Randomized Trial of Thymectomy in Myasthenia Gravis.

BACKGROUND: Thymectomy has been a mainstay in the treatment of myasthenia gravis, but there is no conclusive evidence of its benefit. We conducted a multicenter, randomized trial comparing thymectomy plus prednisone with prednisone alone. METHODS: We compared extended transsternal thymectomy plus alternate-day prednisone with alternate-day prednisone alone. Patients 18 to 65 years of age who had generalized nonthymomatous myasthenia gravis with a disease duration of less than 5 years were included if they had Myasthenia Gravis Foundation of America clinical class II to IV disease (on a scale from I to V, with higher classes indicating more severe disease) and elevated circulating concentrations of acetylcholine-receptor antibody. The primary outcomes were the time-weighted average Quantitative Myasthenia Gravis score (on a scale from 0 to 39, with higher scores indicating more severe disease) over a 3-year period, as assessed by means of blinded rating, and the time-weighted average required dose of prednisone over a 3-year period. RESULTS: A total of 126 patients underwent randomization between 2006 and 2012 at 36 sites. Patients who underwent thymectomy had a lower time-weighted average Quantitative Myasthenia Gravis score over a 3-year period than those who received prednisone alone (6.15 vs. 8.99, P<0.001); patients in the thymectomy group also had a lower average requirement for alternate-day prednisone (44 mg vs. 60 mg, P<0.001). Fewer patients in the thymectomy group than in the prednisone-only group required immunosuppression with azathioprine (17% vs. 48%, P<0.001) or were hospitalized for exacerbations (9% vs. 37%, P<0.001). The number of patients with treatment-associated complications did not differ significantly between groups (P=0.73), but patients in the thymectomy group had fewer treatment-associated symptoms related to immunosuppressive medications (P<0.001) and lower distress levels related to symptoms (P=0.003). CONCLUSIONS: Thymectomy improved clinical outcomes over a 3-year period in patients with nonthymomatous myasthenia gravis. (Funded by the National Institute of Neurological Disorders and Stroke and others; MGTX ClinicalTrials.gov number, NCT00294658.).

Long-term effect of thymectomy plus prednisone versus prednisone alone in patients with non-thymomatous myasthenia gravis: 2-year extension of the MGTX randomised trial.

BACKGROUND: The Thymectomy Trial in Non-Thymomatous Myasthenia Gravis Patients Receiving Prednisone (MGTX) showed that thymectomy combined with prednisone was superior to prednisone alone in improving clinical status as measured by the Quantitative Myasthenia Gravis (QMG) score in patients with generalised non-thymomatous myasthenia gravis at 3 years. We investigated the long-term effects of thymectomy up to 5 years on clinical status, medication requirements, and adverse events. METHODS: We did a rater-blinded 2-year extension study at 36 centres in 15 countries for all patients who completed the randomised controlled MGTX and were willing to participate. MGTX patients were aged 18 to 65 years at enrolment, had generalised non-thymomatous myasthenia gravis of less than 5 years' duration, had acetylcholine receptor antibody titres of 1·00 nmol/L or higher (or concentrations of 0·50-0·99 nmol/L if diagnosis was confirmed by positive edrophonium or abnormal repetitive nerve stimulation, or abnormal single fibre electromyography), had Myasthenia Gravis Foundation of America Clinical Classification Class II-IV disease, and were on optimal anticholinesterase therapy with or without oral corticosteroids. In MGTX, patients were randomly assigned (1:1) to either thymectomy plus prednisone or prednisone alone. All patients in both groups received oral prednisone at doses titrated up to 100 mg on alternate days until they achieved minimal manifestation status. The primary endpoints of the extension phase were the time-weighted means of the QMG score and alternate-day prednisone dose from month 0 to month 60. Analyses were by intention to treat. The trial is registered with ClinicalTrials.gov, number NCT00294658. It is closed to new participants, with follow-up completed. FINDINGS: Of the 111 patients who completed the 3-year MGTX, 68 (61%) entered the extension study between Sept 1, 2009, and Aug 26, 2015 (33 in the prednisone alone group and 35 in the prednisone plus thymectomy group). 50 (74%) patients completed the 60-month assessment, 24 in the prednisone alone group and 26 in the prednisone plus thymectomy group. At 5 years, patients in the thymectomy plus prednisone group had significantly lower time-weighted mean QMG scores (5·47 [SD 3·87] vs 9·34 [5·08]; p=0·0007) and mean alternate-day prednisone doses (24 mg [SD 21] vs 48 mg [29]; p=0·0002) than did those in the prednisone alone group. 14 (42%) of 33 patients in the prednisone group, and 12 (34%) of 35 in the thymectomy plus prednisone group, had at least one adverse event by month 60. No treatment-related deaths were reported during the extension phase. INTERPRETATION: At 5 years, thymectomy plus prednisone continues to confer benefits in patients with generalised non-thymomatous myasthenia gravis compared with prednisone alone. Although caution is appropriate when generalising our findings because of the small sample size of our study, they nevertheless provide further support for the benefits of thymectomy in patients with generalised non-thymomatous myasthenia gravis. FUNDING: National Institutes of Health, National Institute of Neurological Disorders and Stroke.

