AAEM Quality Assurance Committee. American Association of Electrodiagnostic Medicine. Literature review of the usefulness of repetitive nerve stimulation and single fiber EMG in the electrodiagnostic evaluation of patients with suspected myasthenia gravis or Lambert-Eaton myasthenic syndrome

Behavior of jittering potential before and after impulse blockings: a preliminary study in myasthenia gravis

Neuromuscular junction disorders lead to secession of bioelectrical activity transmission between motor nerve endings and muscle fibers. In diseases that are severe enough, impulse blockings are observed. This study aims to reveal the behavior of neuromuscular junction before and after impulse blockings. Fourteen recordings harboring impulse blockings from nine myasthenia gravis (MG) patients were included. Recordings were made from frontalis muscle by using concentric needle electrode during voluntary contraction. One hundred traces were acquired in each session. In addition to well-known jitter parameters, new parameters were calculated such as number of consecutive impulse blocking groups, number of impulse blockings in each group, ratio of maximum number of consecutive impulse blockings to all number of blockings. Graphics were composed to show location change behavior of jittering potential in all traces. For jittering potential, before or after a single impulse blocking the amount of getting further away from trigger peak was greater than getting closer to trigger peak. However, after consecutive impulse blockings the amount of getting closer to trigger peak was greater than the amount of getting further away. The behavior of neuromuscular junction before and after impulse blockings was demonstrated in MG patients. Moreover, new features were extracted for jitter studies. Building models for different diseases according to their impulse blockings may be possible with the developed algorithm.

Graphical abstract

AChR-seropositive myasthenia gravis in muscular dystrophy: diagnostic pitfalls and clinical management challenges

The co-occurrence of genetic myopathies with myasthenia gravis (MG) is extremely rare, however a few studies have been reported. We aim to explore the link between genetically inherited muscle disorders and immune-mediated neuromuscular junction conditions, taking into account the diagnostic and therapeutic implications posed by these combined conditions. We searched all English medical papers registered in Web of Knowledge, PubMed, Google Scholar, and Science Direct between January 1987 concerning the association between muscular dystrophies (MD) and MG, also adding three new cases to the series reported so far. Three new clinical cases in which MG concurs with oculopharyngeal muscular dystrophy (OPMD) or facioscapulohumeral muscular dystrophy (FSHD) or myotonic dystrophy type 2 (DM2) were reported. A comprehensive literature review showed that FSHD is the dystrophy most frequently associated with generalized MG. The AChR antibody titer is high and neurophysiologic tests prove to be an essential tool for the diagnosis. The association between MG and MD is rare but should not be underestimated. The presence of unusual clinical features suggest investigating additional overlapping condition, especially when a treatable disease like MG is suspected.

Case report: Avoidant/restrictive food intake disorder after tonsillectomy

Background

Avoidant Restrictive Food Intake Disorder (ARFID) is a newly classified eating disorder that requires further understanding of its presentation. There is no previous report of ARFID in a child post-tonsillectomy. ARFID may be a potential negative outcome for children following oropharyngeal surgery.

Case presentation

A female child aged 10 years and 2 months presented with ARFID associated with depression, anxiety and nutritional deficiency following tonsillectomy. She had more difficulty in swallowing solids than fluids and had repeated vomiting and spitting food after chewing it. She became dehydrated and malnourished with a BMI of 10.5 and was misdiagnosed with myasthenic gravis.

Conclusions

To our knowledge, this is the first case report of ARFID in a child post-tonsillectomy. We discuss the pathophysiology of ARFID, which remains elusive, and recommend psychiatric assessment when evaluating children post operative tonsillectomy.

Accuracy of Repetitive Ocular Vestibular-Evoked Myogenic Potentials to Diagnose Myasthenia Gravis in Patients With Ptosis or Diplopia

BACKGROUND AND OBJECTIVES

We developed repetitive ocular vestibular-evoked myogenic potentials (roVEMP) as an electrophysiologic test that allows us to elicit the characteristic decrement of extraocular muscles in patients with ocular myasthenia gravis (OMG). Case-control studies demonstrated that roVEMP reliably differentiates patients with OMG from healthy controls. We now aimed to evaluate the diagnostic accuracy of roVEMP for OMG diagnosis in patients with ptosis and/or diplopia.

METHODS

In this blinded prospective diagnostic accuracy trial, we compared roVEMP in 89 consecutive patients presenting with ptosis and/or diplopia suspicious of OMG with a multimodal diagnostic approach, including clinical examination, antibodies, edrophonium testing, repetitive nerve stimulation of accessory and facial nerves, and single-fiber EMG (SFEMG). We calculated the roVEMP decrement as the ratio between the mean of the first 2 responses compared with the mean of the sixth-ninth responses in the train and used cutoff of >9% (unilateral decrement) in a 30 Hz stimulation paradigm.

RESULTS

Following a complete diagnostic work-up, 39 patients (44%) were diagnosed with ocular MG, while 50 patients (56%) had various other neuro-ophthalmologic conditions, but not MG (non-MG). roVEMP yielded 88.2% sensitivity, 30.2% specificity, 50% positive predictive value (PPV), and 76.5% negative predictive value (NPV). For comparison, SFEMG resulted in 75% sensitivity, 56% specificity, 55.1% PPV, and 75.7% NPV. All other diagnostic tests (except for the ice pack test) also yielded significantly higher positive results in patients with MG compared with non-MG.

DISCUSSION

The study revealed a high sensitivity of 88.2% for roVEMP in OMG, but specificity and PPV were too low to allow for the OMG diagnosis as a single test. Thus, differentiating ocular MG from other neuro-ophthalmologic conditions remains challenging, and the highest diagnostic accuracy is still obtained by a multimodal approach. In this study, roVEMP can complement the diagnostic armamentarium for the diagnosis of MG.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that in patients with diplopia and ptosis, roVEMP alone does not accurately distinguish MG from non-MG disorders.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov: NCT03049956.

