Acetylcholine receptors and myasthenia gravis

Recent years have seen considerable progress in understanding the nature of the molecular events involved in neuromuscular transmission. The acetylcholine receptor (AChR) has been purified to homogeneity and acetylcholine-induced ion transport has been reconstituted by incorporation of pure AChR into artificial membranes. Immunization against purified AChR induces a condition, clinically and physiologically similar to the human disease myasthenia gravis, which is due to circulating anti-AChR antibodies. This model, experimental autoimmune myasthenia gravis, is proving useful for investigating the role of genetic factors in determining the immune response to AChRs and for testing various experimental approaches to specific treatment. Myasthenia gravis is an autoimmune disease in which there is loss of acetylcholine receptors at the neuromuscular junction. Anti-AChR antibodies can be detected in the majority of patients and they cause loss of AChR by a variety of mechanisms. Anti-AChR antibody is heterogeneous and not restricted in idiotype. The role of the thymus in MG is still uncertain, but recent experiments implicate the presence of a cell type in MG thymus which may be involved in autosensitization to AChR.     

Therapeutic Apheresis in Myasthenia Gravis

Abstract: Plasma exchange (PE) is an easily applicable technique for rapid and massive removal of antibodies, and its beneficial role is well established in the management of myasthenia gravis (MG), an antibody‐mediated disorder of the neuromuscular junction. PE is useful in myasthenic crisis, in most severe forms of MG before thymectomy, in the early postoperative period, and in cases of symptom worsening during tapering or initiation of immunosuppressive therapy. Clinical efficacy varies from 55% to 100%, and improvement rarely persists for more than 4–10 weeks; thus immunosuppressive therapy has to be associated. New apheretic techniques (double filtration plasmapheresis, immunoadsorption systems with staphylococcal protein A columns or thryptophan‐polyvinyl alcohol gel columns) that allow the selective removal of IgG and anti‐AChR antibody were recently used in the management of MG with positive effects. Whether their therapeutic effect and cost effect prove more favorable than those obtained by PE still must be demonstrated.     

Specific Immunoadsorbent for Myasthenia Gravis Treatment: Development of Synthetic Peptide Designed to Remove Antiacetylcholine Receptor Antibody

Abstract: We have developed Medisorba MG, a new immunoadsorbent column for myasthenia gravis (MG). The a 183–200 segment of the Torpedo Californica acetylcholine receptor (AChR) is recognized as the acetylcholine binding site by the blocking antibody, which is one of the anti-AChR antibodies involved in the pathogenesis of MG. As a specific affinity ligand to remove the blocking antibody, Torpedoα 183–200 was synthesized and immobilized covalently to porous cellulose beads. This immunoadsorbent showed specific removal of the blocking antibody without reducing IgG and albumin levels significantly in clinical evaluation and in vitro study. Clinical improvement was found in 78% of the cases, and no adverse effects were observed in any case. The Medisorba MG column has been confirmed as a useful device for the treatment of MG.     

Immunoadsorption in Myasthenia Gravis Based on Specific Ligands Mimicking the Immunogenic Sites of the Acetylcholine Receptor

Abstract: A specific system for antibody removal from blood circulation in myasthenia gravis (MG) patients was devised by use of the immunoadsorbent bound to an acetylcholine receptor (AChR) peptide that was synthesized corresponding to the sequence of residues 183‐200 of the AChR alpha‐subunit (alpha 183‐200), antibodies which prevent the binding of ACh to AChR. The alpha 183‐200 peptide was confirmed to be immunogenic for induction of an animal model of the disease and for reactivity with MG autoantibodies. We then made use of these results for immunoadsorption therapy through the antigen‐antibody reaction on the molecular level, having given patients relief from myasthenic weakness. The greatest care was taken for the selection of an antigenic region in the molecular structure among various myasthenogenic domains of AChR and for the antigenic conformation of synthetic peptide as the adsorbent to react with antibodies raised against the native protein.     

