Early nodal changes in the acute motor axonal neuropathy pattern of the Guillain-Barré syndrome

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.

Pathology explains various mechanisms of auto-immune inflammatory peripheral neuropathies

Autoimmune neuropathies are a heterogeneous group of rare and disabling diseases in which the immune system is thought to target antigens in the peripheral nervous system: they usually respond to immune therapies. Guillain-Barré syndrome is divided into several subtypes including "acute inflammatory demyelinating polyradiculoneuropathy," "acute motor axonal neuropathy," "acute motor sensory neuropathy," and other variants. Chronic forms such as chronic inflammatory demyelinating polyneuropathy (CIDP) and other subtypes and polyneuropathy associated with IgM monoclonal gammopathy; autoimmune nodopathies also belong to this group of auto-immune neuropathies. It has been shown that immunoglobulin G from the serum of about 30% of CIDP patients immunolabels nodes of Ranvier or paranodes of myelinated axons. Whatever the cause of myelin damage of the peripheral nervous system, the initial attack on myelin by a dysimmune process may begin either at the internodal area or in the paranodal and nodal regions. The term "nodoparanodopathy" was first applied to some "axonal Guillain-Barré syndrome" subtypes, then extended to cases classified as CIDP bearing IgG4 antibodies against paranodal axoglial proteins. In these cases, paranodal dissection develops in the absence of macrophage-induced demyelination. In contrast, the mechanisms of demyelination of other dysimmune neuropathies induced by macrophages are unexplained, as no antibodies have been identified in such cases. The main objective of this presentation is to show that the pathology illustrates, confirms, and may explain such mechanisms.

Clinical and pathophysiological implications of autoantibodies in autoimmune neuropathies

Autoimmune neuropathies are a heterogeneous group of rare and disabling diseases in which the immune system targets peripheral nervous system antigens and that respond to immune therapies. This review focuses on Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, multifocal motor neuropathy, polyneuropathy associated with IgM monoclonal gammopathy, and autoimmune nodopathies. Autoantibodies targeting gangliosides, proteins in the node of Ranvier, and myelin-associated glycoprotein have been described in these disorders, defining subgroups of patients with similar clinical features and response to therapy. This topical review describes the role of these autoantibodies in the pathogenesis of autoimmune neuropathies and their clinical and therapeutic importance.

Early electrophysiological study variants and their relationship with clinical presentation and outcomes of patients with Guillain-Barré syndrome

This study compared the clinical outcomes of the two main neurophysiological types of Guillain-Barré Syndrome (GBS). Sixty-two GBS patients were examined clinically at onset using Medical Research Council (MRC), Hughes disability scales (HDS), and nerve conduction studies were evaluated in four limbs. The Modified Erasmus GBS outcome score (MEGOS) was assessed 2 weeks after onset. Outcomes were measured after 3 months using MRC and HDS scores. According to electrophysiological data two main groups identified acute inflammatory demyelinating polyneuropathy (AIDP = 31 cases) or acute axonal GBS including inexcitable forms (26 cases). The number of days between onset of weakness and admission was significantly shorter, and gastrointestinal symptoms were significantly higher among the axonal type than AIDP. MRC sum scores at onset and at nadir were significantly worse in the axonal type than in AIDP. Neck muscle weakness, impaired cough reflex, the need for mechanical ventilation, hypoalbuminemia, and hypernatremia were more common in the axonal type. At outcome, 74% of the AIDP were healthy/minor symptoms versus 38.46% of the axonal type. There was a high prevalence of the axonal variant (41.9%) compared with European and North American populations. The axonal type had a significantly worse outcome than AIDP type.

Lyme radiculopathy in a septuagenarian

A man in his 70s presented to hospital in early summer with a 5-week history of progressive lower back and right thigh pain, sensory deficit and right leg weakness. There had been limited response to analgesics in the community. Primary investigations on admission revealed no cause for his symptoms. Five days into admission, history emerged of a possible tick bite with subsequent rash sustained 3 months earlier, raising the possibility of neuroborreliosis leading to radiculopathy. Cerebrospinal fluid demonstrated a lymphocytic pleocytosis. An elevated Borrelia burgdorferi antibody index confirmed a diagnosis of Lyme neuroborreliosis. The patient was treated successfully with 28 days of intravenous ceftriaxone, analgesia and physiotherapy. Within the literature, Lyme radiculopathy is a common presentation of neuroborreliosis and should be considered and investigated in patients without radiological evidence of a mechanical cause of worsening lower back pain in settings with endemic Lyme disease.

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.

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.

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.

[Guillain-Barre syndrome in children]

Guillain-Barré syndrome (GBS) is an immune-mediated disease of the peripheral nervous system that can occur in both children and adults. The classic presentation of GBS is characterized by progressive symmetrical, ascending muscle weakness. Patients with GBS require meticulous monitoring due to the risk of bulbar syndrome, respiratory failure and autonomic dysfunction, which can be life-threatening. Early diagnosis and timely prescription of pathogenetic therapy for GBS are particularly important, especially in young children. Meanwhile, the spectrum of disorders covered by GBS has expanded significantly; its eponym is now designate any variant of acute dysimmune polyneuropathy, and its atypical forms pose a serious diagnostic problem for clinicians. This review article provides an analysis of the data available in the medical literature on GBS in children and discusses the tactics for diagnosing and managing patients with GBS, taking into account the Russian and European clinical recommendations.

