Muscle-specific Kinase Antibodies Research Articles

A multicenter, randomized, open-label, phase 2 clinical study of telitacicept in adult patients with generalized myasthenia gravis.

This study aimed to investigate the clinical efficacy and safety of telitacicept in patients with generalized myasthenia gravis (gMG) who tested positive for acetylcholine receptor antibodies or muscle-specific kinase antibodies and were receiving standard-of-care therapy. Patients meeting the eligibility criteria were randomly assigned to receive telitacicept subcutaneously once a week for 24 weeks in addition to standard-of-care treatment. The primary efficacy endpoint was the mean change in the quantitative myasthenia gravis (QMG) score from baseline to week 24. Secondary efficacy endpoints included mean change in QMG score from baseline to week 12 and gMG clinical absolute score from baseline to week 24. Additionally, safety, tolerability and pharmacodynamics were assessed. Twenty-nine of the 41 patients screened were randomly selected and enrolled. The mean (± standard deviation [SD]) reduction in QMG score from baseline to week 24 was 7.7 (± 5.34) and 9.6 (± 4.29) in the 160 mg and 240 mg groups, respectively. At week 12, mean reductions in QMG scores for these two groups were 5.8 (± 5.85) and 9.5 (± 5.03), respectively, indicating rapid clinical improvement. Safety analysis revealed no adverse events leading to discontinuation or mortalities. All patients showed consistent reductions in serum immunoglobulin (Ig) A, IgG and IgM levels throughout the study. Telitacicept demonstrated safety, good tolerability and reduced clinical severity throughout the study period. Further validation of the clinical efficacy of telitacicept in gMG will be conducted in an upcoming phase 3 clinical trial.

Muscle-Specific Receptor Tyrosine Kinase Antibody Positive Myasthenia Gravis

Reportedly, patients with muscle-specific kinase (MuSK) antibody-positive myasthenia gravis (MG) account for approximately 3.0% of all patients with MG in Japan. Compared with patients who have acetylcholine receptor antibody-positive MG, those with MuSK antibody-positive MG show young-onset disease with female predominance, a low rate of ocular involvement (5.9%), and greater severity of dysphagia. The aforementioned types of MG are indistinguishable based on clinical symptoms and electrophysiological tests, and measurement of MuSK antibodies is essential for diagnosis. Thymectomy and complement inhibitors are not indicated for treatment, and acetylcholinesterase inhibitors, steroids, immunosuppressants, plasma exchange, intravenous immunoglobulin therapy, and neonatal Fc receptor inhibitors are used.

Batoclimab vs Placebo for Generalized Myasthenia Gravis

Myasthenia gravis (MG) is caused by autoantibodies that disrupt the neuromuscular junction. The neonatal fragment crystallizable receptor (FcRn) antagonists, efgartigimod and rozanolixizumab, reduce immunoglobulin G (IgG) level in the circulation and alleviate symptoms in patients with generalized MG. To examine the efficacy and safety profile of batoclimab, a monoclonal IgG1 antibody, in patients with generalized MG. This was a multicenter randomized clinical trial conducted from September 15, 2021, to June 29, 2022, at 27 centers in China. Adult patients 18 years or older with generalized MG were screened, and those who were antibody positive were enrolled. Eligible patients received batoclimab or matching placebo in addition to standard of care. Each treatment cycle consisted of 6 weekly subcutaneous injections of batoclimab, 680 mg, or matching placebo followed by 4 weeks of observation. A second treatment cycle was conducted in patients who required continuing treatment. The primary outcome was sustained improvement, as defined by a 3-point or greater reduction in the Myasthenia Gravis Activities of Daily Living (MG-ADL) score from baseline for 4 or more consecutive weeks in the first cycle in individuals who were positive for acetylcholine receptor or muscle-specific kinase antibodies. A total of 178 adult patients with generalized MG were screened, 132 were randomly assigned, 131 tested positive for antibodies, and 1 tested negative for antibodies. A total of 132 patients (mean [SE] age, 43.8 [13.6] years; 88 women [67.2%]) were enrolled. The rate of sustained MG-ADL improvement in the first cycle in antibody-positive patients was 31.3% (20 of 64) in the placebo group vs 58.2% (39 of 67) in the batoclimab group (odds ratio, 3.45; 95% CI, 1.62-7.35; P = .001). The MG-ADL score diverged between the 2 groups as early as week 2. The mean (SE) maximum difference in MG-ADL score reduction occurred 1 week after the last dose (day 43, 1.7 [0.3] in the placebo group vs 3.6 [0.3] in the batoclimab group; group difference, -1.9; 95% CI, -2.8 to -1.0; nominal P < .001). The rates of treatment-related and severe treatment-emergent adverse events in patients were 36.9% (24 of 65) and 7.7% (5 of 65) in the placebo group vs 70.1% (47 of 67) and 3.0% (2 of 67) in the batoclimab group, respectively. Batoclimab increased the rate of sustained MG-ADL improvement and was well tolerated in adult patients with generalized MG. Clinical effects and the extent of IgG reduction were similar to those previously reported for efgartigimod and rozanolixizumab. Future studies of large sample size are needed to further understand the safety profile of batoclimab. ClinicalTrials.gov Identifier: NCT05039190.

