Long-lasting treatment effect of rituximab in MuSK myasthenia

Immunotherapy in myasthenia gravis in the era of biologics

No consensus has been reached on the ideal therapeutic algorithm for myasthenia gravis (MG). Most patients with MG require induction therapy with high doses of corticosteroids and maintenance with an immunosuppressant. Severe cases and acute worsening require intravenous immunoglobulin or plasmapheresis before oral immunosuppressants start having an effect. However, biologics are emerging as important therapeutic tools that promise to provide better corticosteroid sparing effects than standard treatments and can even induce remission. In particular, eculizumab, a monoclonal antibody against complement C5, has been approved by the FDA for refractory MG on the basis of a phase III trial. Rituximab, an anti-CD20 monoclonal antibody that depletes peripheral B cells, has also been effective in many large uncontrolled series, although was not in a small phase III trial. Whether the newer anti-CD20 agents ocrelizumab, ofatumumab, obinutuzumab, ublituximab or inebilizumab will be more effective remains unclear. Belimumab, an antibody against the B cell trophic factor BAFF, was ineffective in phase III trials, and efgartigimod, which depletes antibodies, was effective in a phase II study. Some anti-cytokine agents relevant to MG immunopathogenesis also seem promising. Checkpoint inhibitors can trigger MG in some patients, necessitating early intervention. Increased availability of new biologics provides targeted immunotherapies and the opportunities to develop more specific therapies.

Associations between HLA and autoimmune neurological diseases with autoantibodies

Recently, several autoimmune neurological diseases have been defined by the presence of autoantibodies against different antigens of the nervous system. These autoantibodies have been demonstrated to be specific and useful biomarkers, and most of them are also pathogenic. These aspects have increased the value of autoantibodies in neurological practice, as they enable to establish more accurate diagnosis and to better understand the underlying mechanisms of the autoimmune neurological diseases when they are compared to those lacking them. Nevertheless, the exact mechanisms leading to the autoimmune response are still obscure. Genetic predisposition is likely to play a role in autoimmunity, HLA being the most reported genetic factor. Herein, we review the current knowledge about associations between HLA and autoimmune neurological diseases with autoantibodies. We report the main alleles and haplotypes, and discuss the clinical and pathogenic implications of these findings.

Differential response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients: a single-center retrospective study

BACKGROUND

B-cell targeted therapy with rituximab has shown durable response in treating refractory myasthenia gravis (MG). This study compares the response to rituximab between patients with acetylcholine receptor autoantibody positive (AChR+) and muscle-specific kinase autoantibody positive (MuSK+) MG.

METHODS

This retrospective study included 33 patients with either AChR+ or MuSK+ MG who were treated with rituximab from 05/31/2003 to 05/31/2017. Pretreatment and post-treatment immunotherapy regimens, clinical symptoms, and examination findings were evaluated.

RESULTS

Median MGFA Class of II at baseline improved to an asymptomatic median classification at 12-months and last follow-up (p-values <.001) post-rituximab. Improvement in MGFA class was not significantly different between the groups. Twenty-one patients achieved clinical remission (12/17 AChR+, 9/16 MuSK+) with time to remission of 441.4 ± 336.6 days for AChR+ versus 230 ± 180.8 days for MuSK+ patients (p-value 0.049). The mean prednisone dosage requirement decreased significantly in both groups post-rituximab. AChR+ patients required more hospitalizations for exacerbation post-rituximab (p-value 0.046).

CONCLUSION

Rituximab treatment response is observed in both AChR+ and MuSK+ patients supporting the role of B cell depletion in the management of MG. While there was no significant difference between these groups in terms of clinical improvement, symptom-free state, and prednisone burden, MuSK+ MG patients may experience greater benefits, including earlier time to remission, fewer exacerbations and hospitalizations post-treatment.

Maintenance immunosuppression in myasthenia gravis, an update

Therapies for myasthenia gravis (MG) include symptomatic and immunosuppressive/immunomodulatory treatment. Options for immunosuppression include corticosteroids, azathioprine, mycophenolate mofetil, cyclosporine, tacrolimus, methotrexate, rituximab, cyclophosphamide, eculizumab, intravenous immunoglobulin, subcutaneous immunoglobulin, plasmapheresis, and thymectomy. The practical aspects of long-term immunosuppressive therapy in MG are critically reviewed in this article. Application of one or more of these specific therapies is guided based on known efficacy, adverse effect profile, particular disease subtype and severity, and patient co-morbidities.

Robotic-Extended Rethymectomy for Refractory Myasthenia Gravis: A Case Series

To assess the safety and efficacy of robotic-extended rethymectomy in selected refractory myasthenia gravis (MG) patients with suspected residual thymic tissue. Robotic-extended rethymectomy was performed in 6 MG patients with seropositive acetylcholine receptors (AChR) antibody who had undergone a previous thymectomy (1 cervicotomy, 2 video-assisted thoracoscopic surgeries, and 3 sternotomies). The median observation time before robotic rethymectomy was 108 (24-171) months. The main outcomes were perioperative morbidity, mortality, conversion to open surgery, and clinical outcomes according to the Myasthenia Gravis Foundation of America Post-Intervention Status (MGFA-PIS). Before rethymectomy, all patients required immunosuppressants and 5 patients (83.3%) required intravenous immune globulin and/or plasma exchange to control the symptoms. The median specimen weight was 24.5 (14-144) g after rethymectomy, and residual thymic tissue was found in 5 patients (83.3%). No conversion to open surgery or perioperative morbidity and mortality was observed. With a median follow-up time of 46.5 (13-155) months, 3 patients (50%) achieved "improved" and 3 (50%) were "unchanged" according to the MGFA-PIS. Compared with preoperative use, the median daily dose of corticosteroids statistically decreased (25 [7.5-60] vs 0 [0-5] mg, P = 0.002) without significant change in azathioprine use (100 [0-200] vs 50 [0-150] mg, P = 0.360). AChR antibody positive MG patients with a treatment refractory long-term course after thymectomy might have remaining thymic tissue with the 2 commonly associated thymus pathologies, thymoma, and follicular hyperplasia. Robotic-extended rethymectomy might be considered as a safe and beneficial treatment option in these patients.