Modulation of experimental myasthenia gravis by IVIg

Myasthenia Gravis (MG) is an autoimmune disease mediated by antibodies directed against the acetylcholine receptor (AChR). Treatment by IVIg is effective in acute forms of myasthenia gravis. In order to determine the in vivo effects of the various fractions of human immunoglobulins, we used an experimental model of myasthenia gravis in SCID mice. To this end, thymic cells from MG patients are transferred to these mice according to a well defined protocol. When establishing of the model, we noticed the appearance of anti-AChR antibodies and the loss of AChR expression at the muscle level. After treatment with IVIgG or IVIgM, the mice displayed a lower anti-AChR antibody titer compared to control mice (albumin treated) and the loss of the AChR number at the muscle was significantly reduced. These results obtained from one MG patient indicate that the human immunoglobulin preparations induce significant effects on pathogenic parameters in the SCID mouse model. Therefore this model is interesting to approach the mechanisms of action of human immunoglobulins and deserves further investigation.     

Adsorption column for myasthenia gravis treatment: Medisorba MG-50

Adsorption column Medisorba MG-50 (Kuraray Medical Inc.) for the treatment of myasthenia gravis (MG) is introduced. The adsorbent in this column is composed of cellulose beads as carrier material and covalent-bound synthetic peptide as a ligand that has a specific affinity to the pathogenic anti-acetylcholine receptor antibody of MG. The amino acid sequence of the peptide is modified from the segment of alpha 183-200 of the torpedo acetylcholine receptor (AChR) protein, and the segment is the acetylcholine binding site on AChR and the target site of anti-AChR antibody. The adsorbent showed specific adsorption characteristics to the anti-ACHR antibody (blocking antibody) in vitro. Clinically, MG-50 is used in plasma-perfusion therapy, and it is recognized that MG-50 specifically reduces blocking antibody titer and improves MG symptoms. MG-50 is approved in Japan.     

重症肌无力患者妊娠期临床特点及预后分析

目的:探讨重症肌无力（MG）患者妊娠前后肌无力症状的变化及MG对妊娠预后的影响。方法:回顾性研究2013年1月至2018年10月28例就诊于解放军总医院第八医学中心MG患者38例次妊娠分娩的临床资料。比较妊娠前与妊娠不同时期MG严重程度评分、血乙酰胆碱受体（AChR）抗体变化及药物的使用情况,并分析妊娠后MG不同转归（...     

Myasthenia gravis und myasthene Syndrome

Neuromuscular transmission is compromised in a variety of disorders due to immunological, toxic or congenital mechanisms. Myasthenia gravis (MG) is the most frequent among these disorders. In about 15% of cases, MG is associated with a second autoimmune disorder mainly seen in rheumatologists. Some of the drugs used in rheumatology can exacerbate MG or even trigger immunologically the occurrence of MG. In most MG patients, antibodies to the acetylcholine receptor (AChR) are present, but around 10% have AChR antibodies that are only identified by novel methods, and up to 5% have muscle-specific kinase antibodies which define a different subgroup of myasthenia. Among those MG patients with anti-AChR antibodies, a number of clinical subtypes can be identified including early-onset MG (onset ≤ 40 years), late-onset MG (onset after 40 years) and thymoma-associated MG. Even though less common, it is important to recognize Lambert Eaton myasthenic syndrome (LEMS). The abnormality in LEMS is a presynaptic failure to acetylcholine release caused by antibodies to voltage-gated calcium channels. More than half of LEMS patients have small-cell lung cancer.     

Retrospective analyses of clinical features and therapeutic outcomes in thymectomized patients with myasthenia gravis at Shinshu University

OBJECTIVES: Thymectomy has become recognized as an integral element in the treatment of patients with myasthenia gravis (MG). Although the incidence of elderly-onset MG has recently been increasing, there is little data demonstrating the efficacy and complications of thymectomy in this population. To clarify this point, we divided the thymectomized patients with MG into young and elderly groups, and retrospectively examined their clinical features and therapeutic outcomes. PATIENTS AND METHODS: We reviewed 57 MG patients who had been admitted to our hospital between 1988 and 2002. The patients were classified into young (younger than 60) and elderly (60 or older) groups according to the age of onset, and the therapeutic outcomes of thymectomy were evaluated using myasthenic severity scales and the duration from operation to discharge. RESULTS: Myasthenic severity scales significantly improved after thymectomy in the elderly group both with (p<0.005) and without thymoma (p<0.05) compared with before. With regard to the duration from thymectomy to discharge, no significant difference could be found between the young and elderly groups, irrespective of associated thymoma. There were no serious complications during and after thymectomy in either the young or the elderly group. CONCLUSIONS: Despite various possible complications due to aging, thymectomy should be actively considered also in the treatment of elderly MG patients because it can reliably and safely improve myasthenic symptoms in combination with immunosuppressive agents, including corticosteroid.     

