MG and LEMS overlap syndrome: case report with electrophysiological and immunological evidence

Simulations of active zone structure and function at mammalian NMJs predict that loss of calcium channels alone is not sufficient to replicate LEMS effects

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune-mediated neuromuscular disease thought to be caused by autoantibodies against P/Q-type voltage-gated calcium channels (VGCCs), which attack and reduce the number of VGCCs within transmitter release sites (active zones; AZs) at the neuromuscular junction (NMJ), resulting in neuromuscular weakness. However, patients with LEMS also have antibodies to other neuronal proteins, and about 15% of patients with LEMS are seronegative for antibodies against VGCCs. We hypothesized that a reduction in the number of P/Q-type VGCCs alone is not sufficient to explain LEMS effects on transmitter release. Here, we used a computational model to study a variety of LEMS-mediated effects on AZ organization and transmitter release constrained by electron microscopic, pharmacological, immunohistochemical, voltage imaging, and electrophysiological observations. We show that models of healthy AZs can be modified to predict the transmitter release and short-term facilitation characteristics of LEMS and that in addition to a decrease in the number of AZ VGCCs, disruption in the organization of AZ proteins, a reduction in AZ number, a reduction in the amount of synaptotagmin, and the compensatory expression of L-type channels outside the remaining AZs are important contributors to LEMS-mediated effects on transmitter release. Furthermore, our models predict that antibody-mediated removal of synaptotagmin in combination with disruption in AZ organization alone could mimic LEMS effects without the removal of VGCCs (a seronegative model). Overall, our results suggest that LEMS pathophysiology may be caused by a collection of pathological alterations to AZs at the NMJ, rather than by a simple loss of VGCCs.NEW & NOTEWORTHY We used a computational model of the active zone (AZ) in the mammalian neuromuscular junction to investigate Lambert-Eaton myasthenic syndrome (LEMS) pathophysiology. This model suggests that disruptions in presynaptic active zone organization and protein content (particularly synaptotagmin), beyond the simple removal of presynaptic calcium channels, play an important role in LEMS pathophysiology.

Long-Standing Lambert–Eaton Myasthenic Syndrome Caused by Undetectable Small-Cell Lung Cancer: Why We Should Follow-Up LEMS

Physicians often encounter patients with unexplained muscle weakness and dysphagia. Lambert–Eaton myasthenic syndrome (LEMS) can cause unexplained weakness or dysphagia and is often accompanied by neoplastic conditions. A 64-year-old man who had several risk factors—14 kg weight loss over the last 4 years, 20 years of experience working as a coal miner, and being a 50 pack-year ex-smoker—complained of dysphagia, intermittent diplopia, mild weakness, and hypotonia. The initial computed tomography (CT) and follow-up positron emission tomography (PET) CT did not reveal any malignancy. After continuous follow-up for this LEMS, small-cell lung cancer (SCLC, cTxN1M0) was found on a serial follow-up chest CT 21 months after the LEMS diagnosis. The patient was treated with chemotherapy. LEMS is rare and is often accompanied by malignancy. This case highlights the importance of being concerned about LEMS diagnoses and of long-term follow-up for unexplained LEMS.

Stimulated single-fiber electromyography (sSFEMG) in Lambert-Eaton syndrome

Objective

To report the clinical features and the neurophysiological approach of a patient with Lambert-Eaton myasthenic syndrome (LEMS), highlighting the diagnostic role of the stimulated single fiber electromyography (sSFEMG).

Case report

A 60-year-old woman presenting with the LEMS triad (proximal and axial weakness, autonomic dysfunction and areflexia) was evaluated by neurophysiological tests (electroneuromyography, repetitive stimulation test (TSR), voluntary and stimulated SFEMG). We reported: 1) increase of compound muscle action potential (CMAP) amplitude (>60%) following brief isometric exercise compared to the rest (baseline); 2) decremental/incremental response of CMAP amplitude at low- (3 Hz) and high-frequency (30 Hz) repetitive stimulation test (RST), respectively; 3) increased neuromuscular jitter and blocking at voluntary single-fiber electromyography (vSFEMG); 4) stimulation rate-dependent reduction of the neuromuscular jitter and blocking at sSFEMG. Diagnosis was confirmed by serological demonstration of circulating voltage gated calcium channels (VGCC) antibodies.

