Muscle-Specific Receptor Tyrosine Kinase Antibody Positive Myasthenia Gravis Current Status

Muscle-specific tyrosine-kinase-antibody-positive myasthenia gravis (MuSK-MG) has emerged as a distinct entity since 2001. This disease has been reported worldwide, but with varying rates among patients with generalized acetylcholine-receptor-antibody-negative MG. MuSK-MG was detected in approximately 37% of generalized acetylcholine receptor antibody-negative MG. MuSK-MG patients were predominantly female with more prominent facial and bulbar involvement and more frequent crises. Disease onset tended to be earlier. Patients tended to have a relatively poor edrophonium response but showed prominent decrement in the repetitive nerve stimulation test in the facial muscles. Patients were more likely to display poor tolerance of, or a lack of improvement with, anticholinesterase agents. Somewhat better response was observed with steroids and plasma exchange. Most were managed successfully with aggressive immunomodulatory therapies, although a higher proportion of MuSK-MG patients had a refractory course when compared with other forms of generalized MG. I present here an up-to-date overview on MuSK-MG based on our experience at the University of Alabama at Birmingham and the existing literature.     

重症肌无力患者酪氨酸激酶抗体的检测

目的探讨酪氨酸激酶抗体（MuSKAb）在血清阴性重症肌无力（SNMG）发病中的作用。方法采用放射免疫法检测198例重症肌无力（MG）患者血清中抗乙酰胆碱受体抗体（AChRAb）水平，筛选出SNMG血清样本再行MuSKAb水平检测。结果MG患者血清AChRAb浓度明显高于对照组（P〈0．05），其阳性率为81．3％，SNMG患者血清MuSKAb均为阴性。结论MuSKAb可能在中国SNMG患者中的检出率较低。     

Myopathy in Childhood Muscle-Specific Kinase Myasthenia Gravis

BackgroundAdult and pediatric patients suffering from MuSK (muscle-specific kinase) -antibody positive myasthenia gravis exhibit similar features to individuals with acetylcholine receptor (AChR) antibodies, but they differ in several characteristics such as a predominant bulbar, respiratory and neck weakness, a generally worse disease severity and a tendency to develop muscle atrophy. Muscle atrophy is a rare phenomenon that is usually restricted to the facial muscles.ResultsWe describe a girl with MuSK-antibody positive myasthenia gravis who developed a myopathy with severe generalized muscular weakness, muscle atrophy, and myopathic changes on electromyography.ConclusionThis is the first published example of a generalized myopathic syndrome in myasthenia gravis. We review the relevant literature and discuss the hypothesis of a mitochondrial myopathy as a pathogenic mechanism in MuSK-antibody positive myasthenia gravis.     

中国南方地区20例肌肉特异性酪氨酸激酶抗体阳性重症肌无力患者临床特点分析

目的总结中国南方地区20例肌肉特异性酪氨酸激酶抗体阳性(MuSK+)的重症肌无力(MG)患者的临床特点。方法纳入2016年10月至2019年6月就诊于复旦大学附属华山医院的MuSK+-MG患者20例,回顾性分析患者的人口学资料(性别、年龄,等)、临床特点(起病年龄、受累肌群、临床分型和病程,等)及电生理特点和治疗药物。结果 20例MuSK+-MG患者中女性多见(75%),20~29岁为起病高峰(45%)。首发临床分型以OssermanⅡb型(55%)及MGFAⅡb型(45%)为主,以延髓肌(45%)及眼外肌(35%)受累起病常见,65%患者肌群受累进展在2个月以内。70%患者存在症状每日波动及新斯的明试验阳性。低频重复电刺激阳性率为75%,其中眼轮匝肌睑部阳性率最高(75%),斜方肌重复电刺激阳性率最低(10%),25%患者可见重复复合肌肉动作电位,22.2%患者可见二联束颤。80%患者使用糖皮质激素治疗。结论中国南方地区MuSK+-MG以女性多见、起病年龄多在20~29岁、波动性明显、延髓肌易受累、进展迅速和眼轮匝肌睑部重复性神经电刺激阳性率高的队列特征。     

Clinical and Electrophysiologic Responses to Acetylcholinesterase Inhibitors in MuSK-Antibody-Positive Myasthenia Gravis: Evidence for Cholinergic Neuromuscular Hyperactivity

Background and Purpose

Patients with muscle-specific tyrosine kinase (MuSK) antibody (MuSK-Ab)-positive myasthenia gravis (MG) show distinct responses to acetylcholinesterase inhibitors (AChEIs). Although clinical responses to AChEIs in MuSK-Ab MG are reasonably well known, little is known about the electrophysiologic responses to AChEIs. We therefore investigated the clinical and electrophysiologic responses to AChEIs in MuSK-Ab-positive MG patients.

