A National Cross-Sectional Survey of EMG Physician Volume

Background and Objectives

This study presents results from a survey of physicians performing electrodiagnostic studies to assess average volume. We also assessed how different factors (trainees, technologists, age of the physician, and case complexity) affected volume. Productivity is an important factor for physicians across practice settings. However, unlike evaluation and management services for neurologists, there are no published data for benchmarks of average volume of electrodiagnostic studies.

Methods

A 34-question survey was designed collecting information on demographics, electrodiagnostic study volume, technologists, trainees, referrals, and case complexity. The anonymous survey was disseminated through a QR code or hyperlink to multiple online neurology, physical medicine and rehabilitation, electromyography, and neuromuscular forums. The primary outcome was EMG volume including number of EMGs per half-day and EMG volume per year. We conducted bivariate association analysis between primary outcomes and respondent characteristics using the Pearson χ2 test. Multivariable regression models determined factors associated with each of our outcome variables.

Results

A total of 201 respondents initiated the survey. 71% were certified in adult neurology, 19.6% in physical medicine and rehabilitation, and 2.7% in pediatric neurology. 37.5% practiced in academic medicine. The remaining respondents were from private practice, group, solo, hospital employed, or other. 83% of respondents allotted a dedicated half-day to performing EMGs. The median number of EMGs scheduled during a half-day was within 3-4 (45%). 30% and 7% scheduled 5-6 or more than 7 patients per half-day, respectively. The median number of EMGs performed per year was within 251-500 (37%).

Discussion

This national, cross-sectional survey evaluates average metrics of EMG volume. Our survey showed that the median number of EMGs annually lies between 251 and 500 studies (37%). In addition, for those respondents who allotted a dedicated half-day to performing EMGs, the median number of EMG studies scheduled per half-day lies between 3 and 4 studies (45%). In multivariate analysis, respondent characteristics of age of the physician (older than 45), working with nerve conduction technologists, and holding the position of EMG director were associated with increased EMG volume.

Tumor necrosis factor α receptor 1A transduces the inhibitory effect on axon regeneration triggered by IgG anti-ganglioside GD1a antibodies

Anti-ganglioside antibodies (anti-Gg Abs) have been linked to delayed/poor clinical recovery in both axonal and demyelinating forms of Guillain-Barrè Syndrome (GBS). In many instances, the incomplete recovery is attributed to the peripheral nervous system's failure to regenerate. The cross-linking of cell surface gangliosides by anti-Gg Abs triggers inhibition of nerve repair in both in vitro and in vivo axon regeneration paradigms. This mechanism involves the activation of the small GTPase RhoA, which negatively modulates the growth cone cytoskeleton. At present, the identity/es of the receptor/s responsible for transducing the signal that ultimately leads to RhoA activation remains poorly understood. The aim of this work was to identify the transducer molecule responsible for the inhibitory effect of anti-Gg Abs on nerve repair. Putative candidate molecules were identified through proteomic mass spectrometry of ganglioside affinity-captured proteins from rat cerebellar granule neurons (Prendergast et al., 2014). These candidates were evaluated using an in vitro model of neurite outgrowth with primary cultured dorsal root ganglion neurons (DRGn) and an in vivo model of axon regeneration. Using an shRNA-strategy to silence putative candidates on DRGn, we identified tumor necrosis factor receptor 1A protein (TNFR1A) as a transducer molecule for the inhibitory effect on neurite outgrowth from rat/mouse DRGn cultures of a well characterized mAb targeting the related gangliosides GD1a and GT1b. Interestingly, lack of TNFr1A expression on DRGn abolished the inhibitory effect on neurite outgrowth caused by anti-GD1a but not anti-GT1b specific mAbs, suggesting specificity of GD1a/transducer signaling. Similar results were obtained using primary DRGn cultures from TNFR1a-null mice, which did not activate RhoA after exposure to anti-GD1a mAbs. Generation of single point mutants at the stalk region of TNFR1A identified a critical amino acid for transducing GD1a signaling, suggesting a direct interaction. Finally, passive immunization with an anti-GD1a/GT1b mAb in an in vivo model of axon regeneration exhibited reduced inhibitory activity in TNFR1a-null mice compared to wild type mice. In conclusion, these findings identify TNFR1A as a novel transducer receptor for the inhibitory effect exerted by anti-GD1a Abs on nerve repair, representing a significant step forward toward understanding the factors contributing to poor clinical recovery in GBS associated with anti-Gg Abs.

