IgG from "seronegative" myasthenia gravis patients binds to a muscle cell line, TE671, but not to human acetylcholine receptor

Antibodies to acetylcholine receptor (AChR) are found in 85% of patients with myasthenia gravis (seropositive MG [SPMG]) and are thought to be pathogenic; but in 15% of MG patients, the standard immunoprecipitation test for anti-AChR is negative (seronegative MG [SNMG]). Here, we used a novel approach, fluorescence-activated cell sorting analysis, to measure binding of SPMG and SNMG IgG antibodies to rhabdomyosarcoma cell lines that express human adult (TE671-epsilon) or fetal (TE671-gamma) AChR, and to human embryonic kidney (HEK) fibroblasts that express adult human AChR (HEK-AChR). We found that whereas most SPMG antibodies bind to all three cell lines, IgG from 8 of 15 SNMG sera/plasmas bind to the surface of both TE671 cell lines but not to HEK-AChR cells. These results indicate that SNMG antibodies bind to a muscle surface antigen that is not the AChR, which strongly supports previous studies that suggest that SNMG should be considered a distinct subtype of MG.     

Effect of sera from seronegative myasthenia gravis patients on neuromuscular junctions

About 85 % of patients with generalized myasthenia gravis (MG) have anti-nicotinic acetylcholine receptor (nAChR) antibodies in their sera (seropositive MG; SPMG). The other 15 % (seronegative MG; SNMG) are also considered to have antibody-mediated disease, but the nature of the antibodies in SNMG is not fully understood. We investigated the effect of sera from patients with MG on spontaneous muscle action potentials and acetylcholine (ACh)-induced potentials, and we examined the localization of epitopes recognized by SPMG sera or SNMG sera. SPMG sera and SNMG sera inhibited spontaneous muscle action potentials and ACh-induced potentials in the spinal-muscle co-culture system. However, spontaneous muscle action potentials and ACh-induced potentials in the neuromuscular junctions were strongly blocked by SPMG serum, whereas they were weakly blocked by SNMG serum. Both types of sera reacted strongly with the neuromuscular junctions in normal rat muscles, as shown by double immunostaining with serum and α-bungarotoxin. The SPMG epitope remained in the neuromuscular junctions, whereas that of SNMG disappeared after denervation of the sciatic nerve. Therefore, we suggest that the skeletal muscle weakness in SNMG may be due to an interaction with presynaptic neuromuscular transmission and nAChR.     

Acetylcholine receptor antibodies in myasthenia gravis are associated with greater risk of diabetes and thyroid disease

OBJECTIVE: Myasthenia gravis (MG) may be associated with the presence of acetylcholine receptor antibodies (AChRAb) [seropositive MG (SPMG)] or their absence [seronegative MG (SNMG)]. Along with features of MG, the presence of the AChRAb may relate to the existence of other immune-mediated diseases. We sought to determine the association of SPMG with other potential autoimmune diseases. METHODS: A retrospective evaluation of prospectively identified MG patients at a tertiary care center was performed, with patients separated into SPMG and SNMG. Prevalence of other immune-mediated disorders, as well as the epidemiology, sensitivity of diagnostic testing, and thymic pathology, was contrasted between both patient groups. RESULTS: Of the 109 MG patients identified, 66% were SPMG. SPMG was associated with a greater likelihood of significant repetitive stimulation decrement, the presence of either thymoma or thymic hyperplasia, and the presence of thyroid disease. In addition, all patients with a diagnosis of diabetes, concurrent with MG, were found to be SPMG. CONCLUSIONS: AChRAb and SPMG impart not only a distinctive clinical and electrophysiological phenotype of MG, but are also associated with the heightened presence of endocrinological disease.     

Prognosis of thymectomy in myasthenia gravis patients with thymus hyperplasia

Purpose: To compare the post-thymectomy prognosis in different conditions of myasthenia gravis (MG) patients with thymus hyperplasia. Materials and methods: Collecting medical record and carrying out the follow-up study of 123 myasthenia gravis patients with thymus hyperplasia who have underwent thymectomy during the period between 2003 and 2013. Dividing into different groups based on gender, age of onset, duration of disease and Myasthenia Gravis Association of America (MGFA) clinical classification to analyze different prognosis in different groups. Results: Complete stable remission (CSR) was achieved in 71 of 123 patients (59.5%). There is no gender-related difference in achieving CSR. Patients with early onset of MG (≤40 years old) or disease duration less than 12 months had significantly higher CSR rates than those with late onset of MG (>40 years old) or disease duration more than 12 months respectively, while no difference was found in remission rate between MGFA clinical classification I and MGFA II. Conclusion: Myasthenia gravis patients with thymus hyperplasia who had thymectomy are proved to possess greater chance of achieving CSR. The onset age of disease and duration are the prognostic factors.     

