Glymphatic system dysfunction in obstructive sleep apnea evidenced by DTI-ALPS

Glymphatic pathway dysfunction in severe obstructive sleep apnea: A meta-analysis

BACKGROUND

Obstructive sleep apnea (OSA), a sleep disorder, is associated with cognitive decline and is potentially linked to glymphatic system dysfunction. This meta-analysis investigates glymphatic function in severe OSA (apnea-hypopnea index ≥30) using the Diffusion Tensor Imaging Analysis along the Perivascular Space (DTI-ALPS) index.

METHODS

This study followed PRISMA guidelines for systematic reviews and meta-analyses. A comprehensive search of PubMed, Web of Science, Scopus, and Embase was conducted from inception to January 20, 2024. Studies investigating the ALPS index in OSA using DTI were included. Analyses included a random-effects meta-analysis, sensitivity analysis, meta-regression, publication bias evaluation (funnel plot, Egger's test, and Begg's test), and risk of bias assessment.

RESULTS

Systematic review identified four studies (137 patients with severe OSA and 170 healthy controls (HCs)). Pooled analysis revealed a significant reduction in the DTI-ALPS index in severe OSA patients compared to HCs (standardized mean difference: -0.95, 95 % CI: -1.46 to -0.44, p < 0.001), indicating impaired glymphatic function. Heterogeneity was moderate to high (I2 = 76.07 %), but sensitivity analyses confirmed robustness. Meta-regression analyses identified the sources of heterogeneity as the apnea-hypopnea index (β = -0.039, p = 0.009) and the Epworth Sleepiness Scale (β = -0.150, p = 0.032), with no effects observed for age or male ratio. Qualitative (funnel plot) and quantitative publication bias assessments (Egger's and Begg's tests) showed no significant bias, and risk of bias evaluations using the Newcastle-Ottawa Scale indicated high methodological quality across studies.

CONCLUSIONS

These findings suggest that severe OSA disrupts glymphatic activity. The DTI-ALPS index emerges as a promising tool for assessing glymphatic dysfunction in OSA.

Persistent blood-brain barrier dysregulation in patients with obstructive sleep apnea following long-term continuous positive airway pressure treatment

INTRODUCTION

Blood-brain barrier (BBB) dysfunction has been hypothesized to be a triggering factor in neurodegeneration. This study compared moderate-severe obstructive sleep apnea (OSA) patients with controls to evaluate the effects of this sleep disorder on BBB integrity, as well as explore the impact of continuous positive airway pressure (CPAP) treatment on BBB.

METHODS

This study included moderate-severe OSA patients, OSA patients being treated with CPAP for at least 12 months (OSA-CPAP), and a control group with no neurological or psychiatric diseases. Participants underwent neurological examination, cognitive assessment (to exclude cognitive impairment) and lumbar puncture for cerebrospinal-fluid (CSF) biomarkers analysis [β-amyloid42 (Aβ42), total-tau, phosphorylated tau, ratio between CSF and serum albumin levels (Qalb)].

RESULTS

38 moderate-severe OSA patients (mean age 65.50 ± 9.16), 12 patients with OSA treated with CPAP (OSA-CPAP, mean age 65.42 ± 6.45) and 25 controls (mean age 65.64 ± 8.10) were included. Moderate-severe OSA patients showed higher Qalb than controls (p = 0.026); also OSA-CPAP patients presented higher Qalb than controls (p = 0.044). Qalb did not differ comparing moderate-severe OSA and OSA-CPAP groups. OSA patients showed lower CSF Aβ42 levels compared to both controls (p < 0.001) and the OSA-CPAP patients (p < 0.001).

CONCLUSIONS

These findings confirmed CSF Aβ42 alteration and documented BBB dysfunction, as indicated by the higher Qalb, in OSA patients. The metabolic and oxidative damage caused by hypoxia could account for these phenomenona; however, the BBB impairment seems to be not reversible, as OSA-CPAP patients presented the BBB alteration although normal CSF Aβ42 levels. Further studies exploring BBB function and its clinical implication for neurodegeneration in OSA are needed.

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.

Sleep disturbances are related to glymphatic dysfunction in blepharospasm

Research has shown a close relationship between sleep and glymphatic function, with impaired glymphatic function potentially contributing to sleep problems in a bidirectional way. However, its role in sleep disturbances associated with dystonia remains unknown. This cross-sectional study aimed to investigate whether glymphatic function is impaired in dystonia and to explore its relationship with sleep disturbances. We conducted structural magnetic resonance imaging and diffusion tensor imaging (DTI) on two large cohorts: patients with blepharospasm (BSP, n = 45) and cervical dystonia (CD, n = 43), alongside age- and sex-matched healthy controls (HCs). Anxiety, depression, and sleep quality were evaluated using the Hamilton Anxiety Scale (HAMA), Hamilton Depression Scale (HAMD), and Pittsburgh Sleep Quality Index (PSQI), respectively. Analysis along the perivascular space (DTI-ALPS) index and choroid plexus volume (CPV) was used to assess glymphatic function in these participants. Patients with BSP and CD had higher HAMA, HAMD, and PSQI scores than those of HCs. Patients with BSP exhibited a lower DTI-ALPS index and larger CPV than those of HCs, while no significant differences were found between CD and HCs. In BSP and CD, PSQI scores positively correlated with HAMA and HAMD scores and negatively with the DTI-ALPS index in BSP. Multivariate analysis identified the DTI-ALPS index as a dependent predictive factor of the PSQI in patients with BSP. Our findings suggest that glymphatic function varies across types of focal dystonia, with glymphatic dysfunction potentially playing an important role in the pathogenesis of sleep disturbances in BSP.

Systematic bibliometric and visualized analysis of research hotspots and trends in obstructive sleep apnea neuroimaging

BACKGROUND

Obstructive sleep apnea (OSA) patients exhibit neurological symptoms, driving research in sleep medicine and clinical neurology. Neurologists and radiologists explore detection methods to identify unique neural features associated with OSA in the atypical nervous system. Neuroimaging research in OSA encompasses studying the structural, functional connectivity (FC), and neurometabolic aspects of the brain. Limited resources and OSA's heterogeneity pose challenges to effective neuroimaging research. This study aims to conduct a bibliometric analysis of OSA neuroimaging research to identify key trends and emerging themes.

METHODS

This research utilizes various techniques, including functional MRI, structural MRI, diffusion tensor imaging, magnetic resonance spectroscopy, and electroencephalography, among others. Publications from 1993 to 2023 were retrieved from Web of Science on neuroimaging. Analysis tools included Bibliometric.com, CiteSpace, VOSviewer, and R4.3.2.

RESULTS

A total of 714 papers were published in 47 countries, with 651 articles, 55 reviews, and 8 meeting abstracts. The USA led in publications, with the University of California System contributing most, primarily in "Sleep" journal. The study identified 2916 authors, with Macey PM having the highest publication count. Recent years highlighted burst keywords such as network, classification, sleep staging, FC, and brain activity. Analysis of keyword clusters revealed "electroencephalography" with the longest temporal duration.

CONCLUSIONS

Neuroimaging in OSA research has gained increased attention. Incorporating behavioral sleep medicine insights could enhance understanding of OSA's impact on brain function and behavior. This study aims to assist researchers in identifying potential collaborators, institutions, and key themes, providing a comprehensive perspective on OSA neuroimaging research and related sleep disorders.