Significance

The present case highlights the role of the sSFEMG in the diagnosis of LEMS, underling the stimulation rate-dependency of both neuromuscular jitter and blocks.

Lambert-Eaton myasthenic syndrome with anti-acetylcholine receptor antibody and anterior mediastinal tumor

This report describes the case of a 65-year-old male who complained of muscular weakness of the legs with easy fatigability. Blood and imaging examinations showed positive anti-acetylcholine receptor antibody and an anterior mediastinal tumor (probably a thymic cyst), suggesting the diagnosis of myasthenia gravis (MG). However, neurological and electrophysiological examinations suggested the diagnosis of Lambert-Eaton myasthenic syndrome (LEMS). We searched repeatedly for malignant tumors. Small cell lung cancer (SCLC) was found. Chemotherapy reduced the SCLC and improved the patient's clinical symptoms. On the basis of an accurate diagnosis of LEMS, we were able to detect SCLC and administer chemotherapy at an early stage. Anti-P/Q-type voltage-gated calcium channel antibody was negative. In our case, MG and LEMS overlap syndrome in addition to MG should be differentiated. For the differentiation, the strict electrophysiological criteria of LEMS were useful.

[Seronegative nonparaneoplastic Lambert-Eaton myasthenic syndrome]

The authors studied two patients with Lambert-Eaton myasthenic syndrome (LEMS) in whom the repeated examination did not find specific of LEMS P/Q type voltage-gates calcium channel autoantibodies. The results of clinical testing and electrophysiological examination showed the typical character of movement disorders with the absence of tendon reflexes and signs of disautonomia as well as a decrease in M-response amplitude and phenomena of decrement with low frequency- and increment with high frequency stimulation. Both patients revealed no signs of paraneoplastic process. Autoimmune character of the damage was confirmed by the effectiveness of treatment with glucocorticoid hormones.

Clinical Features of Neuromuscular Disorders in Patients with N-Type Voltage-Gated Calcium Channel Antibodies

Neuromuscular junction disorders affect the pre- or postsynaptic nerve to muscle transmission due to autoimmune antibodies. Members of the group like myasthenia gravis and Lambert-Eaton syndrome have pathophysiologically distinct characteristics. However, in practice, distinction may be difficult. We present a series of three patients with a myasthenic syndrome, dropped-head syndrome, bulbar and respiratory muscle weakness and positive testing for anti-N-type voltage-gated calcium channel antibodies. In two cases anti-acetylcholin receptor antibodies were elevated, anti-P/Q-type voltage-gated calcium channel antibodies were negative. All patients initially responded to pyridostigmine with a non-response in the course of the disease. While one patient recovered well after treatment with intravenous immunoglobulins, 3,4-diaminopyridine, steroids and later on immunosuppression with mycophenolate mofetil, a second died after restriction of treatment due to unfavorable cancer diagnosis, the third patient declined treatment. Although new antibodies causing neuromuscular disorders were discovered, clinical distinction has not yet been made. Our patients showed features of pre- and postsynaptic myasthenic syndrome as well as severe dropped-head syndrome and bulbar and axial muscle weakness, but only anti-N-type voltage-gated calcium channel antibodies were positive. When administered, one patient benefited from 3,4-diaminopyridine. We suggest that this overlap-syndrome should be considered especially in patients with assumed seronegative myasthenia gravis and lack of improvement under standard therapy.

Mapping autoantigen epitopes: molecular insights into autoantibody-associated disorders of the nervous system

BACKGROUND

Our knowledge of autoantibody-associated diseases of the central (CNS) and peripheral (PNS) nervous systems has expanded greatly over the recent years. A number of extracellular and intracellular autoantigens have been identified, and there is no doubt that this field will continue to expand as more autoantigens are discovered as a result of improved clinical awareness and methodological practice. In recent years, interest has shifted to uncover the target epitopes of these autoantibodies.

