Acetylcholine Receptor Antibody-positive Myasthenia Gravis Research Articles

Does Surgical Removal of the Thymus Have Deleterious Consequences?

The role of immunosenescence, particularly the natural process of thymic involution during aging, is increasingly acknowledged as a factor contributing to the development of autoimmune diseases and cancer. Recently, a concern has been raised about deleterious consequences of the surgical removal of thymic tissue, including for patients who undergo thymectomy for myasthenia gravis (MG) or resection of a thymoma. This review adopts a multidisciplinary approach to scrutinize the evidence concerning the long-term risks of cancer and autoimmunity postthymectomy. We conclude that for patients with acetylcholine receptor antibody-positive MG and those diagnosed with thymoma, the removal of the thymus offers prominent benefits that well outweigh the potential risks. However, incidental removal of thymic tissue during other thoracic surgeries should be minimized whenever feasible.

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.

Markedly upregulated serum semaphorin 4A as a novel activity marker of myasthenia gravis.

Myasthenia gravis (MG) is an autoantibody-mediated disease of the neuromuscular junction. Semaphorin 4A (Sema4A) is involved in the activation of T cells in various inflammatory disorders. In this study, we aimed to investigate whether Sema4A is involved in the pathogenesis of MG. We measured serum Sema4A concentrations in 30 treatment-naïve MG patients with acetylcholine receptor (AChR) antibodies, 7 with muscle-specific tyrosine kinase (MuSK) antibodies and 21 normal controls. As a result, serum Sema4A levels were significantly higher in patients with AChR antibody-positive MG and MuSK antibody-positive MG than in controls (p ≤ 0.0001 for both MG groups). Serum Sema4A levels were correlated with AChR antibody levels (Spearman's ρ = 0.39, p = 0.03) and MG Foundation of America clinical classification classes (Spearman's ρ = 0.38, p = 0.04) in patients with AChR antibody-positive MG. In conclusion, high serum Sema4A levels may reflect T-cell activation, and this molecule could be a potential marker of disease activity in MG.

Effectiveness of early glucocorticoids in myasthenia gravis: a retrospective cohort study.

This study aimed to clarify the effect of early glucocorticoid (GC) application on achieving minimal manifestation (MM) status or better in the treatment of myasthenia gravis (MG) in the early clinical phase. A retrospective analysis was performed using data from 336 patients with MG who received GC therapy from January 2015 to September 2022 in the Zhengzhou University Henan Institute of Medical and Pharmaceutical Sciences Myasthenia Gravis Biobank (ZMB). Patients were divided into two groups: the early mono-GC group (treated with GC within 6 months of MG onset) and the delayed mono-GC group. Kaplan-Meier analysis showed that the early mono-GC group achieved MM status earlier and more frequently than the delayed mono-GC group (log-rank test, p = 0.0082; hazard ratio [HR], 1.66; p = 0.011). The early mono-GC group had a lower maintenance oral GC dose than the delayed mono-GC group. In multivariate Cox regression analysis, early mono-GC (HR, 1.50; p = 0.043), early-onset MG (EOMG) (HR, 1.74; p = 0.034), and ocular MG (OMG) (HR, 1.90; p = 0.007) were associated with MM status or better. In conclusion, early mono-GC, EOMG, and OMG were positive predictors of treatment goals. In EOMG, OMG, and acetylcholine receptor antibody-positive MG (AChR-MG) subgroups, the maintenance oral GC doses in the early mono-GC group were significantly lower than the doses in the delayed mono-GC group (p < 0.05). Early intervention with GC led to better long-term outcomes and reduced the necessary maintenance dose of oral GC for patients with MG. EOMG and OMG were positive predictors of MM status or better with mono-GC.

Remission of severe myasthenia gravis after autologous stem cell transplantation.

