A treatment algorithm for Lambert-Eaton myasthenic syndrome

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.

Lambert-Eaton Myasthenic Syndrome Recurrence Induced by Pembrolizumab in a Patient with Non-small-cell Lung Cancer

A 73-year-old woman in complete remission from localized small-cell lung cancer associated with Lambert-Eaton myasthenic syndrome (LEMS) 22 years earlier was referred to our hospital and diagnosed with non-small-cell lung cancer. After three courses of pembrolizumab, an immune checkpoint inhibitor, the patient complained of muscle weakness, fatigue, ptosis, and dysarthria. The anti-voltage-gated calcium channel antibody level was elevated, and waxing was observed on a high-frequency repetitive stimulation test using an electromyogram. We diagnosed her with recurrence of LEMS as an immune-related adverse event (irAE) induced by pembrolizumab. After intravenous immunoglobulin therapy, the patient's symptoms improved, and she was discharged.

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.

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.

Guidelines on the Use of Therapeutic Apheresis in Clinical Practice-Evidence-Based Approach from the Writing Committee of the American Society for Apheresis: The Seventh Special Issue

The American Society for Apheresis (ASFA) Journal of Clinical Apheresis (JCA) Special Issue Writing Committee is charged with reviewing, updating, and categorizing indications for the evidence-based use of therapeutic apheresis in human disease. Since the 2007 JCA Special Issue (Fourth Edition), the Committee has incorporated systematic review and evidence-based approaches in the grading and categorization of apheresis indications. This Seventh Edition of the JCA Special Issue continues to maintain this methodology and rigor to make recommendations on the use of apheresis in a wide variety of diseases/conditions. The JCA Seventh Edition, like its predecessor, has consistently applied the category and grading system definitions in the fact sheets. The general layout and concept of a fact sheet that was used since the fourth edition has largely been maintained in this edition. Each fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis in a specific disease entity. The Seventh Edition discusses 87 fact sheets (14 new fact sheets since the Sixth Edition) for therapeutic apheresis diseases and medical conditions, with 179 indications, which are separately graded and categorized within the listed fact sheets. Several diseases that are Category IV which have been described in detail in previous editions and do not have significant new evidence since the last publication are summarized in a separate table. The Seventh Edition of the JCA Special Issue serves as a key resource that guides the utilization of therapeutic apheresis in the treatment of human disease. J. Clin. Apheresis 31:149-162, 2016. © 2016 Wiley Periodicals, Inc.

The European LEMS Registry: Baseline Demographics and Treatment Approaches

Introduction

Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder affecting the neuromuscular junction, clinically characterized by proximal muscle weakness and autonomic changes. LEMS is often associated with an underlying tumor (paraneoplastic form) but also occurs in the absence of cancer (idiopathic form). Treatment consists of immunomodulation (immunosuppression), anticancer treatment when carcinoma is present, and symptomatic treatment [acetylcholinesterase inhibitors and potassium channel blockers, e.g., amifampridine (3,4-diaminopyridine, i.e., 3,4-DAP), to improve neurotransmission]. Although there has long been information from case reports, several randomized controlled trials, and treatment guidelines, population data are still scarce.

Methods

The LEMS patient registry was launched in the European community in mid-2010 as a voluntary, multinational, observational, non-interventional program to collect structured empirical data on clinical course, treatment utilization, and safety and efficacy from the use of LEMS-specific treatments.

Results

Sixty-nine patients have been enrolled [36 males, 32 females, 1 gender not reported; mean age 61.5 (27–84) years]. Eighteen patients (26%) were diagnosed with an associated carcinoma. At the time of enrollment, the majority of patients (65%) were receiving amifampridine [either compounded 3,4-DAP (22%) or 3,4-DAP phosphate, Firdapse^® (43%)]. At enrollment, most patients demonstrate a profile of mild-to-moderate deficits in daily functioning but generally have good muscle strength, albeit with reduced deep tendon reflexes, frequent ataxia during walking, and signs of autonomic dysfunction including dry mouth, bladder dysfunction, and constipation.