Comparison of three methods for the detection of antibodies against muscle-specific kinase

ObjectivesTo compare 3 different methods for the detection of antibodies against muscle-specific kinase (MuSK). MethodsMuSK antibody testing was performed in 237 serum samples by enzyme-linked immunosorbent assay (ELISA) and fixed cell-based assay (f-CBA-IFA). One hundred and forty-eight (148) of the sera had previously been tested by RIA during clinical testing: 47 MuSK antibody positive and 101 MuSK antibody negative. Of the MuSK RIA negative antibodies, 46 tested positive for other neural antibodies. Additionally, 89 sera were subsequently tested by all three methods: 70 healthy controls and 19 sera positive for other neural antibodies. ResultsQualitative inter-assay agreement based on tiered RIA values was 100% for results of 1.00 nmol/L or greater by both methods; 81% and 94% for results between 0.21 and 0.99 nmol/L by ELISA and f-CBA-IFA, respectively; and 0% for results of 0.04–0.20 nmol/L by both methods. Negative results showed 100% agreement between RIA and both ELISA and f-CBA-IFA (n = 55). None of the controls positive for other neural autoantibodies or healthy controls were positive in any assay. ConclusionOverall, excellent agreement was observed between the 3 methods used to detect antibodies against MuSK. Both the f-CBA-IFA and ELISA performed comparably to RIA and exhibited excellent overall accuracy for MuSK IgG detection, with the f-CBA-IFA demonstrating higher agreement between positive samples with the RIA than the ELISA without identifying false positives in the control samples. Advantages of non-radioactive methods for the detection of MuSK antibodies include reduced handling and disposal of hazardous materials, potential for automation and the reagents having a longer shelf-life, reducing costs associated with both workflow and lot validations. Thus, commercially available ELISA and transfected cell-based assays are viable alternatives to the traditional radioactive assay used for serologic determination of MuSK IgG.

Clinical Features and Pathogenesis of Double Seronegative Myasthenia Gravis

Subjects with double seronegative myasthenia gravis (DNMG) are defined as those who are seronegative to both antibodies against acetylcholine receptor (AChR) and muscle-specific kinase (MuSK) by radioimmunoprecipitation assay (RIA). They are basically heterogeneous. But cell based assay (CBA) with clustered AChR has revealed a considerable part of DNMG are AChR antibody associated. Furthermore, information of clinical features and thymus pathology has raised a possibility that this could extend to those with undetectable antibodies by established assays whose symptoms are mild. Primary sites of antibody production are probably in the thymus in these cases. LOMG pathology is also suspected for a small part of DNMG by age onset, atrophic or age-related thymus and presence of titin antibody. In these cases, tolerance induction may be insufficient, and positive selection of autoimmune T cells such as AChR-specific T cells are promoted rather than negative selection. In addition, CBA detected MuSK antibody associated in a few cases with DNMG. Finally, some DNMG subjects have distinct clinical features with severe symptoms from those with AChR- MG and MuSK-MG in DNMG. They probably have different pathogenesis.

