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

Clinical and laboratory remission with rituximab in anti-MuSK-positive myasthenia gravis

BACKGROUND

Increasing data are available on the use and efficacy of rituximab (RTX) in patients with anti-muscle-specific tyrosine kinase (MuSK)-positive myasthenia gravis (MG), especially those steroid-dependent or unresponsive to traditional immunotherapies.

AIMS

We aimed to evaluate the clinical characteristics and treatment responses of adult patients with generalized anti-MuSK-positive MG treated with RTX.

METHODS

We retrospectively recruited 16 patients who were on RTX, between January 2010 and September 2023. RTX was given 1000 mg/day intravenously twice, two weeks apart. Maintenance treatment was administered at intervals of 3-6 months based on clinical evaluation. The outcome was assessed by Myasthenia Gravis Foundation of America (MGFA) and Myasthenia Gravis Status and Treatment Intensity (MGSTI) scores. Additionally, anti-MuSK antibody levels were retested after treatment in all patients except one.

RESULTS

Twelve patients were female. The mean age at disease onset was 35.3 ± 17.3 years. The median duration between disease onset and RTX administration was 2.4 years (min-max: 0.5-36.5 years). The worst MGFA class before RTX was between IIIb-V. After RTX treatment, 81.3% of patients achieved MGFA minimal manifestations or better and MGSTI level 1 or better. Anti-MuSK antibodies became negative in 12 patients, while they remained positive in three. The changes in antibody levels seemed associated with clinical outcomes.

CONCLUSIONS

RTX is an effective treatment in anti-MuSK-positive MG. Furthermore, our results support the inhibition of antibody production by RTX and we recommend monitoring anti-MuSK antibody titers to follow disease progression and treatment response.

Advancements and prospects of novel biologicals for myasthenia gravis: toward personalized treatment based on autoantibody specificities

Myasthenia gravis (MG) is an antibody-mediated autoimmune disease with a prevalence of 150-250 cases per million individuals. Autoantibodies include long-lived antibodies against the acetylcholine receptor (AChR), mainly of the IgG1 subclass, and IgG4, produced almost exclusively by short-lived plasmablasts, which are prevalent in muscle-specific tyrosine kinase (MuSK) myasthenia gravis. Numerous investigations have demonstrated that MG patients receiving conventional medication today still do not possess satisfactory symptom control, indicating a substantial disease burden. Subsequently, based on the type of the autoantibody and the pathogenesis, we synthesized the published material to date and reached a conclusion regarding the literature related to personalized targeted therapy for MG. Novel agents for AChR MG have shown their efficacy in clinical research, such as complement inhibitors, FcRn receptor antagonists, and B-cell activating factor (BAFF) inhibitors. Rituximab, a representative drug of anti-CD20 therapy, has demonstrated benefits in treatment of MuSK MG patients. Due to the existence of low-affinity antibodies or unidentified antibodies that are inaccessible by existing methods, the treatment for seronegative MG remains complicated; thus, special testing and therapy considerations are necessary. It may be advantageous to initiate the application of novel biologicals at an early stage of the disease. Currently, therapies can also be combined and individualized according to different types of antibodies. With such a wide range of drugs, how to tailor treatment strategies to patients with various conditions and find the most suitable solution for each MG profile are our necessary and urgent aims.

A predictive nomogram for short-term outcomes of myasthenia gravis patients treated with low-dose rituximab

BACKGROUND

This study aims to establish and validate a predictive nomogram for the short-term clinical outcomes of myasthenia gravis (MG) patients treated with low-dose rituximab.

METHODS

We retrospectively reviewed 108 patients who received rituximab of 600 mg every 6 months in Huashan Hospital and Tangdu Hospital. Of them, 76 patients from Huashan Hospital were included in the derivation cohort to develop the predictive nomogram, which was externally validated using 32 patients from Tangdu Hospital. The clinical response is defined as a ≥ 3 points decrease in QMG score within 6 months. Both clinical and genetic characteristics were included to screen predictors via multivariate logistic regression. Discrimination and calibration were measured by the area under the receiver operating characteristic curve (AUC-ROC) and Hosmer-Lemeshow test, respectively.

RESULTS

Disease duration (OR = 0.987, p = 0.032), positive anti-muscle-specific tyrosine kinase antibodies (OR = 19.8, p = 0.007), and genotypes in FCGR2A rs1801274 (AG: OR = 0.131, p = 0.024;GG:OR = 0.037, p = 0.010) were independently associated with clinical response of post-rituximab patients. The nomogram identified MG patients with clinical response with an AUC-ROC (95% CI) of 0.875 (0.798-0.952) in the derivation cohort and 0.741(0.501-0.982) in the validation cohort. Hosmer-Lemeshow test showed a good calibration (derivation: Chi-square = 3.181, p = 0.923; validation: Chi-square = 8.098, p = 0.424).

CONCLUSIONS

The nomogram achieved an optimal prediction of short-term outcomes in patients treated with low-dose rituximab.