Effects of sleep on the glymphatic functioning and multimodal human brain network affecting memory in older adults

Understanding how sleep affects the glymphatic system and human brain networks is crucial for elucidating the neurophysiological mechanism underpinning aging-related memory declines. We analyzed a multimodal dataset collected through magnetic resonance imaging (MRI) and polysomnographic recording from 72 older adults. A proxy of the glymphatic functioning was obtained from the Diffusion Tensor Image Analysis along the Perivascular Space (DTI-ALPS) index. Structural and functional brain networks were constructed based on MRI data, and coupling between the two networks (SC-FC coupling) was also calculated. Correlation analyses revealed that DTI-ALPS was negatively correlated with sleep quality measures [e.g., Pittsburgh Sleep Quality Index (PSQI) and apnea-hypopnea index]. Regarding human brain networks, DTI-ALPS was associated with the strength of both functional connectivity (FC) and structural connectivity (SC) involving regions such as the middle temporal gyrus and parahippocampal gyrus, as well as with the SC-FC coupling of rich-club connections. Furthermore, we found that DTI-ALPS positively mediated the association between sleep quality and rich-club SC-FC coupling. The rich-club SC-FC coupling further mediated the association between DTI-ALPS and memory function in good sleepers but not in poor sleepers. The results suggest a disrupted glymphatic-brain relationship in poor sleepers, which underlies memory decline. Our findings add important evidence that sleep quality affects cognitive health through the underlying neural relationships and the interplay between the glymphatic system and multimodal brain networks.

Decoupling of global signal and cerebrospinal fluid inflow is associated with cognitive decline in patients with obstructive sleep apnoea

OBJECTIVES

The role of cortical glymphatic dysfunction in the cognitive impairment of the obstructive sleep apnea (OSA) requires further study. To compare the coupling between the resting-state blood-oxygen-level-dependent (BOLD) signals and cerebrospinal fluid (CSF) signals (BOLD-CSF coupling), a proxy for the cortical glymphatic function, across patients with differing severities of OSA and relate them with disease characteristics and treatment.

METHODS

A total of 153 participants (89 OSA patients and 64 matched controls) were prospectively included. OSA patients were classified into three groups (mild, moderate, and severe OSA) according to the apnea-hypopnea index (AHI). All participants underwent neuropsychological assessment and BOLD functional magnetic resonance imaging. BOLD-CSF coupling was assessed at global and regional levels and correlated with the cognitive impairment. Alterations in BOLD-CSF coupling and cognitive performance after treatment were assessed in OSA patients.

RESULT

Severe OSA patients exhibited weaker global and anterior BOLD-CSF coupling than mild OSA patients, moderate OSA patients, and healthy controls (HCs). Furthermore, the weaker global and anterior BOLD-CSF coupling was associated with poor cognitive performance in all OSA patients. Notably, cognitive performance and cortical glymphatic function improved significantly in patients with OSA after treatment.

CONCLUSION

Our findings demonstrated cortical glymphatic dysfunction in severe OSA patients, especially in the anterior region of the brain. Cortical glymphatic dysfunction may underlie the cognitive impairment in OSA patients, both of which would improve in OSA patients after treatment.

Diffusion Tensor Imaging in Neurofluids

In this review article, we describe the development and application of diffusion-based MR imaging methods for studying glymphatic physiology. Fluid exchange and solute transport are the 2 key components of the glymphatic system. Here we describe the use of low b-value imaging, free water fraction imaging, and diffusion time sensitization to leverage cerebral spinal fluid, as well as interstitial fluid motion in the parenchyma. We also describe multiple b-value diffusion imaging to better delineate diffusion components within the brain. Finally, we touch upon newer approaches that use advanced models of the diffusion signal, including high b-value imaging.

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.

Perivascular and parenchymal brain fluid diffusivity in patients with a recent small subcortical infarct

PURPOSE

Fluid exchanges between perivascular spaces (PVS) and interstitium may contribute to the pathophysiology of small vessel disease (SVD). We aimed to analyze water diffusivity measures and their relationship with PVS and other SVD imaging markers.

METHODS

We enrolled 50 consecutive patients with a recent small subcortical infarct. We collected clinical variables, including vascular risk factors and sleep quality scales. All patients underwent a 3-Tesla MRI with standard structural sequences and multishell-diffusion images to obtain extracellular free water content (FW) and water diffusivity along the perivascular space (ALPS) index. We obtained volumetric measurements of white matter hyperintensities (WMH) and PVS, and the number of lacunes and microbleeds. To analyze the association between PVS, ALPS index, FW, and SVD imaging features, we utilized linear regression models including age, sex, history of hypertension and diabetes, Pittsburgh Sleep Quality Index, WMH, and brain volume.

RESULTS

All patients (mean age 70 years, 36% women) had usable data. FW and PVS were strongly associated in all models (0.008 < Beta < 0.054; P < 0.045). Higher FW was related to the other SVD features in univariable models and remained significant for WMH (1.175 < Beta < 1.262; P < 0.001) and brain volume (Beta < 0.0001; P < 0.002) in multivariable models. ALPS index was not associated with FW, PVS, or any other SVD markers.

CONCLUSIONS

The increased extracellular water in SVD suggests that impaired brain fluid exchanges, PVS dilation, and other SVD features are linked. Further investigation is needed to determine the specificity of the ALPS index to PVS diffusion.

The Past and Future of Sleep Medicine

The past of sleep medicine is rich with seminal discoveries, from the recognition of clinical syndromes to measurement of sleep itself to classic and novel therapeutics. Advances in neurobiology have mapped a number of sleep circuits, described the central and peripheral circadian system, and identified the cause of narcolepsy with cataplexy. Sleep apnea endotypes and phenotypes now have established clinical relevance, though treatment implications are a work in progress. Artificial intelligence will continue to change sleep medicine in a number of domains from aiding scoring to health outcome predictions. There is a large gap between the known science and clinical translational.

Hourly Variations in Glymphatic Function Based on MRI Scan Times in Cognitively Normal Individuals

RATIONALE AND OBJECTIVES

This study evaluated glymphatic function changes according to MRI scan time over a 24-hour cycle, using diffusion tensor image analysis along the perivascular space (DTI-ALPS) to assess interstitial fluid dynamics.

MATERIAL AND METHODS

This single-center retrospective cohort study included cognitively normal participants between January and August 2023. Participants were grouped by MRI scan time: dawn, early morning, daytime, and evening/night. Glymphatic function was assessed via the ALPS index calculated from DTI. ALPS index values were compared among groups using one-way ANOVA with post hoc pairwise independent t-tests. Multiple linear regression analysis adjusted for age, sex, and mini-mental state examination scores was used to compare daytime ALPS index with other groups. Paired t-tests assessed ALPS index changes in participants with follow-up MRIs.

RESULTS

Among 539 participants (age: 70 ± 10 years, 41.4% male), the dawn group had the highest mean ALPS index, followed by early morning, evening/night, and daytime groups (P =0.024). Daytime ALPS index was significantly lower than dawn (P =0.0036) and early morning (P =0.018). Multiple linear regression confirmed lower daytime ALPS index, with the dawn group showing the largest difference (0.067, 95% CI: 0.025-0.108; P =0.002). No significant difference was observed in ALPS index for follow-up scans from dawn or evening/night to daytime (P =0.353).

