Passive transfer of seronegative myasthenia gravis to mice

Muscle weakness in myasthenia gravis is due to autoantibody-induced loss of functional acetylcholine receptors (AChR). About 15% of myasthenia gravis patients, however, do not have detectable anti-AChR antibodies. To investigate the effect of their plasma immunoglobulins on neuromuscular transmission, mice were injected with plasma (and in some cases purified immunoglobulin G (IgG)) from 7 “seronegative” myasthenia gravis (SMG) patients, and neuromuscular transmission parameters were examined. When injected for 15 days, all patients' plasma caused reductions in miniature endplate potential amplitudes, while endplate potential quantal content was significantly reduced by plasma from 4 of the 7 patients. There were no changes in ACh-induced depolarization or single channel properties, and ₁₂₅l-α-bungarotoxin binding studies showed no effect on AChR number, except in 1 case. Purified IgG injected for 3 days had similar effects to plasma injected for 15 days. Our findings confirm that SMG is autoantibody mediated and that there are pathogenic IgG antibodies. SMG appears to be a heterogeneous disorder and the target(s) for the antibodies may be diverse. © 1994 John Wiley & Sons, Inc.     

Autoimmune antibodies to collagen XIII in myasthenia gravis patients

Introduction: Evaluation of the nerve fascicular structure can be useful in diagnosing nerve damage, but it is a very challenging task with 3T MRI because of limited resolution. In this pilot study, we present the feasibility of high‐resolution 7T MRI for examining the nerve fascicular structure. Methods: A 3‐dimensional (3D) gradient‐spoiled sequence was used for imaging peripheral nerves in extremities. Images acquired with different in‐plane resolutions (0.42 × 0.42 mm vs. 0.12 × 0.12 mm), and different main field strengths (7T vs. 3T) were compared. Results: The individual nerve fascicles were identified at 0.12 × 0.12 mm resolution in both field strengths but not at 0.42 × 0.42 mm resolution. The fascicular structure was more sharply depicted in 7T images than in 3T images. Discussion: High‐resolution 3D imaging with 7T MRI demonstrated feasibility for imaging nerve fascicular structures. Muscle Nerve 57 : 506–510, 2018     

重症肌无力被动转移大鼠模型眼外肌的易感机制研究

目的探讨眼外肌在重症肌无力发病过程中的易感机制。方法给予SD大鼠腹腔注射mAb35建立重症肌无力被动转移(PTMG)大鼠模型,对照组大鼠注射等量生理盐水。选取PTMG组和对照组大鼠眼外肌、膈肌、胫前肌3种骨骼肌组织。采用乙酰胆碱酯酶(AChE)染色法观察神经肌肉接头(NMJ)并检测NMJ面积和灰度;采用银环蛇毒免疫组化法检测乙酰胆碱受体(AChR)数量;采用电镜观察NMJ超微结构和其AChR情况,并分析比较神经末端面积和突触后膜面积的比值以及突触前后膜长度的比值。结果 AChE染色结果显示,对照组眼外肌NMJ面积相对其他两种骨骼肌更小(P<0.01),PTMG组眼外肌与其他两种骨骼肌NMJ面积比较无统计学差异(P>0.05)。银环蛇毒免疫组化结果显示,PTMG组和对照组眼外肌与其它两种骨骼肌间AChR灰度值比较均有统计学差异(P<0.01)。电镜观察结果显示,PTMG组3种骨骼肌突触前后膜长度比值均较对照组下降(P<0.01),神经末端面积与突触后膜面积比值较对照组增加(P<0.01),其中眼外肌的变化较其他骨骼肌更为显著。结论 PTMG大鼠模型眼外肌易感机制可能与眼外肌和其他骨骼肌间NMJ面积、AChR数量差异造成眼外肌NMJ安全系数较低有关。     

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     

Changes in acetylcholinesterase in experimental autoimmune myasthenia gravis and in response to treatment with a specific antisense

