Cerebrospinal fluid in COVID-19 neurological complications: Neuroaxonal damage, anti-SARS-Cov2 antibodies but no evidence of cytokine storm

Neurological Complications of COVID-19: Unraveling the Pathophysiological Underpinnings and Therapeutic Implications

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease (COVID-19), induced a global pandemic with a diverse array of clinical manifestations. While the acute phase of the pandemic may be waning, the intricacies of COVID-19's impact on neurological health remain a crucial area of investigation. Early recognition of the spectrum of COVID-19 symptoms, ranging from mild fever and cough to life-threatening respiratory distress and multi-organ failure, underscored the significance of neurological complications, including anosmia, seizures, stroke, disorientation, encephalopathy, and paralysis. Notably, patients requiring intensive care unit (ICU) admission due to neurological challenges or due to them exhibiting neurological abnormalities in the ICU have shown increased mortality rates. COVID-19 can lead to a range of neurological complications such as anosmia, stroke, paralysis, cranial nerve deficits, encephalopathy, delirium, meningitis, seizures, etc., in affected patients. This review elucidates the burgeoning landscape of neurological sequelae associated with SARS-CoV-2 infection and explores the underlying neurobiological mechanisms driving these diverse manifestations. A meticulous examination of potential neuroinvasion routes by SARS-CoV-2 underscores the intricate interplay between the virus and the nervous system. Moreover, we dissect the diverse neurological manifestations emphasizing the necessity of a multifaceted approach to understanding the disease's neurological footprint. In addition to elucidating the pathophysiological underpinnings, this review surveys current therapeutic modalities and delineates prospective avenues for neuro-COVID research. By integrating epidemiological, clinical, and diagnostic parameters, we endeavor to foster a comprehensive analysis of the nexus between COVID-19 and neurological health, thereby laying the groundwork for targeted therapeutic interventions and long-term management strategies.

Headaches and facial pain attributed to SARS-CoV-2 infection and vaccination: a systematic review

BACKGROUND AND PURPOSE

The aim was to provide insights to the characteristics of headache in the context of COVID-19 on behalf of the Headache Scientific Panel and the Neuro-COVID-19 Task Force of the European Academy of Neurology (EAN) and the European Headache Federation (EHF).

METHODS

Following the Delphi method the Task Force identified six relevant questions and then conducted a systematic literature review to provide evidence-based answers and suggest specific diagnostic criteria.

RESULTS

No data for facial pain were identified in the literature search. (1) Headache incidence during acute COVID-19 varies considerably, with higher prevalence rates in prospective compared to retrospective studies (28.9%-74.6% vs. 6.5%-34.0%). (2) Acute COVID-19 headache is usually bilateral or holocranial and often moderate to severe with throbbing pain quality lasting 2-14 days after first signs of COVID-19; photo-phonophobia, nausea, anosmia and ageusia are common associated features; persistent headache shares similar clinical characteristics. (3) Acute COVID-19 headache is presumably caused by immune-mediated mechanisms that activate the trigeminovascular system. (4) Headache occurs in 13.3%-76.9% following SARS-CoV-2 vaccination and occurs more often amongst women with a pre-existing primary headache; the risk of developing headache is higher with the adenoviral-vector-type vaccines than with other preparations. (5) Headache related to SARS-CoV-2 vaccination is mostly bilateral, and throbbing, pressing, jolting or stabbing. (6) No studies have been conducted investigating the underlying mechanism of headache attributed to SARS-CoV-2 vaccines.

CONCLUSION

The results of this joint EAN/EHF initiative provide a framework for a better understanding of headache in the context of SARS-CoV-2 infection and vaccination.

Topographical Distribution of Neuroanatomical Abnormalities Following COVID-19 Invasion : A Systematic Literature Review

PURPOSE

This systematic review is aimed at synthesising the literature base to date on the frequency and topographical distribution of neuroanatomical changes seen on imaging following COVID-19 invasion with a focus on both the acute and chronic phases of the disease.

METHODS

In this study, 8 databases were systematically searched to identify relevant articles published from December 2019 to March 2022 and supplemented with a manual reference search. Data were extracted from the included studies and narrative synthesis was employed to integrate the findings.

RESULTS

A total of 110 studies met the inclusion criteria and comprised 119,307 participants (including 31,073 acute and 143 long COVID-19 patients manifesting neurological alterations) and controls. Considerable variability in both the localisation and nature of neuroanatomical abnormalities are noted along the continuum with a wide range of neuropathologies relating to the cerebrovascular/neurovascular system, (sub)cortical structures (including deep grey and white matter structures), brainstem, and predominant regional and/or global alterations in the cerebellum with varying degrees of spinal involvement.

CONCLUSION

Structural regional alterations on neuroimaging are frequently demonstrated in both the acute and chronic phases of SARS-CoV‑2 infection, particularly prevalent across subcortical, prefrontal/frontal and cortico-limbic brain areas as well as the cerebrovascular/neurovascular system. These findings contribute to our understanding of the acute and chronic effects of the virus on the nervous system and has the potential to provide information on acute and long-term treatment and neurorehabilitation decisions.

Long term outcomes of hyperbaric oxygen therapy in post covid condition: longitudinal follow-up of a randomized controlled trial

In our previous randomized controlled trial, we documented significant improvements in cognitive, psychiatric, fatigue, sleep, and pain symptoms among long Coronavirus disease 2019 (COVID) patients who underwent hyperbaric oxygen therapy (HBOT). The primary objective of the present study was to evaluate the enduring 1 year long term effects of HBOT on long COVID syndrome. This longitudinal long-term follow-up included 31 patients with reported post COVID-19 cognitive symptoms, who underwent 40 daily sessions of HBOT. Participants were recruited more than one year (486 ± 73) after completion of the last HBOT session. Quality of life, assessed using the short form-36 (SF-36) questionnaire revealed, that the long-term results exhibited a similar magnitude of improvement as the short-term outcomes following HBOT across most domains. Regarding sleep quality, improvements were observed in global score and across five sleep domains with effect sizes of moderate magnitude during the short-term evaluation, and these improvements persisted in the long-term assessment (effect size (ES1) = 0.47-0.79). In the realm of neuropsychiatric symptoms, as evaluated by the brief symptom inventory-18 (BSI-18), the short-term assessment following HBOT demonstrated a large effect size, and this effect persisted at the long-term evaluation. Both pain severity (ES1 = 0.69) and pain interference (ES1 = 0.83), had significant improvements during the short-term assessment post HBOT, which persisted at long term. The results indicate HBOT can improve the quality of life, quality of sleep, psychiatric and pain symptoms of patients suffering from long COVID. The clinical improvements gained by HBOT are persistent even 1 year after the last HBOT session.

Systematic review and evidence gap mapping of biomarkers associated with neurological manifestations in patients with COVID-19

OBJECTIVE

This study aimed to synthesize the existing evidence on biomarkers related to coronavirus disease 2019 (COVID-19) patients who presented neurological events.

METHODS

A systematic review of observational studies (any design) following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines and the Cochrane Collaboration recommendations was performed (PROSPERO: CRD42021266995). Searches were conducted in PubMed and Scopus (updated April 2023). The methodological quality of nonrandomized studies was assessed using the Newcastle‒Ottawa Scale (NOS). An evidence gap map was built considering the reported biomarkers and NOS results.

RESULTS

Nine specific markers of glial activation and neuronal injury were mapped from 35 studies published between 2020 and 2023. A total of 2,237 adult patients were evaluated in the included studies, especially during the acute phase of COVID-19. Neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) biomarkers were the most frequently assessed (n = 27 studies, 77%, and n = 14 studies, 40%, respectively). Although these biomarkers were found to be correlated with disease severity and worse outcomes in the acute phase in several studies (p < 0.05), they were not necessarily associated with neurological events. Overall, 12 studies (34%) were judged as having low methodological quality, 9 (26%) had moderate quality, and 9 (26%) had high quality.

