[The Japanese Clinical Guidelines 2022 for Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome: An Overview]

The new Japanese clinical guidelines for myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) were published in 2022. The Following are the salient features of these guidelines (GLs): (1)These are the first Japanese GLs that include a description of LEMS. (2)Diagnostic criteria for both MG and LEMS are described. (3)A high-dose oral steroid regimen with an escalation and de-escalation schedule is not recommended. (4)Refractory MG is defined. (5)The use of molecular-targeted drugs is included. (6)MG is subcategorized into six clinical subtypes. (7)Treatment algorithms for both MG and LEMS are discussed.

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.

Undiagnosed Lambert-Eaton Myasthenic Syndrome in the Era of Sugammadex: A Case Report

OBJECTIVE

In this case report, we discuss the rare manifestation of prolonged neuromuscular blockade in a patient with history of small cell lung cancer and undiagnosed Lambert-Eaton myasthenic syndrome (LEMS) who had previously received succinylcholine for general anesthesia without incident but subsequently exhibited prolonged neuromuscular blockade during a laparoscopic procedure. We aimed to emphasize the importance of reversal agent safety and precision as well as vigilant perioperative and postoperative care.

METHODS

We used the patient's electronic medical record, direct patient care experiences, and comprehensive literature review for this case report.

RESULTS

Sugammadex was administered with mild improvement. Suspecting undiagnosed LEMS, neostigmine was administered, yielding satisfactory muscle strength and successful extubation. In retrospect, the patient reported history of weakness when lifting weights that improved upon exertion.

CONCLUSIONS

Sugammadex is an efficient and effective agent for reversal of neuromuscular blockade. However, proper monitoring of the depth and recovery of blockade is imperative to when using sugammadex with optimal safety and precision in all patients. Perioperative care teams must remain vigilant with a high index of suspicion for neuromuscular junction pathology to properly plan perioperative care for patients at risk, especially those with small cell lung cancer who may have undiagnosed LEMS.

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.

Lambert-Eaton Myasthenic Syndrome and Botulism

PURPOSE OF REVIEW

This article reviews the pathophysiology, epidemiology, clinical features, diagnosis, and treatment of Lambert-Eaton myasthenic syndrome (LEMS) and botulism, presynaptic disorders of neuromuscular transmission in which rapid diagnosis improves long-term outcomes.

RECENT FINDINGS

Therapy for LEMS has seen significant advances in recent years due to the approval of amifampridine-based compounds. LEMS is likely still underdiagnosed, particularly when no underlying malignancy is identified. Clinicians must have a strong suspicion for LEMS in any patient presenting with proximal weakness and autonomic dysfunction. Botulism is another rare disorder of presynaptic neuromuscular transmission that is most commonly associated with improper storage or preservation of food products. Over the past 2 decades, wound botulism has been increasingly reported among users of black tar heroin. A high degree of clinical suspicion and electrodiagnostic studies can be beneficial in distinguishing botulism from other acute neurologic disorders, and early involvement of state and federal health authorities may assist in confirming the diagnosis and obtaining treatment. When botulism is suspected, electrodiagnostic studies can provide clinical evidence of disordered neuromuscular transmission in advance of serologic confirmation, and providers should not wait for confirmation of the diagnosis to initiate treatment.

SUMMARY

A targeted clinical history and a thorough neurologic examination with support from serologic and electrodiagnostic studies are key to early diagnosis of LEMS and botulism. Early diagnosis of both conditions creates opportunities for therapy and improves outcomes.

Lambert-Eaton Myasthenic Syndrome Caused by Atezolizumab in a Patient with Small-cell Lung Cancer

We herein report a 74-year-old man who developed Lambert-Eaton myasthenic syndrome (LEMS) during atezolizumab treatment for extensive-stage small-cell lung cancer. He was started on maintenance immunotherapy with atezolizumab every three weeks after four cycles of atezolizumab plus carboplatin plus etoposide combination therapy. After 13 cycles of maintenance atezolizumab therapy, he complained of muscular weakness and fatigue. Findings from a nerve conduction study and positive findings for anti-P/Q-type voltage-gated calcium channel antibody resulted in a diagnosis of LEMS. This was a rare case of LEMS as a neurological immune-related adverse event induced by atezolizumab therapy.

