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

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.

Neurologic symptoms as a hallmark of glymphatic alteration in recovered patients with COVID-19

BACKGROUND

The glymphatic system is a glial-based perivascular network that facilitates the clearance of metabolic waste from the brain. Dysfunction of the glymphatic system, along with neurological symptoms such as cognitive deficits and olfactory dysfunction, has been reported in patients with coronavirus disease (COVID-19). However, the link between these neurological symptoms and alterations in the glymphatic system remains unclear. In this study, we aimed to evaluate magnetic resonance imaging (MRI)-based measures of the glymphatic system in patients recovered from COVID-19 with and without neurological symptoms.

METHODS

This study included 89 patients who recovered from respiratory infections, of whom 71 had confirmed COVID-19 (20 experienced anosmia and 41 had cognitive symptoms). Three MRI-based measures were quantified and compared: the dilated perivascular spaces (dPVS), free water (FW) fraction, and diffusion tensor image analysis along the perivascular spaces (DTI-ALPS). A partial correlation network was used to assess the relationships between COVID-19 infection, neurological symptoms, and glymphatic measures.

RESULTS

COVID-19 patients with anosmia had increased FW in the left orbitofrontal area compared to those without anosmia (mean difference: 0.01, p = 0.48), while patients with cognitive symptoms showed decreased left-sided DTI-ALPS (mean difference: 0.06, p = 0.40). Neurological symptoms mediate the relationship between COVID-19 and glymphatic system measures.

CONCLUSIONS

Our findings imply that neurological symptoms accompanied by COVID-19 are linked to distinct alterations in the glymphatic system, suggesting a potential association between neuroinvasion and neuroinflammatory processes related to COVID-19.

Assessing neonatal brain glymphatic system development using diffusion tensor imaging along the perivascular space and choroid plexus volume

PURPOSE

Neonatal brain development constitutes a critical period of structural and functional maturation underpinning sensory, motor, and cognitive capacities. The glymphatic system-a cerebral waste clearance network-remains poorly understood in neonates. We investigated non-invasive magnetic resonance imaging (MRI) biomarkers of glymphatic system and their developmental correlates in neonates.

METHODS

In 117 neonates undergoing high-resolution T1-weighted and diffusion MRI, we quantified two glymphatic metrics: (1) diffusion tensor imaging along the perivascular space (DTI-ALPS) index, reflecting perivascular fluid dynamics; (2) choroid plexus (CP) volume, a cerebrospinal fluid (CSF) production marker. Associations with postmenstrual age (PMA) at MRI scan, gestational age (GA), birth weight (BW), and sex were analyzed using covariate-adjusted models.

RESULTS

Preterm neonates displayed significantly reduced DTI-ALPS indices versus term neonates (total index: 1.01 vs. 1.05, P = 0.002), with reductions persisting after adjustment (P < 0.05). CP volumes showed right-dominant pre-adjustment differences (preterm: 0.33 vs. term: 0.39, P = 0.039) that attenuated post-adjustment (P = 0.348). DTI-ALPS indices demonstrated transient correlations with PMA/GA/BW in unadjusted analyses (P < 0.05), whereas CP volumes maintained robust PMA associations post-adjustment in all neonates (P = 0.037) and term subgroup (P = 0.013). No significant effects of sex on both metrics were observed.

CONCLUSION

Our findings reveal prematurity-associated delays in glymphatic maturation, rather than biological sex. The persistent PMA-CP volume relationship suggests developmental regulation of CSF production, while attenuated DTI-ALPS correlations highlight covariate-mediated effects. These glymphatic metrics show potential for monitoring neurodevelopmental trajectories, though longitudinal validation is required to establish their clinical utility in neonatal care.

CLINICAL TRIAL NUMBER

Not applicable.