CONCLUSION

Glymphatic function varies diurnally, with lower values during daytime. These findings emphasize the importance of circadian timing in evaluating glymphatic function using DTI-ALPS. Further studies are needed to explore intra-individual glymphatic variations.

Clearance rate of contrast extravasation after endovascular therapy is associated with functional outcome and mediated by cerebral edema

The brain's function of clearance and transport is closely related to the prognosis of acute ischemic stroke (AIS). In this study, we proposed a novel method, clearance rate of contrast extravasation (CROCE), to measure brain clearance and transport function in AIS patients undergoing endovascular therapy (EVT), and examined its association with cerebral edema and functional outcome. We conducted a pooled analysis of AIS patients of anterior circulation large vessel occlusion who underwent EVT in two academic hospitals. Patients who experienced contrast extravasation but not intracerebral hemorrhage following EVT were included. CROCE was defined as the mass of contrast agent cleared per hour on non-contrast CT (NCCT). Among the 215 patients finally included, we found that high CROCE was significantly associated with 90-day favorable functional outcome, and the association retained after adjustment for potential confounders. Different correlation analysis demonstrated a significant correlation between CROCE, cerebral edema, and functional outcome. Further mediation analysis revealed that cerebral edema mediated the effect of CROCE on functional outcome. These results revealed that CROCE may be a promising indicator of brain clearance function for patients who received EVT and had contrast extravasation.

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.

Sleep quality and risk of obstructive sleep apnea among breast cancer survivors with and without lymphedema

PURPOSE

Breast cancer survivors (BCSs) tend to have sleep disturbances such as obstructive sleep apnea (OSA). However, limited evidence exists on the role of breast cancer-related lymphedema (BCRL) in sleep disturbances and OSA. Therefore, this study aimed to investigate the quality of sleep (QoS) and OSA risk among women with and without BCRL.

METHODS

The quality of life (QoL) was evaluated using the SF-12 and EORTC-QLQ C-30 questionnaires, while their sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) questionnaire. The STOP-bang questionnaire (SBQ) was utilized to quantify OSA risk. Sleepiness was assessed using the Epworth Sleepiness Scale (ESS). Also, neck and waist circumference and the excessive volume in the affected limb were measured using a tape measure. The statistical analyses were performed using the SPSS 21.0 software.

RESULTS

Seventy-one women with BCRL and 84 BCS without lymphedema were included. The comparison of PSQI, SBQ, ESS, SF-12, and EORTC QLQ-C30 questionnaires exhibited no significant difference between these two groups. The overnight snoring and average neck circumference were significantly higher in the BCRL group than in the control. The BCRL stage significantly correlated with neck circumference and SBQ total score. Additionally, the mean volume difference indicated a significant correlation with the ESS total score and both physical and mental summary components of the SF-12 questionnaire.

CONCLUSION

The prevalence of sleep disturbances among BCSs with and without BCRL is high. Women with advanced stages of BCRL might be at high risk for OSA. Therefore clinical evaluation of BMI, neck circumference, and, snoring overnight should be emphasized among this population.

Preliminary investigations into human neurofluid transport using multiple novel non-contrast MRI methods

We discuss two potential non-invasive MRI methods to study phenomena related to subarachnoid cerebrospinal fluid (CSF) motion and perivascular fluid transport, and their association with sleep and aging. We apply diffusion-based intravoxel incoherent motion (IVIM) imaging to evaluate pseudodiffusion coefficient, D*, or CSF movement across large spaces like the subarachnoid space (SAS). We also performed perfusion-based multi-echo, Hadamard encoded arterial spin labeling (ASL) to evaluate whole brain cortical cerebral blood flow (CBF) and trans-endothelial exchange (Tex) of water from the vasculature into the perivascular space and parenchyma. Both methods were used in young adults (N = 9, 6 F, 23 ± 3 years old) in the setting of sleep and sleep deprivation. To study aging, 10 older adults (6 F, 67 ± 3 years old) were imaged after a night of normal sleep and compared with the young adults. D* in SAS was significantly (p < 0.05) reduced with sleep deprivation (0.016 ± 0.001 mm2/s) compared to normal sleep (0.018 ± 0.001 mm2/s) and marginally reduced with aging (0.017 ± 0.001 mm2/s, p = 0.029). Cortical CBF and Tex were unchanged with sleep deprivation but significantly lower in older adults (37 ± 3 ml/100 g/min, 578 ± 61 ms) than in young adults (42 ± 2 ml/100 g/min, 696 ± 62 ms). IVIM was sensitive to sleep physiology and aging, and multi-echo, multi-delay ASL was sensitive to aging.

Perivascular space diffusivity and brain microstructural measures are associated with circadian time and sleep quality

The glymphatic system is centred around brain cerebrospinal fluid flow and is enhanced during sleep, and the synaptic homeostasis hypothesis proposes that sleep acts on brain microstructure by selective synaptic downscaling. While so far primarily studied in animals, we here examine in humans if brain diffusivity and microstructure is related to time of day, sleep quality and cognitive performance. We use diffusion weighted images from 916 young healthy individuals, aged between 22 and 37 years, collected as part of the Human Connectome Project to assess diffusion tensor image analysis along the perivascular space index, white matter fractional anisotropy, intra-neurite volume fraction and extra-neurite mean diffusivity. Next, we examine if these measures are associated with circadian time of acquisition, the Pittsburgh Sleep Quality Index (high scores correspond to low sleep quality) and age-adjusted cognitive function total composite score. Consistent with expectations, we find that diffusion tensor image analysis along the perivascular space index and orbitofrontal grey matter extra-neurite mean diffusivity are negatively and white matter fractional anisotropy positively correlated with circadian time. Further, we find that grey matter intra-neurite volume fraction correlates positively with Pittsburgh Sleep Quality Index, and that this correlation is driven by sleep duration. Finally, we find positive correlations between grey matter intra-neurite volume fraction and cognitive function total composite score, as well as negative interaction effects between cognitive function total composite score and Pittsburgh Sleep Quality Index on grey matter intra-neurite volume fraction. Our findings propose that perivascular flow is under circadian control and that sleep downregulates the intra-neurite volume in healthy adults with positive impact on cognitive function.

Choroid plexus enlargement in patients with end-stage renal disease: implications for glymphatic system dysfunction

Objectives

The choroid plexus plays a role in eliminating detrimental metabolites from the brain as an integral component of the glymphatic system. This study aimed to investigate alterations in choroid plexus volume in patients with end-stage renal disease (ESRD) compared with healthy controls.

Methods

We enrolled 40 patients with ESRD and 42 healthy controls. They underwent brain magnetic resonance imaging (MRI), specifically using three dimensional T1-weighted imaging. We analyzed choroid plexus volumes and compared them between patients with ESRD and healthy controls. The diffusion tensor image analysis along the perivascular space (DTI-ALPS) index was calculated. We compared the DTI-ALPS index between the ESRD patients and healthy controls. Additionally, we evaluated the association between choroid plexus volume and neuropsychological tests results in patients with ESRD.