Critical illness-associated weakness and related motor disorders

Weakness of limb and respiratory muscles that occurs in the course of critical illness has become an increasingly common and serious complication of adult and pediatric intensive care unit patients and a cause of prolonged ventilatory support, morbidity, and prolonged hospitalization. Two motor disorders that occur singly or together, namely critical illness polyneuropathy and critical illness myopathy, cause weakness of limb and of breathing muscles, making it difficult to be weaned from ventilatory support, commencing rehabilitation, and extending the length of stay in the intensive care unit, with higher rates of morbidity and mortality. Recovery can take weeks or months and in severe cases, and may be incomplete or absent. Recent findings suggest an improved prognosis of critical illness myopathy compared to polyneuropathy. Prevention and treatment are therefore very important. Its management requires an integrated team approach commencing with neurologic consultation, creatine kinase (CK) measurement, detailed electrodiagnostic, respiratory and neuroimaging studies, and potentially muscle biopsy to elucidate the etiopathogenesis of the weakness in the peripheral and/or central nervous system, for which there may be a variety of causes. These tenets of care are being applied to new cases and survivors of the coronavirus-2 disease pandemic of 2019. This chapter provides an update to the understanding and approach to critical illness motor disorders.

Acute/chronic inflammatory polyradiculoneuropathy

Autoimmune neuropathy may present acutely or with a more progressive and/or relapsing and remitting course. Acute inflammatory neuropathy or Guillain-Barré syndrome (GBS) has variable presentations but by far the most common is acute inflammatory demyelinating polyradiculoneuropathy which is characterized by rapidly progressive proximal and distal symmetric weakness, sensory loss, and depressed reflexes. The most common chronic autoimmune neuropathy is chronic inflammatory demyelinating polyradiculoneuropathy, which in its most typical form is clinically similar to acute inflammatory demyelinating polyradiculoneuropathy (proximal and distal symmetric weakness, sensory loss, and depressed reflexes) but differs in that onset is much more gradual, i.e., over at least 8 weeks. While the majority of GBS cases result from a postinfectious activation of the immune system, presumably in a genetically susceptible host, less is understood regarding the etiopathogenesis of chronic inflammatory demyelinating polyradiculoneuropathy. Both acute and chronic forms of these inflammatory neuropathies are driven by some combination of innate and adaptive immune pathways, with differing contributions depending on the neuropathy subtype. Both disorders are largely clinical diagnoses, but diagnostic tools are available to confirm the diagnosis, prognosticate, detect variant forms, and rule out mimics. Given the autoimmune underpinnings of both disorders, immunosuppressive and immunomodulating treatments are typically given in both diseases; however, they differ in their response to treatment.

Sex differences in Guillain Barré syndrome, chronic inflammatory demyelinating polyradiculoneuropathy and experimental autoimmune neuritis

Guillain Barré syndrome (GBS) and its variants, and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP and its variants, are regarded as immune mediated neuropathies. Unlike in many autoimmune disorders, GBS and CIDP are more common in males than females. Sex is not a clear predictor of outcome. Experimental autoimmune neuritis (EAN) is an animal model of these diseases, but there are no studies of the effects of sex in EAN. The pathogenesis of GBS and CIDP involves immune response to non-protein antigens, antigen presentation through non-conventional T cells and, in CIDP with nodopathy, IgG4 antibody responses to antigens. There are some reported sex differences in some of these elements of the immune system and we speculate that these sex differences could contribute to the male predominance of these diseases, and suggest that sex differences in peripheral nerves is a topic worthy of further study.

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.

Elevated monocyte to high-density lipoprotein cholesterol ratio correlates with clinical severity in acute inflammatory demyelinating polyradiculoneuropathy patients

While monocyte to high-density lipoprotein cholesterol ratio (MHR) has been reported to be associated with nervous system lesions, the role of MHR has not been determined in patients with Guillain-Barré Syndrome (GBS). The purpose of our study was to explore the role of MHR in patients with GBS. A total of 52 GBS patients were involved in the study retrospectively, including patients with acute inflammatory demyelinating polyradiculoneuropathy (AIDP), acute motor axonal neuropathy (AMAN), and acute motor sensory axonal neuropathy (AMSAN). We used Hughes Functional Grading Scale (HFGS) score to evaluate functional status in GBS patients. Among patients with different subtypes of GBS, MHR was significantly elevated in those with demyelination compared to patients without demyelination (p < 0.001); AIDP patients had an increased MHR compared with AMAN or AMSAN patients (p = 0.001; p = 0.013). There was a positive correlation between MHR and HFGS score (r = 0.463, p = 0.006) in AIDP patients, but not in AMAN or AMSAN. Multiple linear regression analysis revealed that MHR was independently associated with HFGS score (beta = 0.405, p = 0.013) in AIDP patients. Our study suggests that MHR as an inflammatory marker is elevated in patients with AIDP compared to AMAN or AMSAN patients, while MHR has a positive correlation with clinical severity in AIDP patients, suggesting that MHR may provide an additional information to reflect the pathophysiology of AIDP.

Role of lymphocyte-related immune-inflammatory biomarkers in detecting early progression of Guillain-Barré syndrome

OBJECTIVES

This study aimed to investigate the role of peripheral neutrophil to lymphocyte ratio (NLR), monocyte to lymphocyte ratio (MLR), and platelet to lymphocyte ratio (PLR) in the progression and severity of the Guillain-Barré syndrome (GBS).

METHODS

47 GBS patients and 50 age and sex-matched healthy controls (HC) were retrospectively included. Demographic and clinical assessment data were reviewed and abstracted. NLR, MLR, and PLR were calculated based on the peripheral blood tests by reviewing clinical data. The relationship between the Hughes' score and NLR, MLR, PLR levels was investigated.

