Myasthenia gravis: disease severity and prognosis

Objectives –  To examine myesthenia gravis (MG) severity and long-term prognosis in seronegative, seropositive, and thymoma MG.
Materials and Methods –  Four series of patients were studied retrospectively. Severity and treatment were assessed each year, and muscle antibodies were assayed.
Results –  Seropositive MG patients had a more severe course than seronegative MG patients. MG severity was higher in non-thymectomized compared to thymectomized early-onset MG patients. MG severity did not differ between thymectomized and non-thymectomized late-onset patients. There was no significant difference in MG severity between thymoma and non-thymoma MG patients.
Conclusions –  MG is more severe in seropositive MG patients. With proper treatment, especially early thymectomy, the long-term prognosis is good in seropositive MG patients. The present studies indicate a benefit of thymectomy in early-onset MG, but no dramatic benefit in late-onset MG. Similar MG severity and outcome was seen in thymoma and non-thymoma MG.     

Disease severity and outcome in thymoma myasthenia gravis: a long-term observation study

Thymomas occurring in myasthenia gravis (MG) are usually of the cortical subtype and are usually treated by thymectomy. However, the factors that influence MG outcome in thymoma MG patients are not known. In a long-term study, MG severity and treatment was observed in 24 thymoma and 24 non-thymoma MG patients for up to 30 years, and the occurrence of muscle autoantibodies was assayed. The rate of complete stable remission was low and did not differ between the two groups. There was no significant difference in MG severity between thymoma and non-thymoma MG patients at any time during the study. Titin and ryanodine receptor (RyR) antibody occurrence was significantly higher in thymoma MG patients. Four thymoma (all titin and RyR antibody positive) and two non-thymoma (both titin and one RyR antibody positive) MG patients died from MG-related respiratory insufficiency. Seventy percent of thymoma and 75% of non-thymoma MG patients were treated with immunosuppressive drugs. The number of patients who received plasmapheresis did not differ in those who were treated because of acute MG deterioration, irrespective of planned surgery.This study shows equal MG severity and outcome in thymoma and non-thymoma MG, but the presence of RyR antibodies in thymoma MG and titin/RyR in non-thymoma MG indicates a less favorable prognosis.     

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.     

Muscle antibodies in the cerebrospinal fluid from patients with myasthenia gravis

IgG antibodies to nicotinic acetylcholine receptor (AChR) and to a muscle antigen extracted by citric acid, were quantified in serum and cerebrospinal fluid (CSF) from 28 patients with myasthenia gravis, and the serum:CSF ratios compared with those of total IgG. Agarose-electrophoresis and calculations of the IgG index and Tourtellotte's formula were performed. No evidence of intrathecal antibody synthesis was demonstrated. Compared to the total IgG concentrations in serum and CSF, the CSF concentrations of IgG AChR antibodies were lower than expected.     

Rituximab treatment of myasthenia gravis: A systematic review

Rituximab is a chimeric mouse/human anti‐CD20 monoclonal immunoglobulin. We reviewed the efficacy and safety of rituximab in 169 myasthenia gravis (MG) patients from case reports and series. Antibodies to the acetylcholine receptor (AChR) were present in 59% and muscle‐specific tyrosine kinase (MuSK) in 34%. Modified Myasthenia Gravis Foundation of America postintervention scale of minimal manifestations (MM) or better occurred in 44%, and combined pharmacologic and chronic stable remission in 27% overall; MM or better was achieved in 72% of MuSK MG and 30% of AChR MG (P < 0.001). Posttreatment relapses decreased more in MuSK MG (P = 0.05). Response predictors were MuSK MG, less severe disease, and younger age at treatment. Among a responder subset, 26% of AChR and 82% of MuSK MG patients showed decreased posttreatment antibody titers. Rituximab was generally well tolerated. Detectable serum rituximab and depleted CD20⁺ B‐cells were observed up to 20 and 16 weeks, respectively, after 4 weekly infusions. Muscle Nerve 56 : 185–196, 2017     

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     

利妥昔单抗治疗重症肌无力的临床疗效分析

目的评价利妥昔单抗治疗重症肌无力(MG)的有效性和安全性。方法回顾性收集2018年2月至2019年7月北京医院神经内科收治的MG患者21例,所有患者血清抗乙酰胆碱受体(acetylcholine receptor,AChR)抗体或抗肌肉特异性酪氨酸激酶(muscle specific kinase,MuSK)抗体阳性。给予患者4次500mg利妥昔单抗治疗。分析患者治疗前后许氏评分,血CD19阳性B淋巴细胞、CD20阳性B淋巴细胞百分数以及相关抗体变化情况,同时观察利妥昔单抗的不良反应。结果共20例患者在使用4次500mg利妥昔单抗治疗后复查许氏评分,治疗前基线许氏评分为7~44分,平均(18.5±10.56)分,治疗后许氏评分为0~25分,平均(10.45±7.70)分,经利妥昔单抗治疗后患者许氏评分减低为6.5(3.25,12.75)分〔Md(P25,P75)〕,差异有统计学意义(P<0.01)。共16例患者于第1次、第2次、第3次及第4次利妥昔单抗用药后复查许氏评分,与用药前比较许氏评分降低分别为2(0,7)分〔Md(P25,P75)〕以及(6.12±4.54)、(6.18±5.98)、(8.12±5.80)分,与治疗前相比差异均有统计学意义(均P<0.01)。患者外周血CD19、CD20阳性B淋巴细胞计数于第一次用药后分别下降96%、97%。抗AChR抗体阳性患者共19例,用药后不同时间复查抗体水平14次,共发现2例患者抗体滴度降低。共9例患者出现不良反应,均为良性不良反应。结论4次500mg利妥昔单抗治疗MG显示出良好治疗效果,且安全性高,耐受性好。     

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.     