Controlled regulation of synaptic nicotinic acetylcholine receptors (AChRs) and acetylcholinesterase (AChE), together with maintenance of a dynamic balance between them, is a requirement for proper function of cholinergic synapses. In the present study we assessed whether pathological changes in AChR perturb this balance, and whether such changes can be corrected. We studied the influence of AChR loss, caused by experimental autoimmune myasthenia gravis (EAMG), on muscle AChE, as well as the reciprocal effect of an antisense targeted towards AChE on both AChR and AChE at the neuromuscular synapse. The extensor digitorum longus (EDL) muscles of EAMG Lewis rats were isolated, and AChE levels and isoform compositions were examined. Although AChE levels in the muscles of healthy and EAMG rats were similar, marked changes were observed in isoform composition. Healthy EDL muscles contained globular (G_1,2, G₄) and asymmetric (primarily A₁₂) isoforms. G_1,2‐AChE was significantly reduced in EAMG muscles, whereas both G₄‐ and A₁₂‐AChE remained unchanged. Treatment of EAMG rats with the antisense EN101 resulted in decreased total muscle AChE, with recovery in G_1,2 and reduction in A₁₂‐AChE. AChE/AChR ratios were determined at the neuromuscular junctions (NMJ). The decrease in AChR levels that occurred as the disease progressed resulted in a dramatic increase in this ratio, and a significant recovery towards normal ratios occurred after EN101 treatment. This improvement was primarily due to increased synaptic AChR content. Our findings emphasise the tight connection between AChR and AChE at the myasthenic NMJ, and the importance of the AChE/AChR ratio in maintaining the required cholinergic balance.     

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.     

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.     

Distal myasthenia gravis frequency and clinical course in a large prospective series

OBJECTIVES: In Myasthenia gravis (MG) proximal limb, ocular and/or bulbar muscles are most commonly affected, whereas distal extremity muscles are typically spared. The aim of the current study was to assess the frequency of primarily distal MG in the Tyrol and to describe its clinical peculiarities. MATERIAL AND METHODS: Over the past 20 years 84 patients with MG have undergone follow-up at the Department of Neurology of Innsbruck University. Types of presentation, clinical course and treatment response were followed over a period of 20 years (1980-2000). RESULTS: Six of 84 MG patients showed a predominance of muscle weakness and fatigability in distal limb muscles (two at presentation, four over the later course of the illness). There was no difference between distal MG and MG with a more typical distribution of muscle weakness regarding age, gender and response to therapy. CONCLUSIONS: The case series indicates that predominantly distal presentations of otherwise typical MG are more frequent than generally assumed and should be considered in the differential diagnosis of diseases with distal limb weakness.     

Minimal clinically important difference in myasthenia gravis: Outcomes from a randomized trial

Introduction: The minimal clinically important difference (MCID) is the smallest outcome change that has clinical significance. Its use has not been established in the study of myasthenia gravis (MG). Methods: Patients from a published intravenous immunoglobulin (IVIg) vs. placebo study were studied. One anchor‐based and 3 distribution‐based techniques were used to identify quantitative myasthenia gravis score (QMGS), repetitive nerve stimulation (RNS), and single‐fiber electromyography (SFEMG) MCID cut‐offs. Patients with a change‐score exceeding MCID cut‐offs were compared. Results: MCID cut‐offs were below a QMGS change of 3.0. Anchor‐based and 1 × SEM cut‐offs showed 58.3% vs. 30.7% responders (P = 0.017), ½ SD 54.2% vs. 19.2% responders (P = 0.018), and effect size 0.519 vs. 0.164 (P = 0.011) in IVIg vs. placebo. Anchor‐based (P = 0.73) and effect‐size (P = 0.41) MCID cut‐offs did not show a difference between IVIg and placebo. MCID methods did not produce meaningful RNS cut‐offs. Conclusions: QMGS MCID values provide clinically relevant information and are recommended in MG trials. MCID analysis shows that improvement in MG patients treated with IVIg reflects clinically meaningful changes. Muscle Nerve 49 : 661–665, 2014     

