Anti-acetylcholine receptor antibodies in myasthenia gravis. Part 1. Relation to clinical parameters in 250 patients

Ocular Myasthenia Gravis As Unilateral Ptosis and External Ophthalmoplegia: A Case Report

Myasthenia gravis (MG) is an autoimmune disorder characterized by fluctuating weakness and fatigue in ocular, bulbar, limb, or respiratory muscles. Initially, more than half of MG patients experience isolated ocular symptoms, such as ptosis, diplopia, or muscle paresis. This case report presents a unique occurrence of MG in a four-year-old female, showcasing a two-year history of sudden onset, persistent yet fluctuating unilateral ptosis accompanied by exo-deviation and adduction deficit in the right eye. No diplopia or systemic features were observed. Positive findings in tests, including the ice pack test, Cogan twitch sign, fatiguability, and neostigmine test, indicated ocular myasthenia. Electromyography revealed a decremental response, while anti-acetylcholine antibodies showed borderline results. Computed tomography of the brain ruled out central causes, and routine laboratory testing yielded normal results. Treatment with pyridostigmine and corticosteroids led to significant improvement in symptoms. This case emphasizes the diverse presentation of MG in ophthalmology, with ocular signs serving as indicators in approximately half of the cases. Early diagnosis and prompt treatment are crucial for enhancing long-term prognosis. Emergency physicians should consider MG as a potential cause for unilateral ocular symptoms after excluding central causes. Accurate diagnosis and comprehensive management of MG are complex yet essential for ensuring optimal patient health.

Clinical Characteristics and Prognosis of Very late-onset Myasthenia Gravis in China

Alteration in onset-age distribution in myasthenia gravis (MG) and its increasing prevalence among the elderly underscores the need for a better understanding of the clinical course of MG and the establishment of personalized treatment. In this study we reviewed the demographics, clinical profile, and treatment of MG. Based on onset age, eligible patients were classified as early-onset MG (onset age ≥18 and <50 years), late-onset MG (onset age ≥50 and <65 years), and very late-onset MG (onset age ≥65 years). Overall, 1160 eligible patients were enrolled. Patients with late- and very late-onset MG showed a male predominance (P=0.02), ocular MG subtype (P=0.001), and seropositivity for acetylcholine receptors and titin antibodies (P<0.001). In very late-onset MG, a lower proportion of patients retained minimal manifestations status or better, a higher proportion of patients had MG-related deaths (P<0.001), and a shorter maintenance time of minimal manifestation status or better was seen at the last follow-up (P=0.007) than that in patients with early- and late-onset MG. Non-immunotherapy may associated with a poor prognosis in patients in the very late-onset group. Further studies on very late-onset MG patients should be performed to evaluate the relationship between immunotherapy and prognosis.

Myasthenia Gravis: An Acquired Interferonopathy?

Myasthenia gravis (MG) is a rare autoimmune disease mediated by antibodies against components of the neuromuscular junction, particularly the acetylcholine receptor (AChR). The thymus plays a primary role in AChR-MG patients. In early-onset AChR-MG and thymoma-associated MG, an interferon type I (IFN-I) signature is clearly detected in the thymus. The origin of this chronic IFN-I expression in the thymus is not yet defined. IFN-I subtypes are normally produced in response to viral infection. However, genetic diseases called interferonopathies are associated with an aberrant chronic production of IFN-I defined as sterile inflammation. Some systemic autoimmune diseases also share common features with interferonopathies. This review aims to analyze the pathogenic role of IFN-I in these diseases as compared to AChR-MG in order to determine if AChR-MG could be an acquired interferonopathy.

Ocular Myasthenia: Clinical Course and the Diagnostic Utility of Assaying Acetylcholine Receptor Antibodies

Myasthenia gravis (MG) is an autoimmune disease that causes neuromuscular junction transmission defect and has a predilection for the with neuromuscular junction transmission defect and predilection for extra-ocular and eyelid muscles. Most cases of ocular MG (OMG) convert later to generalised MG (GMG). Assaying acetylcholine receptor antibodies (AchRA) has been used to diagnose MG, but the reported sensitivity in OMG is lower (50%) than in GMG. We report the clinical course and the diagnostic yield of assaying AchRA in a Kuwaiti cohort of patients with OMG. We carried out a retrospective review of 47 patients diagnosed with OMG who were tested for AchRA. Ancillary tests included the ice test, single-fibre electromyography (SFMEG), and repetitive nerve stimulation electromyography (RNS). Progression to GMG occurred in 51% of OMG patients with a mean time to progression of 12.1 months (range 4 to 20 months). AchRAs were positive in 46 of 47 cases (98%), while SFEMG was positive in 31 of 34 cases (91.1%). Older age (44.25 years versus 38 years, p < .05) and higher AchRA titre (2.0 nmol/L versus 1.27 nmol/L, p < .05) were significantly associated with conversion to GMG. We have found a high rate of AchRA seropositivity in relatively younger subjects of OMG. Higher AchRA titres and older age were associated with conversion to GMG, usually within the first 2 years.