Thymus-derived B cell clones persist in the circulation after thymectomy in myasthenia gravis

Myasthenia gravis (MG) is a neuromuscular, autoimmune disease caused by autoantibodies that target postsynaptic proteins, primarily the acetylcholine receptor (AChR) and inhibit signaling at the neuromuscular junction. The majority of patients under 50 y with AChR autoantibody MG have thymic lymphofollicular hyperplasia. The MG thymus is a reservoir of plasma cells that secrete disease-causing AChR autoantibodies and although thymectomy improves clinical scores, many patients fail to achieve complete stable remission without additional immunosuppressive treatments. We speculate that thymus-associated B cells and plasma cells persist in the circulation after thymectomy and that their persistence could explain incomplete responses to resection. We studied patients enrolled in a randomized clinical trial and used complementary modalities of B cell repertoire sequencing to characterize the thymus B cell repertoire and identify B cell clones that resided in the thymus and circulation before and 12 mo after thymectomy. Thymus-associated B cell clones were detected in the circulation by both mRNA-based and genomic DNA-based sequencing. These antigen-experienced B cells persisted in the circulation after thymectomy. Many circulating thymus-associated B cell clones were inferred to have originated and initially matured in the thymus before emigration from the thymus to the circulation. The persistence of thymus-associated B cells correlated with less favorable changes in clinical symptom measures, steroid dose required to manage symptoms, and marginal changes in AChR autoantibody titer. This investigation indicates that the diminished clinical response to thymectomy is related to persistent circulating thymus-associated B cell clones.

Myasthenia gravis (MG) is a neuromuscular disorder caused by autoantibodies targeting components of the neuromuscular junction. Patients with MG experience skeletal muscle weakness, worsened by activity (1, 2). In upwards of 85% of MG patients, autoantibodies specifically target the nicotinic acetylcholine receptor (AChR) (2). Many clinical and experimental studies, including maternal-to-fetal transfer, plasma exchange to deplete antibodies, and passive transfer of patient-derived immunoglobulin show that AChR autoantibodies are demonstrably pathogenic (1, 3–10). AChR-mediated signal transmission is impaired by a number of autoantibody-mediated functions. AChR autoantibodies are predominantly IgG1 and IgG3, two subclasses that effectively activate complement (11–13). Thus, complement-mediated tissue injury and consequent removal of AChR from the muscle membrane represents a major mechanism of immunopathology. Additional mechanisms include autoantibody-mediated antigen cross-linking, resulting in internalization of AChR (by modulating autoantibodies), and a direct blocking of the acetylcholine binding site by the autoantibodies (14–19).A key source of these pathogenic AChR autoantibodies in MG patients is the MG thymus. Thymic lymphofollicular hyperplasia (20) with germinal centers is observed in ∼70% of younger MG patients (21). The thymus in these patients contains both AChR-specific IgG (22) and B cells (10) that can secrete these autoantibodies (23). Transplantation of thymus from AChR-MG patients into immunodeficient mice results in human AChR-specific autoantibody deposits at the neuromuscular junction, and subsequent manifestation of MG-like symptoms (24). Thymus-associated plasma cells and plasmablasts spontaneously produce AChR autoantibodies in vitro (25, 26) and activated memory B cell populations (27–29). B cells residing in the hyperplastic thymus organize within tertiary lymphoid organs, forming structures that share many characteristics associated with germinal centers (30–33). The presence and frequency of these structures positively associates with the presence of circulating AChR autoantibodies (34). Expanded clones among the MG thymus resident B cells is consistent with the presence of ongoing germinal center-based maturation processes (35, 36). These clones feature the characteristics of antigen experience, including isotype class switching, somatic hypermutation, and biased usage of antibody variable region gene segments (35, 37–40).These collective studies clearly demonstrate that the thymus plays a fundamental role in the production of AChR autoantibodies and consequently the immunopathology of MG. Based only on empiric clinical evidence, thymectomy (TX) had already been widely used as a long-standing treatment strategy for AChR autoantibody-positive MG (41). A multicenter, single-blind, randomized clinical trial (MGTX) designed to evaluate the efficacy of thymectomy plus prednisone versus prednisone alone in generalized nonthymomatous AChR-MG was recently performed to formally test the effect of thymectomy (42). The study demonstrated the efficacy of thymectomy as the procedure led to a significant improvement in muscle weakness, decreased steroid usage, and decreased frequency of rehospitalization over the course of 3 y. Results from a 2-y extension study of the MGTX trial (43) demonstrated that the patients who underwent thymectomy were more likely to have a better clinical status compared to patients who were treated with prednisone alone. Moreover, therapeutic effects from thymectomy continue to be observed years after the procedure, but some patients experienced more benefit than others. These findings are consistent with other studies, which showed rates of complete stable remission in only 40 to 50% of patients when followed for years after the procedure (44, 45). Furthermore, the AChR autoantibody titer decreases in the majority of those treated by thymectomy, but almost never reaches undetectable levels (34, 46) and only modestly decreases in many (47). Understanding both the mechanistic basis for heterogeneous responses and why thymectomy does not consistently lead to complete stable remission is therefore critical to improving the management of AChR autoantibody-positive MG patients with thymic lymphofollicular hyperplasia.Given extensive evidence that disease-causing B cells in AChR-MG are found in the thymus alongside clinical evidence showing heterogeneous responses to thymectomy, we sought to test the possibility that B cell clones from the thymus persist in the periphery after removal of the thymus. We hypothesized that B cell clones from the thymus would be found in the circulation and that the persistence of these clones overall would correlate with disease persistence. Thus, in this study, we test the hypothesis that the global depletion of B cell clones from the thymus, including those that produce AChR autoantibodies, is a mechanism by which thymectomy reduces disease burden. To test this hypothesis, we performed adaptive immune receptor repertoire (AIRR) sequencing (AIRR-seq) of B cell receptor (BCR) repertoires from the thymus and paired longitudinal peripheral blood samples from the MGTX trial and an independent center, generating approximately half a million V(D)J sequences in total. AIRR-seq has the capacity and depth to identify rare sequences in the large (10¹¹ B cells) circulating peripheral repertoire found in humans (48). Consequently, this approach allowed us to identify rare B cell clones in the circulation related to those in the thymus and track their frequency over time after thymectomy.     

