Favorable response to rituximab in a patient with anti-VGCC-positive Lambert-Eaton myasthenic syndrome and cerebellar dysfunction

Management of Paraneoplastic Syndromes in the Era of Immune Checkpoint Inhibitors

OPINION STATEMENT

Our understanding of paraneoplastic neurologic syndromes (PNS) has blossomed over the past few decades. Clinicians have access to more robust diagnostic criteria and have a heightened index of suspicion for these disorders. Nonetheless, treatment, which typically includes immunosuppression, and response to treatment, varies. Due to persistent difficulty in making a definitive diagnosis, we favor empiric treatment when a possible diagnosis of PNS is suspected, and other alternative causes have substantially been excluded (e.g., infections, toxic-metabolic derangements, metastasis, or leptomeningeal disease). Treatment of the underlying cancer, if identified, is the first therapeutic step and can prevent disease worsening and in rare cases, can reverse neurologic symptoms. In addition to anti-cancer treatment, first line immunotherapies, which include corticosteroids, intravenous immunoglobulins (IVIG), or plasma exchange (PLEX) are typically used. If partial or no benefit is seen, second line immunotherapeutic agents such as rituximab are considered. Additionally, the severity of the initial presentation and possible risk for relapse influences the use of the latter agents. Symptomatic management is also an important component in our practice and will depend on the syndrome being treated. One of the more novel entities we are facing currently is the management of immune checkpoint (ICI)-induced PNS. In those cases, current American Society of Clinical Oncology (ASCO) guidelines are followed.

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.

Overview of treatment strategies in paraneoplastic neurological syndromes

Treatment strategies in paraneoplastic neurological syndromes rely on the three pillars of tumor treatment, immunotherapy, and symptomatic treatment, the first one being by far the most important in the majority of patients and syndromes. Classically, antibodies against extracellular antigens are directly pathogenic, and patients with these syndromes are more responsive to immunomodulatory or immunosuppressive treatments than the ones with antibodies against intracellular targets. This chapter first discusses some general principles of tumor treatment and immunotherapy, followed by a closer look at specific treatment options for different clinical syndromes, focusing on symptomatic treatments.

A Breakdown of Immune Tolerance in the Cerebellum

Cerebellar dysfunction can be associated with ataxia, dysarthria, dysmetria, nystagmus and cognitive deficits. While cerebellar dysfunction can be caused by vascular, traumatic, metabolic, genetic, inflammatory, infectious, and neoplastic events, the cerebellum is also a frequent target of autoimmune attacks. The underlying cause for this vulnerability is unclear, but it may be a result of region-specific differences in blood–brain barrier permeability, the high concentration of neurons in the cerebellum and the presence of autoantigens on Purkinje cells. An autoimmune response targeting the cerebellum—or any structure in the CNS—is typically accompanied by an influx of peripheral immune cells to the brain. Under healthy conditions, the brain is protected from the periphery by the blood–brain barrier, blood–CSF barrier, and blood–leptomeningeal barrier. Entry of immune cells to the brain for immune surveillance occurs only at the blood-CSF barrier and is strictly controlled. A breakdown in the barrier permeability allows peripheral immune cells uncontrolled access to the CNS. Often—particularly in infectious diseases—the autoimmune response develops because of molecular mimicry between the trigger and a host protein. In this review, we discuss the immune surveillance of the CNS in health and disease and also discuss specific examples of autoimmunity affecting the cerebellum.

Paraneoplastic neurological syndromes: a practical approach to diagnosis and management

Paraneoplastic neurological syndromes (PNS) are the immune-mediated effects of a remote cancer and are characterised by an autoantibody response against antigens expressed by the tumour. Classically, well-characterised 'onconeuronal' antibodies target intracellular antigens and hence cannot access their antigens across intact cell membranes. The pathogenic mediators are likely to be neuronal-specific T cells. There is a variable response to immunotherapies and the clinical syndrome helps to direct the search for a specific set of tumours. By contrast, many newly emerging autoantibodies with oncological associations target cell surface epitopes and can exert direct pathogenic effects on both the central and peripheral nervous systems. Patients with these cell-surface directed autoantibodies often clearly respond to immunotherapies. Overall, the clinical, serological and oncological features in an individual patient helps determine the clinical relevance of the syndrome and hence guide its management. We summarise current knowledge and a practical approach to the investigation, diagnosis, treatment and outcomes of patients with suspected PNS.

Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome is a paraneoplastic or primary autoimmune neuromuscular junction disorder characterized by proximal weakness, autonomic dysfunction and ariflexia. The characteristic symptoms are thought to be caused by antibodies generated against the P/Q-type voltage-gated calcium channels present on presynaptic nerve terminals and by diminished release of acetylcholine. More than half of Lambert-Eaton myasthenic syndrome cases are associated with small cell lung carcinoma. Diagnosis is confirmed by serologic testing and electrophysiologic studies. 3,4-diaminopyridine is effective symptomatic treatment of LEMS.

Immune-mediated ataxias

Immune-mediated cerebellar ataxia (CA) comprises a group of rare diseases that are still incompletely described, and are probably underdiagnosed. Both acute and progressive progressions are possible. Different syndromes have been identified, including CA associated with anti-GAD antibodies, the cerebellar type of Hashimoto encephalopathy, primary autoimmune CA, gluten ataxia, opsoclonus-myoclonus syndrome, and paraneoplastic cerebellar degenerations. Most of these syndromes are associated with autoantibodies targeting neuronal antigens. Additionally, autoimmune CA can be triggered by infections, especially in children, and in rare cases occur in the context of an autoimmune multisystem disease, such as systemic lupus erythematosus, sarcoidosis, or Behçet disease. A careful workup is needed to distinguish autoimmune CA from other causes. In adults, a paraneoplastic origin must be ruled out, especially in cases with subacute onset. Neurologic outcome in adults is frequently poor, and optimal therapeutic strategies remain ill defined. The outcome in children is in general good, but children with a poor recovery are on record. The precise pathophysiologic mechanisms even in the presence of detectable autoantibodies are still largely unknown. Further research is needed on both the clinical and mechanistic aspects of immune-mediated CA, and to determine optimal therapeutic strategies.

Rituximab therapy in pemphigus and other autoantibody-mediated diseases

Rituximab, a monoclonal antibody targeting the B cell marker CD20, was initially approved in 1997 by the United States Food and Drug Administration (FDA) for the treatment of non-Hodgkin lymphoma. Since that time, rituximab has been FDA-approved for rheumatoid arthritis and vasculitides, such as granulomatosis with polyangiitis and microscopic polyangiitis. Additionally, rituximab has been used off-label in the treatment of numerous other autoimmune diseases, with notable success in pemphigus, an autoantibody-mediated skin blistering disease. The efficacy of rituximab therapy in pemphigus has spurred interest in its potential to treat other autoantibody-mediated diseases. This review summarizes the efficacy of rituximab in pemphigus and examines its off-label use in other select autoantibody-mediated diseases.

Autoimmune channelopathies in paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes and autoimmune encephalitides are immune neurological disorders occurring or not in association with a cancer. They are thought to be due to an autoimmune reaction against neuronal antigens ectopically expressed by the underlying tumour or by cross-reaction with an unknown infectious agent. In some instances, paraneoplastic neurological syndromes and autoimmune encephalitides are related to an antibody-induced dysfunction of ion channels, a situation that can be labelled as autoimmune channelopathies. Such functional alterations of ion channels are caused by the specific fixation of an autoantibody upon its target, implying that autoimmune channelopathies are usually highly responsive to immuno-modulatory treatments. Over the recent years, numerous autoantibodies corresponding to various neurological syndromes have been discovered and their mechanisms of action partially deciphered. Autoantibodies in neurological autoimmune channelopathies may target either directly ion channels or proteins associated to ion channels and induce channel dysfunction by various mechanisms generally leading to the reduction of synaptic expression of the considered channel. The discovery of those mechanisms of action has provided insights on the regulation of the synaptic expression of the altered channels as well as the putative roles of some of their functional subdomains. Interestingly, patients' autoantibodies themselves can be used as specific tools in order to study the functions of ion channels. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Proteasome inhibitors for malignancy-related Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder characterized by autoantibodies against presynaptic voltage-gated calcium channels that impair neuromuscular transmission. Malignancies, especially small cell lung cancer (SCLC), have been associated with LEMS and account for approximately 60% of cases, making malignancy management a central step in LEMS therapy. In addition, immunosuppressive therapy is also recommended for symptomatic control. Interestingly, both pathological and epidemiological data suggest that the autoimmune response can inhibit progression of tumors in malignancy-associated LEMS. Thus, conventional broad-spectrum immunosuppressants may not be effective agents for treatment of LEMS, especially in those with malignancy-associated LEMS. Recent preclinical and clinical studies have indicated that proteasome inhibitors can eliminate antibody-producing cells efficiently, block dendritic cell maturation, and have anti-tumor activity. We hypothesize that proteasome inhibitors may be promising agents for treatment of malignancy-related LEMS.