Myasthenia gravis (MG) is an autoantibody-mediated neuromuscular junction disorder involving the acetylcholine receptors on the motor endplate. The safety and response to high-dose chemotherapy (HDIT) and autologous hematopoietic cell transplantation (HCT) were assessed in a patient with severe refractory MG. As part of a pilot study of HDIT/HCT for patients with treatment-resistant autoimmune neurological disorders, a patient with severe refractory MG underwent treatment. After mobilization of hematopoietic stem cells with rituximab, prednisone, and G-CSF, the patient had HDIT consisting of carmustine, etoposide, cytarabine, melphalan, and rabbit antithymocyte globulin, followed by autologous HCT. The effect of treatment on the autoantibody to the acetylcholine receptor (AChR) was assessed. The patient had been diagnosed with AChR antibody-positive MG 14 years before HDIT/HCT and had failed thymectomy, therapeutic plasma exchange, and multiple immunomodulatory agents. The Myasthenia Gravis Foundation of America (MGFA) clinical classification was IVb before HDIT/HCT. She tolerated HDIT/HCT well and started to improve clinically within days of treatment. At both 1 and 2 years after HDIT/HCT, patients remained symptom-free. After HDIT/HCT, AChR-binding autoantibodies persisted, and the relative frequency of immune cell subtypes shifted. HDIT/HCT induced a complete response of disease activity in a patient with severe refractory MG. This response may suggest that a cell-mediated etiology may be a significant contributing factor in refractory MG cases. A phase 2 clinical trial is warranted to establish if HDIT/HCT can be an effective therapy for severe refractory MG and to gain a further understanding of disease pathogenesis.

Two Cases of Anti-PD1 Antibody Associated Neurological Immune-Related Adverse Effects (P5-4.001)

<h3>Objective:</h3> We present two cases of neurological immune-related adverse events (irAEs) indefinitely triggered by pembrolizumab. <h3>Background:</h3> Recently, immune checkpoint inhibitors (ICIs) have revolutionized cancer therapy. Programmed cell death protein 1 (PD-1) is a key immune checkpoint receptor expressed by activated T cells. PD-1/PD-L1 antibody therapy is used to treat multiple malignancies; however, it has been associated with an increasing number of irAEs. Neurological irAEs are highly significant complications of ICI therapy that can cause long-term disability and death. Most commonly, neurological irAEs are neuromuscular complications and occur within 4 months after immunotherapy initiation. The anti-PD-1 agent pembrolizumab is currently approved for treatment of several tumors and has been used increasingly due to its more favorable toxicity profile. <h3>Design/Methods:</h3> NA <h3>Results:</h3> NA <h3>Conclusions:</h3> <h3>Case 1:</h3> Our first case is an 84-year-old man with a history of metastatic colon cancer that was treated with pembrolizumab. This is thought to have elicited myositis with elevated CK as well as acetylcholine receptor antibody-positive myasthenia gravis, causing him diffuse and debilitating weakness and functional limitation. He had multiple exacerbations of these symptoms temporally associated with pembrolizumab administration. With the initiation of maintenance treatment and the cessation of pembrolizumab, he required no further admissions for neurologic irAEs, but ultimately he was transitioned to hospice care for cancer progression. <h3>Case 2:</h3> A 65-year-old man with a history of non-small cell carcinoma of the lung on pembrolizumab and zoledronic acid presented with altered mental status and agitation. He had mild pleocytosis on CSF, MRI brain with left mesial temporal T2 FLAIR hyperintensity and nonspecific encephalopathy markers on continuous EEG. He subsequently had complete recovery with IV high-dose steroids followed by plasmapheresis. His symptoms were therefore suspected to be secondary to autoimmune encephalitis elicited by pembrolizumab administration. His oncologist elected to transition to another treatment regimen, and he has had no relapses to date. <b>Disclosure:</b> Ms. Vitek has nothing to disclose. Dr. Hansra has nothing to disclose.