Conclusion

The LEMS European Union registry will continue to enroll patients and periodically report the accrued longitudinal data obtained on clinical assessments and laboratory findings, treatment practices, the safety and efficacy of treatment approaches, and long-term clinical outcomes.

Funding

BioMarin Pharmaceutical Inc., Novato, CA, USA.

Electronic supplementary material

The online version of this article (doi:10.1007/s40120-015-0034-0) contains supplementary material, which is available to authorized users.

[The pathophysiology and treatment of autoimmune neuromuscular junction diseases]

The neuromuscular junction lacks the protection of the blood-nerve barrier and is vulnerable to antibody-mediated disorders. Myasthenia gravis (MG) is caused by the failure of neuromuscular transmission mediated by autoantibodies against acetylcholine receptors (AChR) and muscle-specific receptor tyrosine kinase (MuSK)/LDL-receptor related protein 4 which are AChR-associated transmembrane post-synaptic proteins involved in AChR aggregation. The seropositivity rates for AChR positive and MuSK positive MG in Japan are 80-85% and 5-10%/less than 1%,respectively. The incidence of late-onset MG, defined as onset after age 50 years, has been increasing worldwide. A nationwide epidemiological survey in Japan also revealed that the rates of late-onset MG had increased from 20% in 1987 to 42% in 2006. In 2010, a guideline for standard treatments of late-onset MG was published by the Japanese Society of Neurological Therapeutics. Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease of the neuromuscular junction and approximately 60% of LEMS patients have a tumor, mostly small cell lung cancer (SCLC), as a paraneoplastic neurological syndrome. The clinical pictures of Japanese LEMS patients are as follows; male dominant sex ratio (3 : 1), mean age 62 years (17-80 years), 61% of LEMS have SCLC, and the remaining are without cancer. In less than 10% of cases there are signs of cerebellar dysfunctions (paraneoplastic cerebellar degeneration with LEMS; PCD-LEMS) as well, often associated with SCLC. Most patients benefit from 3, 4-diaminopyridine plus pyridostigmine. In paraneoplastic LEMS, treatment of the tumor often results in neurological improvement. In non-paraneoplastic LEMS, prednisone alone or combined with immunosuppressants are treatment options. In both MG and LEMS, where weakness is severe, plasma exchange or intravenous immunoglobulin treatment may provide short-term benefit.

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 and solitary cerebellar metastasis in a patient with occult small-cell lung cancer: a rare experience

The authors describe a case of 60-year-old male patient presented with a 6 month history of progressive weakness of all the four limbs, ataxia, droopy eyelids and bulbar features. Further laboratory and electrodiagnostic studies confirmed the diagnosis of Lambert-Eaton myasthenic syndrome (LEMS). MRI of the brain showed a cerebellar tumour which, following surgery was revealed to be a metastatic small-cell lung carcinoma. Paraneoplastic LEMS together with solitary cerebellar metastasis was diagnosed but no evidence of primary malignancy was detected. An extensive search for related malignancies failed to get any clue. The patient underwent a total surgical excision of tumour and the histopathology revealed a metastatic small cell carcinoma. This case highlights that rarely both paraneoplastic LEMS and cerebellar mass can precede the primary malignancy causing them.

Guidelines on the use of therapeutic apheresis in clinical practice--evidence-based approach from the Apheresis Applications Committee of the American Society for Apheresis

The American Society for Apheresis (ASFA) Apheresis Applications Committee is charged with a review and categorization of indications for therapeutic apheresis. Beginning with the 2007 ASFA Special Issue (fourth edition), the subcommittee has incorporated systematic review and evidence-based approach in the grading and categorization of indications. This Fifth ASFA Special Issue has further improved the process of using evidence-based medicine in the recommendations by refining the category definitions and by adding a grade of recommendation based on widely accepted GRADE system. The concept of a fact sheet was introduced in the Fourth edition and is only slightly modified in this current edition. The fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis. The article consists of 59 fact sheets devoted to each disease entity currently categorized by the ASFA as category I through III. Category IV indications are also listed.