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     

High-dose cyclophosphamide in refractory myasthenia gravis with MuSK antibodies

We describe a 48-year-old woman with seronegative myasthenia gravis (MG) and high-titer of anti-MuSK antibody. She had severe bulbar and respiratory weakness with minimal limb weakness for 2 years. Her disease responded poorly to all the conventional immunosuppressive regimens. Treatment with immunoablative dose of cyclophosphamide led to dramatic and sustained remission of her symptoms. High-dose cyclophosphamide is an effective alternative in patients with unusually refractory disease.     

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     

我国华南地区MuSK抗体阳性重症肌无力患者的临床特点

目的分析我国华南地区骨骼肌特异性酪氨酸激酶抗体(MuSK-Ab)阳性重症肌无力(myasthenia gravis,MG)的临床特点。方法回顾性收集2017年8月至2019年8月在中山大学附属第一医院确诊的住院MuSK抗体阳性MG(MuSK-MG)患者26例,并选取同期收治的乙酰胆碱受体抗体(AChR-Ab)阳性MG(AChR-MG)患者157例作为对照组,比较两组患者临床特点以及对治疗反应的差异。结果与AChR-MG患者比较,MuSK-MG患者女性构成(80.8%比58.0%,P<0.05)、平均发病年龄〔(43.12±13.02)岁比(36.04±17.97)岁,P<0.05〕高,球部肌受累(96.2%比70.1%,P<0.01)和肌无力危象(myasthenic crisis,MC;61.4%比28.7%,P<0.05)更常见。两组患者新斯的明试验阳性率(61.5%比70.7%)、低频重复神经电刺激(RNS)阳性率(78.3%比83.3%)比较差异无统计学意义(均P>0.05)。在治疗反应方面,胆碱酯酶抑制剂(AChEIs)对MuSK-MG患者的有效率低于AChR-MG患者(16.0%比58.6%,P<0.01)。两组患者发生MC期间,对血浆置换(PLEX)的反应优于静脉注射丙种球蛋白(IVIG)。结论我国华南地区MuSK-MG以40岁左右女性多见,与AChR-MG比较易累及球部肌和呼吸肌,容易发生MC。MuSK-MG对AChEIs的反应性低于AChR-MG。RNS对我国华南地区MuSK-MG诊断的敏感性与AChR-MG比较无统计学差异,但高于欧美人群。PLEX在MuSK-MG患者的危象前或危象状态中的应用可显著缓解病情。     

Repetitive nerve stimulation of facial muscles in MuSK antibody-positive myasthenia gravis

To better define electrophysiological abnormalities in myasthenia gravis (MG) patients with muscle-specific tyrosine kinase (MuSK) antibodies (Ab), we compared electrophysiological features of 14 MuSK Ab-positive, 73 acetylcholine receptor antibody (AChR Ab)-positive, and 22 MuSK and AChR Ab-negative (seronegative) patients with generalized disease. Repetitive nerve stimulation (RNS) abnormalities were observed in 86% of MuSK Ab-positive and 82% of AChR Ab-positive patients but in only 55% of seronegative patients. RNS decrements in the orbicularis oculi were more common and severe in the MuSK Ab-positive patients than the other two groups. Single-fiber electromyography (SFEMG) of the extensor digitorum communis was abnormal in 90% of MuSK Ab-positive patients. The high frequency of RNS abnormalities in facial muscles in the MuSK Ab-positive population reflects the propensity for facial muscle involvement in this form of MG and emphasizes the importance of including facial muscles in RNS protocols when evaluating these patients.     

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.     

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.     

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.     

Diagnostic difficulties in myasthenia gravis

Four patients with myasthenia gravis presented with severe, largely isolated, bulbar and respiratory muscles weakness. Tensilon tests were positive and antiacetylcholine receptor (anti-AChR) antibody titers were negative in all patients. Only 1 patient had a greater than 10% decremental response during the period of respiratory failure. Although routine nerve conduction studies were normal, all had very low-amplitude diaphragmatic compound muscle action potentials. Three patients had abundant fibrillation potentials and positive sharp waves largely restricted to respiratory muscles. Clinical and electrophysiological findings improved with corticosteroids, and surprisingly, decremental responses became positive in all patients. The assessment of patients with largely isolated bulbar and respiratory muscle weakness due to myasthenia gravis may be difficult and misleading, as anti-AChR antibody titers may be negative, decremental responses may be absent, and electrophysiological assessment atypical. Due consideration of clinical symptomatology, a Tensilon test, and a trial of immunosuppression may be necessary to establish the diagnosis. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:577–583, 1998.