Rituximab as a sole steroid-sparing agent in generalized myasthenia gravis: Long-term outcomes

BACKGROUND

Rituximab, a B-cell depleting monoclonal antibody, represents an option for the treatment of refractory myasthenia gravis (MG). Its use is more established in muscle-specific tyrosine kinase positive (MuSK +) patients, while its role in managing acetylcholine receptor positive (AChR +), or double seronegative (DSN) patients, remains less clear. This study evaluates the long-term effectiveness and safety of rituximab in MG of various serotypes.

METHODS

We conducted an open-label study of MG patients receiving rituximab. Adults with generalized refractory MG, either anti-AChR + or DSN, and anti-MuSK + , refractory or not, who had follow-up > 12 months were selected. Change in quantitative myasthenia gravis (QMG) score at last follow-up, compared with baseline was a primary outcome, as well as factors affecting response to treatment. Secondary outcomes included, long-term safety, the steroid-sparing effect and relapse rates post-rituximab.

RESULTS

Thirty patients (16 anti-AChR + , 6 anti-MuSK + , 8 DSN) followed for a mean of 33.3 months were included. Mean scores pre-rituximab compared to last follow-up significantly decreased (p < 0.001), from 11 ± 4.1 to 4.3 ± 3.8, and from 1.9 to 0.3 regarding QMG and relapse rate per patient/year, respectively, while in 93.1% a daily steroid dose ≤ 10 mg was achieved. Antibody status was the only factor independently influencing several endpoints. Throughout the study period no crises or deaths occurred.

CONCLUSION

The present study supports that rituximab is an effective and well tolerated treatment for refractory anti-AChR + and DSN MG patients, while anti-MuSK + remains the group experiencing the greater benefits.

Rituximab treatment in myasthenia gravis

Myasthenia gravis (MG) is a chronic autoimmune disease mediated by antibodies against post-synaptic proteins of the neuromuscular junction. Up to 10%-30% of patients are refractory to conventional treatments. For these patients, rituximab has been used off-label in the recent decades. Rituximab is a monoclonal antibody against the CD20 protein that leads to B cell depletion and to the synthesis of new antibody-secreting plasma cells. Although rituximab was created to treat B-cell lymphoma, its use has widely increased to treat autoimmune diseases. In MG, the benefit of rituximab treatment in MuSK-positive patients seems clear, but a high variability in the results of observational studies and even clinical trials has been reported for AChR-positive patients. Moreover, few evidence has been reported in seronegative MG and juvenile MG and some questions about regimen of administration or monitoring strategies, remains open. In this review, we intend to revise the available literature on this topic and resume the current evidence of effectiveness of Rituximab in MG, with special attention to results on every MG subtype, as well as the administration protocols, monitoring strategies and safety profile of the drug.

Myasthenia Gravis: Novel Findings and Perspectives on Traditional to Regenerative Therapeutic Interventions

The prevalence of myasthenia gravis (MG), an autoimmune disorder, is increasing among all subsets of the population leading to an elevated economic and social burden. The pathogenesis of MG is characterized by the synthesis of autoantibodies against the acetylcholine receptor (AChR), low-density lipoprotein receptor-related protein 4 (LRP4), or muscle-specific kinase at the neuromuscular junction, thereby leading to muscular weakness and fatigue. Based on clinical and laboratory examinations, the research is focused on distinguishing MG from other autoimmune, genetic diseases of neuromuscular transmission. Technological advancements in machine learning, a subset of artificial intelligence (AI) have been assistive in accurate diagnosis and management. Besides, addressing the clinical needs of MG patients is critical to improving quality of life (QoL) and satisfaction. Lifestyle changes including physical exercise and traditional Chinese medicine/herbs have also been shown to exert an ameliorative impact on MG progression. To achieve enhanced therapeutic efficacy, cholinesterase inhibitors, immunosuppressive drugs, and steroids in addition to plasma exchange therapy are widely recommended. Under surgical intervention, thymectomy is the only feasible alternative to removing thymoma to overcome thymoma-associated MG. Although these conventional and current therapeutic approaches are effective, the associated adverse events and surgical complexity limit their wide application. Moreover, Restivo et al. also, to increase survival and QoL, further recent developments revealed that antibody, gene, and regenerative therapies (such as stem cells and exosomes) are currently being investigated as a safer and more efficacious alternative. Considering these above-mentioned points, we have comprehensively reviewed the recent advances in pathological etiologies of MG including COVID-19, and its therapeutic management.