CONCLUSIONS

Different neurological biomarkers in neurosymptomatic COVID-19 patients were identified in observational studies. Although the evidence is still scarce and conflicting for some biomarkers, well-designed longitudinal studies should further explore the pathophysiological role of NfL, GFAP, and tau protein and their potential use for COVID-19 diagnosis and management.

Cerebrospinal fluid cytokines in COVID-19: a review and meta-analysis

INTRODUCTION

Neurological involvement can occur in patients with SARS-CoV-2 infections, resulting in coronavirus disease 2019 (COVID-19). Cytokine alterations are associated with neurological symptoms in COVID-19. We performed a review of cytokines in the cerebrospinal fluid (CSF) of patients with COVID-19.

METHODS

Two reviewers independently searched PubMed for all relevant articles published prior to November 11, 2022. Active SARS-CoV-2 infection and CSF cytokine analyses were required for inclusion.

RESULTS

Three-hundred forty-six patients with COVID-19 and 356 controls from 28 studies were included. SARS-CoV-2 PCR was positive in the CSF of 0.9% (3/337) of patients with COVID-19. Thirty-seven different cytokines were elevated in the CSF of patients with COVID-19 when compared to controls and the standards set forth by individual assays used in each study. Of the 37 cytokines, IL-6 and IL-8 were most commonly elevated. CSF IL-6 is elevated in 60%, and CSF IL-8 is elevated in 51% of patients with COVID-19.

CONCLUSION

Levels of several inflammatory cytokines are elevated in the CSF of patients with COVID-19, and SARS-CoV-2 PCR is often not isolated in the CSF of patients with COVID-19. Many patients with COVID-19 have neurological symptoms and given the cytokine elevations in the absence of detectable viral RNA in cerebrospinal fluid; further study of the CSF cytokine profiles and pathogenesis of neurological symptoms in COVID-19 is needed.

From 'mental fog' to post-acute COVID-19 syndrome's executive function alteration: Implications for clinical approach

A common symptom of the neuropsychiatric Post-Acute COVID-19 syndrome (neuro-PACS) is the so called 'brain fog'. Patients describe the brain fog as problems with attention, memory and mental fatigue. Brain fog is experienced by 9-55% of people for months after having contracted SARS-CoV-2 virus. Several theories have been proposed to explain PACS's brain fog, including a neuroinflammatory hypothesis, but the hypothesis remains to be proven. Here, we examined inflammatory and immunological blood profile in a cohort of patients with PACS to investigate the association between executive functions and blood inflammatory markers. Executive function was assessed by the Trail Making Test (TMT) Part A and Part B, as well as the Barkley Deficits in Executive Functioning Scale (BDEFS), in 71 patients (36 men), average age of 40 years (range: 15-82, SD: 15.7). Impairment in executive functioning (BDEFS scores and TMT B scores) correlated with increased levels of Interleukin-6 (IL-6), fibrinogen and ferritin. Moreover, elevated levels of Il-6, fibrinogen, ferritin, tumor necrosis factor-alpha and C-reactive protein have been observed in PACS. These findings demonstrate that PACS is characterized by the presence of an immuno-inflammatory process, which is associated with diminished executive functioning. Here, we argue in favour of a shift from the non-descriptive definition of 'mental fog' to a characterization of a subtype of PACS, associated with alteration in executive functioning. Implication for clinical settings and prevention are discussed.

Blood Biomarkers as Prognostic Indicators for Neurological Injury in COVID-19 Patients: A Systematic Review and Meta-Analysis

Coronavirus disease 2019 (COVID-19) has been linked to various neurological complications. This meta-analysis assessed the relationship between glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) levels in the blood and neurological injury in COVID-19 patients. A comprehensive search of various databases was conducted until 18 August 2023, to find studies reporting GFAP and NfL blood levels in COVID-19 patients with neurological complications. GFAP and NfL levels were estimated between COVID-19 patients and healthy controls, and meta-analyses were performed using RevMan 5.4 software for analysis. In the 21 collected studies, it was found that COVID-19 patients had significantly higher levels of pooled GFAP (SMD = 0.52; 95% CI: 0.31, 0.73; p ≤ 0.001) and NfL (SMD = 0.60; 95% CI: 0.37, 0.82; p ≤ 0.001) when compared to the healthy controls. The pooled GFAP (SMD = 0.86; 95% CI: 0.26, 1.45; p ≤ 0.01) and NfL (SMD = 0.87; 95% CI: 0.48, 1.26; p ≤ 0.001) were significantly higher in non-survivors. These findings indicate a significant association between COVID-19 severity and elevated levels of GFAP and NfL, suggesting that GFAP and NfL could serve as potential diagnostic and prognostic markers for the early detection and monitoring of COVID-19-related neurological injuries.

SARS-CoV-2 and autoantibodies in the cerebrospinal fluid of COVID-19 patients: prospective multicentre cohort study

Disease mechanisms underlying neurological and neuropsychiatric symptoms after coronavirus disease 2019 (COVID-19), termed neuro-COVID, are poorly understood. Investigations of the cerebrospinal fluid (CSF) for the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA and antibodies, as well as autoantibodies against neuronal surface antigens, could improve our understanding in that regard. We prospectively collected CSF and blood from patients investigated by lumbar puncture for neurological or neuropsychiatric symptoms during or after COVID-19. Primary outcomes were the presence of (i) SARS-CoV-2 RNA in CSF via polymerase chain reaction (PCR), (ii) SARS-CoV-2 immunoglobulin G (IgG) anti-S receptor-binding-domain antibodies via the Euroimmun and Wantai assays and (iii) IgG autoantibodies against neuronal surface antigens using commercial cell- and tissue-based assays (Euroimmun). Secondary outcomes were (i) routine CSF investigations and (ii) correlation between SARS-CoV-2 antibody levels in CSF with serum levels, blood-brain barrier permeability and peripheral inflammation. We obtained CSF from 38 COVID-19 patients (mean age 56.5 ± 19.2 years, 53% women) who developed neurological and neuropsychiatric symptoms. CSF pleocytosis (>5 cells) was observed in 9/38 patients (23.7%), elevated CSF protein (>0.50 g/L) in 13/38 (34.2%) and elevated CSF/serum albumin ratio in 12/35 (34.3%). PCR for SARS-CoV-2 RNA in CSF was negative in all. SARS-CoV-2 CSF antibodies were detected in 15/34 (44.1%; Euroimmun assay) and 7/31 (22.6%; Wantai assay) individuals, but there were no signs of intrathecal SARS-CoV-2 IgG production. SARS-CoV-2 CSF antibodies were positively correlated with serum levels (R = 0.93, P < 0.001), blood-brain barrier permeability (R = 0.47, P = 0.006), peripheral inflammation (R = 0.51, P = 0.002) and admission to the intensive care unit [odds ratio (OR) 17.65; 95% confidence interval (CI) 1.18-264.96; P = 0.04; n = 15]. Cell-based assays detected weakly positive NMDAR, LGI1 and CASPR2 antibodies in serum of 4/34 (11.8%) patients but not in CSF. The tissue-based assay showed anti-neuronal fluorescence in CSF from one individual, staining for Purkinje cells. In summary, whereas we did not detect active SARS-CoV-2 infection in the CSF, SARS-CoV-2 antibodies were prevalent. The absence of intrathecal antibody production points towards blood-brain barrier impairment as the origin of CSF SARS-CoV-2 antibodies. In contrast, CSF autoantibodies against neuronal surface antigens were rare. There was no evidence for a clinical correlate of these antibodies. We conclude that, rather than specific autoimmune neuronal injury, non-specific effects of critical illness including an impaired blood-brain barrier are more likely to contribute to neuro-COVID.

