Increased serum neurofilament light chain concentration indicates poor outcome in Guillain-Barré syndrome

Serum neurofilament light chain predicts disease severity in axonal variants of acute immune neuropathies: A retrospective monocentric cohort study

BACKGROUND AND PURPOSE

The purpose was to explore the prognostic utility of neurofilament light chain (NfL) in patients with immune-mediated polyradiculoneuropathies (IMPs).

METHODS

This retrospective monocentric study analysed serum and cerebrospinal fluid samples from patients diagnosed with IMP collected prior to treatment initiation. NfL concentrations were correlated with clinical outcomes, including F score and hospitalization duration.

RESULTS

Amongst 115 IMP patients tested, baseline cerebrospinal fluid and serum NfL (sNfL) concentrations were higher in acute inflammatory axonal polyradiculoneuropathy (AIAP) than other IMP variants. In the AIAP cohort, a positive correlation was observed between baseline sNfL concentrations, F score and hospitalization duration. Multivariate linear regression analysis further supported the predictive relationship between elevated baseline sNfL concentrations and clinical outcomes. Using receiver operating characteristic analysis, a cut-off value for sNfL of 351 pg/mL was found to predict an F score >3 in AIAP with a sensitivity of 40% and specificity of 81.8%. AIAP patients with sNfL concentrations above this threshold required longer hospitalization (extended by 15 days).

DISCUSSION

Our findings highlight the potential of baseline sNfL as an effective marker for distinguishing between IMP variants and predicting the prognosis of AIAP. Further validation may facilitate translation of sNfL into clinical practice, potentially identifying high-risk patients for tailored treatment approaches.

All-Cause Mortality Differentials by Diabetes Status and Serum Neurofilament Light-Chain Levels in US General Adults

CONTEXT

Neurofilament light chains (sNFLs) increase in patients with diabetes (DM) and are associated with death.

OBJECTIVE

This work aimed to examine whether sNFL mediates associations of DM with all-cause mortality and the extent of interaction or joint relations of sNFL and DM with mortality.

METHODS

This population-based cohort study was conducted using the 2013 to 2014 cycle of the National Health and Nutrition Examination Survey. A total of 2071 adults aged 20 to 75 years with sNFL measurements were included. sNFL was lg-transformed (LgNfl). Participants were included whose LgNfl was higher than 1.48 pg/mL or who were diagnosed with DM. All-cause mortality was the primary outcome obtained through linkage to registries.

RESULTS

During a median follow-up of 6.1years, 85 participants died. Incidence rates (per 1000 person-years [95% CI]) of all-cause mortality were 27.78 (19.98∼35.58) in adults with LgNfl greater than 1.48 pg/mL and DM, 9.01 (1.99∼16.03) in adults with LgNfl greater than 1.48 pg/mL but no DM, 3.07 (1.01∼5.13) in adults with DM and LgNfl less than or equal to 1.48 pg/mL, and 2.21 (1.15∼3.27) in adults without DM and LgNfl less than or equal to 1.48 pg/mL. Significant interaction but not mediation was observed between LgNfl and DM. Compared with adults without DM and LgNfl less than or equal to 1.48 pg/mL, those with DM and LgNfl greater than 1.48 pg/mL had higher risks of all-cause mortality (hazard ratio; 95% CI, 7.06; 3.52∼14.16).

CONCLUSION

In general US adults with DM, elevated sNFLs were associated with higher all-cause mortality specifically, supporting an important role of sNFLs in predicting health outcome in individuals with DM.

Neurofilament light chain as a diagnostic and prognostic biomarker in Guillain-Barré syndrome

BACKGROUND

Elevated neurofilament light chain (NfL) levels are associated with worse prognosis in Guillain-Barré syndrome (GBS). Our objectives were to determine the utility of serum NfL (sNfL), cerebrospinal fluid (CSF)/serum NfL ratio and NfL index as prognostic and diagnostic biomarkers for GBS.

METHODS

We measured NfL in serum and/or CSF obtained from 96 GBS patients between 1989 and 2014 in western Sweden. The sNfL Z-scores, NfL ratios and NfL indices were calculated. Outcome was determined with the GBS disability scale (GBSDS) at 3 and 12 months. NfL parameters in GBS were compared with healthy controls (HC), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS).

RESULTS

The sNfL Z-score was higher for GBSDS > 2 at 3 months (median [IQR], 3.5 ng/L [3.2-4.0], vs 2.6 [1.7-3.4], p = 0.008) and at 12 months (3.6 ng/L [3.5-3.8] vs 2.6 [1.8-3.5], p = 0.049). NfL ratio and index were not associated with outcome. The area under the curve (AUC) for sNfL Z-score was 0.76 (95% CI 0.58-0.93, p < 0.0001) for GBSDS > 2 at 3 months. NfL ratio and index were lower in GBS than HC, MS, and ALS. The AUC for the NfL ratio was 0.66 (95% CI 0.55-0.78, p = 0.0018) and for the NfL index 0.86 (95% CI 0.78-0.93, p < 0.0001).

DISCUSSION

Our results confirm sNfL as prognostic biomarker for GBS and the precision was improved using the age-adjusted sNfL Z score. NfL index and Qalb are potential diagnostic biomarkers for GBS.

Serum neurofilament light chain levels correlate with small fiber related parameters in patients with hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN)

BACKGROUND

Recent evidence suggests that both serum neurofilament light chain (sNfL) levels and small fiber related diagnostic variables may be valuable disease biomarkers of hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN). Our study aimed to explore the relations between sNfL and small fiber related skin biopsy and quantitative sensory testing (QST) parameters in a cohort of ATTRv-PN patients and pre-symptomatic carriers.

METHODS

We retrospectively analyzed data from 13 ATTRv patients and 21 pre-symptomatic carriers who underwent sNfL dosage, skin biopsy, and QST, and analyzed correlations between sNFL, intraepidermal nerve fiber density (IENFD), and cold (CDT) and warm detection thresholds (WDT).

RESULTS

Both sNfL and small fiber related parameters significantly differed between carriers and patients (sNfL: p < 0.0001; IENFD: p = 0.0008; CDT, WDT: < 0.0001). sNFL levels were normal in all carriers, altered in 85% of patients, negatively correlated with distal IENFD (r = -0.47, p = 0.005), and significantly correlated with CDT (r = -0.68; p < 0.0001) and WDT (r = 0.57; p < 0.0001).

CONCLUSIONS

Our study showed that sNfL reliably discriminates symptomatic ATTRv-PN patients from pre-symptomatic carriers, and found significant relations between sNfL, skin biopsy, and QST small fiber related parameters, suggesting that sNfL might be a valuable biomarker of peripheral nerve involvement in ATTRv-PN and a supportive criterion for symptomatic disease transition.

Guillain-Barré Syndrome Complicated by Severe Acute Respiratory Distress Syndrome: A Case Report

Guillain-Barré syndrome (GBS) stands out as the most prevalent and severe acute immune-mediated paralytic neuropathy. Approximately 30% of patients experience respiratory failure necessitating admission to the intensive care unit (ICU) and invasive mechanical ventilation. The management of diseases concomitant with acute respiratory distress syndrome (ARDS) poses significant challenges. This case report illustrates the swift development of ARDS in a patient with GBS, explores the utility of the biomarker neurofilament light chain, and highlights the unexpected advantages of proactive ARDS intervention.

Diabetic Peripheral Neuropathy: Emerging Treatments of Neuropathic Pain and Novel Diagnostic Methods

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a prevalent and debilitating complication of diabetes, often leading to severe neuropathic pain. Although other diabetes-related complications have witnessed a surge of emerging treatments in recent years, DPN has seen minimal progression. This stagnation stems from various factors, including insensitive diagnostic methods and inadequate treatment options for neuropathic pain.

METHODS

In this comprehensive review, we highlight promising novel diagnostic techniques for assessing DPN, elucidating their development, strengths, and limitations, and assessing their potential as future reliable clinical biomarkers and endpoints. In addition, we delve into the most promising emerging pharmacological and mechanistic treatments for managing neuropathic pain, an area currently characterized by inadequate pain relief and a notable burden of side effects.

RESULTS

Skin biopsies, corneal confocal microscopy, transcutaneous electrical stimulation, blood-derived biomarkers, and multi-omics emerge as some of the most promising new techniques, while low-dose naltrexone, selective sodium-channel blockers, calcitonin gene-related peptide antibodies, and angiotensin type 2 receptor antagonists emerge as some of the most promising new drug candidates.

CONCLUSION

Our review concludes that although several promising diagnostic modalities and emerging treatments exist, an ongoing need persists for the further development of sensitive diagnostic tools and mechanism-based, personalized treatment approaches.

Serum neurofilament light chain levels are associated with depression among US adults: a cross-sectional analysis among US adults, 2013-2014

BACKGROUND

Serum neurofilament light chain (sNfL) has been identified as a biomarker for neurologic diseases. However, sNfL remains unknown to be responsible for depression.

AIMS

The aim of this research was to explore the relationship between sNfL levels and depression in US adults.