Promising efficacy of Low-Dose rituximab in Muscle specific kinase antibody positive Myasthenia Gravis

AimsThe study aims to evaluate the efficacy of low dose rituximab (RTX) in patients with muscle-specific kinase antibody positive myasthenia gravis (MuSK-MG). MethodsThis is a single-center, retrospective study. A total of 10 patients with MuSK-MG were admitted to the Department of Neurology, First Hospital, Shanxi Medical University, between April 2021 to April 2023. Of them, 9 patients had been treated with low dose RTX (500 mg every 6 month) and recruited in this study. The clinical information, including the severity before and after RTX treatment, were collected from the medical records. Clinical effectiveness was assessed by Myasthenia Gravis Foundation of America (MGFA)-postintervention status (PIS), MG-related activities of daily living (MG-ADL), Quantitative Myasthenia Gravis (QMG) scores, Myasthenia Gravis Quality of Life 15-item revised (MG-QOL15r), dosage of steroid at the end of follow up. ResultsAll nine patients showed clinical improvement at the final follow-up after low-dose RTX treatment. The mean dose of prednisolone decreased significantly from 50 mg at baseline to 18.33 mg at the last follow-up (z = -3.417, p = 0.001). The administration of low-dose RTX treatment led to significant improvements in ADL levels (Z = -2.675, P < 0.01), QMG score levels (Z = -2.371, P < 0.05) and QOL-15r levels (Z = -2.547, P < 0.01) at last visit. ConclusionLow-dose RTX is effective for treating MuSK-MG patients. Longer-term follow-up and larger-scale studies are needed to provide further evidence.

Abstract 18700: Immune Checkpoint Inhibitor-Related Myocarditis and Overlapping Syndromes

Background: Immune checkpoint inhibitor (ICI)-related myocarditis is a rare adverse effect of ICI's. When accompanied by overlapping myasthenia gravis, prognosis is worsened. While established guidelines aid in the treatment of ICI-associated adverse events, management of overlapping syndromes is complex and challenging. Case description: A 66-year-old man with metastatic renal cell carcinoma recently started on ipilimumab and nivolumab presented with dizziness and diplopia. He had high-grade atrioventricular (AV) block with junctional escape. He had elevated troponin, transaminases, and creatinine kinase. Coronary angiogram showed no evidence of obstructive coronary artery disease. A permanent pacemaker was placed. Cardiac MRI showed no specific features of myocarditis, though quality was limited by pacemaker artifact; left ventricular ejection fraction was 29%. MRI of the orbits showed no signs of extraocular myositis. Acetylcholine receptor (AChR) antibody and muscle-specific kinase (MuSK) antibody was negative. Given ongoing suspicion for ICI-associated adverse events, the patient underwent endomyocardial biopsy. This revealed lymphocytic myocarditis, confirming the diagnosis of ICI-related myocarditis. Despite improvement of troponin, transminases, and creatinine kinase, he developed progressive weakness, dysphagia, and respiratory failure, and died one month after initial presentation. Discussion: We highlight a case of ICI-related myocarditis presenting as high-grade AV block with concurrent hepatitis, myositis, and probable serologic-negative myasthenia gravis (MG). Overlapping syndromes are common in patients with exposure to ICI's, and are associated with significantly higher mortality. Although steroids are first-line for treating ICI-associated adverse events including myocarditis, they can initially lead to acute worsening of MG symptoms. While our patient had laboratory and biomarker improvement of his myocarditis, hepatitis, and myositis, he developed progressive weakness and respiratory failure. Our case highlights the complexity and challenges of managing ICI-related myocarditis and overlapping syndromes, including MG, and its poor prognosis despite prompt treatment.

B-076 Comparison of Three Methods for the Detection of Antibodies Against Muscle-Specific Kinase