Results

There were significant differences in choroid plexus volumes between patients with ESRD and healthy controls. The choroid plexus volumes in patients with ESRD were higher than those in healthy controls (1.392 vs. 1.138%, p < 0.001). The DTI-ALPS index in patients with ESRD was lower than that in healthy controls (1.470 ± 0.239 vs. 1.641 ± 0.266, p = 0.005). There were no differences in choroid plexus volumes between patients with ESRD, regardless of the presence of cognitive impairment. However, among the neuropsychological tests, the scores for word-list recognition in verbal memory were negatively correlated with the choroid plexus volume (r = -0.428, p = 0.006).

Conclusion

We demonstrated a significant enlargement of the choroid plexus volume in patients with ESRD compared to healthy controls. This finding suggests that patients with ESRD have glymphatic system dysfunction, which may be related to cognitive impairment.

Abnormal temporal variability of thalamo-cortical circuit in patients with moderate-to-severe obstructive sleep apnea

This study investigated the abnormal dynamic functional connectivity (dFC) variability of the thalamo-cortical circuit in patients with obstructive sleep apnea (OSA) and explored the relationship between these changes and the clinical characteristics of patients with OSA. A total of 91 newly diagnosed patients with moderate-to-severe OSA and 84 education-matched healthy controls (HCs) were included. All participants underwent neuropsychological testing and a functional magnetic resonance imaging scan. We explored the thalamo-cortical dFC changes by dividing the thalamus into 16 subregions and combining them using a sliding-window approach. Correlation analysis assessed the relationship between dFC variability and clinical features, and the support vector machine method was used for classification. The OSA group exhibited increased dFC variability between the thalamic subregions and extensive cortical areas, compared with the HCs group. Decreased dFC variability was observed in some frontal-occipital-temporal cortical regions. These dFC changes positively correlated with daytime sleepiness, disease severity, and cognitive scores. Altered dFC variability contributed to the discrimination between patients with OSA and HCs, with a classification accuracy of 77.8%. Our findings show thalamo-cortical overactivation and disconnection in patients with OSA, disrupting information flow within the brain networks. These results enhance understanding of the temporal variability of thalamo-cortical circuits in patients with OSA.

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.

Choroid plexus enlargement in patients with obstructive sleep apnea

OBJECTIVES

The function of choroid plexus is to produce cerebrospinal fluid, which is critical for the glymphatic system function. In this study, we aimed to analyze the differences in choroid plexus volume between patients with obstructive sleep apnea (OSA) and healthy controls, with the goal of discovering the glymphatic system dysfunction in patients with OSA.

METHODS

We prospectively enrolled 40 patients with OSA confirmed by polysomnography and 38 age- and sex-matched healthy controls. All participants underwent three-dimensional T1-weighted brain imaging, which was suitable for volumetric analysis. We compared choroid plexus volumes between patients with OSA and healthy controls, and analyzed the association between choroid plexus volume and polysomnographic findings in patients with OSA.

RESULTS

Choroid plexus volumes were significantly larger in patients with OSA than in healthy controls (2.311 % vs. 2.096 %, p = 0.005). However, no significant association was detected between choroid plexus volume and polysomnographic findings.

CONCLUSION

This study demonstrated enlargement of the choroid plexus in patients with OSA compared with healthy controls. This finding could be related with glymphatic system dysfunction in patients with OSA.

The Relationships of Specific Cognitive Control Abilities with Objective and Subjective Sleep Parameters in Mild Cognitive Impairment: Revealing the Association between Cognitive Planning and Sleep Duration

This study aimed to examine the associations between specific sleep parameters and specific aspects of cognitive functioning in individuals diagnosed with mild cognitive impairment (MCI), compared with healthy controls (HCs) by using cognitive, subjective, and objective sleep measures. A total of 179 participants were enrolled, all aged ≥ 65 years (mean age = 70.23; SD = 4.74) and with a minimum of six years of education (mean = 12.35; SD = 3.22). The sample included 46 HCs (36 females), 75 individuals with amnestic MCI (aMCI) (51 females), and 58 individuals with non-amnestic MCI (naMCI) (39 females). Inhibition, cognitive flexibility as a combined application of inhibitory control and set shifting or task/rule switching, and planning were examined. The following D-KEFS subtests were administered for their evaluation: Verbal Fluency Test, Color-Word Interference Test, and Tower Test. Self-reported sleep questionnaires (Athens Insomnia Scale, Stop-Bang questionnaire, and Pittsburg Sleep Quality Index) were used for subjective sleep assessments. Actigraphy was used for objective sleep measurements. Mixed-measures ANOVA, MANOVA, and one-way ANOVA, as well as the Scheffe post hoc test, were applied to the data. The results showed that the three groups exhibited statistically significant differences in the Tower Test (total achievement score, total number of administered problems, and total rule violations). As regards objective sleep measurements, the total sleep time (TST) was measured using actigraphy, and indicated that there are significant differences, with the HC group having a significantly higher mean TST compared to the naMCI group. The relationships evaluated in the TST Tower Test were found to be statistically significant. The findings are discussed in the context of potential parameters that can support the connection between sleep duration, measured as TST, and cognitive planning, as measured using the Tower Test.

Longitudinal assessment of glymphatic changes following mild traumatic brain injury: Insights from perivascular space burden and DTI-ALPS imaging

Introduction

Traumatic brain injury (TBI) even in the mild form may result in long-lasting post-concussion symptoms. TBI is also a known risk to late-life neurodegeneration. Recent studies suggest that dysfunction in the glymphatic system, responsible for clearing protein waste from the brain, may play a pivotal role in the development of dementia following TBI. Given the diverse nature of TBI, longitudinal investigations are essential to comprehending the dynamic changes in the glymphatic system and its implications for recovery.

Methods

In this prospective study, we evaluated two promising glymphatic imaging markers, namely the enlarged perivascular space (ePVS) burden and Diffusion Tensor Imaging-based ALPS index, in 44 patients with mTBI at two early post-injury time points: approximately 14 days (14Day) and 6-12 months (6-12Mon) post-injury, while also examining their associations with post-concussion symptoms. Additionally, 37 controls, comprising both orthopedic patients and healthy individuals, were included for comparative analysis.

Results

Our key findings include: (1) White matter ePVS burden (WM-ePVS) and ALPS index exhibit significant correlations with age. (2) Elevated WM-ePVS burden in acute mTBI (14Day) is significantly linked to a higher number of post-concussion symptoms, particularly memory problems. (3) The increase in the ALPS index from acute (14Day) to the chronic (6-12Mon) phases in mTBI patients correlates with improvement in sleep measures. Furthermore, incorporating WM-ePVS burden and the ALPS index from acute phase enhances the prediction of chronic memory problems beyond socio-demographic and basic clinical information.

Conclusion

ePVS burden and ALPS index offers distinct values in assessing glymphatic structure and activity. Early evaluation of glymphatic function could be crucial for understanding TBI recovery and developing targeted interventions to improve patient outcomes.

