity in the CNS. It highlights their potential in advancing our understanding of the glymphatic system, facilitating clinical applications, and paving the way for future research endeavors in this field. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 5.

Glymphatic system dysfunction in middle-aged and elderly chronic insomnia patients with cognitive impairment evidenced by diffusion tensor imaging along the perivascular space (DTI-ALPS)

BACKGROUND

Chronic insomnia impairs the glymphatic system and may lead to cognitive impairment and dementia in elderly population. The diffusion tensor image analysis along the perivascular space (DTI-ALPS) has been proposed as a non-invasive method to measure the activity of human brain glymphatic. We aim to explore whether glymphatic function is impaired in middle-aged and elderly chronic insomnia individuals and to identify the relationships between glymphatic dysfunction and cognitive impairment.

METHODS

A total of 33 chronic insomnia patients (57.36 ± 5.44 years, 30 females) and 20 age- and sex-matched healthy controls (57.95 ± 5.78 years, 16 females) were prospectively enrolled between May 2022 and January 2023. All participants completed MRI screening, cognition and sleep assessments, and DTI-ALPS index analysis.

RESULTS

Our findings revealed that the DTI-ALPS index was significantly difference among the chronic insomnia patients with impaired cognition group (1.32 ± 0.14), with normal cognition group (1.46 ± 0.09), and healthy controls (1.61 ± 0.16) (p = 0.0012, p < 0.0001, p = 0.0008, respectively). Mini-Mental State Examination (MMSE) scores of chronic insomnia patients with cognitive impairment were positively correlated with the DTI-ALPS index (Partial correlation analyses after correction for age, sex, education level and duration of chronic insomnia: r = 0.78, p = 0.002). DTI-ALPS had moderate accuracy in distinguishing chronic insomnia patients with cognitive impairment from those with normal cognition.

DATA CONCLUSION

The glymphatic system dysfunction is involved in chronic insomnia among middle-aged and elderly individuals, and it has been found to be correlated with cognitive decline.

The relationship between inflammation, impaired glymphatic system, and neurodegenerative disorders: A vicious cycle

The term "glymphatic" emerged roughly a decade ago, marking a pivotal point in neuroscience research. The glymphatic system, a glial-dependent perivascular network distributed throughout the brain, has since become a focal point of investigation. There is increasing evidence suggesting that impairment of the glymphatic system appears to be a common feature of neurodegenerative disorders, and this impairment exacerbates as disease progression. Nevertheless, the common factors contributing to glymphatic system dysfunction across most neurodegenerative disorders remain unclear. Inflammation, however, is suspected to play a pivotal role. Dysfunction of the glymphatic system can lead to a significant accumulation of protein and waste products, which can trigger inflammation. The interaction between the glymphatic system and inflammation appears to be cyclical and potentially synergistic. Yet, current research is limited, and there is a lack of comprehensive models explaining this association. In this perspective review, we propose a novel model suggesting that inflammation, impaired glymphatic function, and neurodegenerative disorders interconnected in a vicious cycle. By presenting experimental evidence from the existing literature, we aim to demonstrate that: (1) inflammation aggravates glymphatic system dysfunction, (2) the impaired glymphatic system exacerbated neurodegenerative disorders progression, (3) neurodegenerative disorders progression promotes inflammation. Finally, the implication of proposed model is discussed.

Diffusion-Weighted Imaging Reveals Impaired Glymphatic Clearance in Idiopathic Intracranial Hypertension

BACKGROUND AND PURPOSE

The pathophysiology underlying idiopathic intracranial hypertension (IIH) remains incompletely understood. While one theory postulates impaired cerebral glymphatic clearance in IIH, there is a paucity of methods to quantify glymphatic activity in human brains. The purpose of this study was to use advanced diffusion-weighed imaging to evaluate the glymphatic clearance of IIH patients and how it may relate to clinical severity.

MATERIALS AND METHODS

DWI was used to separately evaluate the diffusivity along the cerebral perivascular spaces and lateral association and projection fibers, with the degree of diffusivity used as a surrogate for glymphatic function (diffusion tensor image analysis along the perivascular space. Patients with IIH were compared with normal controls. Glymphatic clearance was correlated with several clinical metrics, including lumbar puncture opening pressure and Frisen papilledema grade (low grade: 0-2; high grade: 3-5).

