[Research progress of silk-based biomaterials for peripheral nerve regeneration].

Objective: To describe the research progress of silk-based biomaterials in peripheral nerve repair and provide useful ideals to accelerate the regeneration of large-size peripheral nerve injury. Methods: The relative documents about silk-based biomaterials used in peripheral nerve regeneration were reviewed and the different strategies that could accelerate peripheral nerve regeneration through building bioactive microenvironment with silk fibroin were discussed. Results: Many silk fibroin tissue engineered nerve conduits have been developed to provide multiple biomimetic microstructures, and different microstructures have different mechanisms of promoting nerve repair. Biomimetic porous structures favor the nutrient exchange at wound sites and inhibit the invasion of scar tissue. The aligned structures can induce the directional growth of nerve tissue, while the multiple channels promote the axon elongation. When the fillers are introduced to the conduits, better growth, migration, and differentiation of nerve cells can be achieved. Besides biomimetic structures, different nerve growth factors and bioactive drugs can be loaded on silk carriers and released slowly at nerve wounds, providing suitable biochemical cues. Both the biomimetic structures and the loaded bioactive ingredients optimize the niches of peripheral nerves, resulting in quicker and better nerve repair. With silk biomaterials as a platform, fusing multiple ways to achieve the multidimensional regulation of nerve microenvironments is becoming a critical strategy in repairing large-size peripheral nerve injury. Conclusion: Silk-based biomaterials are useful platforms to achieve the design of biomimetic hierarchical microstructures and the co-loading of various bioactive ingredients. Silk fibroin nerve conduits provide suitable microenvironment to accelerate functional recovery of peripheral nerves. Different optimizing strategies are available for silk fibroin biomaterials to favor the nerve regeneration, which would satisfy the needs of various nerve tissue repair. Bioactive silk conduits have promising future in large-size peripheral nerve regeneration.

[Peripheral nerves' function recovery by intratissual electric stimulation]. / Vosstanovlenie funktsii perifericheskikh nervov vnutritkanevoi elektrostimulyatsiei.

An intratissual electrical stimulation, accompanied by irritation of their central neurons, is used to recover the function of damaged peripheral nerves. Treatment results exceeded those with the use of cutaneous electrical stimulation, which is confirmed by comparative results of trial animal experiments. The time and quality of peripheral nerves' function recovery in comparison of intratissual and cutaneous electrical stimulation methods remain unknown. OBJECTIVE: To evaluate the time and quality of peripheral nerves' functions recovery after their suturing and conducting two different methods of electrical stimulation, namely intratissual and cutaneous, in projection of central neurons of damaged spinal nerves in the postoperative period. MATERIAL AND METHODS: The basic technical parameters of the method of peripheral nerves' functions recovery in the postoperative period were ptacticed. Postoperative rehabilitation treatment was performed in 77 patients with traumatic peripheral nerves' injuries at the level of the forearm: in 42 with intratissual electrical stimulation, in 35 - using cutaneous one with similar characteristics of electrical current and concomitant pharmacological therapy. The follow-up duration was 2 years. RESULTS: A significant (in 4-6 times) reduction in time of treatment and a greater improvement in qualitative indicators when using intratissual electrical stimulation compared to the use of cutaneous stimulation were obtained. The effectiveness of the restorative therapy was dependent on the number of procedures, and a complete recovery of the damaged peripheral nerves' functions was observed after three courses of intratissual electrical stimulation. CONCLUSION: The time and degree of recovery of peripheral nerves' functions depends on the functional activity of their central neurons at the level of the spinal cord. The activation of these neurons by low-frequency electrical current allows to activate their trophic function. Thus, the cutaneous electrical stimulation does not cause the necessary level of irritation of the neurons due to the fact that the skin is a barrier to electrical current, which reduces its impact in 200-500 times. The intratissual electrical stimulation allows to solve the problem by supplying the needle-electrode much closer to the «target¼. The proposed method of intratissual electrical stimulation has shown its advantage over cutaneous electrical stimulation, significantly reducing the duration of the restorative treatment and increasing its qualitative indicators.

Magnetic Resonance Neurography of the Foot and Ankle.