重症肌无力被动转移动物模型的研究

目的 :探讨血清阳性 (SPMG)和阴性重症肌无力 (SNMG)被动转移动物模型 (P EAMG)的异同。方法 :用ELISA法将重症肌无力 (MG)患者分为SNMG和SPMG两组 ,然后分别用两组患者血清制作P EAMG ,观察两组小鼠的临床表现、电生理及神经肌接头(NMJ)的改变。结果 :SPMG和SNMG组小鼠均表现出明显的肌无力症状 ,低频重复电刺激出现明显衰减反应 ,但SNMG组小鼠肌无力症状较SPMG组明显为轻 ,SPMG和SNMG组小鼠NMJ处棕黄色沉积物明显减少、变细短。结论 :SNMG和SPMG均是自身抗体介导的自身免疫性疾病 ,但两者不完全相同     

Double seronegative myasthenia gravis with anti-LRP 4 antibodies

About 10% of patients with generalized myasthenia gravis do not have detectable antibodies to acetylcholine receptor or muscle specific kinase (double seronegative myasthenia). The presence of anti-low density lipoprotein receptor-related protein 4 antibodies (LRP4 Abs) has recently been reported in variable proportion of double seronegative cases. We report the presenting characteristics of two double seronegative myasthenic patients from Greece with anti-LRP4 antibodies shortly after disease onset. The first patient, a 52-year-old male, presented with a one month history of isolated neck extensor weakness; the second patient is a 52-year-old female with three months history of ocular–bulbar-cervical myasthenic weakness. Both patients presented with mild severity and responded promptly and adequately to pyridostigmine. In the female patient thymic residual tissue was detected on CT of the mediastinum. She underwent thymectomy, and histological examination revealed follicular hyperplasia. This is the first clinical report of the presenting features of newly diagnosed myasthenia with anti-LRP4 antibodies. The clinical and therapeutic implications of the anti-LRP4 antibody positivity remain to be clarified.     

Myasthenia gravis with anti-acetylcholine receptor antibody or anti-muscle specific kinase antibody

Patients with myasthenia gravis (MG) are divided into 3 groups: anti-acetylcholine receptor antibody-positive MG (AChR MG), anti-muscle specific kinase antibody-positive MG (MuSK MG), and AChR-and MuSK-negative MG (double seronegative MG; double SNMG). A recent study on the detection of low-affinity antibodies binding to AChR showed the presence of AChR antibodies in about 70% of double SNMG patients. There is accumulating evidence that double SNMG patients are similar to AChR-MG patients with respect to clinical features and thymic pathology. Since most MG patients are thought to belong to the AChR-MG or MuSK-MG group of patients, this article reviews the pathophysiology, clinical features, and treatments in these 2 groups of MG patients. The pathophysiology of AChR-MG is closely related to the abnormal thymic pathology, such as thymic hyperplasia or presence of thymoma, and thy(mo)mectomy is recommended in patients with generalized AChR-MG. On the contrary, little thymic abnormality in patients with MuSK-MG discourages thymectomy; however, MuSK-MG patients do respond to thymectomy and therefore studies to define the indications of thymectomy in MuSK-MG patients are required. The responses to cholinesterase inhibitors are poor in patients with MuSK-MG, and these patients tend to show hyperactivity to the Tensilon test, such as fasciculation of facial muscles and stuffy sensation in the throat. The adverse responses to a small dose of intravenous edrophonium chloride injection may support the clinical diagnosis of MuSK-MG. Further, only small doses of acetylcholinesterase inhibitors are administered to patients with MuSK-MG in order to avoid cholinergic hyperactivity. In general, both types of MG patients respond well to treatments with immunosuppressants, including steroids, but some patients with MuSK-MG show persistent bulbar symptoms.     

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.     