RESULTS

In total, 99 patients with IIH were identified and compared with 6 healthy controls. Overall, patients with IIH had significantly lower glymphatic clearance based on DWI-derived diffusivity compared with controls (P = .005). Additionally, in patients with IIH, there was a significant association between declining glymphatic clearance and increasing Frisen papilledema grade (P = .046) but no correlation between opening pressure and glymphatic clearance (P = .27). Furthermore, healthy controls had significantly higher glymphatic clearance compared with patients with IIH and low-grade papilledema (P = .015) and high-grade papilledema (P = .002). Lastly, patients with IIH and high-grade papilledema had lower glymphatic clearance compared with patients with IIH and low-grade papilledema (P = .005).

CONCLUSIONS

Patients with IIH possess impaired glymphatic clearance, which is directly related to the extent of clinical severity. The DWI-derived parameters can be used for clinical diagnosis or to assess response to treatment.

Glymphatic system dysfunction in recovered patients with mild COVID-19: A DTI-ALPS study

Central nervous sequelae are often reported in recovered patients with COVID-19. It is not clear whether recovered COVID-19 patients have glymphatic impairment and clinical correlation. In this study, we demonstrated that mild COVID-19 patients experienced asymmetric bilateral glymphatic function decline after four months of recovery, and the decrease in glymphatic function was more obvious in older recovered patients. Our results further showed that recovered patients with right-sided glymphatic dysfunction experienced a greater proportion of cognitive decline (MoCA score <26) than patients with left-sided glymphatic dysfunction. With COVID-19 infection over 90% of the general population currently, future studies of cognitive disorders in the older population should consider the impact of COVID-19 infection.

Imaging of brain barrier inflammation and brain fluid drainage in human neurological diseases

The intricate relationship between the central nervous system (CNS) and the immune system plays a crucial role in the pathogenesis of various neurological diseases. Understanding the interactions among the immunopathological processes at the brain borders is essential for advancing our knowledge of disease mechanisms and developing novel diagnostic and therapeutic approaches. In this review, we explore the emerging role of neuroimaging in providing valuable insights into brain barrier inflammation and brain fluid drainage in human neurological diseases. Neuroimaging techniques have enabled us not only to visualize and assess brain structures, but also to study the dynamics of the CNS in health and disease in vivo. By analyzing imaging findings, we can gain a deeper understanding of the immunopathology observed at the brain-immune interface barriers, which serve as critical gatekeepers that regulate immune cell trafficking, cytokine release, and clearance of waste products from the brain. This review explores the integration of neuroimaging data with immunopathological findings, providing valuable insights into brain barrier integrity and immune responses in neurological diseases. Such integration may lead to the development of novel diagnostic markers and targeted therapeutic approaches that can benefit patients with neurological disorders.

Deregulation of the Glymphatic System in Alzheimer's Disease: Genetic and Non-Genetic Factors

Alzheimer's disease (AD) is the most prevalent form of dementia and is characterized by progressive degeneration of brain function. AD gradually affects the parts of the brain that control thoughts, language, behavior and mental function, severely impacting a person's ability to carry out daily activities and ultimately leading to death. The accumulation of extracellular amyloid-β peptide (Aβ) and the aggregation of intracellular hyperphosphorylated tau are the two key pathological hallmarks of AD. AD is a complex condition that involves both non-genetic risk factors (35%) and genetic risk factors (58-79%). The glymphatic system plays an essential role in clearing metabolic waste, transporting tissue fluid, and participating in the immune response. Both non-genetic and genetic risk factors affect the glymphatic system to varying degrees. The main purpose of this review is to summarize the underlying mechanisms involved in the deregulation of the glymphatic system during the progression of AD, especially concerning the diverse contributions of non-genetic and genetic risk factors. In the future, new targets and interventions that modulate these interrelated mechanisms will be beneficial for the prevention and treatment of AD.

Correlation of glymphatic system abnormalities with Parkinson's disease progression: a clinical study based on non-invasive fMRI

BACKGROUND

The glymphatic system is reportedly involved in Parkinson's disease (PD). Based on previous studies, we aimed to confirm the correlation between the glymphatic system and PD progression by combining two imaging parameters, diffusion tensor image analysis along the perivascular space (DTI-ALPS), and enlarged perivascular spaces (EPVS).

METHODS

Fifty-one PD patients and fifty healthy control (HC) were included. Based on the Hoehn-Yahr scale, the PD group was divided into early-stage and medium-to late-stage. All PD patients were scored using the Unified PD Rating Scale (UPDRS). We assessed the DTI-ALPS indices in the bilateral hemispheres and EPVS numbers in bilateral centrum semiovale (CSO), basal ganglia (BG), and midbrain.