The myasthenia gravis thymus: a rare source of human autoantibody-secreting plasma cells for testing potential therapeutics.

In early-onset myasthenia gravis (EOMG), the thymus is colonized by lymph node-like infiltrates including T cell areas and germinal centers. Our Group(1) showed (1978) spontaneous anti-acetylcholine receptor (AChR) autoantibody production by EOMG thymic cells. Especially after enzymic dispersal, these are enriched in plasma cells that are evidently autonomous, long-lived, terminally differentiated and radio-resistant. Radiolabeled AChR is highly sensitive both for localizing them in situ and detecting their ongoing antibody production in culture at limiting cell numbers. Thus EOMG thymi are a readily available source of specific autoimmune human plasma cells suitable for studying their biology and testing new therapies.

Preferential expression of AChR epsilon-subunit in thymomas from patients with myasthenia gravis.

The role of antigen expression by thymomas in myasthenia gravis (MG) is not clear. Previous reports of acetylcholine receptor (AChR) mRNA expression by the highly sensitive reverse transcription-polymerase chain reactions (RT-PCR) produced varying results. To try to clarify this issue, we first used RT-PCR but then turned to the more accurate and quantitative RNase protection assays (RPA) to assess AChR subunit mRNA expression in thymomas from 25 patients (22 with MG). By RT-PCR, all five AChR subunits could be detected in many thymomas. However, by RPA, the mRNA for the adult-specific AChR epsilon-subunit was found in 13/25 (52%) thymomas, but not mRNA for the other subunits. AChR epsilon-subunit was more frequently detected in thymomas of A or AB histology (WHO classification) than those with B1-B3 histology. Overall, 6/6 with thymomas of A or AB histology were positive compared with only 8/19 with B histology (p=0.02). Autoantibodies in the two patients with the highest levels of epsilon-subunit mRNA bound better to adult (alpha(2)betadeltaepsilon) AChR than to fetal (alpha(2)betadeltagamma) AChR, whereas the other sera bound better to fetal AChR. The greater abundance of mRNA for AChR epsilon-subunit than for other subunits suggests that the AChR epsilon-subunit may play a distinctive role in autosensitization in MG-associated thymomas, particularly those of type A or AB.

The MGTX experience: challenges in planning and executing an international, multicenter clinical trial.

We present our experience planning and launching a multinational, NIH/NINDS funded study of thymectomy in myasthenia gravis. We highlight the additional steps required for international sites and analyze and contrast the time investment required to bring U.S. and non-U.S. sites into full regulatory compliance. Results show the mean time for non-U.S. centers to achieve regulatory approval was significantly longer (mean 13.4+/0.96 [corrected] months) than for U.S. sites (9.67+/0.74 [corrected] months; p=0.003, [corrected] t-test). The delay for non-U.S. sites was mainly attributable to Federalwide Assurance certification and State Department clearance.

The ageing and myasthenic thymus: a morphometric study validating a standard procedure in the histological workup of thymic specimens.

The thymus is believed to play an important role in the pathogenesis of myasthenia gravis (MG). The 80% of MG patients with anti-acetylcholine receptor autoantibodies fall into three clinical subgroups: 1) thymoma; 2) early-onset MG (

Status of the thymectomy trial for nonthymomatous myasthenia gravis patients receiving prednisone.