Sex differences in the association of sleep spindle density and cognitive performance among community-dwelling middle-aged and older adults with obstructive sleep apnea

Recent studies have found associations between obstructive sleep apnea and cognitive decline. The underlying mechanisms are still unclear. Here, we investigate the associations between changes in micro-architecture, specifically sleep spindles, and cognitive function in community-dwelling middle-aged and older adults, some with obstructive sleep apnea, with a focus on sex differences. A total of 125 voluntary participants (mean age 66.0 ± 6.4 years, 64 females) from a larger cohort (participants of the Brain in Motion Studies I and II) underwent 1 night of in-home polysomnography and a neuropsychological battery (sleep and cognitive testing were conducted within 2 weeks of each other). A semi-automatic computerized algorithm was used to score polysomnography data and detect spindle characteristics in non-rapid eye movement Stages 2 and 3 in both frontal and central electrodes. Based on their apnea-hypopnea index, participants were divided into those with no obstructive sleep apnea (apnea-hypopnea index < 5 per hr, n = 21), mild obstructive sleep apnea (5 ≥ apnea-hypopnea index < 15, n = 47), moderate obstructive sleep apnea (15 ≥ apnea-hypopnea index < 30, n = 34) and severe obstructive sleep apnea (apnea-hypopnea index ≥ 30, n = 23). There were no significant differences in spindle characteristics between the four obstructive sleep apnea severity groups. Spindle density and percentage of fast spindles were positively associated with some verbal fluency measures on the cognitive testing. Sex might be linked with these associations. Biological sex could play a role in the associations between spindle characteristics and some verbal fluency measures. Obstructive sleep apnea severity was not found to be a contributing factor in this non-clinical community-dwelling cohort.

Resting-state fMRI network efficiency as a mediator in the relationship between the glymphatic system and cognitive function in obstructive sleep apnea hypopnea syndrome: Insights from a DTI-ALPS investigation

INTRODUCTION

Obstructive sleep apnea hypopnea syndrome (OSAHS) is associated with cognitive impairment and physiological complications, necessitating further understanding of its mechanisms. This study investigates the relationship between glymphatic system function, brain network efficiency, and cognitive impairment in OSAHS patients using diffusion tensor image analysis along the perivascular space (DTI-ALPS) and resting-state fMRI.

MATERIALS AND METHODS

This study included 31 OSAHS patients and 34 age- and gender-matched healthy controls (HC). All participants underwent GE 3.0T magnetic resonance imaging (MRI) with diffusion tensor image (DTI) and resting-state fMRI scans. The DTI-ALPS index and brain functional networks were assessed. Differences between groups and correlations with clinical characteristics were analyzed. Additionally, the mediating role of brain network efficiency was explored. Finally, receiver operating characteristics (ROC) analysis assessed diagnostic performance.

RESULTS

OSAHS patients had significantly lower ALPS-index (1.268 vs. 1.431, p < 0.0001) and moderate negative correlation with Apnea Hypopnea Index (AHI) (r = -0.389, p = 0.031), as well as moderate positive correlation with Montreal Cognitive Assessment (MoCA) (r = 0.525, p = 0.002). Moreover, global efficiency (Eg) of the brain network was positively correlated with the ALPS-index and MoCA scores in OSAHS patients (r = 0.405, p = 0.024; r = 0.56, p = 0.001, respectively). Furthermore, mediation analysis showed that global efficiency partially mediated the impact of glymphatic system dysfunction on cognitive impairment in OSAHS patients (indirect effect = 4.58, mediation effect = 26.9 %). The AUROC for identifying OSAHS and HC was 0.80 (95 % CI 0.69 to 0.91) using an ALPS-index cut-off of 1.35.

CONCLUSIONS

OSAHS patients exhibit decreased ALPS-index, indicating impaired glymphatic system function. Dysfunction of the glymphatic system can affect cognitive function in OSAHS by disrupting brain functional network, suggesting a potential underlying pathological mechanism. Additionally, preliminary findings suggest that the ALPS-index may offer promise as a potential indicator for OSAHS.

Longitudinal Assessment of Glymphatic Changes Following Mild Traumatic Brain Injury: Insights from PVS burden and DTI-ALPS Imaging

Traumatic brain injury (TBI) even in the mild form may result in long-lasting post-concussion symptoms. TBI is also a known risk to late-life neurodegeneration. Recent studies suggest that dysfunction in the glymphatic system, responsible for clearing protein waste from the brain, may play a pivotal role in the development of dementia following TBI. Given the diverse nature of TBI, longitudinal investigations are essential to comprehending the dynamic changes in the glymphatic system and its implications for recovery. In this prospective study, we evaluated two promising glymphatic imaging markers, namely the enlarged perivascular space (ePVS) burden and Diffusion Tensor Imaging-based ALPS index, in 44 patients with mTBI at two early post-injury time points: approximately 14 days (14Day) and 6-12 months (6-12Mon) post-injury, while also examining their associations with post-concussion symptoms. Additionally, 37 controls, comprising both orthopedic patients and healthy individuals, were included for comparative analysis. Our key findings include: 1) White matter ePVS burden (WM-ePVS) and ALPS index exhibit significant correlations with age. 2) Elevated WM-ePVS burden in acute mTBI (14Day) is significantly linked to a higher number of post-concussion symptoms, particularly memory problems. 3) The increase in the ALPS index from acute (14Day) to the chronic (6-12Mon) phases in mTBI patients correlates with improvement in sleep measures. Furthermore, incorporating WM-ePVS burden and the ALPS index from acute phase enhances the prediction of chronic memory problems beyond socio-demographic and basic clinical information, highlighting their distinct roles in assessing glymphatic structure and activity. Early evaluation of glymphatic function could be crucial for understanding TBI recovery and developing targeted interventions to improve patient outcomes.

Association of MRI Indexes of the Perivascular Space Network and Cognitive Impairment in Patients with Obstructive Sleep Apnea

Background The role of perivascular space (PVS) dysfunction in obstructive sleep apnea (OSA) requires further study. Purpose To compare MRI indexes of PVS across patients with differing severities of OSA and relate them with disease characteristics and treatment. Materials and Methods This single-center prospective study included healthy controls (HCs) and patients with complaints of snoring who underwent MRI and cognitive evaluation between June 2021 and December 2022. Participants with complaints of snoring were classified into four groups (snoring, mild OSA, moderate OSA, and severe OSA). PVS networks were assessed at MRI using PVS volume fraction, extracellular free water (FW), and diffusion tensor imaging analysis along the PVS (DTI-ALPS). One-way analysis of variance and Pearson correlation were used for analysis. Alterations in PVS indexes and cognitive performance after treatment were assessed in 15 participants with moderate OSA. Results A total of 105 participants (mean age, 33.4 years ± 8.9 [SD]; 80 males) and 50 HCs (mean age, 37.0 years ± 8.6; 33 males) were included. Higher mean PVS volume fraction was observed in participants with severe OSA (n = 23) than in patients with mild OSA (n = 36) (0.11 vs 0.10; P = .03). Participants with severe OSA exhibited higher mean FW index (0.11) than both HCs (0.10; P < .001) and patients with mild OSA (0.10; P = .003). All patient groups had lower DTI-ALPS than HCs (range, 1.5-1.9 vs 2.1; all P < .001). DTI-ALPS correlated with cognitive performance on the Stroop Color and Word Test (r range, -0.23 to -0.24; P value range, .003-.005). After treatment, PVS indexes changed (P value range, <.001 to .01) and cognitive performance improved (P value range, <.001 to .03). Conclusion Differences in PVS indexes were observed among participants with differing severities of OSA and HCs. Indexes correlated with measures of cognitive function, and changes in indexes and improvement in cognitive performance were observed after treatment in participants with moderate OSA. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Port in this issue.