Methods

We retrospectively reviewed the medical records and electrodiagnostic findings of 17 MG patients (10 MuSK-Ab-positive and 7 MuSK-Ab-negative patients) who underwent electrodiagnostic testing before and after a neostigmine test (NT).

Results

The frequency of intolerance to pyridostigmine bromide (PB) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (50% vs. 0%, respectively; p=0.044), while the maximum tolerable dose of PB was lower in the former (90 mg/day vs. 480 mg/day, p=0.023). The frequency of positive NT results was significantly lower in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (40% vs. 100%, p=0.035), while the nicotinic side effects of neostigmine were more frequent in the former (80% vs. 14.3%, p=0.015). Repetitive compound muscle action potentials (R-CMAPs) developed more frequently after NT in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (90% vs. 14.3%, p=0.004). The frequency of a high-frequency-stimulation-induced decrement-increment pattern (DIP) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (100% vs. 17.7%, p=0.003).

Conclusions

These results suggest that MuSK-Ab-positive MG patients exhibit unique and hyperactive responses to AChEIs. Furthermore, R-CMAP and DIP development on a standard AChEI dose may be a distinct neurophysiologic feature indicative of MuSK-Ab-positive MG.     

重症肌无力患者甲状腺功能和甲状腺抗体情况的临床分析

目的　了解重症肌无力 ( MG)患者甲状腺功能及甲状腺抗体的情况。方法　回顾性分析了 2 67例临床确诊 MG患者的甲状腺素水平 ,对其中 2 64例患者检测了甲状腺球蛋白抗体 ( TGAb)和甲状腺过氧化物酶抗体( TPOAb)或甲状腺微粒体抗体 ( TMAb)。结果　 5 5例 ( 2 0 .6% )患者有甲状腺功能异常 ,48例 ( 1 8.2 % )至少有 1项上述抗体阳性。甲状腺功能异常的 MG患者中 , 、 、 型抗体阳性者较多 ( P <0 .0 1 )。甲状腺抗体阳性者较抗体阴性者 MG发病晚 ( P <0 .0 5 ) ;甲状腺抗体阴性 MG患者有甲状腺功能障碍者 MG发病早于功能正常组 ( P <0 .0 5 )。甲状腺功能异常、抗体阳性的 MG患者病程较抗体阴性者长 ( P <0 .0 5 ) ;甲状腺抗体阳性者伴发胸腺增生或胸腺瘤的几率明显增高 ( P <0 .0 5 )。结论　MG合并甲状腺功能异常并不少见 ,甲状腺抗体阳性、功能异常的 MG患者病程长 ,伴发胸腺增生或胸腺瘤的几率高 ,临床应予以重视。     

Osserman V型重症肌无力5例临床分析及文献复习

目的对Osserman V型重症肌无力(MG)的临床特点及诊治体会进行回顾性总结分析,以提高对此少见疾病中少见类型的认识。方法对作者医院2004-11—2006-11期间收治的491例MG患者中所有OssermanV型患者的临床特点和血清学检测结果进行回顾性分析。结果491例MG患者中5例为Osserman V型,在病程中先后出现不同程度舌肌、颞肌或上肢远端小肌肉萎缩。其中4例肌电图检查重频电刺激低频递减,血清乙酰胆碱受体抗体(AChR-Ab)阳性,另1例抗骨骼肌特异性受体酪氨酸激酶抗体(MuSK-Ab)阳性。5例患者均对溴吡斯的明对症治疗反应差,但对糖皮质激素和静脉丙种球蛋白(IVIG)治疗反应较好。半年后随访肌肉萎缩有不同程度改善。结论Osserman V型MG很罕见,肌肉萎缩的发病机制尚不清楚,部分患者可能与MuSK-Ab有关。血清学检测有助于对Osserman V型MG确诊、避免误诊及改善预后。     