Role of recovery of acetylcholine release in compromised neuromuscular junction function

Everyday physical activities, such as walking, are enabled by repeated skeletal muscle contractions and require a well-functioning neuromuscular transmission. In myasthenic disorders, activities of daily living are debilitated by a compromised neuromuscular transmission leading to muscle weakness and fatiguability in patients. To enable physical activity, acetylcholine (ACh) is released repeatedly from the motor nerve, however, the role of the nerve terminals' capacity to sustain ACh release to support repetitive contractions under compromised neuromuscular transmission remains unclear. To explore this, we studied synaptic and contractile function during repeated contractions in healthy rat skeletal muscles under conditions of pharmacological induced compromised neuromuscular transmission. Using recordings of endplate potentials, compound muscle action potential (CMAP) and force production in isolated skeletal muscles and living, anesthetized animals, we found that force and CMAP were markedly reduced by even very light activity performed up to 5 s prior to contraction showing that recovery of ACh release was insufficient to maintain synaptic transmission strength. Our results suggest that the timing of depletion and restoration of ACh release may impact clinical signs of weakness and fatigability in patients with impaired neuromuscular transmission and affect the sensitivity of electromyographic recordings in the clinic.

Diaphragmatic ultrasonography as a predictor of respiratory muscle fatigue in myasthenia gravis

INTRODUCTION/AIMS

Easy fatigability, the clinical hallmark of generalized myasthenia gravis (GMG), cannot be detected in a dynamic way. The aim of this study was to assess respiratory function dynamically through diaphragmatic ultrasonography (DUS) in GMG patients.

METHODS

GMG patients and controls were recruited in a 1:1 ratio. DUS was performed during one quiet breath and 15 consecutive deep breaths. The diaphragm thicknesses were measured at different positions. Diaphragm thickening fraction (TFdi) and the maximal change in diaphragm thickness (Tmax) during 15 consecutive deep breaths were calculated and transformed to normality, named N-TFdi and N-Tmax, respectively. The percentages of changes in TFdi and Tmax compared with baseline were named ΔTFdi and ΔTmax, respectively. The diagnostic parameter for respiratory muscle fatigue was chosen from ΔTFdi and ΔTmax at different deep breath times according to their ability to distinguish GMG patients from controls and the interrater reliability of TFdi and Tmax.

RESULTS

Thirty-four GMG patients and 30 healthy controls were enrolled. N-TFdi and N-Tmax significantly changed as the number of deep breaths increased (p < .001) in GMG patients, but not in controls. ΔTmax of the 15th deep breath (ΔTmax15) was selected as the diagnostic parameter for respiratory muscle fatigue. There were no significant differences in percentage of predicted values of forced vital capacity and arterial partial pressure of carbon dioxide between patients with normal and abnormal ΔTmax15.

DISCUSSION

DUS could identify diaphragm fatiguability in GMG patients, which may be more reliable and sensitive in assessment of diaphragm fatigue than conventional methods.

Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease characterized by proximal muscle weakness, loss of tendon reflexes, and autonomic dysfunction. Muscle weakness usually starts in the upper legs and can progress to oculobulbar and in severe cases respiratory muscles. P/Q-type voltage-gated calcium channels (VGCCs) localized in the presynaptic motor nerve terminal and in the autonomic nervous system are targeted by antibodies in LEMS patients. These antibodies can be detected in about 90% of patients, and the presence of decrement and increment upon repetitive nerve stimulation is also a highly sensitive diagnostic test. Rapid diagnosis is important because of the association with SCLC in 50%-60% of patients, which stresses the need for vigorous tumor screening after diagnosis. Clinical parameters can predict tumor probability and guide frequency of tumor screening. Treatment of the tumor as well as symptomatic treatment and immunosuppression can effectively control symptoms in the majority of patients.

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.

Symptoms of Myasthenia Gravis Obscured by Old Age and Unilateral Presentation

Myasthenia gravis (MG) is a neuromuscular junction disorder involving autoantibodies affecting the postsynaptic muscle membrane. We report an 81-year-old man who presented to the emergency department with three days of left facial droop, who later developed worsening bilateral ptosis, cervical weakness, dysphagia, and dysarthria following an assessment for Bell's palsy. Ultimately, he was diagnosed with MG. This patient's presentation was atypical and challenging. Specifically, the patient had droopy eyelids from a redundancy of skin and an anatomical neck droop, non-specific findings in older adults, which obscured the development of bilateral ptosis and cervical weakness, a classic sign of bulbar disease. The patient also presented with unilateral facial weakness, a rare finding in MG and concerning stroke in the elderly population. Our aim is to discuss the challenges of identifying MG in older populations and to discuss pharmacological challenges in assessing elderly patients with suspected bulbar palsies.

Repetitive nerve stimulation on survival in amyotrophic lateral sclerosis

Objective

No previous studies investigated the association between decrement of low-frequency repetitive nerve stimulation (LF-RNS) and amyotrophic lateral sclerosis (ALS) survival. We aim to study the relationship between decrement and survival in ALS.

Methods

Sporadic ALS patients diagnosed at the Department of Neurology, the First Medical Center, Chinese PLA General Hospital from January 2018 to December 2019 were enrolled in this study. Experienced neurologists followed up the participants regularly every 6 months until January 2022. A decremental response of 10% or greater at least in one muscle was considered positive. According to the decrement, the participants were divided into LF-RNS (+) and LF-RNS (-) groups.