Peripheral neuropathies of the foot and ankle can be challenging to diagnose clinically due to concomitant traumatic and nontraumatic or degenerative orthopedic conditions. Although clinical history, physical examination, and electrodiagnostic testing comprised of nerve conduction velocities and electromyography are used primarily for the identification and classification of peripheral nerve disorders, MR neurography (MRN) can be used to visualize the peripheral nerves as well as the skeletal muscles of the foot and ankle for primary neurogenic pathology and skeletal muscle denervation effect. Proper knowledge of the anatomy and pathophysiology of peripheral nerves is important for an MRN interpretation.

Cerebrospinal fluid flow extends to peripheral nerves further unifying the nervous system.

Cerebrospinal fluid (CSF) is responsible for maintaining brain homeostasis through nutrient delivery and waste removal for the central nervous system (CNS). Here, we demonstrate extensive CSF flow throughout the peripheral nervous system (PNS) by tracing distribution of multimodal 1.9-nanometer gold nanoparticles, roughly the size of CSF circulating proteins, infused within the lateral cerebral ventricle (a primary site of CSF production). CSF-infused 1.9-nanometer gold transitions from CNS to PNS at root attachment/transition zones and distributes through the perineurium and endoneurium, with ultimate delivery to axoplasm of distal peripheral nerves. Larger 15-nanometer gold fails to transit from CNS to PNS and instead forms "dye-cuffs," as predicted by current dogma of CSF restriction within CNS, identifying size limitations in central to peripheral flow. Intravenous 1.9-nanometer gold is unable to cross the blood-brain/nerve barrier. Our findings suggest that CSF plays a consistent role in maintaining homeostasis throughout the nervous system with implications for CNS and PNS therapy and neural drug delivery.

Collagen protein-chitosan nerve conduits with neuroepithelial stem cells promote peripheral nerve regeneration.

The peripheral nervous system consists of ganglia, nerve trunks, plexuses, and nerve endings, that transmit afferent and efferent information. Regeneration after a peripheral nerve damage is sluggish and imperfect. Peripheral nerve injury frequently causes partial or complete loss of motor and sensory function, physical impairment, and neuropathic pain, all of which have a negative impact on patients' quality of life. Because the mechanism of peripheral nerve injury and healing is still unclear, the therapeutic efficacy is limited. As peripheral nerve injury research has processed, an increasing number of studies have revealed that biological scaffolds work in tandem with progenitor cells to repair peripheral nerve injury. Here, we fabricated collagen chitosan nerve conduit bioscaffolds together with collagen and then filled neuroepithelial stem cells (NESCs). Scanning electron microscopy showed that the NESCs grew well on the scaffold surface. Compared to the control group, the NESCs group contained more cells with bigger diameters and myelinated structures around the axons. Our findings indicated that a combination of chitosan-collagen bioscaffold and neural stem cell transplantation can facilitate the functional restoration of peripheral nerve tissue, with promising future applications and research implications.

Highly-stable, injectable, conductive hydrogel for chronic neuromodulation.

Electroceuticals, through the selective modulation of peripheral nerves near target organs, are promising for treating refractory diseases. However, the small sizes and the delicate nature of these nerves present challenges in simplifying the fixation and stabilizing the electrical-coupling interface for neural electrodes. Herein, we construct a robust neural interface for fine peripheral nerves using an injectable bio-adhesive hydrogel bioelectronics. By incorporating a multifunctional molecular regulator during network formation, we optimize the injectability and conductivity of the hydrogel through fine-tuning reaction kinetics and multi-scale interactions within the conductive network. Meanwhile, the mechanical and electrical stability of the hydrogel is achieved without compromising its injectability. Minimal tissue damage along with low and stable impedance of the injectable neural interface enables chronic vagus neuromodulation for myocardial infarction therapy in the male rat model. Our highly-stable, injectable, conductive hydrogel bioelectronics are readily available to target challenging anatomical locations, paving the way for future precision bioelectronic medicine.

In Vivo Thoracic Dorsal Root Ganglia (DRG) Calcium Imaging and ECG Recording for Studying Peripheral Nerve Stimulation.

The dorsal root ganglia (DRG), housing primary sensory neurons, transmit somatosensory and visceral afferent inputs to the dorsal horn of the spinal cord. They play a pivotal role in both physiological and pathological states, including neuropathic and visceral pain. In vivo calcium imaging of DRG enables real-time observation of calcium transients in single units or neuron ensembles. Accumulating evidence indicates that DRG neuronal activities induced by somatic stimulation significantly affect autonomic and visceral functions. While lumbar DRG calcium imaging has been extensively studied, thoracic segment DRG calcium imaging has been less explored due to surgical exposure and stereotaxic fixation challenges. Here, we utilized in vivo calcium imaging at the thoracic1 dorsal root ganglion (T1-DRG) to investigate changes in neuronal activity resulting from somatic stimulations of the forelimb. This approach is crucial for understanding the somato-cardiac reflex triggered by peripheral nerve stimulations (PENS), such as acupuncture. Notably, synchronization of cardiac function was observed and measured by electrocardiogram (ECG), with T-DRG neuronal activities, potentially establishing a novel paradigm for somato-visceral reflex in the thoracic segments.