METHODS

In this cross-sectional survey of the general population, we investigated representative data involving 10,175 participants from the 2013-2014 cycle of the National Health and Nutrition Examination Survey (NHANES). Depression was diagnosed using the Patient Health Questionnaire-9 (PHQ-9). The effect of related factors on depression was analyzed by conducting a univariate analysis. Stratified analysis was utilized to detect the stability and sensitivity of the relationship. After adjusting for race, education, marital status, smoking status, body mass index (BMI), sleep duration, income, and a history of hypertension, sedentary behavior and stroke, multivariable linear regression was performed to demonstrate the correlation between sNfL and depression.

RESULTS

A total of 1301 individuals between the ages of 20 and 75 were involved in this investigation, of which 108 (8.3%) were diagnosed with depression. A significant positive correlation between sNfL and depression among adults in the US was observed by conducting univariable analyses. After adjusting for confounding factors, the multivariate analyses indicated that elevated sNfL levels might play a pivotal role in the development of depression (odds ratio (OR) = 3.0; 95% confidence interval (CI): (1.5, 6.1), P = 0.002).

CONCLUSION

These results indicated that sNfL is closely linked to depression in a nationally representative individual. However, further studies are needed to confirm the biological mechanism as well as the clinical implications of sNfL and depression.

Neurofilaments in neurologic disease

Neurofilaments (NFs), major cytoskeletal constituents of neurons, have emerged as universal biomarkers of neuronal injury. Neuroaxonal damage underlies permanent disability in various neurological conditions. It is crucial to accurately quantify and longitudinally monitor this damage to evaluate disease progression, evaluate treatment effectiveness, contribute to novel treatment development, and offer prognostic insights. Neurofilaments show promise for this purpose, as their levels increase with neuroaxonal damage in both cerebrospinal fluid and blood, independent of specific causal pathways. New assays with high sensitivity allow reliable measurement of neurofilaments in body fluids and open avenues to investigate their role in neurological disorders. This book chapter will delve into the evolving landscape of neurofilaments, starting with their structure and cellular functions within neurons. It will then provide a comprehensive overview of their broad clinical value as biomarkers in diseases affecting the central or peripheral nervous system.

Increased Cerebrospinal Fluid Adenosine 5'-Triphosphate Levels in Patients with Guillain-Barré Syndrome and Chronic Inflammatory Demyelinating Polyneuropathy

Background

Extracellular adenosine 5'-triphosphate (ATP) acts as a signaling molecule in the peripheral nerves, regulating myelination after nerve injury. The present study examined whether the cerebrospinal fluid (CSF) ATP levels in patients with Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP) are related to disease severity.

Methods

CSF ATP levels in 13 patients with GBS and 18 patients with CIDP were compared with those in a control group of 16 patients with other neurological diseases (ONDs). In patients with CIDP, CSF ATP levels were compared before and after treatment. The correlations between CSF ATP levels and other factors, including clinical data and CSF protein levels, were also evaluated.

Results

Median CSF ATP levels were significantly higher in patients with GBS and CIDP than in those with ONDs. When patients with CIDP were classified into two groups depending on their responsiveness to immunotherapy, median CSF ATP levels were significantly higher in good responders than in ONDs. CSF ATP levels tended to decrease after treatment in patients with CIDP. In patients with CIDP, there is a negative correlation between CSF ATP and CSF protein levels.

Conclusions

CSF ATP levels were increased in patients with GBS and CIDP. In particular, CSF ATP levels tended to decrease following treatment in patients with CIDP. CSF ATP levels may be useful biomarkers for the diagnosis or monitoring of therapeutic effects in patients with GBS and CIDP.

Improving Outcome in Severe Myasthenia Gravis and Guillain-Barré Syndrome

When progressive and severe, myasthenia gravis and Guillain-Barré syndrome may have the potential for fatal and unfavorable clinical outcomes. Regardless of important differences in their clinical course, the development of weakness of oropharyngeal muscles and respiratory failure with requirement of mechanical ventilation is the main driver of poor prognosis in both conditions. The need for prolonged mechanical ventilation is particularly relevant because it immobilizes the patient and care becomes extraordinarily complex due to daily risks of systemic complications. Additionally, patients with myasthenia gravis often require long-term immunosuppressive treatments with associated toxicity and infectious risks. Unlike myasthenia gravis, the recovery period is prolonged in Guillain-Barré syndrome, but often favorable, even in the more severely affected patients. Outcome, for a large part, is determined by expert neurocritical care.

Neurofilaments as biomarkers in neurological disorders - towards clinical application

Neurofilament proteins have been validated as specific body fluid biomarkers of neuro-axonal injury. The advent of highly sensitive analytical platforms that enable reliable quantification of neurofilaments in blood samples and simplify longitudinal follow-up has paved the way for the development of neurofilaments as a biomarker in clinical practice. Potential applications include assessment of disease activity, monitoring of treatment responses, and determining prognosis in many acute and chronic neurological disorders as well as their use as an outcome measure in trials of novel therapies. Progress has now moved the measurement of neurofilaments to the doorstep of routine clinical practice for the evaluation of individuals. In this Review, we first outline current knowledge on the structure and function of neurofilaments. We then discuss analytical and statistical approaches and challenges in determining neurofilament levels in different clinical contexts and assess the implications of neurofilament light chain (NfL) levels in normal ageing and the confounding factors that need to be considered when interpreting NfL measures. In addition, we summarize the current value and potential clinical applications of neurofilaments as a biomarker of neuro-axonal damage in a range of neurological disorders, including multiple sclerosis, Alzheimer disease, frontotemporal dementia, amyotrophic lateral sclerosis, stroke and cerebrovascular disease, traumatic brain injury, and Parkinson disease. We also consider the steps needed to complete the translation of neurofilaments from the laboratory to the management of neurological diseases in clinical practice.

Studying serum neurofilament light chain levels as a potential new biomarker for small fiber neuropathy

BACKGROUND AND PURPOSE

Diagnosing small fiber neuropathies can be challenging. To address this issue, whether serum neurofilament light chain (sNfL) could serve as a potential biomarker of damage to epidermal Aδ- and C-fibers was tested.

METHODS

Serum NfL levels were assessed in 30 patients diagnosed with small fiber neuropathy and were compared to a control group of 19 healthy individuals. Electrophysiological studies, quantitative sensory testing and quantification of intraepidermal nerve fiber density after skin biopsy were performed in both the proximal and distal leg.

RESULTS

Serum NfL levels were not increased in patients with small fiber neuropathy compared to healthy controls (9.1 ± 3.9 and 9.4 ± 3.8, p = 0.83) and did not correlate with intraepidermal nerve fiber density at the lateral calf or lateral thigh or with other parameters of small fiber impairment.

CONCLUSION

Serum NfL levels cannot serve as a biomarker for small fiber damage.

Dynamics and prognostic value of serum neurofilament light chain in Guillain-Barré syndrome

BACKGROUND

Neurofilament light chain (NfL) is a biomarker for axonal damage in several neurological disorders. We studied the longitudinal changes in serum NfL in patients with Guillain-Barré syndrome (GBS) in relation to disease severity, electrophysiological subtype, treatment response, and prognosis.

METHODS

We included patients with GBS who participated in a double-blind, randomised, placebo-controlled trial that evaluated the effects of a second course of intravenous immunoglobulin (IVIg) on clinical outcomes. Serum NfL levels were measured before initiation of treatment and at one, two, four, and twelve weeks using a Simoa HD-X Analyzer. Serum NfL dynamics were analysed using linear mixed-effects models. Logistic regression was employed to determine the associations of serum NfL with clinical outcome and the prognostic value of serum NfL after correcting for known prognostic markers included in the modified Erasmus GBS Outcome Score (mEGOS).

FINDINGS

NfL levels were tested in serum from 281 patients. Serum NfL dynamics were associated with disease severity and electrophysiological subtype. Strong associations were found between high levels of serum NfL at two weeks and inability to walk unaided at four weeks (OR = 1.74, 95% CI = 1.27-2.45), and high serum NfL levels at four weeks and inability to walk unaided at 26 weeks (OR = 2.79, 95% CI = 1.72-4.90). Baseline serum NfL had the most significant prognostic value for ability to walk, independent of predictors included in the mEGOS. The time to regain ability to walk unaided was significantly longer for patients with highest serum NfL levels at baseline (p = 0.0048) and week 2 (p < 0.0001). No differences in serum NfL were observed between patients that received a second IVIg course vs. IVIg and placebo.

INTERPRETATION

Serum NfL levels are associated with disease severity, axonal involvement, and poor outcome in GBS. Serum NfL potentially represents a biomarker to monitor neuronal damage in GBS and an intermediate endpoint to evaluate the effects of treatment.

FUNDING

Prinses Beatrix Spierfonds W.OR19-24.

Guidance for use of neurofilament light chain as a cerebrospinal fluid and blood biomarker in multiple sclerosis management

Neurofilament light chain (NfL) is a long-awaited blood biomarker that can provide clinically useful information about prognosis and therapeutic efficacy in multiple sclerosis (MS). There is now substantial evidence for this biomarker to be used alongside magnetic resonance imaging (MRI) and clinical measures of disease progression as a decision-making tool for the management of patients with MS. Serum NfL (sNfL) has certain advantages over traditional measures of MS disease progression such as MRI because it is relatively noninvasive, inexpensive, and can be repeated frequently to monitor activity and treatment efficacy. sNfL levels can be monitored regularly in patients with MS to determine change from baseline and predict subclinical disease activity, relapse risk, and the development of gadolinium-enhancing (Gd+) lesions. sNfL does not replace MRI, which provides information related to spatial localisation and lesion stage. Laboratory platforms are starting to be made available for clinical application of sNfL in several countries. Further work is needed to resolve issues around comparisons across testing platforms (absolute values) and normalisation (reference ranges) in order to guide interpretation of the results.