RESULTS

The GBS patients had higher NLR levels (P < 0.001), MLR levels (P = 0.001) and PLR levels (P < 0.001) than those in HC. And patients with severe disability score (Hughes' score ≥ 3) had significantly higher NLR (P = 0.007), MLR (P = 0.04), PLR (P = 0.013). Spearman correlation analysis indicated that NLR was positively associated with the Hughes' score (r = 0.331, P = 0.023). In the patients with acute inflammatory demyelinating polyneuropathy (AIDP), Spearman correlation analysis indicated that NLR, MLR and PLR were positively associated to the Hughes' score (r = 0.825, P = 0.001 for NLR, r = 0.727, P = 0.005 for MLR, and r = 0.723, P = 0.005 for PLR).

CONCLUSIONS

NLR, MLR, and PLR may be indicators of disease activity in patients with GBS or AIDP. These parameters may benefit the active treatment of GBS patients with a high degree of disability.

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.

Axonal pathology in early stages of Guillain-Barré syndrome

INTRODUCTION

Guillain-Barré syndrome (GBS) is an acute-onset, immune-mediated disease of the peripheral nervous system. It may be classified into 2 main subtypes: demyelinating (AIDP) and axonal (AMAN). This study aims to analyse the mechanisms of axonal damage in the early stages of GBS (within 10 days of onset).

DEVELOPMENT

We analysed histological, electrophysiological, and imaging findings from patients with AIDP and AMAN, and compared them to those of an animal model of myelin P2 protein-induced experimental allergic neuritis. Inflammatory oedema of the spinal nerve roots and spinal nerves is the initial lesion in GBS. The spinal nerves of patients with fatal AIDP may show ischaemic lesions in the endoneurium, which suggests that endoneurial inflammation may increase endoneurial fluid pressure, reducing transperineurial blood flow, potentially leading to conduction failure and eventually to axonal degeneration. In patients with AMAN associated with anti-ganglioside antibodies, nerve conduction block secondary to nodal sodium channel dysfunction may affect the proximal, intermediate, and distal nerve trunks. In addition to the mechanisms involved in AIDP, active axonal degeneration in AMAN may be associated with nodal axolemma disruption caused by anti-ganglioside antibodies.

CONCLUSION

Inflammatory oedema of the proximal nerve trunks can be observed in early stages of GBS, and it may cause nerve conduction failure and active axonal degeneration.

Axonal pathology in early stages of Guillain-Barré syndrome

INTRODUCTION

Guillain-Barré syndrome (GBS) is an acute-onset, immune-mediated disease of the peripheral nervous system. It may be classified into 2 main subtypes: demyelinating (AIDP) and axonal (AMAN). This study aims to analyse the mechanisms of axonal damage in the early stages of GBS (within 10days of onset).

DEVELOPMENT

We analysed histological, electrophysiological, and imaging findings from patients with AIDP and AMAN, and compared them to those of an animal model of myelin P2 protein-induced experimental allergic neuritis. Inflammatory oedema of the spinal nerve roots and spinal nerves is the initial lesion in GBS. The spinal nerves of patients with fatal AIDP may show ischaemic lesions in the endoneurium, which suggests that endoneurial inflammation may increase endoneurial fluid pressure, reducing transperineurial blood flow, potentially leading to conduction failure and eventually to axonal degeneration. In patients with AMAN associated with anti-ganglioside antibodies, nerve conduction block secondary to nodal sodium channel dysfunction may affect the proximal, intermediate, and distal nerve trunks. In addition to the mechanisms involved in AIDP, active axonal degeneration in AMAN may be associated with nodal axolemma disruption caused by anti-ganglioside antibodies.

CONCLUSION

Inflammatory oedema of the proximal nerve trunks can be observed in early stages of GBS, and it may cause nerve conduction failure and active axonal degeneration.

Guillain-Barré syndrome: expanding the concept of molecular mimicry

Guillain-Barré syndrome (GBS) is a rapidly progressive, monophasic, and potentially devastating immune-mediated neuropathy in humans. Preceding infections trigger the production of cross-reactive antibodies against gangliosides concentrated in human peripheral nerves. GBS is elicited by at least five distinct common bacterial and viral pathogens, speaking to the notion of polymicrobial disease causation. This opinion emphasizes that GBS is the best-supported example of true molecular mimicry at the B cell level. Moreover, we argue that mechanistically, single and multiplexed microbial carbohydrate epitopes induce IgM, IgA, and IgG subclasses in ways that challenge the classic concept of thymus-dependent (TD) versus thymus-independent (TI) antibody responses in GBS. Finally, we discuss how GBS can be exemplary for driving innovation in diagnostics and immunotherapy for other antibody-driven neurological diseases.

Campylobacter jejuni induces autoimmune peripheral neuropathy via Sialoadhesin and Interleukin-4 axes

Campylobacter jejuni is a leading cause of gastroenteritis that has been causally linked with development of the autoimmune peripheral neuropathy Guillain Barré Syndrome (GBS). Previously, we showed that C. jejuni isolates from human enteritis patients induced Type1/17-cytokine dependent colitis in interleukin-10 (IL-10)-/- mice, while isolates from GBS patients colonized these mice without colitis but instead induced autoantibodies that cross-reacted with the sialylated oligosaccharide motifs on the LOS of GBS-associated C. jejuni and the peripheral nerve gangliosides. We show here that infection of IL-10-/- mice with the GBS but not the colitis isolate led to sciatic nerve inflammation and abnormal gait and hind limb movements, with character and timing consistent with this syndrome in humans. Autoantibody responses and associated nerve histologic changes were dependent on IL-4 production by CD4 T cells. We further show that Siglec-1 served as a central antigen presenting cell receptor mediating the uptake of the GBS isolates via interaction with the sialylated oligosaccharide motifs found specifically on the LOS of GBS-associated C. jejuni, and the ensuing T cell differentiation and autoantibody elicitation. Sialylated oligosaccharide motifs on the LOS of GBS-associated C. jejuni therefore acted as both the Siglec-1-ligand for phagocytosis, as well as the epitope for autoimmunity. Overall, we present a mouse model of an autoimmune disease induced directly by a bacterium that is dependent upon Siglec-1 and IL-4. We also demonstrate the negative regulatory role of IL-10 in C. jejuni induced autoimmunity and provide IL-4 and Siglec-1 blockade as potential therapeutic interventions against GBS.