Inpatient Diagnosis and Management of Neuromuscular Disorders

Although many neuromuscular conditions are evaluated on an outpatient basis owing to their chronic or progressive nature, more urgent evaluation and management is often required for the inpatient presenting with acute to subacute focal or generalized numbness or weakness. This review focuses on clinical pattern recognition and basic anatomic localization principles to aid in the identification of common, as well as some less frequently encountered, neuromuscular disorders in hospitalized patients. The characteristic clinical and diagnostic features, associated complications, and recommended treatments of key neuromuscular conditions with acute and subacute manifestations are discussed. These conditions can be life-threatening in some cases, such as in Guillain-Barré syndrome, owing to associated oropharyngeal weakness, respiratory failure, or marked dysautonomia. Prompt recognition of the clinical and pathologic features is therefore necessary to reduce associated morbidity and mortality.

Clinical and therapeutic features of myasthenia gravis in adults based on age at onset

OBJECTIVE

To describe the characteristics of patients with very-late-onset myasthenia gravis (MG).

METHODS

This observational cross-sectional multicenter study was based on information in the neurologist-driven Spanish Registry of Neuromuscular Diseases (NMD-ES). All patients were >18 years of age at onset of MG and onset occurred between 2000 and 2016 in all cases. Patients were classified into 3 age subgroups: early-onset MG (age at onset <50 years), late-onset MG (onset ≥50 and <65 years), and very-late-onset MG (onset ≥65 years). Demographic, immunologic, clinical, and therapeutic data were reviewed.

RESULTS

A total of 939 patients from 15 hospitals were included: 288 (30.7%) had early-onset MG, 227 (24.2%) late-onset MG, and 424 (45.2%) very-late-onset MG. The mean follow-up was 9.1 years (SD 4.3). Patients with late onset and very late onset were more frequently men (p < 0.0001). Compared to the early-onset and late-onset groups, in the very-late-onset group, the presence of anti-acetylcholine receptor (anti-AChR) antibodies (p < 0.0001) was higher and fewer patients had thymoma (p < 0.0001). Late-onset MG and very-late-onset MG groups more frequently had ocular MG, both at onset (<0.0001) and at maximal worsening (p = 0.001). Although the very-late-onset group presented more life-threatening events (Myasthenia Gravis Foundation of America IVB and V) at onset (p = 0.002), they required fewer drugs (p < 0.0001) and were less frequently drug-refractory (p < 0.0001).

CONCLUSIONS

Patients with MG are primarily ≥65 years of age with anti-AChR antibodies and no thymoma. Although patients with very-late-onset MG may present life-threatening events at onset, they achieve a good outcome with fewer immunosuppressants when diagnosed and treated properly.

Diagnosis of Myasthenia Gravis

Myasthenia gravis (MG) diagnosis is primarily clinically based. By the end of the clinical evaluation, clinicians have a sense as to whether presenting symptoms and elicited signs are weakly or strongly supportive of MG. Diagnostic tests can reaffirm the clinicians' impression. Edrophonium testing is rarely used but helpful in cases of measurable ptosis. Decremental response on slow-frequency repetitive nerve stimulation has a modest diagnostic yield in ocular MG but is helpful in generalized MG cases. The most sensitive test is single-fiber electromyography. In this article, the authors review the diagnostic testing approach of practicing clinicians for suspected MG cases.

Baseline Decrement in Patients with Mild Myasthenia Gravis Predicts Immunomodulation Treatment

To explore whether higher degrees of electrophysiological abnormalities are associated with a more frequent exposure to a more aggressive treatment regimen, we performed a retrospective chart review of patients attending the neuromuscular clinic from June 2012 to December 2015 and included 87 patients. We compared treatment regimens during the follow-up period between patients with high and low jitter and decrement. Myasthenia gravis patients with high jitter or decrement at baseline were more frequently treated with intravenous immunoglobulins (IVIG) and/or plasma exchange (PLEX) during the follow-up period. In patients with mild disease, IVIG or PLEX treatment was associated with high decrement.