Multimodal MRI analysis of COVID-19 effects on pediatric brain

The COVID-19 pandemic has raised significant concerns regarding its impact on the central nervous system, including the brain. While the effects on adult populations are well documented, less is known about its implications for pediatric populations. This study investigates alterations in cortical metrics and structural covariance networks (SCNs) based on the Local Gyrification Index (LGI) in children with mild COVID-19, alongside changes in non-invasive MRI proxies related to glymphatic function. We enrolled 19 children with COVID-19 and 22 age-comparable healthy controls. High-resolution T1-weighted and diffusion-weighted MRI images were acquired. Cortical metrics, including thickness, surface area, volume, and LGI, were compared using vertex-wise general linear models. SCNs were analyzed for differences in global and nodal metrics, and MRI proxies, including diffusion tensor imaging along the perivascular space and choroid plexus (CP) volume, were also assessed. Our results showed increased cortical area, volume, and LGI in the left superior parietal cortex, as well as increased cortical thickness in the left lateral occipital cortex among children with COVID-19. SCN analysis revealed altered network topology and larger CP volumes in the COVID group, suggesting virus-induced neuroinflammation. These findings provide evidence of potential brain alterations in children following mild COVID-19, emphasizing the need for further investigation into long-term neurodevelopmental outcomes.

COVID-19 may Enduringly Impact Cognitive Performance and Brain Haemodynamics in Undergraduate Students

To date, 770 million people worldwide have contracted COVID-19, with many reporting long-term "brain fog". Concerningly, young adults are both overrepresented in COVID-19 infection rates and may be especially vulnerable to prolonged cognitive impairments following infection. This calls for focused research on this population to better understand the mechanisms underlying cognitive impairment post-COVID-19. Addressing gaps in the literature, the current study investigated differences in neuropsychological performance and cerebral haemodynamic activity following COVID-19 infection in undergraduate students. 94 undergraduates (age in years: M = 20.58, SD = 3.33, range = 18 to 46; 89 % female) at the University of Otago reported their COVID-19 infection history before completing a neuropsychological battery while wearing a multichannel near-infrared spectroscopy (NIRS) device to record prefrontal haemodynamics. We observed that 40 % retrospectively self-reported cognitive impairment (brain fog) due to COVID-19 and 37 % exhibited objective evidence of cognitive impairment (assessed via computerised testing), with some suggestion that executive functioning may have been particularly affected; however, group-level analyses indicated preserved cognitive performance post COVID-19, which may in part reflect varying compensatory abilities. The NIRS data revealed novel evidence that previously infected students exhibited distinct prefrontal haemodynamic patterns during cognitive engagement, reminiscent of those observed in adults four decades older, and this appeared to be especially true if they reported experiencing brain fog due to COVID-19. These results provide new insights into the potential neuropathogenic mechanisms influencing cognitive impairment following COVID-19.

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.

Choroid plexus volume is enlarged in long COVID and associated with cognitive and brain changes

Patients with post-COVID condition (PCC) present with diverse symptoms which persist at long-term after SARS-CoV-2 infection. Among these symptoms, cognitive impairment is one of the most prevalent and has been related to brain structural and functional changes. The underlying mechanisms of these cognitive and brain alterations remain elusive but neuroinflammation and immune mechanisms have been majorly considered. In this sense, the choroid plexus (ChP) volume has been proposed as a marker of neuroinflammation in immune-mediated conditions and the ChP epithelium has been found particularly susceptible to the effects of SARS-CoV-2. The objective was to investigate the ChP in PCC and evaluate its relationships with cognition, brain, and immunological alterations. One-hundred and twenty-nine patients with PCC after a mean of 14.79 ± 7.17 months of evolution since the infection and 36 healthy controls were recruited. Participants underwent a neuropsychological, and neuroimaging assessment and immunological markers evaluation. Results revealed ChP volume enlargement in PCC compared to healthy controls. The ChP enlargement was associated with cognitive dysfunction, grey matter volume reduction in frontal and subcortical areas, white matter integrity and diffusivity changes and functional connectivity changes. These ChP changes were also related to intermediate monocytes levels. Findings suggest that the ChP integrity may play a relevant role in the pathophysiology of cognitive deficits and the observed brain changes in PCC. The previously documented function of the ChP in maintaining brain homeostasis and regulating the entry of immune cells into the brain supports the presence of neuroinflammatory mechanisms in this disorder.

Neuroinflammation at the Dorsolateral Inferior Medulla: A Possible Central Nervous System Localization for POTS and Long COVID

Both postural orthostatic tachycardia syndrome (POTS) and Long COVID are currently viewed as heterogeneous disorders with complex, multi-factorial and multi-systemic pathophysiology. POTS, one of the most common autonomic disorders, is a frequent sequela of SARS-CoV-2 infection. Both POTS and autonomic dysfunction, in general, are major pathophysiologic mechanisms of Long COVID. There is emerging evidence that neuroinflammation of the brainstem may be one of the mechanisms of POTS and Long COVID. This commentary argues that neuroinflammation at the dorsolateral inferior medulla is a possible central nervous system localization for POTS and Long COVID based on the limited scientific literature available to date and the neurologic manifestations of both disorders. Further studies involving advanced neuroimaging techniques and animal models with immunohistochemical brainstem tissue assessments are needed to understand how and why possible neuroinflammation at the dorsolateral inferior medulla may occur in patients with Long COVID, POTS and other disorders involving autonomic dysfunction.

