Anti-GM1 antibodies cause complement-mediated disruption of sodium channel clusters in peripheral motor nerve fibers

Guillain-Barré syndrome: A comprehensive review

Guillain-Barré syndrome (GBS) is a potentially devastating yet treatable disorder. A classically postinfectious, immune-mediated, monophasic polyradiculoneuropathy, it is the leading global cause of acquired neuromuscular paralysis. In most cases, the immunopathological process driving nerve injury is ill-defined. Diagnosis of GBS relies on clinical features, supported by laboratory findings and electrophysiology. Although previously divided into primary demyelinating or axonal variants, this dichotomy is increasingly challenged, and is not endorsed by the recent European Academy of Neurology (EAN)/Peripheral Nerve Society (PNS) guidelines. Intravenous immunoglobulin and plasma exchange remain the primary modalities of treatment, regardless of the electrophysiological subtype. Most patients recover, but approximately one-third require mechanical ventilation, and 5% die. Disease activity and treatment response are currently monitored through interval neurological examination and outcome measures, and the potential role of fluid biomarkers is under ongoing scrutiny. Novel potential therapies for GBS are being explored but none have yet modified clinical practice. This review provides a comprehensive update on the pathological and clinical aspects of GBS for clinicians and scientists.

Effect of intravenous immunoglobulin and plasmapheresis on nerve conduction parameters compared to the natural course of Guillain-Barré syndrome

BACKGROUND

Intravenous immunoglobulin (IVIg) and plasmapheresis (PLEX) are recommended in moderate to severe Guillain-Barré Syndrome (GBS), but there is paucity of studies evaluating its effect on nerve conduction studies (NCS). We report the effect of IVIg and PLEX on the NCS parameters and clinical outcomes compared to natural course (NC) of GBS patients.

METHOD

Moderate to severe GBS patients were included based on clinical, cerebrospinal fluid, and NCS finding. Six motor and sensory nerves were evaluated at admission, one month and 3 months, and NCS subtyping was done. Axonal and demyelination burden in motor nerves and early reversible conduction block (ERCB) were noted. Patients receiving IVIg, PLEX or on NC were noted. Outcome was defined at 3 months into complete, partial and poor using a 0-6 GBS Disability Scale (GBSDS).

RESULT

Seventy-two patients were included, whose median age was 36 years and 22(30.6 %) were females. 44 patients received IVIg, 9 PLEX and 19 were in NC, and they had comparable peak disability. AIDP was the dominant subtype at admission (58.3 %), which remained so at 3 months (50 %). The shift of subtypes was the highest from the equivocal group followed by AMAN and the least from AIDP. IVIg and PLEX group had more reduction in axonal burden and had ERCB compared to NC. 33(44 %) patients had complete recovery, and 40(55.5 %) patients had concordance in clinical and neurophysiological outcome.

CONCLUSION

Transition of GBS subtype may occur at follow-up from all the subtypes, the highest from the equivocal and the lowest from the AIDP group. IVIg/PLEX treatment may help in reducing conduction block and axonal burden.

Guillain-barré syndrome (GBS) with antecedent chikungunya infection: a case report and literature review

Guillain-Barré Syndrome (GBS) is an autoimmune neuropathy. Antecedent infections have been seen to be significant triggering factors for developing GBS. Among them, arboviral infections are rapidly gaining importance as significant triggers, especially in the areas where they are endemic. Chikungunya, an arboviral infection that usually causes a self-limiting acute febrile illness can lead to GBS as one its severe complications. Herein, we describe a case of a 21-year-old female who presented with weakness in all four limbs and paresthesia. Nerve conduction study and cerebrospinal fluid (CSF) analysis showed axonal, demyelinating motor and sensory neuropathy with albuminocytological dissociation indicating Acute Motor and Sensory Axonal Neuropathy (AMSAN) variant of GBS. Serum IgM antibodies against ganglioside GM1 were detected. Anti-Chikungunya IgM antibodies were found in both serum and CSF samples. The patient was initiated with Intravenous Immunoglobulin (IVIG) therapy. In view of hypoxia, she was intubated and was on mechanical ventilation. After 2 weeks of being comatose, the patient gradually improved and was discharged with no sequelae.A literature review on antecedent infections in GBS is presented alongside the case report to better understand the association of GBS with antecedent infections, especially the endemic arboviral infections like Chikungunya, Dengue and Zika. This will help in reinforcing the significance of having robust surveillance and public health control measures for infectious diseases.

Atypical Guillain-Barré Syndrome in a Pediatric Patient With a Preceding Non-COVID-19 Coronavirus Infection: A Case Report

This study examines a four-year-and-one-month-old male with no significant past medical, family, or surgical history who initially presented to the pediatric clinic with cough, rhinorrhea, conjunctivitis, emesis, leg and arm pain, and increased difficulty ambulating. The patient was transferred to the emergency department and tested positive for a non-COVID-19 coronavirus infection. The patient was stabilized, given intravenous fluids, and discharged only to return to the clinic the next day with the onset of a headache, right eye ptosis, an inability to bear weight, and bilateral upper and lower extremity weakness resulting in an ataxic gait. In addition to the neurological deficits, the patient was found to have an elevated blood pressure and pulse. The patient was promptly transferred to a tertiary care clinic. Through exclusion of various differentials via testing, the patient was diagnosed and managed for atypical Guillain-Barré syndrome. Targeted therapies were initiated to prevent dysautonomia-associated morbidity. Following management, the patient's condition vastly improved and he was admitted to rehabilitation bringing him back to optimal health. This study underlines the importance of prompt identification of atypical presentations of Guillain-Barré syndrome which may aid in avoiding preventable morbidity and mortality.

Macrophages are scavengers for injured myelin in a rabbit model of acute inflammatory demyelinating polyneuropathy

In acute inflammatory demyelinating polyneuropathy (AIDP), myelin vesiculation mediated by complement activation contributes to nerve injury. Macrophage infiltration of the spinal roots has been demonstrated in AIDP, but its pathological significance remains uncertain. The present study aimed to investigate the role of macrophages in the pathogenic sequence of AIDP. A rabbit model of AIDP was induced by immunization with galactocerebroside. Immunostaining was performed to localize the macrophages and myelin injury. The rabbit developed tetraparesis with electrophysiological and pathological features of peripheral nerve demyelination. Immunostaining demonstrated colocalization of IgG antibodies, complement deposition and myelin injury apart from macrophages. Immunostaining and electron microscopy showed myelin injury preceded macrophage infiltration. There was significant disruption of voltage-gated sodium channel clusters at the nodes of Ranvier in the spinal roots. Macrophages acted may as scavengers to remove myelin debris following complement activation-mediated demyelination in the AIDP rabbit. Lesions at the node of Ranvier contribute to conduction failure and muscle weakness.