Diagnosing myasthenia gravis using orthoptic measurements: assessing extraocular muscle fatiguability

IntroductionDiagnosing ocular myasthenia gravis (MG) can be challenging because serum antibodies are often not detected. We aimed to explore whether determining extraocular muscle (EOM) weakness using orthoptic measures, including an...

Practical Management for Use of Eculizumab in the Treatment of Severe, Refractory, Non-Thymomatous, AChR + Generalized Myasthenia Gravis: A Systematic Review.

Myasthenia gravis (MG) is a rare autoimmune disorder caused by specific autoantibodies at the neuromuscular junction. MG is classified by the antigen specificity of these antibodies. Acetylcholine receptor (AChR) antibodies are the most common type (74–88%), followed by anti-muscle specific kinase (MuSK) and other antibodies. While all these antibodies lead to neuromuscular transmission failure, the immuno-pathogenic mechanisms are distinct. Complement activation is a primary driver of AChR antibody-positive MG (AChR+ MG) pathogenesis. This leads to the formation of the membrane attack complex and destruction of AChR receptors and the postsynaptic membrane resulting in impaired neurotransmission and muscle weakness characteristic of MG. Broad-based immune-suppressants like corticosteroids are effective in controlling MG; however, their long-term use can be associated with significant adverse effects. Advances in translational research have led to the development of more directed therapeutic agents that are likely to alter the future of MG treatment. Eculizumab is a humanized monoclonal antibody that inhibits the cleavage of complement protein C5 and is approved for use in generalized MG. In this review, we discuss the pathophysiology of MG; the therapeutic efficacy and tolerability of eculizumab, as well as the practical guidelines for its use in MG; future studies exploring the role of eculizumab in different stages and subtypes of MG subtypes; the optimal duration of therapy and its discontinuation; the characterization of non-responder patients; and the use of biomarkers for monitoring therapy are highlighted. Based on the pathophysiologic mechanisms, emerging therapies and new therapeutic targets are also reviewed.

Advancing research in autoimmune neuromuscular disorders

A new Series on autoimmune neuromuscular disorders in The Lancet Neurology comprises three Reviews 1 Huijbers MG Marx A Plomp JJ Le Panse R Phillips WD Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disorders. Lancet Neurol. 2022; 21: 163-175 Google Scholar , 2 Verschuuren JJGM Palace J Murai H Tannemaat M Kaminski HJ Bril V Advances and ongoing research in the treatment of autoimmune neuromuscular junction disorders. Lancet Neurol. 2022; 21: 189-202 Google Scholar , 3 Punga AR Maddison P Heckmann JM et al. Epidemiology, diagnostics, and biomarkers of autoimmune neuromuscular junction disorders. Lancet Neurol. 2022; 21: 176-188 Google Scholar that altogether provide a broad overview of the current status of, and ongoing research into, the causes and treatment of myasthenia gravis and Lambert-Eaton myasthenic syndrome. The major contribution of this Series is the comprehensive information that they provide about disease mechanisms, 1 Huijbers MG Marx A Plomp JJ Le Panse R Phillips WD Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disorders. Lancet Neurol. 2022; 21: 163-175 Google Scholar new drugs in development, 2 Verschuuren JJGM Palace J Murai H Tannemaat M Kaminski HJ Bril V Advances and ongoing research in the treatment of autoimmune neuromuscular junction disorders. Lancet Neurol. 2022; 21: 189-202 Google Scholar and known and potential biomarkers. 3 Punga AR Maddison P Heckmann JM et al. Epidemiology, diagnostics, and biomarkers of autoimmune neuromuscular junction disorders. Lancet Neurol. 2022; 21: 176-188 Google Scholar Advances and ongoing research in the treatment of autoimmune neuromuscular junction disordersMyasthenia gravis and Lambert-Eaton myasthenic syndrome are antibody-mediated autoimmune diseases of the neuromuscular junction that usually present with weakness in ocular muscles and in proximal muscles of the limb and trunk. Prognosis regarding muscle strength, functional abilities, quality of life, and survival is generally good. However, some patients do not respond to treatment. Symptomatic drugs, corticosteroids, and steroid-sparing immunosuppressive drugs remain the cornerstone of treatment. Full-Text PDF Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disordersMuscle weakness and fatigue are the hallmarks of autoimmune neuromuscular junction disorders. Although a plethora of immunosuppressive treatments exist, no cure is available to date and many patients are left with debilitating muscle weakness. Recent advances in the understanding of the structure and function of the neuromuscular junction, and the development of novel in vitro and in vivo models, have been instrumental in unravelling the pathophysiology of these autoimmune diseases. These advances are providing the rationale for the development of new therapeutic strategies. Full-Text PDF Epidemiology, diagnostics, and biomarkers of autoimmune neuromuscular junction disordersAutoimmune neuromuscular junction disorders are rare. However, myasthenia gravis is being increasingly recognised in people older than 50 years. In the past 5–10 years, epidemiological studies worldwide suggest an incidence of acetylcholine receptor antibody-positive myasthenia gravis of up to 29 cases per 1 million people per year. Muscle-specific tyrosine kinase antibody-positive myasthenia gravis and Lambert-Eaton myasthenic syndrome are about 20 times less common. Several diagnostic methods are available for autoimmune neuromuscular junction disorders, including serological antibody, electrophysiological, imaging, and pharmacological tests. Full-Text PDF