The pathophysiological role of endoneurial inflammatory edema in early classical Guillain-Barré syndrome

The objective of this review was to analyze the pathophysiological role of endoneurial inflammatory edema in initial stages of classic Guillain-Barré syndrome (GBS), arbitrarily divided into very early GBS (≤ 4 days after symptom onset) and early GBS (≤ 10 days). Classic GBS, with variable degree of flaccid and areflexic tetraparesis, encompasses demyelinating and axonal forms. Initial autopsy studies in early GBS have demonstrated that endoneurial inflammatory edema of proximal nerve trunks, particularly spinal nerves, is the outstanding lesion. Variable permeability of the blood-nerve barrier dictates such lesion topography. In proximal nerve trunks possessing epi-perineurium, edema may increase the endoneurial fluid pressure causing ischemic changes. Critical analysis the first pathological description of the axonal form GBS shows a combination of axonal degeneration and demyelination in spinal roots, and pure Wallerian-like degeneration in peripheral nerve trunks. This case might be reclassified as demyelinating GBS with secondary axonal degeneration. Both in acute motor axonal neuropathy and acute motor-sensory axonal neuropathy, Wallerian-like degeneration of motor fibers predominates in the distal part of ventral spinal roots abutting the dura mater, another feature re-emphasizing the pathogenic relevance of this area. Electrophysiological and imaging studies also point to a predominant alteration at the spinal nerve level, which is a hotspot in any early GBS subtype. Serum biomarkers of axonal damage, including neurofilament light chain and peripherin, are increased in the great majority of patients with any early GBS subtype; endoneurial ischemia of proximal nerve trunks could contribute to such axonal damage. It is concluded that inflammatory edema of proximal nerve trunks is an essential pathogenic event in early GBS, which has a tangible impact for accurate approach to the disease.

Elevated plasma neurofilament light chain in immune-mediated neurological disorders (IMND) detected by immunomagnetic reduction (IMR)

BACKGROUND

In cases of immune-mediated neurological disorders (IMND), different syndromes are associated with antibodies against neuronal surface antigens, intra-neuronal antigens, astrocytic aquaporin, and gangliosides. These autoantibodies can be pathogenic or connected to neuroinflammation and resulting neuronal injuries. This study aims to identify a blood biomarker that can detect neuronal damage in individuals with IMND. To this end, we use immunomagnetic reduction (IMR) nanobead technology to measure plasma neurofilament light chain (NfL).

METHODS

The patients with IMND were enrolled in the Chang Gung Memorial Hospital at Keelung from 2018 to 2023. Seronegative patients were excluded based on the results of antibody tests. The healthy controls (HC) were community-dwelling adults from the Northeastern Taiwan Community Medicine Research Cohort (NTCMRC) conducted by the Community Medicine Research Center of the Keelung CGMH from 2020 to 2022. IMR technique detects magnetic susceptibility via measuring magnetic signal reduction caused by antigen-antibody immunocomplex formation on magnetic nanobeads. The plasma level of NfL was determined by the magnetic susceptibility changes in IMR.

RESULTS

The study enrolled 57 IMND patients from the hospital and 73 HC participants from the communities. The plasma NfL was significantly higher in the IMND than in the HC (11.022 ± 2.637 vs. 9.664 ± 2.610 pg/mL, p = 0.004), regardless of age effects on plasma NfL in an analysis of covariance (ANCOVA) (F = 0.720, p = 0.950). In the receiver of operation curve analysis, the area under curve for plasma NfL to discriminate IMND and HC was 0.664 (95% CI = 0.549 to 0.739, p = 0.005). The subgroup analysis of plasma NfL in the IMND patients showed no difference between peripheral immune-mediated neuropathy (IMN) and central immune-mediated encephalomyelitis (IMEM) (11.331 ± 2.895 vs. 10.627 ± 2.260 pg/mL, p = 0.322), nor between tumor and non-tumor IMND (10.784 ± 3.446 vs. 11.093 ± 2.391 pg/mL, p = 0.714). Additionally, the antibody class of ganglioside antibodies in IMN did not have an impact on plasma NfL level (p = 0.857).

CONCLUSION

Plasma NfL measurement is a reliable indicator of axonal injuries in patients with IMND. It is equally effective in detecting nerve injuries in inflammatory peripheral neuropathies and central neuroinflammation. The IMR nanobead technology offers a feasible method of detecting plasma NfL, which helps identify axonal injuries in IMND.

Serum neurofilament light chain as an early diagnostic biomarker for critical illness polyneuropathy

BACKGROUND

Critical illness polyneuropathy (CIP) commonly occurs in critical care unit (CCU) patients, but timely diagnosis can be challenging. Therefore, new biomarkers, such as serum neurofilament light chain (sNfL), could help to improve early identification of patients with this condition.

METHODS

CIP was diagnosed or excluded with neurological assessment and nerve conduction measurement in a prospective study of CCU patients. sNfL and secondary predictors for neuropathy (neuron-specific enolase (NSE), S100, folic acid, and vitamin B12) were measured at admission. Cases and controls were compared regarding the predictors.

RESULTS

Nineteen patients met the inclusion criteria. CIP was considered definitely or most likely present in seven (37%, cases) and definitely or most likely absent in 12 individuals (63%, controls). At admission, sNfL levels were significantly higher in the cases than in the controls: 405 (IQR 77 to 835) vs. 27 (IQR 12 to 90) pg/mL; difference of medians 375, 95% confidence interval [14, 736], pg/mL; P=0.04. We found no significant differences regarding the secondary predictors at baseline. Cases had longer durations of CCU stay (median 19 (IQR 11 to 44) vs. 8 (IQR five to ten) and increased mortality (57% vs. 33% deceased) compared to controls.

CONCLUSIONS

Levels of serum neurofilament light chain are higher in patients who develop CIP soon after CCU admission and might be helpful in identifying those individuals early.

Neuroprognostication: Guillain-Barré Syndrome

Guillain-Barré syndrome is an immune-mediated disease of the peripheral nerves characterized by rapidly progressing symmetric weakness, areflexia, and albuminocytological dissociation. Most patients reach their nadir within 2 weeks. Disease severity can be mild to severe, with 20% of patients requiring mechanical ventilation. Intravenous immunoglobulin and plasma exchange are equally effective treatments. Monitoring strength, respiratory function, blood pressure, and heart rate, as well as pain management and rehabilitative therapy are important aspects of management. About 20% of patients require assistance to walk at 6 months. Older age, preceding diarrhea, and lower Medical Research Council (MRC) sum scores predict poor outcome. Death from cardiovascular and respiratory complications can occur in the acute or recovery phases of the illness in 3 to 7% of the patients. Risk factors for mortality include advanced age and disease severity at onset. Neuropathic pain, weakness, and fatigue can be residual symptoms; risk factors for these include axonal loss, sensory involvement, and severity of illness.

CYBA allelic variants are associated with severity and recovery in Guillain-Barré syndrome

BACKGROUND AND AIMS

Guillain-Barré syndrome (GBS) is a rare, acute neuropathy characterized by ascending muscle weakness. Age, axonal GBS variants, and antecedent Campylobacter jejuni infection are associated with severe GBS, but the detailed mechanisms of nerve damage are only partly explored. Pro-inflammatory myeloid cells express NADPH oxidases (NOX) that generate tissue-toxic reactive oxygen species (ROS) that are implicated in neurodegenerative diseases. This study analyzed the impact of variants of the gene encoding the functional NOX subunit CYBA (p22phox ) on acute severity, axonal damage, and recovery in adult GBS patients.

METHODS

Extracted DNA from 121 patients was genotyped for allelic variation at rs1049254 and rs4673 within CYBA using real-time quantitative polymerase chain reaction. Serum neurofilament light chain was quantified by single molecule array. Patients were followed for severity and motor function recovery for up to 13 years.

RESULTS

CYBA genotypes linked to reduced formation of ROS, i.e. rs1049254/G and rs4673/A, were significantly associated with unassisted ventilation, shorter time to normalization of serum neurofilament light chain and shorter time to regained motor function. Residual disability at follow-up was confined to patients carrying CYBA alleles associated with high formation of ROS.

INTERPRETATION

These findings implicate NOX-derived ROS in GBS pathophysiology and CYBA alleles as biomarkers of severity.

Emerging biomarkers to predict clinical outcomes in Guillain-Barré syndrome

INTRODUCTION

Guillain-Barré syndrome (GBS) is an immune-mediated poly(radiculo)neuropathy with a variable clinical outcome. Identifying patients who are at risk of suffering from long-term disabilities is a great challenge. Biomarkers are useful to confirm diagnosis, monitor disease progression, and predict outcome.

AREAS COVERED

The authors provide an overview of the diagnostic and prognostic biomarkers for GBS, which are useful for establishing early treatment strategies and follow-up care plans.