Current and Future Directions for Upper Extremity Amputations: Comparisons Between Regenerative Peripheral Nerve Interface and Targeted Muscle Reinnervation Surgeries.

Upper extremity amputation can lead to significant functional morbidity. The main goals after amputation are to minimize pain and maintain or improve functional status while optimizing the quality of life. Postamputation pain is common and can be addressed with regenerative peripheral nerve interface surgery or targeted muscle reinnervation surgery. Both modalities are effective in treating residual limb pain and phantom limb pain, as well as improving prosthetic use. Differences in surgical technique between the 2 approaches need to be weighed when deciding what strategy may be most appropriate for the patient.

A systematic review of clinical and laboratory studies comparing vascularised versus non-vascularised nerve grafts in peripheral nerve reconstruction.

BACKGROUND: Peripheral nerve injuries (PNIs) are common, with complex defects posing a significant reconstructive challenge. Although vascularised (VNGs) and non-vascularised nerve grafts (NVNGs) are established treatment options, there is no comprehensive summary of the evidence supporting their clinical, electrophysiological, and histological outcomes. This review aims to systematically evaluate the clinical and laboratory literature comparing VNGs and NVNGs to inform future clinical practice and research. METHODS: This review was prospectively registered and reported according to PRISMA guidelines. PubMed, EMBASE, SCOPUS, and the Cochrane Register were systematically searched. Studies comparing VNGs and NVNGs in PNIs were included. Meta-analyses were performed for outcomes reported in ≥3 laboratory studies. Functional outcomes were synthesised by vote-counting based on direction of effect for clinical studies. Risk-of-bias was assessed using RoB2, ROBINS-I, and SYRCLE, and the certainty of evidence was evaluated using GRADE. RESULTS: Seven clinical and 34 laboratory studies were included. Of the clinical comparisons, 90% and 56% identified an effect on recovery of sensibility (p = 0.01) and motor function (p = 0.05), respectively, that favoured VNGs. Nine (of 13) separate meta-analyses of laboratory studies demonstrated reduced muscular atrophy, superior axonal regeneration, and remyelination in VNGs. VNGs eliminated the 3-day interval of ischaemia otherwise sustained by NVNGs. Overall, the quality of evidence was low. CONCLUSION: This systematic review indicates that VNGs may offer some advantages over NVNGs in PNI reconstruction. However, due to the low quality of evidence, significant statistical heterogeneity, and clinical diversity of the included studies, these conclusions should be interpreted with caution. Further high-quality clinical trials are necessary to validate these findings.

Development of a 3-dimensional organotypic model with characteristics of peripheral sensory nerves.

We developed a rat dorsal root ganglion (DRG)-derived sensory nerve organotypic model by culturing DRG explants on an organoid culture device. With this method, a large number of organotypic cultures can be produced simultaneously with high reproducibility simply by seeding DRG explants derived from rat embryos. Unlike previous DRG explant models, this organotypic model consists of a ganglion and an axon bundle with myelinated A fibers, unmyelinated C fibers, and stereo-myelin-forming nodes of Ranvier. The model also exhibits Ca2+ signaling in cell bodies in response to application of chemical stimuli to nerve terminals. Further, axonal transection increases the activating transcription factor 3 mRNA level in ganglia. Axons and myelin are shown to regenerate 14 days following transection. Our sensory organotypic model enables analysis of neuronal excitability in response to pain stimuli and tracking of morphological changes in the axon bundle over weeks.

Palmitoylethanolamide as a Supplement: The Importance of Dose-Dependent Effects for Improving Nervous Tissue Health in an In Vitro Model.

