Electrophysiological and immunological study in myasthenia gravis: Diagnostic sensitivity and correlation

Juvenile Myasthenia Gravis in North Texas: Clinical Features, Treatment Response, and Outcomes

BACKGROUND

Juvenile myasthenia gravis (JMG) is a rare autoimmune disease that causes fatigable muscle weakness in children aged <18 years. There is currently no curative treatment or internationally accepted standard of care for JMG. The objective is to investigate relationships between clinical presentation, antibody status, severity of disease onset, electrodiagnostic evaluation, and response to therapy in JMG.

METHODS

This study was a retrospective chart review. Congenital myasthenic syndromes were excluded. Data on demographics, treatments, and outcomes were collected. Disease severity was evaluated using Myasthenia Gravis Foundation of America (MGFA) clinical classifications.

RESULTS

We identified 84 patients with JMG at Children's Medical Center Dallas between January 2014 and February 2022. It was found that 52% of patients presented with ocular JMG (median onset age 4.5 years) and 48% with generalized JMG (median onset age 11.5 years); 81% tested positive for acetylcholine receptor antibodies. Patients were 17% non-Hispanic white, 29% Hispanic, 39% black, and 12% Asian. There was a significant difference in average MGFA scores between ethnicities (P = 0.047) and age groups (P = 0.004), with postpubertal patients having higher average MGFA scores than prepubertal patients. Seventy-one percent of patients who underwent thymectomy experienced a decrease in MGFA scores postprocedure.

CONCLUSIONS

Our study showed that there were significant differences in disease severity between ethnicities and age groups and that most patients who underwent thymectomy showed clinical improvement. These outcomes highlight the need for additional therapies in the treatment of JMG and the importance of extending clinical trials to the pediatric population.

Study on the clinical and electrophysiological characteristics of nerve function in myasthenia gravis patients in Vietnam

Background

In Vietnam, there is limited research on the role of nerve conduction in myasthenia gravis and its association with clinical features.

Objective

This study aims to describe the electrophysiological features in patients with myasthenia gravis.

Methods

This descriptive study was conducted from September 2019 to December 2021. The study included 33 myasthenia gravis patients who sought medical consultation or received inpatient treatment during this period. The Myasthenia Gravis Foundation of America classifies myasthenia gravis into five groups: I, IIa, IIb, IIIa, IIIb, IVa, IVb, and V. Notably, Group I involves pure ocular weakness, whereas Group a primarily impacts limb and axial muscles, and Group b mainly affects bulbar and respiratory muscles.

Results

The study revealed that motor and sensory nerve conduction in the upper and lower limbs were within normal limits for the patient group under evaluation. Repetitive nerve stimulation testing at a frequency of 3 Hz showed positive results in 66.7% of myasthenia gravis patients. Myasthenia gravis patients displayed distinct clinical symptoms, with ptosis being the most common (87.9%). Myasthenia Gravis Foundation of America classification indicated the highest proportion in subgroup IIa (24.2%), with myasthenia gravis predominating in limb and axial muscles (Group a) observed in 51.5% of cases. Needle electromyography showed no abnormalities in myasthenia gravis patients. There was an association between acetylcholine receptor antibody titers and the results of the 3 Hz repetitive nerve stimulation test in myasthenia gravis patients, with a significance of p = 0.002.

Conclusion

Nerve conduction studies should be performed in patients with suspected neuromuscular disorders to aid in differential diagnosis and definitive diagnosis of myasthenia gravis.

