Reproducibility of diffusion tensor image analysis along the perivascular space (DTI-ALPS) for evaluating interstitial fluid diffusivity and glymphatic function: CHanges in Alps index on Multiple conditiON acquIsition eXperiment (CHAMONIX) study

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.

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.

Impaired glymphatic function in autoimmune glial fibrillary acidic protein astrocytopathy: a prospective analysis

BACKGROUND

To evaluate the glymphatic dysfunction and its association with disease severity in autoimmune glial fibrillary acidic protein astrocytopathy (A-GFAP-A) patients, and to determine its clinical predictors.

METHODS

A total of 20 A-GFAP-A patients and 20 healthy controls (HC) were included. All participants underwent magnetic resonance imaging, and glymphatic function was assessed using the diffusion tensor imaging along the perivascular space (DTI-ALPS) index. Modified Rankin Scale (mRS) scores were recorded at baseline and 4 weeks post-immunotherapy. Multiple linear regression analysis was conducted to identify independent predictors of short-term prognosis.

RESULTS

The baseline DTI-ALPS index was significantly lower in A-GFAP-A patients compared to HC (mean ± SD: 1.50 ± 0.06 vs. 1.62 ± 0.04 [CI -0.16, -0.08], p = 0.003), after adjusting for confounding factors. Four weeks after immunotherapy, the DTI-ALPS index significantly increased (mean ± SD: 1.52 ± 0.14 vs. 1.59 ± 0.17 [CI 0.01, 0.14], p = 0.037). A significant negative correlation was observed between the residuals of the baseline DTI-ALPS index and the baseline mRS scores (r = -0.50 [CI -0.77, -0.07], p = 0.025). The baseline DTI-ALPS index was identified as an independent predictor of short-term prognosis (coefficient = -3.43 [CI -6.68, -0.04], p = 0.048).

CONCLUSIONS

This study indicates that A-GFAP-A patients exhibit significant glymphatic dysfunction, as detected by the DTI-ALPS index, which is related to the severity of the disease. The DTI-ALPS index may serve as a biomarker for monitoring disease progression and as a predictor of short-term prognosis in A-GFAP-A patients.

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.

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.

Evaluation of the glymphatic system in relapsing remitting multiple sclerosis by measuring the diffusion along the perivascular space

BACKGROUND

In the inflammatory process of multiple sclerosis (MS) several toxic waste products are generated. The clearance of these products might depend on the glymphatic system; however, it's preserved function in MS is uncertain. Recently, it was suggested that this 'waste clearance' system can be examined by measuring the diffusion along the perivascular space (ALPS) index.

METHODS

Reproducibility of the ALPS index was tested with intraclass correlation on two open-source datasets with two methods: calculating ALPS indices from the skeleton map (sk-ALPS) and via registration to the common space (ro-ALPS). ALPS indices of 66 MS patient were calculated via the reorientation method. Spearman's correlation and partial least squares regression were applied to reveal the connection between the ALPS indices and the radiological (lesion count) and clinical parameters (SDMT, BVMT, CVLT, EDSS, disease duration) of the patients.

RESULTS

Repeatability of the ALPS index calculated by the ro-ALPS method is the most reliable (ICC: 0.961). Significant correlation was found between the left ALPS index and SDMT. On the right side, significant correlation was found between the ALPS index and the number of periventricular lesions and black holes. The most important predictors of EDSS are disease duration, age, SDMT and infratentorial lesion count.

CONCLUSION

Reproducibility of the ALPS index ranges from 'good' to 'excellent'. No relationship was found between the ALPS index and clinical disability. A lateralization was observed with cognitive characteristics on the left sided ALPS index and radiological characteristics on the right sided ALPS index.

Association of glymphatic system function with peripheral inflammation and motor symptoms in Parkinson's disease

Growing evidence highlights the roles of glymphatic system and peripheral inflammation in Parkinson's disease (PD). We evaluated their interrelationship and potential mechanisms contributing to motor symptoms using DTI-ALPS and inflammatory markers (leukocyte, lymphocyte, neutrophil counts, neutrophil-to-lymphocyte ratio [NLR], and platelet-to-lymphocyte ratio [PLR]) in 134 PD patients (52 tremor-dominant [TD], 62 postural instability and gait difficulty [PIGD]) and 81 healthy controls (HC, 33 with inflammatory markers). PD exhibited lower DTI-ALPS than HC (1.43 ± 0.19 vs. 1.52 ± 0.21, p = 0.001). DTI-ALPS was negatively correlated with NLR, PLR, and neutrophils in PD (all p < 0.05) and with neutrophils in PIGD (β = -0.043, p = 0.048), and positively correlated with lymphocytes in TD (β = 0.105, p = 0.034). DTI-ALPS mediated the relationship between peripheral inflammation (NLR and neutrophils) and MDS-UPDRS III score in PD. Overall, glymphatic dysfunction correlates with peripheral inflammation and may mediate effects of inflammation on motor symptoms in PD, with distinct inflammation profiles between TD and PIGD.

Impact of effective connectivity within the Papez circuit on episodic memory: moderation by perivascular space function

BACKGROUND AND OBJECTIVES

The formation and retrieval of episodic memory is dependent on the coordinated activity of multiple brain regions and neural networks, with the Papez circuit playing a critical role in this process. Recently, the role of the perivascular space (PVS) in cognitive function has garnered increasing attention. However, the role of PVS function between neural circuits and cognitive function in amnestic mild cognitive impairment (aMCI) patients remains unknown. Therefore, this study aims to (1) investigate alterations in the effective connectivity of the Papez circuit and PVS function in patients with aMCI and (2) explore the role of PVS function between the effective connectivity of the Papez circuit and episodic memory.

METHODS

Sixty participants, all of whom underwent multimodal MRI (fMRI, dMRI, and sMRI) and neuropsychological testing, were recruited for this case‒control study. General linear models were used to compare the effective connectivity within the Papez circuit and PVS function between aMCI patients and healthy controls (HCs) and further explore the role of PVS function between the effective connectivity within the Papez circuit and episodic memory.

RESULTS

The effective connectivity between multiple critical regions within the Papez circuit, notably in the hippocampus, anterior cingulate cortex, and parahippocampal gyrus, was significantly weakened in aMCI patients. Moreover, a significant reduction in the along the perivascular space (ALPS) index was observed among aMCI patients, accompanied by a marked increase in PVS volume, indicating significant PVS dysfunction. Further moderation analysis revealed that PVS function moderated the relationship between effective connectivity within the Papez circuit and episodic memory.

CONCLUSIONS

The effective connectivity within the Papez circuit and PVS function are closely related to cognitive function, particularly episodic memory, and enhancing PVS function may serve as a novel therapeutic target for slowing cognitive decline.

Magnetic resonance imaging indices for early Alzheimer's disease detection: Brain clearance markers

The Alzheimer's disease (AD) continuum is characterized by amyloid and tau protein deposition, which is partly attributable to the dysfunction of the brain clearance system. However, the specific phase in the AD continuum wherein aberrant clearance is present remains unclear. This study aimed to assess noninvasive magnetic resonance imaging (MRI) indices related to brain clearance functions, such as choroid plexus volume (CPV), lateral ventricular volume (LVV), and the index of diffusivity along the perivascular space (ALPS index), across the Alzheimer's disease (AD) spectrum. The CPV, LVV, and ALPS index in amyloid beta (Aβ)-negative healthy controls (HCs) and Aβ-positive HCs as well as in patients with Aβ-negative subjective cognitive decline (SCD), with Aβ-positive SCD, with mild cognitive impairment, and with AD were evaluated. The CPV and LVV were higher, whereas the ALPS index was lower in the patients with more severe disease. The ALPS index was significantly lower in Aβ-positive HCs than in Aβ-negative HCs. In SCD patients and those in the AD continuum, the MRI-based clearance markers were correlated with P-tau and T-tau protein levels and cognitive scores. In summary, brain clearance markers on MRI are associated with tau deposition, neurodegeneration and cognitive dysfunction.

Assessment of glymphatic function and white matter integrity in children with autism using multi-parametric MRI and machine learning

OBJECTIVES

To assess glymphatic function and white matter integrity in children with autism spectrum disorder (ASD) using multi-parametric MRI, combined with machine learning to evaluate ASD detection performance.

MATERIALS AND METHODS

This retrospective study collected data from 110 children with ASD (80 exploratory, 43 validation) and 68 typically developing children (50 exploratory, 18 validation) from two centers. The automated diffusion tensor imaging along the perivascular space (aDTI-ALPS), fractional anisotropy (FA), cerebrospinal fluid volume, and perivascular space (PVS) volume indices were extracted from DTI, three-dimensional T1-weighted, and T2-weighted images. Intergroup comparisons were conducted using t-tests, Mann-Whitney U-test, and tract-based spatial statistics. Correlation analysis assessed the relationship between glymphatic function, white matter integrity, and clinical scales. Machine learning models based on MRI indices were developed using the AutoGluon framework.