重症肌无力患者血脂异常与糖皮质激素敏感的相关性分析

目的探讨无自身免疫性疾病的重症肌无力(MG)患者血脂异常与糖皮质激素治疗的反应性及其临床意义。方法回顾性分析使用糖皮质激素治疗的63例MG患者的临床资料,根据糖皮质激素治疗后患者临床症状改善状况,将患者分为激素治疗敏感组与不敏感组,并比较两组间的临床及生化特征。根据是否伴有血脂升高分为血脂正常组与血脂异常组,并比较两组间糖皮质激素治疗的反应性。结果激素敏感组与不敏感组之间患者性别、年龄、起病方式、累及肌群、WBC、C反应蛋白、血沉、血糖指数、甘油三脂、高密度脂蛋白胆固醇、载脂蛋白A1、载脂蛋白B、脂蛋白A比较无统计学差异(均P0.05),两组间胸腺异常、血脂异常、总胆固醇、低密度脂蛋白胆固醇比较有统计学差异(均P0.05);血脂正常组与血脂异常组之间糖皮质激素治疗敏感性比较有统计学差异(χ~2=9.307,P0.01);血脂异常与糖皮质激素治疗不敏感发生率呈正相关(r=0.384,P0.01)。结论 MG不伴其他自身免疫性疾病患者血脂升高可能降低糖皮质激素治疗疗效,二者之间的关系有助于MG患者的临床治疗评估及预后判断。     

West nile virus infection and myasthenia gravis

Introduction: Viruses are commonly cited as triggers for autoimmune disease. It is unclear if West Nile virus (WNV) initiates autoimmunity. Methods: We describe 6 cases of myasthenia gravis (MG) that developed several months after WNV infection. All patients had serologically confirmed WNV neuroinvasive disease. None had evidence of MG before WNV. Results: All patients had stable neurological deficits when they developed new symptoms of MG 3 to 7 months after WNV infection. However, residual deficits from WNV confounded or delayed MG diagnosis. All patients had elevated acetylcholine receptor (AChR) antibodies, and 1 had thymoma. Treatment varied, but 4 patients required acetylcholinesterase inhibitors, multiple immunosuppressive drugs, and intravenous immune globulin or plasmapheresis for recurrent MG crises. Conclusions: The pathogenic mechanism of MG following WNV remains uncertain. We hypothesize that WNV‐triggered autoimmunity breaks immunological self‐tolerance to initiate MG, possibly through molecular mimicry between virus antigens and AChR subunits or other autoimmune mechanisms. Muscle Nerve 49 : 26–29, 2014     

Epidemiological and immunological profile of muscle-specific kinase myasthenia gravis in Greece

Objectives:  The purposes of this study were to determine the epidemiological characteristics of muscle-specific kinase-myasthenia gravis (MuSK-MG) in Greece and the IgG subclass of the anti-MuSK antibodies.
Methods:  This population-based study was performed on MuSK-MG patients in Greece between 1 January 1986 and 30 June 2006. Epidemiological and clinical data for 33 patients were collected. In addition, the distribution of anti-MuSK IgG autoantibody subclasses in the sera of 14 patients was determined by immunoprecipitation.
Results:  The average annual incidence was 0.32 patients/million population/year. On 1st July 2006, there were 33 prevalent cases, giving a point prevalence rate of 2.92/million (women 4.56 and men 1.25). In females, onset of MuSK-MG occurred after the age of 30, whilst, in males, the disease appears in any decade. The female:male incidence ratio was 3.33:1, whilst the prevalence ratio was 3.65:1. Most patients presented with involvement of the facial and bulbar muscles. Amongst about 800 MG patients seropositive for antibodies against either the AChR or MuSK, one patient was found to be seropositive for anti-MuSK antibodies and ambiguous for anti-acetylcholine receptor (anti-AChR) antibodies. The vast majority of anti-MuSK antibodies were IgG4, whilst total IgG4 levels in these patients were similar to those in two healthy controls.
Conclusions:  The incidence and prevalence of MuSK-MG in Greece are amongst the highest reported previously for other countries. MuSK-MG in Greece affects both sexes, but mainly females. The main epidemiological indices were calculated. The vast majority of anti-MuSK antibodies were IgG4.     

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.     

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.     

Epidemiological study of myasthenia gravis in Sardinia, Italy (1958–1986)

From 1.1.1958 to 31.12.1986, 110 cases of MG were observed in Sardinia, with a mean annual incidence of 2.5 x 1,000,000 inhabitants and prevalence rates of 7.5, 17.6, 31.4 and 45.0 x 1,000,000 inhabitants respectively (prevalence days: 15.10.1961, 24.10.1971, 25.10.1981 and 31.12.1986). The disease was found to be more frequent in women. There were no differences in the distribution of MG in various areas of the island. The muscle group more frequently involved at onset was the ocular. In 6.4% of patients an association with thyroid disorders was observed. The mortality of MG patients was significantly higher than expected. Removal of the thymus, carried out in 58 patients, was shown to be useful in the treatment of the disease, particularly in patients without thymomas. No familial cases were observed.