Bedside and laboratory diagnostic testing in myasthenia

Immune Checkpoint Inhibitor Myopathy: The Double-Edged Sword of Cancer Immunotherapy

Immune checkpoint inhibitor (ICI) therapy has revolutionized the treatment of several malignancies, with improved survival. These monoclonal antibodies target immune checkpoints, including cytotoxic T-lymphocyte-associated protein 4 (ipilimumab and tremelimumab), programmed death 1 (nivolumab, pembrolizumab, cemiplimab, and dostarlimab), programmed death ligand 1 (atezolizumab, avelumab, and durvalumab), and lymphocyte activation gene 3 (relatlimab), and effectively augment the immune response against tumor cells. Releasing the brakes on the immune system has consequences, however, in the form of immune-related adverse events (irAEs), which may affect any organ. Neurologic irAEs represent 1%-3% of all irAEs, with immune-mediated myopathy (ICI myopathy) being the most common manifestation. Recent large patient series and systematic reviews have established the key features and highlighted new insights into ICI myopathy. ICI myopathy is characterized by an acute or subacute onset of oculobulbar and/or proximal limb weakness, with or without associated respiratory insufficiency and myocarditis. Creatine kinase elevation is common. Oculobulbar presentations with or without respiratory failure may be misattributed to neuromuscular junction disorders, particularly because acetylcholine receptor antibodies are present in up to 40% of patients; however, an electrodiagnostic evidence of a defect of neuromuscular transmission is often absent even in patients with severe weakness, highlighting that the myopathic process is the driving force behind these presentations. Muscle histopathology commonly demonstrates a unique signature of multifocal clusters of necrotic and regenerating fibers, differentiating ICI myopathy from other autoimmune myopathies. Transcriptomic analysis has uncovered distinct subgroups within ICI myopathy, revealing varying degrees of type 1 and type 2 interferon pathway activation alongside notable upregulation of the interleukin (IL)-6 pathway in affected muscle tissue. This discovery presents a promising avenue for intervention through the use of therapies that suppress the interferon pathway and target IL-6 or its receptor. Despite clinical improvements with immunomodulatory therapy, with corticosteroids the mainstay of treatment, mortality remains high, particularly in those with associated myocarditis or respiratory failure requiring intubation, where mortality occurs in up to 50%. ICI withdrawal can lead to cancer progression and death, highlighting a need for improved approaches to ICI rechallenge, performed in limited patients with variable success to date.

The changing landscape of autoantibody testing in myasthenia gravis in the setting of novel drug treatments

Acquired myasthenia gravis (MG) is an autoimmune disease targeting the specific proteins in the postsynaptic muscle membrane. 50% of ocular and 80% of generalized MG have acetylcholine receptor antibodies (AChR Abs). 1-10% of MG patients have antibodies against muscle-specific kinase (MuSK), and 2-50 % of seronegative MG cases have antibodies against lipoprotein-receptor-related protein4 antibodies (LRP4 Abs). Serological testing is crucial for diagnosing and determining the appropriate therapeutic approach for MG patients. The radioimmunoprecipitation assay (RIPA) method is a historical standard test for detecting the AChR Abs and MuSK Abs. While it has nearly 100% specificity in the AChR Abs detection, its sensitivity is between 50--92%. The sensitivity and specificity of RIPA for detecting MuSK Abs is much lower. The fixed and live Cell-Based assays (f-CBA and L- CBA) have higher sensitivity than RIPA. With advancements in the serological diagnosis and management of MG, we now recommend a complete reflex testing algorithm on the first pretreatment sample of a suspected MG patient, starting with the binding and blocking assays for AChR Abs by RIPA and/ or f-CBA. If AChR Ab is negative, then reflex to MuSK Abs by RIPA and/ or CBAs. If AChR and MuSK Abs are negative, then use clustered L-CBA by request.