RESULTS

The PVS volume (p < 0.001) was larger, and aDTI-ALPS index (p < 0.001) was lower in children with ASD compared to typically developing children. FA values were reduced in the ASD group and positively correlated with aDTI-ALPS index. The aDTI-ALPS index correlated with ASD severity (r = -0.27, p = 0.02) and developmental delays (r = 0.63, p < 0.001). Mediation analysis indicated the aDTI-ALPS index partially mediated the relationship between white matter integrity and developmental delay. The MRI-based model achieved an area under the curve of 0.84 for ASD diagnosis.

CONCLUSION

Analyzing glymphatic function and white matter integrity enhances understanding of ASD's neurobiological underpinnings. The multi-parametric MRI, combined with machine learning, can facilitate the early detection of ASD.

KEY POINTS

Question How can multi-parametric MRI based on the glymphatic system improve early diagnosis of autism spectrum disorder (ASD) beyond the limitations of current behavioral assessments? Findings Glymphatic dysfunction and disruptions in white matter integrity were associated with clinical symptoms of ASD. Multi-parametric MRI with machine learning can improve early ASD detection. Clinical relevance Multi-parametric MRI, focusing on glymphatic function and white matter integrity, enhances the diagnostic accuracy of ASD by serving as an objective complement to clinical scales.

Association between glymphatic system function and cognitive impairment in elderly patients with late-onset epilepsy

PURPOSE

Recent studies have shown that late-onset epilepsy (LOE) is accompanied with cognitive decline and increased risk of dementia, particularly Alzheimer's disease (AD). However, the pathophysiological mechanism underlying the cognitive decline in LOE remains unclear. The aim of current study was to evaluate the relationship between glymphatic system (GS) function and cognitive decline in LOE patients using the diffusion tensor imaging (DTI) analysis along the perivascular space (DTI-ALPS).

METHODS

Medical records and neuro-imaging data were obtained from 21 LOE patients with cognitive decline, 14 LOE patients without cognitive decline, and 20 age- and sex-matched healthy controls (HCs). Plasma biomarkers including Aβ42 and Aβ40 were examined using single-molecule array (Simoa) assays. The DTI-ALPS parameter was calculated and correlated with the clinical characteristics of LOE, including age, seizure frequency, duration of epilepsy, Mini-Mental State Examination (MMSE), and Aβ42/40. Regression models were used to evaluate the influencing factors of DTI-ALPS index.

RESULTS

LOE patients exhibited a decreased ALPS index and Aβ42/40 compared with the HCs. Post-hoc analysis indicated that the DTI-ALPS index and Aβ42/40 in LOE patients with cognitive decline was significantly lower in relative to LOE patients without cognitive decline and HCs. Spearman correlations showed a negative correlation between DTI-ALPS index and age, seizure frequency and disease duration while a positive correlations between the DTI-ALPS index and Aβ42/40 and MMSE scores in LOE patients. Linear regression analysis suggested that the DTI-ALPS index was independently related to age, Aβ42/40 and MMSE score after correcting for gender, education, and vascular risk factors.

CONCLUSION

Our findings using DTI-ALPS method found a positive correlation between cognitive decline and GS dysfunction in LOE patients, and may indicate a potential internal link between age-related LOEU and dementia formation. Therefore, the DTI-ALPS index may serve as a potential imaging marker for diagnosing and monitoring the GS function in LOE patients.

Widespread and Prolonged Pain May Reduce Brain Clearance Capacity Only via Sleep Impairment: Evidence from Participants with Knee Pain

The brain is key in the pain-sleep relationship, and sleep is needed for glymphatic clearance. However, no studies have examined how pain relates to the glymphatic system (GS). Characterizing the GS alongside sleep quality in well-characterized pain samples is essential for advancing this understanding. Non-invasive MRI techniques, such as Diffusion Tensor Imaging-Analysis aLong the Perivascular Space (DTI-ALPS), are particularly valuable as they are approved for humans. Although the relationship between the DTI-ALPS index and the GS is primarily deductive, the index may be a proxy for waste clearance capacity in deep white matter. Its sensitivity to interstitial space changes-known to be modulated by norepinephrine-offers a unique opportunity to investigate how sleep impairment and chronic pain regulation affect specific components of brain waste clearance. We thus fitted two longitudinal models linking pain, sleep quality and the DTI-ALPS index. We hypothesized that variations in pain characteristics would predict DTI-ALPS index changes, either directly or mediated by sleep quality changes. Alternatively, we hypothesized that variations in sleep quality would predict changes in pain characteristics via DTI-ALPS index modifications. Knee pain participants (n=87) completed an MRI and self-reported measures of pain and sleep impairment at baseline and two years later. We only found evidence supporting that more widespread and longer pain at baseline significantly influenced decreases in the DTI-ALPS index in the left hemisphere through increased sleep impairment two years later (p=0.039, corrected). Perspective: Findings highlight the need for research on the relationship between pain and sleep quality and its implications for brain health.

Lower DTI-ALPS index in patients with major depressive disorder: Correlation with fatigue

BACKGROUND AND PURPOSE

Diffusion tensor imaging along perivascular spaces (DTI-ALPS) is an index that may provide insights into intracranial waste clearance processes. Glymphatic system dysfunction has been suggested to play a role in the development of major depressive disorder (MDD). Additionally, fatigue-a common precursor of MDD-is also closely connected to the waste clearance function of the central nervous system (CNS), further underscoring the significance of efficient waste removal in MDD. However, evidence linking altered DTI-ALPS index to MDD remains limited. This study aims to investigate the changes in the DTI-ALPS index in patients with MDD and explore the potential interplay between DTI-ALPS index alterations, fatigue, and the presence of MDD.

MATERIAL AND METHODS

A total of 46 patients with MDD and 55 healthy controls (HC) were included in the study. All participants underwent diffusion tensor imaging using the same 3-T MRI (3-Tesla Magnetic Resonance Imaging) scanner. The DTI-ALPS index was assessed, and the Chalder Fatigue Scale (CFS) was used to evaluate fatigue levels in both groups, and the 17-item Hamilton Depression Rating Scale (HAMD-17) was used to evaluate the severity of depression in the patients. We compared the DTI-ALPS index and clinical characteristics between the MDD and HC group, and explored the relationship among the DTI-ALPS index, CFS scores, and the presence of MDD through mediation analysis.

RESULTS

The DTI-ALPS index in the right hemisphere (DTI-ALPS-R) is significantly lower in patients with MDD (t = 2.41, P = 0.02). The MDD patients exhibited significantly higher scores on the CFS scales compared with HCs (t = 13.12, P <.001). Mediation analysis showed that the CFS score plays a significant mediating role between DTI-ALPS-R and the presence of MDD, acting as a full mediator (indirect effect β = -0.230, 95 % CI: [-0.388, -0.059]).

CONCLUSION

Our study found that patients with MDD have a reduced DTI-ALPS index. This reduction appears to contribute to the development of MDD by facilitating the accumulation of fatigue symptoms. These findings may provide a new perspective on the pathogenesis of MDD, suggest a potential new biomarker for MDD, and offer new insights for its treatment.

In vivo imaging markers of glymphatic dysfunction in amyotrophic lateral sclerosis: Analysis of ALPS index and choroid plexus volume

BACKGROUND

The glymphatic system, essential for brain waste clearance, has been implicated in neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Emerging imaging markers, such as the analysis along the perivascular space (ALPS) index and choroid plexus volume (CPV), may provide insights into glymphatic function, but their relevance to ALS remains unclear.

OBJECTIVE

To assess glymphatic dysfunction in ALS patients using the ALPS index and CPV.

METHODS

In this prospective single-center study, we analyzed 51 ALS patients and 51 age- and sex-matched healthy controls (HC). The ALPS index was calculated using diffusion tensor imaging, and 3D T1-weighted MRI was used for automated estimation of CPV and its fraction (CPV/total intracranial volume). Diagnostic performance was assessed using area under the receiver operating curve (AUC). Correlations between imaging markers and clinical parameters were also examined.

RESULTS

ALS patients had a significantly lower ALPS index (ALS: 1.45 ± 0.15; HC: 1.55 ± 0.16; p = 0.002) and higher CPV fraction (ALS: 0.12 ± 0.04 %; HC: 0.10 ± 0.02 %; p < 0.001). The ALPS index and CPV fraction had AUCs of 0.70 and 0.72, respectively. A significant inverse correlation was observed between the ALPS index and CPV fraction (r = -0.31, p = 0.002). Both markers correlated with aging but not with clinical disability or progression rate.

CONCLUSION

This study identifies glymphatic dysfunction in ALS, as evidenced by changes in the ALPS index and CPV. Larger studies are warranted to validate these findings and assess their potential as biomarkers for ALS.