Immunotherapies in MuSK-positive Myasthenia Gravis; an IgG4 antibody-mediated disease

Muscle-specific kinase (MuSK) Myasthenia Gravis (MG) represents a prototypical antibody-mediated disease characterized by predominantly focal muscle weakness (neck, facial, and bulbar muscles) and fatigability. The pathogenic antibodies mostly belong to the immunoglobulin subclass (Ig)G4, a feature which attributes them their specific properties and pathogenic profile. On the other hand, acetylcholine receptor (AChR) MG, the most prevalent form of MG, is characterized by immunoglobulin (Ig)G1 and IgG3 antibodies to the AChR. IgG4 class autoantibodies are impotent to fix complement and only weakly bind Fc-receptors expressed on immune cells and exert their pathogenicity via interfering with the interaction between their targets and binding partners (e.g. between MuSK and LRP4). Cardinal differences between AChR and MuSK-MG are the thymus involvement (not prominent in MuSK-MG), the distinct HLA alleles, and core immunopathological patterns of pathology in neuromuscular junction, structure, and function. In MuSK-MG, classical treatment options are usually less effective (e.g. IVIG) with the need for prolonged and high doses of steroids difficult to be tapered to control symptoms. Exceptional clinical response to plasmapheresis and rituximab has been particularly observed in these patients. Reduction of antibody titers follows the clinical efficacy of anti-CD20 therapies, a feature implying the role of short-lived plasma cells (SLPB) in autoantibody production. Novel therapeutic monoclonal against B cells at different stages of their maturation (like plasmablasts), or against molecules involved in B cell activation, represent promising therapeutic targets. A revolution in autoantibody-mediated diseases is pharmacological interference with the neonatal Fc receptor, leading to a rapid reduction of circulating IgGs (including autoantibodies), an approach already suitable for AChR-MG and promising for MuSK-MG. New precision medicine approaches involve Chimeric autoantibody receptor T (CAAR-T) cells that are engineered to target antigen-specific B cells in MuSK-MG and represent a milestone in the development of targeted immunotherapies. This review aims to provide a detailed update on the pathomechanisms involved in MuSK-MG (cellular and humoral aberrations), fostering the understanding of the latest indications regarding the efficacy of different treatment strategies.

A single low-dose rituximab infusion in severe chronic refractory myasthenia gravis in resource-limited settings

The benefits of multi-dose rituximab cycles in patients with refractory anti-muscle-specific kinase antibody myasthenia gravis (MuSK+MG) are well reported, although less consistently in anti-acetylcholine receptor antibody MG (AChR+MG). Responsivity data to single low-dose rituximab infusions for refractory autoimmune myasthenia, are limited. Here, observational outcomes using MG grading scores and prednisone doses, before and after at least six months of a single-dose infusion of rituximab, were audited in previously treatment-refractory MG patients in a resource-limited setting. Seventeen moderately-severe to severely symptomatic MG patients received single low-dose rituximab infusions (median 500-600 mg) after a median MG duration of 6 years; 13 individuals responded including 5/5 MuSK+MG, 7/10 AChR+MG and 1/2 double seronegative MG. Three (60%) MuSK+MG and three (30%) AChR+MG achieved persistent asymptomatic status. Although more MuSK+MG vs AChR+MG cases stopped prednisone (80% vs 20%, respectively), the prednisone doses in the AChR+MG group was significantly reduced ≥30% (p = 0.008) due to improved MG composite scores (p = 0.016) and with durable benefit (median 12 months). There were no differences between responders and non-responders in MG duration and age at infusion. These results suggest that a single low-dose rituximab infusion is worth trying in refractory MG, including AChR+MG patients, as some patients showed good and durable responses. These results are particularly relevant to resource-limited settings.

Knowledge mapping of targeted immunotherapy for myasthenia gravis from 1998 to 2022: A bibliometric analysis

Background

The treatment of myasthenia gravis (MG) has advanced from steroids and traditional immunosuppressants to targeted immunotherapy. Targeted immunotherapy has been successfully employed in clinical practice in recent years. This study aimed to explore the emerging trend of targeted immunotherapy in MG and summarize the knowledge structure through bibliometric methods.

Methods

The Web of Science Core Collection database (WoSCC) was chosen to retrieve the literature on targeted immunotherapy for MG. Two bibliometric analysis software, VOSviewer and CiteSpace, and bibliometric online platform were mainly used to evaluate the contributions from countries/regions, institutions, journals, and authors through the construction and visualization of bibliometric networks. By systematically reviewing a knowledge domain, future research developments were determined. The R version 4.1.2 and Microsoft Excel 365 were used for statistical analysis.

Results

A total of 562 original articles and 262 reviews relevant to MG targeted immunotherapy were included. The number of publications on targeted immunotherapy for MG exhibited a two-phase advancement. The first stage showed a steady growth trend from 1998 to 2016, with an annual number of no more than 35 publications. The second stage revealed an explosive growth trend from 2017, reaching a peak number of publications in 2020. The United States ranked first in the number of publications, citations, and h-index. The author with the highest citation and h-index was Vincent A. And 28.03% of the articles were published in the top 10 journals. In addition to “myasthenia gravis”, the keyword with the highest consideration was “rituximab”, followed by “double-blind”, which indicate research hotspots gradually from basic research to clinical research over time, especially in the field of targeted immunotherapy. The MG treatment has entered a personalized precision treatment phase. Exploration into new target molecules and conducting high-quality randomized controlled trials on existing biological agents are the further research direction.

Conclusion

The current study summarized the global research trends concerning targeted immunotherapy for MG. Research interests gradually advanced from basic research to clinical research. MG treatment has entered a personalized precision treatment phase. Further investigations into new target molecules and high-quality randomized controlled trials on existing biological agents are required urgently to direct future immunotherapy research.