Serum Acetylcholine Receptor Antibodies Before the Clinical Onset of Myasthenia Gravis

A patient with autoimmune myasthenia gravis and a clinical and serological follow-up of 13 years is described. In this unique case, serum samples were available up to two years before the clinical onset of the myasthenia gravis and showed gradual increase of acetylcholine receptor antibodies, starting two years before onset of the clinical symptoms.

Electrophysiological testing is correlated with myasthenia gravis severity

INTRODUCTION

Electrophysiological studies play an important role in the diagnosis of myasthenia gravis (MG). The objectives of this study was to explore the correlation of jitter and decrement with various clinical symptoms and signs and disease severity.

METHODS

We performed a retrospective chart review of 75 MG patients who attended the neuromuscular clinic from April 2013 to May 2014. We compared clinical characteristics between patients with high jitter (>100 µs) and decrement (>10%), and patients with lower values to explore the correlations and optimal thresholds of jitter and decrement for different clinical features.

RESULTS

High jitter and decrement values were associated with more severe disease, manifested by more frequent symptomatic bulbar and limb muscle weakness, more frequent ocular and limb muscle weakness on examination, higher quantitative MG score, and generalized disease.

CONCLUSIONS

The yield of the electrophysiological assessment in MG extends beyond disease diagnosis and correlates with disease severity and the presence of generalized disease. Muscle Nerve 56: 445-448, 2017.

Clinical Utility of Acetylcholine Receptor Antibody Testing in Ocular Myasthenia Gravis

IMPORTANCE

The sensitivity of acetylcholine receptor (AChR) antibody testing is thought to be lower in ocular myasthenia gravis (OMG) compared with generalized disease, although estimates in small-scale studies vary. There is little information in the literature about the implications of AChR antibody levels and progression from OMG to generalized myasthenia gravis.

OBJECTIVES

To test the hypothesis that serum AChR antibody testing is more sensitive in OMG than previously reported and to examine the association between AChR antibody levels and progression from OMG to generalized myasthenia gravis.

DESIGN, SETTING, AND PARTICIPANTS

A retrospective, observational cohort study was conducted of 223 patients (mean [SD] age, 59.2 [16.4] years; 139 [62.3%] male) diagnosed with OMG between July 1, 1986, and May 31, 2013, at 2 large, academic medical centers.

MAIN OUTCOMES AND MEASURES

Baseline characteristics, OMG symptoms, results of AChR antibody testing, and progression time to generalized myasthenia gravis (if this occurred) were recorded for each patient. Multiple logistic regression was used to measure the association between all clinical variables and antibody result. Kaplan-Meier survival analysis was performed to examine time to generalization.

RESULTS

Among the 223 participants, AChR antibody testing results were positive in 158 participants (70.9%). In an adjusted model, increased age at diagnosis (odds ratio [OR], 1.03; 95% CI, 1.01-1.04; P = .007) and progression to generalized myasthenia gravis (OR, 2.92; 95% CI, 1.18-7.26; P = .02) were significantly associated with positive antibody test results. Women were less likely to have a positive antibody test result (OR, 0.36; 95% CI, 0.19-0.68; P = .002). Patients who developed symptoms of generalized myasthenia gravis had a significantly higher mean (SD) antibody level than those who did not develop symptoms of generalized myasthenia gravis (12.7 [16.5] nmol/L vs 4.2 [7.9] nmol/L; P = .002).

CONCLUSIONS AND RELEVANCE

We demonstrate a higher sensitivity of AChR antibody testing than previously reported in the largest cohort of patients with OMG available to date. Older age, male sex, and progression to generalized myasthenia gravis were significantly associated with a positive antibody test result. In addition, to our knowledge, this is the first report of an association between high AChR antibody levels and progression from OMG to generalized disease.