Neuromuscular junction disorders: mimics and chameleons

Neuromuscular junction (NMJ) disorders represent a heterogenous group of acquired and congenital disorders that present in variable and distinctive ways. The diagnosis is typically reached through a combination of clinical, serological, pharmacological and electrophysiological evaluation. While the diagnosis can be fairly straightforward in some cases, the overlap with other neurological disorders can make diagnosis challenging, particularly in pure ocular presentations and in seronegative patients. The over-reliance on serological tests and electrophysiological evaluation in isolation can lead to misdiagnosis. In this article, we provide an overview of the NMJ disorders, discuss red flags for the key differential diagnoses (mimics) and report the atypical ways in which NMJ disorders may present (chameleons).

Non-coding RNA and its network in the pathogenesis of Myasthenia Gravis

Myasthenia Gravis (MG) is a chronic autoimmune disease that primarily affects the neuromuscular junction, leading to muscle weakness in patients with this condition. Previous studies have identified several dysfunctions in thymus and peripheral blood mononuclear cells (PBMCs), such as the formation of ectopic germinal centers in the thymus and an imbalance of peripheral T helper cells and regulatory T cells, that contribute to the initiation and development of MG. Recent evidences suggest that noncoding RNA, including miRNA, lncRNA and circRNA may play a significant role in MG progression. Additionally, the network between these noncoding RNAs, such as the competing endogenous RNA regulatory network, has been found to be involved in MG progression. In this review, we summarized the roles of miRNA, lncRNA, and circRNA, highlighted their potential application as biomarkers in diagnosing MG, and discussed their potential regulatory networks in the abnormal thymus and PBMCs during MG development.

Pitfalls in the Evaluation of Respiratory Failure in Myasthenia Gravis Patients: A Case Series

Objectives

To highlight the importance of recognizing different presentations of respiratory failure due to myasthenic and non-myasthenic etiologies in myasthenia gravis (MG) patients.

Methods

We describe 3 patients with different presentations of respiratory failure in MG.

Cases

Patient 1 is a 49-year-old female with longstanding MG who presented with lethargy and neck weakness without notable respiratory distress. She was found to be in hypercarbic respiratory failure, which improved with plasmapheresis treatment. Patient 2 is a 58-year-old female who presented with ptosis, dysphagia, and dyspnea requiring intubation. Her hypophonia and dyspnea persisted despite escalation in MG treatment, and further workup revealed glottal stenosis secondary to granulomatosis with polyangiitis. Patient 3 is an 85-year-old female with MG presenting with refractory hypoxia, which was secondary to a large patent foramen ovale resulting in right-to-left shunting.

Discussion

All 3 cases emphasize the role of clinical reasoning and careful analysis based on thorough history taking, detailed neurologic exam and comprehensive laboratory findings to determine the etiologies for respiratory dysfunction in MG and provide appropriate treatment.

Conclusion

A lack of overt signs of respiratory distress in MG does not rule out the presence of respiratory failure due to the sedating effect of hypercapnia. There is a need to consider alternative etiologies of hypoxia in MG patients if typical symptoms or signs of MG exacerbations are absent.

Paraneoplastic neurological syndromes of small cell lung cancer

Purpose

This article reviews the relevant literature on paraneoplastic neurological syndromes of small cell lung cancer and discusses the clinical presentation, pathophysiology, and diagnosis of these syndromes. It also includes a summary of the current treatment options for the management of them.

Views

Paraneoplastic syndromes are a group of signs and symptoms that develop due to cancer in a remote site, mainly triggered by an autoantibody produced by the tissues involved or lymphocytes during anti-cancer defense. Among the cancers associated with paraneoplastic syndromes, lung cancers are the most common type, with small cell lung cancer being the most common subtype. The most common antibody associated with paraneoplastic syndromes is anti-Hu. Neurological and neuroendocrine syndromes comprise the majority of small cell lung cancer-related paraneoplastic syndromes. Classical paraneoplastic neurological syndromes include inappropriate antidiuretic hormone secretion, Cushing's syndrome, myasthenia gravis, Lambert-Eaton myasthenic syndrome, limbic encephalitis, paraneoplastic cerebellar degeneration, opsoclonus myoclonus ataxia, sensory neuropathy, and chorea.