Long-Term Remission With Low-Dose Rituximab in Myasthenia Gravis: A Retrospective Study

OBJETIVE

Rituximab (RTX) is a therapeutic option, for patients with myasthenia gravis (MG) not responding to conventional immunosuppressive treatment. In this cohort, we evaluated long-term efficacy of RTX in the treatment of refractory generalized MG.

METHODS

A retrospective study was performed in adult patients with refractory generalized MG and at least 24 months of follow-up, between January/2015 and October/2021. The Myasthenia Gravis Status and Treatment Intensity Score was used to assess outcomes, and CD19/CD20+ B-cell counts were monitored.

RESULTS

Sixteen patients with MG (8 antiacetylcholine receptor+ and 8 muscle-specific antikinase+; mean age 45.5 ± 16.2 years) treated with low-dose RTX protocols were included. CD19/CD20 levels remained undetectable 12 months after induction, and no new relapses were observed during follow-up.

CONCLUSIONS

Low-dose RTX infusions were sufficient to achieve undetectable CD19/20 cell counts and sustained clinical remission. In low and middle-income countries, the impact of low-dose RTX therapy represents a paradigm shift in decision-making for long-term treatment.

Rituximab in Myasthenia Gravis- Experience from a Low- and Middle-Income Country (LMIC) Setting

BACKGROUND

Myasthenia gravis (MG) is an immune-mediated disorder of the neuromuscular junction. About 10% are refractory to immunosuppressive therapy.

AIMS

To analyze the response of patients with generalized MG to rituximab.

METHODS AND MATERIALS

A retrospective review of patients with MG who received rituximab was carried out (n = 13, M:F = 6:7, mean age: 44.84 ± 15.73 years). Myasthenia Gravis Foundation of America (MGFA), MGFA post-intervention status (MGFA-PIS), and Myasthenia Gravis Status and Treatment Intensity (MGSTI) were assessed before and after rituximab.

RESULTS

The duration of MG was 104.07 ± 92.25 months. Before rituximab, the MGFA was IIA/IIB/IIIA/IIIB/IVB/V in 1/1/2/6/2/1 patients and MGSTI was four in eight patients and six in three patients. The mean duration of follow up was 20.92 ± 14.06 months (range, 4 to 42 months). Dose reduction or discontinuation of cholinesterase inhibitors could be achieved 12 patients. Complete stable remission (CSR) and pharmacologic remission (PR) were achieved in one and four patients respectively and five patients had minimal manifestations. Most patients attained level 0, 1 or 2 MGSTI at last follow up. No rituximab infusion-related adverse events were noted. Three patients had exacerbation of MG between one to five weeks after rituximab administration. Three patients died, one each due to a cardiac event unrelated to MG or treatment, complications related to myasthenic crisis, and coronavirus disease.

CONCLUSIONS

Rituximab was effective in bringing about remission in MG and can be considered as a first-line agent. However, it has to be administered under close supervision as some patients develop exacerbation of MG akin to steroid-induced worsening.

Association of early-onset myasthenia gravis and primary Sjögren's syndrome: a case-based narrative review

Coexistent myasthenia gravis (MG) and primary Sjögren's syndrome (pSS) is an absolute rarity. That is kind of a surprise as both entities seem to share the same corresponding immunologic mechanisms. We hereby report the case of a 41-year-old woman with coincident early-onset MG (EOMG) and pSS. Because EOMG was the leading clinical feature, she was primarily treated by innovative non-intubated uniportal subxiphoid video-assisted thoracoscopic surgery (VATS) thymectomy. As the association of EOMG and pSS is so unusual, we contextualize our findings with the relevant literature. Particular relevance is an anti-nuclear antibody screening throughout the clinical course of MG and-in reverse-a screening for MG variables when pSS patients complain either muscle fatigability or fatigable ptosis. As pSS patients do not develop any serious morbidity, supervising MG progress in patients with both diseases is of utmost importance. Apart from conscientious pSS diagnosis, prompt adjusting of EOMG progress is the essential aspect of targeted treatment. In this context, it is relevant that therapeutic decisions are made in a multidisciplinary approach. Due to its rarity, multicenter prospective studies of larger sample sizes are indispensably needed to obtain a better understanding of this unusual link.

Engineering Cell Therapies for Autoimmune Diseases: From Preclinical to Clinical Proof of Concept

Autoimmune diseases are caused by a dysfunction of the acquired immune system. In a subset of autoimmune diseases, B cells escaping immune tolerance present autoantigen and produce cytokines and/or autoantibodies, resulting in systemic or organ-specific autoimmunity. Therefore, B cell depletion with monoclonal Abs targeting B cell lineage markers is standard care therapy for several B cell-mediated autoimmune disorders. In the last 5 years, genetically-engineered cellular immunotherapies targeting B cells have shown superior efficacy and long-term remission of B cell malignancies compared to historical clinical outcomes using B cell depletion with monoclonal Ab therapies. This has raised interest in understanding whether similar durable remission could be achieved with use of genetically-engineered cell therapies for autoimmunity. This review will focus on current human clinical trials using engineered cell therapies for B cell-associated autoimmune diseases.