Emerging treatment landscape for Guillain-Barré Syndrome (GBS): what's new?

INTRODUCTION

Guillain-Barré syndrome (GBS) is a monophasic immune neuropathic disorder characterized by acute paralysis. A significant portion of patients are left with residual deficits, which presents a considerable global healthcare challenge. The precise mechanisms underlying GBS pathogenesis are not fully elucidated. Recent studies have focused on postinfectious molecular mimicry and identified involvement of IgG autoantibodies and innate immune effectors in GBS. Intravenous immunoglobulins (IVIg) and plasma exchange (PE) are two established evidence-based immunomodulatory treatments for GBS, but a significant proportion of GBS patients fails to respond adequately to either therapy. This emphasizes an urgent need for novel and more potent treatments.

AREAS COVERED

We discuss novel immunomodulatory therapies presently at different phases of preclinical and clinical investigation. Some drugs in development target pathophysiologic mechanisms such as IgG autoantibody catabolism and complement activation, which are relevant to GBS.

EXPERT OPINION

There is an unmet need for more effective immune therapies for GBS. New immunomodulatory therapies under development may provide more potent options for GBS patients who do not respond to IVIg or PE. Future directions may include incorporating neuroprotective interventions based on evolving understanding of mechanisms underlying nerve injury and axonal degeneration.

Rejuvenating fecal microbiota transplant enhances peripheral nerve repair in aged mice by modulating endoneurial inflammation

Peripheral nerve injury (PNI) resulting from trauma or neuropathies can cause significant disability, and its prognosis deteriorates with age. Emerging evidence suggests that gut dysbiosis and reduced fecal short-chain fatty acids (SCFAs) contribute to an age-related systemic hyperinflammation (inflammaging), which hinders nerve recovery after injury. This study thus aimed to evaluate the pro-regenerative effects of a rejuvenating fecal microbiota transplant (FMT) in a preclinical PNI model using aged mice. Aged C57BL/6 mice underwent bilateral crush injuries to their sciatic nerves. Subsequently, they either received FMT from young donors at three and four days after the injury or retained their aged gut microbiota. We analyzed gut microbiome composition and SCFA concentrations in fecal samples. The integrity of the ileac mucosal barrier was assessed by immunofluorescence staining of Claudin-1. Flow cytometry was utilized to examine immune cells and cytokine production in the ileum, spleen, and sciatic nerve. Various assessments, including behavioural tests, electrophysiological studies, and morphometrical analyses, were conducted to evaluate peripheral nerve function and repair following injury. Rejuvenating FMT reversed age-related gut dysbiosis by increasing Actinobacteria, especially Bifidobacteriales genera. This intervention also led to an elevation of gut SCFA levels and mitigated age-related ileac mucosal leakiness in aged recipients. Additionally, it augmented the number of T-helper 2 (Th2) and regulatory T (Treg) cells in the ileum and spleen, with the majority being positive for anti-inflammatory interleukin-10 (IL-10). In sciatic nerves, rejuvenating FMT resulted in increased M2 macrophage counts and a higher IL-10 production by IL-10+TNF-α- M2 macrophage subsets. Ultimately, restoring a youthful gut microbiome in aged mice led to improved nerve repair and enhanced functional recovery after PNI. Considering that FMT is already a clinically available technique, exploring novel translational strategies targeting the gut microbiome to enhance nerve repair in the elderly seems promising and warrants further evaluation.

Blockade of Rho-associated kinase prevents inhibition of axon regeneration of peripheral nerves induced by anti-ganglioside antibodies

