Acetylcholine receptor antibody in myasthenia gravis

Radioimmunoassay techniques were used to detect antibodies to the acetylcholine receptor (AAChR) in 164 patients with adult-onset myasthenia gravis. AAChR levels above 0.6 nM/l were considered pathological and were found in 67% of the patients with an average value of 58.99 +/- 125.02 nM/l (0.6-900.0). Correlation, with clinical functional status, the histopathological thymus alterations and the different therapeutics used did not disclose any statistically significant differences.     

Seronegative myasthenia gravis: disease severity and prognosis

Around 10-20% of myasthenia gravis (MG) patients do not have acetylcholine receptor (AChR) antibodies (seronegative), of whom some have antibodies to a membrane-linked muscle specific kinase (MuSK). To examine MG severity and long-term prognosis in seronegative MG compared with seropositive MG, and to look specifically at anti-AChR antibody negative and anti-MuSK antibody negative patients. Seventeen consecutive seronegative non-thymomatous MG patients and 34 age and sex matched contemporary seropositive non-thymomatous MG controls were included in a retrospective follow-up study for a total period of 40 years. Clinical criteria were assessed each year, and muscle antibodies were assayed. There was no difference in MG severity between seronegative and seropositive MG. However, when thymectomized patients were excluded from the study at the year of thymectomy, seropositive MG patients had more severe course than seronegative (P < 0.001). One seropositive patient died from MG related respiratory insufficiency. The need for thymectomy in seronegative MG was lower than in seropositive MG. None of the seronegative patients had MuSK antibodies. This study shows that the presence of AChR antibodies in MG patients correlates with a more severe MG. With proper treatment, especially early thymectomy for seropositive MG, the outcome and long-term prognosis is good in patients with and without AChR antibodies.     

Engineered agrin attenuates the severity of experimental autoimmune myasthenia gravis

Introduction: Agrin is essential for the formation and maintenance of neuromuscular junctions (NMJs). NT‐1654 is a C‐terminal fragment of mouse neural agrin. In this study, we determined the effects of NT‐1654 on the severity of experimental autoimmune myasthenia gravis (EAMG). Methods: EAMG was induced in female Lewis rats by immunization with the Torpedo acetylcholine receptor (tAChR) and complete Freund's adjuvant (CFA). NT‐1654 was dissolved in phosphate‐buffered saline (PBS) and injected daily subcutaneously into tAChR immunized rats during the first 10 days after immunization, and then every other day for the following 20 days. Results: We showed that NT‐1654 attenuated clinical severity, effectively promoted the clustering of AChRs at NMJs, and alleviated the impairment of NMJ transmission and the reduction of muscle‐specific kinase (MuSK) in EAMG rats. Discussion: We demonstrated that NT‐1654 attenuated clinical severity, effectively promoted the clustering of AChRs at NMJs, and alleviated the impairment of NMJ transmission and the reduction of muscle‐specific kinase (MuSK) in EAMG rats. Muscle Nerve 57 : 814–820, 2018     

Juvenile myasthenia gravis with prepubertal onset

Juvenile myasthenia gravis (JMG) with prepubertal onset is an uncommon disease. We studied 19 patients with age at onset ranging from 1.5 to 9.2 years and compared their clinical characteristics and response to therapy with 114 cases with MG onset after the prepubertal age, up to 20 years. Neither sex prevalence nor autoimmune diseases other than MG were found in younger patients. Although ocular myasthenia was more frequent than in later-onset JMG, children with generalized symptoms were often severely affected and respiratory involvement was present in 8/19 patients. Anti-acetylcholine receptor antibodies were detected at a lower rate and, in contrast with results in older patients, seronegativity was more frequent among children with generalized disease. Three out of six patients with onset before the age of five showed spontaneous remission. Nine prepubertal patients underwent thymectomy and, as most of them also received immunosuppressive therapy, the influence of surgery on disease outcome remains unclear; in no case was thymoma found. This is in contrast to the good results after thymectomy and the presence of thymoma in the later-onset group. Eleven patients in the prepubertal series were treated with immunosuppressive therapy. At the end of follow-up, most patients were in good condition. The frequency of immunosuppressive therapy and the rate of good therapeutic results did not differ from those observed in older patients.     

