Anti-acetylcholinesterase antibodies associate with ocular myasthenia gravis

Risk for generalization in ocular onset myasthenia gravis: experience from a neuro-ophthalmology clinic

Conversion to generalized myasthenia gravis (GMG) within the first 2 years has been reported in 18-85% of patients with ocular myasthenia gravis (OMG). The aim of the study was to investigate the risk factors for generalization in patients with OMG admitted to a neuro-ophthalmology clinic and to determine if there were differences between patients with GMG with predominant bulbar (GMG-B) or extremity muscle (GMG-E) involvement according to the 6th and 24th-month Myasthenia Gravis Foundation of America classification ranks. Patients with OMG who were followed-up for at least 24 months were retrospectively analyzed. Demographic, clinical, laboratory features and treatment strategies that can be associated with generalization and time to generalization were evaluated. Of the 139 patients with OMG, 54 (39%) showed generalization with a mean time of 10.3 (range 2-24) months. GMG-B and GMG-E were diagnosed in 31 (22.3%) and 23 patients (16.5%), respectively. Seropositivity for acetylcholine receptor and muscle-specific tyrosine kinase antibodies, abnormal single-fiber electromyography (SFEMG), and the presence of thymic abnormalities (thymoma and hyperplasia) were factors associated with generalization on multivariate analysis without a significant difference between the GMG-B and GMG-E groups. In addition, an abnormal repetitive nerve stimulation test was related to a shortened time to generalization. Bilateral ptosis at onset was found as a risk factor for generalization. In a neuro-ophthalmology clinic, bilateral ptosis as an initial feature of OMG must be approached cautiously because it may be the first sign of impending GMG.

Laboratory Investigation of Hybrid IgG4 k/λ in MuSK Positive Myasthenia Gravis

Myasthenia gravis with antibodies (Abs) against the muscle-specific tyrosine kinase (MuSK) is a rare autoimmune disorder (AD) of the neuromuscular junction (NMJ) and represents a prototype of AD with proven IgG4-mediated pathogenicity. Thanks to the mechanism of Fab-arm exchange (FAE) occurring in vivo, resulting MuSK IgG4 k/λ Abs increase their interference on NMJ and pathogenicity. The characterization of hybrid MuSK IgG4 as a biomarker for MG management is poorly investigated. Here, we evaluated total IgG4, hybrid IgG4 k/λ, and the hybrid/total ratio in 14 MuSK-MG sera in comparison with 24 from MG with Abs against acetylcholine receptor (AChR) that represents the not IgG4-mediated MG form. In both subtypes of MG, we found that the hybrid/total ratio reflects distribution reported in normal individuals; instead, when we correlated the hybrid/total ratio with specific immune-reactivity we found a positive correlation only with anti-MuSK titer, with a progressive increase of hybrid/total mean values with increasing disease severity, indirectly confirming that most part of hybrid IgG4 molecules are engaged in the anti-MuSK pathogenetic immune-reactivity. Further analysis is necessary to strengthen the significance of this less unknown biomarker, but we retain it is full of a diagnostic-prognostic powerful potential for the management of MuSK-MG.

Age at sampling and sex distribution of AChRAb vs. MuSKAb myasthenia gravis in a large Greek population

OBJECTIVE

Myasthenia gravis (MG) is a typical B-cell-mediated neuromuscular junction disease that can be classified into seropositive and seronegative subtypes. Association of patients' age at sampling and sex with the two major seropositive MG subcategories, i.e., MGs linked to antibodies directed against the acetylcholine receptor (AChRAb) and against the muscle-specific kinase (MuSKAb), has not been compared in a large population.

METHODS

We performed a retrospective analysis of samples from patients with MG in Greece who underwent neurochemical diagnostic evaluation between January 2, 2013, and August 31, 2016.

RESULTS

Overall, 1620 adult (623 male and 997 female patients; male-to-female ratio = 0.62) and 51 pediatric patients were found to be seropositive for MG. The distributions in both male and female patients were bimodal in the total and AChRAb MG cases but not in the total MuSKAb MG cases. Significant differences in the age at sampling distribution between the male and female adult patients were observed only in the AChRAb MG subtype. Significant differences between the AChRAb and MuSKAb MG categories were noted in the mean age values (60.10 and 51.49 years, respectively, for female and 65.69 and 56.19 years, respectively, for male adult patients).

CONCLUSION

Our findings confirm an uneven profile of age at sampling and sex between the AChRAb and MuSKAb MG cases in a large population. Future mechanistic studies can elucidate the cause of these differences. Moreover, clinical studies can explore how such differences can affect MG treatment and prognosis.