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.

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.

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.

The electrophysiology of axonal neuropathies: More than just evidence of axonal loss

It is common belief that axonal neuropathies are characterized by simple axonal degeneration and loss and that the electrophysiological correlates are just reduced compound muscle action potential and sensory nerve action potential amplitudes with normal or slightly slow conduction velocity. However, axonal autoimmune neuropathies with involvement of the nodal region and axonal neuropathies due to energy restriction such as occurring in nerve ischemia, thiamine deficiency, critical illness, and mitochondrial disorders present conduction failure that can be either reversible with prompt recovery or progress to axonal degeneration with poor outcome. Moreover autoimmune axonal neuropathies due to nodal voltage gated sodium channels dysfunction/disruption may show slowing of conduction velocity, even in the demyelinating range, possibly due to prolongation of the depolarization time required to reach the threshold for action potential regeneration at subsequent nodes. These observations widen the spectrum of the electrophysiological features in some axonal neuropathies, should be taken into account to avoid misdiagnoses and for correct prognostication, and should stimulate the quest of timely targeted treatments that can eventually halt the progression from conduction failure to axonal degeneration.

Ultrastructural Lesions of Nodo-Paranodopathies in Peripheral Neuropathies

Whatever the cause of myelin damage of the peripheral nervous system, the initial attack on myelin by a dysimmune process may begin either at the internodal area or in the paranodal and nodal regions. The term "nodo-paranodopathy" was first applied to some "axonal Guillain-Barré syndrome" subtypes, then extended to cases classified as chronic inflammatory demyelinating polyradiculoneuropathy bearing IgG4 antibodies against paranodal axoglial proteins. In these cases, paranodal dissection develops in the absence of macrophage-induced demyelination. In contrast, the mechanisms of demyelination of other dysimmune neuropathies induced by macrophages are unexplained, as no antibodies have been identified in such cases. Electron microscopy of longitudinal sections of nerve biopsies is useful to visualize and authenticate the characteristic lesions of paranodes/nodes. However, it should be borne in mind that identical ultrastructural aspects are seen in other types of polyneuropathies: Genetic, experimental, and in a few polyneuropathies for which there is no obvious etiology. Ultrastructural nerve studies confirm the initial involvement of nodes/paranodes in various types of acquired and genetic neuropathies. For some of them, the antibodies or the proteins involved by mutations are clearly identified such as Caspr-1, Contactin-1, NFasc155, and NFasc186; other unidentified proteins are likely to be involved as well.

Axonal degeneration in Guillain-Barré syndrome: a reappraisal

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

Perisynaptic Schwann cells phagocytose nerve terminal debris in a mouse model of Guillain-Barré syndrome

In mouse models of acute motor axonal neuropathy, anti-ganglioside antibodies (AGAbs) bind to motor axons, notably the distal nerve, and activate the complement cascade. While complement activation is well studied in this model, the role of inflammatory cells is unknown. Herein we aimed to investigate the contribution of phagocytic cells including macrophages, neutrophils and perisynaptic Schwann cells (pSCs) to distal nerve pathology. To observe this, we first created a subacute injury model of sufficient duration to allow inflammatory cell recruitment. Mice were injected intraperitoneally with an anti-GD1b monoclonal antibody that binds strongly to mouse motor nerve axons. Subsequently, mice received normal human serum as a source of complement. Dosing was titrated to allow humane survival of mice over a period of 3 days, yet still induce the characteristic neurological impairment. Behaviour and pathology were assessed in vivo using whole-body plethysmography and post-sacrifice by immunofluorescence and flow cytometry. ex vivo nerve-muscle preparations were used to investigate the acute phagocytic role of pSCs following distal nerve injury. Following complement activation at distal intramuscular nerve sites in the diaphragm macrophage localisation or numbers are not altered, nor do they shift to a pro- or anti-inflammatory phenotype. Similarly, neutrophils are not significantly recruited. Instead, ex vivo nerve-muscle preparations exposed to AGAb plus complement reveal that pSCs rapidly become phagocytic and engulf axonal debris. These data suggest that pSCs, rather than inflammatory cells, are the major cellular vehicle for axonal debris clearance following distal nerve injury, in contrast to larger nerve bundles where macrophage-mediated clearance predominates.

History of acute polyradiculoneuropathy (part 2): From 1916 to 2019

First reported by Guillain, Barré, and Strohl during the Great War, the concept of "Guillain-Barré syndrome" (GBS) progressively emerged as a clinical entity in its own right. Despite many debates about its clinical and pathophysiologic characteristics, GBS is now recognized as a disease throughout the world. We describe here the main steps of the rich history of GBS, from 1916 to the present.

Early clinicopathologic description of nodoparanodopathy in the 19th century

Nodoparanodopathy is a recent concept in the field of peripheral neuropathy, corresponding to peripheral nerve disorders stemming from an autoimmune attack directed and limited to the nodal region. This concept was identified using modern techniques of electrophysiology, immunology, and pathology (including electron microscopy). We present here what we believe to be the earlier well-documented case of nodoparanodopathy in the medical literature, based on an article written by Samuel Gilbert Webber (1838–1926) in 1884.

