Available treatment options for the management of Lambert-Eaton myasthenic syndrome

Terahertz waves promote Ca2+ transport in the Cav2.1 channel

CaV2.1 channels are the structural foundation for neurotransmitter transmission and other vital biological processes. If autoimmune-mediated reduction in presynaptic CaV2.1 leads to a decrease in calcium influx during a presynaptic action potential, which decreases chemical neurotransmission, leading to a debilitating neuromuscular weakness, also known as Lambert-Eaton myasthenia syndrome. The selectivity filter is a core structural component of CaV2.1 channels, with a pivotal role in regulating the selective permeation of Ca2+ ions. Due to the vibration and rotation frequencies of the selectivity filter of CaV2.1 being located in the terahertz band, terahertz waves at specific frequencies may resonate with it, thereby affecting Ca2+ current passing through CaV2.1. Therefore, it is highly worthwhile to study how the terahertz waves regulate the CaV2.1 channel. In this study, we investigate the structure of CaV2.1 channels using molecular dynamics simulations. The effect of external terahertz waves on the channel has been examined at different resonant frequencies of the selectivity filter. We found that when the frequency of terahertz waves applied is around the symmetrical vibration frequency of the carboxyl group in the selectivity filter, the PMF of CaV2.1 significantly decreases, promoting the transport of Ca2+ ions through CaV2.1. The reason behind this is that the terahertz waves resonate with the carboxyl groups of the selectivity filter, affecting the hydrogen network between the hydrated water of Ca2+ ions and the selectivity filter. These findings open up new treatment avenues for channel diseases such as Lambert-Eaton myasthenic syndrome treated with terahertz waves.

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.

Potentiation of neuromuscular transmission by a small molecule calcium channel gating modifier improves motor function in a severe spinal muscular atrophy mouse model

Spinal muscular atrophy (SMA) is a monogenic disease that clinically manifests as severe muscle weakness owing to neurotransmission defects and motoneuron degeneration. Individuals affected by SMA experience neuromuscular weakness that impacts functional activities of daily living. We have used a mouse model of severe SMA (SMNΔ7) to test whether a calcium channel gating modifier (GV-58), alone or in combination with a potassium channel antagonist (3,4-diaminopyridine; 3,4-DAP), can improve neuromuscular function in this mouse model. Bath application of GV-58 alone or in combination with 3,4-DAP significantly restored neuromuscular transmission to control levels in both a mildly vulnerable forearm muscle and a strongly vulnerable trunk muscle in SMNΔ7 mice at postnatal days 10-12. Similarly, acute subcutaneous administration of GV-58 to postnatal day 10 SMNΔ7 mice, alone or in combination with 3,4-DAP, significantly increased a behavioral measure of muscle strength. These data suggest that GV-58 may be a promising treatment candidate that could address deficits in neuromuscular function and strength and that the addition of 3,4-DAP to GV-58 treatment could aid in restoring function in SMA.

Chronic Pharmacological Increase of Neuronal Activity Improves Sensory-Motor Dysfunction in Spinal Muscular Atrophy Mice

Dysfunction of neuronal circuits is an important determinant of neurodegenerative diseases. Synaptic dysfunction, death, and intrinsic activity of neurons are thought to contribute to the demise of normal behavior in the disease state. However, the interplay between these major pathogenic events during disease progression is poorly understood. Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by a deficiency in the ubiquitously expressed protein SMN and is characterized by motor neuron death, skeletal muscle atrophy, as well as dysfunction and loss of both central and peripheral excitatory synapses. These disease hallmarks result in an overall reduction of neuronal activity in the spinal sensory-motor circuit. Here, we show that increasing neuronal activity by chronic treatment with the FDA-approved potassium channel blocker 4-aminopyridine (4-AP) improves motor behavior in both sexes of a severe mouse model of SMA. 4-AP restores neurotransmission and number of proprioceptive synapses and neuromuscular junctions (NMJs), while having no effects on motor neuron death. In addition, 4-AP treatment with pharmacological inhibition of p53-dependent motor neuron death results in additive effects, leading to full correction of sensory-motor circuit pathology and enhanced phenotypic benefit in SMA mice. Our in vivo study reveals that 4-AP-induced increase of neuronal activity restores synaptic connectivity and function in the sensory-motor circuit to improve the SMA motor phenotype.SIGNIFICANCE STATEMENT Spinal muscular atrophy (SMA) is a neurodegenerative disease, characterized by synaptic loss, motor neuron death, and reduced neuronal activity in spinal sensory-motor circuits. However, whether these are parallel or dependent events is unclear. We show here that long-term increase of neuronal activity by the FDA-approved drug 4-aminopyridine (4-AP) rescues the number and function of central and peripheral synapses in a SMA mouse model, resulting in an improvement of the sensory-motor circuit and motor behavior. Combinatorial treatment of pharmacological inhibition of p53, which is responsible for motor neuron death and 4-AP, results in additive beneficial effects on the sensory-motor circuit in SMA. Thus, neuronal activity restores synaptic connections and improves significantly the severe SMA phenotype.