Evidence for spontaneous regulation of the humoral IgM anti-GM1 autoimmune response by IgG antibodies in multifocal motor neuropathy patients

BACKGROUND AND AIMS

Multifocal motor neuropathy (MMN) is a peripheral nerve disorder characterized by slow progressive distal asymmetric weakness with minimal or no sensory impairment. Currently, a vast evidence supports a direct pathogenic role of IgM anti-GM1 antibodies on disease pathogenesis. Patients with MMN seropositive for GM1-specific IgM antibodies have significantly more weakness, disability and axon loss than patients without these antibodies. During the screening for IgM anti-GM1 antibodies in a cohort of patients with neuropathy we noticed an absence or significant reduction of natural IgM anti-GM1 autoreactivity in some patients with MMN, suggesting a mechanism of self-control of autoreactivity. We aim to understand the lack of natural reactivity against GM1 in MMN patients.

METHODS

The presence of free IgM anti-GM1 reactivity or its complex to blocking IgG was analysed by combining high performance thin layer chromatography-immunostaining, soluble binding inhibition assays, Protein-G or GM1-affinity columns and dot blot assays.

RESULTS

We identified in MMN patients an immunoregulation of IgM anti-GM1 antibodies mediated by IgG immunoglobulins characterized by: (i) lack of natural IgM anti-GM1 autoreactivity as a result of a immunoregulatory IgG-dependent mechanism; (ii) presence of natural and disease-associated IgM anti-GM1/IgG blocking Ab complexes in sera; and (iii) high levels of IgG blocking against natural IgM anti-GM1 antibodies (Abs.

INTERPRETATION

Our observations unmask a spontaneous IgG-dependent mechanism of immunoregulation against IgM anti-GM1 antibodies that could explain, in part, fluctuations in the usually slowly progressive clinical course that characterizes the disease and, at the same time, allows the identification of an autoimmune response against GM1 ganglioside in seronegative patients.

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.

The Node of Ranvier as an Interface for Axo-Glial Interactions: Perturbation of Axo-Glial Interactions in Various Neurological Disorders

The action potential conduction along the axon is highly dependent on the healthy interactions between the axon and myelin-producing glial cells. Myelin, which facilitates action potential, is the protective insulation around the axon formed by Schwann cells and oligodendrocytes in the peripheral (PNS) and central nervous system (CNS), respectively. Myelin is a continuous structure with intermittent gaps called nodes of Ranvier, which are the sites enriched with ion channels, transmembrane, scaffolding, and cytoskeletal proteins. Decades-long extensive research has identified a comprehensive proteome with strictly regularized localization at the node of Ranvier. Concurrently, axon-glia interactions at the node of Ranvier have gathered significant attention as the pathophysiological targets for various neurodegenerative disorders. Numerous studies have shown the alterations in the axon-glia interactions culminating in neurological diseases. In this review, we have provided an update on the molecular composition of the node of Ranvier. Further, we have discussed in detail the consequences of disruption of axon-glia interactions during the pathogenesis of various CNS and PNS disorders.

Molecular, Electrophysiological, and Ultrasonographic Differences in Selected Immune-Mediated Neuropathies with Therapeutic Implications

The spectrum of immune-mediated neuropathies is broad and the different subtypes are still being researched. With the numerous subtypes of immune-mediated neuropathies, establishing the appropriate diagnosis in normal clinical practice is challenging. The treatment of these disorders is also troublesome. The authors have undertaken a literature review of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), Guillain-Barre syndrome (GBS) and multifocal motor neuropathy (MMN). The molecular, electrophysiological and ultrasound features of these autoimmune polyneuropathies are analyzed, highlighting the differences in diagnosis and ultimately treatment. The immune dysfunction can lead to damage to the peripheral nervous system. In practice, it is suspected that these disorders are caused by autoimmunity to proteins located in the node of Ranvier or myelin components of peripheral nerves, although disease-associated autoantibodies have not been identified for all disorders. The electrophysiological presence of conduction blocks is another important factor characterizing separate subgroups of treatment-naive motor neuropathies, including multifocal CIDP (synonyms: multifocal demyelinating neuropathy with persistent conduction block), which differs from multifocal motor neuropathy with conduction block (MMN) in both responses to treatment modalities and electrophysiological features. Ultrasound is a reliable method for diagnosing immune-mediated neuropathies, particularly when alternative diagnostic examinations yield inconclusive results. In overall terms, the management of these disorders includes immunotherapy such as corticosteroids, intravenous immunoglobulin or plasma exchange. Improvements in clinical criteria and the development of more disease-specific immunotherapies should expand the therapeutic possibilities for these debilitating diseases.

Infectious diseases, autoantibodies, and autoimmunity

Infections are known to trigger flares of autoimmune diseases in humans and serve as an inciting cause of autoimmunity in animals. Evidence suggests a causative role of infections in triggering antigen-specific autoimmunity, previous thought mainly through antigen mimicry. However, an infection can induce bystander autoreactive T and B cell polyclonal activation, believed to result in non-pathogenic and pathogenic autoimmune responses. Lastly, epitope spreading in autoimmunity is a mechanism of epitope changes of autoreactive cells induced by infection, promoting the targeting of additional self-epitopes. This review highlights recent research findings, emphasizes infection-mediated autoimmune responses, and discusses the possible mechanisms involved.

COVID-19 as a trigger of Guillain-Barré syndrome: A review of the molecular mechanism

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a pandemic with serious complications. After coronavirus disease 2019 (COVID-19), several post-acute COVID-19 syndromes (PACSs) and long-COVID sequels were reported. PACSs involve many organs, including the nervous, gustatory, and immune systems. One of the PACSs after SARS-CoV-2 infection and vaccination is Guillain-Barré syndrome (GBS). The incidence rate of GBS after SARS-CoV-2 infection or vaccination is low. However, the high prevalence of COVID-19 and severe complications of GBS, for example, autonomic dysfunction and respiratory failure, highlight the importance of post-COVID-19 GBS. It is while patients with simultaneous COVID-19 and GBS seem to have higher admission rates to the intensive care unit, and demyelination is more aggressive in post-COVID-19 GBS patients. SARS-CoV-2 can trigger GBS via several pathways like direct neurotropism and neurovirulence, microvascular dysfunction and oxidative stress, immune system disruption, molecular mimicry, and autoantibody production. Although there are few molecular studies on the molecular and cellular mechanisms of GBS occurrence after SARS-CoV-2 infection and vaccination, we aimed to discuss the possible pathomechanism of post-COVID-19 GBS by gathering the most recent molecular evidence.