Palmitoylethanolamide (PEA) is a highly lipophilic molecule with low solubility, making absorption difficult. Recent techniques like micronisation, ultra-micronisation and combining PEA with solvents have improved their bioavailability and stability. Our study analysed particle size differences and absorption kinetics using specific solvents (PEAΩ and PEA DynoΩ) over time (0.5 h-6 h) in a dose-dependent manner (200 mg-1800 mg). The results showed that PEAΩ and PEA DynoΩ achieved 82-63% absorption at 3 h, compared to 30-60% for micronised, ultra-micronised PEA and a commercial product, highlighting the optimal dose range of 300 mg-600 mg. In addition, a 3D model of the peripheral nerve was utilised to explain the efficacy after gut passage and support the most effective dose (300 mg or 600 mg) achieved at the gut level. PEAΩ and PEA DynoΩ, which are associated with better intestinal bioavailability compared to PEA-micronised, PEA ultra-micronised and a commercial product, have allowed not only a reduction in the inflammatory context but also an improvement of peripheral nerve well-being by increasing specific markers like MPZ (26-36% vs. 8-15%), p75 (25-32% vs. 13-16%) and NRG1 (22-29.5% vs. 11-14%). These results highlight the potential of advanced PEA formulations to overcome solubility challenges and maintain in vitro efficacy, modulating peripheral nerve well-being.

Automated peripheral nerve segmentation for MR-neurography.

BACKGROUND: Magnetic resonance neurography (MRN) is increasingly used as a diagnostic tool for peripheral neuropathies. Quantitative measures enhance MRN interpretation but require nerve segmentation which is time-consuming and error-prone and has not become clinical routine. In this study, we applied neural networks for the automated segmentation of peripheral nerves. METHODS: A neural segmentation network was trained to segment the sciatic nerve and its proximal branches on the MRN scans of the right and left upper leg of 35 healthy individuals, resulting in 70 training examples, via 5-fold cross-validation (CV). The model performance was evaluated on an independent test set of one-sided MRN scans of 60 healthy individuals. RESULTS: Mean Dice similarity coefficient (DSC) in CV was 0.892 (95% confidence interval [CI]: 0.888-0.897) with a mean Jaccard index (JI) of 0.806 (95% CI: 0.799-0.814) and mean Hausdorff distance (HD) of 2.146 (95% CI: 2.184-2.208). For the independent test set, DSC and JI were lower while HD was higher, with a mean DSC of 0.789 (95% CI: 0.760-0.815), mean JI of 0.672 (95% CI: 0.642-0.699), and mean HD of 2.118 (95% CI: 2.047-2.190). CONCLUSION: The deep learning-based segmentation model showed a good performance for the task of nerve segmentation. Future work will focus on extending training data and including individuals with peripheral neuropathies in training to enable advanced peripheral nerve disease characterization. RELEVANCE STATEMENT: The results will serve as a baseline to build upon while developing an automated quantitative MRN feature analysis framework for application in routine reading of MRN examinations. KEY POINTS: Quantitative measures enhance MRN interpretation, requiring complex and challenging nerve segmentation. We present a deep learning-based segmentation model with good performance. Our results may serve as a baseline for clinical automated quantitative MRN segmentation.

Transplantation of Predegenerated Peripheral Nerves after Complete Spinal Cord Transection in Rats: Effect of Neural Precursor Cells and Pharmacological Treatment with the Sulfoglycolipid Tol-51.

Following spinal cord injury (SCI), the regenerative capacity of the central nervous system (CNS) is severely limited by the failure of axonal regeneration. The regeneration of CNS axons has been shown to occur by grafting predegenerated peripheral nerves (PPNs) and to be promoted by the transplantation of neural precursor cells (NPCs). The introduction of a combinatorial treatment of PPNs and NPCs after SCI has to address the additional problem of glial scar formation, which prevents regenerating axons from leaving the implant and making functional connections. Previously, we discovered that the synthetic sulfoglycolipid Tol-51 inhibits astrogliosis. The objective was to evaluate axonal regeneration and locomotor function improvement after SCI in rats treated with a combination of PPN, NPC, and Tol-51. One month after SCI, the scar tissue was removed and replaced with segments of PPN or PPN+Tol-51; PPN+NPC+Tol-51. The transplantation of a PPN segment favors regenerative axonal growth; in combination with Tol-51 and NPC, 30% of the labeled descending corticospinal axons were able to grow through the PPN and penetrate the caudal spinal cord. The animals treated with PPN showed significantly better motor function. Our data demonstrate that PPN implants plus NPC and Tol-51 allow successful axonal regeneration in the CNS.