Anti-ganglioside antibodies are associated with delayed/poor clinical recovery in Guillain-Barrè syndrome, mostly related to halted axon regeneration. Cross-linking of cell surface gangliosides by anti-ganglioside antibodies triggers inhibition of nerve repair in in vitro and in vivo paradigms of axon regeneration. These effects involve the activation of the small GTPase RhoA/ROCK signaling pathways, which negatively modulate growth cone cytoskeleton, similarly to well stablished inhibitors of axon regeneration described so far. The aim of this work was to perform a proof of concept study to demonstrate the effectiveness of Y-27632, a selective pharmacological inhibitor of ROCK, in a mouse model of axon regeneration of peripheral nerves, where the passive immunization with a monoclonal antibody targeting gangliosides GD1a and GT1b was previously reported to exert a potent inhibitory effect on regeneration of both myelinated and unmyelinated fibers. Our results demonstrate a differential sensitivity of myelinated and unmyelinated axons to the pro-regenerative effect of Y-27632. Treatment with a total dosage of 9 mg/kg of Y-27632 resulted in a complete prevention of anti-GD1a/GT1b monoclonal antibody-mediated inhibition of axon regeneration of unmyelinated fibers to skin and the functional recovery of mechanical cutaneous sensitivity. In contrast, the same dose showed toxic effects on the regeneration of myelinated fibers. Interestingly, scale down of the dosage of Y-27632 to 5 mg/kg resulted in a significant although not complete recovery of regenerated myelinated axons exposed to anti-GD1a/GT1b monoclonal antibody in the absence of toxicity in animals exposed to only Y-27632. Overall, these findings confirm the in vivo participation of RhoA/ROCK signaling pathways in the molecular mechanisms associated with the inhibition of axon regeneration induced by anti-GD1a/GT1b monoclonal antibody. Our findings open the possibility of therapeutic pharmacological intervention targeting RhoA/Rock pathway in immune neuropathies associated with the presence of anti-ganglioside antibodies and delayed or incomplete clinical recovery after injury in the peripheral nervous system.

CSF Findings in Relation to Clinical Characteristics, Subtype, and Disease Course in Patients With Guillain-Barré Syndrome

BACKGROUND AND OBJECTIVES

To investigate CSF findings in relation to clinical and electrodiagnostic subtypes, severity, and outcome of Guillain-Barré syndrome (GBS) based on 1,500 patients in the International GBS Outcome Study.

METHODS

Albuminocytologic dissociation (ACD) was defined as an increased protein level (>0.45 g/L) in the absence of elevated white cell count (<50 cells/μL). We excluded 124 (8%) patients because of other diagnoses, protocol violation, or insufficient data. The CSF was examined in 1,231 patients (89%).

RESULTS

In 846 (70%) patients, CSF examination showed ACD, which increased with time from weakness onset: ≤4 days 57%, >4 days 84%. High CSF protein levels were associated with a demyelinating subtype, proximal or global muscle weakness, and a reduced likelihood of being able to run at week 2 (odds ratio [OR] 0.42, 95% CI 0.25-0.70; p = 0.001) and week 4 (OR 0.44, 95% CI 0.27-0.72; p = 0.001). Patients with the Miller Fisher syndrome, distal predominant weakness, and normal or equivocal nerve conduction studies were more likely to have lower CSF protein levels. CSF cell count was <5 cells/μL in 1,005 patients (83%), 5-49 cells/μL in 200 patients (16%), and ≥50 cells/μL in 13 patients (1%).

DISCUSSION

ACD is a common finding in GBS, but normal protein levels do not exclude this diagnosis. High CSF protein level is associated with an early severe disease course and a demyelinating subtype. Elevated CSF cell count, rarely ≥50 cells/μL, is compatible with GBS after a thorough exclusion of alternative diagnoses.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that CSF ACD (defined by the Brighton Collaboration) is common in patients with GBS.

Predicting Outcome in Guillain-Barré Syndrome: International Validation of the Modified Erasmus GBS Outcome Score

BACKGROUND AND OBJECTIVES

The clinical course and outcome of the Guillain-Barré syndrome (GBS) are diverse and vary among regions. The modified Erasmus GBS Outcome Score (mEGOS), developed with data from Dutch patients, is a clinical model that predicts the risk of walking inability in patients with GBS. The study objective was to validate the mEGOS in the International GBS Outcome Study (IGOS) cohort and to improve its performance and region specificity.

METHODS

We used prospective data from the first 1,500 patients included in IGOS, aged ≥6 years and unable to walk independently. We evaluated whether the mEGOS at entry and week 1 could predict the inability to walk unaided at 4 and 26 weeks in the full cohort and in regional subgroups, using 2 measures for model performance: (1) discrimination: area under the receiver operating characteristic curve (AUC) and (2) calibration: observed vs predicted probability of being unable to walk independently. To improve the model predictions, we recalibrated the model containing the overall mEGOS score, without changing the individual predictive factors. Finally, we assessed the predictive ability of the individual factors.