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.

Neuropsychiatric Manifestations of COVID-19 Disease and Post COVID Syndrome: The Role of N-acetylcysteine and Acetyl-L-carnitine

COVID-19 is associated with neuropsychiatric symptoms, such as anosmia, anxiety, depression, stress-related reactions, and psychoses. The illness can cause persistent cognitive impairment and "brain fog", suggesting chronic brain involvement. Clinical entities of ongoing symptomatic COVID-19 and Post COVID Syndrome (PCS) mainly present neuropsychiatric symptoms such as dysgeusia, headache, fatigue, anxiety, depression, sleep disturbances, and post-traumatic stress disorder. The pathophysiology of COVID-19-related brain damage is unclear, but it is linked to various mechanisms such as inflammation, oxidative stress, immune dysregulation, impaired glutamate homeostasis, glial and glymphatic damage, and hippocampal degeneration. Noteworthy is that the metabotropic receptor mGluR2 was discovered as a mechanism of internalisation of SARS-CoV-2 in Central Nervous System (CNS) cells. N-acetylcysteine (NAC) and acetyl-L-carnitine (ALC) are two supplements that have already been found effective in treating psychiatric conditions. Furthermore, NAC showed evidence in relieving cognitive symptomatology in PCS, and ALC was found effective in treating depressive symptomatology of PCS. The overlapping effects on the glutamatergic system of ALC and NAC could help treat COVID-19 psychiatric symptoms and PCS, acting through different mechanisms on the xc-mGluR2 network, with potentially synergistic effects on chronic pain and neuro-astrocyte protection. This paper aims to summarise the current evidence on the potential therapeutic role of NAC and ALC, providing an overview of the underlying molecular mechanisms and pathophysiology. It proposes a pathophysiological model explaining the effectiveness of NAC and ALC in treating COVID-19-related neuropsychiatric symptoms.

Long COVID Is Not a Functional Neurologic Disorder

Long COVID is a common sequela of SARS-CoV-2 infection. Data from numerous scientific studies indicate that long COVID involves a complex interaction between pathophysiological processes. Long COVID may involve the development of new diagnosable health conditions and exacerbation of pre-existing health conditions. However, despite this rapidly accumulating body of evidence regarding the pathobiology of long COVID, psychogenic and functional interpretations of the illness presentation continue to be endorsed by some healthcare professionals, creating confusion and inappropriate diagnostic and therapeutic pathways for people living with long COVID. The purpose of this perspective is to present a clinical and scientific rationale for why long COVID should not be considered as a functional neurologic disorder. It will begin by discussing the parallel historical development of pathobiological and psychosomatic/sociogenic diagnostic constructs arising from a common root in neurasthenia, which has resulted in the collective understandings of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and functional neurologic disorder (FND), respectively. We will also review the case definition criteria for FND and the distinguishing clinical and neuroimaging findings in FND vs. long COVID. We conclude that considering long COVID as FND is inappropriate based on differentiating pathophysiologic mechanisms and distinguishing clinical findings.

A perspective on the evidence for glymphatic obstruction in spaceflight associated neuro-ocular syndrome and fatigue

Spaceflight associated neuro-ocular syndrome (SANS) alters the vision of astronauts during long-duration spaceflights. Previously, the current authors have discussed the similarities and differences between SANS and idiopathic intracranial hypertension to try to elucidate a possible pathophysiology. Recently, a theory has been advanced that SANS may occur secondary to failure of the glymphatic system caused by venous dilatation within the brain and optic nerves. There is recent evidence to suggest glymphatic obstruction occurs in childhood hydrocephalus, multiple sclerosis and syringomyelia due to venous outflow dilatation similar to that proposed in SANS. The purpose of the current paper is to discuss the similarities and differences between the known CSF and venous pathophysiology in SANS with these other terrestrial diseases, to see if they can shed any further light on the underlying cause of this microgravity-induced disease.