[Favourable outcome after treatment with rituximab in a case of seronegative non-paraneoplastic Lambert-Eaton myasthenic syndrome]

INTRODUCTION

Lambert-Eaton myasthenic syndrome is a rare and autoimmune presynaptic disorder of the neuromuscular junction, due in 85% of cases to autoantibodies directed against voltage-gated calcium channels. It is a paraneoplastic disorder in 50 to 60% of cases. Diagnosis involves a proximal muscle weakness and areflexia, associated with a significant increment after post-exercise stimulation in electrophysiological study. Symptomatic treatment is based on 3,4-diaminopyridine. No etiological treatment has proven its efficacy in both paraneoplastic and non-paraneoplastic Lambert-Eaton myasthenic syndrome.

CASE REPORT

We report a 41-year-old man who presented with a seronegative non-paraneoplastic Lambert-Eaton myasthenic syndrome in whom conventional immunosuppressive treatments (corticosteroids, azathioprine) failed, and who eventually improved after treatment with rituximab.

CONCLUSION

Rituximab was an effective and well-tolerated treatment in this case of seronegative non-paraneoplastic Lambert-Eaton myasthenic syndrome. Its indication should be discussed when conventional immunosuppressive therapy fails in both seropositive and seronegative patients.

Paraneoplastic syndromes of the neuromuscular junction: therapeutic options in myasthenia gravis, lambert-eaton myasthenic syndrome, and neuromyotonia

OPINION STATEMENT

Myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS) and neuromyotonia are neuromuscular transmission disorders occurring with or without associated malignancy. Due to the common antibody-mediated pathophysiology, immunosuppression has an important role in the treatment of each of these disorders. Symptomatic treatment is more variable. Pyridostigmine is first-line treatment in generalized MG. Response seems to be better in patients with acetylcholine receptor (AChR) antibodies than in patients with antibodies against muscle-specific tyrosine kinase (MuSK). Pyridostigmine can be sufficient in mild MG, although most patients need additional immunosuppressive therapy. If so, prednisolone is efficient in the majority of the patients, with a relatively early onset of clinical effect. High drug dosage and treatment duration should be limited as much as possible because of serious corticosteroid-related side effects. As long-term treatment is needed in most patients for sustainable remission, adding non-steroid immunosuppressive drugs should be considered. Their therapeutic response is usually delayed and often takes a period of several months. In the meantime, corticosteroids are continued and doses are tapered down over a period of several months. There are no trials comparing different immunosuppressive drugs. Choice is mainly based on the clinician's familiarity with certain drugs and their side effects, combined with patients' characteristics. Most commonly used is azathioprine. Alternatively, tacrolimus, cyclosporine A, mycophenolate mofetil or rituximab can be used. The use of cyclophosphamide is limited to refractory cases, due to serious side effects. Plasma exchange and intravenous immunoglobulin induce rapid but temporary improvement, and are reserved for severe disease exacerbations because of high costs of treatment. It is recommended that computed tomography (CT) of the thorax is performed in every AChR-positive MG patient, and that patients are referred for thymectomy in case of thymoma. In patients without thymoma, thymectomy can be considered as well, especially in younger, AChR-positive patients with severe disease. However, definite proof of benefit is lacking and an international randomized trial to clarify this topic is currently ongoing. When LEMS is suspected, always search for malignancy, especially small cell lung carcinoma with continued screening up to two years. In paraneoplastic LEMS, cancer treatment usually results in clinical improvement of the myasthenic symptoms. 3,4-Diaminopyridine is first-line symptomatic treatment in LEMS. It is usually well tolerated and effective. When immunosuppressive therapy is needed, the same considerations apply to LEMS as described for MG. Peripheral nerve hyperexcitability in neuromyotonia can be treated with anticonvulsant drugs such as phenytoin, valproic acid or carbamazepine. When response in insufficient, start prednisolone in mild disease and consider the addition of azathioprine. Plasma exchange or intravenous immunoglobulin is indicated in severe neuromyotonia and in patients with neuromyotonia combined with central nervous system symptoms, a clinical picture known as Morvan's syndrome.