Improvement of diaphragm and limb muscle isotonic contractile performance by K+ channel blockade

The K⁺ channel blocking aminopyridines greatly improve skeletal muscle isometric contractile performance during low to intermediate stimulation frequencies, making them potentially useful as inotropic agents for functional neuromuscular stimulation applications. Most restorative applications involve muscle shortening; however, previous studies on the effects of aminopyridines have involved muscle being held at constant length. Isotonic contractions differ substantially from isometric contractions at a cellular level with regards to factors such as cross-bridge formation and energetic requirements. The present study tested effects of 3,4-diaminopyridine (DAP) on isotonic contractile performance of diaphragm, extensor digitorum longus (EDL) and soleus muscles from rats. During contractions elicited during 20 Hz stimulation, DAP improved work over a range of loads for all three muscles. In contrast, peak power was augmented for the diaphragm and EDL but not the soleus. Maintenance of increased work and peak power was tested during repetitive fatigue-inducing stimulation using a single load of 40% and a stimulation frequency of 20 Hz. Work and peak power of both diaphragm and EDL were augmented by DAP for considerable periods of time, whereas that of soleus muscle was not affected significantly. These results demonstrate that DAP greatly improves both work and peak power of the diaphragm and EDL muscle during isotonic contractions, which combined with previous data on isometric contractions indicates that this agent is suitable for enhancing muscle performance during a range of contractile modalities.

Inotropic effects of the K+ channel blocker 3,4-diaminopyridine on fatigued diaphragm muscle

K(+) channels play important roles in skeletal muscle contraction by regulating action potential duration. Blocking these channels, for example with 3,4-diaminopyridine (DAP), augments muscle force considerably, and these force increases are maintained well during fatigue-inducing contractions. The present study tested the hypothesis that K(+) channel blockade also improves force of previously fatigued muscle. Rat diaphragm underwent fatigue-inducing stimulation in vitro with four different stimulation protocols consisting of 20 Hz vs. 50 Hz trains and 1 min vs. 4 min stimulation durations. DAP administered at the onset of the recovery period produced significant force increases irrespective of the amount of antecedent force loss. These force gains considerably exceeded those resulting from normal force recovery in untreated muscle. Furthermore contraction time was prolonged by DAP in all cases, and half-relaxation time was prolonged by DAP in most cases. Several differences were found compared with previous studies of DAP in fresh muscle, including smaller magnitude and slower time course of force increases. Intracellular electrophysiological recordings found smaller effects of DAP on action potential overshoot and time-depolarization integral in previously stimulated compared with fresh muscle. These data indicate that K(+) channel blockade does indeed increase force of fatigued diaphragm, but to an attenuated extent relative to its effects on non-fatigued muscle, which can be explained on the basis of electrophysiological findings. Nonetheless DAP-induced force increases were usually sufficient to restore force to values present prior to the onset of fatigue-inducing stimulation.

Guidelines on the use of therapeutic apheresis in clinical practice—Evidence-based approach from the apheresis applications committee of the American society for apheresis

The American Society for Apheresis (ASFA) Apheresis Applications Committee is charged with a review and categorization of indications for therapeutic apheresis. This elaborate process had been undertaken every 7 years resulting in three prior publications in 1986, 1993, and 2000 of "The ASFA Special Issues." This article is the integral part of the Fourth ASFA Special Issue. The Fourth ASFA Special Issue is significantly modified in comparison to the previous editions. A new concept of a fact sheet has been introduced. The fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis. A detailed description of the fact sheet is provided. The article consists of 53 fact sheets devoted to each disease entity currently categorized by the ASFA. Categories I, II, and III are defined as previously in the Third Special Issue. However, a few new therapeutic apheresis modalities, not yet approved in the United States or are currently in clinical trials, have been assigned category P (pending) by the ASFA Clinical Categories Subcommittee. The diseases assigned to category IV are discussed in a separate article in this issue.

Paraneoplastic syndromes affecting the nervous system

The paraneoplastic neurologic disorders (PND) are a diverse group of diseases characterized by the presence of neurologic dysfunction in the setting of a remote cancer. PND can affect almost any part of the nervous system, and are most commonly associated with lung cancer (small cell) and gynecologic tumors. Laboratory studies have demonstrated that an autoimmune response links the neurologic disorder and the cancer, and established a model whereby the cancer is believed to initiate the syndrome by expressing a protein antigen normally expressed in the nervous system, leading to anti-tumor immune response followed by autoimmune neurologic symptoms. We review the currently known PND and their pathogenesis.