Therapies Directed Against B-Cells and Downstream Effectors in Generalized Autoimmune Myasthenia Gravis: Current Status

Myasthenia gravis is a rare, heterogeneous, classical autoimmune disease characterized by fatigable skeletal muscle weakness, which is directly mediated by autoantibodies targeting various components of the neuromuscular junction, including the acetylcholine receptor, muscle specific tyrosine kinase, and lipoprotein-related protein 4. Subgrouping of myasthenia gravis is dependent on the age of onset, pattern of clinical weakness, autoantibody detected, type of thymic pathology, and response to immunotherapy. Generalized immunosuppressive therapies are effective in all subgroups of myasthenia gravis; however, approximately 15% remain refractory and more effective treatments with improved safety profiles are needed. In recent years, successful utilization of targeted B-cell therapies in this disease has triggered renewed focus in unraveling the underlying immunopathology in attempts to identify newer therapeutic targets. While myasthenia gravis is predominantly B-cell mediated, T cells, T cell-B cell interactions, and B-cell-related factors are increasingly recognized to play key roles in its immunopathology, particularly in autoantibody production, and novel therapies have focused on targeting these specific immune system components. This overview describes the current understanding of myasthenia gravis immunopathology before discussing B-cell-related therapies, their therapeutic targets, and the rationale and evidence for their use. Several prospective studies demonstrated efficacy of rituximab in various myasthenia gravis subtypes, particularly that characterized by antibodies against muscle-specific tyrosine kinase. However, a recent randomized control trial in patients with acetylcholine receptor antibodies was negative. Eculizumab, a complement inhibitor, has recently gained regulatory approval for myasthenia gravis based on a phase III trial that narrowly missed its primary endpoint while achieving robust results in all secondary endpoints. Zilucoplan is a subcutaneously administered terminal complement inhibitor that recently demonstrated significant improvements in functional outcome measures in a phase II trial. Rozanolixizumab, CFZ533, belimumab, and bortezomib are B-cell-related therapies that are in the early stages of evaluation in treating myasthenia gravis. The rarity of myasthenia gravis, heterogeneity in its clinical manifestations, and variability in immunosuppressive regimens are challenges to conducting successful trials. Nonetheless, these are promising times for myasthenia gravis, as renewed research efforts provide novel insights into its immunopathology, allowing for development of targeted therapies with increased efficacy and safety.

Repeated low-dose rituximab treatment based on the assessment of circulating B cells in patients with refractory myasthenia gravis

Background:

The objective of this study was to evaluate the efficacy and safety of repeated low-dose rituximab treatment guided by monitoring circulating CD19+ B cells in patients with refractory myasthenia gravis (MG).

Methods:

Patients with refractory MG who had received rituximab treatment at two teaching hospitals between September 2013 and January 2017 were reviewed retrospectively. The treatment protocol consisted of an induction treatment with low-dose rituximab (375 mg/m² twice with a 2-week interval), followed by retreatment (375 mg/m² once). Retreatment was based on either circulating CD19+ B-cell repopulation or clinical relapse. Outcome measures included the MG Foundation of America (MGFA) clinical classification and postintervention status, prednisolone dose, CD19+ B-cell counts, clinical relapse, and adverse effects.

Results:

Of 17 patients, 11 (65%) achieved the primary endpoint, defined as the minimal manifestation or better status with prednisolone ⩽5 mg/day, after median 7.6 months (range, 2–17 months) following rituximab treatment. Over a median follow up of 24 months (range, 7–49 months), a total of 30 retreatments were undertaken due to clinical relapse without B-cell repopulation (n = 6), on the basis of B-cell repopulation alone (n = 16) and both (n = 8). B-cell recovery appeared to be in parallel with clinical relapse on the group level, although the individual-level association appeared to be modest, with B-cell repopulation observed only at 57% (8/14) of clinical relapses.

Conclusions:

The repeated low-dose rituximab treatment based on the assessment of circulating B-cell depletion could be a cost-effective therapeutic option for refractory MG. Further studies are needed to verify the potentially better cost-effectiveness of low-dose rituximab, and to identify biomarkers that help optimize treatment in MG patients.

Systematic Review of Safety and Efficacy of Rituximab in Treating Immune-Mediated Disorders

Background: During the past years biologic agents (also termed biologicals or biologics) have become a crucial treatment option in immunological diseases. Numerous articles have been published on biologicals, which complicates the decision making process on the use of the most appropriate biologic for a given immune-mediated disease. This systematic review is the first of a series of articles assessing the safety and efficacy of B cell-targeting biologics for the treatment of immune-mediated diseases.

Objective: To evaluate rituximab's safety and efficacy for the treatment of immune-mediated disorders compared to placebo, conventional treatment, or other biologics.

Methods: The PRISMA checklist guided the reporting of the data. We searched the PubMed database between 4 October 2016 and 26 July 2018 concentrating on immune-mediated disorders.

Results: The literature search identified 19,665 articles. After screening titles and abstracts against the inclusion and exclusion criteria and assessing full texts, 105 articles were finally included in a narrative synthesis.

Conclusions: Rituximab is both safe and effective for the treatment of acquired angioedema with C1-inhibitor deficiency, ANCA-associated vasculitis, autoimmune hemolytic anemia, Behçet's disease, bullous pemphigoid, Castleman's disease, cryoglobulinemia, Goodpasture's disease, IgG4-related disease, immune thrombocytopenia, juvenile idiopathic arthritis, relapsing-remitting multiple sclerosis, myasthenia gravis, nephrotic syndrome, neuromyelitis optica, pemphigus, rheumatoid arthritis, spondyloarthropathy, and systemic sclerosis. Conversely, rituximab failed to show an effect for antiphospholipid syndrome, autoimmune hepatitis, IgA nephropathy, inflammatory myositis, primary-progressive multiple sclerosis, systemic lupus erythematosus, and ulcerative colitis. Finally, mixed results were reported for membranous nephropathy, primary Sjögren's syndrome and Graves' disease, therefore warranting better quality trials with larger patient numbers.