EXPERT OPINION

Detecting patients at risk of developing a severe outcome may improve management of disease progression and limit potential complications. Several clinical factors are associated with poor prognosis: higher age, presence of diarrhea within 4 weeks of symptom onset, rapid and severe weakness progression, dysautonomia, decreased vital capacity and facial, bulbar, and neck weakness. Biological, neurophysiological and imaging measures of unfavorable outcome include multiple anti-ganglioside antibodies elevation, increased serum and CSF neurofilaments light (NfL) and heavy chain, decreased NfL CSF/serum ratio, hypoalbuminemia, nerve conduction study with early signs of demyelination or axonal loss and enlargement of nerve cross-sectional area on ultrasound. Depicting prognostic biomarkers aims at predicting short-term mortality and need for cardio-pulmonary support, long-term patient functional outcome, guiding treatment decisions and monitoring therapeutic responses in future clinical trials.

Prediabetes is associated with a higher serum neurofilament light chain level in adolescents

Objective

Serum neurofilament light chain (sNfL) level, which is a biomarker indicative of neuroaxonal damage and cognitive impairment, has been reported in several neurological diseases. There has been a lack of studies on the association between sNfL levels and prediabetes in adolescents. This study investigated whether sNfL levels were higher in adolescents with prediabetes undergoing elective orthopedic surgery.

Methods

The sNfL level was measured in 149 adolescents aged from 12 to 18 years who underwent elective orthopedic surgery at the Hunan Children's Hospital (18 with and 131 without prediabetes). We evaluated the association between prediabetes and sNfL level after adjusting for age, sex, and triglycerides using a multivariable linear regression model.

Results

The prevalence of prediabetes in adolescents was 12.08%. Univariate logistic regression analysis showed that prediabetes was related to sNfL. In multivariate logistic regression analysis, the association between prediabetes with sNfL levels remained significant after adjustment for age, sex, and triglyceride. The relationship between the two was further visualized by a smoothed curve.

Conclusions

Prediabetes is associated with a higher sNfL. Further large-scale and prospective studies are needed to verify the clinical application of sNfL as a monitoring biomarker for adolescent prediabetes in adolescents and to evaluate the performance of sNfL in predicting the incidence of neuropathy and cognitive dysfunction in adolescents with prediabetes.

Kinesin-5 inhibition improves neural regeneration in experimental autoimmune neuritis

BACKGROUND

Autoimmune neuropathies can result in long-term disability and incomplete recovery, despite adequate first-line therapy. Kinesin-5 inhibition was shown to accelerate neurite outgrowth in different preclinical studies. Here, we evaluated the potential neuro-regenerative effects of the small molecule kinesin-5 inhibitor monastrol in a rodent model of acute autoimmune neuropathies, experimental autoimmune neuritis.

METHODS

Experimental autoimmune neuritis was induced in Lewis rats with the neurogenic P2-peptide. At the beginning of the recovery phase at day 18, the animals were treated with 1 mg/kg monastrol or sham and observed until day 30 post-immunisation. Electrophysiological and histological analysis for markers of inflammation and remyelination of the sciatic nerve were performed. Neuromuscular junctions of the tibialis anterior muscles were analysed for reinnervation. We further treated human induced pluripotent stem cells-derived secondary motor neurons with monastrol in different concentrations and performed a neurite outgrowth assay.

RESULTS

Treatment with monastrol enhanced functional and histological recovery in experimental autoimmune neuritis. Motor nerve conduction velocity at day 30 in the treated animals was comparable to pre-neuritis values. Monastrol-treated animals showed partially reinnervated or intact neuromuscular junctions. A significant and dose-dependent accelerated neurite outgrowth was observed after kinesin-5 inhibition as a possible mode of action.

CONCLUSION

Pharmacological kinesin-5 inhibition improves the functional outcome in experimental autoimmune neuritis through accelerated motor neurite outgrowth and histological recovery. This approach could be of interest to improve the outcome of autoimmune neuropathy patients.

Serum neurofilament light chain: a novel biomarker for early diabetic sensorimotor polyneuropathy

AIMS/HYPOTHESIS

No established blood-based biomarker exists to monitor diabetic sensorimotor polyneuropathy (DSPN) and evaluate treatment response. The neurofilament light chain (NFL), a blood biomarker of neuroaxonal damage in several neurodegenerative diseases, represents a potential biomarker for DSPN. We hypothesised that higher serum NFL levels are associated with prevalent DSPN and nerve dysfunction in individuals recently diagnosed with diabetes.

METHODS

This cross-sectional study included 423 adults with type 1 and type 2 diabetes and known diabetes duration of less than 1 year from the prospective observational German Diabetes Study cohort. NFL was measured in serum samples of fasting participants in a multiplex approach using proximity extension assay technology. DSPN was assessed by neurological examination, nerve conduction studies and quantitative sensory testing. Associations of serum NFL with DSPN (defined according to the Toronto Consensus criteria) were estimated using Poisson regression, while multivariable linear and quantile regression models were used to assess associations with nerve function measures. In exploratory analyses, other biomarkers in the multiplex panel were also analysed similarly to NFL.

RESULTS

DSPN was found in 16% of the study sample. Serum NFL levels increased with age. After adjustment for age, sex, waist circumference, height, HbA_1c, known diabetes duration, diabetes type, cholesterol, eGFR, hypertension, CVD, use of lipid-lowering drugs and use of non-steroidal anti-inflammatory drugs, higher serum NFL levels were associated with DSPN (RR [95% CI] per 1-normalised protein expression increase, 1.92 [1.50, 2.45], p<0.0001), slower motor (all p<0.0001) and sensory (all p≤0.03) nerve conduction velocities, lower sural sensory nerve action potential (p=0.0004) and higher thermal detection threshold to warm stimuli (p=0.023 and p=0.004 for hand and foot, respectively). There was no evidence for associations between other neurological biomarkers and DSPN or nerve function measures.

CONCLUSIONS/INTERPRETATION

Our findings in individuals recently diagnosed with diabetes provide new evidence associating higher serum NFL levels with DSPN and peripheral nerve dysfunction. The present study advocates NFL as a potential biomarker for DSPN.

The endogenous calpain inhibitor calpastatin attenuates axon degeneration in murine Guillain-Barré syndrome

Axon degeneration accounts for the poor clinical outcome in Guillain-Barré syndrome (GBS), yet no treatments target this key pathogenic stage. Animal models demonstrate anti-ganglioside antibodies (AGAb) induce axolemmal complement pore formation through which calcium flux activates the intra-axonal calcium-dependent proteases, calpains. We previously showed protection of axonal components using soluble calpain inhibitors in ex vivo GBS mouse models, and herein, we assess the potential of axonally-restricted calpain inhibition as a neuroprotective therapy operating in vivo. Using transgenic mice that over-express the endogenous human calpain inhibitor calpastatin (hCAST) neuronally, we assessed distal motor nerve integrity in our established GBS models. We induced immune-mediated injury with monoclonal AGAb plus a source of human complement. The calpain substrates neurofilament and AnkyrinG, nerve structural proteins, were assessed by immunolabelling and in the case of neurofilament, by single-molecule arrays (Simoa). As the distal intramuscular portion of the phrenic nerve is prominently targeted in our in vivo model, respiratory function was assessed by whole-body plethysmography as the functional output in the acute and extended models. hCAST expression protects distal nerve structural integrity both ex and in vivo, as shown by attenuation of neurofilament breakdown by immunolabelling and Simoa. In an extended in vivo model, while mice still initially undergo respiratory distress owing to acute conduction failure, the recovery phase was accelerated by hCAST expression. Axonal calpain inhibition can protect the axonal integrity of the nerve in an in vivo GBS paradigm and hasten recovery. These studies reinforce the strong justification for developing further animal and human clinical studies using exogenous calpain inhibitors.

Serum C3 complement levels predict prognosis and monitor disease activity in Guillain-Barré syndrome

OBJECTIVE

Biomarkers are needed to predict prognosis and disease activity in patients with Guillain-Barré syndrome (GBS). The complement system is a key player in the pathogenesis of GBS. This study aimed to assess the potential utility of serum complement proteins as novel biomarkers in GBS.

METHODS

We reviewed the medical records of 76 GBS patients with C3 and C4 measurements during hospitalization between 2010 and 2021. Clinical outcomes were correlated with baseline serum C3, C4, and seven additional predictors: four existing biomarkers (GM1, albumin, immunoglobulin G, neutrophil-lymphocyte ratio) and three clinical factors from the modified Erasmus GBS outcome score model. Five complement activation products (C3a, C4a, C5a, soluble C5b-9, factor Bb) were measured in 35 patients and were compared with C3 and C4 levels. Longitudinal changes in C3 and C4 levels were compared with the disease course in 12 patients.

RESULTS

Higher C3, but not C4, was associated with poorer outcomes: lower Medical Research Council sum scores (MRCSS), higher GBS disability score (GBSDS), longer hospitalization, and more frequent treatment-related fluctuations. Age, MRCSS at admission, and baseline serum C3 were significant independent indicators of 1- and 3-month GBSDS. We found that C3 was positively correlated with C3a (r = 0.32) and C5a (r = 0.37), which indicates an activated complement cascade with high C3. Longitudinal change of C3 coincided with clinical severity of the disease course.

INTERPRETATION

This study highlights the use of serum C3 as a novel mechanistic biomarker in GBS. Larger prospective studies are needed to validate our findings.