Clinical aspects of neuromuscular transmission disorders

Autoimmune disorders of neuromuscular transmission are caused by antibodies (abs) directed against membrane proteins at the motor end-plate. Myasthenia gravis (MG) is due, in most cases, to abs against the nicotinic acetylcholine receptor (AChR). Anti-AChR-positive MG actually includes different disease entities: weakness can be confined to extrinsic ocular muscles or can be generalized; patients with generalized MG (G-MG) can be subdivided on the basis of age of onset, HLA association and thymic pathology. About 15% of G-MG patients are anti-AChR-negative; in a proportion of these cases serum abs against the muscle- specific kinase (MuSK) are found. Anti-MuSK-positive MG is characterized by predominant involvement of bulbar muscles and very low frequency of thymic pathology. The Lambert-Eaton myasthenic syndrome (LEMS) is caused by abs against voltage-gated calcium channels at nerve terminal. LEMS is characterized by muscle weakness and autonomic disturbances and it is paraneoplastic in over 50% of the cases. In neuromyotonia and cramp-fasciculation syndrome, that are thought to be due to anti-voltage-gated potassium channel abs, signs of peripheral nerve hyperexcitability can be associated with CNS features.

Myasthenia gravis and myasthenic syndrome: simulation of twitch strength with or without therapy

To examine the quantitative relationship between indirectly evoked twitch and decreases in the number of either postsynaptic receptors or acetylcholine molecules released by a single stimulus, we studied these variables in a computer-simulated model of neuromuscular transmission. Twitch strength decreased if the number of receptors decreased to below 30% of normal or the number of acetylcholine molecules released by a stimulus decreased to below 80%. Inhibition of acetylcholine hydrolysis to 50% restored twitch strength in the presence of a decreased number of receptors. However, twitch strength was more easily restored to normalcy by augmenting the release of acetylcholine, if the release was diminished by disease. The simulations mimic the clinically known therapeutic outcomes in certain disorders of neuromuscular transmission. These results provide useful quantitative insights into the relationship between acetylcholine receptors or the stimulus-induced release of acetylcholine and muscle function in myasthenia gravis or Lambert-Eaton myasthenic syndrome.

Paraneoplastic neurologic syndromes

Cancer can affect the nervous system through many metastatic and nonmetastatic mechanisms, including side effects of cancer treatment, infections, coagulopathy, and metabolic or nutritional deficits. Paraneoplastic neurologic disorders (PND) are an extensive group of syndromes that cannot be explained by any of these complications and may affect any part of the nervous system. PND often develop before the presence of a cancer is known and their recognition may lead to the tumor diagnosis.

Remote neurologic manifestations of cancer

Paraneoplastic disorders may affect any part of the central or peripheral nervous systems. Although relatively uncommon, these disorders are a significant cause of neurologic morbidity for cancer patients. At least some paraneoplastic syndromes are believed to be caused by an autoimmune reaction against shared tumor-neural antigens. This article summarizes the clinical features of paraneoplastic disorders, the current evidence for autoimmunity, and guidelines for diagnosis and treatment.

Lambert-Eaton Myasthenic Syndrome

Weakness and autonomic dysfunction in Lambert-Eaton myasthenic syndrome (LEMS) can be partially or fully controlled by 3,4-Diaminopyridine. Intravenous immunoglobulin or plasma exchange (PE) plasmapheresis) provides short-term improvement in severely affected patients. In those at risk from paraneoplastic LEMS (cigarette smokers), an intensive search for lung cancer should be undertaken, and specific tumor therapy instituted that likely will improve the neurologic deficit. Prednisolone (1.5 mg per kg of body weight administered on alternate days, maximum dosage is 100 mg) is indicated in those with paraneoplastic or nonparaneoplastic LEMS who fail to respond sufficiently to symptomatic treatment. The addition of azathioprine or cyclosporine is indicated as corticosteroid sparing medications in nonparaneoplastic LEMS. When remission or optimal improvement is judged to be present, prednisolone should be tapered to the minimum dose that effectively controls symptoms. If full withdrawal is achieved, azathioprine dose reduction is similarly initiated. In nonparaneoplastic LEMS patients failing to respond to azathioprine after 1 to 2 years of therapy, physicians should consider substituting cyclosporine.