Immune-Mediated Neuropathies: Pathophysiology and Management

Dysfunction of the immune system can result in damage of the peripheral nervous system. The immunological mechanisms, which include macrophage infiltration, inflammation and proliferation of Schwann cells, result in variable degrees of demyelination and axonal degeneration. Aetiology is diverse and, in some cases, may be precipitated by infection. Various animal models have contributed and helped to elucidate the pathophysiological mechanisms in acute and chronic inflammatory polyradiculoneuropathies (Guillain-Barre Syndrome and chronic inflammatory demyelinating polyradiculoneuropathy, respectively). The presence of specific anti-glycoconjugate antibodies indicates an underlying process of molecular mimicry and sometimes assists in the classification of these disorders, which often merely supports the clinical diagnosis. Now, the electrophysiological presence of conduction blocks is another important factor in characterizing another subgroup of treatable motor neuropathies (multifocal motor neuropathy with conduction block), which is distinct from Lewis-Sumner syndrome (multifocal acquired demyelinating sensory and motor neuropathy) in its response to treatment modalities as well as electrophysiological features. Furthermore, paraneoplastic neuropathies are also immune-mediated and are the result of an immune reaction to tumour cells that express onconeural antigens and mimic molecules expressed on the surface of neurons. The detection of specific paraneoplastic antibodies often assists the clinician in the investigation of an underlying, sometimes specific, malignancy. This review aims to discuss the immunological and pathophysiological mechanisms that are thought to be crucial in the aetiology of dysimmune neuropathies as well as their individual electrophysiological characteristics, their laboratory features and existing treatment options. Here, we aim to present a balance of discussion from these diverse angles that may be helpful in categorizing disease and establishing prognosis.

Axolemmal nanoruptures arising from paranodal membrane injury induce secondary axon degeneration in murine Guillain-Barré syndrome

The major determinant of poor outcome in Guillain-Barré syndrome (GBS) is axonal degeneration. Pathways leading to primary axonal injury in the motor axonal variant are well established, whereas mechanisms of secondary axonal injury in acute inflammatory demyelinating polyneuropathy (AIDP) are unknown. We recently developed an autoantibody-and complement-mediated model of murine AIDP, in which prominent injury to glial membranes at the node of Ranvier results in severe disruption to paranodal components. Acutely, axonal integrity was maintained, but over time secondary axonal degeneration occurred. Herein, we describe the differential mechanisms underlying acute glial membrane injury and secondary axonal injury in this model. Ex vivo nerve-muscle explants were injured for either acute or extended periods with an autoantibody-and complement-mediated injury to glial paranodal membranes. This model was used to test several possible mechanisms of axon degeneration including calpain activation, and to monitor live axonal calcium signalling. Glial calpains induced acute disruption of paranodal membrane proteins in the absence of discernible axonal injury. Over time, we observed progressive axonal degeneration which was markedly attenuated by axon-specific calpain inhibition. Injury was unaffected by all other tested methods of protection. Trans-axolemmal diffusion of fluorescent proteins  and live calcium imaging studies indirectly demonstrated the presence of nanoruptures in the axon membrane. This study outlines one mechanism by which secondary axonal degeneration arises in the AIDP variant of GBS where acute paranodal loop injury is prominent. The data also support the development of calpain inhibitors to attenuate both primary and secondary axonal degeneration in GBS.

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.

Repurposing MS immunotherapies for CIDP and other autoimmune neuropathies: unfulfilled promise or efficient strategy?

Despite advances in the treatment of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and other common autoimmune neuropathies (AN), still-many patients with these diseases do not respond satisfactorily to the available treatments. Repurposing of disease-modifying therapies (DMTs) from other autoimmune conditions, particularly multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD), is a promising strategy that may accelerate the establishment of novel treatment choices for AN. This approach appears attractive due to homologies in the pathogenesis of these diseases and the extensive post-marketing experience that has been gathered from treating MS and NMOSD patients. The idea is also strengthened by a number of studies that explored the efficacy of DMTs in animal models of AN but also in some CIDP patients. We here review the available preclinical and clinical data of approved MS therapeutics in terms of their applicability to AN, especially CIDP. Promising therapeutic approaches appear to be B cell-directed and complement-targeting strategies, such as anti-CD20/anti-CD19 agents, Bruton's tyrosine kinase inhibitors and anti-C5 agents, as they exert their effects in the periphery. This is a major advantage because, in contrast to MS, their action in the periphery is sufficient to exert significant immunomodulation.

Reversible conduction failure in acute inflammatory demyelinating polyneuropathy

Reversible conduction failure (RCF) has been documented in acute motor axonal neuropathy (AMAN) and is considered a sign of nodopathy. Several reports of RCF in acute inflammatory demyelinating polyneuropathy (AIDP) have suggested that it could be a manifestation of nodopathy. We conducted this study to determine the frequency of RCF in AMAN and AIDP and to compare the clinical features between the two groups with or without RCF. RCF was observed in 38.9% and 18.5% patients in the AMAN and AIDP groups in our study, respectively. AIDP patients with anti-ganglioside antibodies represented 29.4% of the cohort. The clinical features of AIDP with RCF were more similar to those of AMAN with RCF than to those of typical AIDP. However, there were no significant differences in the frequency of anti-ganglioside antibody status between the groups. AIDP with RCF may be a manifestation of nodopathy. The current dichotomous electrodiagnostic criteria, classifying demyelinating and axonal neuropathy, are insufficient to define nodopathy. Further studies are required to revise the electrodiagnostic criteria for Guillain-Barré syndrome.

The role of gangliosides in the organisation of the node of Ranvier examined in glycosyltransferase transgenic mice

Gangliosides are a family of sialic acid containing glycosphingolipids highly enriched in plasma membranes of the vertebrate nervous system. They are functionally diverse in modulating nervous system integrity, notably at the node of Ranvier, and also act as receptors for many ligands including toxins and autoantibodies. They are synthesised in a stepwise manner by groups of glycosyl- and sialyltransferases in a developmentally and tissue regulated manner. In this review, we summarise and discuss data derived from transgenic mice with different transferase deficiencies that have been used to determine the role of glycolipids in the organisation of the node of Ranvier. Understanding their role at this specialised functional site is crucial to determining differential pathophysiology following directed genetic or autoimmune injury to peripheral nerve nodal or paranodal domains, and revealing the downstream consequences of axo-glial disruption.