Biomarkers of Neurological Damage: From Acute Stage to Post-Acute Sequelae of COVID-19

Background: Neurological symptoms (NS) in COVID-19 are related to both acute stage and long-COVID. We explored levels of brain injury biomarkers (NfL and GFAP) and myeloid activation marker (sCD163) and their implications on the CNS. Materials and Methods: In hospitalized COVID-19 patients plasma samples were collected at two time points: on hospital admission (baseline) and three months after hospital discharge (Tpost). Patients were stratified according to COVID-19 severity based on acute respiratory distress syndrome (ARDS) onset (severe and non-severe groups). A further stratification according to the presence of NS (with and without groups) at baseline (requiring a puncture lumbar for diagnostic purposes) and according to NS self-referred at Tpost was performed. Finally, cerebrospinal fluid (CSF) samples were collected from patients with NS present at baseline. Results: We enrolled 144 COVID-19 patients (62 female/82 male; median age [interquartile range, IQR]): 64 [55-77]) and 53 heathy donors (HD, 30 female/23 male; median age [IQR]: 64 [59-69]). At baseline, higher plasma levels of NfL, GFAP and sCD163 in COVID-19 patients compared to HD were observed (p < 0.0001, p < 0.0001 and p < 0.0001, respectively), especially in those with severe COVID-19 (p < 0.0001, p < 0.0001 and p < 0.0001, respectively). Patients with NS showed higher plasma levels of NfL, GFAP and sCD163 compared to those without (p = 0.0023, p < 0.0001 and 0.0370, respectively). At baseline, in COVID-19 patients with NS, positive correlations between CSF levels of sCD163 and CSF levels of NfL (ρ = 0.7536, p = 0.0017) and GFAP were observed (ρ = 0.7036, p = 0.0045). At Tpost, the longitudinal evaluation performed on 77 COVID-19 patients showed a significant reduction in plasma levels of NfL, GFAP and sCD163 compared to baseline (p < 0.0001, p < 0.0001 and p = 0.0413, respectively). Finally, at Tpost, in the severe group, higher plasma levels of sCD163 in patients with NS compared to those without were reported (p < 0.0001). Conclusions: High plasma levels of NfL, GFAP and sCD163 could be due to a proinflammatory systemic and brain response involving microglial activation and subsequent CNS damage. Our data highlight the association between myeloid activation and CNS perturbations.

The kynurenine pathway of tryptophan metabolism: a neglected therapeutic target of COVID-19 pathophysiology and immunotherapy

SARS-CoV-2 (COVID-19) exerts profound changes in the kynurenine (Kyn) pathway (KP) of tryptophan (Trp) metabolism that may underpin its pathophysiology. The KP is the main source of the vital cellular effector NAD+ and intermediate metabolites that modulate immune and neuronal functions. Trp metabolism is the top pathway influenced by COVID-19. Sixteen studies established virus-induced activation of the KP mediated mainly by induction of indoleamine 2,3-dioxygenase (IDO1) in most affected tissues and of IDO2 in lung by the increased release of proinflammatory cytokines but could additionally involve increased flux of plasma free Trp and induction of Trp 2,3-dioxygenase (TDO) by cortisol. The major Kyn metabolite targeted by COVID-19 is kynurenic acid (KA), the Kyn metabolite with the greatest affinity for the aryl hydrocarbon receptor (AhR), which is also activated by COVID-19. AhR activation initiates two important series of events: a vicious circle involving IDO1 induction, KA accumulation and further AhR activation, and activation of poly (ADP-ribose) polymerase (PARP) leading to NAD+ depletion and cell death. The virus further deprives the host of NAD+ by inhibiting its main biosynthetic pathway from quinolinic acid, while simultaneously acquiring NAD+ by promoting its synthesis from nicotinamide in the salvage pathway. Additionally, the protective effects of sirtuin 1 are minimised by the PARP activation. KP dysfunction may also underpin the mood and neurological disorders acutely and during 'long COVID'. More studies of potential effects of vaccination therapy on the KP are required and exploration of therapeutic strategies involving modulation of the KP changes are proposed.

Neurological manifestations of post-acute sequelae of COVID-19: which liquid biomarker should we use?

Long COVID syndrome, also known as post-acute sequelae of COVID-19 (PASC), is characterized by persistent symptoms lasting 3-12 weeks post SARS-CoV-2 infection. Patients suffering from PASC can display a myriad of symptoms that greatly diminish quality of life, the most frequent being neuropsychiatric. Thus, there is an eminent need to diagnose and treat PASC related neuropsychiatric manifestation (neuro-PASC). Evidence suggests that liquid biomarkers could potentially be used in the diagnosis and monitoring of patients. Undoubtedly, such biomarkers would greatly benefit clinicians in the management of patients; however, it remains unclear if these can be reliably used in this context. In this mini review, we highlight promising liquid (blood and cerebrospinal fluid) biomarkers, namely, neuronal injury biomarkers NfL, GFAP, and tau proteins as well as neuroinflammatory biomarkers IL-6, IL-10, TNF-α, and CPR associated with neuro-PASC and discuss their limitations in clinical applicability.

Human brain microphysiological systems in the study of neuroinfectious disorders

Microphysiological systems (MPS) are 2D or 3D multicellular constructs able to mimic tissue microenvironments. The latest models encompass a range of techniques, including co-culturing of various cell types, utilization of scaffolds and extracellular matrix materials, perfusion systems, 3D culture methods, 3D bioprinting, organ-on-a-chip technology, and examination of tissue structures. Several human brain 3D cultures or brain MPS (BMPS) have emerged in the last decade. These organoids or spheroids are 3D culture systems derived from induced pluripotent cells or embryonic stem cells that contain neuronal and glial populations and recapitulate structural and physiological aspects of the human brain. BMPS have been introduced recently in the study and modeling of neuroinfectious diseases and have proven to be useful in establishing neurotropism of viral infections, cell-pathogen interactions needed for infection, assessing cytopathological effects, genomic and proteomic profiles, and screening therapeutic compounds. Here we review the different methodologies of organoids used in neuroinfectious diseases including spheroids, guided and unguided protocols as well as microglia and blood-brain barrier containing models, their specific applications, and limitations. The review provides an overview of the models existing for specific infections including Zika, Dengue, JC virus, Japanese encephalitis, measles, herpes, SARS-CoV2, and influenza viruses among others, and provide useful concepts in the modeling of disease and antiviral agent screening.

A Multidisciplinary Pediatric Neurology Clinic for Systematic Follow-up of Children with Neurologic Sequelae of COVID-19

Clinical guidance on outpatient follow-up of children hospitalized with acute neurologic complications of SARS-CoV2 infection is needed. We describe the clinical infrastructure of our pediatric neurology post-Covid clinic, including our clinical evaluation and cognitive testing battery specific to this patient population, and a case series of our initial patient cohort. Our findings demonstrate cognitive sequelae in all 4 of our patients months following acute SARS-CoV2 infection with neurologic complications including acute disseminated encephalomyelitis, posterior reversible encephalopathy syndrome, viral encephalitis, and gait difficulties. Verbal and executive function domains were predominantly affected in our cohort, even in patients who did not endorse symptomatic or academic complaints at follow-up. Our recommendations include systematic clinical follow-up for children following hospitalization with SARS-CoV2 infection with a comprehensive cognitive battery to monitor for cognitive sequalae and to assist with developing an individualized education plan for the child as they return to school.