Lambert-Eaton Myasthenic Syndrome, Botulism, and Immune Checkpoint Inhibitor-Related Myasthenia Gravis

PURPOSE OF REVIEW

This article reviews the pathophysiology, epidemiology, clinical presentation, diagnosis, and treatment of Lambert-Eaton myasthenic syndrome (LEMS) and of botulism, and immune-related myasthenia gravis (MG) occurring in the context of immune checkpoint inhibitor therapy for cancer.

RECENT FINDINGS

The suspicion that LEMS is rare but also likely underdiagnosed is supported by recent epidemiologic data. A validated, LEMS-specific scale now exists to assess and monitor disease, and symptomatic and immunomodulatory treatments are available. As presynaptic disorders of neuromuscular transmission, LEMS and botulism share electrodiagnostic abnormalities but have important distinguishing features. Knowledge of the clinical features of botulism is needed, particularly with continued cases of infant botulism, the opioid epidemic increasing the incidence of wound botulism, and medical use of botulinum toxin, which may cause iatrogenic botulism. Foodborne botulism remains rare. Prompt recognition of botulism and administration of antitoxin can improve outcomes. MG may be exacerbated or may present de novo in the context of immune activation from immune checkpoint inhibitor therapies for cancer. Immune-related MG commonly overlaps with myositis and myocarditis. Corticosteroids typically result in improvement. However, immune-related MG can be more fulminant than its idiopathic counterpart and may cause permanent disability or death.

SUMMARY

The diagnosis of LEMS, botulism, or immune-related MG can generally be made from the patient's history, supplemented with directed questions, a physical examination designed to demonstrate abnormalities, and laboratory and electrodiagnostic testing. Early diagnosis and carefully selected treatment not only improve outcomes of the neuromuscular disease but can affect the prognosis of underlying malignancy, when present.

Coexistence of myasthenia gravis and Lambert-Eaton myasthenic syndrome in a small cell lung cancer patient: A case report

RATIONALE

Myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) are both neuromuscular junction diseases, and some controversy exists whether the 2 diseases occur at the same time.

PATIENT CONCERNS

We report a case that a patient with presentation of acetylcholine receptor (AChR) antibody positive MG and LEMS associated with small cell lung cancer (SCLC).

DIAGNOSES

The patient firstly suffered from fluctuant symptoms, including slurred speech, double eyelid ptosis, and weakness of limbs. His clinical characteristics were consistent with the diagnosis of MG and were effective with the treatment of pyridostigmine bromide and corticosteroids. After 8 months, the performance of repeated electrical stimulation suggested presynaptic lesion, which supported the patient with LEMS. After further examination, malignant tumors were found in the liver and right lung, and the pathology proved small cell carcinoma.

INTERVENTIONS

His clinical characteristics were effective with the treatment of pyridostigmine bromide and corticosteroids. Right hilar lesion and multiple metastatic tumors in liver shrunk after chemotherapy.

OUTCOMES

The patient's condition improved gradually. He was followed up for 17 months without tumor progression.

LESSONS

The case report illustrates that MG and LEMS may be coexisted in the same patient. In MG and LEMS, clinicians should consider the possibility of malignant tumors as early detection and treatment may significantly improve the patient's prognosis.

Coexistence of Lambert-Eaton myasthenic syndrome and autoimmune encephalitis with anti-CRMP5/CV2 and anti-GABAB receptor antibodies in small cell lung cancer: A case report

RATIONALE

Autoimmune encephalitis and Lambert-Eaton myasthenic syndrome are classic paraneoplastic neurological conditions common in patients with small cell lung cancer.

PATIENT CONCERNS

The patient complained of tiredness, fluctuating recent memory loss, and inability to find his home. His family members reported a change in character, irritability, and paranoia. One month later, the patient had 1 grand mal seizure lasting 5 minutes.

DIAGNOSIS

The patient was diagnosed with limbic encephalitis combined with Lambert-Eaton myasthenic syndrome. The gamma-aminobutyric acid B (GABAB) receptor and collapsin response mediator protein 5 (CRMP5, also called CV2) antibody test results were positive. Nine months after the onset of symptoms, the patient was diagnosed with small cell lung cancer.

INTERVENTIONS

The patient was administered intravenous immunoglobulin for 5 days. He was then treated with 60 mg prednisone once per day. The prednisone dose was gradually reduced by 1 tablet every 2 weeks. After the diagnosis, the patient underwent 6 courses of chemotherapy with cisplatin combined with sequential chemoradiation therapy.