The anti-acetylcholine receptor antibody test in suspected ocular myasthenia gravis

Aim. To estimate the clinical significance of anti-acetylcholine receptor antibody (anti-AChR-Ab) levels in suspected ocular myasthenia gravis. Methods. In total, 144 patients complaining of fluctuating diplopia and ptosis were evaluated for serum levels of anti-acetylcholine receptor antibody and their medical charts were retrospectively reviewed. Subjects were classified into three groups: variable diplopia only, ptosis only, and both variable diplopia and ptosis. We investigated serum anti-AChR-Ab titer levels and performed thyroid autoantibody tests. Results. Patients' chief complaints were diplopia (N = 103), ptosis (N = 12), and their concurrence (N = 29). Abnormal anti-AChR-Ab was observed in 21 of 144 patients (14.1%). Between the three groups, mean age, number of seropositive patients, and mean anti-AChR-Ab level were not significantly different (P = 0.224, 0.073, and 0.062, resp.). Overall, 27.5% of patients had abnormal thyroid autoantibodies. Conclusion. The sensitivity of anti-AChR-Ab was 14.1% in suspected ocular myasthenia gravis and seropositivity in myasthenia gravis patients showed a high correlation with the presence of thyroid autoantibodies.

Myasthenia gravis: a comprehensive review of immune dysregulation and etiological mechanisms

Autoimmune myasthenia gravis (MG) is characterized by muscle weakness caused by antibodies directed against proteins of the neuromuscular junction. The main antigenic target is the acetylcholine receptor (AChR), but the muscle Specific Kinase (MuSK) and the low-density lipoprotein receptor-related protein (LRP4) are also targets. This review summarizes the clinical and biological data available for different subgroups of patients, who are classified according to antigenic target, age of onset, and observed thymic abnormalities, such as follicular hyperplasia or thymoma. Here, we analyze in detail the role of the thymus in the physiopathology of MG and propose an explanation for the development of the thymic follicular hyperplasia that is commonly observed in young female patients with anti-AChR antibodies. The influence of the pro-inflammatory environment is discussed, particularly the role of TNF-α and Th17-related cytokines, which could explain the escape of thymic T cells from regulation and the chronic inflammation in the MG thymus. Together with this immune dysregulation, active angiogenic processes and the upregulation of chemokines could promote thymic follicular hyperplasia. MG is a multifactorial disease, and we review the etiological mechanisms that could lead to its onset. Recent global genetic analyses have highlighted potential susceptibility genes. In addition, miRNAs, which play a crucial role in immune function, have been implicated in MG by recent studies. We also discuss the role of sex hormones and the influence of environmental factors, such as the viral hypothesis. This hypothesis is supported by reports that type I interferon and molecules mimicking viral infection can induce thymic changes similar to those observed in MG patients with anti-AChR antibodies.

[Myasthenia gravis and autoantibodies: Pathophysiology of the different subtypes]

Myasthenia gravis is characterized by muscle weakness and abnormal fatigability. It is an autoimmune disease caused by the presence of antibodies against components of the muscle membrane localized at the neuromuscular junction. In most cases, the autoantibodies are directed against the acetylcholine receptor (AChR). Recently, other targets have been described, such as muscle-specific kinase protein (MuSK) or lipoprotein related protein 4 (LRP4). The origin of the autoimmune response is not known, but thymic abnormalities and defects in immune regulation certainly play a major role in patients with anti-AChR antibodies. Genetic predisposition probably influences the occurrence of the disease. Sex hormones seem to play a role in the early form of the disease. Muscle weakness is fluctuating and worsens with exercise. Myasthenia gravis could be classified according to the location of the affected muscles (ocular versus generalized), the age of onset of symptoms, thymic abnormalities and profile of autoantibodies. These criteria are used to optimize the management and treatment of patients. In this review, we analyze the latest concepts of the pathophysiology of myasthenia gravis according to the different subgroups of the disease, including a description of the role of immunological, genetic and environmental factors. The potential viral hypothesis of this disease is discussed. Finally, we also discuss the biological assays available to validate the diagnosis.

Correlation between acetylcholine receptor antibody levels and thymic pathology in myasthenia gravis: a review

Myasthenia gravis is the most common chronic autoimmune neuromuscular disease. Anti-acetylcholine receptor (AChR) antibodies are found in at least 80% of patients with generalized myasthenia and have been implicated in disease pathogenesis. Thymic abnormalities are frequently found in seropositive patients, and the thymus is thought to be involved in generation of autoimmunity. This article reviews existing literature on the role of AChR antibodies in the pathogenesis of myasthenia gravis, and the correlation between AChR antibody titers and thymic pathology. Most studies found that highest titers are seen in thymic hyperplasia, followed by intermediate titers in thymoma, and lowest titers in atrophic or normal thymus. One publication found no difference between titers in thymoma and normal thymus.