Glial cells and neurologic autoimmune disorders

Neurologic autoimmune disorders affect people's physical and mental health seriously. Glial cells, as an important part of the nervous system, play a vital role in the occurrence of neurologic autoimmune disorders. Glial cells can be hyperactivated in the presence of autoantibodies or pathological changes, to influence neurologic autoimmune disorders. This review is mainly focused on the roles of glial cells in neurologic autoimmune disorders and the influence of autoantibodies produced by autoimmune disorders on glial cells. We speculate that the possibility of glial cells might be a novel way for the investigation and therapy of neurologic autoimmune disorders.

Skin Biopsy as a Novel Diagnostic Aid in Immune-Mediated Neuropathies

Immune-mediated neuropathies are a heterogenous group of inflammatory peripheral nerve disorders. They can be classified according to the domain where the autoimmune process begins: the internode, paranode, or node. However, conventional diagnostic tools, electrodiagnosis (EDX), and autoantibody testing do not fully address this issue. In this institutional cohort study, we investigated the value of dermal myelinated fiber analysis for target domain-based classification. Twenty-seven consecutive patients with immune-mediated neuropathies underwent skin biopsies. The sections were stained with antibodies representative of myelinated fiber domains and were scanned using a confocal microscope. Clinical and pathological features of each patient were reviewed comprehensively. Quantitative morphometric parameters were subjected to clustering analysis, which stratified patients into 3 groups. Cluster 1 ("internodopathy") was characterized by prominent internodal disruption, intact nodes and paranodes, demyelinating EDX pattern, and absence of nodal-paranodal antibodies. Cluster 2 ("paranodopathy") was characterized by paranodal disruption and corresponding antibodies. Morphological changes were restricted to the nodes in cluster 3; we designated this cluster as "nodopathy." This report highlights the utility of skin biopsy as a diagnostic aid to gain pathogenic insight and classify patients with immune-mediated neuropathies.

Real time imaging of intra-axonal calcium flux in an explant mouse model of axonal Guillain-Barré syndrome

The acute motor axonal variant of Guillain-Barré syndrome is associated with the attack of motor axons by anti-ganglioside antibodies which activate complement on the axonal plasma membrane. Animal models have indirectly implicated complement pore-mediated calcium influx as a trigger of axonal damage, through the activation of the protease calpain. However, this calcium influx has never been imaged directly. Herein we describe a method to detect changes in intra-axonal calcium in an ex vivo mouse model of axonal Guillain-Barré syndrome and describe the influence of calcium on axonal injury and the effects of calpain inhibition on axonal outcome. Using ex vivo nerve-muscle explants from Thy1-TNXXL mice which axonally express a genetically encoded calcium indicator, we studied the effect of the binding and activation of complement by an anti-GD1b ganglioside antibody which targets the motor axon. Using live multiphoton imaging, we found that a wave of calcium influx extends retrogradely from the motor nerve terminal as far back as the large bundles within the muscle explant. Despite terminal complement pores being detectable only at the motor nerve terminal and, to a lesser degree, the most distal node of Ranvier, disruption of axonal proteins occurred at more proximal sites implicating the intra-axonal calcium wave. Morphological analysis indicated two different types of calcium-induced changes: acutely, distal axons showed swelling and breakdown at sites where complement pores were present. Distally, in areas of raised calcium which lacked detectable complement pores, axons developed a spindly, vacuolated appearance suggestive of early signs of degeneration. All morphological changes were prevented with treatment with a calpain inhibitor. This is the first investigation of axonal calcium dynamics in a mouse model of Guillain-Barré syndrome and demonstrates the proximal reach of calcium influx following an injury which is confined to the most distal parts of the motor axon. We also demonstrate that calpain inhibition remains a promising candidate for both acute and sub-acute consequences of calcium-induced calpain activation.

Plexus MRI helps distinguish the immune-mediated neuropathies MADSAM and MMN

BACKGROUND

Among immune-mediated neuropathies, clinical-electrophysiological overlap exists between multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) and multifocal motor neuropathy (MMN). Divergent immune pathogenesis, immunotherapy response, and prognosis exist between these two disorders. MRI reports have not shown distinction of these disorders, but biopsy confirmation is lacking in earlier reports. MADSAM nerves are hypertrophic with onion bulbs, inflammation, and edema, whereas MMN findings are limited to multifocal axonal atrophy.

OBJECTIVES

To understand if plexus MRI can distinguish MADSAM from MMN among pathologically (nerve biopsy) confirmed cases.

METHODS

Retrospective chart review and blinded plexus MRI review of biopsy-confirmed MADSAM and MMN cases at Mayo Clinic.

RESULTS

Nine brachial plexuses (MADSAM-5, MMN-4) and 6 lumbosacral plexuses (MADSAM-4, MMN-2) had fascicular biopsies of varied nerves. Median follow-up in MADSAM was 93 months (range: 7-180) and 27 (range: 12-109) in MMN (p = 0.34). MRI hypertrophy occurred solely in MADSAM (89%, 8/9) with T2-hyperintensity in both. There was no correlation between time to imaging for hypertrophy, symptom onset age, or motor neuropathy impairments (mNIS). At last follow-up, on diverse immunotherapies mNIS improved in MADSAM (median - 4, range: -22 to 0), whereas MMN worsened (median 3, range: 0 to 6, p = 0.03) on largely IVIG.

CONCLUSION

Nerve hypertrophy on plexus MRI helps distinguish MMN from MADSAM, where better immunotherapy treatment outcomes were observed. These findings are consistent with the immune pathogenesis seen on biopsies. Radiologic distinction is possible independent of time to imaging and extent of motor deficits, suggesting MRI is helpful in patients with uncertain clinical-electrophysiologic diagnosis, especially motor-onset MADSAM.

[Introduction to Myelin Research]

Myelin is a multilamellar membrane structure formed by oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS). It has been recognized as an insulator that is essential for the rapid and efficient propagation of action potentials by saltatory conduction. However, recently many studies have shown that myelin and myelin-forming cells interact with axons and regulate the nervous system far more actively than previously thought. For example, myelination changes axons dynamically and divides them into four distinct functional domains: node of Ranvier, paranode, juxtaparanode, and internode. Voltage-gated Na⁺ channels are clustered at the node, while K⁺ channels are at the juxtaparanode, and segregation of these channels by paranodal axoglial junction is necessary for proper axonal function. My research experience began at the neurology ward of the Niigata University Medical Hospital, where I saw a patient with peripheral neuropathy of unknown etiology more than 37 years ago. In the patient's serum, we found an autoantibody against a glycolipid enriched in the PNS. Since then, I have been interested in myelin because of its beautiful structure and unique roles in the nervous system. In this review, our recent studies related to CNS and PNS myelin are presented.

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.