Cerebrospinal fluid biomarkers in SARS-CoV-2 patients with acute neurological syndromes

BACKGROUND AND PURPOSE

Mechanisms underlying acute brain injury in SARS-CoV-2 patients remain poorly understood. A better characterization of such mechanisms remains essential to preventing long-term neurological sequelae. Our present aim was to study a panel of biomarkers of neuroinflammation and neurodegeneration in the cerebrospinal fluid (CSF) of NeuroCOVID patients.

METHODS

We retrospectively collected clinical and CSF biomarkers data from 24 NeuroCOVID adults seen at the University Hospital of Guadeloupe between March and June 2021.

RESULTS

Among 24 NeuroCOVID patients, 71% had encephalopathy and 29% meningoencephalitis. A number of these patients also experienced de novo movement disorder (33%) or stroke (21%). The CSF analysis revealed intrathecal immunoglobulin synthesis in 54% of NeuroCOVID patients (two with a type 2 pattern and 11 with a type 3) and elevated neopterin levels in 75% of them (median 9.1nM, IQR 5.6-22.1). CSF neurofilament light chain (NfL) was also increased compared to a control group of non-COVID-19 patients with psychiatric illnesses (2905ng/L, IQR 1428-7124 versus 1222ng/L, IQR 1049-1566). Total-tau was elevated in the CSF of 24% of patients, whereas protein 14-3-3, generally undetectable, reached intermediate levels in two patients. Finally, CSF Aß1-42 was reduced in 52.4% of patients (median 536ng/L, IQR 432-904) with no change in the Aß1-42/Aß1-40 ratio (0.082, IQR 0.060-0.096).

CONCLUSIONS

We showed an elevation of CSF biomarkers of neuroinflammation in NeuroCOVID patients and a rise of CSF NfL, evocative of neuronal damage. However, longitudinal studies are needed to determine whether NeuroCOVID could evolve into a chronic neurodegenerative condition.

The multifaceted role of neurofilament light chain protein in non-primary neurological diseases

The advancing validation and exploitation of CSF and blood neurofilament light chain protein as a biomarker of neuroaxonal damage has deeply changed the current diagnostic and prognostic approach to neurological diseases. Further, recent studies have provided evidence of potential new applications of this biomarker also in non-primary neurological diseases. In the present review we summarize the state of the art, future perspectives, but also limitations, of neurofilament light chain protein as a CSF and blood biomarker in several medical fields, including intensive care medicine, surgery, internal medicine and psychiatry. In particular, neurofilament light chain protein is associated with the degree of neurological impairment and outcome in patients admitted to intensive care units or in the perioperative phase and it seems to be highly interconnected with cardiovascular risk factors. Beyond that, interesting diagnostic and prognostic insights have been provided by the investigation of neurofilament light chain protein in psychiatric disorders as well as in the current coronavirus disease-19 pandemic and in normal ageing. Altogether, current data outline a multifaceted applicability of CSF and blood neurofilament light chain protein ranging from the critical clinical setting to the development of precision medicine models suggesting a strict interplay between the nervous system pathophysiology and the health-illness continuum.

Clinical usefulness of testing for severe acute respiratory syndrome coronavirus 2 antibodies

In the COVID-19 pandemic era, antibody testing against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has proven an invaluable tool and herein we highlight some of the most useful clinical and/or epidemiological applications of humoral immune responses recording. Anti-spike circulating IgGs and SARS-CoV-2 neutralizing antibodies can serve as predictors of disease progression or disease prevention, whereas anti-nucleocapsid antibodies can help distinguishing infection from vaccination. Also, in the era of immunotherapies we address the validity of anti-SARS-CoV-2 antibody monitoring post-infection and/or vaccination following therapies with the popular anti-CD20 monoclonals, as well as in the context of various cancers or autoimmune conditions such as rheumatoid arthritis and multiple sclerosis. Additional crucial applications include population immunosurveillance, either at the general population or at specific communities such as health workers. Finally, we discuss how testing of antibodies in cerebrospinal fluid can inform us on the neurological complications that often accompany COVID-19.

Neurological symptoms and neuronal damage markers in acute COVID-19: Is there a correlation? A pilot study

A wide spectrum of neurological symptoms (NS) has been described in patients with COVID-19. We examined the plasma levels of neuron-specific enolase (NSE) and neurofilament light chain (NFL) together, as neuronal damage markers, and their relationships with clinical severity in patients with NS at acute COVID-19. A total of 20 healthy controls and 59 patients with confirmed COVID-19 were enrolled in this pilot prospective study. Serum NSE and NFL levels were measured by using the enzyme-linked immunoassay method from serum samples. Serum NSE levels were found to be significantly higher in the severe group than in the nonsevere group (p = 0.034). However, serum NFL levels were similar between the control and disease groups (p > 0.05). For the mild group, serum NFL levels were significantly higher in patients with the sampling time ≥5 days than in those with the sampling time <5 days (p = 0.019). However, no significant results for NSE and NFL were obtained in patients with either single or multiple NS across the groups (p > 0.05). Increased serum NSE levels were associated with disease severity regardless of accompanied NS in patients with acute COVID-19 infection. However, serum NFL levels may have a role at the subacute phase of COVID-19.

ACE2, Circumventricular Organs and the Hypothalamus, and COVID-19

The SARS-CoV-2 virus gains entry to cells by binding to angiotensin-converting enzyme 2 (ACE2). Since circumventricular organs and parts of the hypothalamus lack a blood-brain barrier, and immunohistochemical studies demonstrate that ACE2 is highly expressed in circumventricular organs which are intimately connected to the hypothalamus, and the hypothalamus itself, these might be easy entry points for SARS-CoV-2 into the brain via the circulation. High ACE2 protein expression is found in the subfornical organ, area postrema, and the paraventricular nucleus of the hypothalamus (PVH). The subfornical organ and PVH are parts of a circuit to regulate osmolarity in the blood, through the secretion of anti-diuretic hormone into the posterior pituitary. The PVH is also the stress response centre in the brain. It controls not only pre-ganglionic sympathetic neurons, but is also a source of corticotropin-releasing hormone, that induces the secretion of adrenocorticotropic hormone from the anterior pituitary. It is proposed that the function of ACE2 in the circumventricular organs and the PVH could be diminished by binding with SARS-CoV-2, thus leading to a reduction in the ACE2/Ang (1-7)/Mas receptor (MasR) signalling axis, that modulates ACE/Ang II/AT1R signalling. This could result in increased presympathetic activity/neuroendocrine secretion from the PVH, and effects on the hypothalamic-pituitary-adrenal axis activity. Besides the bloodstream, the hypothalamus might also be affected by SARS-CoV-2 via transneuronal spread along the olfactory/limbic pathways. Exploring potential therapeutic pathways to prevent or attenuate neurological symptoms of COVID-19, including drugs which modulate ACE signalling, remains an important area of unmet medical need.

Citicoline and COVID-19: vis-à-vis conjectured

Coronavirus disease 2019 (COVID-19) is a current pandemic disease caused by a novel severe acute respiratory syndrome coronavirus virus respiratory type 2 (SARS-CoV-2). SARS-CoV-2 infection is linked with various neurological manifestations due to cytokine-induced disruption of the blood brain barrier (BBB), neuroinflammation, and peripheral neuronal injury, or due to direct SARS-CoV-2 neurotropism. Of note, many repurposed agents were included in different therapeutic protocols in the management of COVID-19. These agents did not produce an effective therapeutic eradication of SARS-CoV-2, and continuing searching for novel anti-SARS-CoV-2 agents is a type of challenge nowadays. Therefore, this study aimed to review the potential anti-inflammatory and antioxidant effects of citicoline in the management of COVID-19.