MAIN BODY

The purpose of this review is to discuss the mapping of the epitope targets of autoantibodies in CNS and PNS antibody-mediated disorders, such as N-methyl-D-aspartate receptor (NMDAR), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), leucine-rich glioma-inactivated protein 1 (Lgi1), contactin-associated protein-like 2 (Caspr2), myelin oligodendrocyte glycoprotein (MOG), aquaporin-4 (AQP4), 65 kDa glutamic acid decarboxylase (GAD65), acetylcholine receptor (AChR), muscle-specific kinase (MuSK), voltage-gated calcium channel (VGCC), neurofascin (NF), and contactin. We also address the methods used to analyze these epitopes, the relevance of their determination, and how this knowledge can inform studies on autoantibody pathogenicity. Furthermore, we discuss triggers of autoimmunity, such as molecular mimicry, ectopic antigen expression, epitope spreading, and potential mechanisms for the rising number of double autoantibody-positive patients.

CONCLUSIONS

Molecular insights into specificity and role of autoantibodies will likely improve diagnosis and treatment of CNS and PNS neuroimmune diseases.

Myasthenia gravis Lambert-Eaton overlap syndrome

INTRODUCTION

To assess whether a myasthenia gravis (MG) Lambert-Eaton overlap syndrome (MLOS) exists.

METHODS

Case reports that met the universally accepted diagnostic criteria for MG and Lambert-Eaton myasthenic syndrome (LEMS) were sought through a PubMed search. Fifty-five possible cases of MLOS were identified.

RESULTS

Thirty-nine cases met the diagnostic criteria for MG and LEMS. Analysis of clinical features showed that these patients have common MG and LEMS symptoms: oculo-bulbar paresis and good response to anti-cholinesterase for MG and limb weakness and decreased or absent reflexes for LEMS. All had the classical LEMS pattern in the repetitive nerve stimulation test: low compound muscle action potential amplitude and incremental response > 60% with brief exercise or at high rate of stimulation. Eight patients had combined positive acetylcholine receptor antibody (AChR-ab) or muscle-specific kinase-ab and voltage-gated calcium channel- ab tests.

CONCLUSIONS

A myasthenia gravis Lambert-Eaton overlap syndrome (MLOS) does exist.

Overview of myasthenia gravis

Myasthenia gravis is an antibody-mediated disorder of neuromuscular transmission that is characterized by weakness and fatigue of voluntary muscles. Weakness may be ocular, bulbar, or generalized. Diagnostic evaluation of patients consists of bedside assessment, antibody testing, and electrophysiologic studies. Various therapeutic options are available, which consist of anticholinesterase inhibitors for symptomatic management, immunosuppressive agents as maintenance therapy, and thymectomy. Plasmapheresis and intravenous immunoglobulin are used in patients in crisis or those with rapidly worsening or refractory symptoms. In our article, we elaborate on key aspects of the epidemiology, pathogenesis, diagnostic evaluation, and therapeutic options for patients with myasthenia gravis.

A case of lambert-eaton myasthenic syndrome with small-cell lung cancer and transient increase in anti-acetylcholine-receptor-binding antibody titer

BACKGROUND

Lambert-Eaton myasthenic syndrome (LEMS) is a presynaptic neuromuscular junction disorder that is most frequently associated with small-cell lung cancer (SCLC). The titers of antibodies against voltage-gated calcium channels are frequently increased in LEMS, but only rarely is titer of anti-acetylcholine-receptor-binding antibodies (AChR-abs) increased.

CASE REPORT

A 57-year-old male was admitted to our hospital due to dry mouth and eyes and progressive proximal limb weakness of 2 months duration. The results of a repetitive nerve stimulation test disclosed all criteria for the electrophysiological LEMS pattern, and the patient's AChR-abs titer was 0.587 nmol/L. At a follow-up performed 5 years after successful treatment of SCLC and LEMS, his AChR-abs titer had decreased to 0.001 nmol/L.

CONCLUSIONS

We suggest that this was a case of transient pseudopositivity of AChR-abs in SCLC with LEMS.

A patient with coexisting myasthenia gravis and lambert-eaton myasthenic syndrome

Background

The coexistence of myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) is very rare and remains controversial.

Case Report

A 48-year-old woman initially presented with noticeable right ptosis and intermittent diplopia. She then developed fluctuating proximal limb weakness and difficulty in swallowing. The serum titer of anti-acetylcholine-receptor antibody was elevated and the edrophonium (Tensilon) test was positive. However, repetitive nerve stimulation revealed abnormalities typical of LEMS. The patient exhibited a good response to treatment with anticholinesterase inhibitors and steroids, and long-term evaluation disclosed that she presented with the clinical, electrophysiological, and immunological characteristics of both diseases.