Elimination of activating Fcγ receptors in spontaneous autoimmune peripheral polyneuropathy model protects from neuropathic disease

Spontaneous autoimmune peripheral polyneuropathy (SAPP) is a reproducible mouse model of chronic inflammatory peripheral neuropathy in female non-obese diabetic mice deficient in co-stimulatory molecule, B7-2 (also known as CD86). There is evidence that SAPP is an interferon-γ, CD4+ T-cell-mediated disorder, with autoreactive T-cells and autoantibodies directed against myelin protein zero involved in its immunopathogenesis. Precise mechanisms leading to peripheral nerve system inflammation and nerve injury including demyelination in this model are not well defined. We examined the role of activating Fc-gamma receptors (FcγRs) by genetically ablating Fcγ-common chain (Fcer1g) shared by all activating FcγRs in the pathogenesis of this model. We have generated B7-2/ Fcer1g-double null animals for these studies and found that the neuropathic disease is substantially ameliorated in these animals as assessed by behavior, electrophysiology, immunocytochemistry, and morphometry. Our current studies focused on characterizing systemic and endoneurial inflammation in B7-2-null and B7-2/ Fcer1g-double nulls. We found that accumulation of endoneurial inflammatory cells was significantly attenuated in B7-2/ Fcer1g-double nulls compared to B7-2-single nulls. Whereas, systemically the frequency of CD4+ regulatory T cells and expression of immunosuppressive cytokine, IL-10, were significantly enhanced in B7-2/ Fcer1g-double nulls. Overall, these findings suggest that elimination of activating FcγRs modulate nerve injury by altering endoneurial and systemic inflammation. These observations raise the possibility of targeting activating FcγRs as a treatment strategy in acquired inflammatory demyelinating neuropathies.

Reversible Conduction Failure in Chronic Immune-Mediated Sensorimotor and Autonomic Polyneuropathy

Reversible conduction failure (RCF) has been described in several subtypes of Guillain-Barre syndrome and is typically observed within the first 10 weeks. We describe the presence of RCF lasting for at least 9 months or longer without secondary axonal degeneration in a case of chronic sensorimotor and autonomic polyneuropathy. A 63-year-old woman presented with lower back pain, limb pain, paresthesia, and weakness after a sinus infection. She was diagnosed with mild Guillain-Barre syndrome and treated symptomatically. Four months later, she developed symptoms of dysautonomia and worsening neuropathic pain, and treatment with intravenous immunoglobulin led to significant clinical improvement. Electrodiagnostic study revealed significant improvement, manifesting as increased response amplitudes, improved conduction velocities, shortening of distal latencies, and reduction of sensory and motor response durations without temporal dispersion, thus fitting to the RCF definition. Detection of RCF may have further important implications in the evaluation and management of chronic immune-mediated polyneuropathy.

Functional Domains in Myelinated Axons

Propagation of action potentials along axons is optimized through interactions between neurons and myelinating glial cells. Myelination drives division of the axons into distinct molecular domains including nodes of Ranvier. The high density of voltage-gated sodium channels at nodes generates action potentials allowing for rapid and efficient saltatory nerve conduction. At paranodes flanking both sides of the nodes, myelinating glial cells interact with axons, forming junctions that are essential for node formation and maintenance. Recent studies indicate that the disruption of these specialized axonal domains is involved in the pathophysiology of various neurological diseases. Loss of paranodal axoglial junctions due to genetic mutations or autoimmune attack against the paranodal proteins leads to nerve conduction failure and neurological symptoms. Breakdown of nodal and paranodal proteins by calpains, the calcium-dependent cysteine proteases, may be a common mechanism involved in various nervous system diseases and injuries. This chapter reviews recent progress in neurobiology and pathophysiology of specialized axonal domains along myelinated nerve fibers.

Guillain-Barré Syndrome

Guillain-Barré syndrome (GBS) is an acute immune-mediated polyradiculoneuropathy, and pathophysiologically classified into acute inflammatory demyelinating polyneuropathy (AIDP), acute motor axonal neuropathy (AMAN), and acute motor and sensory axonal neuropathy (AMSAN). The main pathophysiological mechanism is complement-mediated nerve injury caused by antibody-antigen interaction in the peripheral nerves. Antiglycolipid antibodies are most pathogenic factors in the development of GBS, but not found in 40% of patients with GBS. One of the principal target regions in GBS is the node of Ranvier where functional molecules including glycolipids are assembled. Nodal dysfunction induced by the immune response in nodal axolemma, termed "nodopathy," can electrophysiologically show reversible conduction failure, axonal degeneration, or segmental demyelination. To detect new target molecules in antiglycolipid antibody-negative GBS and to elucidate the pathophysiology in the subacute and the subsequent phases of the disorder are the next problems.

Immune-mediated neuropathies

Since the discovery of an acute monophasic paralysis, later coined Guillain-Barré syndrome, almost 100 years ago, and the discovery of chronic, steroid-responsive polyneuropathy 50 years ago, the spectrum of immune-mediated polyneuropathies has broadened, with various subtypes continuing to be identified, including chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and multifocal motor neuropathy (MMN). In general, these disorders are speculated to be caused by autoimmunity to proteins located at the node of Ranvier or components of myelin of peripheral nerves, although disease-associated autoantibodies have not been identified for all disorders. Owing to the numerous subtypes of the immune-mediated neuropathies, making the right diagnosis in daily clinical practice is complicated. Moreover, treating these disorders, particularly their chronic variants, such as CIDP and MMN, poses a challenge. In general, management of these disorders includes immunotherapies, such as corticosteroids, intravenous immunoglobulin or plasma exchange. Improvements in clinical criteria and the emergence of more disease-specific immunotherapies should broaden the therapeutic options for these disabling diseases.