Comparison of diagnosis value for new onset myasthenia gravis by many clinical auxiliary examinations

BACKGROUND: The clinical values of neostigmine test, clinical electrophysiologic study and acetylcholine receptor antibody detection in diagnosing myasthenia gravis (MG) found newly are unclear in China. OBJECTIVE: To investigate the reference value of common clinical diagnosis parameters in correctly diagnosing untreated MG found newly. DESIGN: Retrospective case analysis. SETTING: Department of Neurology, Beijing Hospital, Ministry of Health. PARTICIPANTS: Totally 156 outpatients with MG admitted to Department of Neurology, Beijing Hospital, Ministry of Health between January 1999 and December 2002. The involved patients, 72 males and 84 females, were aged 2–79 years. They were classified according to Osserman's criteria: ⅡA 72，ⅡB 76, Ⅲ 3 and Ⅳ 5. They were all subjected to being inquired of disease history, neostigmine test, and acetylcholine receptor antibody detection, met the diagnosis criteria of Neuroimmunology Committee of China, and confirmed by clinical electrophysiologic detections; Informed consents were obtained from all the involved subjects. METHODS: ①After admission, every patient was intramuscularly injected with 1.5 mg neostigmine; If the patient was a child, the injection dose was decreased according to his/her age. If his/her score of any observation index after injection was improved ≥ 50% as compared with before injection , his positive index was set as positive. Positive neostigmine test was set if there was one positive index. ②Repetitive nerve stimulation and single fiber electromyography were performed with Dantec Keypoint electromyogram (EMG) apparatus. ③Acetylcholine receptor antibody was detected by ELISA method. MAIN OUTCOME MEASURES: Clinical absolute and relative scores of MG, acetylcholine receptor antibody level, and repetitive nerve stimulation and single fiber electromyography examination results. RESULTS: The positive rates of neostigmine test, repetitive nerve stimulation and single fiber electromyography examination for MG were 86.5%, 82.6%, and 69.2%, respectively, and the positive rate of acetylcholine receptor antibody was 78.8%. CONCLUSION: Standardized neostigmine test has the highest sensitivity to diagnose MG.     

Low conversion rate of ocular to generalized myasthenia gravis in Singapore

Introduction: Ocular myasthenia gravis (OMG) is a common condition of the neuromuscular junction that may convert to generalized myasthenia gravis (GMG). Our aim in this study was to determine the conversion rate and predictive factors for generalization in OMG, in an Asian population. Methods: The investigation consisted of a retrospective study of OMG patients with a minimum 2 years of follow‐up. Results: Among 191 patients with OMG, 155 had the minimum 2‐year follow‐up. The conversion rate at median follow‐up (40.8 months) was 10.6% (95% confidence interval 7.9%–13.3%), and at the 2‐year follow‐up it was 7.7% (95% confidence interval 5.6%–9.8%). At baseline, the predictive factors for generalization were positive acetylcholine receptor antibodies (hazard ratio 3.71, P = 0.024), positive repetitive nerve stimulation (RNS) studies (hazard ratio 4.42, P = 0.003), and presence of radiologically presumed or pathologically confirmed thymoma (hazard ratio 3.10, P = 0.013). Discussion: The conversion rate of OMG to GMG in Asian patients is low, as predicted by presence of acetylcholine receptor antibodies, presence of thymoma, and positive RNS studies. Muscle Nerve 57 : 756–760, 2018     