Efficacy and Safety of Immunotherapies in Refractory Myasthenia Gravis: A Systematic Review and Meta-Analysis

Introduction: Approximately 10–20% of patients WITH myasthenia gravis (MG) are refractory to conventional immunotherapies. The purpose of this study was to conduct a systematic review and meta-analysis to explore the optimal therapies for refractory MG.

Method: Correlative studies were performed through a search in PubMed, Cochrane Library, and Embase databases. The primary outcome was defined by changes in the quantitative myasthenia gravis score (QMG). Secondary outcomes were defined by the Myasthenia Gravis Activities of Daily Living Scale (MG-ADL), Myasthenia Gravis Foundation of America (MGFA) post intervention status, adverse events, and disease exacerbation after treatment.

Result: A total of 16 studies were included with 403 patients with refractory MG on therapies with rituximab, eculizumab, tacrolimus, and cladribine. Therapeutic efficacy of rituximab and eculizumab was identified with an estimated reduction in QMG score (4.158 vs. 6.928) and MG-ADL (4.400 vs. 4.344), respectively. No significant changes were revealed in efficacy or exacerbation density between the two independent therapeutic cohorts. The estimated adverse event density of eculizumab was more significant than that in the rituximab group (1.195 vs. 0.134 per patient-year), while the estimated serious event density was similar.

Conclusion: The efficacy and safety of rituximab and eculizumab have been approved in patients with refractory MG. Rituximab had a superior safety profile than eculizumab with a lower incidence of adverse events.

Systematic Review Registration:https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021236818, identifier CRD42021236818.

Comparative Analysis of BIOCHIP Mosaic-Based Indirect Immunofluorescence with Enzyme-Linked Immunosorbent Assay for Diagnosing Myasthenia Gravis

Background: The detection of anti-acetylcholine receptor (AChR) and anti-muscle-specific tyrosine kinase (MuSK) antibodies is useful in myasthenia gravis (MG) diagnosis and management. BIOCHIP mosaic-based indirect immunofluorescence is a novel analytical method, which employs the simultaneous detection of anti-AChR and anti-MuSK antibodies in a single miniature incubation field. In this study, we compare, for the first time, the BIOCHIP MG mosaic with conventional enzyme-linked immunosorbent assay (ELISA) in the diagnosis of MG. Methods: A total of 71 patients with MG diagnosis were included in the study. Anti-AChR and anti-MuSK antibodies were measured separately by two different ELISA and simultaneously by BIOCHIP. The results were then compared. Results: The overall concordance between ELISA and BIOCHIP for anti-AChR reactivity was 74%. Cohen’s kappa was 0.51 (95% CI 0.32–0.71), which corresponds to 90% of the maximum possible kappa (0.57), given the observed marginal frequencies. The overall concordance for anti-MuSK reactivity was 84%. Cohen’s kappa was 0.11 (95% CI 0.00–0.36), which corresponds to 41% of the maximum possible kappa (0.27). Conclusion: The overall concordance among assays is not optimal.

Clinical features, treatment and prognosis of MuSK antibody-associated myasthenia gravis in Northwest China: a single-centre retrospective cohort study

BACKGROUND AND PURPOSE

To summarize the clinical characteristics of patients with muscle-specific kinase antibody-associated myasthenia gravis (MuSK-MG) and to evaluate the therapeutic responses to different treatment regimes.

METHODS

Eighteen MuSK-MG patients admitted in our department between October 2017 and September 2020 were included. Clinical parameters were collected and the responses to different immunosuppressive drugs were assessed by MGFA Postintervention Status (MGFA-PIS). Meanwhile, the correlation between QMG scores and MuSK antibody titers were analyzed and MuSK antibody (MuSK-ab) titers were compared before and after therapy based on different immunosuppressive treatment regimes.

RESULTS

Female predominance (ratio of females to males, 15:3) was evident in the study population, with the average onset age of (40.28 ± 18.57) years and the median disease course of 30.50 months (interquartile range [IQR], 17.50-44.75 months). Ocular manifestation was the most common onset symptom (11/18; 61.11%), and mild symmetrical ptosis was most frequent. Bulbar symptoms had the highest incidence of 88.89% over the entire disease course. Abnormal responses to RNS test were recorded most frequently on the musculus deltoideus (83.33%). All patients were treated with prednisone (Pred) alone or plus azathioprine (AZA), tacrolimus (TAC) or low-dose rituximab (RTX), and 17 (94.44%) of them achieved a favorable outcome defined as minimal manifestation (MM) or better. In general, an obvious positive correlation between QMG score and MuSK-ab titer (r = 0.710, P < 0.001) were found in all patients. A more significant reduction of MuSK-ab titers was observed in patients receiving TAC or RTX plus Pred than those receiving AZA plus Pred.