Results

One hundred and eighty-one sporadic ALS patients were recruited in our study, including 100 males and 81 females. Among them, 10 cases (5.5%) were lost to follow-up, 99 cases (54.7%) died, and 72 patients (39.8%) were still alive at the last follow-up. The median survival time of all ALS patients in this study was 42.0 months. There was no significant difference of median survival in LF-RNS(+) group and LF-RNS(-) group (p = 0.159, Kaplan-Meier method). In multivariate Cox regression analysis, age of onset, diagnostic delay, and ALS Functional Rating Scale-Revised (ALSFRS-R) score were associated with ALS survival, but the decrement was not correlated with ALS survival (p = 0.238).

Conclusion

The decrement in accessory and ulnar nerves was not associated with the survival of ALS. The decrement of LF-RNS could not be an electrophysiological marker to predict ALS survival.

Longitudinal prospective cohort study to assess peripheral motor function with extensive electrophysiological techniques in patients with Spinal Muscular Atrophy (SMA): the SMA Motor Map protocol

BACKGROUND

Hereditary spinal muscular atrophy (SMA) is a motor neuron disorder with a wide range in severity in children and adults. Two therapies that alter splicing of the Survival Motor Neuron 2 (SMN2) gene, i.e. nusinersen and risdiplam, improve motor function in SMA, but treatment effects vary. Experimental studies indicate that motor unit dysfunction encompasses multiple features, including abnormal function of the motor neuron, axon, neuromuscular junction and muscle fibres. The relative contributions of dysfunction of different parts of the motor unit to the clinical phenotype are unknown. Predictive biomarkers for clinical efficacy are currently lacking. The goals of this project are to study the association of electrophysiological abnormalities of the peripheral motor system in relation to 1) SMA clinical phenotypes and 2) treatment response in patients treated with SMN2-splicing modifiers (nusinersen or risdiplam).

METHODS

We designed an investigator-initiated, monocentre, longitudinal cohort study using electrophysiological techniques ('the SMA Motor Map') in Dutch children (≥ 12 years) and adults with SMA types 1-4. The protocol includes the compound muscle action potential scan, nerve excitability testing and repetitive nerve stimulation test, executed unilaterally at the median nerve. Part one cross-sectionally assesses the association of electrophysiological abnormalities in relation to SMA clinical phenotypes in treatment-naïve patients. Part two investigates the predictive value of electrophysiological changes at two-months treatment for a positive clinical motor response after one-year treatment with SMN2-splicing modifiers. We will include 100 patients in each part of the study.

DISCUSSION

This study will provide important information on the pathophysiology of the peripheral motor system of treatment-naïve patients with SMA through electrophysiological techniques. More importantly, the longitudinal analysis in patients on SMN2-splicing modifying therapies (i.e. nusinersen and risdiplam) intents to develop non-invasive electrophysiological biomarkers for treatment response in order to improve (individualized) treatment decisions.

TRIAL REGISTRATION

NL72562.041.20 (registered at https://www.toetsingonline.nl . 26-03-2020).

Chronic mimics of myasthenia gravis: a retrospective case series

Myasthenia gravis often presents a diagnostic challenge and may be misdiagnosed, particularly in seronegative disease with active symptoms. We retrospectively evaluated 61 patients following the introduction of single fibre electromyography at our service, and identified 8 mimics which had been inappropriately diagnosed and treated as refractory myasthenia gravis. 6 of these were seronegative, but two had positive acetylcholine receptor (AChR) antibodies. The final diagnoses included one case each of chronic progressive external ophthalmoplegia, chronic ptosis, oculopharyngeal muscular dystrophy, and an undifferentiated disorder suspicious for either a mitochondrial cytopathy or low-grade myositis. Four were diagnosed with functional neurological disorder, one of which had a superimposed thyroid myopathy and orbitopathy. We found the average duration of misdiagnosis was 9 years (SD±5.2, median 11 years), and patients were often exposed to years of unnecessary treatment. All patients had received anticholinesterase therapy, three had immunotherapy, and three surgical interventions were performed including two thymectomies. We found myasthenic mimics should be suspected in disease that is static and treatment refractory, and functional mimics in disease with frequent flares. Thorough neurophysiologic assessment is important, particularly when making a diagnosis of seronegative myasthenia gravis.

Tracking Eye Movements for Diagnosis in Myasthenia Gravis: A Comprehensive Review

BACKGROUND

Around 60%--75% of myasthenia gravis (MG) patients initially present with nonspecific ocular symptoms. Failed recognition of these symptoms may delay the diagnosis of MG up to 5 years or more, leading to a reduced likelihood of remission and increased morbidity. Current diagnostic tests are either poorly sensitive for patients presenting with ocular symptoms alone or are time consuming, invasive, require a high level of technical expertise, and generally are universally difficult to obtain. This review will explore quantitative eye and pupil tracking as a potential noninvasive, time-effective, and less technically demanding alternative to current diagnostic tests of MG.

EVIDENCE ACQUISITION

Comprehensive literature review.

RESULTS

Thirty-two publications using oculography for the diagnosis of MG and 6 studies using pupillometry were evaluated. In MG patients, extra ocular muscle fatigue was evident in reports of intersaccadic, intrasaccadic and postsaccadic abnormalities, changes in optokinetic nystagmus, slow eye movements, disconjugate saccades, and pupillary constrictor muscle weakness.

CONCLUSIONS

Our review identified several potentially useful variables that derive from oculography and pupillometry studies that could assist with a timely diagnosis of MG. Limitations of this review include heterogeneity in design, sample size, and quality of the studies evaluated. There is a need for larger, well-designed studies evaluating eye-tracking measures in the diagnosis of MG, especially for patients presenting with purely ocular symptoms.