Aminopiridines in the treatment of multiple sclerosis and other neurological disorders

Symptomatic treatment has a great relevance for the management of patients with neurologic diseases, since it reduces disease burden and improves quality of life. Aminopyridines (APs) are a group of potassium (K+) channel blocking agents that exert their activity both at central nervous system level and on neuromuscular junction. This review describes the use of APs for the symptomatic treatment of neurological conditions. We will describe trials leading to the approval of the extended-release 4-aminopyridine for MS and evidence in support of the use in other neurological diseases.

Paraneoplastic syndromes in small cell lung cancer

Paraneoplastic syndromes can commonly occur due to lung cancer, especially small cell lung cancer. Frequently paraneoplastic syndromes can precede the diagnosis of the neoplasm or present with limited stage disease. However, these syndromes can also occur at the time of recurrence or metastasis of disease. This review focuses on the epidemiology, pathogenesis, clinical features, and current management of the most common paraneoplastic syndromes encountered in patients with small cell lung cancer. Manifestations of paraneoplastic syndromes in small cell lung cancer include endocrine syndromes with secretion of excess hormones, and neurologic syndromes due to the production of antibodies causing an autoimmune condition. Recent advances have allowed for greater understanding of these syndromes and for the development of improved diagnostic as well as therapeutic tools. Awareness of paraneoplastic syndromes in small cell lung cancer can lead to an earlier diagnosis and recognition of both the condition and in some cases the disease potentially improving the overall survival and prognosis for patients. Further research examining effective methods to improve recovery from neurologic deficits in patients with a paraneoplastic neurologic illness is warranted.

Long-term follow-up, quality of life, and survival of patients with Lambert-Eaton myasthenic syndrome

Objective

To study survival and to characterize long-term functional impairments and health-related quality of life (HRQOL) of patients with Lambert-Eaton myasthenic syndrome (LEMS).

Methods

In this observational study, survival of patients with LEMS, separately for nontumor (NT) and small cell lung cancer (SCLC), was compared to that of the Dutch general population and patients with SCLC. Disease course in patients with LEMS was recorded retrospectively. Several scales for functional impairments and health-related quality of life were assessed.

Results

We included 150 patients with LEMS. Survival was similar to that of the general population in 65 patients with NT-LEMS. Tumor survival was significantly longer in 81 patients with SCLC-LEMS compared to patients with non-LEMS SCLC (overall median survival 17 vs 7.0 months, p < 0.0001). At diagnosis, 39 (62%) of 63 patients with complete follow-up data were independent for activities of daily living, improving to 85% at the 1-year follow-up. The physical HRQOL composite score (55.9) was significantly lower than in the general population (76.3, p < 0.0001) and comparable to that of patients with myasthenia gravis (60.5). The mental HRQOL composite score was 71.8 in patients with LEMS, comparable to that of the general population (77.9, p = 0.19) and patients with myasthenia gravis (70.3).

Conclusions

This study shows that patients with NT-LEMS have normal survival. Patients with SCLC-LEMS have an improved tumor survival, even after correction for tumor stage. A majority of patients with LEMS report a stable disease course and remain or become independent for self-care after treatment.

Amifampridine for the treatment of Lambert-Eaton myasthenic syndrome

Introduction: The present status of amifampridine (AFP) for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) is reviewed. Areas covered: All relevant literature identified through a PubMed search under treatment of LEMS, aminopyridine, and amifampridine are reviewed. An expert opinion on AFP was formulated. Expert opinion: AFPs, 3,4-DAP and 3,4-DAPP, are the most studied drugs in neuromuscular diseases. Randomized and non-randomized studies showed the most effective drug as symptomatic medication for LEMS. AFPs are safe and tolerable. Thus, AFPs should be the drug of choice for the symptomatic treatment in LEMS. As long as the daily dose is less than 80 mg a day, there is no concern for the serious side-reaction, seizure. Because of short-acting drug effects, it should be given three or four times a day. Peri-oral and finger paresthesia, the most common side-reaction, is accepted as a sign of drug-intake by many patients. Gastro-intestinal side reactions, the next common side-reaction of AFPs, are tolerable. AFPs are also the drug of choice and life-saving for LEMS crisis. For the long-term usage, it is proven to be safe and AFPs can be supplemented with liberal amount of pyridostigmine to sustain a symptomatic improvement without any undue side-reaction.