Methotrexate Use in Generalized Autoimmune Myasthenia Gravis: A Case series

Methotrexate (MTX) is an inexpensive and well-tolerated immunosuppressive medication that is used anecdotally in autoimmune myasthenia gravis (MG). However, the efficacy in MG is unclear at this time. This retrospective analysis describes six patients with acetylcholine receptor antibody positive MG who were treated with MTX and corticosteroids. The efficacy of MTX was measured by steroid-sparing effect and the Myasthenia Gravis Foundation of America (MGFA) classification. MTX initiation was associated with a reduction in prednisone dosage in all patients. Minimal manifestation status was reached at an average duration of 10 months in 5 patients. No patients were hospitalized for myasthenia gravis exacerbations. There were no major side effects experienced with MTX use. This retrospective analysis suggests that MTX is safe and probably efficacious as a corticosteroid-sparing agent in the management of MG.

Serum irisin levels in patients with myasthenia gravis.

Myasthenia gravis (MG) is an autoimmune disorder whose main symptoms are muscle weakness and fatigue. Irisin is a novel skeletal muscle-derived myokine participating in several physiological and pathological processes. The initial objective of the project was to explore serum levels of irisin in patients with MG, as well as its correlation with disease severity. We retrospectively evaluated serum levels of irisin in 77 MG patients and 57 healthy controls (HCs) by enzyme-linked immunosorbent assay. Further, clinical parameters were measured properly. Serum irisin levels were significantly elevated in MG patients compared with HCs (p < 0.001). Furthermore, serum irisin levels were associated with the myasthenia gravis activities of daily living score in ocular myasthenia gravis (OMG) patients (r = 0.476, p = 0.004), but there was no relationship to be considered of any relevant value in generalized myasthenia gravis (GMG) patients. Acetylcholine receptor antibody-positive MG patients had higher serum irisin levels compared with HCs. Thymoma, endotracheal intubation, or intensive care unit treatments subsequently were not found to have effect on serum levels of irisin, but tendencies of increase were observed in negative ones. Serum irisin levels were elevated in patients with MG, suggesting its possible involvement in MG. And irisin is expected to be a signal to evaluate the activities of daily living of OMG patients, while its effect needs further study.