Construction of an efficient evaluative instrument for Myasthenia Gravis: The MG composite

We assessed the performance of items from the Quantitative Myasthenia Gravis (QMG), MMT (Manual Muscle Test), and MG‐ADL (Myasthenia Gravis – Activities of Daily Living) scales, using data from two recently completed treatment trials of generalized MG. Items were selected that were relevant to manifestations of MG, meaningful to both the physician and the patient, and responsive to clinical change. After the 10 items were chosen, they were weighted based on input from MG experts from around the world, considering factors such as quality of life, disease severity, risk, prognosis, validity, and reliability. The MG Composite is easy to administer, takes less than 5 minutes to complete, and requires no equipment. Weighting of the response options of the 10 items should result in ordinal scores that better represent MG status and are more responsive to meaningful clinical change. To better determine its suitability for clinical use and for treatment trials, the MG Composite will be tested prospectively at several academic medical centers and will be used as a secondary measure of efficacy in pending clinical trials of MG. Muscle Nerve 38: 1553–1562, 2008     

sICAM-1在重症肌无力患者血清及外周血单个核细胞培养上清液中的变化

目的：了解可溶性细胞间黏附分子-1（sICAM-1）在重症肌无力（MG）患者血清及外周血单个核细胞（PBMC）培养上清液中的变化情况。方法：用酶联免疫吸附法（ELISA）检测正常对照和MG患者，血清及PBMC培养上清液中sICAM-1的水平，并分析激素对上清液中sICAM-1的影响。结果：正常对照组与MG组血清sICAM-1的水平没有显著差异；而在PBMC培养上清液中，MG组高于正常对照组。加入地塞米松培养48h后，7例MG患者PBMC培养上清液中sICAM-1-1水平降低。结论：MG患者PBMC可分泌更多的sICAM-1，升高的sICAM-1可能是体内ICAM-1产生及循环过程的中间产物；ELISA检测MG患者PBMC培养上清液（加FBS）中sICAM-1的水平是一种有效的检测手段；此外，地塞米松可以下调PBMC分泌sICAM-1。     

黄芪复方对重症肌无力患者血清乙酰胆碱受体抗体水平的影响

目的采用中药黄芪复方调节重症肌无力(myastheniagravis,MG)患者血清乙酰胆碱受体抗体(acetylcholinereceptorantibody,AChRAb)水平,以探讨其治疗MG的可能作用机制。方法应用酶联免疫吸附法(ELISA)检测74例MG患者治疗前后血清AChRAb水平,并采用许(氏)临床绝对和相对记分法观察病情严重程度和判定中药复方疗效。结果MG患者治疗前血清AChRAb水平(108±007)显著高于健康对照组(016±011)(P<001),治疗后MG患者血清AChRAb水平(072±006)明显下降(P<001)。结论具有补益脾肾作用的中药黄芪复方能下调MG患者血清AChRAb水平,从而纠正MG患者免疫失衡状态,临床绝对记分和相对记分对其疗效的判定有一定意义。     

重症肌无力特异性免疫吸附剂的制备及对患者血清的静态吸附作用

目的制备一种对重症肌无力(myastheniagravis,MG)致病性乙酰胆碱受体抗体(AChRAb)具有特异性吸附作用的免疫吸附剂。方法利用悬浮再生法,用环氧氯丙烷活化羟基,以人乙酰胆碱受体(AChR)主要免疫原区10氨基酸多肽作为配基固定于球型纤维素上制备MG特异性免疫吸附剂,以色氨酸为配基制备非特异性免疫吸附剂。应用酶联免疫吸附试验测定其对MG患者血清的静态吸附率。结果以AChR主要免疫原区10氨基酸多肽为配基的吸附剂对AChRAb的吸附率为(4033±229)%,以色氨酸为配基的吸附剂的吸附率为(2235±147)%。结论以球型纤维素为载体,以AChR主要免疫原区10氨基酸多肽作为配基的特异性吸附剂对于MG的治疗可能是一种很有前途的方法。     

Anti-MuSK-positive myasthenia gravis: neuromuscular transmission failure in facial and limb muscles