Electrophysiological evaluation of the neuromuscular junction: a brief review

The nerve terminal and muscle membrane compose the neuromuscular junction. After opening the voltage-gated calcium channels, action potentials from the motor axons provoke a cascade for the acetylcholine release from synaptic vesicles to the synaptic cleft, where it binds to its receptor at the muscle membrane for depolarization. Low amplitude compound muscle action potential typically presents in presynaptic disorders, increasing by more than 100% after a 10-second effort in the Lambert-Eaton myasthenic syndrome and less in botulism. Needle electromyography may show myopathic motor unit action potentials and morphological instability ("jiggle") due to impulse blocking. Low-frequency repetitive nerve stimulation (RNS) is helpful in postsynaptic disorders, such as myasthenia gravis and most congenital myasthenic syndromes, where the number of functioning acetylcholine receptors is reduced. Low-frequency RNS with a decrement >10% is abnormal when comparing the 4th to the first compound muscle action potential amplitude. High-frequency RNS is helpful in presynaptic disorders like Lambert-Eaton myasthenic syndrome, botulism, and some rare congenital myasthenic syndromes. The high-frequency RNS releases more calcium, increasing the acetylcholine with a compound muscle action potential increment. Concentric needle records apparent single-fiber action potentials (spikes). A voluntary activation measures the jitter between spikes from two endplates. An electrical activation measures the jitter of one spike (one endplate). The jitter is the most sensitive test for detecting a neuromuscular junction dysfunction. Most neuromuscular junction disorders are responsive to treatment.

Diagnosis and Management of Seronegative Myasthenia Gravis: Lights and Shadows

Myasthenia gravis (MG) is an antibody-mediated neuromuscular disease affecting the neuromuscular junction. In most cases, autoantibodies can be detected in the sera of MG patients, thus aiding in diagnosis and allowing for early screening. However, there is a small proportion of patients who have no detectable auto-antibodies, a condition termed "seronegative MG" (SnMG). Several factors contribute to this, including laboratory test inaccuracies, decreased antibody production, immunosuppressive therapy, immunodeficiencies, antigen depletion, and immune-senescence. The diagnosis of SnMG is more challenging and is based on clinical features and neurophysiological tests. The early identification of these patients is needed in order to ensure early treatment and prevent complications. This narrative review aims to examine the latest updates on SnMG, defining the clinical characteristics of affected patients, diagnostic methods, management, and therapeutic scenarios.

Ocular Myasthenia Gravis: A Current Overview

Ocular myasthenia gravis (OMG) is a neuromuscular disease characterized by autoantibody production against post-synaptic proteins in the neuromuscular junction. The pathophysiological auto-immune mechanisms of myasthenia are diverse, and this is governed primarily by the type of autoantibody production. The diagnosis of OMG relies mainly on clinical assessment, the use of serological antibody assays for acetylcholine receptors (AchR), muscle-specific tyrosine kinase (MusK), and low-density lipoprotein 4 (LPR4). Other autoantibodies against post-synaptic proteins, such as cortactin and agrin, have been detected; however, their diagnostic value and pathogenic effect are not yet clearly defined. Clinical tests such as the ice test and electrophysiologic tests, particularly single-fiber electromyography, have a valuable role in diagnosis. The treatment of OMG is primarily through cholinesterase inhibitors (pyridostigmine), and steroids are frequently required in cases of ophthalmoplegia. Other immunosuppressive therapies include antimetabolites (azathioprine, mycophenolate mofetil, methotrexate) and biological agents such as B-cell depleting agents (Rituximab) and complement inhibitors (eculizumab). Evidence is scarce on the effect of immunosuppressive therapy on altering the natural course of OMG. Clinicians must be vigilant of a myasthenic syndrome in patients using immune-check inhibitors. Reliable and consistent biomarkers are required to assess disease severity and response to therapy to optimize the management of OMG. The purpose of this review is to summarize the current trends and the latest developments in diagnosing and treating OMG.

Low probability of myasthenia Gravis in patients presenting to neuro-ophthalmology clinic for evaluation of isolated ptosis

BACKGROUND

Concerning causes of ptosis, most notably third nerve palsy and Horner's syndrome, can be ruled out with normal ocular motility and pupillary examination. Myasthenia gravis (MG) however, rarely can present with ptosis as an isolated finding. We reviewed all patients presenting to tertiary neuro-ophthalmology practice with ptosis of unknown etiology to determine the frequency of MG.

METHODS

Retrospective chart review of patients referred to a tertiary neuro-ophthalmology practice with undifferentiated ptosis.