High serum prevalence of autoreactive IgG antibodies against peripheral nerve structures in patients with neurological post-COVID-19 vaccination syndrome.

Background: Patients suffering from neurological symptoms after COVID-19 vaccination (post-COVID-19 vaccination syndrome (PCVS)) have imposed an increasing challenge on medical practice, as diagnostic precision and therapeutic options are lacking. Underlying autoimmune dysfunctions, including autoantibodies, have been discussed in neurological disorders after SARS-CoV-2 infection and vaccination. Here, we describe the frequency and targets of autoantibodies against peripheral nervous system tissues in PCVS. Methods: Sera from 50 PCVS patients with peripheral neurological symptoms after COVID-19 vaccination and 35 vaccinated healthy controls were used in this study. IgG autoreactivity was measured via indirect immunofluorescence assays on mouse sciatic nerve teased fibers. The frequencies of autoantibodies were compared between groups using Fisher's exact test. Serum anti-ganglioside antibodies were measured in ganglioside blots. Autoantibody target identification was performed using immunoprecipitation coupled to mass spectrometry. Subsequent target confirmation was conducted via cell-based assays and ELISA. Results: Compared with controls, PCVS patients had a significantly greater frequency of autoantibodies against peripheral nervous system structures (9/50(18%) vs 1/35(3%); p=0.04). Autoantibodies bound to paranodes (n=5), axons (n=4), Schmidt-Lanterman incisures (n=2) and Schwann cell nuclei (n=1). Conversely, antibodies against gangliosides were absent in PCVS patients. Target identification and subsequent confirmation revealed various subunits of neurofilaments as well as DFS-70 as autoantibody epitopes. Conclusion: Our data suggest that autoantibodies against nervous system tissue could be relevant in PCVS patients. Autoantibodies against neurofilaments and cell nuclei with so far non-established links to this disease spectrum should be further elucidated to determine their biomarker potential.

Ultraconformable cuff implants for long-term bidirectional interfacing of peripheral nerves at sub-nerve resolutions.

Implantable devices interfacing with peripheral nerves exhibit limited longevity and resolution. Poor nerve-electrode interface quality, invasive surgical placement and development of foreign body reaction combine to limit research and clinical application of these devices. Here, we develop cuff implants with a conformable design that achieve high-quality and stable interfacing with nerves in chronic implantation scenarios. When implanted in sensorimotor nerves of the arm in awake rats for 21 days, the devices record nerve action potentials with fascicle-specific resolution and extract from these the conduction velocity and direction of propagation. The cuffs exhibit high biocompatibility, producing lower levels of fibrotic scarring than clinically equivalent PDMS silicone cuffs. In addition to recording nerve activity, the devices are able to modulate nerve activity at sub-nerve resolution to produce a wide range of paw movements. When used in a partial nerve ligation rodent model, the cuffs identify and characterise changes in nerve C fibre activity associated with the development of neuropathic pain in freely-moving animals. The developed implantable devices represent a platform enabling new forms of fine nerve signal sensing and modulation, with applications in physiology research and closed-loop therapeutics.

Optimizing Outcomes in Revision Peripheral Nerve Surgery of the Upper Extremity.

Peripheral nerve surgeries for compressive neuropathy in the upper extremity are generally successful. However, cases that either fail or have complications requiring revision surgery are challenging. During revision consideration, surgeons should perform a comprehensive preoperative workup to understand the etiology of the patient's symptoms and categorize symptoms as persistent, recurrent, or new in relation to the index procedure. Revision surgery often requires an open, extensile approach with additional procedures to optimize outcomes. Even with proper workup and treatment, clinical outcomes of revision surgeries are inferior compared to primary surgeries and patients should be well informed prior to undergoing such procedures.

Focal slowing of nerve conduction velocity in leprosy patients unveiled through multisegmented nerve analysis.