Ocular myasthenia gravis

PURPOSE OF REVIEW

To review ocular myasthenia gravis (OMG), a localized form of myasthenia gravis clinically involving only the extraocular, levator palpebrae superioris, and orbicularis oculi muscles.

RECENT FINDINGS

Ocular manifestations can masquerade as a variety of ocular motility disorders, including central nervous system disorders and peripheral cranial nerve palsies. While sparing the pupils, the diagnosis and management can be challenging.

SUMMARY

Because several diagnostic and treatment options are available for OMG, clinicians must decide the sequence and combination based on the level of disease activity and patient disability.

Refractory acute disseminated encephalomyelitis with anti-galactocerebroside antibody

Acute disseminated encephalomyelitis causes multifocal demyelination in the central nerve system. Although this disease generally responds well to steroid therapy, it is occasionally steroid-resistant, leading to poor outcomes. Serological markers of prognosis are currently unavailable. We measured anti-glycolipid antibodies in 25 consecutive patients with acute disseminated encephalomyelitis, and found that four patients were positive for anti-galactocerebroside antibodies. All four patients had a poor response to steroids. We summarize clinical information on these four patients and three similar patients reported previously. This is the first report to describe concomitant involvement of the central nerve system and peripheral nervous system in anti-galactocerebroside antibody-associated acute disseminated encephalomyelitis, consistent with the location of galactocerebroside, and to document a dramatic response to repeated intravenous immunoglobulin therapy after unsuccessful steroid treatment in one patient.

[Standard treatment for late-onset myasthenia gravis in Japan]

Myasthenia gravis (MG) is caused by the failure of neuromuscular transmission mediated by autoantibodies against acetylcholine receptors (AChR) and muscle-specific receptor tyrosine kinase (MuSK). These seropositivity rates in AChR positive and MuSK positive MG in Japan are 80-85% and 5-10%, respectively. The incidence of late-onset MG has been increasing all over the world. A nationwide epidemiological survey in Japan also revealed that the rates of late-onset MG (onset after 50 years) had increased from 20% in 1987 to 42% in 2006. In 2010, a guideline for standard treatments in late-onset MG was published from Japanese Scoiety of Neurological Therapeutics. Based on individual experiences and the limited evidence, epidemiological characteristics of MG onset age, clinical features, and the standard treatment for late-onset patients are included in it. In this guideline summary, the ocular form was more frequent in late-onset compared to early-onset group, the indication of thymectomy in late-onset MG is less than that of early-onset MG and the combination of corticosteroids and immunosuppressive agents are recommended in order to reduce doses of corticosteroids in late-onset MG.

Diagnostic use of autoantibodies in myasthenia gravis

The diagnostic use of antibodies is dependent on sensitivity and specificity of the methods of antibody detection, which have been developed and improved over the years. Here, we review the different methods for the detection of acetylcholine receptor and muscle-specific kinase antibodies, which are, so far, the only antibodies recognised as pathogenic in myasthenia gravis (MG). Seronegative MG patients will benefit from more sensitive methods of antibody detection. The most recent developments in antibody detection assays, particularly those based on cells expressing target antigens, allow rapid and reliable identification of autoantibodies, improving the diagnosis and treatment of MG patients. The same approaches to antibody detection are now being applied to a wide range of other autoantigens and other autoimmune diseases.

Effect of complement and its regulation on myasthenia gravis pathogenesis

Myasthenia gravis (MG) is primarily caused by antibodies directed towards the skeletal muscle acetylcholine receptor, leading to muscle weakness. Although these antibodies may induce compromise of neuromuscular transmission by blocking acetylcholine receptor function or antigenic modulation, the predominant mechanism of injury to the neuromuscular junction is complement-mediated lysis of the postsynaptic membrane. The vast majority of data to support the role of complement derives from experimentally acquired MG (EAMG). In this article, we review studies that demonstrate the central role of complement in EAMG and MG pathogenesis along with the emerging role of complement in T- and B-cell function, as well as the potential for complement inhibitor-based therapy to treat human MG.

Myasthenia gravis and acetylcholine receptor antibodies: a clinico immunological correlative study on South Indian patients

Acquired myasthenia Gravis (MG), a disorder of impaired neuromuscular transmission is recognized as an autoimmune disorder, with a majority of the patients having antibodies against acetylcholine receptor (AChR antibodies) in the serum.

