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     

Content and release of acetylcholinesterase in skeletal muscle of rats with experimental autoimmune myasthenia gravis

The effects of experimental autoimmune myasthenia gravis (EAMG) on acetylcholinesterase (AChE) were investigated in diaphragms of adult female Lewis rats. Both total AChE activity per muscle and release of enzyme activity during a 3-h incubation in vitro were measured. Two groups of myasthenic animals were used. Acute EAMG was induced by intravenous injection 48 h earlier with a syngeneic monoclonal autoantibody against the nicotinic acetylcholine receptor (AChR) of rat skeletal muscle; age- and weight-matched controls received a monoclonal anti-AChR antibody nonreactive with mammalian muscle. Chronic EAMG was induced by immunization 4 weeks earlier with AChR purified from Torpedo electroplax; controls received only adjuvants. When preparations from rats with acute or chronic EAMG were compared with the appropriate controls, no statistically significant differences in content or release of AChE activity were detected. Neither was there any change in the relative amounts of the various molecular forms of AChE in samples from animals with chronic EAMG. We conclude that the structural and functional changes arising in EAMG are highly specific for the acetylcholine receptor and associated elements of the neuromuscular junction, but have little impact on the biology of AChE.     

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.     

Juvenile myasthenia gravis

Juvenile myasthenia gravis shares a similar pathophysiologic origin with adult myasthenia gravis, but there are important differences, mostly relating to epidemiology, presentation, and therapeutic decision making. Gender ratios and the proportion of seropositive patients differ in the pre‐ and postpubertal age groups. The diagnostic evaluation is similar to that in adults, although special techniques are sometimes necessary to perform single‐fiber electromyography in younger patients. Therapeutic decisions in affected children and adolescents are complicated by the greater long‐term consequences of using steroids, and thus other interventions, such as intravenous immunoglobulin (IVIg) and plasmapheresis, may play a greater therapeutic role in this population than in adults. Steroid‐sparing agents may contribute to the management of refractory cases, but they should be used with caution due to the risk of malignancy. Muscle Nerve, 2008     

Single-fiber electromyography in experimental autoimmune myasthenia gravis

The sensitivity of stimulated single-fiber electromyography in the detection of early abnormalities in neuromuscular transmission in experimental autoimmune myasthenia gravis (EAMG) was tested. Increased jitter and blocking were seen up to 3 weeks before clinical illness or decrement developed. Stimulation at 10 Hz appeared more sensitive in detection of abnormalities than stimulation at 3 or 5 Hz. Jitter values did not correlate with anti-Torpedo acetylcholine receptor (AChR), nor with anti-rat AChR antibody titer. No correlation was found between jitter and AChR loss or AChR-antibody complexes in muscle. It is concluded that, in addition to AChR loss and the presence of AChR-antibody complexes, other factors must determine the neuromuscular dysfunction in EAMG and possibly myasthenia gravis.     

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。     

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.     

Variable effect of calcium channel blockers on the decremental response in experimental autoimmune myasthenia gravis

We tested the effect of intravenous administration of verapamil and nimodipine on the decremental response in rabbits with experimental autoimmune myasthenia. Nimodipine produced an immediate augmentation of the decremental response to 3-Hz nerve stimulation, which lasted about 30 min. In contrast, verapamil caused marked amelioration of the decrement beginning 30 min after injection. Our findings are consistent with previous reports suggesting that verapamil has a presynaptic effect of enhanced acetylcholine release at the neuromuscular junction. Since evaluation of a drug effect in vivo in animals with experimental autoimmune myasthenia gravis may be more pertinent to its effect on patients with myasthenia gravis (MG), verapamil might prove to be safer in MG than nimodipine. However, due to the additional effects of calcium channel blockers, the safety of their use in myasthenia gravis cannot be inferred from the experimental results. © 1994 John & Sons, Inc.     

Myasthenia gravis: a retrospective study comparing thymectomy to conservative treatment

OBJECTIVES: To study the effectiveness of thymectomy (TY) in a group of patients with myasthenia gravis compared to a group of patients submitted to conservative treatment (CT) at a similar clinical stage. METHODS: Among 153 patients with myasthenia gravis, we paired 28 patients who underwent TY, with 28 cases under CT. The following data were analyzed: gender, age, and age at the beginning of symptoms, illness duration, follow-up time and type of medical treatment. There was no statistical difference between these 2 groups. The mean time for TY was 2.5 (0.2-13) years after the onset of the disease. The cases were evaluated through a functional scale at the beginning and at the end of the study. RESULTS: We found complete remission in 15 cases (TY 6, CT 9), improved (normal life with or without minimal symptoms and with or without medication) 9 cases (TY 8, CT 1), improved with partial control and minimal limitation 32 cases (TY 14, CT 18), and poor control 2 cases (TY 2). No death was found in this group. CONCLUSION: There was no statistical difference between the conservative treatment and thymectomy groups, regarding remission or improvement. Furthermore TY done in the first year of the disease or latter, did not change the final outcome.     