Types and Concentrations of Blood-Based Biomarkers in Adults With Peripheral Neuropathies: A Systematic Review and Meta-analysis

Importance

Peripheral neuropathies are common conditions and can result in numbness, paresthesia, motor deficits, and pain. There is increasing evidence for the use of biomarkers as clinical indicators of the presence, severity, and prognosis of nerve lesions; however, biomarker identification has largely been focused on disorders of the central nervous system, and less is known about their role in the peripheral nervous system.

Objective

To assess blood-based biomarker concentrations associated with nerve involvement in patients with peripheral neuropathy compared with control participants.

Data Sources

Ovid, MEDLINE, Embase, and CINAHL were searched from inception to September 23, 2021.

Study Selection

Observational studies reporting on blood biomarkers in patients diagnosed with peripheral neuropathy were included. This review was preregistered on PROSPERO and followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. Data were abstracted by 1 investigator and independently reviewed by a second.

Data Extraction and Synthesis

Data were meta-analyzed when at least 2 studies reported the same biomarker with comparable methodology. Fixed-effects models were used when only 2 studies were included; random-effects models were used when more than 2 studies were included.

Main Outcomes and Measures

The outcome of interest was concentration of biomarkers.

Results

This review included 36 studies reporting on 4414 participants, including 2113 control participants and 2301 patients with peripheral neuropathy with 13 distinct peripheral neuropathy diagnoses. Diabetic neuropathy was the most common neuropathy diagnosis (13 studies), followed by Charcot-Marie-Tooth disease (6 studies) and Guillain-Barre syndrome (6 studies). Overall, 16 different blood-based biomarkers associated with nerve involvement were evaluated. The most used were neurofilament light chain, S100B, brain-derived neurotrophic factor, and neuron-specific enolase. Patients with peripheral neuropathy demonstrated significantly higher levels of neurofilament light chain compared with controls (standardized mean difference [SMD], 0.93 [95% CI, 0.82 to 1.05]; P < .001). There were no significant differences in levels of S100B (SMD, 1.10 [95% CI, -3.08 to 5.28]; P = .38), brain-derived neurotrophic factor (SMD, -0.52 [95% CI, -2.23 to 1.19]; P = .40), or neuron-specific enolase (SMD, -0.00 [95% CI, -1.99 to 1.98]; P = .10) in patients with peripheral neuropathy compared with control participants.

Conclusions and Relevance

The findings of this systematic review and meta-analysis support the use of neurofilament light chain as a blood-based measure associated with the presence of neuronal injury in patients with peripheral neuropathy.

Blood biomarkers of peripheral neuropathy

Traditionally, neurophysiology is the primary diagnostic and prognostic biomarker in peripheral neuropathy clinical practice; however, it may lack responsiveness in the context of slowly progressive neuropathies and where there is significant axonal damage. The development of ultrasensitive platforms for measuring serum proteins at the lower limit of detection of traditional ELISA techniques has transformed the field of blood biomarkers of peripheral neuropathy. A variety of blood biomarkers have been identified from inflammatory cytokines and apokines in diabetic neuropathy through to neuron-specific proteins such as neurofilament light chain, Schwann cell-specific proteins such as TMPRSS5 and microRNAs in other acquired and hereditary neuropathies. In this article, we review blood biomarkers of disease activity for the common subtypes of peripheral neuropathy including inflammatory demyelinating neuropathies, vasculitic neuropathy, diabetic neuropathy, chemotherapy-induced neuropathy and Charcot-Marie-Tooth disease and related disorders including TTR amyloidosis.

Cerebrospinal fluid neurofilament light chain predicts short-term prognosis in pediatric Guillain-Barré syndrome

Introduction

To study cerebrospinal fluid neurofilament light chain (CSF-NfL) levels as a prognostic biomarker in pediatric Guillain-Barré syndrome (GBS).

Methods

Prospective study enrolling 26 pediatric GBS patients and 48 healthy controls (HCs) from neurology units between 2017 to 2021. The CSF-NfL levels were measured by enzyme-linked immunosorbent assay. The children's disability levels were evaluated using Hughes Functional Score (HFS) at nadir, 1 month, and 6 months after onset. The receiver operating characteristic (ROC) curve derived from logistic regression (with age as a covariate) was used to assess the prognostic value of CSF-NfL on the possibility of walking aided at 1 month after symptom onset.

Results

The mean CSF-NfL levels were significantly increased in GBS patients (111.76 pg/mL) as compared to that in HCs (76.82 pg/mL) (t = 6.754, p &lt; 0.001). At follow- up, the mean CSF-NfL levels after treatment (65.69 pg/mL) declined significantly (t = 6.693, p &lt; 0.001). CSF-NfL levels upon admission were significantly associated with the HFS at nadir (rs = 0.461, p = 0.018). Moreover, the mean CSF-NfL levels in GBS patients with poor prognosis (130.47pg/mL) were significantly higher than that in patients with good prognosis (104.87pg/mL) (t = 2.399, p = 0.025). ROC curve analysis of the predictive value of CSF-NfL levels with respect to the inability to walk unaided within 1 month showed a significant difference (area under the curve: 0.857,95% confidence interval 0.702-1.000; p = 0.006).

Conclusion

CSF-NfL levels were increased in pediatric GBS patients. High CSF-NfL level predicted worse motor function, and was strongly associated with poor short-term prognosis of pediatric GBS. We propose a biomarker for early prediction of outcome in pediatric GBS, which would be applicable for clinical practice and efficacy of treatment in the future.

Pragmatic guide to peripheral nerve disease and the role of clinical biomarkers

In clinical neurology practice, there are few sensitive, specific and responsive serological biomarkers reflecting pathological processes affecting the peripheral nervous system. Instead, we rely on surrogate multimodality biomarkers for diagnosis and management. Correct use and interpretation of the available tests is essential to ensure that appropriate treatments are used and adjusted in a timely fashion. The incorrect application or interpretation of biomarkers can result in misdiagnosis and delays in appropriate treatment. Here, we discuss the uses and limitations of such biomarkers and discuss possible future developments.

Schwann cell nodal membrane disruption triggers bystander axonal degeneration in a Guillain-Barré syndrome mouse model

In Guillain-Barré syndrome (GBS), both axonal and demyelinating variants can be mediated by complement-fixing anti-GM1 ganglioside autoantibodies that target peripheral nerve axonal and Schwann cell (SC) membranes, respectively. Critically, the extent of axonal degeneration in both variants dictates long-term outcome. The differing pathomechanisms underlying direct axonal injury and the secondary bystander axonal degeneration following SC injury are unresolved. To investigate this, we generated glycosyltransferase-disrupted transgenic mice that express GM1 ganglioside either exclusively in neurons [GalNAcT-/--Tg(neuronal)] or glia [GalNAcT-/--Tg(glial)], thereby allowing anti-GM1 antibodies to solely target GM1 in either axonal or SC membranes, respectively. Myelinated-axon integrity in distal motor nerves was studied in transgenic mice exposed to anti-GM1 antibody and complement in ex vivo and in vivo injury paradigms. Axonal targeting induced catastrophic acute axonal disruption, as expected. When mice with GM1 in SC membranes were targeted, acute disruption of perisynaptic glia and SC membranes at nodes of Ranvier (NoRs) occurred. Following glial injury, axonal disruption at NoRs also developed subacutely, progressing to secondary axonal degeneration. These models differentiate the distinctly different axonopathic pathways under axonal and glial membrane targeting conditions, and provide insights into primary and secondary axonal injury, currently a major unsolved area in GBS research.

Serum neurofilament light chain, contactin-1 and complement activation in anti-MAG IgM paraprotein-related peripheral neuropathy

INTRODUCTION

In anti-myelin-associated glycoprotein IgM paraprotein-related peripheral neuropathy (anti-MAG PN), there is a lack of reliable biomarkers to select patients eligible for therapy and for evaluating treatment effects, both in routine practice and in clinical trials. Neurofilament light chain (NfL) and contactin-1 (CNTN1) can serve as markers of axonal and paranodal damage. Complement activation is involved in the pathogenesis in anti-MAG PN. We, therefore, hypothesized that serum NfL, CNTN1, C3b/c and C4b/c may function as biomarkers of disease activity in anti-MAG PN.

METHODS

In this prospective cohort study, we included 24 treatment-naïve patients with anti-MAG PN (mean age 69 years, 57% male) that had IgM paraproteinemia, a high IgM MAG-antibody, and clinical diagnosis of anti-MAG PN by a neurologist specialized in peripheral nerve disorders. We measured serum NfL, CNTN1, C3b/c and C4b/c, reference values were based on healthy controls. As controls, 10 treatment-naïve patients with IgM Monoclonal gammopathy of undetermined significance (MGUS) or Waldenström's Macroglobulinemia (mean age 69 years, 60% male) without signs of neuropathy were included (non-PN).

RESULTS

NfL, CNTN1 levels in serum were mostly normal in anti-MAG PN patients and comparable to non-PN patients. C3b/c and C4b/c levels were normal in anti-MAG PN patients.

CONCLUSION

Our results do not support serum NfL, CNTN1, and C3b/c and C4b/c as potential biomarkers in anti-MAG PN, although we cannot exclude that subgroups or subtle abnormalities could be found in a much larger cohort with longitudinal follow-up.