Immunotherapy of Guillain-Barré syndrome

Guillain-Barré syndrome (GBS), the most common cause of acute neuromuscular weakness and paralysis worldwide, encompasses a group of acute immune-mediated disorders restricted to peripheral nerves and roots. Immune-mediated attack of peripheral nervous system myelin, axons or both is presumed to be triggered by molecular mimicry, with both cell- and humoral-dependent mechanisms implicated in disease pathogenesis. Good circumstantial evidence exists for a pathogenic role for molecular mimicry in GBS pathogenesis, especially with its axonal forms, providing insights that could guide future immunotherapy. Intravenous immunoglobulin (IVIg) and plasma exchange (PE) are the most commonly prescribed immunotherapies for GBS with variable efficacy dependent on GBS subtype, severity at initial presentation and other clinical and electrophysiologic prognostic factors. The mechanisms of action of IVIg and PE are not known definitely. Despite recent significant advances in molecular biology that provide insights into GBS pathogenesis, no advances in therapeutics or significant improvements in patient outcomes have occurred over the past three decades. We summarize the clinical aspects of GBS, its current pathogenesis and immunotherapy, and highlight the potential of leukocyte trafficking inhibitors as novel disease-specific immunotherapeutic drugs.

Autoimmune nodo-paranodopathies of peripheral nerve: the concept is gaining ground

Peripheral neuropathies are classified as primarily demyelinating or axonal. Microstructural alterations of the nodal region are the key to understand the pathophysiology of neuropathies with antibodies to gangliosides and the new category of nodo-paranodopathy has been proposed to better characterise these disorders and overcome some inadequacies of the dichotomous classification. Recently, the research in autoimmune neuropathies has been boosted by reports of patients carrying immunoglobulin G4 antibodies against paranodal axo-glial proteins with distinct phenotypes and showing loss of transverse bands, terminal myelin loop detachment, nodal widening and axonal loss. These patients have been classified up to now as chronic inflammatory demyelinating polyradiculoneuropathy but, in our opinion, better fit into the nodo-paranodopathy category because nerve injury is due to dismantling of the paranode, segmental de-remyelination is absent and the pathogenic mechanism is not inflammatory. Evidence from nerve conductions and electron microscopy studies in patients and mutant animal models can reconcile the apparent contrast between the electrophysiological 'demyelinating' features, explainable just by the paranodal involvement and the axonal pathology. These patients broaden the autoimmune nodo-paranodopathy category and re-emphasise the usage of the term that pointing to the site of nerve injury reminds specific pathophysiological mechanisms, reconciles contrasting electrophysiological and pathological findings, and avoids misdiagnosis and taxonomic confusion. In our opinion, the nodo-paranodopathy term more adequately classifies the peripheral nerve disorders due to an autoimmune attack directed and limited to the nodal region integrating the traditional classification of peripheral neuropathies.

Beneficial or Harmful Role of Macrophages in Guillain-Barré Syndrome and Experimental Autoimmune Neuritis

Guillain-Barré syndrome (GBS), an immune-mediated demyelinating peripheral neuropathy, is characterized by acute weakness of the extremities and areflexia or hyporeflexia. Experimental autoimmune neuritis (EAN) is a common animal model for GBS, which represents a CD4+ T cell-mediated inflammatory autoimmune demyelination of the peripheral nervous system (PNS), and is used to investigate the pathogenic mechanism of GBS. It has been found that macrophages play a critical role in the pathogenesis of both GBS and EAN. Macrophages have been primarily classified into two major phenotypes: proinflammatory macrophages (M1) and anti-inflammatory macrophages (M2). The two different macrophage subsets M1 and M2 may play a decisive role in initiation and development of GBS and EAN. However, recently, it has been indicated that the roles of macrophages in immune regulation and autoimmune diseases are more complex than those suggested by a simple M1-M2 dichotomy. Macrophages might exert either inflammatory or anti-inflammatory effect by secreting pro- or anti-inflammatory cytokines, and either inducing the activation of T cells to mediate immune response, resulting in inflammation and demyelination in the PNS, or promoting disease recovery. In this review, we summarize the dual roles of macrophages in GBS and EAN and explore the mechanism of macrophage polarization to provide a potential therapeutic approach for GBS in the future.

Beneficial or Harmful Role of Macrophages in Guillain-Barré Syndrome and Experimental Autoimmune Neuritis

Guillain-Barré syndrome (GBS), an immune-mediated demyelinating peripheral neuropathy, is characterized by acute weakness of the extremities and areflexia or hyporeflexia. Experimental autoimmune neuritis (EAN) is a common animal model for GBS, which represents a CD4⁺ T cell-mediated inflammatory autoimmune demyelination of the peripheral nervous system (PNS), and is used to investigate the pathogenic mechanism of GBS. It has been found that macrophages play a critical role in the pathogenesis of both GBS and EAN. Macrophages have been primarily classified into two major phenotypes: proinflammatory macrophages (M1) and anti-inflammatory macrophages (M2). The two different macrophage subsets M1 and M2 may play a decisive role in initiation and development of GBS and EAN. However, recently, it has been indicated that the roles of macrophages in immune regulation and autoimmune diseases are more complex than those suggested by a simple M1-M2 dichotomy. Macrophages might exert either inflammatory or anti-inflammatory effect by secreting pro- or anti-inflammatory cytokines, and either inducing the activation of T cells to mediate immune response, resulting in inflammation and demyelination in the PNS, or promoting disease recovery. In this review, we summarize the dual roles of macrophages in GBS and EAN and explore the mechanism of macrophage polarization to provide a potential therapeutic approach for GBS in the future.