The p75NTR neurotrophin receptor is required to organize the mature neuromuscular synapse by regulating synaptic vesicle availability

The coordinated movement of organisms relies on efficient nerve-muscle communication at the neuromuscular junction. After peripheral nerve injury or neurodegeneration, motor neurons and Schwann cells increase the expression of the p75NTR pan-neurotrophin receptor. Even though p75NTR targeting has emerged as a promising therapeutic strategy to delay peripheral neuronal damage progression, the effects of long-term p75NTR inhibition at the mature neuromuscular junction have not been elucidated. We performed quantitative neuroanathomical analyses of the neuromuscular junction in p75NTR null mice by laser confocal and electron microscopy, which were complemented with electromyography, locomotor tests, and pharmacological intervention studies. Mature neuromuscular synapses of p75NTR null mice show impaired postsynaptic organization and ultrastructural complexity, which correlate with altered synaptic function at the levels of nerve activity-induced muscle responses, muscle fiber structure, force production, and locomotor performance. Our results on primary myotubes and denervated muscles indicate that muscle-derived p75NTR does not play a major role on postsynaptic organization. In turn, motor axon terminals of p75NTR null mice display a strong reduction in the number of synaptic vesicles and active zones. According to the observed pre and postsynaptic defects, pharmacological acetylcholinesterase inhibition rescued nerve-dependent muscle response and force production in p75NTR null mice. Our findings revealing that p75NTR is required to organize mature neuromuscular junctions contribute to a comprehensive view of the possible effects caused by therapeutic attempts to target p75NTR.

Amifampridine for the Management of Lambert-Eaton Myasthenic Syndrome: A New Take on an Old Drug

Objective: The purpose of this article is to review the literature for both 3,4-diaminopyridine (3,4-DAP) and amifampridine for the treatment of Lambert-Eaton myasthenic syndrome (LEMS). Amifampridine (Firdapse) is the salt form of 3,4-DAP and was approved by the Food and Drug Administration for the treatment of LEMS. Data Sources: PubMed, TRIP database, and EMBASE searches were conducted without a back date (current to June 2019) utilizing the following search terms: amifampridine, 3,4-diaminopyridine, and Lambert-Eaton myasthenic syndrome. Completed trials were also reviewed at clinicaltrials.gov. Study Selection and Data Extraction: Criteria for article inclusion consisted of human subjects, age ≥18 years, phase II or III clinical trials, and English language for both drugs. Observational and pharmacokinetic studies for amifampridine were also included. Data Synthesis: Prior to the approval of amifampridine, 3,4-DAP was first-line for the management of LEMS symptoms. Two phase III trials have evaluated amifampridine to confirm efficacy, both showing superiority over placebo in the management of LEMS symptoms, with minimal adverse effects. A significant improvement in both quantitative myasthenia gravis scores and Subjective Global Impression scores was established at days 4 and 14. Relevance to Patient Care and Clinical Practice: With an improved stability profile and decreased dose variability, amifampridine will likely assume the role of first-line management of LEMS. Conclusions: Amifampridine has been shown to improve symptoms of LEMS and is generally well tolerated.

Amifampridine Phosphate (Firdapse) Is Effective in a Confirmatory Phase 3 Clinical Trial in LEMS

Objective:

To assess tolerability and efficacy of amifampridine phosphate versus placebo for symptomatic treatment of Lambert–Eaton Myasthenic Syndrome (LEMS).

Methods:

This phase 3 randomized, double-blind, placebo-controlled withdrawal trial in 26 adults with LEMS compared efficacy of amifampridine phosphate versus placebo over a 4-day period. The primary endpoints were quantitative myasthenia gravis score (QMG) and subject global impression, and the secondary endpoint was Clinical Global Impression–Improvement. The exploratory endpoints were 3TUG (timed up and go) test and QMG limb domain score. All participants had been receiving amifampridine phosphate (30–80 mg/d divided into 3 or 4 doses daily) in an expanded access protocol and had been titrated to the optimal dose and frequency for at least 1 week before randomization into the current study. After completion of assessments after 4 days of double-blind treatment, patients had the option to return to open-label amifampridine phosphate. The efficacy endpoints were mean changes from baseline in the various evaluation parameters.