Neurofilament light chain and vaccination status associate with clinical outcomes in severe COVID-19

Blood neurofilament light chain (NFL) is proposed to serve as an estimate of disease severity in hospitalized patients with coronavirus disease 2019 (COVID-19). We show that NFL concentrations in plasma collected from 880 patients with COVID-19 within 5 days of hospital admission were elevated compared to controls. Higher plasma NFL associated with worse clinical outcomes including the need for mechanical ventilation, intensive care, prolonged hospitalization, and greater functional disability at discharge. No difference in the studied clinical outcomes between black/African American and white patients was found. Finally, vaccination associated with less disability at time of hospital discharge. In aggregate, our findings support the utility of measuring NFL shortly after hospital admission to estimate disease severity and show that race does not influence clinical outcomes caused by COVID-19 assuming equivalent access to care, and that vaccination may lessen the degree of COVID-19-caused disability.

MRI of Cerebrovascular Injury Associated With COVID-19 and Non-COVID-19 Acute Respiratory Distress Syndrome: A Matched Case-Control Study

OBJECTIVES

Cerebrovascular injury associated with COVID-19 has been recognized, but the mechanisms remain uncertain. Acute respiratory distress syndrome (ARDS) is a severe pulmonary injury, which is associated with both ischemic and hemorrhagic stroke. It remains unclear if cerebrovascular injuries associated with severe COVID-19 are unique to COVID-19 or a consequence of severe respiratory disease or its treatment. The frequency and patterns of cerebrovascular injury on brain MRI were compared among patients with COVID-19 ARDS and non-COVID-19 ARDS.

DESIGN

A case-control study.

SETTING

A tertiary academic hospital system.

PATIENTS

Adult patients (>18 yr) with COVID-19 ARDS (March 2020 to July 2021) and non-COVID-19 ARDS (January 2010-October 2018) who underwent brain MRI during their index hospitalization.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Cerebrovascular injury on MRI included cerebral ischemia (ischemic infarct or hypoxic ischemic brain injury) and intracranial hemorrhage (intraparenchymal, subarachnoid, or subdural, and cerebral microbleed [CMB]).Twenty-six patients with COVID-19 ARDS and sixty-six patients with non-COVID ARDS underwent brain MRI during the index hospitalization, resulting in 23 age- and sex-matched pairs. The frequency of overall cerebrovascular injury (57% vs 61%), cerebral ischemia (35% vs 43%), intracranial hemorrhage (43% vs 48%), and CMB (52% vs 41%) between COVID-19 ARDS and non-COVID-19 ARDS patients was similar (all p values >0.05). However, four of 26 patients (15%) with COVID-19 and no patients with non-COVID-19 ARDS had disseminated leukoencephalopathy with underlying CMBs, an imaging pattern that has previously been reported in patients with COVID-19.

CONCLUSIONS

In a case-control study of selected ARDS patients with brain MRI, the frequencies of ischemic and hemorrhagic cerebrovascular injuries were similar between COVID-19 versus non-COVID-19 ARDS patients. However, the MRI pattern of disseminated hemorrhagic leukoencephalopathy was unique to the COVID-19 ARDS patients in this cohort.

Delayed encephalopathy after COVID-19: A case series of six patients

RATIONALE

Acute encephalopathy is a severe neurological complication of coronavirus disease 2019 (COVID-19). Most cases of acute encephalopathy associated with COVID-19 occur within several weeks of COVID-19 onset. We describe a case series of 6 patients who developed delayed encephalopathy (DE) after COVID-19.

PATIENT CONCERNS AND DIAGNOSES

We evaluated patients who recovered from COVID-19 and showed acute disturbance of consciousness or focal neurological deficits without recurrence of pneumonitis. Six patients, 2 females and 4 males, with ages ranging from 65 to 83 years were included. Durations of hospitalization due to COVID-19 were between 25 and 44 days. The severity of COVID-19 was moderate in 5 and severe in 1 patient. Patients were rehospitalized for acute disturbance of consciousness concomitant with postural tremor and, abnormal behavior, hemiplegia, aphasia, or apraxia between 34 and 67 days after the onset of COVID-19. Chest computed tomography showed no exacerbation of pneumonitis. Brain magnetic resonance imaging showed no specific findings except in 1 patient with an acute lacunar infarction. Electroencephalogram demonstrated diffuse slowing in all patients. Repeat electroencephalogram after recovery from encephalopathy demonstrated normal in all patients. One of the 6 patients had cerebrospinal fluid (CSF) pleocytosis. CSF protein levels were elevated in all patients, ranging from 51 to 115 mg/dL. CSF interleukin-6 levels ranged from 2.9 to 10.9 pg/mL. The immunoglobulin index was 0.39 to 0.44. Qlim(alb) < QAlb indicating dysfunction of the blood-brain barrier was observed in all patients. Severe acute respiratory syndrome coronavirus 2 reverse transcription polymerase chain reaction of CSF was negative in all patients. Neuronal autoantibodies were absent in serum and CSF.

INTERVENTIONS AND OUTCOMES

Immunotherapy including steroid pulses was administered to 3 patients; however, symptoms of encephalopathy resolved within several days in all patients, regardless of treatment with immunotherapy, and their consciousness levels were recovered fully. Notably, postural tremor remained for 2 weeks to 7 months.

LESSONS

In our patients, DE after COVID-19 was characterized by symptoms of acute encephalopathy accompanied with tremor in the absence of worsening pneumonitis after the fourth week of COVID-19 onset. Our findings indicate blood-brain barrier dysfunction may contribute to the pathogenesis of DE after COVID-19.

Pathophysiology of Post-COVID syndromes: a new perspective

Most COVID-19 patients recovered with low mortality; however, some patients experienced long-term symptoms described as "long-COVID" or "Post-COVID syndrome" (PCS). Patients may have persisting symptoms for weeks after acute SARS-CoV-2 infection, including dyspnea, fatigue, myalgia, insomnia, cognitive and olfactory disorders. These symptoms may last for months in some patients. PCS may progress in association with the development of mast cell activation syndrome (MCAS), which is a distinct kind of mast cell activation disorder, characterized by hyper-activation of mast cells with inappropriate and excessive release of chemical mediators. COVID-19 survivors, mainly women, and patients with persistent severe fatigue for 10 weeks after recovery with a history of neuropsychiatric disorders are more prone to develop PCS. High D-dimer levels and blood urea nitrogen were observed to be risk factors associated with pulmonary dysfunction in COVID-19 survivors 3 months post-hospital discharge with the development of PCS. PCS has systemic manifestations that resolve with time with no further complications. However, the final outcomes of PCS are chiefly unknown. Persistence of inflammatory reactions, autoimmune mimicry, and reactivation of pathogens together with host microbiome alterations may contribute to the development of PCS. The deregulated release of inflammatory mediators in MCAS produces extraordinary symptoms in patients with PCS. The development of MCAS during the course of SARS-CoV-2 infection is correlated to COVID-19 severity and the development of PCS. Therefore, MCAS is treated by antihistamines, inhibition of synthesis of mediators, inhibition of mediator release, and inhibition of degranulation of mast cells.