Treatment of Myasthenia Gravis

With specialized care, patients with myasthenia gravis can have very good outcomes. The mainstays of treatment are acetylcholinesterase inhibitors, and immunosuppressive and immunomodulatory therapies. There is good evidence thymectomy is beneficial in thymomatous and nonthymomatous disease. Nearly all of the drugs used for MG are considered "off-label." The 2 exceptions are acetylcholinesterase inhibitors and complement inhibition with eculizumab, which was recently approved by the US Food and Drug Administration for myasthenia gravis. This article reviews the evidence base and provides a framework for the treatment of myasthenia gravis, highlighting recent additions to the literature.

Recent Advances and Therapeutic Options in Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton Myasthenic Syndrome (LEMS) is an autoimmune-mediated neurological disorder that manifests as muscle fatigue, diminished tendon reflexes, with symptoms of cholinergic overactivity. It can be associated with certain neoplastic conditions, the most common being small cell lung carcinoma (SCLC). The basic pathophysiology involved is antibody-mediated targeting of voltage-gated calcium channels (VGCC), which decreases the release of acetylcholine in the synaptic junction. Multiple treatment options have been introduced in the past and, recently, a new drug, amifampridine, has been approved by the Food and Drug Administration (FDA) for the treatment of weakness associated with these patients. We summarize this newly introduced drug with a brief description of other treatment options available.

Critical Care of Neuromuscular Disorders

PURPOSE OF REVIEW

Weakness is a common reason patients are seen in neurologic consultation. This article reviews the differential diagnosis of neuromuscular disorders in the intensive care unit (ICU), discusses the intensive care needs and evaluation of respiratory failure in patients with neuromuscular disorders, and provides a practical guide for management.

RECENT FINDINGS

Although primary neuromuscular disorders used to be the most common cause for weakness from peripheral nervous system disease in the ICU, a shift toward ICU-acquired weakness is observed in today's clinical practice. Therefore, determining the cause of weakness is important and may have significant prognostic implications. Guillain-Barré syndrome and myasthenia gravis remain the most common primary neuromuscular disorders in the ICU. In patients with myasthenia gravis, it is important to be vigilant with the airway and institute noninvasive ventilation early in the course of the disease to attempt to avoid the need for intubation. On the other hand, patients with Guillain-Barré syndrome should be intubated without delay if the airway is at risk to avoid further complications. In patients with ICU-acquired weakness, failure to wean from the ventilator is usually the challenge. Early mobility, glucose control, minimizing sedation, and avoiding neuromuscular blocking agents remain the only therapeutic regimen available for ICU-acquired weakness.

SUMMARY

Critical care management of neuromuscular disorders requires a multidisciplinary approach engaging members of the ICU and consultative teams. Developing an airway management protocol could have implications on outcome and length of stay for patients with neuromuscular disorders in the ICU. Tending to the appropriate nuances of each patient who is critically ill with a neuromuscular disorder through evidence-based medicine can also have implications on length of stay and outcome.

Myasthenia Gravis: Pathogenic Effects of Autoantibodies on Neuromuscular Architecture

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction (NMJ). Autoantibodies target key molecules at the NMJ, such as the nicotinic acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and low-density lipoprotein receptor-related protein 4 (Lrp4), that lead by a range of different pathogenic mechanisms to altered tissue architecture and reduced densities or functionality of AChRs, reduced neuromuscular transmission, and therefore a severe fatigable skeletal muscle weakness. In this review, we give an overview of the history and clinical aspects of MG, with a focus on the structure and function of myasthenic autoantigens at the NMJ and how they are affected by the autoantibodies' pathogenic mechanisms. Furthermore, we give a short overview of the cells that are implicated in the production of the autoantibodies and briefly discuss diagnostic challenges and treatment strategies.

Characterization of pathogenic monoclonal autoantibodies derived from muscle-specific kinase myasthenia gravis patients

Myasthenia gravis (MG) is a chronic autoimmune disorder characterized by muscle weakness and caused by pathogenic autoantibodies that bind to membrane proteins at the neuromuscular junction. Most patients have autoantibodies against the acetylcholine receptor (AChR), but a subset of patients have autoantibodies against muscle-specific tyrosine kinase (MuSK) instead. MuSK is an essential component of the pathway responsible for synaptic differentiation, which is activated by nerve-released agrin. Through binding MuSK, serum-derived autoantibodies inhibit agrin-induced MuSK autophosphorylation, impair clustering of AChRs, and block neuromuscular transmission. We sought to establish individual MuSK autoantibody clones so that the autoimmune mechanisms could be better understood. We isolated MuSK autoantibody-expressing B cells from 6 MuSK MG patients using a fluorescently tagged MuSK antigen multimer, then generated a panel of human monoclonal autoantibodies (mAbs) from these cells. Here we focused on 3 highly specific mAbs that bound quantitatively to MuSK in solution, to MuSK-expressing HEK cells, and at mouse neuromuscular junctions, where they colocalized with AChRs. These 3 IgG isotype mAbs (2 IgG4 and 1 IgG3 subclass) recognized the Ig-like domain 2 of MuSK. The mAbs inhibited AChR clustering, but intriguingly, they enhanced rather than inhibited MuSK phosphorylation, which suggests an alternative mechanism for inhibiting AChR clustering.

A fluorescent tetrameric antigen allows isolation of human myasthenia gravis monoclonal antibodies that interrupt acetylcholine receptor signaling.