Results:

Amifampridine phosphate (n = 13) demonstrated significant benefit in QMG and subject global impression compared with placebo (n = 13) at 4 days. Other measures of efficacy, including Clinical Global Impression–Improvement, 3TUG, and QMG limb domain score were also improved. The most common “adverse events” in the placebo group were muscle weakness (n = 5) and fatigue (n = 4), as expected from withdrawal of amifampridine phosphate, whereas only back pain (n = 1), pain in extremity (n = 1), and headache (n = 1) were reported in amifampridine phosphate group.

Conclusions:

This phase 3 randomized, double-blind, placebo-controlled withdrawal trial in adults with LEMS provided class I evidence of efficacy of amifampridine phosphate as symptomatic treatment in LEMS.

Autoimmune Channelopathies at Neuromuscular Junction

The neuromuscular junction, also called myoneural junction, is a site of chemical communication between a nerve fiber and a muscle cell. There are many types of channels at neuromuscular junction that play indispensable roles in neuromuscular signal transmission, such as voltage-gated calcium channels and voltage-gated potassium channels on presynaptic membrane, and acetylcholine receptors on post-synaptic membrane. Over the last two decades, our understanding of the role that autoantibodies play in neuromuscular junction disorders has been greatly improved. Antibodies against these channels cause a heterogeneous group of diseases, such as Lambert-Eaton syndrome, Isaacs' syndrome and myasthenia gravis. Lambert-Eaton syndrome is characterized by late onset of fatigue, skeletal muscle weakness, and autonomic symptoms. Patients with Isaacs' syndrome demonstrate muscle cramps and fasciculation. Myasthenia gravis is the most common autoimmune neuromuscular junction channelopathy characterized by fluctuation of muscle weakness. All these disorders have a high risk of tumor. Although these channelopathies share some common features, they differ for clinical features, antibodies profile, neurophysiological features, and treatments. The purpose of this review is to give a comprehensive insight on recent advances in autoimmune channelopathies at the neuromuscular junction.

Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome

PURPOSE OF REVIEW

This article discusses the pathogenesis, diagnosis, and management of autoimmune myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS).

RECENT FINDINGS

Recognition of new antigenic targets and improved diagnostic methods promise to improve the diagnosis of MG, although the clinical phenotypes associated with newer antibodies have not yet been defined. Future therapies might specifically target the aberrant immune response. The apparent increase in the prevalence of MG is not fully explained. Results of a long-awaited trial of thymectomy support the practice of performing a thymectomy under specific conditions.

SUMMARY

The current treatment options are so effective in most patients with MG or LEMS that in patients with refractory disease the diagnosis should be reconsidered. The management of MG is individualized, and familiarity with mechanisms, adverse effects, and strategies to manage these commonly used treatments improves outcome. Patient education is important. LEMS, frequently associated with an underlying small cell lung cancer, is uncommon, and the mainstay of treatment is symptomatic in most patients.

Pure Ocular Weakness as the Initial Manifestation of Lambert-Eaton Myasthenic Syndrome

Pure ocular presentation of Lambert–Eaton syndrome is not a common phenomenon. Such presentation poses significant diagnostic challenges and requires conscientious evaluation. In this review, we have described a case of a patient with pure ocular weakness, initially diagnosed as seronegative ocular myasthenia which on further evaluation was found to have ocular Lambert–Eaton myasthenic syndrome (LEMS).

New Cav2 calcium channel gating modifiers with agonist activity and therapeutic potential to treat neuromuscular disease

Voltage-gated calcium channels (VGCCs) are critical regulators of many cellular functions, including the activity-dependent release of chemical neurotransmitter from nerve terminals. At nerve terminals, the Cav2 family of VGCCs are closely positioned with neurotransmitter-containing synaptic vesicles. The relationship between calcium ions and transmitter release is such that even subtle changes in calcium flux through VGCCs have a strong influence on the magnitude of transmitter released. Therefore, modulators of the calcium influx at nerve terminals have the potential to strongly affect transmitter release at synapses. We have previously developed novel Cav2-selective VGCC gating modifiers (notably GV-58) that slow the deactivation of VGCC current, increasing total calcium ion flux. Here, we describe ten new gating modifiers based on the GV-58 structure that extend our understanding of the structure-activity relationship for this class of molecules and extend the range of modulation of channel activities. In particular, we show that one of these new compounds (MF-06) was more efficacious than GV-58, another (KK-75) acts more quickly on VGCCs than GV-58, and a third (KK-20) has a mix of increased speed and efficacy. A subset of these new VGCC agonist gating modifiers can increase transmitter release during action potentials at neuromuscular synapses, and as such, show potential as therapeutics for diseases with a presynaptic deficit that results in neuromuscular weakness. Further, several of these new compounds can be useful tool compounds for the study of VGCC gating and function.