Extraocular muscle susceptibility to myasthenia gravis: unique immunological environment?

Extraocular muscle (EOM) is susceptible to neuromuscular junction disorders, in particular, myasthenia gravis (MG). While EOM physiological characteristics and the ocular motor system requirements contribute to the propensity of ocular motor deficits observed among patients with MG, the authors propose that EOM have immunological features that place the muscles at risk for immune attack. Genomic profiling studies have demonstrated that genes associated with the immune response are differentially expressed in EOM, with particular differences in both classical and alternative complement-mediated immune response pathways. Intrinsic complement regulators are expressed at lower levels at rodent EOM neuromuscular junctions, which would put them at risk for the complement-mediated injury that occurs in MG. In fact, systemic C inhibition in experimental autoimmune MG (EAMG) induced by administration of acetylcholine receptor (AChR) antibodies or immunization with AChR will eliminate complement deposition at junctions of other skeletal muscle, but not EOM. Also, EOM junctions have greater injury in active and passive EAMG by several measures, suggesting that the lack of complement inhibition puts the EOM at risk. Among ocular myasthenia patients, serum AChR antibody levels are low, which would support the concept that EOM junctions are more susceptible to antibody injury than are other junctions. These observations suggest that complement inhibitory therapies may prove to be particularly effective in treatment of ocular myasthenia.

Frequency of seronegativity in adult-acquired generalized myasthenia gravis

We determined the prevalence of muscle acetylcholine receptor (AChR) antibodies in patients with adult-acquired generalized myasthenia gravis (MG), the seroconversion rate at 12 months, and the prevalence of muscle-specific tyrosine kinase (MuSK) antibody among persistently seronegative patients. We identified 562 consecutive Mayo Clinic patients with MG based on clinical and electrophysiological criteria. At presentation, 508 patients (90.4%) tested positive for AChR binding or AChR modulating antibodies. After 12 months, 15.2% of initially seronegative patients had become seropositive, yielding a seronegativity rate of 8.2% (95% confidence interval: 6.2-9.6%). Among seronegative patients not receiving immunosuppressants, 38% were MuSK antibody-positive and 43% were seropositive for nonmuscle autoantibodies. Classification as seronegative MG should be reserved for nonimmunosuppressed patients with generalized MG who lack muscle AChR binding, AChR modulating, or MuSK antibodies at presentation and at follow-up of at least 12 months.

Epidemiology of myasthenia gravis with anti-muscle specific kinase antibodies in The Netherlands

The epidemiology of myasthenia gravis subtypes and the frequency of antibodies to muscle-specific kinase (MuSK) was studied in patients with generalised myasthenia gravis without anti-acetylcholine receptor antibodies who had an onset of symptoms between 1990 and 2004 in a well-defined region in The Netherlands. The nationwide prevalence and incidence of myasthenia gravis with anti-MuSK antibodies were also studied. MuSK antibodies were found in 22% of patients with generalised myasthenia gravis without anti-acetylcholine receptor antibodies. Nationwide, 35 patients with MuSK myasthenia gravis were identified, yielding a prevalence of 1.9 per million (95% confidence interval (CI) 1.22 to 2.59) and an annual incidence 0.10 per million person-years (95% CI 0.06 to 0.14).

Ocular myasthenia: diagnosis, treatment, and pathogenesis

BACKGROUND

Although myasthenia gravis (MG) is often considered the best-understood autoimmune disorder and effective treatments have controlled life-threatening complications, the pathogenesis of ocular myasthenia (OM) remains enigmatic, and its clinical consequences offer therapeutic challenges.

REVIEW SUMMARY

About half of patients with MG present with visual complaints of droopy eyelids or double vision, and many will remain with purely ocular muscle weakness without generalized weakness, defined as OM. OM may be confused with disorders of the brainstem, ocular motor nerves, and eye muscles. Frustrating for the clinician, confirmatory tests such as the edrophonium test, serum acetylcholine receptor antibodies, and standard electrodiagnostic evaluations may fail to positively identify the clinical suspicion of OM. Patients may derive relief from nonpharmacologic interventions and cholinesterase inhibitors, but most will desire better symptom control with corticosteroids or need other immunosuppression. Early corticosteroid therapy may reduce the probability of generalization of the disease. The reasons for ocular muscle involvement by OM include physiologic and cellular properties of the ocular motor system and the unique immunology of OM, which, when better understood, will lead to novel treatments.