Clinical Utility of Repetitive Nerve Stimulation Test in Differentiating Multifocal Motor Neuropathy From Progressive Muscular Atrophy

OBJECTIVES

To evaluate the utility of repetitive nerve stimulation test (RNS) for differentiating multifocal motor neuropathy (MMN) and progressive muscular atrophy (PMA).

METHODS

We retrospectively enrolled 20 patients with MMN or PMA. We extracted the results of the initial 3-Hz RNS in the ulnar and accessory nerves and compared the percentage and frequency of abnormal decremental responses between both groups.

RESULTS

RNS was performed in 8 ulnar and 9 accessory nerves in patients with MMN, and in 8 ulnar and 10 accessory nerves in patients with PMA. Patients with MMN had a significantly lower decrement percentage (0.6 ± 4.0% in MMN vs. 10.3 ± 6.5% in PMA, P < 0.01) and frequency of abnormal decremental response (0 of 9 in MMN vs. 6 of 10 in PMA, P = 0.01) than patients with PMA in the accessory nerve.

CONCLUSIONS

The RNS has clinical utility for differentiating MMN from PMA.

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.

Electrodiagnostic Assessment of Neuromuscular Junction Disorders

Please verify edits, "These techniques", or specify. This article reviews advanced electrodiagnostic techniques used to assess for neuromuscular junction disorders, including repetitive nerve stimulation, conventional or concentric-needle single-fiber electromyography (SFEMG), and stimulated SFEMG. These techniques have high sensitivity but limited specificity. Novel methods currently under investigation are discussed, including vestibular ocular myogenic potential and oculography analysis.

Contribution of Single-Fiber Evaluation on Monitoring Outcomes Following Injection of Botulinum Toxin-A: A Narrative Review of the Literature

Botulinum toxin-A (BoNT-A) blocks acetylcholine release at the neuromuscular junction (NMJ) and is widely used for neuromuscular disorders (involuntary spasms, dystonic disorders and spasticity). However, its therapeutic effects are usually measured by clinical scales of questionable validity. Single-fiber electromyography (SFEMG) is a sensitive, validated diagnostic technique for NMJ impairment such as myasthenia. The jitter parameter (µs) represents the variability of interpotential intervals of two muscle fibers from the same motor unit. This narrative review reports SFEMG use in BoNT-A treatment. Twenty-four articles were selected from 175 eligible articles searched in Medline/Pubmed and Cochrane Library from their creation until May 2020. The results showed that jitter is sensitive to early NMJ modifications following BoNT-A injection, with an increase in the early days’ post-injection and a peak between Day 15 and 30, when symptoms diminish or disappear. The reappearance of symptoms accompanies a tendency for a decrease in jitter, but always precedes its normalization, either delayed or nonexistent. Increased jitter is observed in distant muscles from the injection site. No dose effect relationship was demonstrated. SFEMG could help physicians in their therapeutic evaluation according to the pathology considered. More data are needed to consider jitter as a predictor of BoNT-A clinical efficacy.

Diagnosis of Myasthenia Gravis

The diagnosis of autoimmune Myasthenia Gravis (MG) remains clinical and rests on the history and physical findings of fatigable, fluctuating muscle weakness in a specific distribution. Ancillary bedside tests and laboratory methods help confirm the synaptic disorder, define its type and severity, classify MG according to the causative antibodies, and assess the effect of treatment objectively. We present an update on the tests used in the diagnosis and follow-up of MG and the suggested approach for their application.

End-Plate Disorders in Intensive Care Unit

Even if nerves and muscles are the principal targets of intensive care unit-acquired weakness, the neuromuscular junction may be as well involved. In intensive care units, neuromuscular blocking agents are classically used, and side effects are possible. Sepsis, immobilization, and denervation which are common in intensive care units may be the cause of neuromuscular junction disorders and participate to the pathophysiology of weakness. We propose here a review of end-plate disorders in intensive care units to highlight their mechanisms and propose diagnosis tools.

Improving accuracy of myasthenia gravis autoantibody testing by reflex algorithm

OBJECTIVE

To improve myasthenia gravis (MG) autoantibody testing.

METHODS

MG serologic tests with confirmatory or refuting clinical-electrodiagnostic (EDX) testing and cancer evaluations were reviewed over 4 years (2012-2015). All patients had acetylcholine receptor-binding (AChR-Bi), modulating (AChR-Mo), and striational (STR) autoantibody testing, and negatives reflexed to muscle-specific kinase (MuSK). Thymoma and cancer occurrences were correlated with STR and reflexed glutamic acid decarboxylase 65 (GAD65), ganglionic acetylcholine receptor (α3), collapsin response mediating protein-5, and voltage-gated potassium channel complex autoantibodies.

RESULTS

Of 433 samples tested, 133 (31%) met clinical-EDX criteria for MG. Best sensitivity (90%) occurred at AChR-Bi >0.02 nmol/L, leaving 14 negative (6 ocular MG, 7 generalized MG, 1 MuSK MG) with specificity 90% (31 false-positives). Using AChR-Mo antibodies (>20% loss), specificity was better (92%, 24 false-positives), but sensitivity dropped (85%). Specificity improved (95%) by testing AChR-Mo when AChR-Bi are positive, resulting in 45% reduction of false-positives (31-17), maintaining AChR-Bi 90% sensitivity. Cutoff values recommended by area under the curve analysis did not outperform this approach. AChR-Bi and AChR-Mo values were significantly higher in true-positives. CT evaluations in 121 MG samples revealed 16 thymomas. Historical or subsequent cancers occurred in 22. STR and reflexed autoantibodies were not more common in MG with thymoma or other cancers. Full-body CT (n = 34) was performed in those with STR and reflex autoantibody positivity, but without additional cancers found.