Paraneoplastic neurological syndromes: general treatment overview

OPINION STATEMENT

Major recent discoveries have bringing out a revised definition of paraneoplastic neurological syndromes (PNS), bringing out the concept of antibody-mediated neurological disorders, triggered or not by cancer. Classification of these diseases is not based anymore on the clinical pattern or an underlying tumor, but on the location of the targeted antigens. Indeed, evolution, response to treatment, and pathophysiology are radically different according to the associated antibodies. In some patients with newly described antibodies targeting cell-surface antigens, humoral immunity seems to play a direct role and a dramatic improvement is observed with immunomodulator treatments. In these patients, an associated tumor is less frequent. Conversely, patients with antibodies directed against intracellular targets are, in most cases, characterized by a high degree of irreversible neuronal death mediated by cytotoxic T-cells and do not improve after immunomodulator treatments. In these patients, an associated tumor is highly frequent and must be cured as soon as possible. A third group of patients can be identified with anti-GAD65 and anti-Amphiphysin antibodies. In patients with these antibodies, the efficiency of immunomodulator treatments is less clear as well as the type of immune response that could be a mix between humoral and cellular. In this last group, the antigen is intracellular, but patients may improve with immunomodulator treatments and associated tumors are rare. Thus, identification of associated antibodies should be prompt and the treatment guided according the identified antibody. Mainstream of treatment include the quest of a tumor and its cure. Immunotherapy must be promptly initiated, targeting humoral, or cellular immune response, or both, according to the associated antibodies. Furthermore, in some situations such as Lambert-Eaton Myasthenic Syndromes and Stiff-Person Syndromes, symptomatic drugs can be useful to control the symptoms.

Antibody repertoire in paraneoplastic cerebellar degeneration and small cell lung cancer

The goal of this study is to determine whether patients with paraneoplastic cerebellar degeneration (PCD) and small-cell lung cancer (SCLC) have a specific repertoire of antibodies, if SOX1 antibodies (SOX1-ab) can predict the presence of SCLC, and if antibodies to cell surface antigens occur in this syndrome. Antibody analysis was done using immunohistochemistry on rat brain, immunoblot with recombinant antigens, screening of cDNA expression libraries, and immunolabeling of live neurons in 39 patients with PCD and SCLC. VGCC-ab were measured by RIA, and SOX1-ab, Hu-ab, and ZIC4-ab by immunoblot. Lambert-Eaton myastenic syndrome (LEMS) was present in 10 of 23 patients with electrophysiological studies. At least one antibody was detected in 72% of patients. The individual frequencies were: 49% SOX1-ab, 44% VGCC-ab, 31% Hu-ab, and 13% ZIC4-ab. SOX1-ab occurred in 76% of patients with VGCC-ab and 27% of those without VGCC-ab (p = 0.0036). SOX1-ab were not found in 39 patients with sporadic late-onset cerebellar ataxia, 23 with cerebellar ataxia and glutamic acid decarboxylase antibodies, and 73 with PCD and cancer types other than SCLC (31 without onconeural antibodies, 25 with Yo-ab , 17 with Tr-ab). Five patients (13%) had antibodies against unknown neuronal cell surface antigens but none of them improved with immunotherapy. One serum immunoreacted against the axon initial segment of neurons and another serum against ELKS1, a protein highly expressed in the cerebellum that interacts with the beta4-subunit of the VGCC. In conclusion, 72% of patients with PCD and SCLC had one or more antibodies that indicate the presence of this tumor. In these patients, VGCC-ab and SOX1-ab occur tightly associated. SOX1-ab are predictors of SCLC in ataxia patients with a specificity of 100% and sensitivity of 49%. Unlike limbic encephalitis with SCLC, antibodies to cell surface antigens other than VGCC-ab, are infrequent and do not predict response to treatment.