RESULTS

Sixty patients were included in the study. Twenty eight (47%) patients had ptosis along with various abnormalities of ocular motility and/or alignment and 32 (53%) had isolated unilateral ptosis defined as ptosis with absence of diplopia, or symptoms of generalized MG (GMG). Final diagnosis was aponeurotic ptosis due to levator palpebrae dehiscence in the majority (73%) of patients, while 10 (17%) were diagnosed with MG (6 with OMG, 4 with GMG). Diplopia was present in 9/10 patients with MG and 8/10 had abnormal ocular findings on clinical examination such as orbicularis oculi weakness, Cogan's lid twitch or fatiguability of ptosis on sustained upgaze. Only one patient referred for isolated unilateral ptosis was diagnosed with OMG and this patient had orbicularis oculi weakness.

CONCLUSIONS

None of the patients with isolated unilateral ptosis and otherwise normal examination had MG. All patients eventually diagnosed with MG had diplopia or orbicularis weakness on examination. Thus, the yield of investigating patients with isolated ptosis for MG is exceedingly low.

Neurological Emergencies in the Intensive Care Unit

Neurological emergencies carry significant morbidity and mortality, and it is necessary to have a multidisciplinary approach involving the emergency physician, the neurologist, the intensivist, and the critical care nursing staff. These disorders can be broadly divided into noninfectious and infectious etiologies. In this article, we review a few of the neurological emergencies that present to the neurological intensive unit, with emphasis on convulsive status epileptics, myasthenia gravis, Guillain-Barré syndrome, meningitis, encephalitis, and brain abscess.

Electrophysiologic evaluation of myasthenia gravis and its mimics: real-world experience with single-fiber electromyography

OBJECTIVES

In centers which routinely perform single fiber electromyography (SFEMG) for suspected myasthenia gravis (MG), the additional benefit of other neurophysiologic investigations and the frequency of myasthenia mimics has not been ascertained. We aimed to illustrate the range of neurological and non-neurological myasthenia mimics referred for evaluation, and contrast features of their electrophysiologic evaluation with confirmed MG.

METHODS

We reviewed all SFEMG studies performed at our center between 1 January 2018 and 31 December 2020. Patient demographics, clinical phenotype, antibody status and final diagnosis were recorded. Electrophysiologic findings were correlated with clinical features and sensitivity analyses performed.

RESULTS

A total of 528 SFEMG studies were performed, of which 213 (41%) were abnormal. A diagnosis of MG was made in 101 individuals, including 46 with ocular MG and 35 with seronegative disease. Compared to myasthenia mimics with an abnormal SFEMG, individuals with MG had higher median jitter (mean consecutive difference 61 μs vs. 42 μs, p < 0.001) and a greater percentage of abnormal pairs (61% vs. 33%, p < 0.001) on SFEMG. Repetitive nerve stimulation was abnormal in 27.1% of people with MG and was associated with a generalized clinical phenotype (OR 4.17; 95% CI 1.67-10.48). Thirteen (2%) individuals with MG had normal SFEMG, of whom 10 were in clinical remission. Functional neurological disorders, cranial nerve palsies, primary ocular disease and myopathy were frequent myasthenia mimics.

CONCLUSION

SFEMG can be abnormal in a number of myasthenia mimics, and routine nerve conduction studies and electromyography should always be undertaken. In centers where SFEMG is performed routinely for the investigation of suspected MG, extensive proximal repetitive nerve stimulation can be foregone without substantially affecting diagnostic evaluation. Normal SFEMG in those with confirmed myasthenia gravis may help indicate clinical remission.