Role Of Retroelements In The Development Of COVID-19 Neurological Consequences

Retroelements play a key role in brain functioning in humans and other animals, since they represent dynamic regulatory elements controlling the expression of specific neuron types. The activity of retroelements in the brain is impaired under the influence of SARS-CoV-2, penetrating the blood-brain barrier. We propose a new concept, according to which the neurological complications of COVID-19 and their long-term effects are caused by modified expression of retroelements in neurons due to viral effect. This effect is implemented in several ways: a direct effect of the virus on the promoter regions of retroelement-encoding genes, virus interaction with miRNAs causing silencing of transposons, and an effect of the viral RNA on the products of retroelement transcription. Aging-related physiological activation of retroelements in the elderly is responsible for more severe course of COVID-19. The associations of multiple sclerosis, Parkinson’s disease, Guillain-Barré syndrome, acute disseminated encephalomyelitis with coronavirus lesions also indicate the role of retroelements in such complications, because retroelements are involved in the mechanisms of the development of these diseases. According to meta-analyses, COVID-19-caused neurological complications ranged 36.4-73%. The neuropsychiatric consequences of COVID-19 are observed in patients over a long period after recovery, and their prevalence may exceed those during the acute phase of the disease. Even 12 months after recovery, unmotivated fatigue, headache, mental disorders, and neurocognitive impairment were observed in 82%, 60%, 26.2-45%, and 16.2-46.8% of patients, correspondingly. These manifestations are explained by the role of retroelements in the integration of SARS-CoV-2 into the human genome using their reverse transcriptase and endonuclease, which results in a long-term viral persistence. The research on the role of specific retroelements in these changes can become the basis for developing targeted therapy for neurological consequences of COVID-19 using miRNAs, since epigenetic changes in the functioning of the genome in neurons, affected by transposons, are reversible.

Herbal Medicines for Post-Acute Sequelae (Fatigue or Cognitive Dysfunction) of SARS-CoV-2 Infection: A Phase 2 Pilot Clinical Study Protocol

Long-term sequelae refer to persistent symptoms or signs for >6 months after SARS-CoV-2 infection. The most common symptoms of sequelae are fatigue and neuropsychiatric symptoms (concentration difficulty, amnesia, cognitive dysfunction, anxiety, and depression). However, approved treatments have not been fully established. Herbal medicines are administered for 12 weeks to patients who continuously complain of fatigue or cognitive dysfunction for >4 weeks that only occurred after COVID-19 diagnoses. Based on the Korean Medicine syndrome differentiation diagnosis, patients with fatigue will be administered Bojungikgi-tang or Kyungok-go, whereas those with cognitive dysfunction will be administered Cheonwangbosim-dan. Results could support evidence that herbal medicines may mitigate fatigue and cognitive dysfunction caused by COVID-19. Furthermore, by investigating the effects of herbal medicines on changes in metabolite and immune response due to COVID-19, which may be responsible for sequelae, the potential of herbal medicines as one of the therapeutic interventions for post-acute sequelae of SARS-CoV-2 infection can be evaluated. Therefore, the effects of herbal medicine on fatigue and cognitive dysfunction sequelae due to COVID-19 will be elucidated in this study to provide an insight into the preparation of medical management for the post-acute sequelae of SARS-CoV-2 infection.

Widespread white matter oedema in subacute COVID-19 patients with neurological symptoms

While neuropathological examinations in patients who died from COVID-19 revealed inflammatory changes in cerebral white matter, cerebral MRI frequently fails to detect abnormalities even in the presence of neurological symptoms. Application of multi-compartment diffusion microstructure imaging (DMI), that detects even small volume shifts between the compartments (intra-axonal, extra-axonal and free water/CSF) of a white matter model, is a promising approach to overcome this discrepancy. In this monocentric prospective study, a cohort of 20 COVID-19 inpatients (57.3 ± 17.1 years) with neurological symptoms (e.g. delirium, cranial nerve palsies) and cognitive impairments measured by the Montreal Cognitive Assessment (MoCA test; 22.4 ± 4.9; 70% below the cut-off value <26/30 points) underwent DMI in the subacute stage of the disease (29.3 ± 14.8 days after positive PCR). A comparison of whole-brain white matter DMI parameters with a matched healthy control group (n = 35) revealed a volume shift from the intra- and extra-axonal space into the free water fraction (V-CSF). This widespread COVID-related V-CSF increase affected the entire supratentorial white matter with maxima in frontal and parietal regions. Streamline-wise comparisons between COVID-19 patients and controls further revealed a network of most affected white matter fibres connecting widespread cortical regions in all cerebral lobes. The magnitude of these white matter changes (V-CSF) was associated with cognitive impairment measured by the MoCA test (r = -0.64, P = 0.006) but not with olfactory performance (r = 0.29, P = 0.12). Furthermore, a non-significant trend for an association between V-CSF and interleukin-6 emerged (r = 0.48, P = 0.068), a prominent marker of the COVID-19 related inflammatory response. In 14/20 patients who also received cerebral 18F-FDG PET, V-CSF increase was associated with the expression of the previously defined COVID-19-related metabolic spatial covariance pattern (r = 0.57; P = 0.039). In addition, the frontoparietal-dominant pattern of neocortical glucose hypometabolism matched well to the frontal and parietal focus of V-CSF increase. In summary, DMI in subacute COVID-19 patients revealed widespread volume shifts compatible with vasogenic oedema, affecting various supratentorial white matter tracts. These changes were associated with cognitive impairment and COVID-19 related changes in 18F-FDG PET imaging.

Therapeutic Approaches to the Neurologic Manifestations of COVID-19

As of May 2022, there have been more than 527 million infections with severe acute respiratory disease coronavirus type 2 (SARS-CoV-2) and over 6.2 million deaths from Coronavirus Disease 2019 (COVID-19) worldwide. COVID-19 is a multisystem illness with important neurologic consequences that impact long-term morbidity and mortality. In the acutely ill, the neurologic manifestations of COVID-19 can include distressing but relatively benign symptoms such as headache, myalgias, and anosmia; however, entities such as encephalopathy, stroke, seizures, encephalitis, and Guillain-Barre Syndrome can cause neurologic injury and resulting disability that persists long after the acute pulmonary illness. Furthermore, as many as one-third of patients may experience persistent neurologic symptoms as part of a Post-Acute Sequelae of SARS-CoV-2 infection (Neuro-PASC) syndrome. This Neuro-PASC syndrome can affect patients who required hospitalization for COVID-19 or patients who did not require hospitalization and who may have had minor or no pulmonary symptoms. Given the large number of individuals affected and the ability of neurologic complications to impair quality of life and productivity, the neurologic manifestations of COVID-19 are likely to have major and long-lasting personal, public health, and economic consequences. While knowledge of disease mechanisms and therapies acquired prior to the pandemic can inform us on how to manage patients with the neurologic manifestations of COVID-19, there is a critical need for improved understanding of specific COVID-19 disease mechanisms and development of therapies that target the neurologic morbidities of COVID-19. This current perspective reviews evidence for proposed disease mechanisms as they inform the neurologic management of COVID-19 in adult patients while also identifying areas in need of further research.

Cerebral dysfunctions caused by sepsis during ageing

Systemic inflammation elicited by sepsis can induce an acute cerebral dysfunction known as sepsis-associated encephalopathy (SAE). Recent evidence suggests that SAE is common but shows a dynamic trajectory over time. Half of all patients with sepsis develop SAE in the intensive care unit, and some survivors present with sustained cognitive impairments for several years after initial sepsis onset. It is not clear why some, but not all, patients develop SAE and also the factors that determine the persistence of SAE. Here, we first summarize the chronic pathology and the dynamic changes in cognitive functions seen after the onset of sepsis. We then outline the cerebral effects of sepsis, such as neuroinflammation, alterations in neuronal synapses and neurovascular changes. We discuss the key factors that might contribute to the development and persistence of SAE in older patients, including premorbid neurodegenerative pathology, side effects of sedatives, renal dysfunction and latent virus reactivation. Finally, we postulate that some of the mechanisms that underpin neuropathology in SAE may also be relevant to delirium and persisting cognitive impairments that are seen in patients with severe COVID-19.