白细胞介素-6与重症肌无力患者临床特点的关系

目的　探讨白细胞介素 6(IL 6)与重症肌无力(MG)患者临床特点的关系。方法　采用双抗体 夹心ELISA法检测36例MG患者及20名健康对照者的血清IL 6和乙酰胆碱受体抗体(AchRAb)水平,并分 析其与MG临床特点的关系。结果　MG患者血清IL 6水平高于健康对照者(P<0.01);AchRAb阳性患者 高于阴性患者(P<0.05);全身型患者高于眼肌型患者(P<0.05);病情重者高于病情轻者(P<0.05);急性 期高于非急性期(P<0.01);预后差者高于预后好者(P<0.05);伴胸腺异常者高于胸腺正常者(P<0.05)。 结论　IL 6与MG临床特点相关,在MG发病机制中起重要作用。血清IL 6水平可间接反映体内免疫功能紊 乱的程度,对判断MG患者病情、预后和指导治疗有重要的参考价值。     

Complement activation profiles in anti-acetylcholine receptor positive myasthenia gravis

Background and purpose

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.

Methods

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.

Results

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.

Conclusions

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.     

The effectiveness of thymectomy on seronegative generalized myasthenia gravis: comparing with seropositive cases

OBJECTIVES: To investigate the efficacy of thymectomy between patients with seronegative myasthenia gravis (SNMG) and seropositive myasthenia gravis (SPMG). METHODS: We present here the first Taiwanese retrospective paired cohort study comparing the effectiveness of thymectomy among 16 seronegative and 32 seropositive MG patients after matching for age-of-onset and time-to-thymectomy, and following up over a mean of 35 +/- 20 (7-86) months. Clinical characteristics and complete stable remission (CSR) rates were compared and analyzed between the groups. RESULTS: There were no major clinical differences between the two groups except for our finding of a lower percentage of SNMG receiving preoperative plasmapheresis or human immunoglobulin than SPMG (31% for SNMG vs 72% for SPMG, P = 0.007). CSR rates calculated using the Kaplan-Meier method were similar in the two groups (38% for SNMG vs 50% for SPMG, P = 0.709). The median time for CSR was 47.4 months for SNMG and 48.2 months for SPMG. Thymic hyperplasia were the most common pathology (69% for SNMG vs 88% for SPMG, P = 0.24). During the follow-up period, we found no group difference on prednisolone or pyridostigmine dosages. Significant postoperative dosage reductions on pyridostigmine, but not on prednisolone, were found in both groups. CONCLUSIONS: Thymectomy has a comparable response among SNMG and SPMG in our study. Thymic hyperplasia is prevalent in our SNMG patients and thymectomy may also be a therapeutic option to increase the probability of remission or improvement in SNMG. More prospective controlled trial will be helpful in the future.     

Frequency of seronegativity in adult-acquired generalized myasthenia gravis

We determined the prevalence of muscle acetylcholine receptor (AChR) antibodies in patients with adult-acquired generalized myasthenia gravis (MG), the seroconversion rate at 12 months, and the prevalence of muscle-specific tyrosine kinase (MuSK) antibody among persistently seronegative patients. We identified 562 consecutive Mayo Clinic patients with MG based on clinical and electrophysiological criteria. At presentation, 508 patients (90.4%) tested positive for AChR binding or AChR modulating antibodies. After 12 months, 15.2% of initially seronegative patients had become seropositive, yielding a seronegativity rate of 8.2% (95% confidence interval: 6.2-9.6%). Among seronegative patients not receiving immunosuppressants, 38% were MuSK antibody-positive and 43% were seropositive for nonmuscle autoantibodies. Classification as seronegative MG should be reserved for nonimmunosuppressed patients with generalized MG who lack muscle AChR binding, AChR modulating, or MuSK antibodies at presentation and at follow-up of at least 12 months.     