Lack of Immunotherapy as the Only Predictor of Secondary Generalization in Very-Late-Onset Myasthenia Gravis With Pure Ocular Onset

During the past two decades, an increasing number of patients with very-late-onset myasthenia gravis (v-LOMG) with an onset age of 65 years or older have been identified. However, few studies explore the predictors of secondary generalization in patients with v-LOMG with pure ocular onset. In this retrospective cohort study, 69 patients with v-LOMG were divided into ocular MG (OMG) and generalized MG (GMG), and the clinical characteristics and outcomes were compared. Cox regression analysis was performed to explore the predictors of generalization. The average onset age of the study population was 73.1 ± 4.2 years and the median disease duration was 48.0 months (interquartile range, 32.5-64.5 months). Serum acetylcholine receptor (AChR) antibody was detected in up to 86% of patients and concomitant diseases in approximately half of the patients. Male predominance was seen in OMG group while female predominance in GMG group (p = 0.043). Patients with OMG showed a lower positive rate of repetitive nerve stimulation (RNS) than those with GMG (p = 0.014), and favorable outcomes were obtained in more patients with OMG than those with GMG (p < 0.001). Of the 51 patients with pure ocular onset, 25 (49.0%) underwent secondary generalization. A higher probability of generalization was found in patients with positive RNS results and without immunotherapy (p = 0.018 and <0.001). Upon Cox regression analysis, immunotherapy was negatively associated with secondary generalization [HR (hazard ratio) 0.077, 95%CI [0.024-0.247], p < 0.001]. Altogether, compared to the patients with very-late-onset GMG, the counterparts with OMG exhibit a significantly higher female predominance and a lower positive rate of RNS tests, especially on facial and accessory nerves. Lack of immunotherapy is the only predictor of secondary generalization in those with pure ocular onset.

Bedside and laboratory diagnostic testing in myasthenia

Myasthenia gravis (MG) and congenital myasthenic syndromes (CMS) are a group of disorders with a well characterised autoimmune or genetic and neurophysiological basis. We reviewed the literature from the last 20 years assessing the utility of various neurophysiological, immunological, provocative and genetic tests in MG and CMS. Diagnostic sensitivity of repetitive nerve stimulation test ranges between 14 and 94% and specificity between 73 and 100%; sensitivity of single-fibre EMG (SFEMG) test ranges between 64 and 100% and specificity between 22 and 100%; anti-acetylcholine receptor (AChR) antibody sensitivity ranges from 13 to 97% and specificity ranges from 95 to 100%. Overall, SFEMG has the highest sensitivity while positive anti-AChR antibodies have the highest specificity. Newer testing strategies that have been investigated over the last couple of decades include ocular vestibular-evoked myogenic potentials, otoacoustic emissions and disease-specific circulating miRNAs in serum for autoimmune myasthenia, as well as next-generation sequencing for genetic testing of CMS. While there has been significant progress in developing newer testing strategies for diagnosing MG and CMS over the last couple of decades, more research is needed to assess the utility of these newer tools regarding their sensitivity and specificity.

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.

Neuromuscular Respiratory Failure

Neuromuscular respiratory failure can result from any disease that causes weakness of bulbar and/or respiratory muscles. Once compensatory mechanisms are overwhelmed, hypoxemic and hypercapnic respiratory failure ensues. The diagnosis of neuromuscular respiratory failure is primarily clinical, but arterial blood gases, bedside spirometry, and diaphragmatic ultrasonography can help in early assessment. Intensive care unit (ICU) admission is indicated for patients with severe bulbar weakness or rapidly progressing appendicular weakness. Intubation should be performed electively, particularly in patients with dysautonomia. Patients with an underlying treatable cause have the potential to regain functional independence with meticulous ICU care.

Occipitalis muscle: using for repetitive facial nerve stimulation in myasthenia gravis

Repetitive nerve stimulation (RNS) is a highly sensitive electrophysiological test used for diagnosing myasthenia gravis (MG). Here, we evaluated electrodiagnostic value of RNS using facial nerve and occipitalis muscle. Patients with generalized MG were included. Clinical findings were assessed. RNS test was performed on occipitalis, nasalis, trapezius, abductor policis brevis (APB) and abductor digiti minimi (ADM) muscles. Twenty-five (78%) patients had relevant decrement during RNS test of at least one muscle. Nasalis muscle had the highest diagnostic potential (68.8%), followed by trapezius (53.3%), occipitalis (50%), APB (30%) and ADM (16.7%) muscles. There was not a significant relationship between clinical symptoms and facial RNS recorded on occipitalis muscle. In conclusion, we suggest that facial RNS recording over occipitalis muscle can be added in electrodiagnosis of MG because of cranial nerve innervation and proximal location. Facial RNS recording over occipitalis muscle provides a good choice under the conditions such as atrophy, cosmetic surgery, or botulinum toxin application in which nasalis muscle is unavailable for use.