Myasthenia Gravis: Autoantibody Specificities and Their Role in MG Management

Myasthenia gravis (MG) is the most common autoimmune disorder affecting the neuromuscular junction, characterized by skeletal muscle weakness and fatigability. It is caused by autoantibodies targeting proteins of the neuromuscular junction; ~85% of MG patients have autoantibodies against the muscle acetylcholine receptor (AChR-MG), whereas about 5% of MG patients have autoantibodies against the muscle specific kinase (MuSK-MG). In the remaining about 10% of patients no autoantibodies can be found with the classical diagnostics for AChR and MuSK antibodies (seronegative MG, SN-MG). Since serological tests are relatively easy and non-invasive for disease diagnosis, the improvement of methods for the detection of known autoantibodies or the discovery of novel autoantibody specificities to diminish SN-MG and to facilitate differential diagnosis of similar diseases, is crucial. Radioimmunoprecipitation assays (RIPA) are the staple for MG antibody detection, but over the past years, using cell-based assays (CBAs) or improved highly sensitive RIPAs, it has been possible to detect autoantibodies in previously SN-MG patients. This led to the identification of more patients with antibodies to the classical antigens AChR and MuSK and to the third MG autoantigen, the low-density lipoprotein receptor-related protein 4 (LRP4), while antibodies against other extracellular or intracellular targets, such as agrin, K_v1.4 potassium channels, collagen Q, titin, the ryanodine receptor and cortactin have been found in some MG patients. Since the autoantigen targeted determines in part the clinical manifestations, prognosis and response to treatment, serological tests are not only indispensable for initial diagnosis, but also for monitoring treatment efficacy. Importantly, knowing the autoantibody profile of MG patients could allow for more efficient personalized therapeutic approaches. Significant progress has been made over the past years toward the development of antigen-specific therapies, targeting only the specific immune cells or autoantibodies involved in the autoimmune response. In this review, we will present the progress made toward the development of novel sensitive autoantibody detection assays, the identification of new MG autoantigens, and the implications for improved antigen-specific therapeutics. These advancements increase our understanding of MG pathology and improve patient quality of life by providing faster, more accurate diagnosis and better disease management.

Autoantibody Specificities in Myasthenia Gravis; Implications for Improved Diagnostics and Therapeutics

Myasthenia gravis (MG) is an autoimmune disease characterized by muscle weakness and fatiguability of skeletal muscles. It is an antibody-mediated disease, caused by autoantibodies targeting neuromuscular junction proteins. In the majority of patients (~85%) antibodies against the muscle acetylcholine receptor (AChR) are detected, while in 6% antibodies against the muscle-specific kinase (MuSK) are detected. In ~10% of MG patients no autoantibodies can be found with the classical diagnostics for AChR and MuSK antibodies (seronegative MG, SN-MG), making the improvement of methods for the detection of known autoantibodies or the discovery of novel antigenic targets imperative. Over the past years, using cell-based assays or improved highly sensitive immunoprecipitation assays, it has been possible to detect autoantibodies in previously SN-MG patients, including the identification of the low-density lipoprotein receptor-related protein 4 (LRP4) as a third MG autoantigen, as well as AChR and MuSK antibodies undetectable by conventional methods. Furthermore, antibodies against other extracellular or intracellular targets, such as titin, the ryanodine receptor, agrin, collagen Q, K_v1.4 potassium channels and cortactin have been found in some MG patients, which can be useful biomarkers. In addition to the improvement of diagnosis, the identification of the patients' autoantibody specificity is important for their stratification into respective subgroups, which can differ in terms of clinical manifestations, prognosis and most importantly their response to therapies. The knowledge of the autoantibody profile of MG patients would allow for a therapeutic strategy tailored to their MG subgroup. This is becoming especially relevant as there is increasing progress toward the development of antigen-specific therapies, targeting only the specific autoantibodies or immune cells involved in the autoimmune response, such as antigen-specific immunoadsorption, which have shown promising results. We will herein review the advances made by us and others toward development of more sensitive detection methods and the identification of new antibody targets in MG, and discuss their significance in MG diagnosis and therapy. Overall, the development of novel autoantibody assays is aiding in the more accurate diagnosis and classification of MG patients, supporting the development of advanced therapeutics and ultimately the improvement of disease management and patient quality of life.