The Role of the Complement System in Chronic Inflammatory Demyelinating Polyneuropathy: Implications for Complement-Targeted Therapies

Chronic inflammatory demyelinating polyneuropathy (CIDP) is the most common, heterogeneous, immune-mediated neuropathy, characterized by predominant demyelination of motor and sensory nerves. CIDP follows a relapsing-remitting or a progressive course and causes substantial disability. The pathogenesis of CIDP involves a complex interplay of multiple aberrant immune responses, creating a pro-inflammatory environment, subsequently inflicting damage on the myelin sheath. Though the exact triggers are unclear, diverse immune mechanisms encompassing cellular and humoral pathways are implicated. The complement system appears to play a role in promoting macrophage-mediated demyelination. Complement deposition in sural nerve biopsies, as well as signs of increased complement activation in serum and CSF of patients with CIDP, suggest complement involvement in CIDP pathogenesis. Here, we present a comprehensive overview of the preclinical and clinical evidence supporting the potential role of the complement system in CIDP. This understanding furnishes a strong rationale for targeting the complement system to develop new therapies that could serve the unmet needs of patients affected by CIDP, particularly in those refractory to standard therapies.

Immunoglobulin and Monoclonal Antibody Therapies in Guillain-Barré Syndrome

Guillain-Barré syndrome (GBS) is an acute autoimmune polyradiculoneuropathy affecting 1-2 subjects per 100,000 every year worldwide. It causes, in its classic form, symmetric weakness in the proximal and distal limb muscles with common involvement of the cranial nerves, particularly facial weakness. Respiratory function is compromised in a case in four. Randomised controlled trials have demonstrated the benefit of therapeutic plasma exchange in hastening time to recovery. Intravenous immunoglobulin was subsequently shown to be as efficacious as plasma exchange in adult subjects. In children, few trials have shown the benefit of intravenous immunoglobulin versus supportive care. Pharmacokinetic studies suggested a relationship between increase in immunoglobulin G level post-infusion and outcome, implying administration of larger doses may be beneficial in subjects with poor prognosis. However, a subsequent trial of a second dose of immunoglobulin in such subjects failed to show improved outcome, while demonstrating a higher risk of thromboembolic side-effects. Monoclonal antibody therapy has more recently been investigated for GBS, after multiple studies in animal models, with different agents and variable postulated mechanisms of action. Eculizumab, a humanised monoclonal antibody against the complement protein C5, was tested in in two randomised, double-blind, placebo-controlled phase 2 trials. Neither showed benefit versus immunoglobulins alone on disability level at 4 weeks, although one study importantly suggested possible, clinically highly relevant, late effects on normalising function. A phase 3 trial is in progress. Preliminary results of a placebo-controlled ongoing study of ANX005, a humanised recombinant antibody against C1q inhibiting the complement cascade, have been promising.

Asymmetric limb weakness in Guillain-Barré syndrome: Three case reports

BACKGROUND

Guillain-Barré syndrome (GBS) is an autoimmune-mediated peripheral neuropathy characterized by symmetric weakness. Asymmetric weakness in GBS is uncommon and may be easily confused with other differential diagnoses. We herein present three cases of asymmetric GBS and review the literature on this atypical subtype of GBS in order to describe the characteristics of asymmetric GBS and to provide experience for clinicians.

CASE SUMMARY

Different from patients in the previous reports, our patients showed persistent asymmetric limb weakness from the onset to recovery phase. All three patients were serologically positive for antecedent infections. Two of the three cases had IgG antibodies against ganglioside GM1. Two patients received immunotherapy including intravenous immunoglobulin and plasma exchange, while one patient received only supportive treatment. Autoantibodies against gangliosides, asymmetry of congenital development of blood-nerve barrier and limb use may contribute to the development of asymmetric limb weakness in GBS.

CONCLUSION

Asymmetric GBS may be a rare clinical variant and should be considered when a patient develops acute and progressive asymmetric limb weakness. The differences in clinical features and prognosis between asymmetric GBS and classic GBS deserve further investigation in a large study.

Comparison of the effects of different doses of Glucocorticoids on distinct subtypes of Guillain-Barré syndrome in Southern China

Background

The effect of Glucocorticoids (GCs) on the treatment of Guillain-Barré syndrome (GBS) has been controversial. There is no information on whether specific subtypes of GBS respond differently to GCs. In this setting, we aimed to discuss whether GCs treating yield different effects in the distinct subtypes (acute inflammatory demyelinating polyneuropathy, AIDP; acute motor axonal neuropathy, AMAN). And further, we analyzed the impact of different doses on the outcome.

Methods

Medical records of 448 patients with a diagnosis of classic GBS admitted to 31 tertiary hospitals, located in 14 provinces of Southern China, from 1 January 2013 to 30 September 2016, were retrospectively collected. And 251 patients treated with GCs alone (AIDP=189, AMAN=62) were reviewed and analyzed.

Results

After GCs treatment, the Hughes score of AIDP patients was significantly lower than that of AMAN patients at discharge (P=0.005) and 3 months after onset (P<0.001). Further analysis revealed that among AIDP patients, the high-dose group had significantly shorter hospital stay (P=0.023), lower Hughes score at nadir (P<0.001), at discharge (P=0.005), and 3 months after onset (P<0.001), compared with the low-dose group. However, for AMAN patients, the outcome difference between groups was nonsignificant.

Conclusion

Our data suggest that the high doses of GCs may result, at least in part, from the side of the duration of hospital stay and short-term outcome, favorable outcomes in AIDP patients. Therefore, we cannot completely deny the priority of GCs in the treatment of GBS, because the effect of different doses of GCs varies in treating different subtypes. More studies are needed in the future to further validate this issue.

Trial registration

ChiCTR-RRC-17014152. Registered 26 December 2017- Retrospectively registered.

Electrophysiology of Guillain-Barré syndrome in Bangladesh: A prospective study of 312 patients

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Classification of neurophysiologic subtypes of Guillain-Barré syndrome largely depended on the applied criteria.

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Anti-GM1 antibodies were not exclusively associated with axonal Guillain-Barré syndrome.

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Conduction block was not exclusively associated with demyelinating Guillain-Barré syndrome.

Objective

To describe the electrophysiological features in relation to clinical and serological findings of Guillain-Barré syndrome (GBS) in the national neuroscience hospital in Bangladesh. This is one of the few studies that investigated GBS patients using standardized electrophysiology in low-income countries.

Methods

In a prospective and observational study, we investigated 312 GBS patients by standardized clinical, serological and electrophysiological methods. Unilateral motor and sensory nerve conduction studies (NCS) were performed within two weeks of onset of weakness. Follow up NCS were performed in 189 patients and classified according to eight sets of established GBS criteria. Serology included assessment of anti-GM1 antibodies and anti-campylobacter jejuni lipo-oligosaccharide (LOS) antibodies.