RESULTS

For validation of mEGOS at entry, 809 patients were eligible (Europe/North America [n = 677], Asia [n = 76], other [n = 56]), and 671 for validation of mEGOS at week 1 (Europe/North America [n = 563], Asia [n = 65], other [n = 43]). AUC values were >0.7 in all regional subgroups. In the Europe/North America subgroup, observed outcomes were worse than predicted; in Asia, observed outcomes were better than predicted. Recalibration improved model accuracy and enabled the development of a region-specific version for Europe/North America (mEGOS-Eu/NA). Similar to the original mEGOS, severe limb weakness and higher age were the predominant predictors of poor outcome in the IGOS cohort.

DISCUSSION

mEGOS is a validated tool to predict the inability to walk unaided at 4 and 26 weeks in patients with GBS, also in countries outside the Netherlands. We developed a region-specific version of mEGOS for patients from Europe/North America.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that the mEGOS accurately predicts the inability to walk unaided at 4 and 26 weeks in patients with GBS.

TRIAL REGISTRATION INFORMATION

NCT01582763.

Precision Intravenous Immunoglobulin Dosing and Clinical Outcomes: A Retrospective Chart Review

OBJECTIVES

Intravenous immunoglobulin (IVIg) is used for treatment of acute neurologic conditions such as Guillain-Barre syndrome, chronic inflammatory demyelinating polyradiculoneuropathy relapse, and myasthenia gravis exacerbation. Precision dosing (adjusted or ideal body weight) is proposed to conserve IVIg. There have been no published studies comparing clinical outcomes in traditional dosing (actual body weight) with precision dosing. In 2014, our institution began dosing patients with precision dosing. This decision was largely performed by administration rather than physicians' preference. We sought to analyze our retrospective data to understand the change in dosing methods with neurologic outcomes.

METHODS

We performed a retrospective review of all patients hospitalized at a single center who received IVIg for myasthenia gravis, Guillain-Barre syndrome, and chronic inflammatory demyelinating polyradiculoneuropathy from January 2010 to October 2017. We collected baseline information and clinical outcomes including mortality, readmission, need for second rescue treatment, length of stay, discharge disposition, treatment-related adverse events, and modified research council posttreatment sum score.

RESULTS

Length of stay was significantly shorter with precision dosing. There was no statistically significant difference in discharge disposition, readmission, rescue treatment, or modified research council posttreatment sum score with precision dosing.

CONCLUSION

Precision dosing did not adversely affect short-term neurologic outcomes.

Guillain-Barré Syndrome

PURPOSE OF REVIEW

This article reviews the clinical features, diagnosis and differential diagnosis, prognosis, pathogenesis, and current and upcoming treatments of Guillain-Barré syndrome (GBS).

RECENT FINDINGS

GBS is an acute inflammatory neuropathic illness with striking clinical manifestations and significant morbidity. A substantial proportion of patients with GBS do not respond to current immunomodulatory therapies (ie, plasma exchange and IV immunoglobulin [IVIg]), highlighting the need for new therapies. Prognostic models that can accurately predict functional recovery and the need for artificial ventilation have emerged. These models are practical, and online calculators are available for clinical use, facilitating early recognition of patients with poor outcome and the opportunity to personalize management decisions. Clinical and experimental studies have identified innate immune effectors (complement, macrophage lineage cells, and activating Fcγ receptors) as important mediators of inflammatory nerve injury. Two complement inhibitors are undergoing clinical testing for efficacy in GBS.

SUMMARY

GBS is the most common cause of acute flaccid paralysis in the United States and worldwide. New treatments for GBS have not emerged since the 1990s. Our understanding of the pathogenesis of this disorder has progressed, particularly over the past decade; as a result, new therapeutic agents targeting different components of the complement cascade are at advanced stages of clinical development.