Role of Multivalency and Antigenic Threshold in Generating Protective Antibody Responses

Vaccines play a vital role in protecting our communities against infectious disease. Unfortunately, some vaccines provide only partial protection or in some cases vaccine-mediated immunity may wane rapidly, resulting in either increased susceptibility to that disease or a requirement for more booster vaccinations in order to maintain immunity above a protective level. The durability of antibody responses after infection or vaccination appears to be intrinsically determined by the structural biology of the antigen, with multivalent protein antigens often providing more long-lived immunity than monovalent antigens. This forms the basis for the Imprinted Lifespan model describing the differential survival of long-lived plasma cell populations. There are, however, exceptions to this rule with examples of highly attenuated live virus vaccines that are rapidly cleared and elicit only short-lived immunity despite the expression of multivalent surface epitopes. These exceptions have led to the concept that multivalency alone may not reliably determine the duration of protective humoral immune responses unless a minimum number of long-lived plasma cells are generated by reaching an appropriate antigenic threshold of B cell stimulation. Examples of long-term and in some cases, potentially lifelong antibody responses following immunization against human papilloma virus (HPV), Japanese encephalitis virus (JEV), Hepatitis B virus (HBV), and Hepatitis A virus (HAV) provide several lessons in understanding durable serological memory in human subjects. Moreover, studies involving influenza vaccination provide the unique opportunity to compare the durability of hemagglutinin (HA)-specific antibody titers mounted in response to antigenically repetitive whole virus (i.e., multivalent HA), or detergent-disrupted “split” virus, in comparison to the long-term immune responses induced by natural influenza infection. Here, we discuss the underlying mechanisms that may be associated with the induction of protective immunity by long-lived plasma cells and their importance in future vaccine design.

Myasthenia gravis: from autoantibodies to therapy

PURPOSE OF REVIEW

The current article reviews the recent advances in the field of myasthenia gravis, which span from autoantibody profiling and pathogenic mechanisms to therapy innovation. The overview is highlighting specifically the data and the needs of targeted treatments in the light of precision medicine in myasthenia gravis.

RECENT FINDINGS

Novel data published recently further increased our knowledge on myasthenia gravis. The use of cell-based assays has greatly improved autoantibody detection in myasthenia gravis patients, and the mechanisms of action of these antibodies have been described. The role of Toll-like receptor activation in the generation of thymic alterations and anti-acetylcholine receptor autosensitization has been further investigated implementing our understanding on the relationships between innate immunity and autoimmunity. Additional studies have been focused on the alterations of T-cell/B-cell regulatory mechanisms in thymus and peripheral blood of myasthenia gravis patients. microRNAs and genetic factors are also emerging as key biomarkers in myasthenia gravis pathogenesis and prediction of drug efficacy in individual patients.

SUMMARY

The recent immunological and pathological findings in myasthenia gravis promise to improve myasthenia gravis treatment, via the development of more precise and personalized therapies.

A Neurologist's Perspective on Understanding Myasthenia Gravis: Clinical Perspectives of Etiologic Factors, Diagnosis, and Preoperative Treatment

Myasthenia gravis (MG) is a disease of neuromuscular transmission caused by antibodies directed toward proteins concentrated at the neuromuscular junction. Mild to life-threatening weakness varies in severity over time and with level of activity. Therefore, clinical diagnosis is often challenging. MG may be categorized by autoantibody type, thymic pathologic condition, and age of onset. Treatments are tailored for each group. A key management concern is severe exacerbation of weakness resulting from infections or exposure to certain medications, including antibiotics, which may be severe enough to produce respiratory decompensation. The article reviews key diagnostic issues and treatment options.

Efgartigimod improves muscle weakness in a mouse model for muscle-specific kinase myasthenia gravis

Myasthenia gravis is hallmarked by fatigable muscle weakness resulting from neuromuscular synapse dysfunction caused by IgG autoantibodies. The variant with muscle-specific kinase (MuSK) autoantibodies is characterized by prominent cranial and bulbar weakness and a high frequency of respiratory crises. The majority of MuSK MG patients requires long-term immunosuppressive treatment, but the result of these treatments is considered less satisfactory than in MG with acetylcholine receptor antibodies. Emergency treatments are more frequently needed, and many patients develop permanent facial weakness and nasal speech. Therefore, new treatment options would be welcome. The neonatal Fc receptor protects IgG from lysosomal breakdown, thus prolonging IgG serum half-life. Neonatal Fc receptor antagonism lowers serum IgG levels and thus may act therapeutically in autoantibody-mediated disorders. In MuSK MG, IgG4 anti-MuSK titres closely correlate with disease severity. We therefore tested efgartigimod (ARGX-113), a new neonatal Fc receptor blocker, in a mouse model for MuSK myasthenia gravis. This model involves 11 daily injections of purified IgG4 from MuSK myasthenia gravis patients, resulting in overt myasthenic muscle weakness and, consequently, body weight loss. Daily treatment with 0.5 mg efgartigimod, starting at the fifth passive transfer day, reduced the human IgG4 titres about 8-fold, despite continued daily injection. In muscle strength and fatigability tests, efgartigimod-treated myasthenic mice outperformed control myasthenic mice. Electromyography in calf muscles at endpoint demonstrated less myasthenic decrement of compound muscle action potentials in efgartigimod-treated mice. These substantial in vivo improvements of efgartigimod-treated MuSK MG mice following a limited drug exposure period were paralleled by a tendency of recovery at neuromuscular synaptic level (in various muscles), as demonstrated by ex vivo functional studies. These synaptic improvements may well become more explicit upon longer drug exposure. In conclusion, our study shows that efgartigimod has clear therapeutic potential in MuSK myasthenia gravis and forms an exciting candidate drug for many autoantibody-mediated neurological and other disorders.

Rituximab in neurological disease: principles, evidence and practice

Rituximab is a widely used B-cell-depleting monoclonal antibody. It is unlicensed for use in neurological disorders and there are no treatment guidelines. However, as a rapidly acting, targeted therapy with growing evidence of efficacy and tolerability in several neuroinflammatory disorders, it is an attractive alternative to conventional immunomodulatory medications. This practical review aims to explain the basic principles of B-cell depletion with therapeutic monoclonal antibodies. We present the evidence for using rituximab in neurological diseases, and describe the practical aspects of prescribing, including dosing, monitoring, safety, treatment failure and its use in special circumstances such as coexisting viral hepatitis, pregnancy and lactation. We provide an administration guide, checklist and patient information leaflet, which can be adapted for local use. Finally, we review the safety data of rituximab and ocrelizumab (a newer and recently licensed B-cell-depleting therapy for multiple sclerosis) and suggest monitoring and risk reduction strategies.