Cholinergic hyperactivity in patients with myasthenia gravis with MuSK antibodies: A neurophysiological study

ObjectivePatients with myasthenia gravis associated with muscle-specific tyrosine kinase antibodies (MuSK-MG) often manifest signs of cholinergic hyperactivity with standard doses of acetylcholinesterase inhibitors (AChE-Is). Aim of the study was to investigate whether repetitive compound muscle action potential (R-CMAP), the neurophysiological correlate of cholinergic hyperactivity, was present in MuSK-MG irrespective of AChE-I treatment. MethodsPatients with confirmed diagnosis of MuSK-MG were consecutively enrolled during follow-up visits, from January 2019 to April 2020. All these subjects underwent the same neurophysiological protocol, including motor nerve conduction studies and repetitive nerve stimulation. In patients taking pyridostigmine, neurophysiological testing was performed at least 12 hours after the last dose. For comparison, the presence of R-CMAP was investigated in 20 consecutive acetylcholine receptor antibody positive myasthenia gravis (AChR-MG) patients. ResultsWe enrolled 25 MuSK-MG patients (20 females), aged 16–79 years at the study time, with disease duration ranging 0.6–48.8 years (median: 17.7 years). R-CMAP was detected in 12/25 (48%) MuSK-MG cases and in none of the AChR-MG controls (p = 0.0003). In the MuSK-MG population, a history of muscle cramps and fasciculations, during low-dose pyridostigmine therapy, was significantly more frequent in R-CMAP positive than in R-CMAP negative patients (100% vs 31%, p = 0.001). At the time of the study, the proportion of patients still symptomatic for MG was higher among R-CMAP positive cases (92% vs 23%, p = 0.0005). ConclusionsCholinergic hyperactivity is a relatively common finding in MuSK-MG patients, independent of AChE-I treatment, and may constitute an intrinsic feature of the disease. SignificanceR-CMAP detection can represent a useful diagnostic clue for MuSK-MG and predicts poor tolerance to AChE-Is.

MuSK-antibodies are associated with worse outcome in myasthenic crisis requiring mechanical ventilation

Myasthenic crisis (MC) is a life-threatening condition for patients with myasthenia gravis (MG). Muscle-specific kinase-antibodies (MuSK-ABs) are detected in ~ 6% of MG, but data on outcome of MuSK-MCs are still lacking. We made a subgroup analysis of patients who presented with MC with either acetylcholine-receptor-antibody positive MG (AchR-MG) or MuSK-MG between 2006 and 2015 in a retrospective German multicenter study. We identified 19 MuSK-AB associated MCs in 15 patients and 161 MCs in 144 patients with AchR-ABs only. In contrast to patients with AchR-AB, MuSK-AB patients were more often female (p = 0.05, OR = 2.74) and classified as Myasthenia Gravis Foundation of America-class IV before crisis (p = 0.04, OR = 3.25). MuSK-AB patients suffer more often from multiple chronic disease (p = 0.016, OR = 4.87) and were treated more invasively in terms of plasma exchanging therapies (not significant). The number of days of mechanical ventilation (MV) (43.0 ± 53.1 vs. 17.4 ± 18; p < 0.0001), days on an intensive care unit (ICU) (45.3 ± 49.5 vs. 21.2 ± 19.7; p < 0.0001), and hospital-length of stay (LOS) (55.9 ± 47.6 vs. 28.8 ± 20.9 days; p < 0.0001) were significantly increased in MuSK-MC. Remarkable is that these changes were mainly due to patients with MusK-ABs only, whereas patients’ outcome with both antibodies was similar to AchR-MCs. Furthermore, our data showed a shortened duration of MV after treatment with plasma exchanging therapies compared to treatment with intravenous immunoglobulin in MuSK-MCs. We conclude that MuSK-AB-status is associated with a longer need of MV, ICU-LOS, and hospital-LOS in MC, and therefore recommend early initiation of a disease-specific therapy.

Changes in serum complements and their regulators in generalized myasthenia gravis.