Autoimmune channelopathies of the nervous system

Ion channels are complex transmembrane proteins that orchestrate the electrical signals necessary for normal function of excitable tissues, including the central nervous system, peripheral nerve, and both skeletal and cardiac muscle. Progress in molecular biology has allowed cloning and expression of genes that encode channel proteins, while comparable advances in biophysics, including patch-clamp electrophysiology and related techniques, have made the functional assessment of expressed proteins at the level of single channel molecules possible. The role of ion channel defects in the pathogenesis of numerous disorders has become increasingly apparent over the last two decades. Neurological channelopathies are frequently genetically determined but may also be acquired through autoimmune mechanisms. All of these autoimmune conditions can arise as paraneoplastic syndromes or independent from malignancies. The pathogenicity of autoantibodies to ion channels has been demonstrated in most of these conditions, and patients may respond well to immunotherapies that reduce the levels of the pathogenic autoantibodies. Autoimmune channelopathies may have a good prognosis, especially if diagnosed and treated early, and if they are non-paraneoplastic. This review focuses on clinical, pathophysiologic and therapeutic aspects of autoimmune ion channel disorders of the nervous system.

Lambert-Eaton myasthenic syndrome: from clinical characteristics to therapeutic strategies

Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular autoimmune disease that has served as a model for autoimmunity and tumour immunology. In LEMS, the characteristic muscle weakness is thought to be caused by pathogenic autoantibodies directed against voltage-gated calcium channels (VGCC) present on the presynaptic nerve terminal. Half of patients with LEMS have an associated tumour, small-cell lung carcinoma (SCLC), which also expresses functional VGCC. Knowledge of this association led to the discovery of a wide range of paraneoplastic and non-tumour-related neurological disorders of the peripheral and central nervous systems. Detailed clinical studies have improved our diagnostic skills and knowledge of the pathophysiological mechanisms and association of LEMS with SCLC, and have helped with the development of a protocol for early tumour detection.

3,4-diaminopyridine for the treatment of Lambert-Eaton myasthenic syndrome

The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease in which antibodies against voltage-gated calcium channels inhibit cholinergic neurotransmission. LEMS is clinically characterized by muscle weakness and autonomic dysfunction. 3,4-diaminopyridine (3,4-DAP) blocks potassium channels in nerve terminals, resulting in an increase in acetylcholine release. This article describes the four randomized placebo-controlled trials of 3,4-DAP in patients with LEMS. All trials demonstrated a significant effect on muscle strength and compound muscle action potential amplitude. Furthermore, the safety and tolerability of 3,4-DAP are reviewed. The side effects of 3,4-DAP are generally mild and most frequently consist of paresthesias, but epileptic seizures and arrhythmias have been described in patients using high doses. Given the efficacy and safety of 3,4-DAP in LEMS, this drug is the mainstay for symptomatic treatment of LEMS.

[Monoclonal antibodies in inflammatory disease of the muscle and peripheral nervous system]

INTRODUCTION

A significant group of neuromuscular diseases are of autoimmune origin, but the classic immunomodulatory drugs are not often effective. For this reason, there is a need to find new more effective treatments that will lead to better control of these conditions, particularly those that are usually more resistant. In the last few years, the use of monoclonal antibodies against specific antigens of lymphocyte populations or against pro-inflammatory molecules has seen a great expansion, and has been demonstrated to be a useful alternative in autoimmune diseases. An intensive search was made in Medline using the Keywords neuromuscular, myopathy, neuropathy, myasthenia, Lambert-Eaton, monoclonal antibody, rituximab, alemtuzumab, and anti-TNF-α.