CONCLUSIONS

The prominent clinical manifestations of ocular and bulbar muscles involvements, together with abnormal RNS response mostly recorded on the musculus deltoideus and better efficacy associated with TAC or low-dose RTX plus Pred, provide a more exhaustive picture of MuSK-MG, particularly in Northwest China.

Effectiveness and Safety of Rituximab for Refractory Myasthenia Gravis: A Systematic Review and Single-Arm Meta-Analysis

Background and Objective: Myasthenia gravis (MG) is an autoimmune neuromuscular disease. Nearly 10-30% of patients with MG are refractory to conventional therapy. Rituximab (RTX), a monoclonal antibody targeting CD20, is increasingly used in autoimmune disorders. We performed a systematic review and meta-analysis to evaluate the effectiveness and safety of RTX for refractory MG. Methods: Studies published between January 1, 2000 and January 17, 2021 were searched in PubMed, EMBASE, Cochrane Library, and ClincalTrails.gov. Primary outcomes included proportion of patients achieving minimal manifestation status (MMS) or better and quantitative MG (QMG) score change from baseline. Secondary outcomes were glucocorticoids (GC) doses change from baseline and proportion of patients discontinuing oral immunosuppressants. Results: A total of 24 studies involving 417 patients were included in the meta-analysis. An overall 64% (95% confidence interval, 49-77%) of patients achieved MMS or better. The estimated reduction of QMG score was 1.55 (95% confidence interval, 0.88-2.22). The mean reduction of GC doses was 1.46 (95% confidence interval, 1.10-1.82). The proportion of patients discontinuing oral immunosuppressants was 81% (95% confidence interval, 66-93%). Subgroup analyses showed that the proportion of patients achieving MMS or better and discontinuing oral immunosuppressants was higher in MuSK-MG group than those in AChR-MG group. Improvement was more pronounced in patients with mild to moderate MG compared to those with severe MG. Moreover, the efficacy appeared to be independent of the dose of RTX. 19.6% of patients experienced adverse events, most of which were mild to moderate. Only one patient developed progressive multifocal leukoencephalopathy. Conclusions: RTX can alleviate the symptom of weakness, decrease QMG score and reduce the doses of steroids and non-steroid immunosuppressive agents in refractory MG. It is well-tolerated with few severe adverse events. Randomized controlled trials are urgently needed to study the efficacy of RTX in treating refractory MG and to identify the characteristics of patients who might respond well to RTX.

Short- and Long-Lived Autoantibody-Secreting Cells in Autoimmune Neurological Disorders

As B cells differentiate into antibody-secreting cells (ASCs), short-lived plasmablasts (SLPBs) are produced by a primary extrafollicular response, followed by the generation of memory B cells and long-lived plasma cells (LLPCs) in germinal centers (GCs). Generation of IgG4 antibodies is T helper type 2 (Th2) and IL-4, -13, and -10-driven and can occur parallel to IgE, in response to chronic stimulation by allergens and helminths. Although IgG4 antibodies are non-crosslinking and have limited ability to mobilize complement and cellular cytotoxicity, when self-tolerance is lost, they can disrupt ligand-receptor binding and cause a wide range of autoimmune disorders including neurological autoimmunity. In myasthenia gravis with predominantly IgG4 autoantibodies against muscle-specific kinase (MuSK), it has been observed that one-time CD20⁺ B cell depletion with rituximab commonly leads to long-term remission and a marked reduction in autoantibody titer, pointing to a short-lived nature of autoantibody-secreting cells. This is also observed in other predominantly IgG4 autoantibody-mediated neurological disorders, such as chronic inflammatory demyelinating polyneuropathy and autoimmune encephalitis with autoantibodies against the Ranvier paranode and juxtaparanode, respectively, and extends beyond neurological autoimmunity as well. Although IgG1 autoantibody-mediated neurological disorders can also respond well to rituximab induction therapy in combination with an autoantibody titer drop, remission tends to be less long-lasting and cases where titers are refractory tend to occur more often than in IgG4 autoimmunity. Moreover, presence of GC-like structures in the thymus of myasthenic patients with predominantly IgG1 autoantibodies against the acetylcholine receptor and in ovarian teratomas of autoimmune encephalitis patients with predominantly IgG1 autoantibodies against the N‐methyl‐d‐aspartate receptor (NMDAR) confers increased the ability to generate LLPCs. Here, we review available information on the short-and long-lived nature of ASCs in IgG1 and IgG4 autoantibody-mediated neurological disorders and highlight common mechanisms as well as differences, all of which can inform therapeutic strategies and personalized medical approaches.

Efficacy and safety of different dosages of rituximab for refractory generalized AChR myasthenia gravis: A meta-analysis

BACKGROUND

Rituximab (RTX) is a mouse-human chimeric anti-CD20 monoclonal antibody and has been increasingly used for preventing relapses in myasthenia gravis (MG). However, the appropriate dose for maximizing the beneficial effects in refractory MG with acetylcholine receptor (AChR) autoantibody is a long-standing and critical debating question.

METHODS

We performed a meta-analysis to evaluate the efficacy and safety of the different doses of RTX in 260 refractory AChR-MG patients.