CONCLUSIONS

OM is a challenging disorder for the clinician and scientist, with both learning from the other for the betterment of the patient. The future requires answers to why the ocular muscles are so frequently involved by MG, whether the generalization of the disease may be limited by early corticosteroid treatment, and what treatment options may be developed which will improve symptoms without long-term complications.

A systematic review of diagnostic studies in myasthenia gravis

We performed a systematic review to identify studies that reported the accuracy of tests for the diagnosis of myasthenia gravis. We identified 20 studies of reasonable, although variable, methodological quality upon which to base estimates of the accuracy of the ice test, rest test, Tensilon test, acetylcholine receptor antibodies, repetitive nerve stimulation and single fiber electromyography for the diagnosis of myasthenia gravis. After examining inter-study heterogeneity for each diagnostic modality, we calculated pooled estimates of sensitivity and specificity as well as positive and negative likelihood ratios. Results are reported separately for ocular and generalized myasthenia. Studies that have examined the performance of anti-acetylcholine receptor antibody testing and single fiber electromyography were generally of better quality than those that examined other diagnostic modalities. We suggest that caution should be exercised in the interpretation of the diagnostic performance of these tests given the methodological limitations of the studies upon which test performance is based.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the autoimmune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosyl phosphatidyl inositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

Non-ptotic ocular myasthenia gravis: a common presentation of an uncommon disease

BACKGROUND

Myasthenia gravis (MG) is an acquired autoimmune disease of the neuromuscular junction which causes rapid muscle fatigue and weakness. Two thirds of all cases of myasthenia gravis (MG) initially manifest ptosis. In the absence of the characteristic variable ptosis, MG can present a challenge to the clinician. This article will review the current diagnostic and management strategies for MG.

CASE REPORTS

Five cases will be presented that did not initially present with ptosis. Each of these cases was previously misdiagnosed as a result of presentation of atypical myasthenia gravis signs and symptoms. The first two cases had signs and symptoms of a typical accommodative/vergence anomaly. The others manifested diplopia not normally associated with MG: one had a noncomitant vertical deviation; another had a stable 6(th) nerve palsy; and the third had a basic esotropia.

CONCLUSION

Although the hallmark findings of MG are ptosis and eye muscle palsy with variability, MG may present without ptosis, affect nonstriated muscles, and/or manifest either as a nonstrabismic vergence anomaly or as comitant nonvariable strabismic deviation.

Increase in incidence of elderly-onset patients with myasthenia gravis in Nagano Prefecture, Japan

OBJECTIVES

In European countries and the United States the incidence of elderly-onset myasthenia gravis (MG) has recently been increasing. To investigate whether the incidence of the elderly-onset MG has increased in Nagano Prefecture of Japan, we divided the patients into young and elderly groups, and retrospectively examined their incidence.

PATIENTS AND METHODS

On the basis of two-step questionnaires sent to hospitals and the patient list of the intractable disease registration system in Nagano Prefecture we studied 213 MG patients diagnosed between 1982 and 2001. This 20-year period was divided into 4 five-year terms, and the incidence of MG in young- (younger than 65) and elderly-onset (65 or older) groups was investigated separately for each term.

RESULTS

The ratio of the elderly-onset group showed a significantly positive correlation with terms irrespective of associated thymoma (r=0.98, p<0.05). There was a significant difference in the mean onset age among the 4 terms (p<0.005). The standardized incidence of MG gradually increased in both young- and elderly-onset groups as well as in the whole age range. The elderly group showed a particularly high incidence in females (12.01/million/year) and in patients without thymoma (8.78/million/year) in the final five years.

CONCLUSIONS

We confirmed that the incidence of elderly-onset MG has recently been increasing in the Nagano Prefecture. Since the change of the age distribution in this district is almost identical to that of the whole country, the incidence of MG might have been increasing in Japan as a whole, particularly in the elderly population.

Retrospective analyses of clinical features and therapeutic outcomes in thymectomized patients with myasthenia gravis at Shinshu University

OBJECTIVES

Thymectomy has become recognized as an integral element in the treatment of patients with myasthenia gravis (MG). Although the incidence of elderly-onset MG has recently been increasing, there is little data demonstrating the efficacy and complications of thymectomy in this population. To clarify this point, we divided the thymectomized patients with MG into young and elderly groups, and retrospectively examined their clinical features and therapeutic outcomes.