DEVELOPMENT

Clinical trials performed to evaluate the efficacy of monoclonal antibodies in neuromuscular disease are very limited and of reduced size. Thus, the experience in this field is basically limited to anecdotal cases or short series of patients on open-label treatment. The published data are encouraging, with favourable responses having been observed in patients resistant to classic treatments and in diseases that do not normally respond to the usual immunosuppressant drugs. On the other hand, it has been observed that anti-TNF-α antibodies may trigger the appearance of autoimmune neuromuscular diseases.

CONCLUSIONS

Monoclonal antibodies could be an effective alternative treatment in autoimmune neuromuscular diseases, but the favourable responses observed need to be confirmed by means of controlled clinical trials with a sufficient number of patients.

Current therapy for Lambert-Eaton myasthenic syndrome: development of 3,4-diaminopyridine phosphate salt as first-line symptomatic treatment

BACKGROUND

Lambert-Eaton myasthenic syndrome (LEMS) is a rare pre-synaptic auto-immune disorder of neuromuscular transmission that is characterised by proximal muscle weakness, depressed tendon reflexes and autonomic dysfunction. This review summarises the clinical symptoms, aetiology, diagnosis and treatment options for LEMS. Focus is placed on symptomatic treatment with the potassium channel blocker 3,4-diaminopyridine (3,4-DAP).

RESEARCH METHODS

English-language publications were searched in MEDLINE and EMBASE to retrieve relevant literature on LEMS. The data submitted to obtain regulatory approval of 3,4-DAP phosphate by the European Medicines Agency (EMA) were also used.

FINDINGS

LEMS is a rare disease with few treatment options which are generally categorised as anti-tumour, immunomodulating or immunosuppressing, and symptomatic treatments. Anti-tumour treatment is recommended for patients with the paraneoplastic form of LEMS. While several immunomodulating or immunosuppressing treatments have been identified, these treatments should be initiated when symptomatic treatments are inadequate. As expected, due to the rarity of the disease, few reports of randomised controlled trials (RCTs) exist. Seven RCTs have been conducted to evaluate treatment of patients with LEMS. One RCT evaluated immunomodulating treatment with intravenous immunoglobulin (ivIg), while six evaluated symptomatic treatment with the potassium channel blocker 3,4-DAP. Improvements in LEMS symptoms after ivIg treatment were observed, leading to the recommendation for treatment in patients when symptomatic treatment does not provide satisfactory improvement. Potassium channel blockers evaluated for the treatment of LEMS include guanidine, 4-aminopyridine (4-AP) and 3,4-DAP. However, only 3,4-DAP has been evaluated in RCTs. Results of these RCTs demonstrated that treatment with 3,4-DAP is efficacious in treatment of LEMS and has an acceptable tolerability profile. Hence, 3,4-DAP has been recommended as first-line symptomatic treatment for LEMS by the European Federation of Neurological Societies. While 3,4-DAP base has only been available via named-patient programmes, requiring ad hoc preparations in compounding pharmacies, tablets containing 3,4-DAP phosphate salt, equivalent to 10 mg base, have become available. This formulation has obtained the orphan medicinal product status both in the European Union and in the United States of America, and has received marketing authorisation in Europe as Firdapse*. These tablets have been shown to be essentially bioequivalent with the base preparation.

CONCLUSIONS

The results of this review show that anti-tumour treatment is recommended for patients with the paraneoplastic form of LEMS and that one RCT has shown that immunomodulating treatments should be initiated when symptomatic treatments do not provide satisfactory results. A number of RCTs have shown that 3,4-DAP is effective in symptomatic treatment of patients with LEMS and has been recommended as first-line symptomatic treatment of patients with LEMS. The 3,4-DAP phosphate salt formulation was shown to be safe and effective in the treatment of LEMS with a positive benefit:risk ratio.