The primary study [MGTX] aims to answer three questions: does extended transsternal thymectomy combined with the prednisone protocol, when compared with the prednisone protocol alone: (1) result in a greater improvement in myasthenic weakness, (2) result in a lower total dose of prednisone, thus decreasing the likelihood of concurrent and long-term toxic effects, (3) enhance the quality of life by reducing adverse events and symptoms associated with the therapies? Inclusion criteria are MGFA Class 2, 3, or 4; acetylcholine receptor antibody positive; age at least 18.0 years and <60.0 years; MG history of <3 years. Patients can be prednisone naïve or not. The National Institute for Neurological Disorders and Stroke awarded funding for MGTX in September 2005, and NIH awarded funding for the ancillary Biomarkers study (BioMG) in February 2006. Diverse regulatory obstacles have been encountered in this international study, but we now have a total of over 70 centers in 22 countries (North America, South America, Europe, Australasia, South Africa) either actively recruiting or at various levels of readiness.

Myasthenia gravis seronegative for acetylcholine receptor antibodies.

Antibodies to muscle-specific kinase (MuSK) are found in a variable proportion of patients with myasthenia without typical acetylcholine receptor (AChR) antibodies, but their characteristics and pathogenic mechanisms are not fully understood. We discuss the incidence and pathogenicity of MuSK antibodies and how clinical studies, animal models, and cultured cell lines can be used to elucidate their pathogenic mechanisms. Patients without either AChR or MuSK antibodies (seronegative myasthenia) appear to present another disease subtype that is highly similar to that of typical myasthenia gravis. We demonstrate a new method that detects AChR antibodies in these patients and show that these low-affinity AChR antibodies are predominantly IgG1 and can activate complement C3b deposition. Similarly MuSK antibodies, although mainly IgG4, are partially IgG1 and can activate C3b deposition. Overall, these results suggest that complement-activation may be an important pathogenic mechanism even in patients without conventional AChR antibodies.

Congenital myasthenic syndromes and the formation of the neuromuscular junction.

The congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders affecting neuromuscular transmission. Underlying mutations have been identified in at least 11 different genes. The majority of CMS patients have disorders due to mutations in postsynaptic proteins. Initial studies focused on dysfunction of the acetylcholine receptor (AChR) itself as the major cause of CMS. However, it is becoming apparent that mutations of proteins involved in clustering the AChR and maintaining neuromuscular junction structure form important subgroups. Analysis of the mutations in the AChR-clustering protein, rapsyn, show diverse causes for defective AChR localization and suggest that the common mutation rapsyn-N88K results in AChR clusters that are less stable than those generated by wild-type rapsyn. More recently, mutations in the newly identified endplate protein Dok-7 have been shown to affect AChR clustering and the generation and maintenance of specialized structures at the endplate. Dok-7 binds MuSK and many of the mutations of DOK7 impair the MuSK signaling pathway. Components of this pathway will provide attractive gene candidates for additional forms of CMS. The phenotypic characteristics of the different CMS in which muscle groups may be differentially affected not only provide clues for targeted genetic screening, but also pose further intriguing questions about underlying molecular mechanisms.

Clinical features of the DOK7 neuromuscular junction synaptopathy.

Mutations in DOK7 have recently been shown to underlie a recessive congenital myasthenic syndrome (CMS) associated with small simplified neuromuscular junctions ('synaptopathy') but normal acetylcholine receptor and acetylcholinesterase function. We identified DOK7 mutations in 27 patients from 24 kinships. Mutation 1124_1127dupTGCC was common, present in 20 out of 24 kinships. All patients were found to have at least one allele with a frameshift mutation in DOK7 exon 7, suggesting that loss of function(s) associated with the C-terminal region of Dok-7 underlies this disorder. In 15 patients, we were able to study the clinical features in detail. Clinical onset was usually characterized by difficulty in walking developing after normal motor milestones. Proximal muscles were usually more affected than distal, leading to a 'limb-girdle' pattern of weakness; although ptosis was often present from an early age, eye movements were rarely involved. Patients did not show long-term benefit from anticholinesterase medication and sometimes worsened, and where tried responded to ephedrine. The phenotype can be distinguished from 'limb-girdle' myasthenia associated with tubular aggregates, where DOK7 mutations were not detected and patients respond to anticholinesterase treatments. CMS due to DOK7 mutations are common within our UK cohort and is likely to be under-diagnosed; recognition of the phenotype will help clinical diagnosis, targeted genetic screening and appropriate management.