Longstanding and Refractory Anti-Muscle Specific Tyrosine Kinase Antibody-Associated Myasthenia Gravis (Anti-MuSK-MG) in a Child Successfully Treated with Rituximab

Anti-muscle specific tyrosine kinase antibody-associated myasthenia gravis (MuSK-MG) is a rare subtype of MG characterized by more frequent relapses and a clinical course that is refractory to standard treatments. Rituximab, a monoclonal antibody targeting CD20+ B cells, has been used effectively in the adult population to achieve stable remission. We describe a pediatric patient with MuSK-MG who demonstrated an excellent response to rituximab after failing standard therapy.

MuSK (Muscle Specific Kinase) Positive Myasthenia: Grave Prognosis or Undue Prejudice?

Objectives

Patients with muscle-specific kinase (MuSK)-positive myasthenia are generally considered to have a grave prognosis. We present our experience of patients with myasthenia with different antibody status. This is followed by a short discourse on previous studies and the current view on MuSK-positive myasthenia, focusing on the associated prejudice.

Materials and Methods

This study compares 23 patients with MuSK-positive myasthenia with 55 patients with acetylcholine receptor-positive myasthenia and 9 patients with double-seronegative myasthenia at a tertiary level center.

Results

We did not find any significant difference in terms of clinical characteristics, treatment response to immunosuppressants, long-term prognosis, and quality of life.

Conclusion

Seropositivity for antibodies should not be used in isolation to guide the management or predict the prognosis. Undue negative prognostication may affect the morale of patient. Clinical features and response to therapy in addition to antibody status must be considered before planning therapy.

Intensive Care Management of the Neuromuscular Patient

Neuromuscular emergencies are a distinct group of acute neurological diseases with distinct characteristic presentations. Patients who suffer from this group of diseases are at immediate risk of losing protection of their native airway as well as aspirating orogastric contents. This is secondary to weakness of the muscles of the oropharynx and respiratory muscles. Although some neuromuscular emergencies such as myasthenia gravis or Guillain-Barré syndrome are well understood, others such as critical illness myopathy and neuropathy are less well characterized. In this chapter, we have discussed the pathophysiology, diagnostic evaluation, and management options in patients who are admitted to the intensive care unit. We have also emphasized the importance of a thorough understanding of the use of pharmacological anesthetic agents in this patient population.

Tacrolimus inhibits Th1 and Th17 responses in MuSK-antibody positive myasthenia gravis patients

Muscle specific tyrosine kinase antibody positive myasthenia gravis (MuSK- MG) is characterized by autoantibodies against the MuSK protein of the neuromuscular junction resulting in weakness of bulbar and proximal muscles. We previously demonstrated that patients with MuSK-MG have increased pro-inflammatory Th1 and Th17 responses. Tacrolimus, an immunosuppressant used in AChR-MG and transplantation patients, inhibits T cell responses through interference with IL-2 transcription. The therapeutic efficacy and immunological effect of tacrolimus in MuSK-MG is unclear. In the current study we examined the proliferation, phenotype and cytokine production of CD4+ and CD8+ T cells in peripheral blood mononuclear cells of MuSK-MG following a 3-day in vitro culture with or without tacrolimus. We determined that tacrolimus profoundly suppressed CD4 and CD8 T cell proliferation and significantly suppressed Th1 and Th17 responses, as demonstrated by a reduced frequency of IFN-γ, IL-2, and IL-17 producing CD4 T cells and reduced frequencies of IFN-γ and IL-2 producing CD8 T cells. Tacrolimus also inhibits pathogenic Th17 cells coproducing IL-17 and IFN-γ. In addition, tacrolimus suppressed follicular T helper cell (Tfh) and regulatory T helper cell (Treg) subsets. These findings provide preliminary support for tacrolimus as a potential alternative immunosuppressive therapy for MuSK-MG.

Advances in autoimmune myasthenia gravis management

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder with no cure and conventional treatments limited by significant adverse effects and variable benefit. In the last decade, therapeutic development has expanded based on improved understanding of autoimmunity and financial incentives for drug development in rare disease. Clinical subtypes exist based on age, gender, thymic pathology, autoantibody profile, and other poorly defined factors, such as genetics, complicate development of specific therapies. Areas covered: Clinical presentation and pathology vary considerably among patients with some having weakness limited to the ocular muscles and others having profound generalized weakness leading to respiratory insufficiency. MG is an antibody-mediated disorder dependent on autoreactive B cells which require T-cell support. Treatments focus on elimination of circulating autoantibodies or inhibition of effector mechanisms by a broad spectrum of approaches from plasmapheresis to B-cell elimination to complement inhibition. Expert commentary: Standard therapies and those under development are disease modifying and not curative. As a rare disease, clinical trials are challenged in patient recruitment. The great interest in development of treatments specific for MG is welcome, but decisions will need to be made to focus on those that offer significant benefits to patients.

Anti-MuSK Antibody-positive Myasthenia Gravis Successfully Treated with Outpatient Periodic Weekly Blood Purification Therapy

A 37-year-old man with anti-muscle-specific tyrosine kinase (MuSK) antibody-positive myasthenia gravis (MG) presented with subacute progressive dysphagia and muscle weakness of the neck and bilateral upper extremities. Conventional immune-suppressive treatments and high-dose intravenous immunoglobulin were ineffective. He then displayed repeated exacerbations and remissions over the course of two years, despite two to four sessions of plasma exchange (PE) every two months. The patient was successfully treated with outpatient periodic weekly blood purification therapy with alternative PE and double-filtration plasmapheresis using an internal shunt. This case report suggests the benefits of blood purification therapy with an internal shunt against anti-MuSK antibody-positive MG.