Results

Depending on the criteria used, 44–59% patients had axonal GBS with anti-GM1 antibodies being present in 55–58% and 9–42% patients had demyelinating GBS with anti-GM1 antibodies being present in 7–35%. Conduction block (CB) with demyelinative slowing in the same nerve segment was found in 24% (74/312) patients, and CB without demyelinative slowing in the same nerve segment was found in 18% (56/312) patients, of whom anti-GM1 antibodies were found in 27% and 57% patients respectively. Follow-up NCS showed a change in GBS classification in 11–26% of patients, mainly from demyelinating to axonal GBS.

Conclusions

The predominant subtype of GBS in Bangladesh is axonal but demyelinating GBS also occurs with classification being strongly dependent on the applied criteria.

Significance

The present study demonstrates the importance of reaching international agreement on GBS criteria that should be based on the best evidence.

Pathophysiology of the Different Clinical Phenotypes of Chronic Inflammatory Demyelinating Polyradiculoneuropathy (CIDP)

Chronic inflammatory demyelinating polyneuropathy (CIDP) is the most common form of autoimmune polyneuropathy. It is a chronic disease and may be monophasic, progressive or recurrent with exacerbations and incomplete remissions, causing accumulating disability. In recent years, there has been rapid progress in understanding the background of CIDP, which allowed us to distinguish specific phenotypes of this disease. This in turn allowed us to better understand the mechanism of response or non-response to various forms of therapy. On the basis of a review of the relevant literature, the authors present the current state of knowledge concerning the pathophysiology of the different clinical phenotypes of CIDP as well as ongoing research in this field, with reference to key points of immune-mediated processes involved in the background of CIDP.

Complement and Coagulation System Crosstalk in Synaptic and Neural Conduction in the Central and Peripheral Nervous Systems

Complement and coagulation are both key systems that defend the body from harm. They share multiple features and are similarly activated. They each play individual roles in the systemic circulation in physiology and pathophysiology, with significant crosstalk between them. Components from both systems are mapped to important structures in the central nervous system (CNS) and peripheral nervous system (PNS). Complement and coagulation participate in critical functions in neuronal development and synaptic plasticity. During pathophysiological states, complement and coagulation factors are upregulated and can modulate synaptic transmission and neuronal conduction. This review summarizes the current evidence regarding the roles of the complement system and the coagulation cascade in the CNS and PNS. Possible crosstalk between the two systems regarding neuroinflammatory-related effects on synaptic transmission and neuronal conduction is explored. Novel treatment based on the modulation of crosstalk between complement and coagulation may perhaps help to alleviate neuroinflammatory effects in diseased states of the CNS and PNS.

Novel Immunological and Therapeutic Insights in Guillain-Barré Syndrome and CIDP

Inflammatory neuropathies are a heterogeneous group of rare diseases of the peripheral nervous system that include acute and chronic diseases, such as Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). The etiology and pathophysiological mechanisms of inflammatory neuropathies are only partly known, but are considered autoimmune disorders in which an aberrant immune response, including cellular and humoral components, is directed towards components of the peripheral nerve causing demyelination and axonal damage. Therapy of these disorders includes broad-spectrum immunomodulatory and immunosuppressive treatments, such as intravenous immunoglobulin, corticosteroids, or plasma exchange. However, a significant proportion of patients do not respond to any of these therapies, and treatment selection is not optimized according to disease pathophysiology. Therefore, research on disease pathophysiology aiming to reveal clinically and functionally relevant disease mechanisms and the development of new treatment approaches are needed to optimize disease outcomes in CIDP and GBS. This topical review describes immunological progress that may help guide therapeutic strategies in the future in these two disorders.

IgG1 pan-neurofascin antibodies identify a severe yet treatable neuropathy with a high mortality

OBJECTIVES

We aimed to define the clinical and serological characteristics of pan-neurofascin antibody-positive patients.

METHODS

We tested serum from patients with suspected immune-mediated neuropathies for antibodies directed against nodal/paranodal protein antigens using a live cell-based assay and solid-phase platform. The clinical and serological characteristics of antibody-positive and seronegative patients were then compared. Sera positive for pan-neurofascin were also tested against live myelinated human stem cell-derived sensory neurons for antibody binding.

RESULTS

Eight patients with IgG₁-subclass antibodies directed against both isoforms of the nodal/paranodal cell adhesion molecule neurofascin were identified. All developed rapidly progressive tetraplegia. Cranial nerve deficits (100% vs 26%), autonomic dysfunction (75% vs 13%) and respiratory involvement (88% vs 14%) were more common than in seronegative patients. Four patients died despite treatment with one or more modalities of standard immunotherapy (intravenous immunoglobulin, steroids and/or plasmapheresis), whereas the four patients who later went on to receive the B cell-depleting therapy rituximab then began to show progressive functional improvements within weeks, became seronegative and ultimately became functionally independent.

CONCLUSIONS

IgG₁ pan-neurofascin antibodies define a very severe autoimmune neuropathy. We urgently recommend trials of targeted immunotherapy for this serologically classified patient group.

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.

Costs of Guillain-Barré Syndrome in the Brazilian Federal District: the patients' perspective

BACKGROUND

Although rare, Guillain-Barré Syndrome (GBS) has a high economic burden, with consequences for families and society. This study aimed to estimate the total cost of GBS, per individual and per variant of the disease, as well as its effect on household income, from the perspective of patients.

METHODS

This was a cost-of-illness study from the perspective of patients and their families, with a time horizon from disease onset to 6 mo after discharge. The total cost of GBS was estimated by bottom-up microcosting, considering direct and indirect costs.

RESULTS

The median cost of GBS per individual was US$1635.5, with direct costs accounting for 64.3% of this amount. Among the variants analyzed, acute motor sensory axonal neuropathy (US$4660.1) and acute inflammatory demyelinating polyneuropathy (US$2017.0) exhibited the highest costs compared with acute motor axonal neuropathy (US$1635.5) and Miller Fisher Syndrome (US$1464.8). The costs involved compromise more than 20% of the household income of 22 (47.8%) patients.

CONCLUSIONS

This study demonstrated how costly GBS can be. It is hoped that decision-makers will analyze these results with a view to improving the structure of healthcare services.