Lambert-Eaton myasthenic syndrome: mouse passive-transfer model illuminates disease pathology and facilitates testing therapeutic leads

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder caused by antibodies directed against the voltage-gated calcium channels that provide the calcium ion flux that triggers acetylcholine release at the neuromuscular junction. To study the pathophysiology of LEMS and test candidate therapeutic strategies, a passive-transfer animal model has been developed in mice, which can be created by daily intraperitoneal injections of LEMS patient serum or IgG into mice for 2-4 weeks. Results from studies of the mouse neuromuscular junction have revealed that each synapse has hundreds of transmitter release sites but that the probability for release at each one is likely to be low. LEMS further reduces this low probability such that transmission is no longer effective at triggering a muscle contraction. The LEMS-mediated attack reduces the number of presynaptic calcium channels, disorganizes transmitter release sites, and results in the homeostatic upregulation of other calcium channel types. Symptomatic treatment is focused on increasing the probability of release from dysfunctional release sites. Current treatment uses the potassium channel blocker 3,4-diaminopyridine (DAP) to broaden the presynaptic action potential, providing more time for calcium channels to open. Current research is focused on testing new calcium channel gating modifiers that work synergistically with DAP.

Therapeutic Apheresis in Immunologic Renal and Neurological Diseases

Since the mid 1970s, when membrane modules became available, plasma separation techniques have gained in importance especially in the past few years. The advantages of this method are a complete separation of the corpuscular components from the plasma and due to increased blood flow rate and higher efficacy. Systemic autoimmune diseases based on an immune pathogenesis produce autoantibodies and circulating immune complexes, which cause inflammation in the tissues of various organs. In most cases, these diseases have a poor prognosis without treatment. Therapeutic apheresis (TA) in combination with immunosuppressive therapies has led to a steady increase in survival rates over the last 40 years. The updated information on immunology and molecular biology of different immunologic diseases are discussed in relation to the rationale for apheresis therapy and its place in combination with other modern treatments. The different diseases can be treated by various apheresis methods such as therapeutic plasma exchange (TPE) with substitution solution, or with online plasma or blood purification using adsorption columns, which contain biological or non-biological agents. Here, the authors provide an overview of the most important pathogenic aspects indicating that TA can be a supportive therapy in systemic autoimmune diseases such as renal and neurological disorders. For the immunological diseases that can be treated with TA, the guidelines of the German Working Group of Clinical Nephrology and of the Apheresis Committee of the American Society for Apheresis are cited.

The Production Processes and Biological Effects of Intravenous Immunoglobulin

Immunoglobulin is a highly diverse autologous molecule able to influence immunity in different physiological and diseased situations. Its effect may be visible both in terms of development and function of B and T lymphocytes. Polyclonal immunoglobulin may be used as therapy in many diseases in different circumstances such as primary and secondary hypogammaglobulinemia, recurrent infections, polyneuropathies, cancer, after allogeneic transplantation in the presence of infections and/or GVHD. However, recent studies have broadened the possible uses of polyclonal immunoglobulin showing that it can stimulate certain sub-populations of T cells with effects on T cell proliferation, survival and function in situations of lymphopenia. These results present a novel and considerable impact of intravenous immunoglobulin (IVIg) treatment in situations of severe lymphopenia, a situation that can occur in cancer patients after chemo and radiotherapy treatments. In this review paper the established and experimental role of polyclonal immunoglobulin will be presented and discussed as well as the manufacturing processes involved in their production.

Electrophysiologic features of SYT2 mutations causing a treatable neuromuscular syndrome

OBJECTIVES

To describe the clinical and electrophysiologic features of synaptotagmin II (SYT2) mutations, a novel neuromuscular syndrome characterized by foot deformities and fatigable ocular and lower limb weakness, and the response to modulators of acetylcholine release.