Age-related susceptibility to experimental autoimmune myasthenia gravis: Immunological and electrophysiological aspects

Susceptibility to experimental autoimmune myasthenia gravis (EAMG) was found to decrease with aging in both Lewis and Brown Norway (BN) rats. In this study, the difference in susceptibility between young and aged Lewis and BN rats was used to analyze factors determining the clinical severity of EAMG. The incidence and severity of muscular weakness did not correlate with acetylcholine receptor (AChR) loss nor with the ability of antibodies to interfere with AChR function. Aged rats showed significantly lower anti-rat AChR antibody titers than young rats and developed less severe or no clinical signs of disease. In individual young or aged rats, however, no significant correlation was found between the clinical signs of disease and anti-rat AChR titer. Neuromuscular transmission was found to change with aging as measured by single-fiber electromyography (SFEMG). In aged BN rats, increased jitter and blockings were found even before EAMG induction. Despite this disturbed neuromuscular transmission, these aged BN rats were clinically resistant against induction of EAMG. The results of this study indicate that the age-related susceptibility to EAMG is influenced by factors determined by the immune attack as well as mechanisms at the level of the neuromuscular junction. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1091–1101, 1997     

预防性双类似物鼻粘膜耐受对EAMG的影响

目的选择双类似物(Lys262-Ala207)通过不同时间点对实验性自身免疫性重症肌无力(EAMG)模型进行鼻粘膜耐受预防性给药,观察其临床及免疫指标变化,并评价疗效,探讨预防性鼻粘膜耐受在EAMG中的预防作用机制。方法应用乙酰胆碱受体(AChR)加CFA致敏Lewis大鼠建立EAMG模型,并在致敏前10 d(预防耐受A组)及致敏当日(预防耐受B组)给予耐受肽Lvs262-Ala207及相应对照组CA、CB采用相同剂量对照肽MBP-p83-99鼻腔给药。检测给药后A、B组及相应对照组大鼠的体重、临床评分、肌电图、肌肉中AChR含量丢失变化及致敏第42 d血清抗AChR抗体IgG含量。结果急性期和慢性期A、B组体重明显超过相应对照组,临床症状明显轻于相应对照组,慢性期A组体重明显超过B组、病情明显轻于B组;A、B组低频重复电刺激出现衰减反应D5阳性率低于相应对照组;A、B组肌肉AChR含量丢失分别明显低于相应对照组,而A组低于B组;慢性期42 d A、B组IgG含量明显低于相应对照组,同时A组明显低于B组。结论本实验表明,预防耐受的疗效与自身免疫启动时间有关,启动前优于启动时耐受;双类似物鼻粘膜耐受预防不仅可有效地抑制临床症状,且可特异性减低致病性循环抗体含量和减少神经肌接头AChR含量丢失,为采用双类似物鼻粘膜耐受防治人类重症肌无力(MG)提供了依据。     

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     

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。     

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.     

Correlation of C3 level with severity of generalized myasthenia gravis

Acute exacerbation of generalized myasthenia gravis (GMG) can cause swallowing impairment, respiratory failure, or death. It is important to identify immunological factors that might be regarded reliably as an index of the patient's clinical condition, response to treatment, and measure of certain immune aberrations of MG. In this study we investigated correlations between complement component C3, acetylcholine receptor antibody (AChRab) titer, and clinical severity of GMG. AChRab titer and C3 concentration were determined by radioimmunoassay and nephelometry, respectively. The clinical severity of GMG was assessed by the quantitative MG score (QMGS) according to Besinger and colleagues. Our findings indicate that the C3 level correlates with clinical severity of AChRab‐positive GMG. Muscle Nerve, 2009     

Myasthenia gravis with muscle‐specific tyrosine kinase antibodies: A narrative review

Growing evidence provides new insights about myasthenia gravis (MG) with antibodies against muscle‐specific tyrosine kinase (MuSK‐MG), including its pathogenesis, clinical and electrophysiological manifestations, and treatment. Data now support the presence of both presynaptic and postsynaptic dysfunction in MuSK‐MG. This is 1 of many key differences between MuSK‐MG and acetylcholine receptor antibody‐MG (AChR‐MG), especially as it pertains to potential therapeutic implications. In comparison to AChR‐MG, MuSK‐MG is generally more refractory to treatment. However, because MuSK‐MG is better understood and more readily recognized today, there are more reports of a relatively benign course. The most effective immunotherapies for MuSK‐MG are corticosteroids, plasmapheresis, and rituximab. With appropriate therapy, most patients with MuSK‐MG achieve minimal manifestation status or better on the postintervention status outlined by the Myasthenia Gravis Foundation of America. A minority of patients remain refractory to treatment, and optimal management for this group remains a considerable challenge. Muscle Nerve 58 : 344–358, 2018     

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     

Decremental response of the nasalis and hypothenar muscles in myasthenia gravis

Repetitive nerve stimulation (RNS) is a standard diagnostic procedure in myasthenia gravis (MG). Although RNS sensitivity is highest in weak muscles, RNS is easier to perform in distal muscles that are often not affected. Twenty-five patients with MG were assessed to compare the sensitivity of RNS of the nasalis muscle to that of the hypothenar muscles. Abnormal decrement was found in hypothenar muscles in 9 patients (36%) and in the nasalis muscle in 13 patients (52%). RNS of the nasalis muscle appeared more useful to detect abnormal neuromuscular transmission in patients with oculobulbar MG (5 of 5) than hypothenar RNS (1 of 5). In patients with generalized MG, hypothenar muscles had a similar yield of abnormal RNS tests.