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.

Evaluation of glymphatic system activity by diffusion tensor image analysis along the perivascular space in presbycusis

PURPOSE

Previous studies have suggested that presbycusis (age-related hearing loss) is accompanied with cognitive decline and dementia. However, the neural mechanism underlying the cognitive decline in presbycusis remains unclear. This study aimed to evaluate the glymphatic system function in presbycusis patients compared to healthy controls using diffusion tensor imaging (DTI) with the perivascular space (DTI-ALPS) method.

METHODS

DTI scans were obtained from 30 presbycusis patients with cognitive decline (PCD), 30 presbycusis patients with no cognitive decline (PNCD) and 40 age-, gender-, and education-matched healthy controls (HCs). The DTI-ALPS index was calculated for each group. We evaluated the differences in the DTI-ALPS index among PCD, PNCD and HCs. In addition, we conducted a correlation analysis between the DTI-ALPS index and cognitive performance.

RESULTS

There were significant differences of the DTI-ALPS index among three groups. Post-hoc analysis suggested that the DTI-ALPS index in PCD was significantly lower patients in relative to PNCD and HCs (1.49147 vs. 1.57441 vs. 1.62020, p < 0.001). After correcting for age, gender, and education, the DTI-ALPS index is positively correlated with the MoCA scores (rho = 0.426, p = 0.026).

CONCLUSION

Presbycusis patients with cognitive impairment exhibited decreased glymphatic activity than those without cognitive impairment and HCs. The DTI-ALPS index may provide useful disease progression or treatment biomarkers for patients with presbycusis as an indicator of modulation of glymphatic activity.

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 glymphatic system and multiple sclerosis: An evolving connection

Multiple sclerosis (MS) is a complex autoimmune disorder that affects the central nervous system, resulting in demyelination and an array of neurological manifestations. Recently, there has been significant scientific interest in the glymphatic system, which operates as a waste-clearance system for the brain. This article reviews the existing literature, and explores potential links between the glymphatic system and MS, shedding light on its evolving significance in the context of MS pathogenesis. The authors consider the pathophysiological implications of glymphatic dysfunction in MS, the impact of disrupted sleep on glymphatic function, and the bidirectional relationship between MS and sleep disturbances. By offering an understanding of the intricate interplay between the glymphatic system and MS, this review provides valuable insights which may lead to improved diagnostic techniques and more effective therapeutic interventions.

The relationship between amyloid pathology, cerebral small vessel disease, glymphatic dysfunction, and cognition: a study based on Alzheimer's disease continuum participants

BACKGROUND

Glymphatic dysfunction is a crucial pathway for dementia. Alzheimer's disease (AD) pathologies co-existing with cerebral small vessel disease (CSVD) is the most common pathogenesis for dementia. We hypothesize that AD pathologies and CSVD could be associated with glymphatic dysfunction, contributing to cognitive impairment.

METHOD

Participants completed with amyloid PET, diffusion tensor imaging (DTI), and T2 fluid-attenuated inversion-recovery (FLAIR) sequences were included from the Alzheimer's Disease Neuroimaging Initiative (ADNI). White matter hyperintensities (WMH), the most common CSVD marker, was evaluated from T2FLAIR images and represented the burden of CSVD. Amyloid PET was used to assess Aβ aggregation in the brain. We used diffusion tensor image analysis along the perivascular space (DTI-ALPS) index, the burden of enlarged perivascular spaces (PVS), and choroid plexus volume to reflect glymphatic function. The relationships between WMH burden/Aβ aggregation and these glymphatic markers as well as the correlations between glymphatic markers and cognitive function were investigated. Furthermore, we conducted mediation analyses to explore the potential mediating effects of glymphatic markers in the relationship between WMH burden/Aβ aggregation and cognition.

RESULTS

One hundred and thirty-three participants along the AD continuum were included, consisting of 40 CN - , 48 CN + , 26 MCI + , and 19 AD + participants. Our findings revealed that there were negative associations between whole-brain Aβ aggregation (r =  - 0.249, p = 0.022) and WMH burden (r =  - 0.458, p < 0.001) with DTI-ALPS. Additionally, Aβ aggregation (r = 0.223, p = 0.041) and WMH burden (r = 0.294, p = 0.006) were both positively associated with choroid plexus volume. However, we did not observe significant correlations with PVS enlargement severity. DTI-ALPS was positively associated with memory (r = 0.470, FDR-p < 0.001), executive function (r = 0.358, FDR-p = 0.001), visual-spatial (r = 0.223, FDR-p < 0.040), and language (r = 0.419, FDR-p < 0.001). Conversely, choroid plexus volume showed negative correlations with memory (r =  - 0.315, FDR-p = 0.007), executive function (r =  - 0.321, FDR-p = 0.007), visual-spatial (r =  - 0.233, FDR-p = 0.031), and language (r =  - 0.261, FDR-p = 0.021). There were no significant correlations between PVS enlargement severity and cognitive performance. In the mediation analysis, we found that DTI-ALPS acted as a mediator in the relationship between WMH burden/Aβ accumulation and memory and language performances.

CONCLUSION

Our study provided evidence that both AD pathology (Aβ) and CSVD were associated with glymphatic dysfunction, which is further related to cognitive impairment. These results may provide a theoretical basis for new targets for treating AD.

Sleep disorders and Alzheimer's disease pathophysiology: The role of the Glymphatic System. A scoping review

BACKGROUND

Alzheimer's disease (AD) is highly intertwined with sleep disturbances throughout its whole natural history. Sleep consists of a major compound of the functionality of the glymphatic system, as the synchronized slow-wave activity during NREM facilitates cerebrospinal and interstitial long-distance mixing.

OBJECTIVE

The present study undertakes a scoping review of research on the involvement of the glymphatic system in AD-related sleep disturbances.

DESIGN

we searched Medline, Embase, PsychInfo and HEAL-link databases, without limitations on date and language, along with reference lists of relevant reviews and all included studies. We included in vivo, in vitro and post-mortem studies examining glymphatic implications of sleep disturbances in human populations with AD spectrum pathology. A thematic synthesis of evidence based on the extracted content was applied and presented in a narrative way.

RESULTS

In total, 70 original research articles were included and were grouped as following: a) Protein aggregation and toxicity, after sleep deprivation, along with its effects on sleep architecture, b) Glymphatic Sequalae in SDB, yielding potential glymphatic markers c) Circadian Dysregulation, d) Possible Interventions.

CONCLUSIONS

this review sought to provide insight into the role of sleep disturbances in AD pathogenesis, in the context of the glymphatic disruption.

Impaired glymphatic system revealed by DTI-ALPS in cerebral palsy due to periventricular leukomalacia: relation with brain lesion burden and hand dysfunction

PURPOSE

Preterm children with cerebral palsy (CP) often have varying hand dysfunction, while the specific brain injury with periventricular leukomalacia (PVL) cannot quite explain its mechanism. We aimed to investigate glymphatic activity using diffusion tensor image analysis along the perivascular space (DTI-ALPS) method and evaluate its association with brain lesion burden and hand dysfunction in children with CP secondary to PVL.