RESULTS

The AChR-MG patients were divided into low or routine RTX dose groups. An overall proportion of 77% (p = 0.000) AChR-MG patients demonstrated improved clinical status as indicated by the Myasthenia Gravis Foundation of America post-intervention scale (MGFA-PIS). There were 77.1% patients showed improved clinical status in lower dose of RTX group (p = 0.000) and 76.8% in routine protocol group (p = 0.000). Although we found there was no significant difference in the proportion of AChR-MG patients with improved clinical status or adverse reactions between the two groups, adverse reactions might be lower in the lower dose RTX group.

CONCLUSION

Most of refractory MG patients with anti-AChR autoantibody were well responsive and tolerated to RTX treatment. Repeated application of lower dose of RTX was effective and might be more appropriate for refractory AChR-MG patients with potential lower side effects.

Rituximab in Refractory Myasthenia Gravis: Experience in a Single Healthcare Center in Mexico

Background: Ten to fifteen percent of patients with myasthenia gravis (MG) have treatment-refractory disease. In short series and case reports, rituximab has proven to be effective in refractory MG.

Methods: A retrospective, longitudinal study was conducted. Recruitment was performed in an MG cohort from a single third-level healthcare center in Mexico. The selection included refractory MG patients that were treated with rituximab. Response after rituximab therapy was assessed with MG composite score (MGCS) and prednisone dose reduction at 6, 12, and 18 months after initiation. Wilcoxon signed-rank test was used to evaluate differences between related groups for non-continual variables. P<0.05 was considered statistically significant.

Results: Ten patients (7%) fulfilled criteria for refractory MG, and eight of them were treated with rituximab. The mean age at MG diagnosis was 25.5 (±2) years, with a female predominance (75%). All our patients (100%) had positive acetylcholine receptor (AchR) antibodies. The median MG duration was six years (interquartile range [IQR] 4.2-6) before rituximab initiation. All patients were previously treated with azathioprine and 50% additionally with cyclophosphamide. The median prednisone doses before rituximab treatment and 18-month follow-up were 50 mg (IQR 30-50 mg) and 10 mg (IQR 0-20 mg), respectively (p=0.011). The median baseline MGCS and at 18-month follow-up were 19.5 (IQR 11-31) and 6 (IQR0-16), respectively (p = 0.012).

Conclusion: Rituximab appears to be associated with clinical improvement and prednisone dose reduction in Latin-American patients diagnosed with anti-AchR MG. Our findings need to be interpreted in light of the limitations mentioned.

Treatment of refractory myasthenia gravis by double-filtration plasmapheresis and rituximab: A case series of nine patients and literature review

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune disease mediated by circulating autoantibodies (anti-AchR, anti-MuSK, etc.). More than 20% of myasthenic patients are refractory to conventional treatments (plasma exchange, IVIg, steroids, azathioprine, mycophenolate mofetil). Rituximab (B-lymphocyte-depleting anti-CD20) and apheresis (double-filtration plasmapheresis [DFPP] and immunoadsorption [IA]) are interesting therapeutic alternatives.

METHODS

This monocentric pilot study included nine refractory myasthenic patients (March 2018 to May 2020) treated by DFPP and/or IA associated with rituximab (375 mg/m² ). Clinical responses were assessed using the Myasthenia Gravis Foundation of America (MGFA) score.

RESULTS

Average age of patients was 53 ± 17 years. Gender ratio (M/F) was 3:6. The combination of apheresis and rituximab reduced median MGFA score from IV to II after 12 months of follow-up. Clinical improvement assessed by MGFA score was sustained in the long-term for all patients, during an average follow-up of 14 ± 9 months, allowing them to be self-sufficient and out sick-leave. The median number of apheresis sessions was 7 (5-30). The dose of prednisolone was reduced in two patients from 40 mg/d and 30 mg/d to 7.5 mg/d and 10 mg/d, respectively. It was stopped in a patient who was taking 30 mg/d. No infectious, bleeding, or thrombosis complications were noted.

CONCLUSION

The combination of rituximab and DFPP was effective to treat refractory MG.

Immunopathology of Autoimmune Myasthenia Gravis: Implications for Improved Testing Algorithms and Treatment Strategies

Myasthenia gravis (MG) is a heterogeneous condition, characterized by autoantibodies (Abs) that target functionally important structures within neuromuscular junctions (NMJ), thus affecting nerve-to-muscle transmission. MG patients are more often now subgrouped based on the profile of serum autoantibodies, which segregate with clinical presentation, immunopathology, and their response to therapies. The serological testing plays an essential role in confirming MG diagnosis and guiding disease management, although a small percentage of MG patients remain negative for antibodies. With the advancements in new highly effective pathophysiologically-specific immunotherapeutic options, it has become increasingly important to identify the specific Abs responsible for the pathogenicity in individual MG patients. There are several new assays and protocols being developed for the improved detection of Abs in MG patients. This review focuses on the divergent immunopathological mechanisms in MG, and discusses their relevance to improved diagnostic and treatment. We propose a comprehensive "reflex testing," algorithm for the presence of MG autoantibodies, and foresee that in the near future, the convenience and specificity of novel assays will permit the clinicians to consider them into routine systematic testing, thus stimulating laboratories to make these tests available. Moreover, adopting treatment driven testing algorithms will be crucial to identify subgroups of patients potentially benefiting from novel immunotherapies for MG.