OUTCOMES

The patient was able to take care of himself. Neurological examination revealed a lower limb proximal muscle strength level of 4 and a reduced limb tendon reflex. The patient had deficits in short-term memory, a Mini-Mental State Examination score of 26, Montreal Cognitive Assessment score of 24, Self-rating Depression Scale score of 54 (mild depression), and Self-Rating Anxiety Scale score of 42 (normal).

LESSONS

Autoimmune diseases of the peripheral and central nervous systems can be observed at the same time in patients with small cell lung cancer, even when magnetic resonance imaging findings are negative and immune therapy is effective.

Five years experience on 3,4-diaminopyridine phosphate in Lambert-Eaton syndrome: Case reports

RATIONALE

To report our experience on 7 patients (4 males and 3 females), affected by nonparaneoplastic Lambert-Eaton myasthenic syndrome, treated with 3,4-diaminopyridine phosphate (3,4-DAPP) either alone or in combination with other immunosuppressants or steroids.

PATIENT CONCERNS

Patients have been evaluated at specific timepoints (ie, baseline and last 5 year follow-up), with neurological examination, autoantibodies against presynaptic voltage-gated Cav2.1 (P/Q type) calcium ion channel (VGCC) dosage, neurophysiological evaluation focusing on the increased amplitude of the compound muscle action potential (cMAP) after maximum voluntary effort, quantitative myasthenia gravis (QMG) and activities of daily living scales, and autonomic nervous system involvement evaluation.

OUTCOMES

Five out of 7 patients presented a clinical improvement persisting at last 5-year follow-up; 2 out of them improved taking only 3,4-DAPP at the maximal dosage, whereas the remaining received concomitant medications, such as prednisone and azathioprine. However, the clinical amelioration was not statistically significant. No one of the patients reported severe adverse events, except one, complaining of transient chin and perioral paresthesias. A significant association between QMG and the type of pharmacological drugs therapy (P = .028) emerged. Indeed, we observed an improvement of the clinical condition in all 3 subjects treated with 3,4-DAPP and prednisone.

CONCLUSIONS

In this study, we confirm 3,4-DAPP treatment efficacy on muscle strength, but minor evidence of drug effectiveness have been demonstrated on the autonomic nervous system involvement and on the deep tendon reflexes reappearance, a part from patients who received 3,4-DAPP associated to prednisone.

Population Pharmacokinetics/Pharmacodynamics of 3,4-Diaminopyridine Free Base in Patients With Lambert-Eaton Myasthenia

Lambert-Eaton myasthenia (LEM) is a rare autoimmune disorder associated with debilitating muscle weakness. There are limited treatment options and 3,4-diaminopyridine (3,4-DAP) free base is an investigational orphan drug used to treat LEM-related weakness. We performed a population pharmacokinetic/pharmacodynamic (PK/PD) analysis using 3,4-DAP and metabolite concentrations collected from a phase II study in patients with LEM. The Triple Timed Up & Go (3TUG) assessment, which measures lower extremity weakness, was the primary outcome measure. A total of 1,270 PK samples (49 patients) and 1,091 3TUG data points (32 randomized patients) were included in the PK/PD analysis. A two-compartment and one-compartment model for parent and metabolite, respectively, described the PK data well. Body weight and serum creatinine partially explained the variability in clearance for the final PK model. A fractional inhibitory maximum effect (Emax ) model characterized the exposure-response relationship well. The PK/PD model was applied to identify a suggested dosing approach for 3,4-DAP free base.

Ophthalmoplegia associated with lung adenocarcinoma in a patient with the Lambert-Eaton myasthenic syndrome: A case report

RATIONALE

The Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular disease; its unique symptoms of LEMS include dry mouth with a metallic taste, constipation, and erectile dysfunction. As it is quite rare, isolated ocular muscle impairment associated with LEMS east to ignore.

PATIENT CONCERNS

A 65-year-old man presented with alternating ptosis and diplopia. Isolated ocular muscle impairment had lasted for 6 years, and the patient was initially diagnosed with ocular myasthenia gravis (MG). Treatment with azathioprine only slightly improved symptoms over the first 2 months; long-term treatment was not effective.

DIAGNOSES

Dynamic observation of chest computed tomography images revealed a slowly progressing nodule in the lower lobe of the left lung. The subsequent pathologic examination following mass resection confirmed a diagnosis of lung adenocarcinoma.