CONCLUSION

Accuracy of MG serologic testing is improved by reflexing AChR-Bi-positive cases to AChR-Mo. STR and other reflexed cancer evaluation autoantibodies did not provide value beyond standard CT chest imaging at the time of MG diagnosis. Diagnostic certainty is informed by AChR-Bi and AChR-Mo with higher values increasing specificity.

Sensitivity and specificity of repetitive nerve stimulation with lower cutoffs for abnormal decrement in myasthenia gravis

INTRODUCTION

The sensitivity of repetitive nerve stimulation (RNS) in myasthenia gravis (MG) is dependent on the cutoff for abnormal decrement.

METHODS

RNS data of adults with and without MG from 2014 to 2017 were reviewed retrospectively. The maximum reliable RNS amplitude/area decrement before and after exercise from facial, spinal accessory (SA), ulnar, and fibular nerves was recorded. Sensitivity/specificity using 5%, 7%, and 10% cutoffs were calculated.

RESULTS

Seventy-nine of 141 patients had MG (46 generalized, 21 ocular, 12 bulbar). A total of 608 unique RNS recordings were analyzed. Overall RNS sensitivity/specificity at ≥5%, ≥7%, and ≥10% amplitude cutoffs were as follows: SA, 65.6%/86.3%, 49.2%/94.1%, and 29.5%/96.1%; facial, 51.0%/82.5%, 43.1%/95.0%, and 37.3%/100%; ulnar, 43.6%/100%, 41.0%/100%, and 41.0%/100%; and fibular, 52.6%/89.5%, 42.1%/94.7%, and 42.1%/100%.

DISCUSSION

Lowering amplitude cutoff from 10% to 7% increased or maintained sensitivity with little loss in specificity. Post-exercise and area analysis resulted in increased sensitivity in some circumstances.

Lambert-Eaton myasthenia syndrome: specified description of a response pattern to low-frequency repetitive nerve stimulation

OBJECTIVE

We aimed to specify and quantify the characteristics of the decrement in low-frequency repetitive nerve stimulation response in Lambert-Eaton myasthenia syndrome (LEMS) and compare it to those of myasthenia gravis (MG).

PATIENTS AND METHODS

We retrospectively reviewed 18 patients with LEMS and 24 patients with MG. Ten consecutive stimulations were applied at 3 Hz to the abductor pollicis brevis. We determined the position of the smallest wave in the stimulation sequence, and we calculated the decrement and recovery.

RESULTS

The median sequential order of the minimum wave was 8 in the LEMS group and 5 in the MG group (p < 0.001). The median decrement in the LEMS group was 36.7%, while that in the MG group was 21.0% (p = 0.047). The recovery percentage was 1.4% in the LEMS group and 3.5% in the MG group (p = 0.001). The area under the curve for the sequential order of the minimum wave was 0.90, and the reciprocal optimum cut-off point was 6.5.

CONCLUSIONS

We elucidated a pattern with a delayed nadir and subsequent poor recovery, featuring a low-frequency decrement; furthermore, we determined the most likely sequential order of the minimum wave in patients with LEMS, and the indicator was useful for differentiation.

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.

Lowering the cutoff value for increment increases the sensitivity for the diagnosis of Lambert-Eaton myasthenic syndrome

Background

Increment of compound muscle action potential amplitude is a diagnostic hallmark of Lambert‐Eaton myasthenic syndrome (LEMS). Making a diagnosis can be challenging, therefore, a proper cutoff for abnormal increment is highly relevant for improved recognition of this rare disease.

Methods

We determined the sensitivity and specificity of 60% and 100% cutoff values in all consecutive patients who underwent increment testing in our hospital from 1999 to 2016.

Results

We included 156 patients, 63 with LEMS and 93 without LEMS. Sensitivity of a 60% cutoff for increment testing was 77.8% (95% confidence interval 65.5%–87.3%) and 58.7% (45.6%–71.0%) for 100%. Specificity was 98.9% (94.2%–100%) and 100% (96.1%–100%) using a threshold of 60% and 100%, respectively.

Conclusions

Lowering the cutoff value for abnormal increment to 60% greatly increases sensitivity to diagnose LEMS without an overt loss in specificity.

Reference Jitter Values for Concentric Needle Electrode of Orbicularis Oculi and Frontalis Muscles Using Voluntary Activation Method in Sudanese Population

Single fibre electromyography is the most sensitive neurophysiological test for the diagnosis of neuromuscular junction disorders, particularly myasthenia gravis. The study aimed at establishing concentric needle (CN) normal jitter values for voluntarily activated orbicularis-oculi (V-OOc) & Frontalis (V-FRO) muscles in Sudanese population. 57 healthy volunteers (20 males & 37 females) were included in the study (mean Age 43.6 ± 14.2 years, range 18–70 years). V-OOc and V-FRO were tested in the same individual using CN. Jitter values were expressed as the mean consecutive difference (MCD) of 30 potential pairs in microseconds. The mean jitter, mean individual fibre pairs jitter & mean outliers jitter values with (upper 95% Confidence Limit-CL) for [OOc] were [26.9 ± 3.3 (31.97), 26.1 ± 8.9 (41.8) & 38.5 ± 5.7 (49.0) µs] & for [FRO] were [27.1 ± 3.0 (31.32), 26.4 ± 9.4 (42.9) & 39.9 ± 5 (49.2) µs] respectively. The suggested practical upper limits for mean jitter & for outliers were (32, 49 µs) for OOc & (31, 49 µs) for FRO. Our CN-jitter values were within the range of the few published studies. The study was unique in that it established and compared between CN reference jitter values of two voluntarily activated facial muscles (V-OOc & V-FRO) in the same individual in large number of healthy subjects.