Subcutaneous immunoglobulin treatment for chronic inflammatory demyelinating polyneuropathy

Immunoglobulin G (IgG) therapy is an established long‐term treatment in chronic inflammatory demyelinating polyneuropathy (CIDP) that is commonly administered intravenously (IVIg). The subcutaneous immunoglobulin (SCIg) administration route is a safe and effective alternative option, approved by the United States Food and Drug Administration (FDA) in 2018, for maintenance treatment of adults with CIDP. Physicians and patients alike need to be aware of all their treatment options in order to make informed decisions and plan long‐term treatment strategies. In this review, we collate the evidence for SCIg in CIDP from all published studies and discuss their implications and translation to clinical practice. We also provide guidance on the practicalities of how and when to transition patients from IVIg to SCIg and ongoing patient support. Evidence suggests that IVIg and SCIg have comparable long‐term efficacy in CIDP. However, SCIg can provide additional benefits for some patients, including no requirement for venous access or premedication, and reduced frequency of systemic adverse events. Local‐site reactions are more common with SCIg than IVIg, but these are mostly well‐tolerated and abate with subsequent infusions. Data suggest that many patients prefer SCIg following transition from IVIg. SCIg preference may be a result of the independence and flexibility associated with self‐infusion, whereas IVIg preference may be a result of familiarity and reliance on a healthcare professional for infusions. In practice, individualizing maintenance dosing based on disease behavior and determining the minimally effective IgG dose for individuals are key considerations irrespective of the administration route chosen.

Heat shock protein is a key therapeutic target for nerve repair in autoimmune peripheral neuropathy and severe peripheral nerve injury

Guillain-Barré syndrome (GBS) is an autoimmune peripheral neuropathy and a common cause of neuromuscular paralysis. Preceding infection induces the production of anti-ganglioside (GD) antibodies attacking its own peripheral nerves. In severe proximal peripheral nerve injuries that require long-distance axon regeneration, motor functional recovery is virtually nonexistent. Damaged axons fail to regrow and reinnervate target muscles. In mice, regenerating axons must reach the target muscle within 35 days (critical period) to reform functional neuromuscular junctions and regain motor function. Successful functional recovery depends on the rate of axon regeneration and debris removal (Wallerian degeneration) after nerve injury. The innate-immune response of the peripheral nervous system to nerve injury such as timing and magnitude of cytokine production is crucial for Wallerian degeneration. In the current study, forced expression of human heat shock protein (hHsp) 27 completely reversed anti-GD-induced inhibitory effects on nerve repair assessed by animal behavioral assays, electrophysiology and histology studies, and the beneficial effect was validated in a second mouse line of hHsp27. The protective effect of hHsp27 on prolonged muscle denervation was examined by performing repeated sciatic nerve crushes to delay regenerating axons from reaching distal muscle from 37 days up to 55 days. Strikingly, hHsp27 was able to extend the critical period of motor functional recovery for up to 55 days and preserve the integrity of axons and mitochondria in distal nerves. Cytokine array analysis demonstrated that a number of key cytokines which are heavily involved in the early phase of innate-immune response of Wallerian degeneration, were found to be upregulated in the sciatic nerve lysates of hHsp27 Tg mice at 1 day postinjury. However, persistent hyperinflammatory mediator changes were found after chronic denervation in sciatic nerves of littermate mice, but remained unchanged in hHsp27 Tg mice. Taken together, the current study provides insight into the development of therapeutic strategies to enhance muscle receptiveness (reinnervation) by accelerating axon regeneration and Wallerian degeneration.

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.

Anti-glycan antibodies halt axon regeneration in a model of Guillain Barrè Syndrome axonal neuropathy by inducing microtubule disorganization via RhoA-ROCK-dependent inactivation of CRMP-2

Several reports have linked the presence of high titers of anti-Gg Abs with delayed recovery/poor prognosis in GBS. In most cases, failure to recover is associated with halted/deficient axon regeneration. Previous work identified that monoclonal and patient-derived anti-Gg Abs can act as inhibitory factors in an animal model of axon regeneration. Further studies using primary dorsal root ganglion neuron (DRGn) cultures demonstrated that anti-Gg Abs can inhibit neurite outgrowth by targeting gangliosides via activation of the small GTPase RhoA and its associated kinase (ROCK), a signaling pathway common to other established inhibitors of axon regeneration. We aimed to study the molecular basis of the inhibitory effect of anti-Gg abs on neurite outgrowth by dissecting the molecular dynamics of growth cones (GC) cytoskeleton in relation to the spatial-temporal analysis of RhoA activity. We now report that axon growth inhibition in DRGn induced by a well characterized mAb targeting gangliosides GD1a/GT1b involves: i) an early RhoA/ROCK-independent collapse of lamellipodia; ii) a RhoA/ROCK-dependent shrinking of filopodia; and iii) alteration of GC microtubule organization/and presumably dynamics via RhoA/ROCK-dependent phosphorylation of CRMP-2 at threonine 555. Our results also show that mAb 1B7 inhibits peripheral axon regeneration in an animal model via phosphorylation/inactivation of CRMP-2 at threonine 555. Overall, our data may help to explain the molecular mechanisms underlying impaired nerve repair in GBS. Future work should define RhoA-independent pathway/s and effectors regulating actin cytoskeleton, thus providing an opportunity for the design of a successful therapy to guarantee an efficient target reinnervation.