Guidelines for single fiber EMG

This document is the consensus of international experts on the current status of Single Fiber EMG (SFEMG) and the measurement of neuromuscular jitter with concentric needle electrodes (CNE - CN-jitter). The panel of authors was chosen based on their particular interests and previous publications within a specific area of SFEMG or CN-jitter. Each member of the panel was asked to submit a section on their particular area of interest and these submissions were circulated among the panel members for edits and comments. This process continued until a consensus was reached. Donald Sanders and Erik Stålberg then edited the final document.

Intensive Care Management of the Neuromuscular Patient

Neuromuscular emergencies are a distinct group of acute neurological diseases with distinct characteristic presentations. Patients who suffer from this group of diseases are at immediate risk of losing protection of their native airway as well as aspirating orogastric contents. This is secondary to weakness of the muscles of the oropharynx and respiratory muscles. Although some neuromuscular emergencies such as myasthenia gravis or Guillain-Barré syndrome are well understood, others such as critical illness myopathy and neuropathy are less well characterized. In this chapter, we have discussed the pathophysiology, diagnostic evaluation, and management options in patients who are admitted to the intensive care unit. We have also emphasized the importance of a thorough understanding of the use of pharmacological anesthetic agents in this patient population.

Epidemiology of Myasthenia Gravis in Slovakia in the Years 1977-2015

PURPOSE

The objective of the study was to evaluate changes of epidemiological parameters in patients with myasthenia gravis (MG) in Slovakia during the period 1977-2015.

METHODS

Data from medical records of MG patients registered in Slovakia were analyzed. Epidemiological rates (incidence, prevalence, mortality) were assessed for several periods to identify changes and drifts over the period of study.

RESULTS

Out of 2,074 patients, 892 were males (43.0%) and 1,193 were females (57.0%). The thymoma associated MG (TAMG) was diagnosed in 123 patients (5.9%). The mean age at onset shifted from 35.8 years in 1977-1989 to 60.0 years in -2010-2015. The crude incidence increased from 0.36/100,000 in 1977-1989 to 1.74/100,000 in 2010-2015. The average annual incidence of TAMG was 0.05/100,000. Maximum increase of MG incidence was registered among the elderly (≥50 years), particularly in the group of patients in the age range 70-79 years (0.34/100,000 in 1977-1989→7.10/100,000 in 2010-2015) and 80-89 years (0.00/100,000 in 1977-1989→5.31/100,000 in 2010-2015). The crude MG prevalence on December 31, 2015 was 24.75/100,000. The average MG mortality was 0.27/100,000.

CONCLUSION

The age at onset and incidence increased significantly over the study period due to marked increase of MG incidence in elderly, particularly over 70 years. Possible reasons for this trend are discussed.