Abstract Background Myasthenia gravis (MG) is a neuromuscular disease characterized by skeletal muscle weakness and fatigue. These symptoms are due to a reduction in synaptic signal transduction caused by autoantibodies against post-synaptic proteins in the neuromuscular junction. Approximately 85% of patients with MG have autoantibodies against acetylcholine receptors (AChR); however, autoantibodies against muscle specific kinase (MuSK) and low-density lipoprotein receptor-related protein 4 (LRP4) may also be found in patients with MG. Detection and identification of these antibodies is important in the diagnosis and treatment of patients under evaluation for MG. MuSK, a transmembrane protein expressed on skeletal muscles, is essential to the formation and maintenance of the neuromuscular junction. Approximately 6% of MG patients have MuSK autoantibodies. Traditionally, radioimmunoprecipitation assays (RIA) have been used to detect MuSK antibodies in patient sera. However, RIA has several limitations, including safety and regulatory concerns associated with using radioactive materials and the short half-life of reagents. Alternatives to RIA, such as enzyme-linked immunosorbent assays (ELISA) and cell-based assays (CBA), do not have the same challenges. Recent studies outside of the USA suggest that cell-based assays may have equal or superior sensitivity than RIA; particularly in the detection of MuSK antibodies in patients previously diagnosed with seronegative MG (MG patients without detectable AChR or MuSK antibodies by RIA). The objective of this study was to compare the performance of two commercially available ELISA and fixed cell-based assay (f-CBA) kits to RIA for the detection of MuSK antibodies. Methods A total of 237 sera were evaluated by RIA, ELISA and/or f-CBA. These sera include 47 MuSK RIA positive sera, 55 MuSK RIA negative sera, 70 self-reported healthy control sera, and 65 sera positive for other neural antibodies associated with MG, Lambert-Eaton Myasthenic Syndrome, paraneoplastic neurologic syndromes, or autoimmune encephalitis. Results Both f-CBA and ELISA demonstrated 100% specificity for MuSK antibodies in sera from self-reported healthy controls and sera from patients positive for other antibodies. Forty-seven sera tested positive for anti-MuSK antibodies by RIA; of those 47 sera, 7 sera tested negative by ELISA and 5 tested negative by f-CBA kits while the remaining 40 were concordant between ELISA, f-CBA and RIA. The discrepancy between RIA and the commercial kits for ELISA and f-CBA was only observed in low positive sera (0.04–0.21 nmol/L ARUP RIA). Clinical information was not available for discrepant specimens. However, a review of MuSK RIA results for University of Utah patients shows that of 7 patients with an ARUP RIA result of 0.04–0.21 nmol/L, only 1 had symptoms that may possibly be consistent with MG. The remaining 6 low positive patients did not have symptoms consistent with a diagnosis of MG. This may suggest an issue with RIA specificity rather than ELISA and f-CBA sensitivity. However, further studies are needed to confirm this. Conclusion Commercially available ELISA and f-CBA kits offer viable alternatives to traditional RIA for detection of MuSK antibodies.

Clinical characteristics and treatment outcomes in patients with double-seronegative myasthenia gravis.

Double-seronegative myasthenia gravis (dSNMG) is defined as myasthenia gravis (MG) without detectable or low affinity antibodies to acetylcholine receptor (AChR) and muscle-specific kinase (MuSK). There are limited data on detailed clinical features and outcomes after treatment in dSNMG patients. The aim was to describe the clinical characteristics and outcomes in dSNMG patients based on MG scales. A retrospective study was performed of patients diagnosed with MG who had negative AChR or MuSK antibodies and they were compared with an AChR-positive MG cohort. Correlations were made with data from the first and last clinic visits, between demographics, clinical characteristics, treatment and disease severity, based on the Myasthenia Gravis Foundation of America category, Myasthenia Gravis Impairment Index (MGII), Patient Acceptable Symptom State and simple single question (SSQ). Eighty patients met the inclusion criteria for dSNMG. The baseline MGII and SSQ scores in the dSNMG cohort showed no significant differences from the AChR group (p = 0.94 and p = 0.46). The dSNMG cohort MGII and SSQ scores improved significantly at the last clinical evaluation (p = 0.001 and p = 0.047). The MGII improvement in the AChR cohort was significantly better (p = 0.003). The initial severity of dSNMG based on clinical scores is similar to antibody-positive MG patients. There is significant clinical improvement in dSNMG patients after therapy, measured in the last clinical evaluation. This supports an immune pathophysiology of many dSNMG patients.

IgG1-3 MuSK Antibodies Inhibit AChR Cluster Formation, Restored by SHP2 Inhibitor, Despite Normal MuSK, DOK7, or AChR Subunit Phosphorylation.