Severe Myasthenic Manifestation of Leptospirosis Associated with New Sequence Type of Leptospira interrogans

We report the rapid development of a myasthenic crisis as the first-time manifestation of myasthenia gravis. The symptoms developed in the course of acute leptospirosis associated with a new sequence type of Leptospira interrogans. Antibiotic treatment led to rapid amelioration of myasthenia.

Clinical neurophysiology of neuromuscular junction disease

The neuromuscular junction (NMJ) is a cholinergic synapse where quantal release of acetylcholine (ACh) from motor nerve terminals generates a local endplate potential (EPP) on the muscle fiber. EPPs that reach threshold depolarize the entire muscle fiber and initiate the process of excitation-contraction coupling. Deficits of neuromuscular transmission result in clinical weakness that is fatigable and may fluctuate. Repetitive nerve stimulation (RNS) testing can unmask the reduced safety factor common to all NMJ disorders via depletion of immediate ACh stores at the presynaptic motor nerve terminal with decremental responses to low-frequency RNS (LF-RNS). The facilitated responses characterizing presynaptic NMJ disorders can be revealed by brief exercise or high stimulation rates that augment presynaptic calcium levels. Activation with isometric exercise may increase the sensitivity of RNS testing. Attention to technical detail and reproducibility of findings are essential in generating valid results in RNS testing. Motor unit potential (MUP) instability or jiggle is the main finding seen in NMJ disorders on conventional needle EMG and reflects the moment-to-moment variability in the number and synchrony of muscle fiber action potentials (MFAPs) that compose a MUP. Single fiber EMG (SFEMG) is a highly selective technique that assesses jitter, the temporal variability in MFAPs generated in response to motor nerve action potentials.

Single fiber electromyography

Single fiber electromyography (SFEMG) is a highly selective technique that permits assessment of individual muscle fiber action potentials (MFAPs). This selectivity is achieved with a specialized concentric needle electrode with a 25-μm diameter recording surface located in a side port 3mm from the needle tip. Additional selectivity is achieved with 500-Hz low-frequency filtering. An oscilloscope with a trigger and delay line enables identification of time-locked MFAPs within the same motor unit. SFEMG techniques allow assessment of two important features of the motor unit: jitter and fiber density (FD). Neuromuscular jitter is a direct measure of neuromuscular transmission and reflects the temporal variation in end-plate potentials reaching threshold to elicit a MFAP. SFEMG may be used to assess paired jitter with voluntary activation or by axonal stimulation of motor nerve branches to individual end plates. SFEMG is the most sensitive clinical test for neuromuscular junction disease and is often abnormal in clinically unaffected muscles in patients with myasthenia gravis (MG) and Lambert-Eaton myasthenia (LEM). Normal jitter findings in a clinically weak muscle exclude neuromuscular junction disease as a cause for weakness in that muscle. FD measurements assess the local concentration of muscle fibers within a motor unit and provide a sensitive in vivo assessment of reinnervation.

Asymmetric pattern in generalized myasthenia gravis: A case report

RATIONALE

Myasthenia gravis (MG) is an uncommon autoimmune disease mediated by antibodies that attack the postsynaptic acetylcholine receptors (AchRs) at the neuromuscular junction, causing fluctuating muscle weakness, aggravated with use, and relieved with rest.

PATIENT CONCERNS

A 32-year-old woman with a diagnosis of MG based on clinical findings, eletroneuromyography, and brain magnetic resonance imaging (MRI) was admitted to our hospital with dysphagia, dysphonia, diplopia, and intense weakness, associated with a 2-day viral gastroenteritis.

DIAGNOSES

Physical examination revealed globally reduced deep tendon reflexes, and tetraparesis, with muscle strength grade 4 in the left limbs and grade 2 in the right limbs. Autoantibody dosing against AchR was elevated and computed tomography scan of the thorax revealed a thymic remnant.

INTERVENTIONS

Pyridostigmine and human immunoglobulin were infused.

OUTCOMES

After 7 days of the reintroduction of pyridostigmine and human immunoglobulin infusion, the patient developed complete resolution of symptoms, being discharged from the hospital. Her symptoms are still well controlled 6 months later. The patient was evaluated by a thoracic surgeon and is awaiting elective thymectomy.

LESSONS

Although our patient presented all the diagnostic criteria of MG, the markedly asymmetric limb weakness presented in previous history and clinical examination of admission was an unusual and unexpected presentation, especially considering the pathophysiology of the disease. MRI of brain without abnormalities was fundamental to rule out another associated etiology. Our review of the literature revealed just 1 case report of MG with similar presentation. This clinical manifestation becomes valuable because it contributes to the list of unexpected presentation that should motivate its suspicion.

Electrophysiological abnormalities in iatrogenic botulism: Two case reports and review of the literature

Therapeutic use of botulinum neurotoxin type A (BoNT/A) is effective, and generally safe. Nevertheless, iatrogenic botulism (IB) is rarely reported as a result of systemic spread of the BoNT/A, causing general weakness, bulbar symptoms and dysautonomia. Suggestive clinical feature are decisive to raise the diagnostic suspicion, which however needs a confirmation in the electrodiagnostic (EDX) study, above all to exclude other treatable diseases. In this study, we report 2 patients who developed IB after receiving therapeutic doses of BoNT/A, assessing the EDX changes, and reviewing the literature on EDX in IB. Although there is not enough data to draw solid conclusions we propose that, in a subject with suggestive clinical features and recent exposure to BoNT/A, the absence of a decremental or incremental response to repetitive nerve stimulation in muscles showing acute denervation changes, is a suggestive finding for the diagnosis of IB.