Clinical and CN-SFEMG evaluation of neostigmine test in myasthenia gravis

Neostigmine test (NT) is a pharmacological test, demonstrating a clinical improvement in patients affected by myasthenia gravis (MG). We aim to compare clinical evaluation and neurophysiological recordings by concentric-needle single-fiber electromyography (CN-SFEMG) in response to acute administration of neostigmine in ocular and generalized MG patients. Twenty-three MG patients (10 with ocular MG and 13 with generalized MG) were evaluated before and after 90 min neostigmine 0.5-mg administration. Clinical responsiveness was assessed by MG composite (MGC) scale. Neurophysiological evaluation by CN-SFEMG considered analysis of mean value of consecutive differences (MCD), single-pair jitter, and blocks. MGC scores significantly improved after NT in generalized MG patients (MGC 11.1 ± 7.6 vs 9.1 ± 6.7, p = 0.02), whereas the improvement was not significant in the ocular group. CN-SFEMG recordings significantly improved after NT in generalized MG patients (MCD 58.9 ± 18.8 vs 45.9 ± 23.2 μs, p = 0.003; single-pair jitter 49.8 ± 26.9 vs 24.1 ± 26.7%, p = 0.0001; blocks 6.2 ± 9.5 vs 2.6 ± 7.4%, p = 0.03) as well as in ocular MG patients (MCD 50.8 ± 22.7 vs 40.1 ± 22.9 μs, p = 0.01; single-pair jitter 35.9 ± 23.7 vs 20.0 ± 25.1%, p = 0.001). CN-SFEMG is a reliable tool to evaluate responsiveness to acute administration of neostigmine in MG. Moreover, neurophysiological modifications to NT could show subclinical improvement in ocular MG better than that of the clinical scale.

Palpebral portion of the orbicularis oculi muscle to repetitive nerve stimulation testing: A potential assessment indicator in patients with generalized myasthenia gravis

Repetitive nerve stimulation (RNS) is a valuable diagnostic method for myasthenia gravis (MG). However, its association with clinical severity was scarcely studied. We reviewed medical records and retrospectively enrolled 121 generalized MG patients. Sensitivity of different muscles to RNS and clinical scoring systems was evaluated. RNS testing revealed facial muscles have the highest positive rate, followed by proximal muscles and distal muscles, with the palpebral portion of the orbicularis oculi muscle most sensitive. Amplitude decrement of compound muscle action potential (CMAP) in the palpebral portion of the orbicularis oculi muscle is related to quantitative myasthenia gravis (QMG) scores, MG-specific manual muscle testing (MMT) scores and myasthenia gravis-related activities of daily living (MG-ADL) scores. We suggest that RNS testing of the palpebral portion of the orbicularis oculi muscle is a potential assessment indicator in patients with generalized MG.

Diagnostic Accuracy of Single Fiber Electromyography for Myasthenia Gravis in Patients Followed Longitudinally

INTRODUCTION

The literature lacks data on accuracy of single fiber electromyography (SFEMG) for myasthenia gravis (MG) patients followed longitudinally.

METHODS

We included patients with a clinical suspicion of MG who received SFEMG and follow-up at our institution between 2003 and 2013. Data collected included demographics, symptom details, clinical deficits, other diagnostic testing results, MG medication regimen, duration on treatment, response to therapy, and ultimate diagnosis after follow-up. When available, information was also extracted from the MG-specific Activities of Daily Living, MG Quality of Life, and European Quality of Life assessments before and after SFEMG.

RESULTS

Three hundred forty eight SFEMG patients met inclusion criteria. Myasthenia gravis was ultimately diagnosed in 31% (19% ocular, 12% generalized). A sensitivity of 78% was seen for MG regardless of subtype, 73% for ocular MG, and 85% for generalized MG. A specificity of 91% was obtained for MG of either ocular or generalized subtype.

CONCLUSIONS

The diagnostic accuracy of SFEMG using this methodology minimizing incorporation bias is more reliable than that usually described in previous studies. There is utility in increasing diagnostic yield when SFEMG results are combined with clinical data and those from other diagnostic tests, particularly serology.

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.

Genome-Wide Association Study of Late-Onset Myasthenia Gravis: Confirmation of TNFRSF11A and Identification of ZBTB10 and Three Distinct HLA Associations