Minimally invasive surgery in the management of resectable thymoma: a retrospective analysis from the National Cancer Database

BackgroundThymomas are relatively uncommon tumors traditionally resected via open sternotomy. Despite the appeal of minimally invasive techniques, concerns persist regarding their oncologic efficacy. We hypothesized that minimally-invasive thymectomies for resectable thymomas are oncologically safe when compared to open thymectomy.MethodsThe National Cancer Database (NCDB) was queried for patients with thymoma undergoing resection as the first mode of treatment between 2010–2015. Patient demographics, tumor characteristics and perioperative outcomes were examined for each approach (robotic, thoracoscopic, or open). The primary endpoints were rates of complete (R0) resection and need for adjuvant radiotherapy. Chi-square and Student’s t-test and logistic regression were used for analysis.ResultsA total of 2,312 patients were identified. The utilization of myocardial infarction (MI) surgery increased during the study period (robotic: 7.6% to 19.5%; thoracoscopic: 9.3% to 18.4%, both P<0.0001). Median tumor size was higher and mediastinal invasion was more common in open thymectomies. R0 resection was more common in robotic and adjuvant radiotherapy was less frequent in thoracoscopic thymectomies. In multivariate analysis absence of mediastinal invasion (P<0.0001) was the only prognostic factor for R0 resection. Positive margins, mediastinal invasion (both P<0.0001) and younger age (P<0.01) were the only predictors of the need for adjuvant radiotherapy.ConclusionsUtilization of MI approaches for resectable thymoma has increased from 2010 to 2015. After adjusting for tumor size and mediastinal invasion, minimally-invasive thymectomy was not associated with lower R0 resection rates or increased use of adjuvant radiotherapy. MI thymectomy for resectable thymoma is oncologically equivalent to open thymectomy.     