Myasthenia gravis and Lambert-Eaton myasthenic syndrome in the same patient

An 18-year-old-woman developed symptoms of generalized myasthenia gravis (MG). Antibodies to the acetylcholine receptor were found in her serum, but electrodiagnostic testing showed abnormalities typical of the Lambert-Eaton myasthenic syndrome (LEMS). Following thymectomy, the thymus gland showed thymic hyperplasia typical of MG, and the patient responded to treatment with 3,4-diaminopyridine and pyridostigmine. There have been few reports in the literature of MG and LEMS coexisting in the same patient. In this case, electrodiagnostic tests, antibody studies, thymus pathology, and response to treatment suggest that both disorders contributed to the patient's symptoms. Thymic hyperplasia, so far only known to be associated with MG, provides strong evidence that both diseases were symptomatic.     

Relapse of ocular symptoms after remission of myasthenia gravis--a comparison of relapsed and complete remission cases

Extended thymectomy and high-dose alternate-day prednisolone administration may increase the chance of remission in myasthenia gravis (MG) patients. In cases of remission, ocular symptoms sometimes reappear after a gradual decrease or discontinuation of prednisolone administration. We compared relapsed patients with those who experienced complete remission. We found that the period from onset of MG to thymectomy and initiation of prednisolone administration was longer in the relapsed cases, which suggests that early thymectomy and administration of prednisolone can lead to a superior outcome in MG patients.     

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.     

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。     

Low-dose tacrolimus for two cases of myasthenia gravis with invasive thymoma that relapsed shortly after thymectomy

Two patients with myasthenia gravis (Ossermann IIb) involving invasive thymoma who underwent extensive thymectomy manifested myasthenic crisis shortly after the procedure; however, both patients were treated with intravenous immunoglobulin and recovered from myasthenic crisis that had been deteriorating for about 1 week. Subsequently, the patients were administered a low-dose of tacrolimus (3 mg/day) in addition to prednisolone. Several months later, tacrolimus continued to control fluctuations of myasthenic symptoms and maintained remission in these patients. The serum titer of anti-Ach-receptor antibodies decreased in parallel with clinical improvement due to tacrolimus, and we accordingly reduced the dosage of prednisolone. Tacrolimus is a new immunosuppressive agent acting through the selective inhibition of helper-T-cell activation that can be reduced dosage of steroids and can maintain remission of myasthenia gravis with invasive thymoma.     

MuSK-positive myasthenia gravis is rare in the Polish population

Background and purpose:  MuSK-positive myasthenia gravis (MG) is diagnosed in 0–48% of cases with generalized seronegative MG in different populations. The presence of anti-MuSK antibodies generally relates to a severe course and lack of response to thymectomy. We analyzed for the first time the serology and clinical characteristics of MuSK-positive MG in the Polish population.
Methods:  One hundred and fifty-one patients were tested for the presence of anti-AChR and anti-MuSK antibodies: 62 with seronegative MG, including 14 with ocular seronegative MG, 48 age-matched patients with seropositive MG and 41 controls.
Results: All patients with seropositive MG and the disease controls were MuSK-negative. Anti-MuSK antibodies were detected only in four patients with seronegative MG (8.7% of generalized seronegative cases): three women and one man. All four had predominantly bulbar involvement, and underwent thymectomy, with no apparent benefit. All of them improved clinically after immunosuppressive treatment with remissions lasting up to 7 years.
Conclusion: MuSK-positive MG is rare in Polish population accounting for only 8.7% of seronegative cases with generalized MG. This is consistent with emerging evidence for lower MuSK antibodies at more northerly latitudes.     

重症肌无力病人胸腺切除术后血清自身抗体水平变化和临床转归分析

６９例重症肌无力（ＭＧ）病人行胸腺切除术，术前血清乙酰胆碱受体抗体水平均高于正常，术后半年抗体水平明显下降，胸腺增生组（２０例）尤为显著．胸腺瘤组（４９例）术前胸腺瘤相关抗体水平增高，但术后半年内无明显变化．６９例ＭＧ患者胸腺切除术后４年，症状总缓解率为７６．８１％，其中胸腺增生组９５％，胸腺瘤组６９．３９％。作者认为，对于伴有胸腺增生或胸腺瘤的ＭＧ患者，胸腺切除术是有效的，应该列为治疗的第一选择。     

„Seronegative“ Myasthenie mit Antikörpern gegen die muskelspezifische Tyrosin-Kinase