Up to 50% of patients with myasthenia gravis (MG) without acetylcholine receptor antibodies (AChR-Abs) have antibodies to muscle-specific kinase (MuSK). Most MuSK antibodies (MuSK-Abs) are IgG4 and inhibit agrin-induced MuSK phosphorylation, leading to impaired clustering of AChRs at the developing or mature neuromuscular junction. However, IgG1-3 MuSK-Abs also exist in MuSK-MG patients, and their potential mechanisms have not been explored fully. C2C12 myotubes were exposed to MuSK-MG plasma IgG1-3 or IgG4, with or without purified agrin. MuSK, Downstream of Kinase 7 (DOK7), and βAChR were immunoprecipitated and their phosphorylation levels identified by immunoblotting. Agrin and agrin-independent AChR clusters were measured by immunofluorescence and AChR numbers by binding of 125I-α-bungarotoxin. Transcriptomic analysis was performed on treated myotubes. IgG1-3 MuSK-Abs impaired AChR clustering without inhibiting agrin-induced MuSK phosphorylation. Moreover, the well-established pathway initiated by MuSK through DOK7, resulting in βAChR phosphorylation, was not impaired by MuSK-IgG1-3 and was agrin-independent. Nevertheless, the AChR clusters did not form, and both the number of AChR microclusters that precede full cluster formation and the myotube surface AChRs were reduced. Transcriptomic analysis did not throw light on the pathways involved. However, the SHP2 inhibitor, NSC-87877, increased the number of microclusters and led to fully formed AChR clusters. MuSK-IgG1-3 is pathogenic but seems to act through a noncanonical pathway. Further studies should throw light on the mechanisms involved at the neuromuscular junction.

A multicentre, prospective, double-blind study comparing the accuracy of autoantibody diagnostic assays in myasthenia gravis: the SCREAM study

Laboratory determination of autoantibodies against acetylcholine receptor (AChR), muscle-specific kinase (MuSK) and other autoantigens have been integrated into the diagnosis of myasthenia gravis (MG). However, evidence supporting the selection of methodologies is lacking. In this prospective, multicentre cohort study, we recruited patients with suspected MG to evaluate the diagnostic accuracy of cell-based assay (CBA), radioimmunoprecipitation assay (RIPA) and enzyme-linked immunosorbent assay (ELISA) in detecting AChR and MuSK autoantibodies. This study is registered with www.clinicaltrials.gov, number NCT05219097. 2272 eligible participants were recruited, including 2043MG, 229 non-MG subjects. AChR antibodies were detected in 1478, 1310, and 1280 out of a total of 2043MG patients by CBA, RIPA, and ELISA, respectively; sensitivity, 72.3% (95% CI, 70.3-74.3), 64.1% (95% CI, 62.0-66.2), 62.7% (95% CI, 60.5-64.8); specificity, 97.8% (95% CI, 95.0-99.3), 97.8% (95% CI, 95.0-99.3), 94.8% (95% CI, 91.9-97.7). MuSK antibodies were found in 59, 50, and 54 from 2043MG patients by CBA, RIPA and ELISA, respectively; sensitivity, 2.9% (95% CI, 2.2-3.7), 2.4% (95% CI, 1.8-3.2), 2.6% (95% CI, 2.0-3.4); specificity, 100% (95% CI, 98.4-100), 100% (95% CI, 98.4-100), and 99.1% (95% CI, 96.9-99.9). The area under the curve of AChR antibodies tested by CBA was 0.858, and there were statistical differences with RIPA (0.843; p=0.03) and ELISA (0.809; p<0.0001). CBA has a higher diagnostic accuracy compared to RIPA or ELISA in detecting AChR and MuSK autoantibodies for MG diagnosis. New Terrain Biotechnology, Inc., Tianjin, China.

Autoantibodies, clinical phenotypes and quality of life in Lebanese patients with myasthenia gravis.

Myasthenia gravis (MG) is a rare autoimmune disease that affects the neuromuscular junction. It is characterized by the production of heterogeneous autoantibodies that bind to the neuromuscular junction and alter neural transmission. Recently, more attention was given to MG-related antibodies and their clinical influence. In Lebanon, studies about MG are very rare. To date, there is still no research on the different autoantibodies developed by Lebanese MG patients. We conducted a study aimed at detecting the prevalence of different antibodies in a group of seventeen Lebanese patients with MG, and exploring their associations with clinical phenotypes and quality of life (QOL). MG antibody test in Lebanon is restricted only to two antibodies: acetylcholine receptor (anti-AChR) and muscle-specific kinase (anti-MUSK) antibodies. Results showed that 70.6% of patients were anti-AChR positive and all of them were anti-MUSK negative. Association between MG serological profiles, clinical outcomes and QOL was not significant. Together, current findings suggest that anti-MUSK antibody is not common and difference in antibody profile may not change the clinical phenotypes and QOL of MG Lebanese patients. In the future, it is recommended to check also for autoantibodies other than anti-AChR and anti-MUSK, which may reveal new antibody profiles and possible associations with clinical outcomes.