PATIENTS AND METHODS

We reviewed 57 MG patients who had been admitted to our hospital between 1988 and 2002. The patients were classified into young (younger than 60) and elderly (60 or older) groups according to the age of onset, and the therapeutic outcomes of thymectomy were evaluated using myasthenic severity scales and the duration from operation to discharge.

RESULTS

Myasthenic severity scales significantly improved after thymectomy in the elderly group both with (p<0.005) and without thymoma (p<0.05) compared with before. With regard to the duration from thymectomy to discharge, no significant difference could be found between the young and elderly groups, irrespective of associated thymoma. There were no serious complications during and after thymectomy in either the young or the elderly group.

CONCLUSIONS

Despite various possible complications due to aging, thymectomy should be actively considered also in the treatment of elderly MG patients because it can reliably and safely improve myasthenic symptoms in combination with immunosuppressive agents, including corticosteroid.

Double trouble

A 78-year-old woman presented with vertical double vision. The Bielschowsky-Parks' three-step test suggested a left inferior rectus muscle paresis. Diagnostic testing confirmed the diagnosis of myasthenia gravis. Despite treatment with pyridostigmine bromide (mestinon) the diplopia persisted. She refused corticosteroid treatment and sought a second opinion, resulting in three unsuccessful strabismus surgeries to correct her ocular misalignment. The evaluation and management of ocular myasthenia gravis is reviewed and the appropriate timing of strabismus surgery is discussed.

The role of antibodies in myasthenia gravis

Myasthenia gravis is an autoimmune disease associated with antibodies directed to the postsynaptic acetylcholine receptor. These antibodies reduce the number of receptors. Autoantibodies against AChR and other muscle antigens can be used for the diagnosis of myasthenia gravis and related disorders. The origin and the role of these antibodies in the disease are discussed. Experimental autoimmune myasthenia gravis, an experimental model closely mimicking the disease, has provided answers to many questions about the role of antibodies, complement macrophages and AChR anchor proteins. Genetically modified anti-AChR antibodies may also be used in the future to treat myasthenia.

Abnormal expression of CTLA-4 by T cells from patients with myasthenia gravis: effect of an AT-rich gene sequence

Cytolytic T lymphocyte-associated antigen-4 (CTLA-4) plays a critical role in the down-regulation of antigen-activated immune responses. The aberrant CTLA-4 expression is characterized by low surface and intracellular levels of CTLA-4 protein, impaired up-regulation of CTLA-4 in T cells in response to ConA stimulation and high levels of soluble CTLA-4 (sCTLA-4) in serum. The serum levels of sCTLA-4 are positively correlated with the serum concentration of antibodies against the acetylcholine receptor. The (AT)(n) polymorphism in the 3'-untranslated region contributes to decreased mRNA stability and, hence, to reduced expression of CTLA-4.

Immunosuppressive treatment of ocular myasthenia gravis

Myasthenia gravis (MG) is caused by autoantibodies against proteins at the neuromuscular junction. This autoimmune process leads to abnormal fatiguability and weakness of striated muscle. Ptosis and diplopia are among the most common manifestations of MG. The term "ocular MG" (OMG) as opposed to "generalised MG" (GMG) is used to define the clinical subtype of MG with isolated eye muscle weakness. Although OMG may appear to cause only moderate disability, it can significantly impair the patient's activities of daily living and progress to generalised myasthenia. Therefore, a clear management plan should be installed early in these patients. Since prospective treatment trials have not been performed, basic management strategies for OMG have to be deduced from retrospective studies, trials in GMG, and generally accepted clinical experience. Cholinesterase inhibitors are used in all types of MG, but are often less helpful in OMG. In the absence of thymoma, thymectomy is usually not considered in OMG, although a few studies have described histological abnormalities in thymuses from patients with OMG. Corticosteroids are of great short term benefit in most patients with OMG but potential adverse effects limit their long term use. Azathioprine is needed to reduce long term corticosteroid adverse effects, but this agent requires about 6 months to be effective. In summary, OMG has a good prognosis in most patients, with corticosteroids and azathioprine being the major treatment options. The challenges for the clinician are to recognise the condition despite the large number of differential diagnoses, to minimise the patient's symptoms using the therapies available and to carefully limit potentially hazardous therapeutic efforts, especially in mild or even uncertain cases.