Glymphatic system: a self-purification circulation in brain

The glymphatic system theory introduces a new perspective on fluid flow and homeostasis in the brain. Here, cerebrospinal fluid and interstitial fluid (CSF-ISF) moves from the perivascular spaces (PVS) of arteries to those of veins for drainage. Aquaporin-4 (AQP4) plays a crucial role in driving fluid within the PVS. The impairment to AQP4 is closely linked to the dysfunction of the glymphatic system. The function of the glymphatic system is less active during waking but enhanced during sleep. The efficiency of the glymphatic system decreases with aging. Damage to the glymphatic system will give rise to the development and progression of many brain diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), chronic traumatic encephalopathy (CTE), and vascular dementia (VaD). Here, we reviewed previous research associated with the glymphatic system, including its concepts, principles, and influencing factors. We hypothesize that AQP4 could be a target for the prevention and treatment of certain brain diseases through the regulation on the glymphatic system.

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.

MR Imaging Indices for Brain Interstitial Fluid Dynamics and the Effects of Orexin Antagonists on Sleep

PURPOSE

The purpose of this study was to assess the extent to which improvement in sleep with lemborexant contributed to changes in interstitial fluid dynamics.

METHODS

The 3 methods including diffusion tensor image analysis along the perivascular space (DTI-ALPS), dynamic contrast-enhanced method to assess tissue vascular permeability (Ktrans), and choroid plexus volume (CPV) were used. Correlations between these imaging indices and sleep parameters (latency to persistent sleep [LPS], wake after sleep onset [WASO], total sleep time [TST], and sleep efficiency [SE]) were evaluated using Pearson correlation analysis. Additionally, multiple regression analysis and linear mixed model analysis were employed to assess the relationship between baseline sleep status and imaging parameter changes. MRI and sleep assessments were performed before treatment initiation (week 0, w0) and at 12 weeks after lemborexant administration (week 12, w12).

RESULTS

The ALPS-index was inversely correlated with LPS and positively correlated with TST and SE at w0. In multiple regression analysis, ALPS-index was lower when sleep parameters other than LPS were poor at w0. A linear mixed model analysis suggested that poor sleep status in LPS and SE at w0 may have an effect on greater ALPS-index. In the evaluation of Ktrans measurement, the single regression analysis showed a statistically significant correlation between the reduction in Ktrans and the shortening in LPS. Examination of CPV and sleep parameters showed a significant negative correlation between TST and CPV at w0 and w12. Multiple regression analysis also showed that TST of w12 had a significant effect on CPV at w12.

CONCLUSION

Our results suggested that poor sleep status is related to the greater change of ALPS-index and CPV improvement after lemborexant administration may be related to in part to sleep parameter improvement.

Glymphatic function decline as a mediator of core memory-related brain structures atrophy in aging

Background and Objectives

This study aimed to elucidate the role of the glymphatic system-a crucial pathway for clearing waste in the brain-in the aging process and its contribution to cognitive decline. We specifically focused on the diffusion tensor imaging analysis along the perivascular space (ALPS) index as a noninvasive biomarker of glymphatic function.

Methods

Data were drawn from the Alzheimers Disease Neuroimaging Initiative (ADNI) database and a separate validation cohort to analyze the ALPS index in cognitively normal older adults. The relationships among the ALPS index, brain morphometry, and memory performance were examined.

Results

As a biomarker of glymphatic function, the ALPS index appeared to decline with age in both cohorts. According to the brain morphology analysis, the ALPS index was positively correlated with the thickness of the left entorhinal cortex (r = 0.258, P false discovery rate (FDR) = 2.96 × 10-4), and it played a mediating role between aging and left entorhinal cortex thinning. The independent cohort further validated the correlation between the ALPS index and the left entorhinal cortex thickness (r = 0.414, P FDR = 0.042). Additionally, in both the primary and validation cohorts, the ALPS index played a significant mediating role in the relationship between age and durable or delayed memory decline.

Conclusion

This study highlights the ALPS index as a promising biomarker for glymphatic function and links it to atrophy of the core memory brain regions during aging. Furthermore, these results suggest that targeting glymphatic dysfunction could represent a novel therapeutic approach to mitigate age-related memory decline.

MRI free water mediates the association between diffusion tensor image analysis along the perivascular space and executive function in four independent middle to aged cohorts

INTRODUCTION

Diffusion tensor image analysis along the perivascular space (DTI-ALPS) index was proposed for assessing glymphatic clearance function. This study evaluated DTI-ALPS as a biomarker for cerebral small vessel disease (cSVD) related vascular cognitive impairment and dementia (VCID).

METHODS

Four independent cohorts were examined. A composite score of executive function (UDS3-EF) was used to evaluate EF status. The association between the ALPS index and UDS3-EF scores and the mediator effect of free water in white matter (WM-FW) on such association was analyzed.

RESULTS

The ALPS index was significantly associated with UDS3-EF scores in all cohorts. Additionally, WM-FW mediates the relationship between the ALPS index and UDS3-EF scores.

DISCUSSION

Lower ALPS index may be a surrogate marker of glymphatic dysfunction, which is associated with impaired EF, and this association is mediated by the interstitial fluid (ISF) drainage ISF in WM, providing a clinical rationale for using ALPS index as a biomarker for cSVD-related VCID.

HIGHLIGHTS

This is the first study to investigate the mediation role of interstitial FW fraction (WM-FW) on the relationship between glymphatic clearance (ALPS index) and EF (UDS3-EF scores) in four independent middle to aged cohorts at risk for cSVD. This study identified that ALPS index was independently associated with UDS3-EF scores after adjusting for demographics, VRFs, and WM hyperintensity burden and that WM-FW mediated this association in all middle to aged cohorts. Our findings suggest that in middle to aged individuals, glymphatic dysfunction (reflected by ALPS index) is strongly associated with EF and that this association is mediated by the ISF drainage in WM. This study provides a strong clinical rationale for the use of the ALPS index as a marker of cognitive function in multi-site observational studies and clinical trials to monitor and prevent VCID.

Relationships Between Glymphatic System Activity and Tau Burden, Dopaminergic Impairment, Abnormal Glucose Metabolism in Progressive Supranuclear Palsy

BACKGROUND

Progressive supranuclear palsy (PSP) is a primary tauopathy characterized by dopaminergic impairment and abnormal glucose metabolism. The glymphatic system can promote the elimination of tau protein. The association between glymphatic function and pathological hallmark in neuroimaging remains unknown.

METHODS

Diffusion tensor imaging (DTI) and positron emission tomography (PET) scanning with 18F-Florzolotau, 18F-FPCIT, and 18F-FDG were performed in PSP patients. DTI analysis along the perivascular space (ALPS) index was computed to assess glymphatic function, while the semi-quantitative value was employed to measure tau burden and dopaminergic impairment. The PSP-related pattern (PSPRP) served as an indicator of abnormal metabolic brain network activity.

RESULTS

PSP patients exhibited changes in ALPS index and tau deposition. ALPS index, tau deposition, and PSPRP expression showed significant correlations with clinical scores. Additionally, ALPS index was correlated with tau deposition and PSPRP expression. However, neither ALPS index nor the clinical scores were correlated with striatum dysfunction. Finally, tau deposition in subcortical regions and PSPRP expression exhibited mediating effects between ALPS index and clinical scores.

CONCLUSION

The glymphatic dysfunction is associated with tau deposition and abnormal metabolic brain network activity and is independent of dopaminergic impairment in PSP.

Glymphatic system dysfunction in epilepsy related to focal cortical dysplasia and its relationship with antiseizure medication response

PURPOSE

Glymphatic function has not been explored in patients with focal cortical dysplasia (FCD)-related epilepsy. This study aimed to investigate the glymphatic system's involvement in these patients and to evaluate its correlation with response patterns to different antiseizure medications (ASMs) using diffusion tensor imaging along the perivascular space (DTI-ALPS).

METHODS

Fifty-two patients with FCD-related epilepsy (10 with drug-responsive epilepsy and 42 with drug-resistant epilepsy) and 24 healthy controls (HC) were included. Bilateral DTI-ALPS index were calculated and compared among drug-responsive epilepsy, drug-resistant epilepsy, and HC groups. Additionally, we analyzed correlations between the DTI-ALPS index and clinical characteristics.

RESULTS

Compared to HC, patients with FCD-related epilepsy showed significantly lower DTI-ALPS index in the bilateral hemispheres (p < 0.001). Notably, a significant decrease in the DTI-ALPS index was noted in the hemisphere ipsilateral to the epileptogenic foci, compared to the contralateral hemisphere (p < 0.001). Further analysis revealed that, in patients with drug-resistant epilepsy, the ipsilateral DTI-ALPS index was significantly lower than the contralateral DTI-ALPS index (p < 0.001), whereas patients with drug-responsive epilepsy did not show a significant difference between ipsilateral and contralateral DTI-ALPS index. No significant correlations were found between the DTI-ALPS index and clinical characteristics such as age and duration of epilepsy.

CONCLUSION

Our findings suggest a correlation between glymphatic system dysfunction and patients with FCD-related epilepsy, particularly in drug-resistant patients.