METHODS

We retrospectively enrolled 18 children with bilateral spastic CP due to PVL and 29 age- and sex-matched typically developing controls. The Manual Ability Classification System (MACS) was used to assess severity of hand dysfunction in CP. A mediation model was performed to explore the relationship among the DTI-ALPS index, brain lesion burden, and the MACS level in children with CP.

RESULTS

There were significant differences in the DTI-ALPS index between children with CP and their typically developing peers. The DTI-ALPS index of the children with CP was lower than that of the controls (1.448 vs. 1.625, P = 0.003). The mediation analysis showed that the DTI-ALPS index fully mediated the relationship between brain lesion burden and the MACS level (c' = 0.061, P = 0.665), explaining 80% of the effect.

CONCLUSION

This study provides new insights into the neural basis of hand dysfunction in children with CP, demonstrating an important role of glymphatic impairment in such patients. These results suggest that PVL might affect hand function in children with CP by disrupting glymphatic drainage.

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.

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.

Traumatic brain injury and sleep in military and veteran populations: A literature review

BACKGROUND

Traumatic brain injury (TBI) is a hallmark of wartime injury and is related to numerous sleep wake disorders (SWD), which persist long term in veterans. Current knowledge gaps in pathophysiology have hindered advances in diagnosis and treatment.

OBJECTIVE

We reviewed TBI SWD pathophysiology, comorbidities, diagnosis and treatment that have emerged over the past two decades.

METHODS

We conducted a literature review of English language publications evaluating sleep disorders (obstructive sleep apnea, insomnia, hypersomnia, parasomnias, restless legs syndrome and periodic limb movement disorder) and TBI published since 2000. We excluded studies that were not specifically evaluating TBI populations.

RESULTS

Highlighted areas of interest and knowledge gaps were identified in TBI pathophysiology and mechanisms of sleep disruption, a comparison of TBI SWD and post-traumatic stress disorder SWD. The role of TBI and glymphatic biomarkers and management strategies for TBI SWD will also be discussed.

CONCLUSION

Our understanding of the pathophysiologic underpinnings of TBI and sleep health, particularly at the basic science level, is limited. Developing an understanding of biomarkers, neuroimaging, and mixed-methods research in comorbid TBI SWD holds the greatest promise to advance our ability to diagnose and monitor response to therapy in this vulnerable population.

Anti-seizure medication response and the glymphatic system in patients with focal epilepsy

BACKGROUND AND PURPOSE

We aimed to evaluate (i) glymphatic system function in patients with focal epilepsy in comparison with healthy controls, and (ii) the association between anti-seizure medication (ASM) response and glymphatic system function by using diffusion tensor image analysis along the perivascular space (DTI-ALPS).

METHODS

We retrospectively enrolled 100 patients with focal epilepsy who had normal brain magnetic resonance imaging (MRI) findings, and classified them as "poor" or "good" ASM responders according to their seizure control at the time of brain MRI. We also included 79 age- and sex-matched healthy controls. All patients and healthy controls underwent conventional brain MRI and diffusion tensor imaging. The DTI-ALPS index was calculated using the DSI studio program.

RESULTS

Of the 100 patients with focal epilepsy, 38 and 62 were poor and good ASM responders, respectively. The DTI-ALPS index differed significantly between patients with focal epilepsy and healthy controls and was significantly lower in patients with focal epilepsy (1.55 vs. 1.70; p < 0.001). The DTI-ALPS index also differed significantly according to ASM response and was lower in poor ASM responders (1.48 vs. 1.59; p = 0.047). Furthermore, the DTI-ALPS index was negatively correlated with age (r = -0.234, p = 0.019) and duration of epilepsy (r = -0.240, p = 0.016) in patients with focal epilepsy.

CONCLUSION

Our study is the first to identify, in focal epilepsy patients, a greater reduction in glymphatic system function among poor ASM responders compared to good responders. To confirm our results, further prospective multicenter studies with large sample sizes are needed.

Interstitial Fluidopathy of the Central Nervous System: An Umbrella Term for Disorders with Impaired Neurofluid Dynamics

Interest in interstitial fluid dynamics has increased since the proposal of the glymphatic system hypothesis. Abnormal dynamics of the interstitial fluid have been pointed out to be an important factor in various pathological statuses. In this article, we propose the concept of central nervous system interstitial fluidopathy as a disease or condition in which abnormal interstitial fluid dynamics is one of the important factors for the development of a pathological condition. We discuss the aspects of interstitial fluidopathy in various diseases, including Alzheimer's disease, Parkinson's disease, normal pressure hydrocephalus, and cerebral small vessel disease. We also discuss a method called "diffusion tensor image analysis along the perivascular space" using MR diffusion images, which is used to evaluate the degree of interstitial fluidopathy or the activity of the glymphatic system.

Glymphatic system dysfunction in restless legs syndrome: evidenced by diffusion tensor imaging along the perivascular space

STUDY OBJECTIVES

There is growing evidence pointing at glymphatic system dysfunction in diseases with circadian disruption, such as sleep disorders. Lower diffusivity in the direction of perivascular space has been shown in several neurological and sleep-related disorders; however, its role in restless legs syndrome (RLS) is unclear. We hypothesized that similarly, in RLS the diffusivity in glymphatic system is decreased. Here, we aimed to evaluate glymphatic system functionality in patients with RLS, compare it to healthy controls, and analyze the correlation between its function and clinical characteristics.

METHODS

Sixty-nine patients with primary RLS and 51 healthy controls were recruited at a tertiary hospital. All participants underwent diffusion tensor imaging (DTI) and magnetic resonance imaging (MRI) using a 3T MRI scanner, and the DTI along the perivascular space (DTI-ALPS) index was calculated using DTI data. We compared the DTI-ALPS index between the patients with RLS and healthy controls. We also conducted the correlation analysis between the DTI-ALPS index and clinical characteristics, including age, age of onset, symptom duration, and RLS severity.

RESULTS

DTI-ALPS index differed significantly between the patients with RLS and healthy controls; the DTI-ALPS index in the patients with RLS was lower than that in the healthy controls (1.48 vs. 0.60, p = 0.008). There was no significant correlation between the DTI-ALPS index and clinical characteristics.

CONCLUSION

A significantly lower DTI-ALPS index in patients with RLS suggests that the glymphatic system function is impaired in patients with RLS.

Sleep and Perivascular Spaces

PURPOSE OF REVIEW

The glymphatic system is hypothesized to act as the brain's filtration system to remove toxic solutes that accumulate throughout the day. Perivascular spaces (PVSs) play a fundamental role in the ability of the glymphatic system to function, and sleep influences the effectiveness of this system. This article reviews the complexity of the interplay between sleep, the glymphatic system, and PVS.

RECENT FINDINGS

New imaging techniques have illuminated the structure of PVS and their associations with differing disease states. Research has shown that sleep may play a key role in the function of PVS and the influence of adenosine, astrocyte, and aquaporin-4 channel in the function of the glymphatic system. Emerging data suggest that differing pathological states such as neuroinflammatory conditions, neurodegenerative diseases, and cognitive dysfunction may be associated with underlying glymphatic system dysfunction, and sleep disorders could be a potential intervention target.