METHODS

We performed detailed clinical and neurophysiologic assessment in 2 multigenerational families with dominant SYT2 mutations (c.920T>G [p.Asp307Ala] and c.923G>A [p.Pro308Leu]). Serial clinical and electrophysiologic assessments were performed in members of one family treated first with pyridostigmine and then with 3,4-diaminopyridine.

RESULTS

Electrophysiologic testing revealed features indicative of a presynaptic deficit in neurotransmitter release with posttetanic potentiation lasting up to 60 minutes. Treatment with 3,4-diaminopyridine produced both a clinical benefit and an improvement in neuromuscular transmission.

CONCLUSION

SYT2 mutations cause a novel and potentially treatable complex presynaptic congenital myasthenic syndrome characterized by motor neuropathy causing lower limb wasting and foot deformities, with reflex potentiation following exercise and a uniquely prolonged period of posttetanic potentiation.

Genetic variation in aryl N-acetyltransferase results in significant differences in the pharmacokinetic and safety profiles of amifampridine (3,4-diaminopyridine) phosphate

The clinical use of amifampridine phosphate for neuromuscular junction disorders is increasing. The metabolism of amifampridine occurs via polymorphic aryl N-acetyltransferase (NAT), yet its pharmacokinetic (PK) and safety profiles, as influenced by this enzyme system, have not been investigated. The objective of this study was to assess the effect of NAT phenotype and genotype on the PK and safety profiles of amifampridine in healthy volunteers (N = 26). A caffeine challenge test and NAT2 genotyping were used to delineate subjects into slow and fast acetylators for PK and tolerability assessment of single, escalating doses of amifampridine (up to 30 mg) and in multiple daily doses (20 mg QID) of amifampridine. The results showed that fast acetylator phenotypes displayed significantly lower C max, AUC, and shorter t 1/2 for amifampridine than slow acetylators. Plasma concentrations of the N-acetyl metabolite were approximately twofold higher in fast acetylators. Gender differences were not observed. Single doses of amifampridine demonstrated dose linear PKs. Amifampridine achieved steady state plasma levels within 1 day of dosing four times daily. No accumulation or time-dependent changes in amifampridine PK parameters occurred. Overall, slow acetylators reported 73 drug-related treatment-emergent adverse events versus 6 in fast acetylators. Variations in polymorphic NAT corresponding with fast and slow acetylator phenotypes significantly affects the PK and safety profiles of amifampridine.

Synaptic Pathophysiology and Treatment of Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease that disrupts the normally reliable neurotransmission at the neuromuscular junction (NMJ). This disruption is thought to result from an autoantibody-mediated removal of a subset of the P/Q-type Ca(2+) channels involved with neurotransmitter release. With less neurotransmitter release at the NMJ, LEMS patients experience debilitating muscle weakness. The underlying cause of LEMS in slightly more than half of all patients is small cell lung cancer, and cancer therapy is the priority for these patients. In the remaining cases, the cause of LEMS is unknown, and these patients often rely on symptomatic treatment options, as there is no cure. However, current symptomatic treatment options, such as 3,4-diaminopyridine (3,4-DAP), can have significant dose-limiting side effects; thus, additional treatment approaches would benefit LEMS patients. Recent studies introduced a novel Ca(2+) channel agonist (GV-58) as a potential therapeutic alternative for LEMS. Additionally, this work has shown that GV-58 and 3,4-DAP interact in a supra-additive manner to completely restore the magnitude of neurotransmitter release at the NMJs of a LEMS mouse model. In this review, we discuss synaptic mechanisms for reliability at the NMJ and how these mechanisms are disrupted in LEMS. We then discuss the current treatment options for LEMS patients, while also considering recent work demonstrating the therapeutic potential of GV-58 alone and in combination with 3,4-DAP.

Evaluation of a novel calcium channel agonist for therapeutic potential in Lambert-Eaton myasthenic syndrome

We developed a novel calcium (Ca(2+)) channel agonist that is selective for N- and P/Q-type Ca(2+) channels, which are the Ca(2+) channels that regulate transmitter release at most synapses. We have shown that this new molecule (GV-58) slows the deactivation of channels, resulting in a large increase in presynaptic Ca(2+) entry during activity. GV-58 was developed as a modification of (R)-roscovitine, which was previously shown to be a Ca(2+) channel agonist, in addition to its known cyclin-dependent kinase activity. In comparison with the parent molecule, (R)-roscovitine, GV-58 has a ∼20-fold less potent cyclin-dependent kinase antagonist effect, a ∼3- to 4-fold more potent Ca(2+) channel agonist effect, and ∼4-fold higher efficacy as a Ca(2+) channel agonist. We have further evaluated GV-58 in a passive transfer mouse model of Lambert-Eaton myasthenic syndrome and have shown that weakened Lambert-Eaton myasthenic syndrome-model neuromuscular synapses are significantly strengthened following exposure to GV-58. This new Ca(2+) channel agonist has potential as a lead compound in the development of new therapeutic approaches to a variety of disorders that result in neuromuscular weakness.