Repetitive Nerve Stimulation in Amyotrophic Lateral Sclerosis

Background

Nowadays, it is widely known that decremental responses in low-frequency repetitive nerve stimulation (LF-RNS) are frequently observed in patients with amyotrophic lateral sclerosis (ALS). The pathological mechanism of this phenomenon remains unknown. This study aimed to illuminate the features of RNS in Chinese patients with ALS.

Methods

Clinical and electrophysiological data of 146 probable and definite ALS patients who underwent RNS were retrospectively enrolled and analyzed. LF-RNS (3 Hz) was performed in trapezius, deltoid, abductor digiti minimi (ADM), quadriceps femoris, and tibialis anterior. High-frequency RNS (HF-RNS, 10 Hz) was performed only in ADM. The two-sample t-test and Chi-squared test were used for statistical analysis.

Results

Decremental responses to LF-RNS (≥10%) in at least one muscle were detected in 83 (56.8%) of the cases and were most commonly seen in trapezius and deltoid. The incidence of decremental response was higher in patients with upper limb onset. Incremental responses to HF-RNS (≥60%) in ADM were observed in 6 (5.6%) of the cases. In 106 muscles with decremental response, 62 (57.4%) muscles had a continuous decremental pattern, more than a U-shape pattern (37 cases, 34.3%). Nineteen cases showed definite decrements in LF-RNS tests in trapezius, while no abnormalities were found in the electromyography and neurological examination of the sternocleidomastoid muscle, supplied by the accessory nerve as well.

Conclusions

Decremental responses in the RNS are commonly observed in ALS patients. The findings regarding the trapezius indicated that some ALS onsets could be initiated by a "dying back" process, with destruction of neuromuscular junctions (NMJs) before motor neurons. Incremental responses in the ADM implied damage of the NMJs involved both the post and presynaptic membranes.

Open source modular ptosis crutch for the treatment of myasthenia gravis

INTRODUCTION

Pharmacologic treatment of Myasthenia Gravis presents challenges due to poor tolerability in some patients. Conventional ptosis crutches have limitations such as interference with blinking which causes ocular surface drying, and frequent irritation of the eyes. To address this problem, a modular and adjustable ptosis crutch for elevating the upper eyelid in Myasthenia Gravis patients has been proposed as a non-surgical and low-cost solution.

AREAS COVERED

This paper reviews the literature on the challenges in the treatment of Myasthenia Gravis globally and focuses on a modular and adjustable ptosis crutch that has been developed by the Medical Device Laboratory at the University of Cape Town.

EXPERT COMMENTARY

The new medical device has potential as a simple, effective and unobtrusive solution to elevate the drooping upper eyelid(s) above the visual axis without the need for medication and surgery. Access to the technology is provided through an open source platform which makes it available globally. Open access provides opportunities for further open innovation to address the current limitations of the device, ultimately for the benefit not only of people suffering from Myasthenia Gravis but also of those with ptosis from other aetiologies.

Utilizing Physiological Principles of Motor Unit Recruitment to Reduce Fatigability of Electrically-Evoked Contractions: A Narrative Review

Neuromuscular electrical stimulation (NMES) is used to produce contractions to restore movement and reduce secondary complications for individuals experiencing motor impairment. NMES is conventionally delivered through a single pair of electrodes over a muscle belly or nerve trunk using short pulse durations and frequencies between 20 and 40Hz (conventional NMES). Unfortunately, the benefits and widespread use of conventional NMES are limited by contraction fatigability, which is in large part because of the nonphysiological way that contractions are generated. This review provides a summary of approaches designed to reduce fatigability during NMES, by using physiological principles that help minimize fatigability of voluntary contractions. First, relevant principles of the recruitment and discharge of motor units (MUs) inherent to voluntary contractions and conventional NMES are introduced, and the main mechanisms of fatigability for each contraction type are briefly discussed. A variety of NMES approaches are then described that were designed to reduce fatigability by generating contractions that more closely mimic voluntary contractions. These approaches include altering stimulation parameters, to recruit MUs in their physiological order, and stimulating through multiple electrodes, to reduce MU discharge rates. Although each approach has unique advantages and disadvantages, approaches that minimize MU discharge rates hold the most promise for imminent translation into rehabilitation practice. The way that NMES is currently delivered limits its utility as a rehabilitative tool. Reducing fatigability by delivering NMES in ways that better mimic voluntary contractions holds promise for optimizing the benefits and widespread use of NMES-based programs.

Five years experience on 3,4-diaminopyridine phosphate in Lambert-Eaton syndrome: Case reports

RATIONALE

To report our experience on 7 patients (4 males and 3 females), affected by nonparaneoplastic Lambert-Eaton myasthenic syndrome, treated with 3,4-diaminopyridine phosphate (3,4-DAPP) either alone or in combination with other immunosuppressants or steroids.

PATIENT CONCERNS

Patients have been evaluated at specific timepoints (ie, baseline and last 5 year follow-up), with neurological examination, autoantibodies against presynaptic voltage-gated Cav2.1 (P/Q type) calcium ion channel (VGCC) dosage, neurophysiological evaluation focusing on the increased amplitude of the compound muscle action potential (cMAP) after maximum voluntary effort, quantitative myasthenia gravis (QMG) and activities of daily living scales, and autonomic nervous system involvement evaluation.

OUTCOMES

Five out of 7 patients presented a clinical improvement persisting at last 5-year follow-up; 2 out of them improved taking only 3,4-DAPP at the maximal dosage, whereas the remaining received concomitant medications, such as prednisone and azathioprine. However, the clinical amelioration was not statistically significant. No one of the patients reported severe adverse events, except one, complaining of transient chin and perioral paresthesias. A significant association between QMG and the type of pharmacological drugs therapy (P = .028) emerged. Indeed, we observed an improvement of the clinical condition in all 3 subjects treated with 3,4-DAPP and prednisone.