Fluorescently-tagged anti-ganglioside antibody selectively identifies peripheral nerve in living animals

Selective in vivo delivery of cargo to peripheral nervous system (PNS) has broad clinical and preclinical applications. An important applicability of this approach is systemic delivery of fluorescently conjugated ligands that selectively label PNS, which could allow visualization of peripheral nerves during any surgery. We examine the use of an anti-ganglioside monoclonal antibody (mAb) as selective neuronal delivery vector for surgical imaging of peripheral nerves. Systemic delivery of an anti-ganglioside mAb was used for selective intraneuronal/axonal delivery of fluorescent agents to visualize nerves by surgical imaging in living mice. In this study, we show that intact motor, sensory, and autonomic nerve fibers/paths are distinctly labeled following a single nanomolar systemic injection of fluorescently labeled anti-ganglioside mAb. Tissue biodistribution studies with radiolabeled mAb were used to validate neuronal uptake of fluorescently labeled mAb. Implications of this proof of concept study are that fluorescent conjugates of anti-ganglioside mAbs are valuable delivery vectors to visualize nerves during surgery to avoid nerve injury and monitor nerve degeneration and regeneration after injury. These findings support that antibodies, and their derivatives/fragments, can be used as selective neuronal delivery vector for transport of various cargos to PNS in preclinical and clinical settings.

Dissecting the Role of Anti-ganglioside Antibodies in Guillain-Barré Syndrome: an Animal Model Approach

Guillain-Barré syndrome (GBS) is an autoimmune polyneuropathy disease affecting the peripheral nervous system (PNS). Most of the GBS patients experienced neurological symptoms such as paresthesia, weakness, pain, and areflexia. There are also combinations of non-neurological symptoms which include upper respiratory tract infection and diarrhea. One of the major causes of GBS is due largely to the autoantibodies against gangliosides located on the peripheral nerves. Gangliosides are sialic acid-bearing glycosphingolipids consisting of a ceramide lipid anchor with one or more sialic acids attached to a neutral sugar backbone. Molecular mimicry between the outer components of oligosaccharide of gangliosides on nerve membrane and lipo-oligosaccharide of microbes is thought to trigger the autoimmunity. Intra-peritoneal implantation of monoclonal ganglioside antibodies secreting hybridoma into animals induced peripheral neuropathy. Recent studies demonstrated that injection of synthesized anti-ganglioside antibodies raised by hybridoma cells into mice initiates immune response against peripheral nerves, and eventually failure in peripheral nerve regeneration. Accumulating evidences indicate that the conjugation of anti-ganglioside monoclonal antibodies to activating FcγRIII present on the circulating macrophages inhibits axonal regeneration. The activation of RhoA signaling pathways is also involved in neurite outgrowth inhibition. However, the link between these two molecular events remains unresolved and requires further investigation. Development of anti-ganglioside antagonists can serve as targeted therapy for the treatment of GBS and will open a new approach of drug development with maximum efficacy and specificity.

Inhibition of Rho-kinase differentially affects axon regeneration of peripheral motor and sensory nerves

The small GTPase RhoA and its down-stream effector Rho-kinase (ROCK) are important effector molecules of the neuronal cytoskeleton. Modulation of the RhoA/ROCK pathway has been shown to promote axonal regeneration, however in vitro and animal studies are inconsistent regarding the extent of axonal outgrowth induced by pharmacological inhibition of ROCK. We hypothesized that injury to sensory and motor nerves result in diverse activation levels of RhoA, which may impact the response of those nerve fiber modalities to ROCK inhibition. We therefore examined the effects of Y-27632, a chemical ROCK inhibitor, on the axonal outgrowth of peripheral sensory and motor neurons grown in the presence of growth-inhibiting chondroitin sulfate proteoglycans (CSPGs). In addition we examined the effects of three different doses of Y-27632 on nerve regeneration of motor and sensory nerves in animal models of peripheral nerve crush. In vitro, sensory neurons were less responsive to Y-27632 compared to motor neurons in a non-growth permissive environment. These differences were associated with altered expression and activation of RhoA in sensory and motor axons. In vivo, systemic treatment with high doses of Y-27632 significantly enhanced the regeneration of motor axons over short distances, while the regeneration of sensory fibers remained largely unchanged. Our results support the concept that in a growth non-permissive environment, the regenerative capacity of sensory and motor axons is differentially affected by the RhoA/ROCK pathway, with motor neurons being more responsive compared to sensory. Future treatments, that are aimed to modulate RhoA activity, should consider this functional diversity.