Iron Rims in Patients With Multiple Sclerosis as Neurodegenerative Marker? A 7-Tesla Magnetic Resonance Study

Introduction: Multiple sclerosis (MS) is a demyelinating and neurodegenerative disease of the central nervous system, characterized by inflammatory-driven demyelination. Symptoms in MS manifest as both physical and neuropsychological deficits. With time, inflammation is accompanied by neurodegeneration, indicated by brain volume loss on an MRI. Here, we combined clinical, imaging, and serum biomarkers in patients with iron rim lesions (IRLs), which lead to severe tissue destruction and thus contribute to the accumulation of clinical disability.

Objectives: Subcortical atrophy and ventricular enlargement using an automatic segmentation pipeline for 7 Tesla (T) MRI, serum neurofilament light chain (sNfL) levels, and neuropsychological performance in patients with MS with IRLs and non-IRLs were assessed.

Methods: In total 29 patients with MS [15 women, 24 relapsing-remitting multiple sclerosis (RRMS), and five secondary-progressive multiple sclerosis (SPMS)] aged 38 (22–69) years with an Expanded Disability Status Score of 2 (0–8) and a disease duration of 11 (5–40) years underwent neurological and neuropsychological examinations. Volumes of lesions, subcortical structures, and lateral ventricles on 7-T MRI (SWI, FLAIR, and MP2RAGE, 3D Segmentation Software) and sNfL concentrations using the Simoa SR-X Analyzer in IRL and non-IRL patients were assessed.

Results: (1) Iron rim lesions patients had a higher FLAIR lesion count (p = 0.047). Patients with higher MP2Rage lesion volume exhibited more IRLs (p <0.014) and showed poorer performance in the information processing speed tested within 1 year using the Symbol Digit Modalities Test (SDMT) (p <0.047). (2) Within 3 years, patients showed atrophy of the thalamus (p = 0.021) and putamen (p = 0.043) and enlargement of the lateral ventricles (p = 0.012). At baseline and after 3 years, thalamic volumes were lower in IRLs than in non-IRL patients (p = 0.045). (3) At baseline, IRL patients had higher sNfL concentrations (p = 0.028). Higher sNfL concentrations were associated with poorer SDMT (p = 0.004), regardless of IRL presence. (4) IRL and non-IRL patients showed no significant difference in the neuropsychological performance within 1 year.

Conclusions: Compared with non-IRL patients, IRL patients had higher FLAIR lesion counts, smaller thalamic volumes, and higher sNfL concentrations. Our pilot study combines IRL and sNfL, two biomarkers considered indicative for neurodegenerative processes. Our preliminary data underscore the reported destructive nature of IRLs.

[Pathophysiological and diagnostic aspects of Guillain-Barré syndrome]

Guillain-Barré syndrome (GBS) is the most common cause of acute neuropathy. It usually onset with a rapidly progressive ascending bilateral weakness with sensory disturbances, and patients may require intensive treatment and close monitoring as about 30% have a respiratory muscle weakness and about 10% have autonomic dysfunction. The diagnosis of GBS is based on clinical history and examination. Complementary examinations are performed to rule out a differential diagnosis and to secondarily confirm the diagnosis. GBS is usually preceded by an infectious event in ≈ 2/3 of cases. Infection leads to an immune response directed against carbohydrate antigens located on the infectious agent and the formation of anti-ganglioside antibodies. By molecular mimicry, these antibodies can target structurally similar carbohydrates found on host's nerves. Their binding results in nerve conduction failure or/and demyelination which can lead to axonal loss. Some anti-ganglioside antibodies are associated with particular variants of GBS: the Miller-Fisher syndrome, facial diplegia and paresthesias, the pharyngo-cervico-brachial variant, the paraparetic variant, and the Bickerstaff brainstem encephalitis. Their semiological differences might be explained by a distinct expression of gangliosides among nerves. The aim of this review is to present pathophysiological aspects and the diagnostic approach of GBS and its variants.

Re-evaluating the accuracy of optimized electrodiagnostic criteria in very early Guillain-Barré syndrome: a sequential study

Using recent optimized electrodiagnostic criteria sets, we aimed at verifying the accuracy of initial nerve conduction studies (NCS) in classic very early Guillain-Barré syndrome (VEGBS), ≤ 4 days after onset, compared with the results of serial NCS. This is a retrospective study based on unreported and consecutive VEGBS patients admitted to two university hospitals between 2015 and 2019. Each patient had serial NCS in at least four nerves. Initial NCS studies were done within 4 days after onset, and serial ones from days 20 to 94. Electrophysiological recordings were blinded evaluated by four of the authors, GBS subtype being established accordingly. Seven adult classic VEGBS patients were identified with a median age of 58 years. At first NCS, GBS subtyping was only possible in 1 case that exhibited an axonal pattern, the remaining patterns being equivocal in 3, and mixed (combining axonal and demyelinating criteria) in the remaining 3. Upon serial NSC there was a rather intricate evolution of electrophysiological GBS patterns, 3 of them being classified as axonal or demyelinating, and the remaining 4 as equivocal or mixed. NCS in VEGBS systematically allows detection of changes suggestive of peripheral neuropathy, though even after serial studies accurate GBS subtyping was only possible in 43% of cases. We provide new pathophysiological insights for better understanding of the observed electrophysiological changes.

Case Report: Plasma Biomarkers Reflect Immune Mechanisms of Guillain-Barré Syndrome

This case series reported a group of patients with Guillain-Barré syndrome (GBS) and their plasma cytokine changes before and after immunotherapy. We aimed to understand GBS's pathogenesis and pathophysiology through observing the interval differences of the representative cytokines, which were the thymus and activation regulated chemokine (TARC) for T-cell chemotaxis, CD40 ligand (CD40L) for cosimulation of B and T cells, activated complement component C5/C5a, and brain-derived neurotrophic factor (BDNF) for survival and regenerative responses to nerve injuries. The fluorescence magnetic bead-based multiplexing immunoassay simultaneously quantified the five cytokines in a single sample. From June 2018 to December 2019, we enrolled five GBS patients who had completed before-after blood cytokine measurements. One patient was diagnosed with paraneoplastic GBS and excluded from the following cytokine analysis. The BDNF level decreased consistently in all the patients and made it a potential biomarker for the acute stage of GBS. Interval changes of the other four cytokines were relatively inconsistent and possibly related to interindividual differences in the immune response to GBS triggers, types of GBS variants, and classes of antiganglioside antibodies. In summary, utilizing the multiplexing immunoassay helps in understanding the complex immune mechanisms of GBS and the variation of immune responses in GBS subtypes; this method is feasible for identifying potential biomarkers of GBS.

Neurochemical signs of astrocytic and neuronal injury in acute COVID-19 normalizes during long-term follow-up

Background

Neurologic manifestations are well-recognized features of coronavirus disease 2019 (COVID-19). However, the longitudinal association of biomarkers reflecting CNS impact and neurological symptoms is not known. We sought to determine whether plasma biomarkers of CNS injury were associated with neurologic sequelae after COVID-19.

Methods

Patients with confirmed acute COVID-19 were studied prospectively. Neurological symptoms were recorded during the acute phase of the disease and at six months follow-up, and blood samples were collected longitudinally. Healthy age-matched individuals were included as controls. We analysed plasma concentrations of neurofilament light-chain (NfL), glial fibrillary acidic protein (GFAp), and growth differentiation factor 15 (GDF-15).

Findings

One hundred patients with mild (n = 24), moderate (n = 28), and severe (n = 48) COVID-19 were followed for a median (IQR) of 225 (187–262) days. In the acute phase, patients with severe COVID-19 had higher concentrations of NfL than all other groups (all p < 0·001), and higher GFAp than controls (p < 0·001). GFAp was also significantly increased in moderate disease (p < 0·05) compared with controls. NfL (r = 0·53, p < 0·001) and GFAp (r = 0·39, p < 0·001) correlated with GDF-15 during the acute phase. After six months, NfL and GFAp concentrations had normalized, with no persisting group differences. Despite this, 50 patients reported persistent neurological symptoms, most commonly fatigue (n = 40), “brain-fog” (n = 29), and changes in cognition (n = 25). We found no correlation between persistent neurological symptoms and CNS injury biomarkers in the acute phase.

Interpretation

The normalization of CNS injury biomarkers in all individuals, regardless of previous disease severity or persisting neurological symptoms, indicates that post COVID-19 neurological sequelae are not accompanied by ongoing CNS injury.

Funding

The Swedish State Support for Clinical Research, SciLifeLab Sweden, and the Knut and Alice Wallenberg Foundation have provided funding for this project.

Neurological symptoms and blood neurofilament light levels

Neurofilament light chain (NfL) is an incredibly specific marker of neuronal injury that is not specific for cause or location of the neuronal damage. NfL is increasingly considered as possible biomarker of disease activity in neurological conditions. Several works reviewed the utility of NfL in the different diseases. Nonetheless, NfL is a universal marker of neuronal damage, which interpretation spaces beyond the single disease. Because of this, the interpretation of NfL may benefit by also considering how neurological symptoms relate to its blood concentration. Here, we review how different neurological symptoms can be associated with blood NfL levels with a practical interpretation of it.