Beneficial or Harmful Role of Macrophages in Guillain-Barré Syndrome and Experimental Autoimmune Neuritis

Guillain-Barré syndrome (GBS), an immune-mediated demyelinating peripheral neuropathy, is characterized by acute weakness of the extremities and areflexia or hyporeflexia. Experimental autoimmune neuritis (EAN) is a common animal model for GBS, which represents a CD4⁺ T cell-mediated inflammatory autoimmune demyelination of the peripheral nervous system (PNS), and is used to investigate the pathogenic mechanism of GBS. It has been found that macrophages play a critical role in the pathogenesis of both GBS and EAN. Macrophages have been primarily classified into two major phenotypes: proinflammatory macrophages (M1) and anti-inflammatory macrophages (M2). The two different macrophage subsets M1 and M2 may play a decisive role in initiation and development of GBS and EAN. However, recently, it has been indicated that the roles of macrophages in immune regulation and autoimmune diseases are more complex than those suggested by a simple M1-M2 dichotomy. Macrophages might exert either inflammatory or anti-inflammatory effect by secreting pro- or anti-inflammatory cytokines, and either inducing the activation of T cells to mediate immune response, resulting in inflammation and demyelination in the PNS, or promoting disease recovery. In this review, we summarize the dual roles of macrophages in GBS and EAN and explore the mechanism of macrophage polarization to provide a potential therapeutic approach for GBS in the future.

Axonal damage in central and peripheral nervous system inflammatory demyelinating diseases: common and divergent pathways of tissue damage

PURPOSE OF REVIEW

Axonal injury is the pathological correlate of fixed disability in the inflammatory demyelinating disorders of the central and peripheral nervous system. The mechanisms that initiate and propagate neurodegeneration in these conditions are poorly understood, and a lack of available neuroprotective and proreparative therapies represent a significant unmet clinical need. In this article, we review new data pertaining to the convergent and divergent immunological, cellular, and molecular mechanisms that underpin neurodegeneration in multiple sclerosis and the chronic inflammatory demyelinating neuropathies that will inform the development of targeted therapies.

RECENT FINDINGS

New insights have been gained from recognition of the axon as an integral component of the axon-myelin unit, identification of defects in axonal transport, elucidation of mechanisms of Wallerian degeneration and, in the central nervous system, the appreciation of trans-synaptic axonal degeneration, and widespread cortical synaptopathy. Concurrently, specific immune triggers of axonal injury, particularly in the peripheral immune system; and inhibitors of repair and regrowth, have been identified.

SUMMARY

Neurodegeneration is a critical determinant of disability in the inflammatory demyelinating diseases of both the central nervous system and peripheral nervous system. Current therapies are restricted to agents that (effectively) treat the inflammatory components of these conditions. Although propagated, and in some instances triggered, by inflammation, axon damage will in future years be treated or prevented with adjuvant, targeted therapies that exploit emerging pathways to neurodegeneration.

Avian Ganglioneuritis in Clinical Practice

Avian ganglioneuritis (AG) comprises one of the most intricate pathologies in avian medicine and is researched worldwide. Avian bornavirus (ABV) has been shown to be a causative agent of proventricular dilatation disease in birds. The avian Bornaviridae represent a genetically diverse group of viruses that are widely distributed in captive and wild populations around the world. ABV and other infective agents are implicated as a cause of the autoimmune pathology that leads to AG, similar to human Guillain Barrè syndrome. Management of affected birds is beneficial and currently centered at reducing neurologic inflammation, managing secondary complications, and providing nutritional support.

Partial Conduction Block as an Early Nerve Conduction Finding in Neurolymphomatosis

BACKGROUND AND PURPOSE

Neurolymphomatosis is a rare manifestation of hematological malignancy and is characterized by direct infiltration of the peripheral nervous system. The objective of this study was to identify the clinical and electrophysiological features of neurolymphomatosis.

METHODS

We retrospectively analyzed the medical records of 13 patients with neurolymphomatosis. Seven (54%) of the patients were men, and the median age at symptom onset was 60.0 years.

RESULTS

The most common type of underlying malignancy was diffuse large B-cell lymphoma (69%). Twelve patients had painful asymmetric neuropathies. The median survival time after diagnosis was 7 months, and 12 patients died during the study period. Thirty-eight motor nerve conduction studies (NCSs) were performed in the affected nerves. Ten and 28 motor nerves were classified into the conduction-block and simple-axon-degeneration groups, respectively. The median time interval between symptom onset and the NCS was significantly shorter in the conduction-block group than in the simple-axon-degeneration group (p=0.032). However, no significant differences in the motor nerve conduction velocities, terminal latencies, and distal compound muscle action potential amplitudes were identified between the conduction-block and simple-axon-degeneration groups. The conduction-block group showed excessive temporal dispersion in only five of the ten NCSs (50%). Follow-up NCSs revealed that partial conduction blocks had changed into axonal degeneration patterns.

CONCLUSIONS

This is the first study to analyze the electrophysiological features of patients with neurolymphomatosis. Our findings showed that a partial conduction block is not rare and is an early nerve conduction abnormality in neurolymphomatosis.