Sural sparing pattern discriminates Guillain-Barré syndrome from its mimics

INTRODUCTION

Electrodiagnostic features of demyelination are essential for establishing the diagnosis in demyelinating subtypes of Guillain-Barré syndrome (GBS), but they may also occur in disorders that mimic GBS clinically. Information about their frequency in GBS mimics is sparse.

METHODS

Evaluation of electrodiagnostic features from 38 patients with suspected GBS in whom the diagnosis was later refuted (GBS mimics). Their diagnostic accuracy was analyzed by comparison with nerve conduction studies (NCS) from 73 confirmed GBS patients.

RESULTS

Disorders that mimicked GBS clinically at the time of hospital admission included other inflammatory, metabolic, toxic, or infectious neuropathies and spinal cord disorders. The sural sparing pattern was the most specific electrodiagnostic feature for demyelinating GBS.

CONCLUSIONS

Common electrodiagnostic abnormalities in early demyelinating GBS do not usually exclude other rare differential diagnoses. An exception to this is the sural sparing pattern described here, which strongly supports the diagnosis of demyelinating GBS.

Fcγ receptor-mediated inflammation inhibits axon regeneration

Anti-glycan/ganglioside antibodies are the most common immune effectors found in patients with Guillain-Barré Syndrome, which is a peripheral autoimmune neuropathy. We previously reported that disease-relevant anti-glycan autoantibodies inhibited axon regeneration, which echo the clinical association of these antibodies and poor recovery in Guillain-Barré Syndrome. However, the specific molecular and cellular elements involved in this antibody-mediated inhibition of axon regeneration are not previously defined. This study examined the role of Fcγ receptors and macrophages in the antibody-mediated inhibition of axon regeneration. A well characterized antibody passive transfer sciatic nerve crush and transplant models were used to study the anti-ganglioside antibody-mediated inhibition of axon regeneration in wild type and various mutant and transgenic mice with altered expression of specific Fcγ receptors and macrophage/microglia populations. Outcome measures included behavior, electrophysiology, morphometry, immunocytochemistry, quantitative real-time PCR, and western blotting. We demonstrate that the presence of autoantibodies, directed against neuronal/axonal cell surface gangliosides, in the injured mammalian peripheral nerves switch the proregenerative inflammatory environment to growth inhibitory milieu by engaging specific activating Fcγ receptors on recruited monocyte-derived macrophages to cause severe inhibition of axon regeneration. Our data demonstrate that the antibody orchestrated Fcγ receptor-mediated switch in inflammation is one mechanism underlying inhibition of axon regeneration. These findings have clinical implications for nerve repair and recovery in antibody-mediated immune neuropathies. Our results add to the complexity of axon regeneration in injured peripheral and central nervous systems as adverse effects of B cells and autoantibodies on neural injury and repair are increasingly recognized.

Axonal degeneration in dorsal columns of spinal cord does not induce recruitment of hematogenous macrophages

It is generally accepted that there are two populations of macrophages that respond to neural injuries and successful recruitment of hematogenous macrophages has been shown to help the process of nerve repair in the peripheral nervous system (PNS). Meanwhile, the recruitment of circulating macrophages after central nerve system (CNS) injuries is considered mild and delayed. We compared the recruitment of circulating macrophages in the peripheral nerves and spinal cord after dorsal root ganglionectomies, which induce selective and approximately similar extent of sensory fiber degeneration in PNS and CNS, in bone marrow chimeric mice. Our results showed that circulating macrophages were efficiently recruited in PNS but virtually no recruitment in CNS despite degeneration of peripheral and central sensory projections emanating from the same dorsal root ganglion (DRG) neurons. The mechanisms that prevent recruitment of circulating macrophages in CNS after injury remain poorly elucidated.