Conclusions

Antibodies mediate paraneoplastic syndromes, and antibody detection is a crucial part of diagnosing these entities. Managing the underlying tumor is the best treatment approach for most paraneoplastic syndromes. Therefore, early diagnosis of small cell lung cancer may significantly improve the prognosis of paraneoplastic syndromes associated with it.

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.

MuSK Myasthenia Gravis-Potential Pathomechanisms and Treatment Directed against Specific Targets

Myasthenia gravis (MG) is an autoimmune disease in which autoantibodies target structures within the neuromuscular junction, affecting neuromuscular transmission. Muscle-specific tyrosine kinase receptor-associated MG (MuSK-MG) is a rare, often more severe, subtype of the disease with different pathogenesis and specific clinical features. It is characterized by a more severe clinical course, more frequent complications, and often inadequate response to treatment. Here, we review the current state of knowledge about potential pathomechanisms of the MuSK-MG and their therapeutic implications as well as ongoing research in this field, with reference to key points of immune-mediated processes involved in the background of myasthenia gravis.

Immunosensors for Autoimmune-Disease-Related Biomarkers: A Literature Review

Immunosensors are a special class of biosensors that employ specific antibodies for biorecognition of the target analyte. Immunosensors that target disease biomarkers may be exploited as tools for disease diagnosis and/or follow-up, offering several advantages over conventional analytical techniques, such as rapid and easy analysis of patients' samples at the point-of-care. Autoimmune diseases have been increasingly prevalent worldwide in recent years, while the COVID-19 pandemic has also been associated with autoimmunity. Consequently, demand for tools enabling the early and reliable diagnosis of autoimmune diseases is expected to increase in the near future. To this end, interest in immunosensors targeting autoimmune disease biomarkers, mainly, various autoantibodies and specific pro-inflammatory proteins (e.g., specific cytokines), has been rekindled. This review article presents most of the immunosensors proposed to date as potential tools for the diagnosis of various autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis, and multiple sclerosis. The signal transduction and the immunoassay principles of each immunosensor have been suitably classified and are briefly presented along with certain sensor elements, e.g., special nano-sized materials used in the construction of the immunosensing surface. The main concluding remarks are presented and future perspectives of the field are also briefly discussed.

Oculomotor fatigability with decrements of saccade and smooth pursuit for diagnosis of myasthenia gravis

BACKGROUND AND OBJECTIVES

As the efficacy of current diagnostic methods for myasthenia gravis (MG) remains suboptimal, there is ongoing interest in developing more effective diagnostic models. As oculomotor fatigability is one of the most common and diagnostic symptoms in MG, we aimed to investigate whether quantitative saccadic and smooth-pursuit fatigability analyses with video-oculography (VOG) are useful for diagnosis of MG.

METHODS

A convenience cohort of 46 MG patients was recruited prospectively, including 35 with ocular and 11 with generalized MG (mean age, 50.9 ± 14.5 years; 17 females); 24 healthy controls (HCs) (mean age, 50.6 ± 16.3 years; 13 females) also were enrolled. Seventy-five repetitive saccades and smooth pursuits were recorded in ranges of 20° (horizontal plane) and 15° (vertical plane) using a three-dimensional VOG system. Based on the oculomotor range of the second saccade and smooth pursuit and the mean ranges of the last five of each, the estimated decrements (%) reflecting oculomotor fatigability were calculated.

RESULTS

The baseline oculomotor ranges did not show significant difference between the MG and HCs groups. However, following repetitive saccades and pursuits, the oculomotor ranges were decreased substantially during the last five cycles compared to baseline in the MG group. No such decrements were observed in the HC group (p < 0.01, Mann-Whitney U test). Receiver operating characteristic (ROC) analysis revealed that repetitive vertical saccades yielded the best differentiation between the MG and HC groups, with a sensitivity of 78.3% and specificity of 95.8% when using a decrement with an amplitude of 6.4% as the cutoff.