Preliminary cross-sectional investigations into the human glymphatic system using multiple novel non-contrast MRI methods

We discuss two potential non-invasive MRI methods to cross-sectionally study two distinct facets of the glymphatic system and its association with sleep and aging. We apply diffusion-based intravoxel incoherent motion (IVIM) imaging to evaluate pseudodiffusion coefficient, D * , or cerebrospinal fluid (CSF) movement across large spaces like the subarachnoid space (SAS). We also performed perfusion-based multi-echo, Hadamard encoded multi-delay arterial spin labeling (ASL) to evaluate whole brain cortical cerebral blood flow (CBF) and transendothelial exchange (Tex) of water from the vasculature into the perivascular space and parenchyma. Both methods were used in young adults (N=9, 6F, 23±3 years old) in the setting of sleep and sleep deprivation. To study aging, 10 older adults, (6F, 67±3 years old) were imaged after a night of normal sleep only and compared with the young adults. D * in SAS was significantly (p<0.05) lesser after sleep deprivation (0.014±0.001 mm2/s) than after normal sleep (0.016±0.001 mm2/s), but was unchanged with aging. Cortical CBF and Tex on the other hand, were unchanged after sleep deprivation but were significantly lower in older adults (37±3 ml/100g/min, 476±66 ms) than young adults (42±2 ml/100g/min, 624±66 ms). IVIM was thus, sensitive to sleep physiology and multi-echo, multi-delay ASL was sensitive to aging.

Circadian therapy interventions for glymphatic dysfunction in concussions injuries: A narrative review

There are two primary threats to the brain after concussion. The first is a buildup of neurotoxic proteins in the brain. The second, a partial consequence of the first, is a sustained neuroinflammatory response that may lead to central sensitization and the development of persistent post-concussive symptoms. These threats make neurotoxin clearance a high clinical priority in the acute period after injury. The glymphatic system is the brain's primary mechanism for clearing neurotoxic waste. The glymphatic system is intimately tied to the sleep cycle and circadian dynamics. However, glymphatic dysfunction and sleep disturbances are nearly ubiquitous in the acute period after concussion injury. Because of this, sleep optimization via circadian therapy is a time-sensitive and critical tool in acute concussion management.

Glymphatic pathway in sporadic cerebral small vessel diseases: From bench to bedside

Cerebral small vessel diseases (CSVD) consist of a group of diseases with high heterogeneity induced by pathologies of intracranial small blood vessels. Endothelium dysfunction, bloodbrain barrier leakage and the inflammatory response are traditionally considered to participate in the pathogenesis of CSVD. However, these features cannot fully explain the complex syndrome and related neuroimaging characteristics. In recent years, the glymphatic pathway has been discovered to play a pivotal role in clearing perivascular fluid and metabolic solutes, which has provided novel insights into neurological disorders. Researchers have also explored the potential role of perivascular clearance dysfunction in CSVD. In this review, we presented a brief overview of CSVD and the glymphatic pathway. In addition, we elucidated CSVD pathogenesis from the perspective of glymphatic failure, including basic animal models and clinical neuroimaging markers. Finally, we proposed forthcoming clinical applications targeting the glymphatic pathway, hoping to provide novel ideas on promising therapies and preventions of CSVD.

Impaired glymphatic drainage underlying obstructive sleep apnea is associated with cognitive dysfunction

Obstructive sleep apnea (OSA) is highly prevalent but easily undiagnosed and is an independent risk factor for cognitive impairment. However, it remains unclear how OSA is linked to cognitive impairment. In the present study, we found the correlation between morphological changes of perivascular spaces (PVSs) and cognitive impairment in OSA patients. Moreover, we developed a novel set of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) methods to evaluate the fluid dynamics of glymphatic drainage system. We found that the inflow and outflow parameters of the glymphatic drainage system in patients with OSA were obviously changed, indicating impairment of glymphatic drainage due to excessive perfusion accompanied with deficient drainage in OSA patients. Moreover, parameters of the outflow were associated with the degree of cognitive impairment, as well as the hypoxia level. In addition, continuous positive airway pressure (CPAP) enhances performance of the glymphatic drainage system after 1 month treatment in OSA patients. We proposed that ventilation improvement might be a new strategy to ameliorate the impaired drainage of glymphatic drainage system due to OSA-induced chronic intermittent hypoxia, and consequently improved the cognitive decline.

The effect of sleep disorders on dementia risk in patients with traumatic brain injury: A large-scale cohort study

INTRODUCTION

We investigated the association between sleep disorders (SDs) and incident dementia in adults with traumatic brain injury (TBI).

METHODS

Adults with a TBI between 2003 and 2013 were followed until incident dementia. Sleep disorders at TBI were predictors in Cox regression models, controlling for other dementia risks.

RESULTS

Over 52 months, 4.6% of the 712,708 adults (59% male, median age 44, <1% with SD) developed dementia. An SD was associated with a 26% and a 23% of increased risk of dementia in male and female participants (hazard ratio [HR] 1.26, 95% confidence interval [CI] 1.11-1.42 and HR 1.23, 95% CI 1.09-1.40, respectively). In male participants, SD was associated with a 93% increased risk of early-onset dementia (HR 1.93, 95% CI 1.29-2.87); this did not hold in female participants (HR 1.38, 95% CI 0.78-2.44).

DISCUSSION

In a province-wide cohort, SDs at TBI were independently associated with incident dementia. Clinical trials testing sex-specific SD care after TBI for dementia prevention are timely.

HIGHLIGHTS

TBI and sleep disorders are linked to each other, and to dementia.It is unclear if sleep disorders pose a sex-specific dementia risk in brain injury.In this study, presence of a sleep disorder increased dementia risk in both sexes.The risk differed by type of sleep disorder, which differed between the sexes.Sleep disorder awareness and care in persons with brain injury is vital for dementia prevention.

More extensive white matter disruptions present in untreated obstructive sleep apnea than we thought: A large sample diffusion imaging study

Obstructive sleep apnea (OSA) may lead to white mater (WM) disruptions and cognitive deficits. However, no studies have investigated the full extent of the brain WM, and its associations with cognitive deficits in OSA remain unclear. We thus applied diffusion tensor imaging (DTI) tractography with multi-fiber models and used atlas-based bundle-specific approach to investigate the WM abnormalities for various tracts of the cerebral cortex, thalamus, brainstem, and cerebellum in patients with untreated OSA. We enrolled 100 OSA patients and 63 healthy controls. Fractional anisotropy (FA) and mean diffusivity (MD) values mapped on 33 regions of interest including WM tracts of cortex, thalamus, brainstem, and cerebellum were obtained from tractography-based reconstructions. We compared FA/MD values between groups and correlated FA/MD with clinical data in the OSA group after controlling for age and body mass index. OSA patients showed significantly lower FA values in multiple WM fibers including corpus callosum, inferior fronto-occipital fasciculus, middle/superior longitudinal fasciculi, thalamic radiations, and uncinate (FDR <0.05). Higher FA values were found in medial lemniscus of patients compared to controls (FDR <0.05). Lower FA values of rostrum of corpus callosum correlated with lower visual memory performance in OSA group (p < .005). Our quantitative DTI analysis demonstrated that untreated OSA could negatively impact the integrity of pathways more broadly, including brainstem structures such as medial lemniscus, in comparison to previous findings. Fiber tract abnormalities of the rostral corpus callosum were associated with impaired visual memory in untreated OSA may provide insights into the related pathomechanism.