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.     

Acetylcholine receptors loss and postsynaptic damage in MuSK antibody-positive myasthenia gravis

Muscle-specific tyrosine kinase (MuSK) antibodies are found in some patients with "seronegative" myasthenia gravis (MG), but how they cause myasthenic symptoms is not clear. We visualized acetylcholine receptors (AChRs) and complement component 3 (C3) in muscle biopsies from 10 Japanese MG patients with MuSK antibodies, compared with 42 with AChR antibodies. The AChR density was not significantly decreased in MuSK antibody (Ab)-positive end-plates compared with AChR antibody-positive end-plates, and C3 was detected in only two of eight MuSK Ab-positive patients. MuSK antibodies do not appear to cause substantial AChR loss, complement deposition, or morphological damage. Effects on MuSK function need to be explored.     

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.     

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     

Acetylcholine receptor antibodies in myasthenia gravis

A multivariate statistical analysis of levels of serum acetylcholine receptor antibody (AChR Ab) obtained from 197 patients with various clinical forms of myasthenia gravis (MG) was performed. Elevated AChR Ab levels are specific for MG, but normal AChR Ab levels do not rule out MG. Patients in remission or with purely ocular MG had the lowest incidence of elevation of serum AChR Ab levels, while patients with generalized, severe MG, particularly in the presence of thymoma, tended to have the greatest antibody elevations. Corticosteroids depressed AChR Ab levels, but thymectomy did not exert a consistent effect on antibody levels within a 24- to 30-month postoperative period. The relatively low 55% positivity of antibody elevations in all 197 patients probably reflects the use of heterologous (rat) AChR.     

Differences between ocular and generalized myasthenia gravis: binding characteristics of anti-acetylcholine receptor antibody against bovine muscles

We studied the binding characteristics of anti-acetylcholine receptor antibody (AChR Ab) in sera of nine patients with myasthenia gravis (MG) using affinity-purified extraocular muscles (EOM) and foot muscles (FM) of bovine species. The titer of AChR Ab measured with EOM was the same as that measured with FM for both ocular and generalized MG. In patients with ocular MG, the affinity of AChR Ab, determined by Scatchard analysis, was higher for FM than for EOM (P less than 0.05), whereas it was the same for EOM and FM in those with generalized MG. On the other hand, the affinity of AChR Ab for FM was lower in generalized MG than in ocular MG (P less than 0.05), but that for EOM did not differ between the two types of MG. The affinity of AChR Ab did not change after passing the patients' sera through an EOM-affinity column. The EOM-affinity column treatment of the sera decreased the AChR Ab titer measured with EOM in all patients, but the AChR Ab titer measured with FM was decreased in only some of the patients. These data indicate that there are polyclonal or heterogeneous AChR Abs in the sera of MG patients, which does not help to explain the clinical difference between ocular and generalized MG.     

AChR myasthenia gravis switching to MuSK or double antibody positive myasthenia gravis in two children and literature review

Muscle–specific tyrosine kinase antibody (MuSK–Ab) and acetylcholine receptor antibody (AChR–Ab) coexistence in myasthenia gravis (MG) is very rare. In this report, two children with AChR–Ab switching to double antibody positive MG (DP–MG) or MuSK–Ab positive MG (MuSK–MG) are described. Six similar cases were found in the literature via online database search. Therefore, this study describes eight patients in total, six female and two male. The average age of onset was 7.25 ± 5.95 years. Four AChR–MG patients switched to DP–MG with no known precipitating factor and four switched after thymectomy (two to MuSK–MG and two to DP–MG). After the serological switch, the patients transitioned to the phenotype of MuSK–MG and responded poorly to cholinesterase inhibitors and well to corticosteroids and plasma exchange.     

Multiple forms of anti-acetylcholine receptor antibody in myasthenia gravis

Sera of patients with myasthenia gravis (MG) contain anti-acetylcholine receptor (AChR) lgG antibodies (Ab) which have different antigenic specificities. Three Ab types were detected: (1) MG-I, which forms immune complexes with AChR; (2) MG-C, which decreases binding of AChR to concanavalin A; and MG-B, which blocks α-bungarotoxin binding to AChR. Sera from 152 MG patients were screened for the Ab types. Sixty-one percent contained MG-I, 26% contained MG-C, 10% contained MG-B, and 5% contained both MG-C and MG-B. The latter Ab types were associated with more severe forms of MG but showed no other clinical correlations. IgG antibodies of defined type were purified, and their interaction with unlabeled and toxin-prelabeled AChR from denervated rat muscle was studied in detail. Receptors are homogeneous with respect to determinants recognized by MG-I, but heterogeneous with respect to determinants recognized by MG-C (3 subpopulations, 22%, 28%, and 50% of AChR) and by MG-B (2 subpopulations, 30% and 70% of AChR). The stoichiometry of AChR interaction with the antibodies indicates that for each toxin-binding site, the receptor is divalent as an antigen for MG-I and MG-C but is tetravalent for MG-B. Denervated muscle AChR appears to be a mixture of at least 3 molecular forms of AChR, each of which has distinct immunological features as well as components common to all the receptor subpopulations.     