About 10-20% of patients with generalized myasthenia gravis do not have acetylcholin receptor (AChR) antibodies and are referred to as having "seronegative" myasthenia. Recently, antibodies to muscle-specific kinase (MuSK), which mediates aggregation of AChR, were detected in half of these patients. We investigated six patients with seronegative myasthenia and identified two characteristic cases with MuSK antibodies. A 56-year-old woman developed ptosis and double vision followed by bulbar symptoms and respiratory insufficiency. She showed moderate response to treatment with pyridostigmine and no response to prednisolone, azathioprine, or intravenous immunoglobulin but good response to several plasma exchanges. A 46-year-old man with exercise-induced weakness of the upper limbs and mild bulbar and respiratory symptoms had a milder course for 9 years. These cases highlight the clinical spectrum of MuSK-positive myasthenia and the differences to AChR-positive myasthenia with predominant bulbar symptoms and often severe symptoms with respiratory insufficiency. Finally, they illustrate the therapeutic difficulties with less response to pyridostigmine and immunosuppressive drugs.     

Thymectomy and immunosuppression in myasthenia gravis: a prospective study

Between 1982 and 1988 24 women and 6 men with myasthenia gravis were included in a prospective and standardized diagnostic and therapeutic protocol. Age varied between 10 and 74 years (34 +/- 16, mean +/- standard deviation). Three patients with the ocular form were treated with pyridostigmine. Four patients with the generalized form and advanced age received steroids and/or azathioprine. Twenty-three patients with the generalized form underwent thymectomy followed by prednisone and/or azathioprine. One patient died after complex thymectomy for invasive thymoma. Another died soon after admission in myasthenic/cholinergic crisis. Two other patients had minor complications of thymectomy. Of 19 patients followed for 1-60 (mean 24) months, 11 (58%) are in remission, one of them without any medication.     

Repeat thymectomy in chronic refractory myasthenia gravis

Encouraged by recent results with "extended" thymectomy in the treatment of myasthenia gravis, we carried out repeat thymectomy in six patients with chronic, refractory disease who did not initially have extended thymectomy. All were completely disabled with longstanding myasthenia. Initial thymectomy (four transsternal, one transcervical, and one substernal) was carried out at a mean of 8.9 years previously (range, 5 to 18). There was no residual thymus observed with CT, but at repeat thymectomy, residual thymic tissue was present in five of six patients. Five patients significantly improved and four returned to full-time work. Mean prednisone dose declined from 51 mg to 18 mg/d, and mean pyridostigmine dose fell from 1,290 mg to 415 mg/d. No patient to date has had a complete remission. These results suggest that repeat thymectomy may benefit some patients with chronic disabling myasthenia gravis, especially when it is uncertain from a review of the operative report whether all thymic tissue was removed at the initial thymectomy.     

Outcomes after robotic thymectomy in nonthymomatous versus thymomatous patients with acetylcholine-receptor-antibody-associated myasthenia gravis

The aim of this study was to investigate the surgical and long-term neurological outcomes of patients with acetylcholine-receptor-antibody-associated myasthenia gravis (AChR-MG) who underwent robotic thymectomy (RATS). We retrospectively analyzed the clinical-pathological data of all patients with AChR-MG who underwent RATS using the DaVinci® Robotic System at the MUMC+ between April 2004 and December 2018. Follow-up data were collected from 60 referring Dutch hospitals. In total, 230 myasthenic patients including 76 patients with a thymoma (33.0%) were enrolled in this study. Mean follow-up time, procedure time and hospitalization were, respectively 65.7 ± 43.1 months, 111±52.5 min and 3.3 ± 2.2 days. Thymomatous patients had significantly more frequently and more severe complications than nonthymomatous patients (18.4% vs. 3.9%, p<0.001). Follow up data was available in 71.7% of the included patients. The Myasthenia Gravis Foundation of America postintervention score showed any kind of improvement of MG-symptoms after RATS in 82.4% of the patients. Complete stable remission (CSR) or pharmacological remission (PR) of MG was observed in 8.4% and 39.4% of the patients, respectively. Mean time till CSR/PR remission after thymectomy was 26.2 ± 29.2 months. No statistical difference was found in remission or improvement in MGFA scale between thymomatous and nonthymomatous patients. RATS is safe and feasible in patients with MG. The majority of the patients (82.4%) improved after thymectomy. CSR and PR were observed in 8.4% and 39.4% of the patients, respectively, with a mean of 26.2 months after thymectomy. Thymomatous patients had more frequently and more severe complications compared to nonthymomatous patients.