Conclusions

The reported clinical and electrophysiological features suggest that this patient was a very rare case of combined MG and LEMS.

An interesting collection of paraneoplastic syndromes in a patient with a malignant thymoma

Paraneoplastic neurological syndromes are conditions that manifest as the remote effects of cancer. These are very rare, occurring in 1/10000 patients with a malignancy, and include Lambert-Eaton myasthenic syndrome, limbic encephalitis, subacute cerebellar ataxia, opsoclonus-myoclonus, Stiff-Person Syndrome, retinopathies, chronic gastrointestinal pseudo-obstruction and sensory neuropathy. This report describes a case of 41-year-old man who presented with elements of multiple paraneoplastic syndromes, including chronic gastrointestinal pseudo-obstruction, myasthenia gravis-Lambert-Eaton overlap syndrome and polymyositis, and who was subsequently found to have a malignant thymoma. There are only three reported cases in the literature describing cases of Lambert-Eaton myasthenic syndrome in association with a thymoma, and only one case of a myasthenia gravis-Lambert-Eaton overlap syndrome in a patient with thymoma. However, there are no documented cases in the literature of this constellation of syndromes in a patient with a malignant thymoma.

Severe, focal tibialis anterior and triceps brachii weakness in myasthenia gravis: a case report

We report a case of a patient with myasthenia gravis who presented with an atypically focal distribution of severe weakness in the triceps brachii and tibialis anterior muscles. Repetitive nerve stimulation studies demonstrated the typical decrement at rest, but also demonstrated marked facilitation after brief exercise. This case adds to the clinical and electrophysiological spectrum of variations of presentation of myasthenia gravis.

Paraneoplastic syndromes: an approach to diagnosis and treatment

Recent medical advances have improved the understanding, diagnosis, and treatment of paraneoplastic syndromes. These disorders arise from tumor secretion of hormones, peptides, or cytokines or from immune cross-reactivity between malignant and normal tissues. Paraneoplastic syndromes may affect diverse organ systems, most notably the endocrine, neurologic, dermatologic, rheumatologic, and hematologic systems. The most commonly associated malignancies include small cell lung cancer, breast cancer, gynecologic tumors, and hematologic malignancies. In some instances, the timely diagnosis of these conditions may lead to detection of an otherwise clinically occult tumor at an early and highly treatable stage. Because paraneoplastic syndromes often cause considerable morbidity, effective treatment can improve patient quality of life, enhance the delivery of cancer therapy, and prolong survival. Treatments include addressing the underlying malignancy, immunosuppression (for neurologic, dermatologic, and rheumatologic paraneoplastic syndromes), and correction of electrolyte and hormonal derangements (for endocrine paraneoplastic syndromes). This review focuses on the diagnosis and treatment of paraneoplastic syndromes, with emphasis on those most frequently encountered clinically. Initial literature searches for this review were conducted using PubMed and the keyword paraneoplastic in conjunction with keywords such as malignancy, SIADH, and limbic encephalitis, depending on the particular topic. Date limitations typically were not used, but preference was given to recent articles when possible.

Myasthenia gravis with presynaptic electrophysiologic abnormalities

OBJECTIVES

To describe the clinical, serologic, and electrophysiologic features of 2 patients with myasthenia gravis (MG), who also had presynaptic electrophysiologic abnormalities.

METHODS

Case reports.

RESULTS

Two patients developed clinical symptoms consistent with MG. They lacked autonomic symptoms or signs, and their reflexes were not absent. Acetylcholine receptor antibody studies were positive, but assays for voltage-gated calcium channel antibodies were negative. Low-amplitude baseline compound muscle action potentials combined with large incremental responses immediately after exercise were consistent with a presynaptic disorder. Thymic pathology in 1 patient was characteristic of autoimmune MG showing lymphoid follicular hyperplasia. No underlying malignancy was found in either patient.