Development and characterization of agonistic antibodies targeting the Ig-like 1 domain of MuSK

Muscle-specific kinase (MuSK) is crucial for acetylcholine receptor (AChR) clustering and thereby neuromuscular junction (NMJ) function. NMJ dysfunction is a hallmark of several neuromuscular diseases, including MuSK myasthenia gravis. Aiming to restore NMJ function, we generated several agonist monoclonal antibodies targeting the MuSK Ig-like 1 domain. These activated MuSK and induced AChR clustering in cultured myotubes. The most potent agonists partially rescued myasthenic effects of MuSK myasthenia gravis patient IgG autoantibodies in vitro. In an IgG4 passive transfer MuSK myasthenia model in NOD/SCID mice, MuSK agonists caused accelerated weight loss and no rescue of myasthenic features. The MuSK Ig-like 1 domain agonists unexpectedly caused sudden death in a large proportion of male C57BL/6 mice (but not female or NOD/SCID mice), likely caused by a urologic syndrome. In conclusion, these agonists rescued pathogenic effects in myasthenia models in vitro, but not in vivo. The sudden death in male mice of one of the tested mouse strains revealed an unexpected and unexplained role for MuSK outside skeletal muscle, thereby hampering further (pre-) clinical development of these clones. Future research should investigate whether other Ig-like 1 domain MuSK antibodies, binding different epitopes, do hold a safe therapeutic promise.

Myasthenic crisis.

Myasthenic crisis (MC) is a life-threatening manifestation of myasthenia gravis (MG) defined by respiratory insufficiency that requires the use of invasive or non-invasive ventilation. This is often the result of respiratory muscle weakness but can also be due to bulbar weakness with upper airway collapse. MC occurs in approximately 15%-20% of patients with MG usually within the first 2 to 3 y of the disease course. Many crises have a specific trigger with respiratory infections being most common; however, no specific trigger is found in 30%-40% of patients. MG patients with a history of MC, severe disease, oropharyngeal weakness, muscle-specific kinase (MuSK) antibodies and thymoma appear to be at higher risk. Most episodes of MC do not occur suddenly, providing a window of opportunity for prevention. Immediate treatment is directed toward airway management and removing any identified triggers. Plasmapheresis is preferred over intravenous immune globulin as the treatments of choice for MC. The majority of patients are able to be weaned from mechanical ventilation within 1 mo and the outcomes of MC are generally favorable. The mortality rate in United States cohorts is less than 5% and mortality in MC seems to be driven by age and other medical co-morbidities. MC does not appear to affect long-term prognosis as many patients are able to eventually achieve good MG control.

Complement activation profiles in anti-acetylcholine receptor positive myasthenia gravis.

Complement component 5 (C5) targeting therapies are clinically beneficial in patients with acetylcholine receptor antibody+ (AChR-Ab+ ) generalized myasthenia gravis (MG). That clearly implicates antibody-mediated complement activation in MG pathogenesis. Here, classical and alternative complement pathways were profiled in patients from different MG subgroups. In a case-control study, concentrations of C3a, C5a and sC5b9 were simultaneously quantified, indicating general activation of the complement system, whether via the classical and lectin pathways (C4a) or the alternative pathway (factors Ba and Bb) in MG patients with AChR or muscle-specific kinase antibodies (MuSK-Abs) or seronegative MG compared to healthy donors. Treatment-naïve patients with AChR-Ab+ MG showed substantially increased plasma levels of cleaved complement components, indicating activation of the classical and alternative as well as the terminal complement pathways. These increases were still present in a validation cohort of AChR-Ab+ patients under standard immunosuppressive therapies; notably, they were not evident in patients with MuSK-Abs or seronegative MG. Neither clinical severity parameters (at the time of sampling or 1 year later) nor anti-AChR titres correlated significantly with activated complement levels. Markers indicative of complement activation are prominently increased in patients with AChR-Ab MG despite standard immunosuppressive therapies. Complement inhibition proximal to C5 cleavage should be explored for its potential therapeutic benefits in AChR-Ab+ MG.