Clinical findings in MuSK‐antibody positive myasthenia gravis: A U.S. experience

We performed a retrospective chart review on 53 muscle‐specific kinase antibody (MuSK‐Ab)‐positive myasthenia gravis (MG) patients at nine university‐based centers in the U.S. Of these, 66% were Caucasian, 85% were women, and age of onset was 9–79 years. Twenty‐seven patients were nonresponsive to anticholinesterase therapy. Myasthenia Gravis Foundation of America improvement status was achieved in 53% patients on corticosteroids, 51% with plasma exchange, and in 20% on intravenous immunoglobulin (IVIG). Thymectomy was beneficial in 7/18 patients at 3 years. Long‐term (≥3 years) outcome was very favorable in 58% of patients who achieved remission and/or minimal manifestation status. Overall, 73% improved. There was one MG‐related death. This survey reinforces several cardinal features of MuSK‐Ab‐positive MG, including prominent bulbar involvement and anticholinesterase nonresponsiveness. Facial or tongue atrophy was rare. Most patients respond favorably to immunotherapy. The best clinical response was to corticosteroids and plasma exchange, and the poorest response was to IVIG. Long‐term outcome is favorable in about 60% of cases. Muscle Nerve, 2009     

放射免疫法定量检测乙酰胆碱受体抗体与重症肌无力患者临床特征的相关性

目的探讨乙酰胆碱受体抗体(AChR-Ab)与重症肌无力(MG)临床特征的相关性。方法采用放射免疫法检测115例MG患者及92例对照组(非MG神经系统疾病患者42例,健康体检者50名)血清AChRAb浓度,应用临床绝对评分记录MG患者病情严重程度。分析各组血清AChR-Ab浓度的差异,以及AChR-Ab浓度与MG患者临床特征的相关性。采用ROC工作特征曲线探讨AChR-Ab诊断MG的敏感度和特异度。结果MG患者血清AChR-Ab浓度中位数(四分位数间距,下同)为3.45(39.38)nmol/L,较非MG神经系统疾病患者[0(0)nmol/L]和健康体检者[0(0)nmol/L]增高(P0.01)。全身型MG(GMG)患者AChR-Ab浓度[25.45(46.14)nmol/L]较眼肌型MG(OMG)患者[0.58(3.56)nmol/L]增高(P0.01)。用ROC曲线法分析显示,以血清AChR-Ab浓度≥0.50nmol/L作为诊断MG界值时灵敏度为72.17%,特异度为100%,曲线下面积(AUC)=0.895(95%CI:0.849~0.941)。AChR-Ab浓度与发病年龄、病程及改良Osserman分型呈正相关(r=0.220,P0.05;r=0.184,P0.05;r=0.382,P0.01),但相关性较弱(均r0.5),与临床绝对记分无相关性(r=0.147,P0.05)。结论用放射免疫法检测血清AChR-Ab浓度诊断MG的灵敏度和特异度均高,有助于减少MG的漏诊率及误诊率,值得临床推广。     

The B-cell repertoire in myasthenia gravis includes all four acetylcholine receptor subunits

By enumerating cells secreting IgG antibodies of particular specificities using an enzyme-linked immunospot (ELISPOT) assay, the B-cell responses to Torpedo acetylcholine receptor (AChR) and its α-, β-, γ- and δ-subunits in peripheral blood from patients with myasthenia gravis (MG), and controls with other neurological diseases (OND) as well as healthy subjects were determined. Compared to controls, the patients with MG had elevated numbers of B cells secreting antibodies against AChR and its α-, β-, γ- and δ-subunits in peripheral blood in parallel. The mean numbers of anti-AChR antibody secreting cells were about 17 per 10⁵ blood MNC, and for the subunits 10 to 15 in MG patients, compared to between 0.8 and 1.9 per 10⁵ blood MNC in OND patients, and 0.1 to 0.3 in healthy controls. Such B cells detected in controls probably represent naturally occurring B cells responded to AChR and its subunits. The finding that most (60%) MG patients had B cells predominantly recognizing the α-subunit may be an indirect argument for the existence of a main immunogenic region (MIR). In the remaining 40% of patients with MG the predominant B-cell responses were directed to β-, γ- or δ-subunit. The data suggest that all four AChR subunits may function as strong immunogens in MG, though the α-subunit may be the major immune target in a substantial proportion of MG patients.     