RESULTS

The DTI-ALPS indices were significantly lower bilaterally in PD patients than in the HC group, and EPVS numbers in any of the bilateral CSO, BG, and midbrain were significantly higher, especially for the medium- to late-stage group and the BG region. In PD patients, the DTI-ALPS index was significantly negatively correlated with age, while the BG-EPVS numbers were significantly positively correlated with age. Furthermore, the DTI-ALPS index was negatively correlated with UPDRS II and III scores, while the BG-EPVS numbers were positively correlated with UPDRS II and III scores. Similarly, the correlation was more pronounced in the medium- to late-stage group.

CONCLUSION

The DTI-ALPS index and EPVS numbers (especially in the BG region) are closely related to age and PD progression and can serve as non-invasive assessments for glymphatic dysfunction and its interventions in clinical studies.

Impaired Glymphatic Flow on Diffusion Tensor MRI as a Marker of Neurodegeneration in Alzheimer's Disease: Correlation with Gray Matter Volume Loss and Cognitive Decline Independent of Cerebral Amyloid Deposition

Background

Impaired glymphatic flow on the Alzheimer's disease (AD) spectrum may be evaluated using diffusion tensor image analysis along the perivascular space (DTI-ALPS).

Objective

We aimed to validate impaired glymphatic flow and explore its association with gray matter volume, cognitive status, and cerebral amyloid deposition on the AD spectrum.

Methods

80 participants (mean age, 76.9±8.5 years; 57 women) with AD (n = 65) and cognitively normal (CN) (n = 15) who underwent 3T brain MRI including DTI and/or amyloid PET were included. After adjusting for age, sex, apolipoprotein E status, and burden of white matter hyperintensities, the ALPS-index was compared according to the AD spectrum. The association between the ALPS-index and gray matter volume, cognitive status, and quantitative amyloid from PET was assessed.

Results

The ALPS-index in the AD was significantly lower (mean, 1.476; 95% CI, 1.395-1.556) than in the CN (1.784;1.615-1.952; p = 0.026). Volumes of the entorhinal cortex, hippocampus, temporal pole, and primary motor cortex showed significant associations with the ALPS-index (all, p < 0.05). There was a positive correlation between the ALPS-index and MMSE score (partial r = 0.435; p < 0.001), but there was no significant correlation between the ALPS-index and amyloid SUVRs (all, p > 0.05).

Conclusions

Decreased glymphatic flow measured by DTI-ALPS in AD may serve as a marker of neurodegeneration correlating with structural atrophy and cognitive decline.

Decreased DTI-ALPS and choroid plexus enlargement in fibromyalgia: a preliminary multimodal MRI study

PURPOSE

The glymphatic system is a fluid exchange pathway that clears waste products that is crucial for the maintenance of brain homeostasis. However, the exact role it plays in the emergence of fibromyalgia (FM) is still not fully understood. Here, we explored the changes in non-invasive MRI proxy probably related to the glymphatic function in FM patients, and explored brain-behavior relationships.

METHODS

A total of 40 participants, consisting of 20 individuals with FM and 20 healthy controls (HCs), were included in the study. The participants underwent structural T1-weighted MRI, diffusion tensor imaging (DTI), and clinical assessment. The data was obtained from an open access dataset. The study compared non-invasive MRI indices, including choroid plexus (CP) volume and DTI analysis along the perivascular space (ALPS), between the FM and HC groups. Furthermore, correlation analysis was conducted to determine the correlation between clinical parameters and both CP volume and DTI-ALPS index.

RESULTS

Patients with FM had significantly higher CP volume and a lower DTI-ALPS index than HCs adjusting for age and intracranial volume. Higher CP volume was associated with lower DTI-ALPS index, and longer disease duration.

CONCLUSION

Our findings demonstrate aberrant glymphatic function in FM, and that dysfunction in the brain glymphatic system may play a role in the neural mechanisms underlying FM.

REM Behavior Disorder: Implications for PD Therapeutics

PURPOSE

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia that occurs during REM sleep, characterized by REM sleep without atonia (RSWA) and dream enactment behavior (DEB). RBD is associated with several diseases and medications but most notably is a prodromal feature of synucleinopathies, including Parkinson's disease (PD). This article reviews RBD, its treatments, and implications for PD therapeutics.

RECENT FINDINGS

Recent research recognizes RBD as a prodromal marker of PD, resulting in expansion of basic science and clinical investigations of RBD. Current basic science research investigates the pathophysiology of RBD and explores animal models to allow therapeutic development. Clinical research has focused on natural history observation, as well as potential RBD treatments and their impact on sleep and phenoconversion to neurodegenerative disease. RBD serves as a fresh access point to develop both neuroprotective and symptomatic therapies in PD. These types of investigations are novel and will benefit from the more established basic science infrastructure to develop new interventions.