Quantitative EMG of facial muscles in myasthenia patients with MuSK antibodies.

OBJECTIVE: Our aim was to study the pathophysiological process leading to facial muscle atrophy in 13 patients with MuSK antibody positive myasthenia gravis (MuSK-MG), and to compare with findings from 12 acetylcholine receptor antibody positive myasthenia patients (AChR-MG), selected because they suffered from the same degree of disease severity and required similar treatment. METHODS: Motor unit action potential (MUAP) and interference pattern analysis from orbicularis oculi (O oculi) and orbicularis oris (O oris) muscles were studied using a concentric needle electrode, and compared with findings in 20 normal subjects, 6 patients receiving botulinum toxin injections (representing a neurogenic model) and 6 patients with a muscle dystrophy (representing a myopathic model). The techniques and control data have been reported previously. RESULTS: The mean MUAP durations for O oculi and O oris were significantly reduced (p<0.001) in both MG cohorts when compared with healthy subjects, and were similar to those in the myopathic control group. They were significantly different from those obtained from the neurogenic control group (p<0.001 for both O oculi and O oris). The MUAP findings in O oculi occurred independently from neuromuscular blocking on single fibre EMG (SFEMG) in the same muscle. On turns amplitude analysis (TAA), 50% of MuSK-MG patients and 42% of AChR-MG patients had a pattern in O oculi which was similar to that in the myopathic control group, and 62% of MuSK-MG patients and 50% of AChR-MG patients had a pattern in O oris that was also similar to that in the myopathic control group. The TAA findings for O oculi and O oris in both MG cohorts were different from those obtained from the neurogenic control group. CONCLUSIONS: Facial muscle atrophy in MuSK-MG patients is not neurogenic and the pathophysiological changes are akin to a myopathic process. The selected AChR-MG patients also show evidence of a similar pathophysiological process in the facial muscles albeit to a lesser degree. SIGNIFICANCE: We propose that muscle atrophy in MuSK-MG is a myopathic process consisting of either muscle fibre shrinkage or loss of muscle fibres from motor units. The duration of disease and long-term steroid treatment may be further contributory factors.

MRI and clinical studies of facial and bulbar muscle involvement in MuSK antibody-associated myasthenia gravis.

A proportion of patients with myasthenia gravis (MG) without acetylcholine receptor (AChR) antibodies have antibodies to muscle-specific kinase (MuSK). MG with MuSK antibodies (MuSK-MG) is often associated with persistent bulbar involvement, including marked facial weakness and tongue muscle wasting. The extent of muscle wasting in MuSK-MG, and whether it is also found in the few acetylcholine receptor (AChR-MG) patients who have persistent bulbar involvement, is not clear. We studied 12 MuSK-MG patients and recruited 14 AChR-MG patients matched broadly for age, sex ratio, duration of disease and degree of ocular, bulbar and facial weakness. We used coronal and sagittal T1-weighted (T1W) and T2-weighted (T2W) magnetic resonance imaging (MRI) to assess muscle wasting in facial and tongue muscles. Hyperintense signal on T1W MRI and comparison of axial T1W sequences with cUTE sequences were used to assess fibrous/fatty tissue in the tongue. We compared the results with those of four patients with myotonic dystrophy and 12 healthy individuals. We correlated the changes with clinical and treatment histories, and established a new ocular-bulbar-facial-respiratory (OBFR) score. At the time of study, none of the clinical measures, including the OBFR score, differed between the two MG groups. MRI demonstrated thinning of the buccinator, orbicularis oris (O.oris) and orbicularis oculi (O.oculi) muscles in MuSK-MG patients compared with healthy controls, whereas thinning of these muscles was not significant in AChR-MG. Tongue areas with T1W high signal were increased in MuSK-MG patients and the intensity of the signal on axial T1W sequences was greater in MuSK-MG than in controls. To look for possible correlations between imaging and clinical findings, we pooled results from all MG patients. The duration of treatment with prednisolone at >40 mg on alternate days (AD) correlated positively with the percentage of tongue area with high signal (P = 0.006) and negatively with MRI measurements of individual muscles and with the mean muscle dimensions (P = 0.001). The new OBFR score correlated positively with current Myasthenia Gravis Foundation of America grades and with the percentage of high signal (P = 0.004) and negatively with the mean muscle dimensions (P < 0.001). The results show that bulbar and facial muscle weakness and wasting are associated with significant muscle atrophy and fatty replacement in MuSK-MG, which was not found in the AChR-MG patients. MuSK antibodies per se may predispose to muscle thinning, but the difficulties in obtaining clinical remission under steroid therapy in some patients, resulting in long duration of treatment with higher doses (>40 mg AD), may be an additional factor.