Diffusion tensor image analysis along the perivascular space and quantitative susceptibility mapping in the diagnosis and severity assessment of Parkinson's disease

Background

Increased iron accumulation measured by quantitative susceptibility mapping (QSM) has been observed in various brain regions, especially substantia nigra (SN), in Parkinson's disease (PD). Glymphatic dysfunction evaluated by diffusion tensor image analysis along the perivascular space (DTI-ALPS) in PD has also attracted much attention recently. This study aimed to compare and combine DTI-ALPS and QSM of SN in the diagnosis and severity assessment of PD.

Methods

As a case-control study, we retrospectively recruited 60 PD patients and 60 matched healthy controls. The DTI-ALPS index, QSM of SN, and their combination were calculated and further compared between the two groups. Receiver operating characteristic (ROC) curves were used to assess the diagnostic performance. We further analyzed the correlation of the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score with DTI-ALPS and QSM of SN.

Results

The average DTI-ALPS was significantly lower, whereas the average QSM of bilateral SN was significantly higher in PD [median (interquartile range): 1.38 (1.26-1.53); 0.09 (0.07-0.10)] compared to healthy controls [1.52 (1.41-1.71), P<0.001; 0.08 (0.07-0.09), P=0.020]. The combination showed a significantly higher area under the curve (AUC) of 0.801 than that of DTI-ALPS (0.729) or QSM of SN (0.624) in discriminating PD from healthy controls. Moreover, the average QSM of bilateral SN showed significant correlations with the MDS-UPDRS III score (rho =-0.276, P=0.034).

Conclusions

DTI-ALPS and QSM of SN are potential biomarkers for the diagnosis and severity assessment of PD. The combination of them may improve the diagnostic performance.

Association of Glymphatic Function With Clinical Characteristics in Patients With Clinical and Asymptomatic Creutzfeldt-Jakob Disease

BACKGROUND AND OBJECTIVES

Abnormal glymphatic system-related proteins have been identified in a small-scale pathologic study of patients with Creutzfeldt-Jakob disease (CJD). However, it remains unclear whether glymphatic dysfunction occurs in vivo in patients with CJD and whether this decline begins during the preclinical stage. This study aimed to investigate the relationship between glymphatic dysfunction and clinical characteristics in patients with CJD, as well as potential glymphatic impairment in preclinical CJD.

METHODS

This prospective cohort study recruited patients with CJD and healthy controls (HCs) from the Department of Neurology at Xuanwu Hospital, Capital Medical University, Beijing, China, from 2018 to 2022. In addition, a family with preclinical genetic CJD carrying the G114V pathogenic variant was followed over 6 years with 3 evaluations. All participants underwent diffusion tensor imaging along the perivascular space (DTI-ALPS) to measure glymphatic function in vivo and 18F-fludeoxyglucose-PET to identify CJD-related metabolic patterns. Associations between the DTI-ALPS index and Medical Research Council Prion Disease Rating Scale (MRC-PDRS) score were evaluated using multiple linear regression.

RESULTS

We enrolled 35 patients with CJD (mean age 59.6 ± 10.7 years, 40% female, with the time from onset to glymphatic dysfunction assessment averaging 39% of the total disease course), 28 age-matched and sex-matched HCs, and a family with preclinical genetic CJD consisting of 7 carriers and 7 noncarriers. Patients with CJD exhibited lower DTI-ALPS values compared with HCs (p < 0.001). Partial correlation analyses revealed significant correlations between the DTI-ALPS index and MRC-PDRS score (r = 0.346, p = 0.049) and disease progression (r = -0.468, p = 0.006), but not with disease duration or cognitive severity after adjusting for age and sex. Multivariate linear analysis demonstrated that poorer MRC-PDRS scores (β = 0.702, p = 0.014) were associated with a lower DTI-ALPS index. The DTI-ALPS index of asymptomatic G114V carriers showed no significant difference compared with noncarriers. However, a preclinical CJD case exhibited an 8.2% decrease in the DTI-ALPS index 3.3 years before onset. No significant correlation was found between regional metabolic standardized uptake value ratios and DTI-ALPS index.

DISCUSSION

Our study indicates that glymphatic dysfunction is associated with CJD severity and disease progression. Glymphatic dysfunction may occur in the preclinical stage, but these findings should be interpreted with caution because they are based on individual findings.

Genome-wide association study unravels mechanisms of brain glymphatic activity

Brain glymphatic activity, as indicated by diffusion-tensor imaging analysis along the perivascular space (ALPS) index, is involved in developmental neuropsychiatric and neurodegenerative diseases, but its genetic architecture is poorly understood. Here, we identified 17 unique genome-wide significant loci and 161 candidate genes linked to the ALPS-indexes in a discovery sample of 31,021 individuals from the UK Biobank. Seven loci were replicated in two independent datasets. Genetic signals located at the 2p23.3 locus yielded significantly concordant effects in both young and aging cohorts. Genetic correlation and polygenic overlap analyses indicate a common underlying genetic mechanism between the ALPS-index, ventricular volumes, and cerebrospinal fluid tau levels, with GMNC (3q28) and C16orf95 (16q24.2) as the shared genetic basis. Our findings enhance the understanding of the genetics of the ALPS-index and provide insight for further research into the neurobiological mechanisms of glymphatic clearance activity across the lifespan and its relation to neuropsychiatric phenotypes.

DTI-ALPS index as a predictor of cognitive decline over 1 year

PURPOSE

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline and impaired daily functioning. The glymphatic system removes neurotoxic waste, including amyloid-beta (Aβ), an important factor in AD pathogenesis. This study used the Diffusion Tensor Imaging Analysis Along the Perivascular Space (DTI-ALPS) index, which reflects glymphatic function, to explore its relationship with cognitive decline in patients with probable AD.

METHODS

We conducted a longitudinal study of 16 participants aged 60-79 years with probable AD who were evaluated using the Clinical Dementia Rating (CDR) and Mini-Mental State Examination (MMSE). Glymphatic function was assessed using the DTI-ALPS index; plasma Aβ 42/40 ratios were measured to account for amyloid pathology. The relationship between the DTI-ALPS index and baseline cognitive function was analyzed using multiple regression models adjusted for age, sex, and plasma Aβ 42/40 ratios. Associations between the DTI-ALPS index and cognitive decline over 1 year were assessed by a model using the percentage change in the MMSE z-score as the outcome variable.

RESULTS

Higher DTI-ALPS index was significantly associated with better baseline cognitive function as assessed by MMSE (standardized beta = 1.17, p < 0.001) and lower clinical severity as assessed by CDR (standardized beta = - 1.00, p = 0.006). Over the 1-year follow-up, greater baseline DTI-ALPS index values were associated with less cognitive decline (standardized beta = - 0.85, p = 0.018).

CONCLUSION

Our findings suggest that DTI-ALPS index is associated with cognitive performance and is a biomarker for predicting cognitive decline in AD. Future studies should consider larger sample sizes and longer follow-up periods to validate these findings.

Neuroglia in neurodegeneration: Amyotrophic lateral sclerosis and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are devastating neurodegenerative diseases sharing significant pathologic and genetic overlap, leading to consider these diseases as a continuum in the spectrum of their pathologic features. Although FTD compromises only specific brain districts, while ALS involves both the nervous system and the skeletal muscles, several neurocentric mechanisms are in common between ALS and FTD. Also, recent research has revealed the significant involvement of nonneuronal cells, particularly glial cells such as astrocytes, oligodendrocytes, microglia, and peripheral immune cells, in disease pathology. This chapter aims to provide an extensive overview of the current understanding of the role of glia in the onset and advancement of ALS and FTD, highlighting the recent implications in terms of prognosis and future treatment options.

Correlation Between Dietary Nutrition and Glymphatic System Activity in Healthy Participants

Background Dietary nutrition is an important approach to the prevention and treatment of the physical and mental states of humans. Nowadays, many studies show the neuroprotective and antioxidative effects of nutrients, such as B vitamins, zinc, and iron, on the central nervous system (CNS). However, there were no studies focusing on the relationships between the serum concentration of nutrients and the brain glymphatic system activity and macroscopic waste clearance system, including reactive oxygen species. Objectives This study tries to evaluate the relationships between them using diffusion tensor image analysis along the perivascular space (DTI‑ALPS) index as the proxy of glymphatic system activity. Methods The subjects were 159 healthy participants who underwent 1.5-Tesla DTI (diffusion tensor imaging) and blood sampling. We computed the DTI‑ALPS index and estimated the relationships between the DTI‑ALPS index and the serum concentrations of vitamin B6, vitamin B12, folate, zinc, ferritin, and iron. Results There were significant positive correlations of the DTI‑ALPS index with age and sex. Additionally, we found that age, sex, and serum zinc level were good independent variables that predicted the dependent variable, the DTI‑ALPS index, as revealed by multiple regression analyses. Conclusion We found a significant correlation between brain clearance system activity and serum zinc levels in healthy participants. Though zinc is known to play an important physiological role in the CNS, excessive zinc accumulation or zinc deficiency might induce neurodegeneration. Further works with varying serum zinc concentrations would reveal the neuroprotective effect of zinc in its proper concentration.