Neurochemical biomarkers to study CNS effects of COVID-19: a narrative review and synthesis

Neurological symptoms are frequently reported in patients suffering from COVID‐19. Common CNS‐related symptoms include anosmia, caused by viral interaction with either neurons or supporting cells in nasal olfactory tissues. Diffuse encephalopathy is the most common sign of CNS dysfunction, which likely results from the CNS consequences of the systemic inflammatory syndrome associated with severe COVID‐19. Additionally, microvascular injuries and thromboembolic events likely contribute to the neurologic impact of acute COVID‐19. These observations are supported by evidence of CNS immune activation in cerebrospinal fluid (CSF) and in autopsy tissue, along with the detection of microvascular injuries in both pathological and neuroimaging studies. The frequent occurrence of thromboembolic events in patients with COVID‐19 has generated different hypotheses, among which viral interaction with perivascular cells is particularly attractive, yet unproven. A distinguishing feature of CSF findings in SARS‐CoV‐2 infection is that clinical signs characteristic of neurotropic viral infections (CSF pleocytosis and blood–brain barrier injury) are mild or absent. Moreover, virus detection in CSF is rare and often of uncertain significance. In this review, we provide an overview of the neurological impact that occurs in the acute phase of COVID‐19, and the role of CSF biomarkers in the clinical management and research to better treat and understand the disease. In addition to aiding as diagnostic and prognostic tools during acute infection, the use of comprehensive and well‐characterized CSF and blood biomarkers will be vital in understanding the potential impact on the CNS in the rapidly increasing number of individuals recovering from COVID‐19.

Seven day pre-analytical stability of serum and plasma neurofilament light chain

Neurofilament light chain (NfL) has emerged as a biomarker of neuroaxonal damage in several neurologic conditions. With increasing availability of fourth-generation immunoassays detecting NfL in blood, aspects of pre-analytical stability of this biomarker remain unanswered. This study investigated NfL concentrations in serum and plasma samples of 32 patients with neurological diagnoses using state of the art Simoa technology. We tested the effect of delayed freezing of up to 7 days and statistically determined stability and validity of measured concentrations. We found concentrations of NfL in serum and plasma to remain stable at room temperature when processing of samples is delayed up to 7 days (serum: mean absolute difference 0.9 pg/mL, intraindividual variation 1.2%; plasma: mean absolute difference 0.5 pg/mL, intraindividual variation 1.3%). Consistency of these results was nearly perfect for serum and excellent for plasma (intraclass correlation coefficients 0.99 and 0.94, respectively). In conclusion, the soluble serum and plasma NfL concentration remains stable when unprocessed blood samples are stored up to 7 days at room temperature. This information is essential for ensuring reliable study protocols, for example, when shipment of fresh samples is needed.

Serum neurofilament light chain in chronic inflammatory demyelinating polyneuropathy

OBJECTIVES

Neurofilament light chain (NfL) levels have been suggested as reflecting axonal damage in various inflammatory and neurodegenerative disorders, including acquired peripheral neuropathies. We aimed to investigate if serum NfL (sNfL) levels can be a biomarker of disease activity and treatment response in patients with chronic inflammatory demyelinating polyneuropathy (CIDP).

MATERIALS AND METHODS

The sNfL levels of eleven newly diagnosed patients with CIDP were retrospectively assayed and compared with seven healthy volunteers. The levels were assayed before and after intravenous immunoglobulin treatment in patients with CIDP and were also assayed in the remission period.

RESULTS

Baseline sNfL levels in patients with CIDP before treatment were significantly higher than those in healthy controls. The levels significantly decreased overtime after one month of treatment and in remission period. There were significant negative correlations between the sNfL levels and the disease duration (the interval between the onset of the disease and the time of sampling), and weak correlations between the sNfL levels and overall neuropathy limitations scale.

CONCLUSIONS

sNfL may be a potential biomarker reflecting the disease activity in patients with CIDP.

Prognostic value of neurofilament light chain in chronic inflammatory demyelinating polyneuropathy

Chronic inflammatory demyelinating polyneuropathy is a neuroinflammatory disorder with considerable variation in clinical phenotype, disease progression and therapy response among patients. Recently, paranodal antibodies associated with poor response to intravenous immunoglobulin therapy and more aggressive disease course have been described in small subsets of patients, but reliable serum-based prognostic biomarkers are not yet available for the general population. In current retrospective longitudinal study, we utilized logistic regression models to investigate the associations of serum neurofilament light chain levels with 1-year disease progression and therapy response during follow-up in chronic inflammatory demyelinating polyneuropathy. One-year disease progression was defined as a decrease of four or more points (the minimal clinically important difference) on an 80-point Medical Research Council sum-score scale 1 year after sampling. Patients who, compared to treatment received at time of sampling, required therapy switch during follow-up due to insufficient effect were classified as non-responders. Serum neurofilament light chain was measured by electrochemiluminescence assay in clinical residual serum samples of 76 patients diagnosed with probable (13 patients) or definite (63 patients) chronic inflammatory demyelinating polyneuropathy according to European Federation of Neurological Societies/Peripheral Nerve Society diagnostic criteria. Eleven (15%) patients were female, and the mean (standard deviation) cohort age was 61.5 (11.7) years. In both univariate and multivariable (including demographics) models, elevated serum neurofilament light chain harboured increased odds for 1-year disease progression (respectively odds ratio, 1.049; 95% confidence interval, 1.022-1.084 and odds ratio, 1.097; 95% confidence interval, 1.045-1.169; both P = 0.001). Patients with levels above the median cohort neurofilament light chain level (28.3 pg/ml) had largely increased odds of 1-year disease progression (univariate: odds ratio, 5.597; 95% confidence interval, 1.590-26.457; P = 0.01; multivariable: odds ratio, 6.572; 95% confidence interval, 1.495-39.702; P = 0.02) and of insufficient treatment response (univariate: odds ratio, 4.800; 95% confidence interval, 1.622-16.442; P = 0.007; multivariable: odds ratio, 6.441; 95% confidence interval, 1.749-29.357; P = 0.009). In a combined approach analysis, patients with levels above median cohort serum neurofilament light chain level reported strongly increased odds of demonstrating 1-year disease progression and/or therapy non-response during follow-up (univariate: odds ratio, 6.337; 95% confidence interval, 2.276-19.469; P < 0.001; multivariable: odds ratio, 10.138; 95% confidence interval, 2.801-46.404; P = 0.001). These results show that in various logistic regression models, serum neurofilament light chain was associated with both 1-year disease progression and therapy response during follow-up in chronic inflammatory demyelinating polyneuropathy. Hence, our findings warrant further prospective research regarding the value of neurofilament light chain as potential prognostic biomarker in chronic inflammatory demyelinating polyneuropathy.

Guillain-Barré syndrome

Guillain-Barré syndrome is the most common cause of acute flaccid paralysis worldwide. Most patients present with an antecedent illness, most commonly upper respiratory tract infection, before the onset of progressive motor weakness. Several microorganisms have been associated with Guillain-Barré syndrome, most notably Campylobacter jejuni, Zika virus, and in 2020, the severe acute respiratory syndrome coronavirus 2. In C jejuni-related Guillain-Barré syndrome, there is good evidence to support an autoantibody-mediated immune process that is triggered by molecular mimicry between structural components of peripheral nerves and the microorganism. Making a diagnosis of so-called classical Guillain-Barré syndrome is straightforward; however, the existing diagnostic criteria have limitations and can result in some variants of the syndrome being missed. Most patients with Guillain-Barré syndrome do well with immunotherapy, but a substantial proportion are left with disability, and death can occur. Results from the International Guillain-Barré Syndrome Outcome Study suggest that geographical variations exist in Guillain-Barré syndrome, including insufficient access to immunotherapy in low-income countries. There is a need to provide improved access to treatment for all patients with Guillain-Barré syndrome, and to develop effective disease-modifying therapies that can limit the extent of nerve injury. Clinical trials are currently underway to investigate some of the potential therapeutic candidates, including complement inhibitors, which, together with emerging data from large international collaborative studies on the syndrome, will contribute substantially to understanding the many facets of this disease.

Serum Neurofilament Light Chain Measurement in MS: Hurdles to Clinical Translation

Measurement of serum neurofilament light chain concentration (sNfL) promises to become a convenient, cost effective and meaningful adjunct for multiple sclerosis (MS) prognostication as well as monitoring disease activity in response to treatment. Despite the remarkable progress and an ever-increasing literature supporting the potential role of sNfL in MS over the last 5 years, a number of hurdles remain before this test can be integrated into routine clinical practice. In this review we highlight these hurdles, broadly classified by concerns relating to clinical validity and analytical validity. After setting out an aspirational roadmap as to how many of these issues can be overcome, we conclude by sharing our vision of the current and future role of sNfL assays in MS clinical practice.

Current application of neurofilaments in amyotrophic lateral sclerosis and future perspectives

Motor neuron disease includes a heterogeneous group of relentless progressive neurological disorders defined and characterized by the degeneration of motor neurons. Amyotrophic lateral sclerosis is the most common and aggressive form of motor neuron disease with no effective treatment so far. Unfortunately, diagnostic and prognostic biomarkers are lacking in clinical practice. Neurofilaments are fundamental structural components of the axons and neurofilament light chain and phosphorylated neurofilament heavy chain can be measured in both cerebrospinal fluid and serum. Neurofilament light chain and phosphorylated neurofilament heavy chain levels are elevated in amyotrophic lateral sclerosis, reflecting the extensive damage of motor neurons and axons. Hence, neurofilaments are now increasingly recognized as the most promising candidate biomarker in amyotrophic lateral sclerosis. The potential usefulness of neurofilaments regards various aspects, including diagnosis, prognosis, patient stratification in clinical trials and evaluation of treatment response. In this review paper, we review the body of literature about neurofilaments measurement in amyotrophic lateral sclerosis. We also discuss the open issues concerning the use of neurofilaments clinical practice, as no overall guideline exists to date; finally, we address the most recent evidence and future perspectives.