Diagnosis of Myasthenia Gravis

Myasthenia gravis (MG) diagnosis is primarily clinically based. By the end of the clinical evaluation, clinicians have a sense as to whether presenting symptoms and elicited signs are weakly or strongly supportive of MG. Diagnostic tests can reaffirm the clinicians' impression. Edrophonium testing is rarely used but helpful in cases of measurable ptosis. Decremental response on slow-frequency repetitive nerve stimulation has a modest diagnostic yield in ocular MG but is helpful in generalized MG cases. The most sensitive test is single-fiber electromyography. In this article, the authors review the diagnostic testing approach of practicing clinicians for suspected MG cases.

Ocular myasthenia gravis: an update on diagnosis and treatment

PURPOSE OF REVIEW

Myasthenia gravis is an autoimmune disease that commonly affects the palpebral and extraocular muscles. Ocular myasthenia gravis (OMG) is a variant of the disease that is confined to the ocular muscles but frequently becomes generalized over time. The diagnosis of OMG is often challenging but both clinical and laboratory findings are helpful in confirming the clinical suspicion. This review provides an update on the diagnostic approach and therapeutic options for OMG.

RECENT FINDINGS

Antimuscle-specific tyrosine kinase and LDL-related receptor-related protein 4 are newly available serologic testing for myasthenia gravis that can help in increasing the diagnostic sensitivity of OMG. They should be included to the diagnostic algorithm of OMG in appropriate clinical situations.

SUMMARY

OMG remains a primarily clinical diagnosis, but recent advances in laboratory testing can improve the diagnostic accuracy and should be used in appropriate clinical settings. The mainstay of treatment for OMG has not significantly changed over the past years, but the increasing availability of steroid-sparing agents improved the disease control while minimizing steroid-induced complications.

Correlation of HLA-DQ and TNF-α gene polymorphisms with ocular myasthenia gravis combined with thyroid-associated ophthalmopathy

The present study aims to explore the correlation of human leucocyte antigen (HLA)-DQ and tumour necrosis factor (TNF)-α gene polymorphisms with ocular myasthenia gravis (OMG) combined with thyroid-associated ophthalmopathy (TAO). From March 2009 to March 2015, 56 OMG patients complicated with TAO (OMG + TAO group), 134 patients diagnosed with OMG only (OMG group) and 236 healthy individuals (control group) were enrolled in the present study. PCR-sequence specific primer (PCR-SSP) was used for HLA-DQ genotyping and PCR-restriction fragment length polymorphism (PCR-RFLP) for TNF-α genotyping. ELISA kit was applied to detect acetylcholine receptor antibody (AchRAb) level and chemiluminescence immunoassay (CLIA) to measure thyroid-associated antibody (T-Ab) level. Logistic regression analysis was carried out to analyse the risk factors for OMG combined with TAO. DQA1*0103 showed lower frequency in the OMG group than in the control group. DQA1*0301 showed increased and DQB1*0601 showed decreased frequency in the OMG + TAO group. DQB1*0501 showed higher frequency in the OMG and OMG + TAO groups than in the control group. Patients carrying TNF-α -863C > A (CA + AA) might confront with greater risks of OMG combined with TAO. Frequency of DQA1*0103/*0301 and DQB1*0501/*0601, and TNF-α -863C > A, -238G > A and -308G > A were associated with the levels of AchRAb and T-Ab. TNF-α -863C > A (CA + AA) and high level of T-Ab were risk factors for OMG combined with TAO. Our results demonstrate that TNF-α -863 polymorphism is possibly correlated with the risk of OMG combined with TAO.

Flow Cytofluorimetric Analysis of Anti-LRP4 (LDL Receptor-Related Protein 4) Autoantibodies in Italian Patients with Myasthenia Gravis

BACKGROUND

Myasthenia gravis (MG) is an autoimmune disease in which 90% of patients have autoantibodies against the muscle nicotinic acetylcholine receptor (AChR), while autoantibodies to muscle-specific tyrosine kinase (MuSK) have been detected in half (5%) of the remaining 10%. Recently, the low-density lipoprotein receptor-related protein 4 (LRP4), identified as the agrin receptor, has been recognized as a third autoimmune target in a significant portion of the double sero-negative (dSN) myasthenic individuals, with variable frequency depending on different methods and origin countries of the tested population. There is also convincing experimental evidence that anti-LRP4 autoantibodies may cause MG.

METHODS

The aim of this study was to test the presence and diagnostic significance of anti-LRP4 autoantibodies in an Italian population of 101 myasthenic patients (55 dSN, 23 AChR positive and 23 MuSK positive), 45 healthy blood donors and 40 patients with other neurological diseases as controls. All sera were analyzed by a cell-based antigen assay employing LRP4-transfected HEK293T cells, along with a flow cytofluorimetric detection system.