Autoantibodies Against the Node of Ranvier in Seropositive Chronic Inflammatory Demyelinating Polyneuropathy: Diagnostic, Pathogenic, and Therapeutic Relevance

Discovery of disease-associated autoantibodies has transformed the clinical management of a variety of neurological disorders. Detection of autoantibodies aids diagnosis and allows patient stratification resulting in treatment optimization. In the last years, a set of autoantibodies against proteins located at the node of Ranvier has been identified in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). These antibodies target neurofascin, contactin1, or contactin-associated protein 1, and we propose to name CIDP patients with these antibodies collectively as seropositive. They have unique clinical characteristics that differ from seronegative CIDP. Moreover, there is compelling evidence that autoantibodies are relevant for the pathogenesis. In this article, we review the current knowledge on the characteristics of autoantibodies against the node of Ranvier proteins and their clinical relevance in CIDP. We start with a description of the structure of the node of Ranvier followed by a summary of assays used to identify seropositive patients; and then, we describe clinical features and characteristics linked to seropositivity. We review knowledge on the role of these autoantibodies for the pathogenesis with relevance for the emerging concept of nodopathy/paranodopathy and summarize the treatment implications.

The impact of rituximab infusion protocol on the long-term outcome in anti-MuSK myasthenia gravis

Objective

To evaluate whether the clinical benefit and relapse rates in anti‐muscle‐specific kinase (MuSK) myasthenia gravis (MG) differ depending on the protocol of rituximab followed.

Methods

This retrospective multicentre study in patients with MuSK MG compared three rituximab protocols in terms of clinical status, relapse, changes in treatment, and adverse side effects. The primary effectiveness endpoint was clinical relapse requiring a further infusion of rituximab. Survival curves were estimated using Kaplan–Meier methods and survival analyses were undertaken using Cox proportional‐hazards models.

Results

Twenty‐five patients were included: 11 treated with protocol 4 + 2 (375 mg/m²/4 weeks, then monthly for 2 months), five treated with protocol 1 + 1 (two 1 g doses 2 weeks apart), and nine treated with protocol 4 (375 mg/m²/4 weeks). Mean follow‐up was 5.0 years (SD 3.3). Relapse occurred in 18.2%, 80%, and 33.3%, and mean time to relapse was 3.5 (SD 1.5), 1.1 (SD 0.4), and 2.5 (SD 1.4) years, respectively. Based on Kaplan–Meier estimates, patients treated with protocol 4 + 2 had fewer and later relapses than patients treated with the other two protocols (log‐rank test P = 0.0001). Patients treated with protocol 1 + 1 had a higher risk of relapse than patients treated with protocol 4 + 2 (HR 112.8, 95% CI, 5.7–2250.4, P = 0.002). Patients treated with protocol 4 showed a trend to a higher risk of relapse than those treated with protocol 4 + 2 (HR 9.2, 95% CI 0.9–91.8, P = 0.059).

Interpretation

This study provides class IV evidence that the 4 + 2 rituximab protocol has a lower clinical relapse rate and produces a more durable response than the 1 + 1 and 4 protocols in patients with MuSK MG.

Serological Immunoglobulin-Free Light Chain Profile in Myasthenia Gravis Patients

Background

Serological levels of free immunoglobulin light chains (FLCs), produced in excess of heavy chains during synthesis of immunoglobulins by plasma cells, can be considered a direct marker of B cell activity in different systemic inflammatory-autoimmune conditions and may represent a useful predictor of rituximab (RTX) therapeutic efficacy, as reported for rheumatoid arthritis and systemic lupus erythematosus. Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction with antibodies (abs) targeting the acetylcholine receptor (AChR) or the muscle-specific tyrosine kinase (MuSK), inducing muscle weakness and excessive fatigability. As MG course may be remarkably variable, we evaluated the possible use of FLCs as biomarkers of disease activity.

Subjects and Methods

We assessed FLC levels in 34 sera from 17 AChR-MG and from 13 MuSK-MG patients, in comparison with 20 sera from patients with systemic autoimmune rheumatic diseases and 18 from healthy blood donors, along with titers of specific auto-abs and IgG subclass distribution.

Results

We found a statistically significant increase in free κ chains in both AChR- and MuSK-MG patients, while free λ chain levels were increased only in AChR-MG. We also observed a significant reduction of both free κ and λ chains in 1/4 MuSK-MG patients along with specific abs titer, two months after RTX treatment.

Conclusions

From our data, FLCs appear to be a sensitive marker of B cell activation in MG. Further investigations are necessary to exploit their potential as reliable biomarkers of disease activity.

Randomized study of adjunctive belimumab in participants with generalized myasthenia gravis

Objective

To investigate the efficacy and safety of belimumab, a fully human immunoglobulin G1λ monoclonal antibody against B-lymphocyte stimulator, in participants with generalized myasthenia gravis (MG) who remained symptomatic despite standard of care (SoC) therapy.

Methods

Eligible participants with MG were randomized 1:1 to receive IV belimumab 10 mg/kg or placebo in this phase II, placebo-controlled, multicenter, double-blind study (NCT01480596; BEL115123). Participants received SoC therapies throughout the 24-week treatment phase and 12-week follow-up period. The primary efficacy endpoint was mean change from baseline in the Quantitative Myasthenia Gravis (QMG) scale at week 24; safety assessments included the frequency and severity of adverse events (AEs) and serious AEs.

Results

Forty participants were randomized (placebo n = 22; belimumab n = 18). The mean change in QMG score from baseline at week 24 was not significantly different for belimumab vs placebo (p = 0.256). There were no statistically significant differences between treatment groups for secondary endpoints, including the MG Composite and MG–Activity of Daily Living scores. Acetylcholine receptor antibody levels decreased over time in both treatment groups. No unexpected AEs were identified and occurrence was similar in the belimumab (78%) and placebo (91%) groups. One participant receiving placebo died (severe sepsis) during the treatment phase.

Conclusions

The primary endpoint was not met for belimumab in participants with generalized MG receiving SoC. There was no significant difference in mean change in the QMG score at week 24 for belimumab vs placebo. The safety profile of belimumab was consistent with previous systemic lupus erythematosus studies.

Classification of evidence

This study provides Class I evidence that for participants with generalized MG, belimumab did not significantly improve QMG score compared with placebo.