Acetylcholine receptor antibody in Thai generalized myasthenia gravis patients.

The authors studied acetylcholine receptor antibody (AChR Ab) in twenty-six Thai patients diagnosed as having generalized myasthenia gravis and fifteen control cases. AChR Ab assay was done by radio-immunoassay technique and reported by titer in nmole/L. The positive result was defined by titer more than 0.5 nmole/L. In the myasthenia gravis group, age ranged from 18 to 64 years old with mean of 34 years old. The female: male ratio was 4.2:1. Duration of disease before taking blood sample ranged from 1 month to 14 years with a mean of 3.9 year The AChR Ab could be detected in 21 out of 26 patients (80.7%). In the control group, tests were all negative. The results of the test made the sensitivity of 80.7% and specificity of 100%. The positive predictive value was 100%, the negative predictive value was 75%, and the prevalence was 60.3%. There was no correlation between AChR Ab titer and clinical features. This test is a very valuable test in case of uncertainly in the diagnosis of myasthenia gravis.

Neuromuscular junction channelopathies: a brief overview.

The neuromuscular junction lacks the protection of the blood-nerve barrier and is vulnerable to antibody-mediated disorders. In myasthenia gravis (MG), 85% of patients have IgG antibodies to acetylcholine receptors (AChRs). About half the remaining patients have IgG antibodies to Muscle Specific Kinase (MuSK), an AChR-associated transmembrane post-synaptic protein concerned in AChR aggregation. Bulbar weakness is typically predominant in this form of MG, and females are more often affected. The Lambert-Eaton Myasthenic Syndrome (LEMS) can occur in a paraneoplastic form (P-LEMS) usually with small cell lung cancer, or in a non-paraneoplastic form (NP-LEMS). In both, IgG antibodies to nerve terminal voltage-gated calcium channels (VGCCs), detectable in over 90% of patients, lead to VGCC loss and impaired quantal release of transmitter and may be implicated in the occasionally associated cerebellar ataxia. Neuromyotonia (NMT) and Cramp-Fasciculation syndrome (C-FS) are manifestations of peripheral nerve hyperexcitability and share some clinical and electromyographic features. Antibodies to voltage-gated potassium channels (VGKCs) are present in about 40% of NMT patients, but less frequently in C-FS, and appear to cause loss of functional VGKCs. They may also be implicated in the Maladie de Morvan and limbic encephalitis that can associate with NMT: The antibodies described here provide valuable aids to diagnosis and management. The Congenital Myasthenic Syndromes are a group of genetically determined heterogeneous disorders, usually recessively inherited. The commonest mutation sites appear to be the acetylcholine receptor epsilon-subunit and rapsyn.

Seronegative generalised myasthenia gravis: clinical features, antibodies, and their targets.

Myasthenia gravis (MG) is a well-recognised disorder of neuromuscular transmission that can be diagnosed by the presence of antibodies to the acetylcholine receptor (AChR). However, some patients (about 15%) with generalised MG do not have detectable AChR antibodies. There is some evidence, however, that this "seronegative" MG is an antibody-mediated disorder. Plasma from patients with the disorder seems to contain various distinct humoral factors: IgG antibodies that reversibly inhibit AChR function; a non-IgG (possibly IgM) factor that indirectly inhibits AChR function; and an IgG antibody against the muscle-specific kinase (MuSK). The presence of antibodies against MuSK appears to define a subgroup of patients with seronegative MG who have predominantly localised, in many cases bulbar, muscle weaknesses (face, tongue, pharynx, etc) and reduced response to conventional immunosuppressive treatments. Moreover, muscle wasting may be present, which prevents complete response to these therapies.