To investigate changes in serum complements and their regulators in the pathogenesis of myasthenia gravis (MG). Forty-four patients with acetylcholine receptor antibody-positive MG, as well as 20 patients with non-inflammatory neurological disorders were enrolled. Serum complements (C3, C4 and soluble C5b-9) and complement regulators (vitronectin, clusterin and properdin) were extensively analysed by enzyme-linked immunosorbent assay and their associations with clinical profiles of MG were examined. Serum C3, C4 and clusterin levels were not significantly different between patients with MG and controls. The patients with MG had higher soluble C5b-9 (P=0.09) and vitronectin (P=0.001) levels than the controls; moreover, vitronectin levels decreased after treatment (P=0.09). Serum properdin (P=0.03) levels were lower in the patients with MG than in the controls, and negatively correlated with the MG Activities of Daily Living score (rs=-0.26, P=0.09) and with the presence of bulbar palsy (P=0.04). Our results show that activation of complements and an altered complement network could contribute to the inflammatory pathogenesis of MG.

Management Issues in Myasthenia Gravis Patients Living With HIV: A Case Series and Literature Review.

South Africa is home to more than seven million people living with human immunodeficiency virus (HIV) and a high prevalence of tuberculosis. Human immunodeficiency virus–infected individuals may develop myasthenia gravis (MG), which raises questions regarding their management. An MG database, with 24 years of observational data, was audited for HIV-infected persons. Case reports of MG in HIV-infected persons were reviewed. We identified 17 persons with MG and HIV infection. All had generalized MG with a mean age at onset of 37.8 years. Eleven had acetylcholine receptor antibody–positive MG; one had antibodies against muscle-specific kinase. Six developed MG prior to HIV infection (mean CD4+ 361 cells/mm3); four worsened <6 months of starting antiretrovirals. Eleven developed MG while HIV-infected (mean CD4+ 423 cells/mm3); five presented with mild MG; three in MG crisis requiring rescue therapies (intravenous immune globulin or plasma exchange and/or intravenous cyclophosphamide). Two were diagnosed with HIV infection and MG at the same time. Fifteen required maintenance steroid-sparing immune therapies, predominantly azathioprine, or methotrexate. Plasma HIV viral loads remained below detectable levels on antiretrovirals during immunosuppressant treatment. Over the average follow-up of 6 years, 10 achieved minimal manifestation status, and the remainder improved to mild symptoms. Three cases had tuberculosis before MG, but none developed tuberculosis reactivation on immunosuppressive therapy; one used isoniazid prophylaxis. Herpes zoster reactivation during treatment occurred in one. Conclusions include the following: MG in HIV-infected patients should be managed similarly to individuals without HIV infection; half develop moderate–severe MG; MG symptoms may worsen within 6 months of antiretroviral initiation; safety monitoring must include plasma HIV viral load estimation. Isoniazid prophylaxis may not be indicated in all cases.

Complement Inhibitor Therapy for Myasthenia Gravis.

Complement activation as a driver of pathology in myasthenia gravis (MG) has been appreciated for decades. The terminal complement component [membrane attack complex (MAC)] is found at the neuromuscular junctions of patients with MG. Animals with experimental autoimmune MG are dependent predominantly on an active complement system to develop weakness. Mice deficient in intrinsic complement regulatory proteins demonstrate a significant increase in the destruction of the neuromuscular junction. As subtypes of MG have been better defined, it has been appreciated that acetylcholine receptor antibody-positive disease is driven by complement activation. Preclinical assessments have confirmed that complement inhibition would be a viable therapeutic approach. Eculizumab, an antibody directed toward the C5 component of complement, was demonstrated to be effective in a Phase 3 trial with subsequent approval by the Federal Drug Administration of the United States and other worldwide regulatory agencies for its use in acetylcholine receptor antibody-positive MG. Second- and third-generation complement inhibitors are in development and approaching pivotal efficacy evaluations. This review will summarize the history and present the state of knowledge of this new therapeutic modality.