To investigate the genetics of late-onset myasthenia gravis (LOMG), we conducted a genome-wide association study imputation of>6 million single nucleotide polymorphisms (SNPs) in 532 LOMG cases (anti-acetylcholine receptor [AChR] antibody positive; onset age≥50 years) and 2,128 controls matched for sex and population substructure. The data confirm reported TNFRSF11A associations (rs4574025, P = 3.9 × 10^-7, odds ratio [OR] 1.42) and identify a novel candidate gene, ZBTB10, achieving genome-wide significance (rs6998967, P = 8.9 × 10^-10, OR 0.53). Several other SNPs showed suggestive significance including rs2476601 (P = 6.5 × 10^-6, OR 1.62) encoding the PTPN22 R620W variant noted in early-onset myasthenia gravis (EOMG) and other autoimmune diseases. In contrast, EOMG-associated SNPs in TNIP1 showed no association in LOMG, nor did other loci suggested for EOMG. Many SNPs within the major histocompatibility complex (MHC) region showed strong associations in LOMG, but with smaller effect sizes than in EOMG (highest OR ~2 versus ~6 in EOMG). Moreover, the strongest associations were in opposite directions from EOMG, including an OR of 0.54 for DQA1*05:01 in LOMG (P = 5.9 × 10^-12) versus 2.82 in EOMG (P = 3.86 × 10^-45). Association and conditioning studies for the MHC region showed three distinct and largely independent association peaks for LOMG corresponding to (a) MHC class II (highest attenuation when conditioning on DQA1), (b) HLA-A and (c) MHC class III SNPs. Conditioning studies of human leukocyte antigen (HLA) amino acid residues also suggest potential functional correlates. Together, these findings emphasize the value of subgrouping myasthenia gravis patients for clinical and basic investigations and imply distinct predisposing mechanisms in LOMG.

Reliability of SFEMG in diagnosing myasthenia gravis: sensitivity and specificity calculated on 100 prospective cases

OBJECTIVE

The study aimed to determine the utility of single-fibre electromyography (SFEMG) in the diagnosis of myasthenia gravis (MG) in subjects with a clinical suspicion of the disease.

METHODS

We performed a prospective, single-blinded study on 100 consecutive patients. SFEMG was not considered a criterion in making the MG diagnosis. For all cases, a different physician than the one performing SFEMG made the diagnosis of MG. All subjects underwent standard SFEMG of a single muscle, the orbicularis oculi.

RESULTS

SFEMG was abnormal in 67 of 100 patients. A final diagnosis of definite MG was made in 54 patients (30 men/24 women). SFEMG was positive in 53 of 54 patients diagnosed with MG. The sensitivity of SFEMG in diagnosing MG was 98% (95% CI: 0.94-1.02), while the specificity was 70% (95% CI: 0.54-0.86), with a positive predictive value of 79% (95% CI: 0.74-0.79) and a negative predictive value of 97% (95% CI: 0.94-0.99).

CONCLUSIONS

In this cohort of patients, normal SFEMG findings were unlikely to occur in patients with MG.

SIGNIFICANCE

SFEMG is not a confirmatory test for the diagnosis of MG, but it has a high negative predictive value in identifying patients without MG.

Neuro-ophthalmology Annual Review

PURPOSE

To provide a clinical update of the neuro-ophthalmology literature over the last twelve months.

DESIGN

This is an annual review of current literature from August 1, 2011 to August 1, 2012.

METHODS

The authors conducted a one year English language neuro-ophthalmology literature search using PubMed from August 1, 2011 to August 1, 2012 using the following search terms: pupil abnormalities, eye movements, diseases of muscle and musculoskeletal junction, optic nerve disorders, optic neuritis and multiple sclerosis, chiasm and posterior primary visual pathway lesions, increased intracranial pressure and related entities, tumors (e.g., meningioma) and aneurysm affecting the visual pathways, vascular diseases, higher visual functions, advances in neuroimaging, and miscellaneous topics in neuro-ophthalmology. The authors included original articles, review articles, and case reports, which revealed the new aspects and updates in neuro-ophthalmology. Letters to the editor, unpublished work, and abstracts were not included in this annual literature review. We propose to update the practicing clinical ophthalmologist on the most clinically relevant literature from the past year. However, this review is not meant to be all-inclusive and highlights only the literature most applicable to the practicing clinical ophthalmologist.

RESULTS

We reviewed the literature over the past year in neuro-ophthalmology of potential interest and relevance to the comprehensive ophthalmologist.

CONCLUSION

This annual review provides a brief update on a number of neuroophthalmic conditions that might be of interest to the practicing clinical ophthalmologist.