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.

Clinical applications of immunoglobulin: update

Human immunoglobulin is the most used blood product in the clinical practice. Immunoglobulin applications have increased quickly since the elucidation of its immunomodulatory and antiinflammatory properties which turned this blood product into a precious tool in the treatment of numerous diseases that present with humoral immune deficiency or that cause immune system dysfunction. Currently, the approved indications for Ig are: primary immunodeficiencies, secondary immunodeficiencies (multiple myeloma or chronic lymphoid leukemia), Kawasaki syndrome, immune thrombocytopenic purpura, Guillain Barré syndrome, graft-versus-host disease following bone marrow transplantation and repeat infections in HIV children. On the other hand, there are numerous "off-label" indications of immunoglobulin, which represent 20-60% of all clinical applications of this drug. It is important to study all these indications and, above all, the scientific evidence for its use, in order to provide patients with a new therapeutic option without burdening the health system. This review results from a wide selection of papers identified in the Pubmed and Lilacs scientific electronic databases. A group of descriptors were used from human immunoglobulin to the names of each disease that immunoglobulin is clinically applied. Our main objective is to list the numerous indications of immunoglobulin, both authorized and "off-label" and to analyze these indications in the light of the most recent scientific evidence.

Immunotherapies in neurologic disorders

Therapy for autoimmune demyelinating disorders has evolved rapidly over the past 10 years to include traditional immunosuppressants as well as novel biologicals. Antibody-mediated neuromuscular disorders are treated with therapies that acutely modulate pathogenic antibodies or chronically inhibit the humoral immune response. In other inflammatory autoimmune disorders of the peripheral and central nervous system, corticosteroids, often combined with conventional immunosuppression, and immunomodulatory treatments are used. Because autoimmune neurologic disorders are so diverse, evidence from randomized controlled trials is limited for most of the immunotherapies used in neurology. This review provides an overview of the immunotherapies currently used for neurologic disorders.

Lung cancer-induced paraneoplastic syndromes

PURPOSE OF REVIEW

Paraneoplastic syndromes occur commonly in patients with lung cancer, especially cancers of neuroendocrine origin. The syndromes can be the first clinical manifestation of malignant disease or a harbinger of cancer recurrence. To update the knowledge that would facilitate the care of lung cancer patients with paraneoplastic syndromes, this review focuses on the epidemiology, pathogenesis, clinical features, and current management of the more common and clinically relevant syndromes.

RECENT FINDINGS

Certain combinations of clinical signs and symptoms (endocrine, neurologic, immunologic, dermatologic, metabolic, constitutional, and hematologic) are associated with lung carcinoma as a manifestation of the secretion of cytokines and hormones by these cells or as an associated immunologic response. These syndromes can be categorized by common causative mechanisms: hormonal syndromes, autoimmune syndromes, and other syndromes of less clear cause. Recent advances in medical technology have allowed better understanding of these syndromes and the development of novel diagnostic and therapeutic tools.

SUMMARY

Increased awareness of paraneoplastic syndromes associated with lung cancer should lead to the earlier recognition and diagnosis of malignancies, thereby improving the overall prognosis of patients and alleviating associated comorbidities. Despite the recent advances in recognizing and treating paraneoplastic syndromes, many questions remain to be answered.

Lambert-eaton myasthenic syndrome

Lambert Eaton myasthenic syndrome (LEMS) is a rare neuromuscular junction disease. Often, the signs and symptoms of LEMS are mistaken for myasthenia gravis and therefore the workup is misdirected. A physician must look for an occult malignancy when the diagnosis is made and then continue to search for a malignancy for at least 5 years after diagnosis. The diagnosis of LEMS can be confirmed with electrophysiologic studies or with serum calcium channel antibodies. In most patients with LEMS, 3,4-diaminopyridine will improve strength. In patients without malignancy, immunosuppressants do have a role in the treatment of LEMS. Patients and physicians must be aware that certain situations and drugs may exacerbate weakness.