Antibodies against the main immunogenic region of the acetylcholine receptor correlate with disease severity in myasthenia gravis

Objective We developed an assay that detects autoantibodies against the main immunogenic region (MIR) located at the extracellular end of the nicotinic acetylcholine receptor (AChR) α subunit, and investigated its clinical relevance in myasthenia gravis (MG). Methods In this retrospective cohort study, we measured MIR antibody (Ab) titres in sera obtained before treatment and analysed their associations with clinical parameters in 102 MG patients from two neurological centres. MIR Ab titres were determined using a modified competition immunoprecipitation assay in the presence or absence of monoclonal antibody 35. Results 11 of 23 (47.8%) ocular type and 66 of 72 (91.7%) generalised type MG patients were positive for the presence of MIR Abs, defined as a titre >16.8% (3 SDs above the mean for 70 healthy controls). A significantly higher MIR Ab titre (p<0.001) was shown in generalised type (47.9±19.2%) rather than in ocular type MG patients (16.4±8.4%). Bivariate regression analysis using both titre levels of MIR Ab and routine AChR binding Ab as variables revealed MIR Abs to be an exclusive indicator positively associated with disease severity (Myasthenia Gravis Foundation of America classification, p<0.0001; Quantitative MG score, p=0.008), the presence of bulbar symptoms (p<0.0001) and thymoma (p=0.016), and negatively associated with ocular MG (p<0.0001). Conclusions MIR Ab titre levels show much better correlations with factors related to disease severity compared with AChR binding Ab titres. The MIR Ab assay may be useful for predicting MG symptom severity, especially for discriminating between ocular and generalised types of MG.     

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.     

Nonthymoma early-onset- and late-onset-generalized myasthenia gravis--a retrospective hospital-based study

OBJECTIVE: Acquired myasthenia gravis (MG) is predominantly due to nicotinic acetylcholine receptor (AChR) autoantibodies (Ab). Differences between nonthymoma early-onset and late-onset MG were reported. We studied the clinical and serological characteristics of nonthymoma AChR Ab-positive-generalized MG patients. PATIENTS AND METHODS: Chinese AChR Ab-positive-generalized MG patients who had generalized disease for 3 years or longer were studied. RESULTS: Among 41 such patients, 25 (61%) were female. The mean onset age was 43.5 years (range 9-78 years) and the mean follow-up duration was 7.8 years (range 3-20 years). Sixteen (39%) patients had late-onset disease (onset age >or=50 years). Compared to early-onset patients (onset age <50 years), late-onset patients were characterized by male predominance (p=0.002), absence of thymic lymphofollicular hyperplasia (p=0.036), and a higher striated muscle Ab seropositivity rate (94% versus 4%, p<0.001). Although there was no statistically significant difference in clinical severity and outcome or response to treatment between late-onset and early-onset patients, 50% and 75% of late-onset patients had moderate or severe disease at onset and worst status, respectively, compared to 28% and 52% for early-onset patients at onset and worst status, respectively. Also 63% of late-onset patients had disease progressed within first 3 years compared to only 40% of early-onset patients did. CONCLUSION: Nonthymoma late-onset-generalized MG patients were common among Hong Kong Chinese, with a statistically non-significant trend that it was clinically more severe than early-onset MG but with similar clinical outcome or response to treatment; >90% of these patients were seropositive for striated muscle Ab.     

Involvement of HLA in clinical courses of myasthenia gravis

The relationship between the histocompatibility leukocyte antigen (HLA) phenotypes and the clinical course of myasthenia gravis (MG) was studied in 53 Japanese patients with MG. The frequency of HLA-DRw9 antigen was high in the MG patients who did not need immunosuppressive therapy but only anticholinesterase agents (RR = 4.52; CP less than 0.02), who achieved remission of the disease (RR = 2.98; CP less than 0.05) or who showed a decrease in AChR antibody (Ab) titer (RR = 6.32; CP less than 0.0002), whereas the frequency of HLA-DRw8 antigen was increased in MG patients who underwent immunosuppressive therapy (RR = 4.03; CP less than 0.01), who did not have remission (RR = 4.75; CP less than 0.1) or who showed an increase in AChR Ab titer (RR = 6.48; CP less than 0.01). These data suggest that immunogenetic heterogeneity in MG might be reflected in its clinical course.     