A New Classification System for IgG4 Autoantibodies

IgG4 autoimmune diseases are characterized by the presence of antigen-specific autoantibodies of the IgG4 subclass and contain well-characterized diseases such as muscle-specific kinase myasthenia gravis, pemphigus, and thrombotic thrombocytopenic purpura. In recent years, several new diseases were identified, and by now 14 antigens targeted by IgG4 autoantibodies have been described. The IgG4 subclass is considered immunologically inert and functionally monovalent due to structural differences compared to other IgG subclasses. IgG4 usually arises after chronic exposure to antigen and competes with other antibody species, thus "blocking" their pathogenic effector mechanisms. Accordingly, in the context of IgG4 autoimmunity, the pathogenicity of IgG4 is associated with blocking of enzymatic activity or protein-protein interactions of the target antigen. Pathogenicity of IgG4 autoantibodies has not yet been systematically analyzed in IgG4 autoimmune diseases. Here, we establish a modified classification system based on Witebsky's postulates to determine IgG4 pathogenicity in IgG4 autoimmune diseases, review characteristics and pathogenic mechanisms of IgG4 in these disorders, and also investigate the contribution of other antibody entities to pathophysiology by additional mechanisms. As a result, three classes of IgG4 autoimmune diseases emerge: class I where IgG4 pathogenicity is validated by the use of subclass-specific autoantibodies in animal models and/or in vitro models of pathogenicity; class II where IgG4 pathogenicity is highly suspected but lack validation by the use of subclass specific antibodies in in vitro models of pathogenicity or animal models; and class III with insufficient data or a pathogenic mechanism associated with multivalent antigen binding. Five out of the 14 IgG4 antigens were validated as class I, five as class II, and four as class III. Antibodies of other IgG subclasses or immunoglobulin classes were present in several diseases and could contribute additional pathogenic mechanisms.

Serological and experimental studies in different forms of myasthenia gravis

Antibodies to the acetylcholine receptor (AChR) have been recognized for over 40 years and have been important in the diagnosis of myasthenia gravis (MG), and its recognition in patients of different ages and thymic pathologies. The 10-20% of patients who do not have AChR antibodies are now known to comprise different subgroups, the most commonly reported of which is patients with antibodies to muscle-specific kinase (MuSK). The use of cell-based assays has extended the repertoire of antibody tests to clustered AChRs, low-density lipoprotein receptor-related protein 4, and agrin. Autoantibodies against intracellular targets, namely cortactin, titin, and ryanodine receptor (the latter two being associated with the presence of thymoma), may also be helpful as biomarkers in some patients. IgG4 MuSK antibodies are clearly pathogenic, but the coexisting IgG1, IgG2, and IgG3 antibodies, collectively, have effects that question the dominance of IgG4 as the sole pathologic factor in MuSK MG. After a brief historical review, we define the different subgroups and summarize the antibody characteristics. Experiments to demonstrate the in vitro and in vivo pathogenic roles of MuSK antibodies are discussed.

IgG4-mediated autoimmune diseases: a niche of antibody-mediated disorders

Immunoglobulin 4 (IgG4) is one of four human IgG subclasses and has several unique functional characteristics. It exhibits low affinity for complement and for most Fc receptors. It furthermore has generally high affinity for its antigen, with binding occurring in a monovalent fashion, as IgG4 can exchange Fab-arms with other IgG4 molecules. Because of these characteristics, IgG4 is believed to block its targets and prevent inflammation, which, depending on the setting, can have a protective or pathogenic effect. One example of IgG4 pathogenicity is muscle-specific kinase (MuSK) myasthenia gravis (MG), in which patients develop IgG4 MuSK autoantibodies, resulting in muscle weakness. As a consequence of the distinct IgG4 characteristics, the pathomechanism of MuSK MG is very different from IgG1-and IgG3-mediated autoimmune diseases, such as acetylcholine receptor MG. In recent years, new autoantibodies in a spectrum of autoimmune diseases have been discovered. Interestingly, some were found to be predominantly IgG4. These IgG4-mediated autoimmune diseases share many pathomechanistic aspects with MuSK MG, suggesting that IgG4-mediated autoimmunity forms a separate niche among the antibody-mediated disorders. In this review, we summarize the group of IgG4-mediated autoimmune diseases, discuss the role of IgG4 in MuSK MG, and highlight interesting future research questions for IgG4-mediated autoimmunity.

Passive transfer models of myasthenia gravis with muscle-specific kinase antibodies

Myasthenia gravis (MG) with antibodies to muscle-specific kinase (MuSK) is characterized by fluctuating fatigable weakness. In MuSK MG, involvement of bulbar muscles, neck, and shoulder and respiratory weakness are more prominent than in acetylcholine receptor (AChR) MG. MuSK autoantibodies are mainly of the IgG4 subclass, and as such are unable to activate complement, have low affinity for Fc receptors, and are functionally monovalent. Therefore, the pathogenicity of IgG4 MuSK autoantibodies was initially questioned. A broad collection of in vitro active immunization and passive transfer models has been developed that have shed light on the pathogenicity of MuSK autoantibodies. Passive transfer studies with purified IgG4 from MuSK MG patients confirmed that IgG4 is sufficient to reproduce clear clinical, electrophysiological, and histological signs of myasthenia. In vitro experiments revealed that MuSK IgG4 autoantibodies preferably bind the first Ig-like domain of MuSK, correlate with disease severity, and interfere with the association between MuSK and low-density lipoprotein receptor-related protein 4 and collagen Q. Some patients have additional IgG1 MuSK autoantibodies, but their role in the disease is unclear. Altogether, this provides a rationale for epitope-specific or IgG4-specific treatment strategies for MuSK MG and emphasizes the importance of the development of different experimental models.