BACKGROUND AND AIMS: Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae), an intracellular bacillus that systematically invades the peripheral nerves. Diagnosing leprosy neuropathy is still a defying skill, and late diagnosis and treatment are still a reality. Based on the biological characteristics of M. leprae, particularly its preference for invading the Schwann cells localized at the coldest areas of human body, we hypothesized that these areas have focal demyelination that may escape detection through standard nerve conduction studies (NCSs) protocols. METHODS: Twenty-five patients with confirmed multibacillary leprosy and 14 controls were accessed. A multisegmented NCS protocol (MP) was performed, targeting short segments through the coldest areas, to identify focal areas of slowed conduction velocity. The effectiveness of this multisegmented protocol was compared to the standard protocol (SP) to detect abnormalities. RESULTS: All leprosy patients presented an abnormal study with the MP, contrasting to 19 with the SP. The most frequent NCS pattern was an asymmetric neuropathy with focal slowing of conduction velocity, found in 23 out of 25 leprosy patients. Significant differences favoring the proposed method were observed when comparing the MP with the SP. Notably, the MP increased the sensitivity to detect abnormalities by 122%, 133%, and 257% for the median, peroneal, and tibial nerves, respectively. MP also increases sensitivity to detect focal abnormalities in the ulnar nerve. INTERPRETATION: The MP protocol significantly increases the sensitivity of NCSs to detect neurophysiological abnormalities in leprosy neuropathy.

Comparison of intravenous versus perineural dexamethasone as a local anaesthetic adjunct for peripheral nerve blocks in the lower limb: A meta-analysis and systematic review.

BACKGROUND: As a local anaesthetic adjunct, the systemic absorption of perineural dexamethasone in the lower limb could be restricted because of decreased vascularity when compared with the upper limb. OBJECTIVES: To compare the pharmacodynamic characteristics of intravenous and perineural dexamethasone in the lower limb. DESIGN: Systematic review of randomised controlled trials with meta-analysis. DATA SOURCES: Systematic search of Central, Google Scholar, Ovid Embase and Ovid Medline to 18 July 2023. ELIGIBILITY CRITERIA: Randomised controlled trials, which compared the intravenous with perineural administration of dexamethasone as a local anaesthetic adjunct in peripheral nerve blocks for surgery of the lower limb. RESULTS: The most common peripheral nerve blocks were femoral, sciatic and ankle block. The local anaesthetic was long acting in all trials and the dose of dexamethasone was 8 mg in most trials. The primary outcome, the duration of analgesia, was investigated by all nine trials ( n  = 546 patients). Overall, compared with intravenous dexamethasone, perineural dexamethasone increased the duration of analgesia from 19.54 to 22.27 h, a mean difference [95% confidence interval (CI) of 2.73 (1.07 to 4.38) h; P  = 0.001, I2  = 87]. The quality of evidence was moderate owing to serious inconsistency. However, analysis based on the location of the peripheral nerve block, the type of local anaesthetic or the use of perineural adrenaline showed no difference in duration between intravenous and perineural dexamethasone. No differences were shown for any of the secondary outcomes related to efficacy and side effects. CONCLUSION: In summary, moderate evidence supports the superiority of perineural dexamethasone over intravenous dexamethasone in prolonging the duration of analgesia. However, this difference is unlikely to be clinically relevant. Consideration of the perineural use of dexamethasone should recognise that this route of administration remains off label.

High levels of plasma neurofilament light chain correlated with brainstem and peripheral nerve damage.

BACKGROUND AND OBJECTIVES: Blood neurofilament light chain (NfL) is a minimally invasive, but highly sensitive biomarker of neurological diseases. However, diseases and neurological damage associated with increased NfL remain unclear. Therefore, the present study investigated factors associated with increased plasma NfL levels in various neurological diseases, focal lesions and pathological processes. METHODS: This was a retrospective cohort study on 410 participants with various neurological diseases and 17 healthy and cognitively unimpaired controls (HCU). Plasma samples were analyzed to measure NfL using ECL immunoassay. The focal lesions were classified as the cerebrum, cerebellum, brainstem, meninges, spinal cord, peripheral nerves, neuromuscular junction, and muscles based on medical records. A multiple regression analysis and receiver operating characteristic curve (ROC) analysis were performed to investigate whether plasma NfL levels predict specific diseases and focal lesions. RESULTS: Plasma NfL levels discriminated between the HCU and all disease groups (area under the curve (AUC), 0.97), with a cut-off value of 63.4 pg/mL. A multiple regression analysis of focal lesions adjusted by pathogenic processes showed that brainstem and peripheral nerve involvement was associated with higher plasma NfL levels. A cut-off value of 53.8 pg/mL of NfL discriminated between the HCU and neurological disease group except for brainstem or peripheral disorders (AUC 0.962), while a cut-off value of 208.0 pg/mL distinguished this group from brainstem or peripheral nervous system disorders (AUC 0.716). DISCUSSION: These results demonstrate that plasma NfL has a potential to be a highly sensitive biomarker for neurological diseases and focal lesions.