Neuronally expressed a-series gangliosides are sufficient to prevent the lethal age-dependent phenotype in GM3-only expressing mice

Gangliosides are expressed on plasma membranes throughout the body and enriched in the nervous system. A critical role for complex a- and b-series gangliosides in central and peripheral nervous system ageing has been established through transgenic manipulation of enzymes in ganglioside biosynthesis. Disrupting GalNAc-transferase (GalNAc-T), thus eliminating all a- and b-series complex gangliosides (with consequent over-expression of GM3 and GD3) leads to an age-dependent neurodegeneration. Mice that express only GM3 ganglioside (double knockout produced by crossing GalNAc-T-/- and GD3 synthase-/- mice, Dbl KO) display markedly accelerated neurodegeneration with reduced survival. Degenerating axons and disrupted node of Ranvier architecture are key features of complex ganglioside-deficient mice. Previously, we have shown that reintroduction of both a- and b-series gangliosides into neurons on a global GalNAcT-/- background is sufficient to rescue this age-dependent neurodegenerative phenotype. To determine the relative roles of a- and b-series gangliosides in this rescue paradigm, we herein reintroduced GalNAc-T into neurons of Dbl KO mice, thereby reconstituting a-series but not b-series complex gangliosides. We assessed survival, axon degeneration, axo-glial integrity, inflammatory markers and lipid-raft formation in these Rescue mice compared to wild-type and Dbl KO mice. We found that this neuronal reconstitution of a-series complex gangliosides abrogated the adult lethal phenotype in Dbl KO mice, and partially attenuated the neurodegenerative features. This suggests that whilst neuronal expression of a-series gangliosides is critical for survival during ageing, it is not entirely sufficient to restore complete nervous system integrity in the absence of either b-series or glial a-series gangliosides.

SARS-CoV-2 Infection and Guillain-Barré Syndrome: A Review on Potential Pathogenic Mechanisms

Since December 2019, the world has been facing an outbreak of a new disease called coronavirus disease 2019 (COVID-19). The COVID-19 pandemic is caused by a novel beta-coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The SARS-CoV-2 infection mainly affects the respiratory system. Recently, there have been some reports of extra-respiratory symptoms such as neurological manifestations in COVID-19. According to the increasing reports of Guillain-Barré syndrome following COVID-19, we mainly focused on SARS-CoV-2 infection and Guillain-Barré syndrome in this review. We tried to explain the possibility of a relationship between SARS-CoV-2 infection and Guillain-Barré syndrome and potential pathogenic mechanisms based on current and past knowledge.

Determining the Utility of the Guillain-Barré Syndrome Classification Criteria

Background and Purpose

Several variants of Guillain-Barré syndrome (GBS) and Miller Fisher syndrome (MFS) exist, but their frequencies vary in different populations and do not always meet the inclusion criteria of the existing diagnostic criteria. However, the GBS classification criteria by Wakerley and colleagues recognize and define the clinical characteristics of each variant. We applied these criteria to a GBS and MFS cohort with the aim of determining their utility.

Methods

Consecutive GBS and MFS patients presenting to our center between 2010 and 2020 were analyzed. The clinical characteristics, electrophysiological data, and antiganglioside antibody profiles of the patients were utilized in determining the clinical classification.

Results

This study classified 132 patients with GBS and its related disorders according to the new classification criteria as follows: 64 (48.5%) as classic GBS, 2 (1.5%) as pharyngeal-cervical-brachial (PCB) variant, 7 (5.3%) as paraparetic GBS, 29 (22%) as classic MFS, 3 (2.3%) as acute ophthalmoparesis, 2 (1.5%) as acute ataxic neuropathy, 2 (1.5%) as Bickerstaff brainstem encephalitis (BBE), 17 (12.9%) as GBS/MFS overlap, 4 (3%) as GBS/BBE overlap, 1 (0.8%) as MFS/PCB overlap, and 1 (0.8%) as polyneuritis cranialis. The electrodiagnosis was demyelinating in 55% of classic GBS patients but unclassified in 79% of classic MFS patients. Anti-GM1, anti-GD1a, anti-GalNAc-GD1a, and anti-GD1b IgG ganglioside antibodies were more commonly detected in the axonal GBS subtype, whereas the anti-GQ1b and anti-GT1a IgG ganglioside antibodies were more common in classic MFS and its subtypes.

Conclusions

Most of the patients in the present cohort met the criteria of either classic GBS or MFS, but variants were seen in one-third of patients. These findings support the need to recognize variants of both syndromes in order to achieve a more-complete case ascertainment in GBS.

Macrophages and Autoantibodies in Demyelinating Diseases

Myelin phagocytosis by macrophages has been an essential feature of demyelinating diseases in the central and peripheral nervous systems, including Guillain–Barré syndrome (GBS), chronic inflammatory demyelinating polyneuropathy (CIDP), and multiple sclerosis (MS). The discovery of autoantibodies, including anti-ganglioside GM1 antibodies in the axonal form of GBS, anti-neurofascin 155 and anti-contactin 1 antibodies in typical and distal forms of CIDP, and anti-aquaporin 4 antibodies in neuromyelitis optica, contributed to the understanding of the disease process in a subpopulation of patients conventionally diagnosed with demyelinating diseases. However, patients with these antibodies are now considered to have independent disease entities, including acute motor axonal neuropathy, nodopathy or paranodopathy, and neuromyelitis optica spectrum disorder, because primary lesions in these diseases are distinct from those in conventional demyelinating diseases. Therefore, the mechanisms underlying demyelination caused by macrophages remain unclear. Electron microscopy studies revealed that macrophages destroy myelin as if they are the principal players in the demyelination process. Recent studies suggest that macrophages seem to select specific sites of myelinated fibers, including the nodes of Ranvier, paranodes, and internodes, for the initiation of demyelination in individual cases, indicating that specific components localized to these sites play an important role in the behavior of macrophages that initiate myelin phagocytosis. Along with the search for autoantibodies, the ultrastructural characterization of myelin phagocytosis by macrophages is a crucial step in understanding the pathophysiology of demyelinating diseases and for the future development of targeted therapies.

Changes in motor nerve excitability in acute phase Guillain-Barré syndrome

BACKGROUND

The most common subtypes of Guillain-Barré syndrome (GBS) are acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN). In the first days after the onset of weakness, standard nerve conduction studies (NCS) may not distinguish GBS subtypes. Reduced nerve excitability may be an early symptom of nerve dysfunction, which can be determined with the compound muscle action potential (CMAP) scan. The aim of this study was to explore whether early changes in motor nerve excitability in GBS patients are related to various subtypes.

METHODS

Prospective case-control study in 19 GBS patients from The Netherlands and 22 from Bangladesh. CMAP scans were performed within 2 days of hospital admission and NCS 7-14 days after onset of weakness. CMAP scans were also performed in age- and country-matched controls.

RESULTS

CMAP scan patterns of patients who were classified as AMAN were distinctly different compared to the CMAP scan patterns of the patients who were classified as AIDP. The most pronounced differences were found in the stimulus intensity parameters.