The presence of antibodies against muscle-specific receptor tyrosine kinase (MuSK) appears to define a subgroup of patients with myasthenia gravis (MG) characterized by weakness predominant in bulbar, facial and neck muscles compared with anti-acetylcholine receptor (AChR) antibody-positive MG. To investigate the patterns and severity of neuromuscular transmission failure in different muscles in MuSK-positive MG, we performed single fiber electromyography (SFEMG) in the facial (frontalis) and limb (extensor digitorum communis, EDC) muscles in three anti-Musk-positive patients, and compared results with those of 11 anti-AChR-positive patients. Only one of the three MuSK-positive patients had abnormal jitter in EDC, but all the three showed clearly increased jitter in the frontalis. By contrast, the AChR-positive patients showed similarly abnormal jitter for the two muscles. These results suggest that when the diagnosis of anti-MuSK-positive MG is suspected, SFEMG should be performed in most prominently affected muscles.     

乙酰胆碱受体抗体与大鼠中枢神经元烟碱型乙酰胆碱受体之间免疫结合反应

本研究旨在探讨长期以来无定论的重症肌无力（MG）患者血和脑脊液（CSF）中的乙酰胆碱受体抗体（AChRab）能否与中枢神经元烟碱型乙酰胆碱受体（神经-nAChR）结合，并引起中枢神经系统（CNS）功能障碍。用免疫亲和层析法从AChRab阳性的全身型MG患者血中提取纯化AChRab，然后用免疫组化法探讨AChRab与大鼠中枢神经-nAChR之间的免疫结合反应。结果首次表明，AChRab与神经-nAChR之间的阳性免疫结合反应广泛分布于大鼠大脑皮层、脑干颅神经运动核团、脊髓前角运动神经元等部位，提示MG患者AChRab不仅可与神经肌接头（NMJ）处肌-nAChR结合引起肌无力等症状，还可与CNS神经-nAChR结合，并可能引起CNS功能障碍。     

Clinical Significance of Repetitive Compound Muscle Action Potentials in Patients with Myasthenia Gravis: A Predictor for Cholinergic Side Effects of Acetylcholinesterase Inhibitors

MethodsWe retrospectively reviewed the clinical records and electrodiagnostic findings of MG patients who underwent electrodiagnostic studies and diagnostic neostigmine testing (NT).ResultsAmong 71 MG patients, 9 could not tolerate oral pyridostigmine bromide (PB) and 17 experienced side effects of PB. R-CMAPs developed in 24 patients after NT. The highest daily dose of PB was lower in the patients with R-CMAPs (240 mg/day vs. 480 mg/day, p<0.001). The frequencies of PB intolerance and side effects were higher in the patients with R-CMAPs than in those without R-CMAPs [37.5% vs. 0% (p<0.001) and 45.8% vs. 12.8% (p=0.002), respectively]. The MG Foundation of America postintervention status did not differ significantly between MG patients with and without R-CMAPs, and the response to immunotherapy was also good in both groups.ConclusionsSide effects of and intolerance to AChEIs are more common in MG patients with R-CMAPs than in those without R-CMAPs. AChEIs should be used carefully in MG patients with R-CMAPs. The presence of R-CMAPs after NT may be a good indicator of the risks of PB side effects and intolerance.     

Autoantibody detection by a live cell-based assay in conventionally antibody-tested triple seronegative Myasthenia gravis

Autoantibody testing is the mainstay in confirming the diagnosis of autoimmune myasthenia gravis (MG). However, in approximately 15% of patients, antibody testing in clinical routine remains negative (seronegative MG). This study aimed at assessing the prevalence of “clustered” AChR- and MuSK- and LRP4- autoantibodies using a live cell-based assay in a large German cohort of seronegative myasthenia gravis (SNMG) patients. A total of 67 SNMG patients were included. Clustered AChR-ab were identified in 4.5% (n = 3) of patients. Two out of the three patients showed binding to the adult AchR as well as the fetal AchR. None of the patients was positive for MuSK- or LRP4-autoantibodies. There were no differences in clinical characteristics between the patients with and without clustered AChR-ab detection. Comparison of clinical data of our cohort with clinical data from the nationwide Myasthenia gravis registry showed broad similarities between seronegative MG patients of both cohorts.     

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.