CONCLUSIONS

In this study, we confirm 3,4-DAPP treatment efficacy on muscle strength, but minor evidence of drug effectiveness have been demonstrated on the autonomic nervous system involvement and on the deep tendon reflexes reappearance, a part from patients who received 3,4-DAPP associated to prednisone.

Autoimmune paraneoplastic syndromes associated to lung cancer: A systematic review of the literature Part 4: Neurological paraneoplastic syndromes, involving the peripheral nervous system and the neuromuscular junction and muscles

The development of new immune treatment in oncology and particularly for lung cancer may induce new complications, particularly activation or reactivation of auto-immune diseases. In this context, a systematic review on the auto-immune paraneoplastic syndromes that can complicate lung cancer appears useful. This article is the fourth of a series of five and deals mainly with neurological paraneoplastic syndromes involving the peripheral nervous system and the neuromuscular junction and muscles.

Correlations between slow-rate repetitive nerve stimulation and characteristics associated with amyotrophic lateral sclerosis in Chinese patients

[Purpose] To clarify the features associated with decrements in compound muscle action potentials (CMAP) during slow-rate repetitive nerve stimulation (RNS) of muscles involved in amyotrophic lateral sclerosis (ALS) in mainland China. [Subjects and Methods] A retrospective study of decremental responses to slow-rate RNS was performed to compare patients with ALS to those with myasthenia gravis (MG). [Results] A significant decrement (>5%) was observed in at least one muscle in 54% of ALS patients. The trapezius muscle was the most commonly affected (67%). In the ALS group, the CMAP amplitude evoked by the first stimulus was negatively correlated with the CMAP decrement in ulnar but not accessory nerves. Additionally, a positive decrement was associated with disease progression but not gender, age at onset, disease duration, region of onset, ALSFRS-R scores, or ALS diagnostic subgroup in ALS. Furthermore, the incidence of positive decrements and the decremental percentages were significantly higher in myasthenia gravis (MG) than in ALS. [Conclusions] The lower CMAP amplitude by the first RNS stimulus was more likely to induce a positive decrement in the ulnar nerve in ALS patients. The positive decremental responses to RNS observed in ALS indicate the faster progress of the disease, which is helpful for evaluating prognoses.

Repetitive nerve stimulation as a diagnostic aid for distinguishing cervical spondylotic amyotrophy from amyotrophic lateral sclerosis

PURPOSE

To identify and compare the features of compound muscle action potential (CMAP) decrements in repetitive nerve stimulation (RNS) in patients with cervical spondylotic amyotrophy (CSA) and in patients with amyotrophic lateral sclerosis (ALS).

METHODS

The cohort consisted of 43 CSA (distal-type to proximal-type ratio: 27-16) and 35 ALS patients. Five muscles, including abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), middle deltoid (Del), and upper trapezius (Trap), were tested by 3-Hz RNS. Decrements greater than cutoff values (APB > 5.8%; ADM > 4.8%; BB > 5.2%; Del > 6%; Trap > 5.1%) determined using receiver operating characteristic (ROC) curves were defined as abnormal, and the conventional criterion (≥10%) was also considered.

RESULTS

A significant CMAP decrement (>cutoff values) was recorded from at least one tested muscle in 91.4% of ALS patients, and was most common in the proximal muscle, a finding that differed significantly from CSA patients (32.6%, P < 0.05). The application of cutoff values greatly improved the sensitivity of RNS over the conventional criterion (≥10%) for the detection of ALS (P < 0.05). The specificity of this technique remained higher when performing RNS in the proximal muscles, especially in the upper trapezius (AUC = 0.864, sensitivity = 0.643, and specificity = 1.000). The decrement percentages were significantly greater in the proximal muscles of ALS patients than in those of the CSA patients (P < 0.05). In addition, illness duration was not correlated with decrement percentage in either patient group, and no difference in the frequency of decrement among different ALS diagnostic categories was observed (P > 0.05).

CONCLUSIONS

The application of RNS, especially in proximal muscles, may provide a simple accurate and noninvasive supplementary test for distinguishing CSA from ALS, even in the early stage of these diseases. A combination of RNS, needle EMG, clinical features and cervical magnetic resonance imaging may yield sufficient diagnostic information to differentiate CSA and ALS.

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.

Repetitive Facial Nerve Stimulation Using Occipitalis Muscle

PURPOSE

We aimed to evaluate the reliability and reproducibility of repetitive nerve stimulation recorded on occipitalis muscle by comparing recordings on nasalis muscle in healthy subjects.

METHODS

A total of 23 healthy subjects (mean age: 44.7 ± 13.8 years) underwent detailed neurological examination and repetitive nerve stimulation using nasalis and occipitalis muscles. Amplitude and area percentage changes of compound muscle action potentials (CMAPs) after repetitive nerve stimulation with different frequency were compared between right and left sides and between recordings on nasalis and occipitalis muscles.

RESULTS

Comparisons of percentage amplitude changes of nasalis and occipitalis CMAPs showed no differences (+0.1% ± 3.8% vs. +1.4% ± 3.9%, P = 0.129). Average area percentage change of nasalis CMAPs was 0.3% ± 19.0%, whereas the value of occipitalis CMAP was +2.8% ± 15.2% (P = 0.851). Comparisons of nasalis and occipitalis CMAPs values showed no differences.

CONCLUSIONS

The repetitive nerve stimulation recorded on occipitalis muscle is simple, easy to apply, noninvasive, consistent, and reproducible.