Update on treatment options for Lambert-Eaton myasthenic syndrome: focus on use of amifampridine

In Lambert-Eaton myasthenic syndrome (LEMS), antibodies against presynaptic voltage-gated calcium channels reduce the quantal release of acetylcholine, causing muscle weakness and autonomic dysfunction. More than half of the affected patients have associated small cell lung cancer, and thorough screening for an underlying malignancy is crucial. The mainstay of treatment for LEMS is symptomatic but immunotherapy is needed in more severely affected patients. Symptomatic therapies aim at increasing the concentration of acetylcholine at the muscle endplate. While acetylcholinesterase inhibitors were the first drugs to be used for the amelioration of symptoms, 3,4-diaminopyridine (3,4-DAP, amifampridine) has been shown to be more effective. 3,4-DAP blocks presynaptic potassium channels, thereby prolonging the action potential and increasing presynaptic calcium concentrations. This then results in increased quantal release of acetylcholine. The efficacy of 3,4-DAP for increasing muscle strength and resting compound muscle action potentials has been demonstrated by four placebo-controlled trials. Side effects are usually mild, and the most frequently reported are paresthesias. The most common serious adverse events are epileptic seizures. 3,4-DAP is currently the treatment of choice in patients with Lambert-Eaton myasthenic syndrome.

Non-paraneoplastic Lambert-Eaton myasthenic syndrome: a brief review of 10 cases

Lambert-Eaton myasthenic syndrome (LEMS) is an immune-mediated disorder of the presynaptic neuromuscular transmission, which more frequently occurs as the remote effect of a neoplasm, in the paraneoplastic form (P-LEMS), or in a non-paraneoplastic form (NP-LEMS); but few studies describe the clinical features of NP-LEMS. We analyzed the clinical manifestations, laboratory findings, electrophysiological studies, and treatment responses in ten Brazilian patients suffering from NP-LEMS. The mean age was 41.5 years. More often neurological findings were hyporeflexia or areflexia with a post-exercise improvement. Treatment response occurred with pyridostigmine, guanidine, prednisone, azathioprine, and cyclosporine; but not response was observed after intravenous immunoglobulin and plasma exchange. Age at onset, clinical manifestations, and electrophysiological abnormalities can help more in the diagnosis than serum antibodies; the symptomatic treatment with pyridostigmine was effective; and the immunosuppressive treatment with prednisone, azathioprine, or cyclosporine was more beneficial than plasma exchange or intravenous immunoglobulin treatment.

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.

Paraneoplastic syndromes in neuro-ophthalmology

PURPOSE OF REVIEW

The aim of this review is to discuss and highlight the recent advances in our understanding of paraneoplastic syndromes in neuro-ophthalmology and their significance.

RECENT FINDINGS

The pathophysiologic mechanism in neuro-ophthalmic paraneoplastic syndromes involves an immune response triggered by aberrant expression of onconeuronal antigens that cross-react with antigens in the visual system. Recently, 18-fluoro-deoxy-glucose/positron emission tomography with computed tomography scanning has emerged as a useful modality in diagnosing occult tumors responsible for paraneoplastic syndromes. Paraneoplastic optic neuropathy has been recently associated with the anti-CV2/CRMP-5 antibody. The use of serologic analysis of recombinantly expressed clones (SEREX) has led to the identification of new antigens associated with melanoma-associated retinopathy, such as visual arrestin, rhodopsin, titin, and mitofilin. Calcium-channel blockers and alemtuzumab have been found to improve visual function in cancer-associated retinopathy. Rituximab has been found to be effective in childhood opsoclonus-myoclonus syndrome.

SUMMARY

A high index of suspicion is needed to diagnose neuro-ophthalmic paraneoplastic syndromes. There have been recent advances in our understanding of the pathophysiology and treatment of these disorders. This will facilitate early treatment of causative occult tumors and improves the prognosis.

Perioperative care of patients with neuromuscular disease and dysfunction

A variety of different pathologies result in disease phenotypes that are summarized as neuromuscular diseases because they share commonalty in their clinical consequences for the patient: a progressive weakening of the skeletal muscles. Distinct caution and appropriate changes to the anesthetic plan are advised when care is provided during the perioperative period. The choice of anesthetic technique, anesthetic drugs, and neuromuscular blockade always depends on the type of neuromuscular disease and the surgical procedure planned. A clear diagnosis of the underlying disease and sufficient knowledge and understanding of the pathophysiology are of paramount importance to the practitioner and guide optimal perioperative management of affected patients.