Acute Neurologic Complications of COVID-19 and Postacute Sequelae of COVID-19

Neurologic complications can be seen in mild to severe COVID-19 with a higher risk in patients with severe COVID-19. These can occur as a direct consequence of viral infection or consequences of treatments. The spectrum ranges from non-life-threatening, like headache, fatigue, malaise, anosmia, dysgeusia, to life-threatening complications, like stroke, encephalitis, coma, Guillain-Barre syndrome. A high index of suspicion can aid in early recognition and treatment. Outcomes depend on severity of underlying COVID-19, patient age, comorbidities, and severity of the complication. Postacute sequelae of COVID-19 range from fatigue, headache, dysosmia, brain fog, anxiety, depression to an overlap with postintensive care syndrome.

Mechanisms of Entry Into the Central Nervous System by Neuroinvasive Pathogens

BACKGROUND

The literature on neurological manifestations, cerebrospinal fluid analyses, and autopsies in patients with COVID-19 continues to grow. The proposed mechanisms for neurological disease in patients with COVID-19 include indirect processes such as inflammation, microvascular injury, and hypoxic-ischemic damage. An alternate hypothesis suggests direct viral entry of SARS-CoV-2 into the brain and cerebrospinal fluid, given varying reports regarding isolation of viral components from these anatomical sites.

EVIDENCE ACQUISITION

PubMed, Google Scholar databases, and neuroanatomical textbooks were manually searched and reviewed.

RESULTS

We provide clinical concepts regarding the mechanisms of viral pathogen invasion in the central nervous system (CNS); advances in our mechanistic understanding of CNS invasion in well-known neurotropic pathogens can aid in understanding how viruses evolve strategies to enter brain parenchyma. We also present the structural components of CNS compartments that influence viral entry, focusing on hematogenous and transneuronal spread, and discuss this evidence as it relates to our understanding of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2).

CONCLUSIONS

Although there is a paucity of data supporting direct viral entry of SARS-CoV-2 in humans, increasing our knowledge of the structural components of CNS compartments that block viral entry and pathways exploited by pathogens is fundamental to preparing clinicians and researchers for what to expect when a novel emerging virus with neurological symptoms establishes infection in the CNS, and how to design therapeutics to mitigate such an infection.

Autoimmune Voltage-Gated Potassium Channel Limbic Encephalitis With Auditory and Visual Hallucinations

The limbic system (LS) coordinates an important role in memory generation, creating an emotional response to stress, and helping regulate autonomic and endocrine functions. Dysfunction of the limbic system can present secondary to many pathologies including autoimmune, infectious, paraneoplastic, etc. Lesions to the limbic system can also lead to varying symptoms which can be challenging for physicians to correctly identify and treat. Here we report a 59-year-old male with aggressive mood changes and acute onset of auditory and visual hallucinations. The cerebrospinal fluid (CSF) and serum immunological antibody panel confirmed the presence of voltage-gated potassium channel (VGKC) antibodies. Significant radiographic findings included an MRI revealing T2 hyperintensities in the bilateral hippocampus. Paraneoplastic screening with testicular ultrasound and chest CT was completed and was negative. A primary diagnosis of voltage-gated potassium channel limbic encephalitis (VGKC-LE) was made. Management included five days of intravenous immunoglobulin (IVIG) with subsequent resolution of symptoms. The limbic system is an intricate network of neurons that generates and relays key information to other parts of the brain. Its function and, in this case, its dysfunction remain an area of continued research. This case aimed to highlight the importance of recognizing the clinical presentation and objective findings of a rare type of autoimmune encephalitis and identifies the significance of paraneoplastic screening.

Viral Antigen and Inflammatory Biomarkers in Cerebrospinal Fluid in Patients With COVID-19 Infection and Neurologic Symptoms Compared With Control Participants Without Infection or Neurologic Symptoms

IMPORTANCE

Neurologic symptoms are common in COVID-19, but the central nervous system (CNS) pathogenesis is unclear, and viral RNA is rarely detected in cerebrospinal fluid (CSF).

OBJECTIVE

To measure viral antigen and inflammatory biomarkers in CSF in relation to neurologic symptoms and disease severity.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study was performed from March 1, 2020, to June 30, 2021, in patients 18 years or older who were admitted to Sahlgrenska University Hospital, Gothenburg, Sweden, with COVID-19. All patients had CSF samples taken because of neurologic symptoms or within a study protocol. Healthy volunteer and prepandemic control groups were included.

EXPOSURE

SARS-CoV-2 infection.

MAIN OUTCOMES AND MEASURES

Outcomes included CSF SARS-CoV-2 nucleocapsid antigen (N-Ag) using an ultrasensitive antigen capture immunoassay platform and CSF biomarkers of immune activation (neopterin, β2-microglobulin, and cytokines) and neuronal injury (neurofilament light protein [NfL]).

RESULTS

Forty-four patients (median [IQR] age, 57 [48-69] years; 30 [68%] male; 26 with moderate COVID-19 and 18 with severe COVID-19 based on the World Health Organization Clinical Progression Scale), 10 healthy controls (median [IQR] age, 58 [54-60] years; 5 [50%] male), and 41 patient controls (COVID negative without evidence of CNS infection) (median [IQR] age, 59 [49-70] years; 19 [46%] male) were included in the study. Twenty-one patients were neuroasymptomatic and 23 were neurosymptomatic (21 with encephalopathy). In 31 of 35 patients for whom data were available (89%), CSF N-Ag was detected; viral RNA test results were negative in all. Nucleocapsid antigen was significantly correlated with CSF neopterin (r = 0.38; P = .03) and interferon γ (r = 0.42; P = .01). No differences in CSF N-Ag concentrations were found between patient groups. Patients had markedly increased CSF neopterin, β2-microglobulin, interleukin (IL) 2, IL-6, IL-10, and tumor necrosis factor α compared with controls. Neurosymptomatic patients had significantly higher median (IQR) CSF interferon γ (86 [47-172] vs 21 [17-81] fg/mL; P = .03) and had a significantly higher inflammatory biomarker profile using principal component analysis compared with neuroasymptomatic patients (0.54; 95% CI, 0.03-1.05; P = .04). Age-adjusted median (IQR) CSF NfL concentrations were higher in patients compared with controls (960 [673-1307] vs 618 [489-786] ng/L; P = .002). No differences were seen in any CSF biomarkers in moderate compared with severe disease.

CONCLUSIONS AND RELEVANCE

In this study of Swedish adults with COVID-19 infection and neurologic symptoms, compared with control participants, viral antigen was detectable in CSF and correlated with CNS immune activation. Patients with COVID-19 had signs of neuroaxonal injury, and neurosymptomatic patients had a more marked inflammatory profile that could not be attributed to differences in COVID-19 severity. These results highlight the clinical relevance of neurologic symptoms and suggest that viral components can contribute to CNS immune responses without direct viral invasion.

CSF Biomarkers in COVID-19 Associated Encephalopathy and Encephalitis Predict Long-Term Outcome

Patients with coronavirus disease 2019 (COVID-19) frequently develop acute encephalopathy and encephalitis, but whether these complications are the result from viral-induced cytokine storm syndrome or anti-neural autoimmunity is still unclear. In this study, we aimed to evaluate the diagnostic and prognostic role of CSF and serum biomarkers of inflammation (a wide array of cytokines, antibodies against neural antigens, and IgG oligoclonal bands), and neuroaxonal damage (14-3-3 protein and neurofilament light [NfL]) in patients with acute COVID-19 and associated neurologic manifestations (neuro-COVID). We prospectively included 60 hospitalized neuro-COVID patients, 25 (42%) of them with encephalopathy and 14 (23%) with encephalitis, and followed them for 18 months. We found that, compared to healthy controls (HC), neuro-COVID patients presented elevated levels of IL-18, IL-6, and IL-8 in both serum and CSF. MCP1 was elevated only in CSF, while IL-10, IL-1RA, IP-10, MIG and NfL were increased only in serum. Patients with COVID-associated encephalitis or encephalopathy had distinct serum and CSF cytokine profiles compared with HC, but no differences were found when both clinical groups were compared to each other. Antibodies against neural antigens were negative in both groups. While the levels of neuroaxonal damage markers, 14-3-3 and NfL, and the proinflammatory cytokines IL-18, IL-1RA and IL-8 significantly associated with acute COVID-19 severity, only the levels of 14-3-3 and NfL in CSF significantly correlated with the degree of neurologic disability in the daily activities at 18 months follow-up. Thus, the inflammatory process promoted by SARS-CoV-2 infection might include blood-brain barrier disruption in patients with neurological involvement. In conclusion, the fact that the levels of pro-inflammatory cytokines do not predict the long-term functional outcome suggests that the prognosis is more related to neuronal damage than to the acute neuroinflammatory process.