NCMP-21. PEMBROLIZUMAB-ASSOCIATED MYOSITIS, MYASTHENIC CRISIS, AND MYOCARDITIS IN A PATIENT WITH METASTATIC UROTHELIAL CARCINOMA

Abstract Although immune checkpoint inhibitors (ICIs) have improved systemic cancer care, in rare cases, patients develop neuromuscular immune related adverse events (irAEs), which carry high morbidity and mortality. This case study describes an 85-year-old male who developed the triad of myositis, myasthenic crisis, and myocarditis in association with ICI treatment for metastatic urothelial carcinoma (T3N0M1). The patient developed progressive weakness and gait impairment five weeks after initiating treatment with pembrolizumab. Later, he developed reduced ambulation, fatigue, shortness of breath, and orthopnea with concomitant ECG changes. Clinical exam demonstrated dysphagia, ptosis, proximal muscle weakness, fatigable weakness, and areflexia, ultimately resulting in respiratory failure, intubation, and inability to stand. Lab workup revealed elevated creatinine kinase, myoglobin, lactate dehydrogenase, and aldolase, but was notably negative for acetylcholine receptor and muscle specific kinase antibodies. Labs, clinical timeline, and clinical features supported his diagnoses. Interestingly, the cytokine panel demonstrated a high-normal soluble IL-2 receptor alpha which supports autoimmune pathology and elevated IL-10. The patient was treated with pyridostigmine, prednisone, and plasma exchange (PLEX) for 10 exchanges. EMG 10 days into treatment supported evidence of inflammatory myositis. After methylprednisone and PLEX treatment, the patient’s symptoms improved to ambulation with a walker and occasional BiPap support. His metastatic disease remained stable for several weeks while holding pembrolizumab due to toxicity. This case illustrates how early intervention and aggressive treatment for neuromuscular ICI-induced triad can stabilize patients and improve neurologic recovery. Due to the high morbidity and mortality for these irAEs, the authors support increased clinical scrutiny when evaluating these rare conditions and consideration of investigating the acute inflammatory processes. With improved pathophysiologic understanding of these rare conditions, the community can improve outcomes and refine treatments.

Enrichment of serum IgG4 in MuSK myasthenia gravis patients

Muscle-specific kinase (MuSK) myasthenia gravis (MG) is a neuromuscular autoimmune disease belonging to a growing group of IgG4 autoimmune diseases (IgG4-AIDs), in which the majority of pathogenic autoantibodies are of the IgG4 subclass. The more prevalent form of MG with acetylcholine receptor (AChR) antibodies is caused by IgG1–3 autoantibodies. A dominant role for IgG4 in autoimmune disease is intriguing due to its anti-inflammatory characteristics. It is unclear why MuSK autoantibodies are predominantly IgG4. We hypothesized that MuSK MG patients have a general predisposition to generate IgG4 responses, therefore resulting in high levels of circulating IgG4. To investigate this, we quantified serum Ig isotypes and IgG subclasses using nephelometric and turbidimetric assays in MuSK MG and AChR MG patients not under influence of immunosuppressive treatment. Absolute serum IgG1 was increased in both MuSK and AChR MG patients compared to healthy donors. In addition, only MuSK MG patients on average had significantly increased and enriched serum IgG4. Although more MuSK MG patients had elevated serum IgG4, for most the IgG4 serum levels fell within the normal range. Correlation analyses suggest MuSK-specific antibodies do not solely explain the variation in IgG4 levels. In conclusion, although serum IgG4 levels are slightly increased, the levels do not support ubiquitous IgG4 responses in MuSK MG patients as the underlying cause of dominant IgG4 MuSK antibodies.

Clinical value of cell-based assays in the characterisation of seronegative myasthenia gravis

ObjectivePatients with myasthenia gravis without acetylcholine receptor (AChR) or muscle-specific kinase (MuSK) antibodies detected by radioimmunoprecipitation assays (RIAs) are classified as seronegative myasthenia gravis (SNMG). Live cell-based assays (l-CBAs) can...