Immunosuppressive and immunomodulatory therapies for neuromuscular diseases. Part II: New and novel agents.

While traditional immunosuppressive and immunomodulatory therapies remain the cornerstone of immune-mediated neuromuscular disease management, new and novel agents including antigen-specific, monoclonal antibody drugs, have emerged as important treatment options. This article is the second of a two-part series that reviews immune-based therapies in neuromuscular diseases. The first article provides an update on the use of traditional immune-based therapies such as corticosteroids, plasma exchange, steroid-sparing immunosuppressive drugs, and intravenous immunoglobulin G. This second article focuses on new and novel immune-based therapies, including eculizumab, a complement inhibitor approved for acetylcholine receptor antibody-positive myasthenia gravis; rituximab, a B-cell depletion therapy with evolving indications in neuromuscular diseases; and the subcutaneous formulation of immunoglobulin G that gained approval for use in chronic inflammatory demyelinating polyradiculoneuropathy in 2018. Finally, several novel antigen-specific drugs at different stages of investigation in neuromuscular disease are also reviewed.

Factors predicting remission in thymectomized patients with acetylcholine receptor antibody-positive myasthenia gravis.

Although thymectomy is an important therapeutic option for myasthenia gravis (MG), factors predicting remission after thymectomy are not well known. We retrospectively reviewed patients with acetylcholine receptor antibody (AChR-Ab)-positive MG who had undergone thymectomy. Prognostic factors predicting remission were investigated. Changes in AChR-Ab titer before and after thymectomy were also evaluated. Among the 179 patients, 52.5% achieved complete stable or pharmacologic remission. Nonthymomatous pathology and mild preoperative status were favorable predictors of remission. The decrease in AChR-Ab titer after thymectomy was significant in nonthymomatous MG but not in thymomatous MG. Nonthymomatous pathology and mild preoperative status are prognostic factors that may predict remission after thymectomy. The decrease in AChR-Ab titer after thymectomy was significant in nonthymomatous MG but not in thymomatous MG, suggesting that the pathogenic role of the thymus differs according to pathology. Muscle Nerve 58:796-800, 2018.

THUR 213 An unusual case of cluster acetylcholine receptor antibody positive myasthenia gravis

A 73-year-old builder presented with fatigable ptosis and ophthalmoplegia. He was started on pyridostigmine for presumed ocular myasthenia gravis (MG). Despite making an initial improvement he subsequently developed dysarthia, dysphonia and a head drop within 3 weeks. At this time, he also had mild proximal weakness and marked asymmetrical distal weakness of the upper limbs and mild distal lower limb weakness.Conventional serological screening for acetylcholine receptor (AChR) and muscle specific kinase antibodies were negative. However, extended testing using a cell-based cluster assays demonstrated AChR antibody positivity. Repetitive nerve stimulation demonstrated significant decrement more prominent in distal muscles.Despite high dose prednisolone, azathioprine, several courses of IV Immunoglobulins and plasma exchange the patient has had frequent admissions to the high dependency and intensive care setting with respiratory failure.Cluster AChR antibody positive MG has been described only within the last decade and is usually mild and treatment responsive. This is the first case reported to have required intubation and ventilation due to respiratory failure. This case highlights the importance of extending the routine panels for antibody testing in patients with ‘seronegative’ MG and the need to remain vigilant in patients with cluster-AChR positive disease.

Autoantibodies in Myasthenia Gravis

Myasthenia gravis (MG) is one of the autoantibody-mediated neuroimmunological diseases. Autoantibodies to the muscle-type nicotinic acetylcholine receptor (AChR) were detected in more than 80% of MG patients. The gene structure and pathogenicity of some AChR antibodies produced in MG have already been identified and elucidated, respectively. Therefore, the AChR antibody is similar in nature to innovative drug development targets with respect to MG treatment. Here, we discuss the development of molecular target drugs for AChR antibody-positive MG.