Comparative Study of Clinical Effects Between Plasma Adsorption and Double Filtration Plasmapheresis in Patients with Myasthenia Gravis

Abstract: Plasma exchange (PE) has been one of the most powerful treatments for patients with myasthenia gravis (MG) since Pinching et al. reported its clinical usefulness in 1976, despite the need for supplemental human plasma. However, new apheresis techniques, e.g., plasma adsorption (PA) and double filtration plasmapheresis (DFPP), which do not need human plasma, were developed and have been introduced for clinical use in MG. We compared the effects of these plasma purification therapies in patients with MG and found that DFPP improved such subjective symptoms as chest compression and general fatigue better than PA while both of them could decrease the serum level of acetylcholine receptor (AChR) antibodies and relieve objective muscle weakness to a similar degree. It may be that DFPP can remove some circulating pathogenic factors other than AChR antibodies more efficiently than PA.—     

A comparative study of ocular and generalized myasthenia gravis

We compared the relations and therapeutic outcomes of ocular and generalized types of myasthenia gravis (MG) and used retrospective analysis for 65 patients with myasthenia gravis during a mean follow-up time of 30.4 months. There were 35 ocular and 30 generalized MG patients. Items of comparison included sex, age, clinical presentations, serum antibody titer, the association with thymus status, and therapeutic outcome. Of the patients with generalized MG, males were significantly older than females. Ptosis and diplopia were the most common symptoms in patients with MG, but there were no significant differences between the two types of MG. The eyelid levator muscle and lateral rectus muscle were the most commonly involved extraocular muscles in patients with MG. The associations with thymoma or thymus hyperplasia were more common in generalized MG than in ocular MG, and more common in younger than in older patients. The result of positive neostigmine test was 93.8% in all patients, but there were no significant differences between the two types of MG. Acetylcholine receptor antibody (AchRAb) presented an 81.1% positive rate and was significantly higher in generalized MG than that in ocular MG (96.2% vs 66.7%). There were no significant differences between the two types of MG regarding successful treatment strategies in both initial therapy and maintenance therapy. Only two of 16 patients had complete remissions after thymectomy. From the viewpoint of clinical presentations or from the therapeutic strategy outcome, the boundary between both types of MG seems to be vague. Both types of MG probably share the same entity in nature and the difference is just a matter of degree of severity. The benefit of thymectomy in treatment of MG needs further investigation.     

Patient reported outcomes (PROs) after minimally invasive and open esophagectomy

Esophagectomy for esophageal malignancies remains an operation with significant potential morbidity and mortality. However, surgical outcomes continue to improve over time and focus has shifted toward not just good outcomes, but quality of life post operatively. Patient reported outcomes (PROs) focus of quality of life measures via validated patient surveys has increasingly become a significant focus. While PROs do have their limitations, they represent a glimpse into the symptomatology, quality of life, and well-being of a patient undergoing a procedure with inherent morbidity. Working to improve outcomes from the perspective of the patient is not a new concept, but has becoming increasingly relevant as surgical quality for all procedures improves. The optimal approach to esophagectomy is controversial. Minimally invasive approaches attempt to avoid laparotomy and thoracotomy with the thought of improving post-operative quality of life by mitigating complications related to those open surgical approaches. The data in favor of laparoscopy and thoracoscopy is quite strong and multiple randomized controlled trials exist in this realm supporting minimally invasive approaches with regards to quality of life outcomes and more rapid return to patient’s preoperative baseline. The data in favor of a robotic approach for esophagectomy is not quite as robust, but more studies show that these approaches mirror the benefits of the laparoscopic and thoracoscopic approaches without robotic assistance.     

Left- and right-sided video-assisted thoracoscopic thymectomy exhibit similar effects on myasthenia gravis

Background

Unilateral video-assisted thoracoscopic (VATS) thymectomy features less operative trauma, improved cosmesis, and similar efficiency compared with transsternal (TS) thymectomy for treatment of patients with myasthenia gravis (MG). Unilateral VATS thymectomy can be easily performed from either side of the thorax, because thymus is located in the middle of mediastinum. Nevertheless, the side that provides better outcomes remains controversial. This study presents our experience on treatments for MG and reveals the differences between the unilateral VATS thymectomy performed on each side.

Methods

Eighty-one consecutive patients with MG who underwent TS or VATS thymectomy on either side between January 2003 and December 2012 were enrolled in the study. Clinicopathologic data and surgical outcomes were retrospectively analyzed and compared among different surgical approaches.