Clinical and experimental features of MuSK antibody positive MG in Japan

We investigated the presence of antibodies (Abs) against muscle-specific tyrosine kinase (MuSK) in Japanese myasthenia gravis (MG) patients. MuSK Abs were found in 23 (27%) of 85 generalized seronegative MG (SNMG) patients but not in any of the ocular MG patients. MuSK Ab-positive patients were characterized as having female dominance (M:F, 5:18), age range at onset 18 to 72 (median 45) years old, and prominent oculobulbar symptoms (100%) with neck (57%) or respiratory (35%) muscle weakness. Limb muscle weakness was comparatively less severe (52%), thymoma absent. Most patients had good responses to simple plasma exchange and steroid therapy. MuSK IgG from all 18 patients was exclusively the IgG 4 subclass and bound mainly with the MuSK Ig 1–2 domain. Serial studies of 12 individuals showed a close correlation between the variation in MuSK Ab titers and MG clinical severity ( P  = 0.01 by Kruskal–Wallis). MuSK Ab titers were sharply decreased in patients who had a good response to early steroid therapy or simple plasma exchange, but there was no change, or a rapid increase on exacerbation after thymectomy. Measurement of MuSK Ab titers aids in the diagnosis of MG and the monitoring of clinical courses after treatment.     

Myasthenia in SCID mice grafted with myasthenic patient lymphocytes: role of CD4+ and CD8+ cells

OBJECTIVES: Acetylcholine receptor (AChR)-specific CD4+ cells are present in MG patients, and synthesis of the high-affinity immunoglobulin G (IgG) autoantibodies (autoAb) against the muscle AChR that causes MG symptoms requires intervention of CD4+ cells. The role of CD4+ cells in MG pathogenesis has been postulated but never proven. MG patients do not have anti-AChR cytotoxic phenomena, and it has been assumed that CD8+ cells do not have a pathogenic role in MG. However, CD8+ cells may facilitate rodent experimental MG, raising the possibility that CD8+ cells might be necessary also in MG. In this study we examined whether CD4+ and CD8+ cells play a role in the pathogenesis of MG and whether CD4+ cells specific for AChR epitope sequences recognized by most MG patients ("universal" epitopes) drive the synthesis of pathogenic antibodies. METHODS: First we characterized a chimeric human-mouse model of MG in severe combined immunodeficiency (SCID) mice engrafted with blood lymphocytes (BL) from MG patients. We used that model to determine whether CD4+ and CD8+ cells are necessary for transfer of MG symptoms. We engrafted SCID mice intraperitoneum with BL from 19 MG patients and 5 healthy controls. We engrafted some mice with either BL, BL depleted in CD4+ or CD8+ cells from the same patient, or CD4+ depleted BL reconstituted with CD4+ T cells from the same patient, specific for "universal" AChR epitopes or for two unrelated antigens, tetanus and diphtheria toxoids. We tested the mice for myasthenic symptoms for 7 to 18 weeks. RESULTS: Mice transplanted with BL, or CD8+ depleted BL, or CD4+-depleted BL reconstituted with anti-AChR CD4+ cells from MG patients frequently developed myasthenic weakness. The mice had human anti-AChR Ab in the serum and bound to muscle AChR. Mice transplanted with BL from controls, or CD4+-depleted BL from MG patients, or CD4+-depleted BL from an MG patient reconstituted with CD4+ cells specific for tetanus or diphtheria toxoids did not develop myasthenic weakness or anti-AChR Ab. CONCLUSIONS: CD4+ cells are necessary for MG pathogenesis; CD8+ cells may not be. CD4+ cells specific for "universal" AChR epitopes help the synthesis of pathogenic Ab.     

Anti-MuSK antibody myasthenia gravis: clinical findings and response to treatment in two large cohorts

Introduction: Myasthenia gravis (MG) patients with autoantibodies to muscle‐specific tyrosine kinase (MuSK) represent a distinct subset of those with this disease. Treatment and outcomes data in these patients are limited and conflicting. Methods: We reviewed 110 MuSK‐MG patients from two large clinics in Italy and the USA. Results: Thirty‐nine to 49% of patients with generalized, acetylcholine receptor antibody (AChR‐Ab)–negative MG had MuSK‐MG. Eighty‐five percent were female, with disease onset typically in the fourth decade. Ocular and/or bulbar symptoms were present at onset in 79% of those studied. Eighty‐five percent were MGFA class III or greater, and crisis occurred in 28%. Plasma exchange (PLEX) produced improvement in 93%, whereas only 61% improved after intravenous immunoglobulin. Long‐term outcomes were comparable to those of patients with AChR‐Ab–positive MG. Conclusions: MuSK‐MG has a marked female predominance with frequent oculobulbar weakness and crises. Many patients deteriorate rapidly early in the disease, and PLEX is usually the preferred treatment. Long‐term outcomes are similar to those of patients with AChR‐Ab⁺ MG. Muscle Nerve 44: 36–40, 2011     