The cognitive and psychiatric subacute impairment in severe Covid-19

Neurologic impairment persisting months after acute severe SARS-CoV-2 infection has been described because of several pathogenic mechanisms, including persistent systemic inflammation. The objective of this study is to analyze the selective involvement of the different cognitive domains and the existence of related biomarkers. Cross-sectional multicentric study of patients who survived severe infection with SARS-CoV-2 consecutively recruited between 90 and 120 days after hospital discharge. All patients underwent an exhaustive study of cognitive functions as well as plasma determination of pro-inflammatory, neurotrophic factors and light-chain neurofilaments. A principal component analysis extracted the main independent characteristics of the syndrome. 152 patients were recruited. The results of our study preferential involvement of episodic and working memory, executive functions, and attention and relatively less affectation of other cortical functions. In addition, anxiety and depression pictures are constant in our cohort. Several plasma chemokines concentrations were elevated compared with both, a non-SARS-Cov2 infected cohort of neurological outpatients or a control healthy general population. Severe Covid-19 patients can develop an amnesic and dysexecutive syndrome with neuropsychiatric manifestations. We do not know if the deficits detected can persist in the long term and if this can trigger or accelerate the onset of neurodegenerative diseases.

Potential role of neurofilament in COVID-19 and preeclampsia

Neurofilament light (NFL) is a promising circulating biomarker in preeclampsia and COVID-19, even without evident neurological complications. Several pathways might contribute to the elevated serum NFL levels seen in both pathologies. Future studies will determine whether NFL is a long COVID marker and delineate NFL’s role in COVID-19-associated preeclampsia.

Can SARS-CoV-2 Infection Lead to Neurodegeneration and Parkinson's Disease?

The SARS-CoV-2 pandemic has affected the daily life of the worldwide population since 2020. Links between the newly discovered viral infection and the pathogenesis of neurodegenerative diseases have been investigated in different studies. This review aims to summarize the literature concerning COVID-19 and Parkinson's disease (PD) to give an overview on the interface between viral infection and neurodegeneration with regard to this current topic. We will highlight SARS-CoV-2 neurotropism, neuropathology and the suspected pathophysiological links between the infection and neurodegeneration as well as the psychosocial impact of the pandemic on patients with PD. Some evidence discussed in this review suggests that the SARS-CoV-2 pandemic might be followed by a higher incidence of neurodegenerative diseases in the future. However, the data generated so far are not sufficient to confirm that COVID-19 can trigger or accelerate neurodegenerative diseases.

Neuropathogenesis of severe acute respiratory syndrome coronavirus 2

PURPOSE OF REVIEW

The purpose of this review is to address our current understanding of the pathophysiology of neurologic injury resulting from severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection on the developing nervous system.

RECENT FINDINGS

SARS-CoV2 may enter the brain through three potential mechanisms: transsynaptic spread from the olfactory bulb following intranasal exposure, migration across the blood-brain barrier through endothelial cell infection, and migration following disruption of the blood-brain barrier from resulting inflammation. SARS-CoV2 does not appear to directly infect neurons but rather may produce an inflammatory cascade that results in neuronal injury. Additionally, autoantibodies targeting neuronal tissue resulting from the immune response to SARS-CoV2 are present in select patients and may contribute to central nervous system (CNS) injury.

SUMMARY

These findings suggest that neuronal injury during SARS-CoV2 infection is immune mediated rather than through direct viral invasion. Further multimodal studies evaluating the pathophysiology of neurologic conditions in pediatric patients specifically following SARS-CoV2 infection are needed to improve our understanding of mechanisms driving neurologic injury and to identify potential treatment options.

Dynamic Changes in Central and Peripheral Neuro-Injury vs. Neuroprotective Serum Markers in COVID-19 Are Modulated by Different Types of Anti-Viral Treatments but Do Not Affect the Incidence of Late and Early Strokes

The balance between neurodegeneration, neuroinflammation, neuroprotection, and COVID-19-directed therapy may underly the heterogeneity of SARS-CoV-2's neurological outcomes. A total of 105 patients hospitalized with a diagnosis of COVID-19 had serum collected over a 6 month period to assess neuroinflammatory (MIF, CCL23, MCP-1), neuro-injury (NFL, NCAM-1), neurodegenerative (KLK6, τ, phospho τ, amyloids, TDP43, YKL40), and neuroprotective (clusterin, fetuin, TREM-2) proteins. These were compared to markers of nonspecific inflammatory responses (IL-6, D-dimer, CRP) and of the overall viral burden (spike protein). Data regarding treatment (steroids, convalescent plasma, remdasavir), pre-existing conditions, and incidences of strokes were collected. Amyloid β42, TDP43, NF-L, and KLK6 serum levels declined 2-3 days post-admission, yet recovered to admission baseline levels by 7 days. YKL-40 and NCAM-1 levels remained elevated over time, with clusters of differential responses identified among TREM-2, TDP43, and YKL40. Fetuin was elevated after the onset of COVID-19 while TREM-2 initially declined before significantly increasing over time. MIF serum level was increased 3-7 days after admission. Ferritin correlated with TDP-43 and KLK6. No treatment with remdesivir coincided with elevations in Amyloid-β40. A lack of convalescent plasma resulted in increased NCAM-1 and total tau, and steroidal treatments did not significantly affect any markers. A total of 11 incidences of stroke were registered up to six months after initial admission for COVID-19. Elevated D-dimer, platelet counts, IL-6, and leukopenia were observed. Variable MIF serum levels differentiated patients with CVA from those who did not have a stroke during the acute phase of COVID-19. This study demonstrated concomitant and opposite changes in neurodegenerative and neuroprotective markers persisting well into recovery.

Cellular and Molecular Effects of SARS-CoV-2 Linking Lung Infection to the Brain

In December 2019, a new viral disease emerged and quickly spread all around the world. In March 2020, the COVID-19 outbreak was classified as a global pandemic and by June 2021, the number of infected people grew to over 170 million. Along with the patients' mild-to-severe respiratory symptoms, reports on probable central nervous system (CNS) effects appeared shortly, raising concerns about the possible long-term detrimental effects on human cognition. It remains unresolved whether the neurological symptoms are caused directly by the SARS-CoV-2 infiltration in the brain, indirectly by secondary immune effects of a cytokine storm and antibody overproduction, or as a consequence of systemic hypoxia-mediated microglia activation. In severe COVID-19 cases with impaired lung capacity, hypoxia is an anticipated subsidiary event that can cause progressive and irreversible damage to neurons. To resolve this problem, intensive research is currently ongoing, which seeks to evaluate the SARS-CoV-2 virus' neuroinvasive potential and the examination of the antibody and autoantibody generation upon infection, as well as the effects of prolonged systemic hypoxia on the CNS. In this review, we summarize the current research on the possible interplay of the SARS-CoV-2 effects on the lung, especially on alveolar macrophages and direct and indirect effects on the brain, with special emphasis on microglia, as a possible culprit of neurological manifestation during COVID-19.