When myasthenia gravis is deemed refractory: clinical signposts and treatment strategies

The prognosis for patients with myasthenia gravis (MG) has improved significantly over the past half century, including substantial reductions in mortality and morbidity. However, approximately 10% of patients fails to respond adequately to current therapies and are considered treatment refractory, or treatment intolerant, and up to 80% have disease that fails to achieve complete stable remission. Although patients with autoantibodies to muscle-specific tyrosine kinase (anti-MuSK positive) are more likely to become treatment refractory than those with autoantibodies to the acetylcholine receptor (anti-AChR positive), each of these serotypes is substantially represented in the refractory MG population. Other risk factors for becoming treatment refractory include history of thymoma or thymectomy and female sex. A modified treatment algorithm for MG is proposed: patients who have disease that fails to respond to the stepwise approach to therapy, are treatment intolerant, or who require chronic rescue measures despite ongoing therapy, should be considered treatment refractory and emerging therapies should be considered. Three emerging monoclonal antibody-based therapies are discussed: the anti-B-cell agent rituximab; the terminal complement activation inhibitor eculizumab; and belimumab, which targets B-cell activating factor. Increased understanding of molecular pathophysiology and accurate antibody subtyping in MG should lead to the use of new therapeutic agents and successful management of treatment-refractory patients.

Mechanisms underlying B cell immune dysregulation and autoantibody production in MuSK myasthenia gravis

Pathogenic autoantibodies to muscle-specific tyrosine kinase (MuSK) can be found in patients with myasthenia gravis (MG) who do not have detectable antibodies to the acetylcholine receptor. Although the autoantibody-mediated pathology is well understood, much remains to be learned about the cellular immunology that contributes to autoantibody production. To that end, our laboratory has investigated particular components associated with the cellular immunopathology of MuSK MG. First, we found that B cell tolerance defects contribute to the abnormal development of the naive repertoire, which indicates that dysregulation occurs before the production of autoantibodies. Second, both the naive and antigen-experienced memory B cell repertoire, which we examined through the application of high-throughput adaptive immune receptor repertoire sequencing, include abnormalities not found in healthy controls. This highlights a broad immune dysregulation. Third, using complementary approaches, including production of human monoclonal antibodies, we determined that circulating plasmablasts directly contribute to the production of MuSK-specific autoantibodies in patients experiencing relapse following B cell depletion therapy. These collective findings contribute to defining a mechanistic model that describes MuSK MG immunopathogenesis.

Update on ocular myasthenia gravis in Taiwan

Myasthenia gravis (MG) is an autoimmune disease involving the neuromuscular junction. Autoantibodies to the acetylcholine receptor or, less frequently, to muscle-specific kinase, attack against the postsynaptic junctional proteins, resulting in fluctuating and variable weakness of muscles. Extraocular, levator palpebrae superioris, and orbicularis oculi muscles are particularly susceptible. The majority of patients with MG present with purely ocular symptoms including ptosis and diplopia initially. About half of these patients progress to generalized disease within 2 years. The prevalence of MG in Taiwan is 140 per million with male to female ratio of 0.7. The incidence rate is higher in the elderly. Several immune-related diseases such as lymphoid malignancy, diabetes, and thyroid diseases are associated with MG in the national population-based studies in Taiwan. Ice pack test, rest test, Tensilon/neostigmine test, circulating antibody measurement, and electrophysiological studies are useful diagnostic tools with variable sensitivity and specificity. For the patients with ocular MG, acetylcholinesterase inhibitors are usually the first-line treatment. Corticosteroids and immunosuppressant could provide better disease control and may reduce the risk of conversion to generalized form although there is still some controversy. A thymectomy is also beneficial for ocular MG, especially in refractory cases. The correction of ptosis and strabismus surgery could improve the visual outcome but should be performed only in stable disease.

Mechanisms of Caspr2 antibodies in autoimmune encephalitis and neuromyotonia

OBJECTIVE

To determine the pathogenic mechanisms of autoantibodies to the cell adhesion molecule Caspr2 in acquired neuromyotonia and autoimmune encephalitis.

METHODS

Caspr2-positive samples were confirmed using a cell-based assay, and their IgG subtypes were determined by enzyme-linked immunosorbent assay and cell-based assay. A solid phase binding assay quantified the binding of Caspr2 to contactin-2 in the presence of Caspr2 autoantibodies. Living cultures of primary rat hippocampal neurons were incubated with Caspr2-positive or control sera, and the distribution of Caspr2-positive immunofluorescent puncta and total surface Caspr2 was quantified. HEK cells transfected to express Caspr2 were incubated with Caspr2-positive or control samples, and cell-surface biotinylation and Western blot were used to assess total, internalized, and surface levels of Caspr2.

RESULTS

We confirmed 6 samples with strong Caspr2 reactivity. IgG4 Caspr2 antibodies were present in all 6 cases. Caspr2 interacted with another cell adhesion molecule, contactin-2, with nanomolar affinity in the solid phase assay, and Caspr2 autoantibodies inhibited this interaction. Caspr2 autoantibodies did not affect the surface expression of Caspr2 in rat primary hippocampal neurons or transfected HEK cells.

INTERPRETATION

Caspr2 autoantibodies inhibit the interaction of Caspr2 with contactin-2 but do not cause internalization of Caspr2. Functional blocking of cell adhesion molecule interactions represents a potential mechanism with therapeutic implications for IgG4 autoantibodies to cell adhesion molecules in neurological diseases. Ann Neurol 2018;83:40-51.

Myasthenia gravis with antibodies to MuSK: an update

Myasthenia gravis with antibodies to the muscle-specific tyrosine kinase (MuSK⁺ MG) is a rare disease with distinctive pathogenic mechanisms and clinical features. An acute onset and predominant bulbar muscle weakness are very common and highly suggestive of the disease. On the other hand, a more indolent course, atypical ocular presentation, and signs of cholinergic hyperactivity may complicate the diagnosis. Though MuSK⁺ MG is still a severe disease, over the years we have observed a steady reduction in the rate of respiratory crisis and a significant improvement in the clinical outcome, both likely related to earlier diagnosis and timely treatment. Despite the improved management, MuSK⁺ MG patients tend to remain dependent on long-term immunosuppressive treatment and may develop permanent disabling weakness. In uncontrolled studies, B cell depletion with rituximab proved effective in most patients with refractory disease, inducing prolonged clinical responses associated with a sustained reduction of serum antibody levels. Promising results from experimental studies and case reports suggest that both 3,4-diaminopyridine and albuterol may be effective as symptomatic agents.