Myasthenia Gravis Coexisting With Primary Sjögren's Syndrome: Report of Three Cases and Literature Review

Objective: The coexistence of myasthenia gravis (MG) and primary Sjögren's syndrome (pSS) is rarely reported. This study aims to describe the clinical features, treatment and outcome of MG coexisting with pSS.

Materials and Methods: Herein we reported three cases with the two coexisting diseases, and also searched the PubMed, Medline databases, and China Wanfang databases for the relevant case reports written in English, Chinese, or Japanese with detailed data.

Results: We reviewed a total of 17 patients with both diseases. Fifteen patients were female. The median age at onset was 48 years (range 28–78 years). MG was the initial disease in nine of 17 cases. The median interval between the onsets of the two diseases was 30 months (range 7 months to 20 years). The symptoms of MG included fatigable ptosis (64.7%), bulbar symptoms (58.8%), muscle fatigability (64.7%), diplopia (64.7%), dyspnea (23.5%), and facial paralysis (5.9%). Anti-acetylcholine receptor antibody was positive in 70.6% patients. All the patients had sicca symptoms. Manifestations of pSS also included swollen exocrine glands (23.5%), joint pain (23.5%), hair loss (11.8%), leukopenia (11.8%), recurrent oral ulcers (5.9%), Raynaud phenomenon (5.9%), and fever (5.9%). ANA positivity was present in 70.6% patients, anti-SSA positivity in 47.1%, and double positivity of anti-SSA and anti-SSB in 17.6%. There were 12 patients (70.6%) with two autoimmune diseases (pSS and MG), and five patients with more than two autoimmune diseases. Cholinesterase inhibitors were the most commonly prescribed drugs (82.4%). Seven patients received thymectomy and one patient improved after the operation. Two patients were given intravenous methylprednisolone pulse therapy, and four patients oral steroids combined with immunosuppressants initially. Intravenous immunoglobulin and plasma exchange were used in two patients, respectively, for the respiratory failure. All the patients improved following treatment except one patient who died of MG crisis due to medication withdrawal.

Conclusion: The coexistence of SS with MG is quite rare. The onset of MG may occur before or after the diagnosis of SS. Co-morbidity with MG does not seem to adversely affect the course of SS. Thus, controlling the progress of MG is the critical aspect of treatment.

Myasthenia Gravis: From the Viewpoint of Pathogenicity Focusing on Acetylcholine Receptor Clustering, Trans-Synaptic Homeostasis and Synaptic Stability

Myasthenia gravis (MG) is a disease of the postsynaptic neuromuscular junction (NMJ) where nicotinic acetylcholine (ACh) receptors (AChRs) are targeted by autoantibodies. Search for other pathogenic antigens has detected the antibodies against muscle-specific tyrosine kinase (MuSK) and low-density lipoprotein-related protein 4 (Lrp4), both causing pre- and post-synaptic impairments. Agrin is also suspected as a fourth pathogen. In a complex NMJ organization centering on MuSK: (1) the Wnt non-canonical pathway through the Wnt-Lrp4-MuSK cysteine-rich domain (CRD)-Dishevelled (Dvl, scaffold protein) signaling acts to form AChR prepatterning with axonal guidance; (2) the neural agrin-Lrp4-MuSK (Ig1/2 domains) signaling acts to form rapsyn-anchored AChR clusters at the innervated stage of muscle; (3) adaptor protein Dok-7 acts on MuSK activation for AChR clustering from “inside” and also on cytoskeleton to stabilize AChR clusters by the downstream effector Sorbs1/2; (4) the trans-synaptic retrograde signaling contributes to the presynaptic organization via: (i) Wnt-MuSK CRD-Dvl-β catenin-Slit 2 pathway; (ii) Lrp4; and (iii) laminins. The presynaptic Ca²⁺ homeostasis conditioning ACh release is modified by autoreceptors such as M1-type muscarinic AChR and A2A adenosine receptors. The post-synaptic structure is stabilized by: (i) laminin-network including the muscle-derived agrin; (ii) the extracellular matrix proteins (including collagen Q/perlecan and biglycan which link to MuSK Ig1 domain and CRD); and (iii) the dystrophin-associated glycoprotein complex. The study on MuSK ectodomains (Ig1/2 domains and CRD) recognized by antibodies suggested that the MuSK antibodies were pathologically heterogeneous due to their binding to multiple functional domains. Focussing one of the matrix proteins, biglycan which functions in the manner similar to collagen Q, our antibody assay showed the negative result in MG patients. However, the synaptic stability may be impaired by antibodies against MuSK ectodomains because of the linkage of biglycan with MuSK Ig1 domain and CRD. The pathogenic diversity of MG is discussed based on NMJ signaling molecules.