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.

Altered brain glymphatic function on diffusion-tensor MRI in patients with spontaneous intracerebral hemorrhage: an exploratory study

Objectives

To investigate the function of the glymphatic system (GS) and its association with neuropsychological tests in spontaneous intracerebral hemorrhage (sICH) by diffusion tensor imaging analysis along the perivascular space (DTI-ALPS).

Methods

This retrospective study included 58 patients with sICH and 63 age- and sex-matched healthy controls (HCs). Partial correlation analyses were performed to examine the relationships between the DTI-ALPS index and radiological as well as clinical data. Mediation analyses were performed to explore the mediating role of the grey matter proportion (GM%) in the relationship between DTI-ALPS index and Montreal Cognitive Assessment (MoCA) score.

Results

Significantly lower DTI-ALPS index values were observed in sICH compared with HCs (FDR-p < 0.001). In the acute-subacute sICH group, the ALPS index was significantly correlated with hematoma volume (r = -0.572, FDR-p = 0.031). In the chronic sICH group, the ALPS index was significantly correlated with MoCA scores (r = 0.425, FDR-p = 0.014). In chronic sICH groups, GM% served as a significant mediator in the relationship between the DTI-ALPS index and MoCA scores (indirect effects β = 4.925, 95%CI: 0.028, 11.841). The ALPS index was identified as an independent prognostic indicator for unfavorable outcomes in sICH (β = -9.851, p = 0.018).

Conclusion

Our study demonstrated that the DTI-ALPS index decreased in sICH patients, suggesting potential functional impairment of the lymphoid system. Additionally, the DTI-ALPS index served as an independent predictor of poor 90-day prognosis. In the acute-subacute stage of sICH, the DTI-ALPS index had negative correlation with hematoma volume. In the chronic sICH group, the GM% partially mediated the relationship between the GS and cognitive function.

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.

The association between structural connectivity and anti-seizure medication response in patients with temporal lobe epilepsy

OBJECTIVES

This study aimed to investigate the differences in structural connectivity and glymphatic system function between patients with temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS) and healthy controls. Additionally, we analyzed the association between structural connectivity, glymphatic system function, and antiseizure medication (ASM) response.

METHODS

We retrospectively enrolled patients with TLE and HS and healthy controls who underwent diffusion tensor imaging at our hospital. We assessed structural connectivity in patients with TLE and HS and healthy controls by calculating network measures using graph theory and evaluated glymphatic system function using the diffusion tensor image analysis along the perivascular space (DTI-ALPS) index. Patients with TLE and HS were categorized into two groups: ASM poor and good responders.

RESULTS

We enrolled 55 patients with TLE and HS and 53 healthy controls. Of the 55 patients with TLE and HS, 39 were ASM poor responders, and 16 were ASM good responders. The assortativity coefficient in patients with TLE and HS was higher than that in healthy controls (0.004 vs. -0.007, p = 0.004), and the assortativity coefficient in ASM poor responders was lower than that in ASM good responders (-0.001 vs. -0.197, p = 0.003). The DTI-ALPS index in patients with TLE and HS was lower than that in healthy controls (1.403 vs. 1.709, p < 0.001); however, the DTI-ALPS index did not differ between ASM poor and good responders (1.411 vs. 1.385, p = 0.628). The DTI-ALPS index had a significant negative correlation with age in patients with TLE and HS (r = -0.267, p = 0.049).

SIGNIFICANCE

We confirmed increased assortativity coefficient in structural connectivity and decreased DTI-ALPS index in patients with TLE and HS compared with healthy controls. Additionally, we demonstrated an association between decreased assortativity coefficient in structural connectivity and ASM poor response in patients with TLE patients and HS.

PLAIN LANGUAGE SUMMARY

This study investigates the relationship between brain connectivity changes and glymphatic system function with antiseizure medication response in patients with temporal lobe epilepsy and hippocampal sclerosis. The research reveals that these patients show altered brain connectivity and glymphatic function compared to healthy individuals. A key finding is the strong link between a specific connectivity measure (assortativity coefficient) and antiseizure medication response, providing valuable insights that could influence epilepsy treatment and future research directions.

Diffusion tensor imaging along the perivascular space: the bias from crossing fibres

Non-invasive evaluation of glymphatic function has emerged as a crucial goal in neuroimaging, and diffusion tensor imaging along the perivascular space (DTI-ALPS) has emerged as a candidate method for this purpose. Reduced ALPS index has been suggested to indicate impaired glymphatic function. However, the potential impact of crossing fibres on the ALPS index has not been assessed, which was the aim of this cross-sectional study. For this purpose, we used DTI-ALPS in a cohort with three groups: Parkinson's disease (PD) (n = 60, mean age 63.3 ± 1.5, 33 males), progressive supranuclear palsy (PSP) (n = 17, mean age 70.9 ± 1.5, 9 males) and healthy controls (n = 41, mean age 64.5 ± 8.4, 15 males). The ALPS index was calculated blinded to diagnosis, by manually placing two sets of regions of interest (ROI) on the projection and association fibres of each hemisphere. Annotation was performed twice: once on conventional diffusion-encoded colour maps weighted by fractional anisotropy and once on maps with weights adjusted for high incidence of crossing fibres. PSP patients had significantly lower conventional ALPS indices compared with both healthy controls (right hemisphere: P = 0.009; left hemisphere: P < 0.001) and PD patients (right hemisphere: P = 0.024; left hemisphere: P < 0.001). There were no differences between healthy controls and PD patients. After adjusting the ROI to avoid regions of crossing fibres, the ALPS index significantly decreased in healthy controls (right hemisphere: P < 0.001; left hemisphere: P < 0.001) and PD (right hemisphere: P < 0.001; left hemisphere: P < 0.001). In PSP, the adjusted ALPS index was lower compared with the conventional one only in the right hemisphere (P = 0.047). Overall, this adjustment led to less significant differences among diagnostic groups. Specifically, with the adjusted ALPS index, PSP patients showed significantly lower ALPS index compared with healthy controls (right hemisphere: P = 0.044; left hemisphere: P = 0.029) and PD patients (P = 0.003 for the left hemisphere only). Our results suggest that crossing fibres significantly inflate the ALPS index and should be considered a critical pitfall of this method. This factor could partly explain the variability observed in previous studies. Unlike previous research, we observed no differences between PD and healthy controls, likely because most patients in our cohort were in the early phase of the disease. Thus, the ALPS index may not be a sensitive indicator of glymphatic function at least in the initial stages of neurodegeneration in PD.

Unveiling the link between glymphatic function and cortical microstructures in post-traumatic stress disorder

PURPOSE

The discovery of the glymphatic system, crucial for cerebrospinal and interstitial fluid exchange, has enhanced our grasp of brain protein balance and its potential role in neurodegenerative disease prevention and therapy. Detecting early neurodegenerative shifts via noninvasive biomarkers could be key in identifying at-risk individuals for Alzheimer's disease (AD). Our research explores a diffusion tensor imaging (DTI) method that measures cortical mean diffusivity (cMD), potentially a more sensitive indicator of neurodegeneration than traditional macrostructural methods.

MATERIALS AND METHODS

We analyzed 67 post-traumatic stress disorder (PTSD)-diagnosed veterans from the Alzheimer's Disease Neuroimaging Initiative database. Participants underwent structural MRI, DTI, Aβ PET imaging, and cognitive testing. We focused on the DTI-ALPS technique to assess glymphatic function and its relation to cMD, cortical Aβ accumulation, and thickness, accounting for age and APOE ε4 allele variations.

RESULTS

The cohort, all male with an average age of 68.1 (SD 3.4), showed a strong inverse correlation between DTI-ALPS and cMD in AD-affected regions, especially in the entorhinal, parahippocampal, and fusiform areas. Higher DTI-ALPS readings were consistently linked with greater cortical thickness, independent of Aβ deposits and genetic risk factors. Age and cMD emerged as inversely proportional predictors of DTI-ALPS, indicating a complex interaction with age.

CONCLUSION

The study confirms a meaningful association between glymphatic efficiency and cMD in AD-sensitive zones, accentuating cortical microstructural alterations in PTSD. It positions DTI-ALPS as a viable biomarker for assessing glymphatic function in PTSD, implicating changes in DTI-ALPS as indicative of glymphatic impairment.

Evaluation of the Glymphatic System in Schizophrenia Spectrum Disorder Using Proton Magnetic Resonance Spectroscopy Measurement of Brain Macromolecule and Diffusion Tensor Image Analysis Along the Perivascular Space Index

BACKGROUND AND HYPOTHESIS

The glymphatic system (GS), a brain waste clearance pathway, is disrupted in various neurodegenerative and vascular diseases. As schizophrenia shares clinical characteristics with these conditions, we hypothesized GS disruptions in patients with schizophrenia spectrum disorder (SCZ-SD), reflected in increased brain macromolecule (MM) and decreased diffusion-tensor-image-analysis along the perivascular space (DTI-ALPS) index.