Miller-Fisher syndrome after COVID-19: neurochemical markers as an early sign of nervous system involvement

Miller-Fisher syndrome (MFS) is classified as a variant of Guillain-Barré syndrome (GBS), accounting for 5%-25% of all GBS cases. Since the coronavirus disease-2019 (COVID-19) outbreak, increasing evidence has been reported of the neurological manifestations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, affecting both the central and peripheral nervous system. Here we report the clinical course, detailed cerebrospinal fluid (CSF) profile including CSF/blood antibody status, and neurochemical characteristics of a patient with a typical clinical presentation of MFS after a positive SARS-CoV-2 infection test.

Serum neurofilament light chain withstands delayed freezing and repeated thawing

Serum neurofilament light chain (sNfL) and its ability to expose axonal damage in neurologic disorders have solicited a considerable amount of attention in blood biomarker research. Hence, with the proliferation of high-throughput assay technology, there is an imminent need to study the pre-analytical stability of this biomarker. We recruited 20 patients with common neurological diagnoses and 10 controls (i.e. patients without structural neurological disease). We investigated whether a variation in pre-analytical variables (delayed freezing up to 24 h and repeated thawing/freezing for up to three cycles) affects the measured sNfL concentrations using state of the art Simoa technology. Advanced statistical methods were applied to expose any relevant changes in sNfL concentration due to different storing and processing conditions. We found that sNfL concentrations remained stable when samples were frozen within 24 h (mean absolute difference 0.2 pg/ml; intraindividual variation below 0.1%). Repeated thawing and re-freezing up to three times did not change measured sNfL concentration significantly, either (mean absolute difference 0.7 pg/ml; intraindividual variation below 0.2%). We conclude that the soluble sNfL concentration is unaffected at 4–8 °C when samples are frozen within 24 h and single aliquots can be used up to three times. These observations should be considered for planning future studies.

Serum neurofilament light chain predicts long-term prognosis in Guillain-Barré syndrome patients

OBJECTIVE

To study baseline serum neurofilament light chain (sNfL) levels as a prognostic biomarker in Guillain-Barré syndrome (GBS).

METHODS

We measured NfL in serum (98 samples) and cerebrospinal fluid (CSF) (24 samples) of patients with GBS prospectively included in the International GBS Outcome Study (IGOS) in Spain using single-molecule array (SiMoA) and compared them with 53 healthy controls (HCs). We performed multivariable regression to analyse the association between sNfL levels and functional outcome at 1 year.

RESULTS

Patients with GBS had higher NfL levels than HC in serum (55.49 pg/mL vs 9.83 pg/mL, p<0.0001) and CSF (1308.5 pg/mL vs 440.24 pg/mL, p=0.034). Patients with preceding diarrhoea had higher sNfL than patients with respiratory symptoms or no preceding infection (134.90 pg/mL vs 47.86 pg/mL vs 38.02 pg/mL, p=0.016). sNfL levels correlated with Guillain-Barré Syndrome Disability Score and Inflammatory Rasch-built Overall Disability Scale (I-RODS) at every timepoint. Patients with pure motor variant and Miller Fisher syndrome showed higher sNfL levels than patients with sensorimotor GBS (162.18 pg/mL vs 95.50 pg/mL vs 38.02 pg/mL, p=0.025). Patients with acute motor axonal neuropathy cute motor axonal neuropathy had higher sNfL levels than other variants (190.55 pg/mL vs 46.79 pg/mL, p=0.013). sNfL returned to normal levels at 1 year. High baseline sNfL levels were associated with inability to run (OR=1.65, 95% CI 1.14 to 2.40, p=0.009) and lower I-RODS (β -2.60, 95% CI -4.66 to -0.54, p=0.014) at 1 year. Cut-off points predicting clinically relevant outcomes at 1 year with high specificity were calculated: inability to walk independently (>319 pg/mL), inability to run (>248 pg/mL) and ability to run (<34 pg/mL).

CONCLUSION

Baseline sNfL levels are increased in patients with GBS, are associated with disease severity and axonal variants and have an independent prognostic value in patients with GBS.

Inflammatory oedema of nerve trunks may be pathogenic in very early Guillain-Barré syndrome

The aim of this paper is to analyse the pathological background of very early Guillain-Barré (VEGBS) (≤ 4 days after onset) comparing it with initial stages of experimental autoimmune neuritis (EAN). The pathological hallmark of VEGBS is inflammatory oedema predominating in proximal nerve trunks. In EAN inflammatory oedema precedes the development of demyelination or axonal degeneration; such oedema may increase endoneurial fluid pressure (EFP) stretching the perineurium and constricting the transperineurial microcirculation. Centrofascicular or wedge-shaped areas of nerve ischemia have been reported in GBS and EAN. Additional support for proximal VEGBS pathology comes from electrophysiology showing alterations in late responses as the most frequent features, and ultrasonography illustrating that main changes rely on ventral rami of spinal nerves. Selective inefficiency of the blood-nerve barrier would explain the topography of changes in VEGBS. Increased serum neurofilament light chain concentration has recently been reported in VEGBS, with no difference between demyelinating and axonal subtypes. This is a marker of axonal damage, which could be correlated with endoneurial ischemia caused by increased EFP. Inflammatory oedema of proximal nerve trunks may be pathogenic in VEGBS, and consequently there is a pressing need for therapeutic strategies to stop its rapid impact on the axons.

Axonal degeneration in Guillain-Barré syndrome: a reappraisal

The aim of this review was to analyse the pathophysiology of axonal degeneration in Guillain-Barré syndrome (GBS) with emphasis on early stages (≤ 10 days after onset). An overview of experimental autoimmune neuritis (EAN) models is provided. Originally GBS and acute inflammatory demyelinating polyneuropathy were equated, presence of axonal degeneration being attributed to a "bystander" effect. Afterwards, primary axonal GBS forms were reported, designated as acute motor axonal neuropathy/acute motor-sensory axonal neuropathy. Revision of the first pathological description of axonal GBS indicates the coexistence of active axonal degeneration and demyelination in spinal roots, and pure Wallerian-like degeneration in peripheral nerve trunks. Nerve conduction studies are essential for syndrome subtyping, though their sensitivity is scanty in early GBS. Serum markers of axonal degeneration include increased levels of neurofilament light chain and presence of anti-ganglioside reactivity. According to nerve ultrasonographic features and autopsy studies, ventral rami of spinal nerves are a hotspot in early GBS. In P₂-induced EAN models, the initial pathogenic change is inflammatory oedema of spinal roots and sciatic nerve, which is followed by demyelination, and Wallerian-like degeneration in nerve trunks possessing epi-perineurium; a critical elevation of endoneurial fluid pressure is a pre-requisite for inducing ischemic axonal degeneration. Similar lesion topography may occur in GBS. The repairing role of adaxonal Schwann cytoplasm in axonal degeneration is analysed. A novel pathophysiological mechanism for nerve trunk pain in GBS, including pure motor forms, is provided. The potential therapeutic role of intravenous boluses of methylprednisolone for early severe GBS and intractable pain is argued.

Sural nerve biopsy: current role and comparison with serum neurofilament light chain levels

The diagnosis of peripheral neuropathies can be challenging with consequent difficulties in patients' management. The aim of this study was to explore the current diagnostic role of sural nerve biopsy and to compare pathological findings with serum neurofilament light chain levels (NfL) as biomarkers of axonal damage. We collected demographic, clinical, and paraclinical data of patients referred over 1 year to the Neurology Unit, University of Verona, Italy, to perform nerve biopsy for diagnostic purposes, and we analyzed NfL levels in available paired sera using a high sensitive technique (Quanterix, Simoa). Eighty-two patients were identified (37.8% females, median age 65.5 years). Neuropathy onset was frequently insidious (68.3%) with a slowly progressive course (76.8%). Lower limbs were usually involved (81.7%), with a predominance of sensory over motor symptoms (74.4% vs 42.7%). The most common neuropathological findings were a demyelinating pattern (76.8%), clusters of regenerations (58.5%), and unmyelinated fibers involvement on ultrastructural evaluation (52.4%). A definite pathological diagnosis was achieved in 29 cases, and in 20.7% of patients, the referral clinical diagnosis was modified. Coexistent hematological conditions and hepatitis were diagnostic confounding factors (p = 0.012 and 0.034, respectively). In the analyzed paired sera (n = 37), an inverse despite not significant relationship between NfL values and fiber density was observed (Spearman's rho - 0.312, p = 0.056). In addition, we noted increased serum NfL values of patients with active axonal degeneration. Nerve biopsy remains a useful diagnostic investigation to achieve a correct diagnosis and guide patients' management in selected cases of peripheral neuropathy. Serum NfL is an accessible and potential valuable marker of axonal damage in these conditions.