Paraneoplastic syndromes of the spinal cord, nerve, and muscle

Cancer can affect the peripheral nervous system by non-metastatic, sometimes immune-mediated mechanisms. Recognition of these paraneoplastic syndromes is important because it can lead to the detection of the tumor, and also helps to avoid unnecessary studies to determine the cause of the neurologic symptoms in patients with cancer. Many paraneoplastic syndromes of the peripheral nervous system are not associated with serum antibodies that serve as markers of paraneoplasia. For this group of disorders the diagnosis depends on the clinician's index of suspicion and conventional electrophysiologic and laboratory tests. Treatment of the tumor, immunotherapy, or both may improve some of these syndromes. This review focuses on paraneoplastic syndromes of the spinal cord, peripheral nerve, and muscle.

Chronic multiple paraneoplastic syndromes

A patient presented with symptoms of limbic and brainstem encephalitis, motor and sensory neuronopathy, cerebellar dysfunction, and highly positive anti-Hu antibodies. He also harbored P/Q-type calcium channel antibodies and manifested the Lambert-Eaton myasthenic syndrome (LEMS). Small-cell lung cancer was found, and he received both antineoplastic therapy and intravenous immunoglobulin (IVIg). Remission of the malignancy was achieved. Although the anti-Hu-related manifestations improved after therapy, LEMS has persisted, leading to IVIg dependency.

Apheresis treatment in Lambert-Eaton myasthenic syndrome

The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of peripheral cholinergic transmission in which autoantibodies decrease the presynaptic release of acetylcholine at the neuromuscular junction and autonomic system. Recent results suggest that the antibodies to P/Q-type calcium channels are the principal pathogenic factors in LEMS. Here, we present our experience with cases of LEMS who are noncarcinomatous. We studied the efficacy of plasmapheresis, analyzing the clinical score, electrophysiological finding, and the titer of anti-P/Q-type voltage-gated calcium channel (P/Q-VGCC) antibody. The first case, a 72-year-old female presenting with leg weakness, was treated by plasma exchange (PE). However, clinical improvement was transient; intravenous immunoglobulin (IVIg) therapy was followed by additional PE. She had a clinical and electromyologic improvement, and her P/Q-VGCC antibody titers decreased. Her clinical status and CMAP amplitude correlated closely with the anti-P/Q-VGCC antibody titers. The second case, a 73-year-old male presenting with leg weakness, was treated by PE and double-filtration plasmapheresis. The P/Q-VGCC antibody titres decreased immediately after these aphereses, but recovered to the pretreatment levels 1 week after them. After the immunosuppressive drugs prednisolone and azathioprine were started, his clinical symptoms improved. His antibody titers decreased gradually after immunosuppressive therapy. It is speculated that no sufficient efficacious improvement could be obtained by apheresis alone because of a high rate of P/Q-VGCC antibody production. Considering our experiences and other literature, we discuss the indication of apheresis treatment of LEMS.

Lambert-Eaton myasthenic syndrome

The Lambert-Eaton myasthenic syndrome is a neuromuscular disorder characterised by defective neurotransmitter release at autonomic neurones and presynaptic terminals of the neuromuscular junction. It is caused by an IgG autoantibody formed against especially the P/Q type of voltage-gated calcium channels (VGCC) which is an essential component of the mechanism of neurotransmitter release. Many patients have an associated small cell carcinoma of the lung which appears to provide the antigenic stimulus for antibody production, although there is another group with no underlying malignancy. Both groups show an association with immunological disorders. Assay of VGCC antibody titres and electrophysiological tests help to differentiate Lambert-Eaton myasthenic syndrome from other disorders of the neuromuscular junction. Several drugs and therapeutic interventions capable of producing significant clinical improvement are currently available. Patients should also be investigated for underlying tumours, the specific treatment of which can result in remission or amelioration of symptoms.