STUDY DESIGN

Forty-seven healthy controls (HCs) and 103 patients with SCZ-SD were studied. Data included 135 proton magnetic resonance spectroscopy (1H-MRS) sets, 96 DTI sets, with 79 participants contributing both. MM levels were quantified in the dorsal-anterior cingulate cortex (dACC), dorsolateral prefrontal cortex, and dorsal caudate (point resolved spectroscopy, echo-time = 35ms). Diffusivities in the projection and association fibers near the lateral ventricle were measured to calculate DTI-ALPS indices. General linear models were performed, adjusting for age, sex, and smoking. Correlation analyses examined relationships with age, illness duration, and symptoms severity.

STUDY RESULTS

MM levels were not different between patients and HCs. However, left, right, and bilateral DTI-ALPS indices were lower in patients compared with HCs (P < .001). In HCs, age was positively correlated with dACC MM and negatively correlated with left, right, and bilateral DTI-ALPS indices (P < .001). In patients, illness duration was positively correlated with dACC MM and negatively correlated with the right DTI-ALPS index (P < .05). In the entire population, dACC MM and DTI-ALPS indices showed an inverse correlation (P < .01).

CONCLUSIONS

Our results suggest potential disruptions in the GS of patients with SCZ-SD. Improving brain's waste clearance may offer a potential therapeutic approach for patients with SCZ-SD.

Glymphatic dysfunction in multiple sclerosis and its association with disease pathology and disability

BACKGROUND

The role of the glymphatic system in multiple sclerosis (MS)-related disability remains underexplored. Diffusion-tensor image analysis along the perivascular space (DTI-ALPS) offers a non-invasive method to assess glymphatic function.

OBJECTIVE

To evaluate glymphatic function in MS patients with lower and higher disability.

METHODS

This study included 118 MS patients who underwent structural, diffusion-weighted imaging, and clinical assessment. The participants were divided into lower (MS-L, n = 57) and higher disability (MS-H, n = 61) subgroups. Brain parenchymal fraction (BPF), lesion load (LL), and DTI-ALPS index were measured. Subgroup differences and correlations between DTI-ALPS index and other measures were explored. Logistic regression was performed to evaluate BPF, LL, and DTI-ALPS index in classifying lower and higher disability patients.

RESULTS

Significant differences in DTI-ALPS index between MS-H and MS-L (d = -0.71, false discovery rate-corrected p-value (p-FDR) = 0.001) were found. The DTI-ALPS index correlated significantly with disease duration (rp = -0.29, p-FDR = 0.002) and EDSS (rsp = -0.35, p-FDR = 0.0002). It also showed significant correlations with BPF and LL. DTI-ALPS index and LL were significant predictors of disability subgroup (DTI-ALPS: odds ratio (OR) = 1.77, p = 0.04, LL: OR = 0.94, p = 0.02).

CONCLUSION

Our findings highlight DTI-ALPS index as an imaging biomarker in MS, suggesting the involvement of glymphatic impairment in MS pathology, although further research is needed to elucidate its role in contributing to MS-related disability.

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.

Cerebral small vessel disease and glymphatic system dysfunction in multiple sclerosis: A narrative review

As the multiple sclerosis (MS) population ages, the prevalence of vascular comorbidities increases, potentially accelerating disease progression and brain atrophy. Recent studies highlight the prevalence of cerebral small vessel disease (CSVD) in MS, suggesting a potential link between vascular comorbidities and accelerated disability. CSVD affects the brain's small vessels, often leading to identifiable markers on MRI such as enlarged perivascular spaces (EPVS). EPVS are increasingly recognized also in MS and have been associated with vascular comorbidities, lower percentage of MS-specific perivenular lesions, brain atrophy and aging. The exact sequence of event leading to MRI visible EPVS is yet to be determined, but an impaired perivascular brain fluid drainage appears a possible physiopathological explanation for EPVS in both CSVD and MS. In this context, a dysfunction of the brain fluid clearance system - also known as "glymphatic system" - appears associated in MS to aging, neuroinflammation, and vascular dysfunction. Advanced imaging techniques show an impaired glymphatic function in both MS and CSVD. Additionally, lifestyle factors such as physical exercise, diet, and sleep quality appear to influence glymphatic function, potentially revealing novel therapeutic strategies to mitigate microangiopathy and neuroinflammation in MS. This review underscores the potential role of glymphatic dysfunction in the complex and not-yet elucidated interplay between neuroinflammation and CSVD in MS.

Decreased diffusivity along the perivascular space and cerebral hemodynamic disturbance in adult moyamoya disease

Moyamoya disease (MMD) causes cerebral arterial stenosis and hemodynamic disturbance, the latter of which may disrupt glymphatic system activity, the waste clearance system. We evaluated 46 adult patients with MMD and 33 age- and sex-matched controls using diffusivity along the perivascular space (ALPS) measured with diffusion tensor imaging (ALPS index), which may partly reflect glymphatic system activity, and multishell diffusion MRI to generate freewater maps. Twenty-three patients were also evaluated via 15O-gas positron emission tomography (PET), and all patients underwent cognitive tests. Compared to controls, patients (38.4 (13.2) years old, 35 females) had lower ALPS indices in the left and right hemispheres (1.94 (0.27) vs. 1.65 (0.25) and 1.94 (0.22) vs. 1.65 (0.19), P < 0.001). While the right ALPS index showed no correlation, the left ALPS index was correlated with parenchymal freewater (ρ = -0.47, P < 0.001); perfusion measured with PET (cerebral blood flow, ρ = 0.70, P < 0.001; mean transit time, ρ = -0.60, P = 0.003; and oxygen extraction fraction, ρ = -0.52, P = 0.003); and cognitive tests (trail making test part B for executive function; ρ = -0.37, P = 0.01). Adult patients with MMD may exhibit decreased glymphatic system activity, which is correlated with the degree of hemodynamic disturbance, increased interstitial freewater, and cognitive dysfunction, but further investigation is needed.

Early detection of dopaminergic dysfunction and glymphatic system impairment in Parkinson's disease

PURPOSE

This study aimed to assess the glymphatic function and its correlation with clinical characteristics and the loss of dopaminergic neurons in Parkinson's disease (PD) using hybrid positron emission tomography (PET)-magnetic resonance imaging (MRI) combined with diffusion tensor image analysis along the perivascular space (DTI-ALPS), choroid plexus volume (CPV), and enlarged perivascular space (EPVS) volume.

METHODS

Twenty-five PD patients and thirty matched healthy controls (HC) participated in the study. All participants underwent 18F-fluorodopa (18F-DOPA) PET-MRI scanning. The striatal standardized uptake value ratio (SUVR), DTI-ALPS index, CPV, and EPVS volume were calculated. Furthermore, we also analysed the relationship between the DTI-ALPS index, CPV, EPVS volume and striatal SUVR as well as clinical characteristics of PD patients.

RESULTS

PD patients demonstrated significantly lower values in DTI-ALPS (t = 3.053, p = 0.004) and larger CPV (t = 2.743, p = 0.008) and EPVS volume (t = 2.807, p = 0.008) compared to HC. In PD group, the ALPS-index was negatively correlated with the Unified Parkinson's Disease Rating Scale III (UPDRS-III) scores (r = -0.730, p < 0.001), and positively correlated with the mean putaminal SUVR (r = 0.560, p = 0.007) and mean caudal SUVR (r = 0.459, p = 0.032). Moreover, the mean putaminal SUVR was negatively associated with the UPDRS-III scores (r = -0.544, p = 0.009).

CONCLUSION

DTI-ALPS has the potential to uncover glymphatic dysfunction in patients with PD, with this dysfunction correlating strongly with the severity of disease, together with the mean putaminal and caudal SUVR. PET- MRI can serve as a potential multimodal imaging biomarker for early-stage PD.

The Glymphatic System and its Relationship to Migraine

PURPOSE OF REVIEW

We aim to critically review animal and human studies of the glymphatic system in migraine and propose a model for how the glymphatic system may function in migraine, based on the available evidence.

RECENT FINDINGS

Early studies in animal models report migraine attacks temporarily disrupt glymphatic flow. Human imaging studies suggest chronic migraine may be associated with alterations in glymphatic system function, albeit with conflicting results. Presently, it remains unknown whether repetitive migraine attacks or frequent nights of insomnia impair glymphatic system function over time in those with migraine, and whether alterations in glymphatic function could contribute to worsening migraine disability or risk for cognitive disease. Longitudinal studies of glymphatic function in patients with migraine and insomnia, with inclusion of cognitive assessments, may be informative.

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.