Mortality in myasthenia gravis: A nationwide population–based follow‐up study in Denmark

Introduction: In previous studies of myasthenia gravis (MG), increased mortality has been reported. The aim of this study was to estimate mortality in patients with acetylcholine receptor antibody–positive (AChR‐Ab–seropositive) MG in a nationwide population–based, long‐term follow‐up study. Methods: All AChR‐Ab–seropositive MG patients, diagnosed between 1985 and 2005, were identified. Defined by age at diagnosis (≤50 or >50 years), patients were classified as having early‐ or late‐onset MG. For comparison, 10 non‐MG individuals from the general population were matched with each patient. All patients and controls were followed until January 1, 2009. Mortality rates and estimated mortality rate ratios (MRRs) were calculated. Results: Of 702 AChR‐Ab–seropositive MG patients, 302 died during follow‐up. Overall mortality was higher for patients with MG (MRR = 1.41, range 1.24–1.60). In late‐onset women and men, the MRRs were 1.64 (1.36–1.99) and 1.22 (1.02–1.46), respectively. Total MRR was highest during the first 5 years after diagnosis. Conclusions: MG diagnosis is still associated with increased mortality. Muscle Nerve 53 : 73–77, 2016     

Acetylcholine receptor antibody positivity rate in ocular myasthenia gravis: a matter of age?

Journal of Neurology - Anti-acetylcholine receptor antibodies (AChR Abs) are detected in 85% of myasthenia gravis (MG) patients, at higher rates in patients with late-onset disease. AChR Ab...     

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.     

The predictive value of the presence of different antibodies and thymus pathology to the clinical outcome in patients with generalized myasthenia gravis

Objectives

To analyze the predictive value of anti-acetylcholine receptor antibodies (anti-AChR Ab) and anti-muscle specific kinase antibodies (anti-MuSK Ab), as well as the thymus pathology to the clinical outcome in patients with generalized myasthenia gravis (MG).

Methods

We analyzed 138 patients with generalized MG, who were thymectomized and assayed for anti-AChR Ab and anti-MuSK Ab.

Results

Anti-AChR Ab were detected in 84% of patients, while anti-MuSK Ab were present in 36% of the AChR Ab negative patients. Severe forms of the disease were more frequent in MuSK Ab positive, compared to the AChR Ab positive and complete seronegative patients. Thymic lymphoid follicular hyperplasia (LFH) was present in 60%, thymoma in 23%, atrophic thymus in 9% and the normal thymus in 8% of patients. LFH was more frequent among women, while thymoma and atrophic thymus were more frequent in men. The younger patients mainly had LFH and normal thymus, while thymoma and atrophic thymus were more frequent in older patients. The mildest clinical presentation was present in patients with normal thymus, while severe forms of the disease were registered in the patients with thymoma. The AChR Ab positive patients had more often LFH and thymoma, while within MuSK Ab positive patients atrophic thymus was most common.

Conclusion

The best disease outcome was observed in patients with normal thymus or LFH with anti-AChR Ab or without both types of antibodies.     

Autonomic function and autoantibodies to autonomic nervous tissues at follow-up in a cohort of young patients with type 1 diabetes. Effects of serum from diabetic patients on human adrenergic cells

Recent studies have linked autoimmunity to nervous tissue structures and diabetic autonomic neuropathy. To evaluate prospectively the early stage of type 1 diabetes and the natural history of this association, we monitored the autonomic function and the presence of autoantibodies (Ab) to sympathetic and parasympathetic nervous structures in a cohort of 92 diabetic adolescent patients, recruited and followed-up after 40+/-3 months. The presence of circulating Ab and their ability to activate complement was also assessed using a human adrenergic neuroblastoma cell line, and the effect of patients' sera on these cells was evaluated by different methods assessing cytotoxic effects and apoptosis. Thirty-nine percent of the Ab-positive patients had one abnormal test (p=0.07 vs. Ab-negative patients). Serum from four patients positive for anti-cervical ganglia Ab showed positive staining of neuroblastoma cells and displayed ability to activate complement. Serum from two adolescent patients with anti-cervical ganglia and anti-neuroblastoma cells Ab, induced cytotoxic effects and damaged the plasma membrane of the neuroblastoma cells. Moreover, sera from two adult patients with overt autonomic neuropathy, used as positive controls, induced apoptosis of these cells, assessed by TUNEL. Our data indicate that symptomatic autonomic neuropathy is not characteristic of young diabetic patients, but that autoantibodies to autonomic structures are present and persist in the first 20 years of disease, possibly associated with subtle autonomic dysfunction and cytotoxic effect on sympathetic cells.