CONCLUSIONS

Patients with MG may rarely have presynaptic electrophysiologic abnormalities. This may occur even in the absence of the typical clinical and serologic features of the Lambert-Eaton syndrome. It is possible that there is another antibody present that is modulating presynaptic acetylcholine release.

Lambert-Eaton myasthenic syndrome in childhood

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder of the neuromuscular junction. LEMS can be associated with a variety of neoplasms. Patients present with proximal muscle weakness and fatigability, often combined with areflexia. Only 5% of reported cases are children. We report a case of 11-year old boy with non-neoplastic Lambert-Eaton myasthenic syndrome. Repetitive nerve stimulation test showed 83% increment after maximal voluntary contraction, presence of antibodies against voltage-gated calcium channels confirmed the diagnosis. The boy responded well to immunosuppressive treatment with prednisone and azathioprine and remains cancer-free for 4 years.

Myasthenia gravis and Lambert–Eaton myasthenic syndrome in the same patient

An 18-year-old-woman developed symptoms of generalized myasthenia gravis (MG). Antibodies to the acetylcholine receptor were found in her serum, but electrodiagnostic testing showed abnormalities typical of the Lambert-Eaton myasthenic syndrome (LEMS). Following thymectomy, the thymus gland showed thymic hyperplasia typical of MG, and the patient responded to treatment with 3,4-diaminopyridine and pyridostigmine. There have been few reports in the literature of MG and LEMS coexisting in the same patient. In this case, electrodiagnostic tests, antibody studies, thymus pathology, and response to treatment suggest that both disorders contributed to the patient's symptoms. Thymic hyperplasia, so far only known to be associated with MG, provides strong evidence that both diseases were symptomatic.

A Diagnostic and Management Dilemma

BACKGROUND

Neuromuscular junction disorders are usually categorized as either presynaptic or postsynaptic. The most frequently encountered disorder of the postsynaptic neuromuscular junction is acquired myasthenia gravis. Lambert-Eaton myasthenic syndrome is a well-known prototype of the presynaptic autoimmune disorders of neuromuscular transmission. These major disorders of neuromuscular transmission are relatively common and distinctly recognized, but co-occurrence of these disorders (overlap myasthenic syndrome) is rare and has so far attracted little attention.

REVIEW SUMMARY

This report describes a patient with acquired myasthenia gravis and immunologic coexistence of Lambert-Eaton myasthenic syndrome (overlap myasthenic syndrome) in association with abdominal/uterine leiomyosarcoma. The patient presented with acute respiratory failure, making identification and management of her illness challenging. A general overview of the complexities associated with overlap between myasthenia gravis and Lambert-Eaton myasthenic syndrome is provided and this patient's complicated clinical course and response to therapy are discussed.

CONCLUSION

To our knowledge, this is the first report of overlap myasthenic syndrome in conjunction with abdominal leiomyosarcoma. The immunologic coexistence of acquired myasthenia gravis and Lambert-Eaton myasthenic syndrome in a patient with a malignant smooth-muscle tumor is intriguing and suggests that a common paraneoplastic process targeting 2 different onconeural antigens was the underlying pathogenic mechanism in this patient.

Electrophysiological diagnostic criteria of Lambert-Eaton myasthenic syndrome

Various parameters of the repetitive nerve stimulation (RNS) test of the abductor digiti quinti muscle were analyzed statistically in 34 patients with Lambert-Eaton myasthenic syndrome (LEMS). The sensitivity and specificity of the increments after exercise and after 50-HZ stimulation for the diagnosis of LEMS were compared with reference values in 40 normal subjects and data from 538 tests in patients with myasthenia gravis (MG). When we used a 100% increment (the "gold standard") as the normal limit for the postexercise facilitation (PEF) or the high-rate stimulation (HRS) test, the diagnosis of LEMS was confirmed in 29 (85%) cases. When a 60% increment was used as the normal limit, the diagnosis of LEMS was made in 97% of cases. In MG, a 60% increment was observed in only 4 of 538 cases by HRS and in none by the exercise test. Thus, the use of a 60% increment showed a sensitivity of 97% for the diagnosis of LEMS and a specificity of 99% in excluding MG. A 60% increment in either the PEF or HRS test for the diagnosis of LEMS is a desirable alternative to the 100% increment previously considered to be the gold standard for this diagnosis.