CONCLUSIONS

CMAP scans made at hospital admission demonstrate several characteristics that can be used as an early indicator of GBS subtype.

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.

Antiglycolipid antibodies in Guillain-Barré and Fisher syndromes: discovery, current status and future perspective

Guillain-Barré syndrome (GBS) and Fisher syndrome (FS) are acute autoimmune neuropathies, often preceded by an infection. Antiglycolipid antibody titres are frequently elevated in sera from the acute-phase patients. Particularly, IgG anti-GQ1b antibodies are positive in as high as 90% of FS cases and thus useful for diagnosis. The development of animal models of antiglycolipid antibody-mediated neuropathies proved that some of these antibodies are directly involved in the pathogenetic mechanisms by binding to the regions where the respective target glycolipid is specifically localised. Discovery of the presence of the antibodies that specifically recognise a new conformational epitope formed by two different gangliosides (ganglioside complex) in the acute-phase sera of some patients with GBS suggested the carbohydrate-carbohydrate interaction between glycolipids. This finding indicated the need for further research in basic glycobiological science. Antiglycolipid antibodies, in particular antigangliosides antibodies, are mostly detected in acute motor axonal neuropathy type of GBS and in FS, and less frequently in the acute inflammatory demyelinating polyneuropathy (AIDP) type of GBS or in central nervous system (CNS) diseases. In the future, the search for the putative antibodies in AIDP and those that might be present in CNS diseases should continue. In addition, more efficient standardisation of antiglycolipid antibody detection methods and use as biomarkers in daily clinical practice in neurology is needed.

Acute Axonal Motor Neuropathy With Completely Reversible Conduction Failure-Is It Really Axonal?

ABSTRACT

We present the case of a 24-year-old man with a 3-day history of limb weakness and flaccid tetraparesis, hyporreflexia, and gait difficulties (Hughes grade 3) in the examination. Electromyography at presentation revealed severe amplitude reduction in distal compound muscle action potentials of several nerves without features of demyelination, fulfilling electrodiagnostic criteria for acute axonal motor neuropathy. The patient was treated with immunoglobulin and recovered completely 21 days after symptom onset. Electromyography at this timepoint showed normalization of compound muscle action potentials without increased temporal dispersion. The electroclinical recovery profile in this patient is consistent with reversible conduction failure in distal nerve segments in detriment of axonal degeneration. Thus, it is an "axonal motor neuropathy" where axonopathy is unlikely, giving strength to the concept of "nodopathies/paranodopathies."

The Neuroimmunology of Guillain-Barré Syndrome and the Potential Role of an Aging Immune System

Guillain-Barré syndrome (GBS) is a paralyzing autoimmune condition affecting the peripheral nervous system (PNS). Within GBS there are several variants affecting different aspects of the peripheral nerve. In general, there appears to be a role for T cells, macrophages, B cells, and complement in initiating and perpetuating attacks on gangliosides of Schwann cells and axons. Of note, GBS has an increased prevalence and severity with increasing age. In addition, there are alterations in immune cell functioning that may play a role in differences in GBS with age alongside general age-related declines in reparative processes (e.g., delayed de-differentiation of Schwann cells and decline in phagocytic ability of macrophages). The present review will explore the immune response in GBS as well as in animal models of several variants of the disorder. In addition, the potential involvement of an aging immune system in contributing to the increased prevalence and severity of GBS with age will be theorized.

Macrophage roles in peripheral nervous system injury and pathology: Allies in neuromuscular junction recovery

Peripheral nerve injuries remain challenging to treat despite extensive research on reparative processes at the injury site. Recent studies have emphasized the importance of immune cells, particularly macrophages, in recovery from nerve injury. Macrophage plasticity enables numerous functions at the injury site. At early time points, macrophages perform inflammatory functions, but at later time points, they adopt pro-regenerative phenotypes to support nerve regeneration. Research has largely been limited, however, to the injury site. The neuromuscular junction (NMJ), the synapse between the nerve terminal and end target muscle, has received comparatively less attention, despite the importance of NMJ reinnervation for motor recovery. Macrophages are present at the NMJ following nerve injury. Moreover, in denervating diseases, such as amyotrophic lateral sclerosis (ALS), macrophages may also play beneficial roles at the NMJ. Evidence of positive macrophages roles at the injury site after peripheral nerve injury and at the NMJ in denervating pathologies suggest that macrophages may promote NMJ reinnervation. In this review, we discuss the intersection of nerve injury and immunity, with a focus on macrophages.

[Successful treatment of Guillain-Barré syndrome-like acute inflammatory demyelinating polyneuropathy caused by pembrolizumab with a combination of corticosteroid and immunoglobulins: a case report]

A 74-year-old man, who received pembrolizumab for the treatment for non-small cell lung cancer, developed quadriparesis 10 days after the first course of treatment accompanied by gait disturbance. Dysesthesia was observed in the distal extremities, and tendon reflexes were absent. Neurological examination and peripheral nerve conduction study supported the diagnosis of Guillain-Barré syndrome-like acute inflammatory demyelinating polyneuropathy caused by pembrolizumab. The administration of pembrolizumab was discontinued. Moreover, he was initially treated with intravenous immunoglobulin therapy, followed by intravenous methylprednisolone therapy and oral prednisolone. The limb weakness improved to a degree that he could walk alone on discharge. Pembrolizumab, which is an immune checkpoint inhibitor with a high anti-tumor effect, is reported to cause various adverse events. However, neuromuscular complications following cancer treatment with immune checkpoint inhibitors are relatively rare. Treatment with corticosteroids is considered to be effective for treating immune-related adverse events. Corticosteroids were effective in treating peripheral neuropathy caused by immune checkpoint inhibitors in this patient. Thorough treatment should be considered with a combination of corticosteroids and immunoglobulin therapy, in addition to discontinuation of immune checkpoint inhibitors, for this rare entity, which differs from that for idiopathic Guillain-Barré syndrome.

Mechanisms of node of Ranvier assembly

The nodes of Ranvier have clustered Na⁺ and K⁺ channels necessary for rapid and efficient axonal action potential conduction. However, detailed mechanisms of channel clustering have only recently been identified: they include two independent axon-glia interactions that converge on distinct axonal cytoskeletons. Here, we discuss how glial cell adhesion molecules and the extracellular matrix molecules that bind them assemble combinations of ankyrins, spectrins and other cytoskeletal scaffolding proteins, which cluster ion channels. We present a detailed molecular model, incorporating these overlapping mechanisms, to explain how the nodes of Ranvier are assembled in both the peripheral and central nervous systems.