Glymphatic system dysfunction in mood disorders: Evaluation by diffusion magnetic resonance imaging

The glymphatic system, an expansive cerebral waste-disposal network, harbors myriad enigmatic facets necessitating elucidation of their nexus with diverse pathologies. Murine investigations have revealed a relationship between the glymphatic system and affective disorders. This study aimed to illuminate the interplay between bipolar disorder and the glymphatic system. Fifty-eight individuals afflicted with bipolar disorder were identified through meticulous psychiatric assessment. These individuals were juxtaposed with a cohort of 66 comparably aged and sex-matched, mentally stable subjects. Subsequent analysis entailed the application of covariance analysis to evaluate along with the perivascular space (ALPS) index, a novel magnetic resonance imaging method for assessing brain interstitial fluid dynamics via diffusion tensor imaging within the bipolar and control cohorts. We also evaluated the correlation between the ALPS index and clinical parameters, which included the Hamilton Depression scale scores, disease duration, and other clinical assessments. Moreover, partial correlation analyses, incorporating age and sex as covariates, were performed to investigate the relationships between the ALPS index and clinical measures within the two cohorts. A noteworthy adverse correlation was observed between the ALPS index and illness duration. A free-water imaging analysis revealed a substantial elevation in the free-water index within the white-matter tracts, prominently centered on the corpus callosum, within the bipolar cohort relative to that in the control group. In analogous cerebral regions, a conspicuous affirmative correlation was observed between the free-water-corrected radial diffusivity and depression rating scales. Our results showed that the protracted course of bipolar disorder concomitantly exacerbated glymphatic system dysregulation.

Early Improvement in Interstitial Fluid Flow in Patients With Severe Carotid Stenosis After Angioplasty and Stenting

BACKGROUND AND PURPOSE

This study aimed to investigate early changes in interstitial fluid (ISF) flow in patients with severe carotid stenosis after carotid angioplasty and stenting (CAS).

METHODS

We prospectively recruited participants with carotid stenosis ≥80% undergoing CAS at our institute between October 2019 and March 2023. Magnetic resonance imaging (MRI), including diffusion tensor imaging (DTI), and the Mini-Mental State Examination (MMSE) were performed 3 days before CAS. MRI with DTI and MMSE were conducted within 24 hours and 2 months after CAS, respectively. The diffusion tensor image analysis along the perivascular space (DTI-ALPS) index was calculated from the DTI data to determine the ISF status. Increments were defined as the ratio of the difference between post- and preprocedural values to preprocedural values.

RESULTS

In total, 102 participants (age: 67.1±8.9 years; stenosis: 89.5%±5.7%) with longitudinal data were evaluated. The DTI-ALPS index increased after CAS (0.85±0.15; 0.85 [0.22] vs. 0.86±0.14; 0.86 [0.21]; P=0.022), as did the MMSE score (25.9±3.7; 24.0 [4.0] vs. 26.9±3.4; 26.0 [3.0]; P<0.001). Positive correlations between increments in the DTI-ALPS index and MMSE score were found in all patients (rs=0.468; P<0.001).

CONCLUSION

An increased 24-hour post-CAS DTI-ALPS index suggests early improvement in ISF flow efficiency. The positive correlation between the 24-hour DTI-ALPS index and 2-month MMSE score increments suggests that early ISF flow improvement may contribute to long-term cognitive improvement after CAS.

Correlation between glymphatic dysfunction and cranial defect in severe traumatic brain injury: a retrospective case-control study based on a diffusion tensor image analysis along the perivascular space (DTI-ALPS) investigation

Background

To date, limited research has been conducted on the functionality of the glymphatic system during the recovery phase of severe traumatic brain injury (sTBI). This study aimed to use a diffusion tensor image analysis along the perivascular space (DTI-ALPS) to evaluate glymphatic system function in patients recovering from sTBI who underwent unilateral decompressive craniectomy, and to examine the correlation between the ALPS index and the size of the cranial defect. We hypothesized that assessments would reveal ongoing impairments in glymphatic system function among sTBI patients during the recovery phase.

Methods

A total of 23 patients with a history of sTBI who had previously undergone unilateral decompressive craniectomy at Xiangya Hospital of Central South University from January 2020 to December 2020 were enrolled in the study, along with 33 healthy control (HC) subjects. All the subjects underwent magnetic resonance imaging (MRI) with DTI scans, and the ALPS index was subsequently calculated to assess glymphatic system functionality. Additionally, the circumference and sectional area of the cranial defect were measured for each patient. An analysis of variance (ANOVA) was used to compare the ALPS index values between the sTBI patients and HC subjects, while a Pearson correlation analysis was used to examine the correlation between the ALPS index and cranial defect characteristics.

Results

The ALPS index values of both the craniectomy side (t=-9.08, P<0.001) and non-craniectomy side (t=-5.06, P<0.001) of the sTBI group were significantly lower than those of the HC group. However, no statistically significant differences were observed between the ALPS index values of the craniectomy and non-craniectomy sides. Additionally, no significant differences were observed in the ALPS index values of both the craniectomy and non-craniectomy sides among the early, intermediate, and late recovery phases. In the sTBI patients, a moderately strong negative correlation was found between the circumference of the cranial defect and the ALPS index of the craniectomy side (r=-0.62, P=0.002), and a moderately negative correlation was found between the sectional area of the cranial defect and the ALPS index of the craniectomy side (r=-0.56, P=0.005).

Conclusions

The non-invasive DTI-ALPS technique revealed significantly reduced ALPS index values during the recovery phase of sTBI, indicating persistent impairment in glymphatic system function. A significant negative correlation was found between the ALPS index value of the craniectomy side and the size of the cranial defect. These findings suggest that the ALPS index may serve as a valuable prognostic factor in the recovery phase of sTBI.

Diffusion Tensor Imaging-Along the Perivascular-Space Index Is Associated with Disease Progression in Parkinson's Disease

BACKGROUND

The glymphatic clearance pathway is a waste clearance system that allows for removal of soluble proteins such as amyloid β (Aβ) from the brain. Higher Aβ levels are associated with cognitive dysfunction in Parkinson's disease (PD). Diffusion tensor imaging-along the perivascular space (DTI-ALPS) is an imaging measure proposed to indirectly measure glymphatic function.

OBJECTIVES

Evaluate differences in DTI-ALPS-index between PD and healthy controls (HC) and characterize relationships between this proposed measure of glymphatic clearance, cognition, and disease severity in PD.

METHODS

PD (n = 32) and HC (n = 23) participants underwent brain imaging to assess DTI-ALPS. PD participants were classified as PD-normal cognition (PD-NC; n = 20) or PD-mild cognitive impairment (PD-MCI; n = 12) based on a Level II comprehensive cognitive assessment. A subgroup of PD participants (n = 21) returned for annual assessments for up to 4 years after baseline. Longitudinal outcomes included changes in performance on the comprehensive cognitive assessment and changes in the Movement Disorders Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS).

RESULTS

PD participants had lower DTI-ALPS-index compared to HC. PD participants classified as PD-MCI had significantly lower DTI-ALPS-index compared to PD-NC. Lower DTI-ALPS-index at baseline was associated with longitudinal cognitive decline and worse longitudinal disease severity.

CONCLUSIONS

Glymphatic clearance, as measured with DTI-ALPS, has potential to serve as a marker of longitudinal disease progression. Interventions targeting glymphatic function should be explored for potential to slow cognitive decline in PD. © 2024 International Parkinson and Movement Disorder Society.

Glymphatic function assessment with diffusion tensor imaging along the perivascular space in patients with major depressive disorder and its relation to cerebral white-matter alteration

Background

The link between glymphatic system function in the brain and alterations in white-matter microstructure among individuals with major depressive disorder (MDD) remains unclear. This study aimed to examine the assessment of glymphatic system function in patients with MDD using the diffusion tensor imaging along the perivascular space (DTI-ALPS) index and to evaluate its association with cerebral-white-matter abnormalities and neuropsychological scores.

Methods

From February 2023 to November 2023, this cross-sectional study recruited 35 patients with MDD from the Psychosomatic Diseases Department of the First Affiliated Hospital of Dalian Medical University. In this time period, 23 healthy controls (HCs) were enlisted from the community and matched with the MDD cohort in terms of years of education, gender, and age. All participants underwent magnetic resonance imaging, depression, anxiety, and cognitive assessments. The tract-based spatial statistics (TBSS) analyzed DTI parameters and identified significant clusters. Automated fiber quantification (AFQ) was used to automatically identify fiber bundles with statistical differences. Mann-Whitney tests or two-sample t-tests were used for comparisons. Interobserver consistency of the DTI-ALPS measurements was evaluated using the interclass correlation coefficient (ICC). Partial correlation analyses and linear regression analyses were used to examine relationships. A comparison of the DTI-ALPS index was made between the two groups. Correlations among diffusion characteristics, neuropsychological scores, and the DTI-ALPS index were analyzed.