CONCLUSION

This study presents an objective and reproducible method for measuring decrements of oculomotor ranges after repetitive saccadic and pursuit movements. Quantification of oculomotor fatigability using VOG could be a sensitive and specific diagnostic tool for MG and allows easy, cost-effective, accurate, and non-invasive measurements.

CLASSIFICATION OF EVIDENCE

This study provides class III evidence that VOG-based quantification of saccadic and pursuit fatigability accurately identifies patients with MG.

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.

Development and Assessment of an Artificial Intelligence-Based Tool for Ptosis Measurement in Adult Myasthenia Gravis Patients Using Selfie Video Clips Recorded on Smartphones

Introduction

Myasthenia gravis (MG) is a rare autoimmune disease characterized by muscle weakness and fatigue. Ptosis (eyelid drooping) occurs due to fatigue of the muscles for eyelid elevation and is one symptom widely used by patients and healthcare providers to track progression of the disease. Margin reflex distance 1 (MRD1) is an accepted clinical measure of ptosis and is typically assessed using a hand-held ruler. In this work, we develop an AI model that enables automated measurement of MRD1 in self-recorded video clips collected using patient smartphones.

Methods

A 3-month prospective observational study collected a dataset of video clips from patients with MG. Study participants were asked to perform an eyelid fatigability exercise to elicit ptosis while filming "selfie" videos on their smartphones. These images were collected in nonclinical settings, with no in-person training. The dataset was annotated by non-clinicians for (1) eye landmarks to establish ground truth MRD1 and (2) the quality of the video frames. The ground truth MRD1 (in millimeters, mm) was calculated from eye landmark annotations in the video frames using a standard conversion factor, the horizontal visible iris diameter of the human eye. To develop the model, we trained a neural network for eye landmark detection consisting of a ResNet50 backbone plus two dense layers of 78 dimensions on publicly available datasets. Only the ResNet50 backbone was used, discarding the last two layers. The embeddings from the ResNet50 were used as features for a support vector regressor (SVR) using a linear kernel, for regression to MRD1, in mm. The SVR was trained on data collected remotely from MG patients in the prospective study, split into training and development folds. The model's performance for MRD1 estimation was evaluated on a separate test fold from the study dataset.

Results

On the full test fold (N = 664 images), the correlation between the ground truth and predicted MRD1 values was strong (r = 0.732). The mean absolute error was 0.822 mm; the mean of differences was -0.256 mm; and 95% limits of agreement (LOA) were -0.214-1.768 mm. Model performance showed no improvement when test data were gated to exclude "poor" quality images.

Conclusions

On data generated under highly challenging real-world conditions from a variety of different smartphone devices, the model predicts MRD1 with a strong correlation (r = 0.732) between ground truth and predicted MRD1.

Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome: New Developments in Diagnosis and Treatment

"Myasthenia Gravis is, like it or not, the neurologist's disease!" (Thomas Richards Johns II, MD Seminars in Neurology 1982). The most common disorders in clinical practice involving defective neuromuscular transmission are myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS). The hallmark of weakness related to malfunction of the neuromuscular junction (NMJ) is variability in severity of symptoms from minute to minute and hour to hour. Fatigable weakness and fluctuation in symptoms are common in patients whether the etiology is autoimmune, paraneoplastic, genetic, or toxic. Autoimmune MG is the most common disorder of neuromuscular transmission affecting adults with an estimated prevalence of 1 in 10,000. While LEMS is comparatively rare, the unique clinical presentation, the association with cancer, and evolving treatment strategies require the neurologist to be familiar with its presentation, diagnosis, and management. In this paper we provide a summary of the meaningful recent clinical developments in the diagnosis and treatment of both MG and LEMS.