Results

TS thymectomy was administered in 50 patients, whereas unilateral VATS approaches were performed on the remaining 31 patients, 15 on the left side and 16 on the right side. The VATS group exhibited a significantly shorter surgery duration (P<0.001), less intraoperative blood loss (P=0.009), shorter postoperative hospital stay (P=0.025), smaller thoracic drainage volume (P=0.033), shorter thoracic drainage duration (P=0.006), and less postoperative complications (P<0.001) compared with the TS group. However, disease remission rates did not significantly differ among the groups (P=0.988). The left-sided group exhibited considerably longer thoracic drainage duration than the right-sided group (P=0.041). Moreover, surgical time (P=0.736), intraoperative blood loss (P=0.281), postoperative hospital stay (P=0.599), thoracic drainage volume (P=0.571), postoperative complications (P=0.742) and therapeutic effect (P=1.000) did not significantly differ among the groups. Multivariate analysis revealed that the ocular type of MG is the only independent factor for clinical remission (P=0.002).

Conclusions

Unilateral VATS thymectomy can reduce surgical risks and shorten hospitalization duration without threatening the therapeutic effect. This technique can be safely and effectively performed by experienced surgeons in either side of the thorax.     

Oral administration of a dual analog of two myasthenogenic T cell epitopes down-regulates experimental autoimmune myasthenia gravis in mice

Myasthenia gravis (MG) and experimental autoimmune MG (EAMG) are T cell-regulated, antibody-mediated autoimmune diseases. The major autoantigen in MG is the nicotinic acetylcholine receptor (AChR). Two peptides, representing sequences of the human AChR alpha-subunit, p195-212 and p259-271, were previously shown to be immunodominant T cell epitopes in MG patients as well as, respectively, in SJL and BALB/c mice. A dual analog (termed Lys-262-Ala-207) composed of the tandemly arranged two single amino acid analogs of p195-212 and p259-271 was shown to inhibit, in vitro and in vivo, MG-associated autoimmune responses. Furthermore, the dual analog could down-regulate myasthenogenic manifestations in mice with EAMG that was induced by inoculation of a pathogenic T cell line. In the present study, the ability of the dual analog to treat EAMG induced in susceptible C57BL/6 mice by native Torpedo AChR was evaluated. Mice that were diagnosed to have clinical symptoms of EAMG were treated with the dual analog by oral administration, 500 microg per mouse three times a week for 5-8 weeks. Treatment with the dual analog down-regulated the clinical manifestations of the ongoing disease as assessed by the clinical score, grip strength (measured by a grip strength meter), and electromyography. The effects on the clinical EAMG correlated with a reduced production of anti-AChR antibody as well as a decrease in the secretion of interleukin-2 and, more dramatically, interferon-gamma, in response to AChR triggering. Thus, the dual analog is an efficient immunomodulator of EAMG in mice and might be of specific therapeutic potential for MG.     

Contribution of intravenous immunoglobulins to the treatment of myasthenia

Myasthenia Gravis (MG) is an autoimmune disease characterized by the production of auto antibodies directed against the acetylcholine receptor of the neuro-muscular synapse. The signs and symptoms are a muscular deficit involving the spinal or cranial muscles. The degree of weakness changes spontaneously over shorter or longer periods. Some exacerbations, called myasthenia crisis, involve the respiratory muscle and are life-threatening. The prognosis of these crisis has been transformed by the use of mechanical ventilation. Treatments directed on immune-regulation such as thymectomy, corticosteroids or immunossupressive drugs contribute to the improvement in functional status and reduce the risk of exacerbation. Plasma exchanges lead to a rapid improvement of weakness during exacerbations. They are, despite the lack of controlled study, the reference treatment for acute exacerbations. More recently, high doses of immunoglobulins have been proposed and a controlled study has shown that they could be an alternative for the treatment of acute exacerbations of MG. Indication of immunoglobulin in the long term management of MG is not established.     

Concurrent inflammatory myopathy and myasthenia gravis with or without thymic pathology: A case series and literature review

Objectives

The association of myasthenia gravis (MG) and inflammatory myositis (IM) is rare and typically only one of the diseases is present. The management of the 2 diseases differs, therefore it is important to recognize the concomitant presentation. Here, we report a case series of 7 patients with co-existing MG and IM with review of the literature.