Laryngeal Manifestations of Myasthenia Gravis

Laryngeal Manifestations of Myasthenia Gravis Jessica B. Howell (bio) and Jaime Eaglin Moore (bio) CARE OF THE PROFESSIONAL VOICE WHAT IS MYASTHENIA GRAVIS? Myasthenia Gravis (MG) is an autoimmune disease characterized by immunoglobulin G (IgG) autoantibodies against the postsynaptic acetylcholine receptor (Ach-R).1 This leads to a decrease in the number of receptors at motor end plates, subsequently causing a defect in neuromuscular transmission. This involves mainly skeletal muscle, and is manifested clinically as fatigability and weakness of voluntary muscle activity.2 This muscle weakness worsens with exercise.3 The most commonly affected muscles include extraocular muscles and the levator palpebrae.4 The incidence of MG is approximately 1:100,000, with women affected more than men (2:1).5 Elderly patients constitute roughly one third of all cases, with a peak incidence in men at ages sixty to seventy years; and in women there is a bimodal peak at twenty to forty years and around seventy years of age.6 WHAT ARE THE SYMPTOMS OF MYASTHENIA GRAVIS? Ocular muscles are most frequently affected with MG. The most common presenting complaints include diplopia (double vision) and ptosis (drooping eyelid). However, it is important to note that these symptoms can be absent in other forms of the disease, including bulbar (hindbrain) and laryngeal.7 Bulbar involvement is seen in 20% of MG patients, with symptoms including dysphagia (swallowing difficulty) and hypernasal speech secondary to fatigability of the esophageal and pharyngeal muscles.8 Isolated bulbar involvement typically occurs in late onset MG, which given its symptomatology, can easily be misdiagnosed. The diagnosis can be blurred further, as 40% of patients with late onset MG are seronegative, meaning titers of acetylcholine receptor antibodies (Ach-R) are undetectable.9 The otolaryngologic manifestations of MG include facial weakness, dysphagia, and dysphonia. Up to 27% of patients will present with swallowing and voice difficulties.10 Laryngeal involvement may lead to intermittent aphonia (loss of voice), hoarseness, vocal fatigue, hypernasality, inability to control pitch, slurred speech, monotone voice, and stridor (noisy breathing).11 The latter may be seen in the setting of respiratory failure, termed a myasthenic crisis. Respiratory failure secondary to MG is uncommon, occurring in 3- 8% of cases usually late in the disease.12 However, there have been case reports [End Page 355] of patients with initial presentation of myasthenic crisis. This subset of patients may require intubation and ventilatory support. Muscle relaxants used for rapid sequence intubation, such as succinylcholine, can cause prolonged paralysis in patients with MG; increasing time to extubation.13 HOW DO YOU DIAGNOSIS MYASTHENIA GRAVIS? The diagnosis of MG can be made with clinical, laboratory, pharmacologic, and electrophysiologic criteria. As previously discussed, patients present clinically with voluntary muscle weakness that improves with rest and worsens with exertion or throughout the day. Patients also can be diagnosed with a simple laboratory test aimed at identifying antibodies to acetylcholine receptors. Antibody levels greater than 0.2 nmol/L are deemed diagnostic.14 However, not all patients with MG have detectable levels of ACh-R antibodies, specifically those patients with isolated laryngeal and ocular forms.15 In these patients, muscle specific kinase antibodies (MuSK) can be used as an alternative.16 However, multiple studies have demonstrated that patients with laryngeal MG have undetectable anti-MuSK levels, as well.17 Anti-striated muscle antibodies are also found in some patient with MG and are associated with the presence of thymomas.18 If abnormal antibody levels are present, these levels cannot be used to monitor treatment success or progression of the disease. MG can be diagnosed with the "Tensilon test," which employs edrophonium, a short acting acetylcholinesterase inhibitor.19 Tensilon (Alliance Pharmaceuticals; Wiltshire, UK), which is no longer available, has now been replaced by Enlon (Mylan Teoranta; Rockford, IL). Edrophonium acts to prevent degradation of acetylcholine, increasing its ability to bind to remaining postsynaptic receptors. Objectively, this causes temporary improved muscle strength following intravenous administration and assessment can include electrophysiological testing.20 In generalized MG, this test has a sensitivity of 95%. However those with isolated ocular symptoms are less likely to demonstrate improvement. For those with laryngeal involvement, Tensilon testing was found to be positive in 97.4% of patients...

MG-LEMS overlap syndrome associated with musk antibody

Myasthenia Gravis (MG) and Lambert-Eaton Myasthenic syndrome (LEMS) are immune-mediated disorders of the neuromuscular junction. Clinical, electrophysiological and immunological overlap of these two conditions have been uncommonly reported. We report the unusual association of LEMS with muscle-specific kinase (MuSK) antibody associated MG.