RESULTS

We found a 14.5% (8/55) frequency of positivity in the dSN-MG group and a 13% frequency of co-occurrence (3/23) in both AChR and MuSK positive patients; moreover, we report a younger female prevalence with a mild form of disease in LRP4-positive dSN-MG individuals.

CONCLUSION

Our data confirm LRP4 as a new autoimmune target, supporting the value of including anti-LRP4 antibodies in further studies on Myasthenia gravis.

Prevalence of myasthenia gravis and associated autoantibodies in paraneoplastic pemphigus and their correlations with symptoms and prognosis

BACKGROUND

Paraneoplastic pemphigus (PNP) involves multiple organs, but little is known about its neurological involvement.

OBJECTIVES

To investigate the symptoms, prognosis and profiles of associated autoantibodies in myasthenia gravis (MG), and their correlations in patients with PNP.

METHODS

Fifty-eight patients with PNP were assessed for myasthenic symptoms and laboratory evidence. Serum autoantibodies against acetylcholine receptor (AChR), acetylcholinesterase (AChE), titin, ryanodine receptor (RyR) and muscle-specific kinase (MuSK) were measured by enzyme-linked immunosorbent assay. Patients with pemphigus vulgaris (PV), pemphigus foliaceus (PF), connective tissue disease (CTD) and non-PNP MG (NP-MG), and healthy donors, served as controls. These autoantibodies in PNP were also compared in the presence or absence of dyspnoea or muscle weakness. Cox regression and log-rank tests were used for survival analysis.

RESULTS

Overall 39% of patients with PNP experienced muscle weakness, and 35% were diagnosed with MG. Moreover, 35% had positive anti-AChR and 28% had anti-AChE antibodies, similarly to NP-MG (33% and 17%, respectively, P > 0·05). However, both were negative in all patients with PV, PF and CTD and healthy donors (P < 0·005). No other antibodies showed significant differences among groups. Anti-AChR and anti-AChE antibody levels were significantly increased in patients with PNP with dyspnoea, while anti-AChR, anti-titin and anti-RyR were significantly increased in patients with PNP with muscle weakness (P < 0·05). Nevertheless, levels and positive rates of these autoantibodies showed no significant differences between PNP with Castleman disease and thymoma. Although anti-AChE levels impacted survival duration (P  =  0·027, odds ratio 3·14), MG complications did not affect the overall survival percentage in PNP.

CONCLUSIONS

MG is a complication of PNP. Anti-AChR and anti-AChE antibodies are prominent in patients with PNP, especially those with dyspnoea.

Myasthenia gravis: two case reports and review of the literature

BACKGROUND AND OBJECTIVES

Myasthenia gravis (MG) is an autoimmune neurologic disease that affects the postsynaptic portion of the neuromuscular junction. It represents a challenge for anesthesiologists due to the diversity of disease manifestations and possibility of postoperative respiratory complications. The objective of this study was to demonstrate the importance of adequate monitoring of the neuromuscular blockade (NMB) due to the multiple presentations of MG.

CONTENTS

In this paper we report two cases of patients with MG. The first patient presented with the classical sensitivity to the neuromuscular blocker (NMB) and the second had a similar response to that of a normal patient. The literature review will be restricted to disease characteristics, while the description of its pathophysiology will focus on its reactions to NMB.

CONCLUSIONS

We suggest that, due to the multiple presentation and treatment of MG, neuromuscular transmission monitors are fundamental when using NMB.

Topical naphazoline in the treatment of myasthenic blepharoptosis

INTRODUCTION

When treating ocular myasthenia gravis (MG), the risk/benefit profile of corticosteroids is unclear, and acetylcholinesterase inhibitors are not very effective. We examined the efficacy of topical naphazoline in the treatment of myasthenic blepharoptosis.

METHODS

Sixty MG patients with blepharoptosis (32 with ocular symptoms only and 28 with mild generalized symptoms) were enrolled in a multicenter open trial of topical naphazoline. The effects were reported by patients via a questionnaire and were also confirmed for each patient at the clinic.

RESULTS

Among 70 eyes of 60 patients, 20 eyes (28.6%) of 17 patients (28.3%) exhibited a marked response (full eye opening), and 24 eyes (34.3%) of 20 patients (33.3%) showed a good response (adequate but incomplete eye opening). Topical naphazoline was evaluated as useful in the treatment of myasthenic blepharoptosis by >70% of the patients.

CONCLUSIONS

Topical naphazoline was found to be an effective supplementary symptomatic treatment for myasthenic blepharoptosis.