A Simple Approach to Induce Experimental Autoimmune Neuritis in C57BL/6 Mice for Functional and Neuropathological Assessments

Experimental autoimmune neuritis (EAN) is a well-appreciated experimental model of autoimmune peripheral demyelinating diseases. EAN disease is induced by immunizing mice with neurogenic peptides to direct an inflammatory attack toward components of the peripheral nervous system (PNS). Recent advances have enabled the induction of EAN in the relatively resistant C57BL/6 mouse line using myelin protein zero (P0)106-125 or P0180-199 peptides delivered in adjuvant combined with the injection of pertussis toxin. The ability to induce EAN in the C57BL/6 strain allows for the use of the numerous genetic tools that exist on this mouse background, and thus allows the sophisticated study of disease pathogenesis and interrogation of the mechanistic action of novel therapeutics in combination with transgenic approaches. In this study, we demonstrate a simple approach to successfully induce EAN using the P0180-199 peptide in C57BL/6 mice. We also outline a protocol for the assessment of functional deficits that occur in this model, accompanied by an array of neuropathological features. Thus, this model is a powerful experimental model to study the pathogenesis of human peripheral demyelinating neuropathies, and to determine the efficacy of potential therapies that aim to promote myelin repair and protect against nerve damage in autoimmune neuritis.

Did Jules Dejerine describe AMAN at the end of the 19th century?

Guillain-Barré syndrome (GBS) is a heterogeneous group of acute immune-mediated neuropathies, including acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN). AMAN is an axonal subtype of GBS that has been known since the 1990s; this term was first used to describe a summer epidemic of acute ascending paralysis observed in children in northern China (and Mexico). It is pathologically characterized by noninflammatory axonal degeneration of the motor nerves (with little or no demyelination). The French neurologist Jules Dejerine (1849-1917) conducted a clinical and pathologic description of AMAN in the late 19th century. We describe his observations, which provide us with valuable information on the course of pathologic lesions in this disease.

Transplanted human fecal microbiota enhanced Guillain Barré syndrome autoantibody responses after Campylobacter jejuni infection in C57BL/6 mice

BACKGROUND

Campylobacter jejuni is the leading antecedent infection to the autoimmune neuropathy Guillain-Barré syndrome (GBS), which is accompanied by an autoimmune anti-ganglioside antibody attack on peripheral nerves. Previously, we showed that contrasting immune responses mediate C. jejuni induced colitis and autoimmunity in interleukin-10 (IL-10)-deficient mice, dependent upon the infecting strain. Strains from colitis patients elicited T helper 1 (T_H1)-dependent inflammatory responses while strains from GBS patients elicited T_H2-dependent autoantibody production. Both syndromes were exacerbated by antibiotic depletion of the microbiota, but other factors controlling susceptibility to GBS are unknown.

METHODS

Using 16S rRNA gene high-throughput sequencing, we examined whether structure of the gut microbial community alters host (1) gastrointestinal inflammation or (2) anti-ganglioside antibody responses after infection with C. jejuni strains from colitis or GBS patients. We compared these responses in C57BL/6 mice with either (1) stable human gut microbiota (^Humicrobiota) transplants or (2) conventional mouse microbiota (^Convmicrobiota).

RESULTS

Inoculating germ-free C57BL/6 wild-type (WT) mice with a mixed human fecal slurry provided a murine model that stably passed its microbiota over >20 generations. Mice were housed in specific pathogen-free (SPF) facilities, while extra precautions of having caretakers wear sterile garb along with limited access ensured that no mouse pathogens were acquired. ^Humicrobiota conferred many changes upon the WT model in contrast to previous results, which showed only colonization with no disease after C. jejuni challenge. When compared to ^Convmicrobiota mice for susceptibility to C. jejuni enteric or GBS patient strains, infected ^Humicrobiota mice had (1) 10-100 fold increases in C. jejuni colonization of both strains, (2) pathologic change in draining lymph nodes but only mild changes in colon or cecal lamina propria, (3) significantly lower Th1/Th17-dependent anti-C. jejuni responses, (4) significantly higher IL-4 responses at 5 but not 7 weeks post infection (PI), (5) significantly higher Th2-dependent anti-C. jejuni responses, and (6) significantly elevated anti-ganglioside autoantibodies after C. jejuni infection. These responses in ^Humicrobiota mice were correlated with a dominant Bacteroidetes and Firmicutes microbiota.

CONCLUSIONS

These data demonstrate that ^Humicrobiota altered host-pathogen interactions in infected mice, increasing colonization and Th-2 and autoimmune responses in a C. jejuni strain-dependent manner. Thus, microbiota composition is another factor controlling susceptibility to GBS.

Optimizing the electrodiagnostic accuracy in Guillain-Barré syndrome subtypes: Criteria sets and sparse linear discriminant analysis

OBJECTIVE

To optimize the electrodiagnosis of Guillain-Barré syndrome (GBS) subtypes at first study.

METHODS

The reference electrodiagnosis was obtained in 53 demyelinating and 45 axonal GBS patients on the basis of two serial studies and results of anti-ganglioside antibodies assay. We retrospectively employed sparse linear discriminant analysis (LDA), two existing electrodiagnostic criteria sets (Hadden et al., 1998; Rajabally et al., 2015) and one we propose that additionally evaluates duration of motor responses, sural sparing pattern and defines reversible conduction failure (RCF) in motor and sensory nerves at second study.

RESULTS

At first study the misclassification error rates, compared to reference diagnoses, were: 15.3% for sparse LDA, 30% for our criteria, 45% for Rajabally's and 48% for Hadden's. Sparse LDA identified seven most powerful electrophysiological variables differentiating demyelinating and axonal subtypes and assigned to each patient the diagnostic probability of belonging to either subtype. At second study 46.6% of axonal GBS patients showed RCF in two motor and 8.8% in two sensory nerves.

CONCLUSIONS

Based on a single study, sparse LDA showed the highest diagnostic accuracy. RCF is present in a considerable percentage of axonal patients.

SIGNIFICANCE

Sparse LDA, a supervised statistical method of classification, should be introduced in the electrodiagnostic practice.