Results

Compared to HCs, patients with MDD exhibited a lower DTI-ALPS score (P=0.001). According to using linear regression analysis, the ALPS index was found to be an independent predictor of the Hamilton Depression Rating Scale [B=-25.32; P=0.001; 95% confidence interval (CI): -40.35 to -11.55], Hamilton Anxiety Rating Scale (B=-33.48; P=0.003; 95% CI: -55.38 to -11.24), and Montreal Cognitive Assessment total score (B=8.59; P=0.008; 95% CI: 2.38 to 14.79). According to the TBSS analysis, there were clusters of increased axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) in patients with MDD as compared to HCs (all P values <0.05). A lower DTI-ALPS score was correlated with higher AD (r=-0.592; P<0.001), MD (cluster 1: r=-0.567, P=0.001; cluster 2: r=-0.581, P<0.001), and RD (r=-0.491; P=0.004) values. AFQ analysis identified the significantly different diffusion indicators in the left cingulum bundle (CB_L), left inferior longitudinal fasciculus (ILF_L), and left uncinate fasciculus (UF_L) between the two groups (all false discovery rate P values <0.05). DTI-ALPS score was negatively correlated with the AD value of CB_L (r=-0.304; P=0.024), ILF_L (r=-0.35; P=0.008), and UF_L (r=-0.354; P=0.008) in AFQ tract-level analysis. In point-wise analysis, the MD value of CB_L at nodes 33 to 36 was negatively correlated with DTI-ALPS score (r ranging from -0.504 to -0.535; P<0.01).

Conclusions

Our results indicated a decrease in DTI-ALPS index score in patients with MDD. DTI-ALPS score was associated with depression, anxiety, declined cognitive ability, and white-matter microstructural abnormalities and may thus be a promising biomarker for the partial evaluation of glymphatic system function in patients with MDD.

Glymphatic System Dysfunction Underlying Schizophrenia Is Associated With Cognitive Impairment

BACKGROUND AND HYPOTHESIS

Despite the well-documented structural and functional brain changes in schizophrenia, the potential role of glymphatic dysfunction remains largely unexplored. This study investigates the glymphatic system's function in schizophrenia, utilizing diffusion tensor imaging (DTI) to analyze water diffusion along the perivascular space (ALPS), and examines its correlation with clinical symptoms.

STUDY DESIGN

A cohort consisting of 43 people with schizophrenia and 108 healthy controls was examined. We quantified water diffusion metrics along the x-, y-, and z-axis in both projection and association fibers to derive the DTI-ALPS index, a proxy for glymphatic activity. The differences in the ALPS index between groups were analyzed using a 2-way ANCOVA controlling for age and sex, while partial correlations assessed the association between the ALPS index and clinical variables.

STUDY RESULTS

People with schizophrenia showed a significantly reduced DTI-ALPS index across the whole brain and within both hemispheres (F = 9.001, P = .011; F = 10.024, P = .011; F = 5.927, P = .044; false discovery rate corrected), indicating potential glymphatic dysfunction in schizophrenia. The group by cognitive performance interaction effects on the ALPS index were not observed. Moreover, a lower ALPS index was associated with poorer cognitive performance on specific neuropsychological tests in people with schizophrenia.

CONCLUSION

Our study highlights a lower ALPS index in schizophrenia, correlated with more pronounced cognitive impairments. This suggests that glymphatic dysfunction may contribute to the pathophysiology of schizophrenia, offering new insights into its underlying mechanisms.

A "glympse" into neurodegeneration: Diffusion MRI and cerebrospinal fluid aquaporin-4 for the assessment of glymphatic system in Alzheimer's disease and other dementias

The glymphatic system (GS) is a whole-brain perivascular network, consisting of three compartments: the periarterial and perivenous spaces and the interposed brain parenchyma. GS dysfunction has been implicated in neurodegenerative diseases, particularly Alzheimer's disease (AD). So far, comprehensive research on GS in humans has been limited by the absence of easily accessible biomarkers. Recently, promising non-invasive methods based on magnetic resonance imaging (MRI) along with aquaporin-4 (AQP4) quantification in the cerebrospinal fluid (CSF) were introduced for an indirect assessment of each of the three GS compartments. We recruited 111 consecutive subjects presenting with symptoms suggestive of degenerative cognitive decline, who underwent 3 T MRI scanning including multi-shell diffusion-weighted images. Forty nine out of 111 also underwent CSF examination with quantification of CSF-AQP4. CSF-AQP4 levels and MRI measures-including perivascular spaces (PVS) counts and volume fraction (PVSVF), white matter free water fraction (FW-WM) and mean kurtosis (MK-WM), diffusion tensor imaging analysis along the perivascular spaces (DTI-ALPS) (mean, left and right)-were compared among patients with AD (n = 47) and other neurodegenerative diseases (nAD = 24), patients with stable mild cognitive impairment (MCI = 17) and cognitively unimpaired (CU = 23) elderly people. Two runs of analysis were conducted, the first including all patients; the second after dividing both nAD and AD patients into two subgroups based on gray matter atrophy as a proxy of disease stage. Age, sex, years of education, and scanning time were included as confounding factors in the analyses. Considering the whole cohort, patients with AD showed significantly higher levels of CSF-AQP4 (exp(b) = 2.05, p = .005) and FW-WM FW-WM (exp(b) = 1.06, p = .043) than CU. AQP4 levels were also significantly higher in nAD in respect to CU (exp(b) = 2.98, p < .001). CSF-AQP4 and FW-WM were significantly higher in both less atrophic AD (exp(b) = 2.20, p = .006; exp(b) = 1.08, p = .019, respectively) and nAD patients (exp(b) = 2.66, p = .002; exp(b) = 1.10, p = .019, respectively) compared to CU subjects. Higher total (exp(b) = 1.59, p = .013) and centrum semiovale PVS counts (exp(b) = 1.89, p = .016), total (exp(b) = 1.50, p = .036) and WM PVSVF (exp(b) = 1.89, p = .005) together with lower MK-WM (exp(b) = 0.94, p = .006), mean and left ALPS (exp(b) = 0.91, p = .043; exp(b) = 0.88, p = .010 respectively) were observed in more atrophic AD patients in respect to CU. In addition, more atrophic nAD patients exhibited higher levels of AQP4 (exp(b) = 3.39, p = .002) than CU. Our results indicate significant changes in putative MRI biomarkers of GS and CSF-AQP4 levels in AD and in other neurodegenerative dementias, suggesting a close interaction between glymphatic dysfunction and neurodegeneration, particularly in the case of AD. However, the usefulness of some of these biomarkers as indirect and standalone indices of glymphatic activity may be hindered by their dependence on disease stage and structural brain damage.

Automated diffusion-weighted image analysis along the perivascular space index reveals glymphatic dysfunction in association with brain parenchymal lesions

Brain glymphatic dysfunction is critical in neurodegenerative processes. While animal studies have provided substantial insights, understandings in humans remains limited. Recent attention has focused on the non-invasive evaluation of brain glymphatic function. However, its association with brain parenchymal lesions in large-scale population remains under-investigated. In this cross-sectional analysis of 1030 participants (57.14 ± 9.34 years, 37.18% males) from the Shunyi cohort, we developed an automated pipeline to calculate diffusion-weighted image analysis along the perivascular space (ALPS), with a lower ALPS value indicating worse glymphatic function. The automated ALPS showed high consistency with the manual calculation of this index (ICC = 0.81, 95% CI: 0.662-0.898). We found that those with older age and male sex had lower automated ALPS values (β = -0.051, SE = 0.004, p < .001, per 10 years, and β = -0.036, SE = 0.008, p < .001, respectively). White matter hyperintensity (β = -2.458, SE = 0.175, p < .001) and presence of lacunes (OR = 0.004, 95% CI < 0.002-0.016, p < .001) were significantly correlated with decreased ALPS. The brain parenchymal and hippocampal fractions were significantly associated with decreased ALPS (β = 0.067, SE = 0.007, p < .001 and β = 0.040, SE = 0.014, p = .006, respectively) independent of white matter hyperintensity. Our research implies that the automated ALPS index is potentially a valuable imaging marker for the glymphatic system, deepening our understanding of glymphatic dysfunction.

Cross-Vendor Test-Retest Validation of Diffusion Tensor Image Analysis along the Perivascular Space (DTI-ALPS) for Evaluating Glymphatic System Function

The diffusion tensor image analysis along the perivascular space (DTI-ALPS) method was proposed to evaluate glymphatic system (GS) function. However, few studies have validated its reliability and reproducibility. Fifty participants' DTI data from the MarkVCID consortium were included in this study. Two pipelines by using DSI studio and FSL software were developed for data processing and ALPS index calculation. The ALPS index was obtained by the average of bilateral ALPS index and was used for testing the cross-vendor, inter-rater and test-retest reliability by using R studio software. The ALPS index demonstrated favorable inter-scanner reproducibility (ICC=0.77 to 0.95, P< 0.001), inter-rater reliability (ICC=0.96 to 1, P< 0.001) and test-retest repeatability (ICC=0.89 to 0.95, P< 0.001), offering a potential biomarker for in vivo evaluation of GS function.