Myasthenia gravis in a woman with congenital AChR deficiency due to epsilon-subunit mutations.

A reduction in the number of acetylcholine receptors (AChR) on the postsynaptic membrane is characteristic of MG. This may be inherited (AChR deficiency syndrome) or acquired (MG). The authors report two sisters with AChR deficiency caused by heteroallelic mutations in the AChR epsilon-subunit gene. The younger sister developed MG at 34 years. This unusual case raises the possibility that genetic defects of the AChR might be a factor in the etiology of autoimmune MG.

Thymic myoid cells and germinal center formation in myasthenia gravis; possible roles in pathogenesis.

In early-onset myasthenia gravis (EOMG), the thymus usually shows medullary lymph node-type infiltrates, rearranged bands of hyperplastic epithelium and focal fenestrations in the intervening laminin borders. This resemblance to autoimmune target organs may reflect autoantigen expression by rare thymic myoid cells, long ago implicated circumstantially as agents provocateurs. In this quantitative study, they were frequently seen at the laminin fenestrations; if so, germinal centers (GC) were significantly commoner nearby, our most EOMG-specific finding (not seen in a distinct MG patient subset). As autoantibodies became detectable, myoid cell involvement apparently progressed. Our unifying hypothesis--that an early autoantibody attack on myoid cells provokes local GC formation--helps to resolve many puzzles.

Pathogenic autoantibodies in the lambert-eaton myasthenic syndrome.

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular transmission in which antibodies are directed against voltage-gated calcium channels (VGCCs). We studied the action of LEMS immunoglobulin G (IgG) on cloned human VGCCs stably transfected into human embryonic kidney cells (HEK293). All LEMS IgGs tested bound to the surface of the P/Q-type VGCC cell line and caused a significant reduction in whole-cell calcium currents in these cells. By contrast, only 2 out of 6 IgGs bound extracellularly to the N-type VGCC cell line, and none of the LEMS IgGs tested was able to reduce whole-cell calcium currents in these cells. We used this apparent specificity of LEMS IgG for the P/Q-type VGCC to investigate the action of these IgGs on model systems where a number of different VGCC populations exist in equilibrium. LEMS IgG caused a significant downregulation in the omega-agatoxin IVA-sensitive P/Q-type VGCCs of cultured rat cerebellar neurons, but this was accompanied by a concomitant rise in the "resistant" R-type VGCCs. By using the passive transfer model of LEMS, similar results were observed at the mouse neuromuscular junction, where a significant reduction in P/Q-type VGCCs was paralleled by an increase in L- and R-type VGCCs. These results demonstrate an unexpected plasticity in the expression of VGCCs in mammalian neurons and may represent a mechanism by which the pathogenic effects of LEMS IgG are reduced.

Autoimmune disorders of neuronal potassium channels.

Antibodies to voltage-gated potassium channels (VGKCs) appear likely to be the effector mechanisms in many patients with acquired peripheral nerve hyperexcitability (APNH) syndromes, a group of disorders that include neuromyotonia, cramp-fasciculation syndrome, and Isaacs' syndrome. They may contribute to the associated autonomic changes. Through a central action, they may also be the effector mechanism in those with Morvan's syndrome and in some patients with limbic encephalitis. Evidence supporting this hypothesis includes the increased association of APNH with autoimmune diseases (in particular, myasthenia gravis and thymoma), the response to plasmapheresis, passive transfer of APNH to experimental animals by patients' plasma or immunoglobulins, the action of their serum on VGKC currents studied in vitro, and the presence in many patients of IgG antibodies to VGKCs.

Development of a thymectomy trial in nonthymomatous myasthenia gravis patients receiving immunosuppressive therapy.

Thymectomy has been regularly used in the management of nonthymomatous autoimmune myasthenia gravis (MG), but its benefits have not been established in a randomized, controlled trial. The widespread use of thymectomy in MG patients without thymoma is largely based on retrospective, nonrandomized case series that have produced a consensus that the procedure is sometimes beneficial. Still, the benefits and utilization of thymectomy are actively debated among MG experts. In this paper, we describe the development of a multicenter, international trial to determine whether extended transsternal thymectomy reduces corticosteroid requirements for patients with generalized AChR antibody-positive nonthymomatous MG.