Inhibition of peripheral blood natural killer cell cytotoxicity in patients with myasthenia gravis treated with plasmapheresis

Background and purpose: Myasthenia gravis (MG) is an autoimmune disorder that may involve natural killer (NK) cells. Although NK cells are part of the innate immune system, they also influence adaptive immune responses. Double‐filtration plasmapheresis (DFP) is an effective therapy for MG crisis. Thus, we examined the effects of DFP on the cytotoxicity of NK cells. Methods: A total of 20 patients with MG and 16 healthy controls were recruited for the study. Ficoll‐Paque‐isolated peripheral blood mononuclear cells (PBMCs) and K562 cells were used as the effector and target cells, respectively. NK cell cytotoxicity was analyzed using flow cytometry immediately before and after DFP and upon course completion. Results: Double‐filtration plasmapheresis treatment decreased significantly the NK cell cytotoxicity in patients with MG, especially in good responders, those who were positive for acetylcholine receptor (AChR) antibodies, and those receiving immunosuppressants. Conclusions: The decrease in NK cell cytotoxicity after DFP and the decline of AChR antibody titer were observed in good responders indicating that this could benefit patients with MG.     

雷诺丁受体抗体阳性的重症肌无力临床特点

雷诺丁受体（ryanodine receptor, RyR）是存在于内质网/肌质网中的一种重要钙离子通道,在骨骼肌兴奋收缩偶联机制中起重要作用。RyR抗体阳性的重症肌无力（myasthenia gravis, MG）患者常合并胸腺瘤,对常规治疗不敏感,会导致延误临床早期识别及治疗。血清RyR抗体水平与患者临床症状的严重程度显著相关。该文就4例RyR抗体阳性MG患者的临床特点及治疗过程进行讨论并文献复习,旨在提高对RyR抗体阳性MG的认识及诊疗水平。     

Lifetime course of myasthenia gravis

Between 1940 and 2000 a total of 1976 patients with myasthenia gravis (MG) were studied. Diagnosis was made by improvement in weakness after anticholinesterase medication. The historical developments in diagnosis and treatment of MG are reviewed. We analyzed the clinical course of MG as influenced by age, gender, thymectomy, thymomectomy, and the presence of antibodies to acetylcholine receptors (AChR). The clinical course of MG was significantly influenced by age and gender, and these need special attention in managing patients. The most severe level of weakness and high mortality occurred during the first 1 to 2 years of the disease, after which many patients experienced improvement. For treating MG patients the usefulness of thymectomy remains to be proven, and novel drugs need to be developed to increase the number as well as normal functioning of the AChRs and other components of the neuromuscular system.     

Mortality in myasthenia gravis: A nationwide population–based follow‐up study in Denmark

Introduction: In previous studies of myasthenia gravis (MG), increased mortality has been reported. The aim of this study was to estimate mortality in patients with acetylcholine receptor antibody–positive (AChR‐Ab–seropositive) MG in a nationwide population–based, long‐term follow‐up study. Methods: All AChR‐Ab–seropositive MG patients, diagnosed between 1985 and 2005, were identified. Defined by age at diagnosis (≤50 or >50 years), patients were classified as having early‐ or late‐onset MG. For comparison, 10 non‐MG individuals from the general population were matched with each patient. All patients and controls were followed until January 1, 2009. Mortality rates and estimated mortality rate ratios (MRRs) were calculated. Results: Of 702 AChR‐Ab–seropositive MG patients, 302 died during follow‐up. Overall mortality was higher for patients with MG (MRR = 1.41, range 1.24–1.60). In late‐onset women and men, the MRRs were 1.64 (1.36–1.99) and 1.22 (1.02–1.46), respectively. Total MRR was highest during the first 5 years after diagnosis. Conclusions: MG diagnosis is still associated with increased mortality. Muscle Nerve 53 : 73–77, 2016