INTERVENTIONS

The patient was ultimately diagnosed with the Lambert-Eaton myasthenic syndrome associated with pulmonary adenocarcinoma.

OUTCOMES

Resection of the lung tumor relieved all symptoms.

LESSONS

Other causes of ocular MG symptoms should be considered when standard MG therapy is ineffective, especially the Lambert-Eaton myasthenic syndrome.

Long-term disease history, clinical symptoms, health status, and healthcare utilization in patients suffering from Lambert Eaton myasthenic syndrome: Results of a patient interview survey in Germany

INTRODUCTION

The burden of disease in Lambert-Eaton myasthenic syndrome (LEMS) patients is unclear. This study focused on the patient's perspective to obtain patient-reported information on clinical symptoms, burden of illness, impact of LEMS on activities of daily living (ADL), and management of LEMS.

METHODS

Semi-structured, face-to-face interviews with LEMS patients from two specialized centres in Germany between September and December 2010.

RESULTS

Twelve patients participated; mean age 66.7 ± 9.8 years. First symptoms occurred at age 52.5 ± 14.0 years. Mean time between first symptoms and diagnosis was 4.4 ± 6.2 years. Patients reported neuromuscular, cranial, and autonomic symptoms plus general fatigue. Two-thirds of patients reported 10 or more symptoms. The most frequent symptoms were leg weakness (91.7%) and general fatigue (83.3%). Restrictions in ADL were reported always or often in 75% of patients. Over half of the patients (n = 7) reported poor or very poor health status. Mean EQ-5D utility scores were 0.34 ± 0.35, with little day-to-day variation. Patients visited a number of different clinicians; most had been hospitalized at some point in the course of their disease. The most frequent drug treatments were 3,4-diaminopyridine (3,4-DAP) (83.3%) and pyridostigmine (41.5%). The study has several limitations, including small sample size and the potential influence of recall bias.

CONCLUSION

LEMS patients report long individual disease histories. Most patients suffer multiple symptoms which are frequently severe and troublesome, and almost all are restricted in ADL with poor health status. There is high utilization of healthcare resources from diagnosis to ongoing treatment. Physicians should be aware of this rare disease to ensure that patients receive an early diagnosis and prompt and appropriate treatment.

Treatment for Lambert-Eaton myasthenic syndrome

BACKGROUND

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular transmission. Treatments attempt to overcome the harmful autoimmune process, or improve residual neuromuscular transmission

OBJECTIVES

The objective was to examine the efficacy of treatment in Lambert-Eaton myasthenic syndrome.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Specialized Register (12 October 2010), the Cochrane Central Register of Controlled Trials (CENTRAL) (12 October 2010, Issue 4 2010 in the Cochrane Library), MEDLINE (January 1966 to September 2010) and EMBASE (January 1980 to September 2010).

SELECTION CRITERIA

All randomised or quasi-randomised trials of adults and children with a diagnosis of Lambert-Eaton myasthenic syndrome, with or without small-cell lung cancer, receiving any form of pharmacological or physical treatment.

DATA COLLECTION AND ANALYSIS

All authors independently assessed studies for inclusion and extracted data. Study authors were contacted for missing information when possible.

MAIN RESULTS

Four controlled trials of 3,4-diaminopyridine compared with placebo in a total of 54 participants with Lambert-Eaton myasthenic syndrome were eligible: three cross-over trials and one parallel group. Two were added at this update. One of these trials also assessed pyridostigmine in conjunction with 3,4-diaminopyridine. A further cross-over trial compared intravenous immunoglobulin (IVIg) to placebo in nine participants.Four trials of 3,4-diaminopyridine reported significant improvement in the primary outcome, muscle strength score, or myometric limb measurement for between hours and a week following treatment, and significant improvement in resting compound muscle action potential (CMAP) amplitude following 3,4-diaminopyridine, compared with placebo.A meta-analysis of the primary endpoint showed Quantitative Myasthenia Gravis (QMG) muscle score assessed between three and eight days was likely to improve by a mean of 2.44 points (95% confidence interval 3.6 to 1.22). Meta-analysis of the secondary endpoint CMAP amplitude also showed a mean improvement of 1.36 mV (95% confidence interval 0.99 to 1.72) over the same period. The risk of bias was determined to be low, and quality of evidence moderate to high.A single cross-over trial reported significant improvement in myometric limb strength and non-significant improvement in mean resting CMAP amplitude with IVIg compared to placebo. Clinical improvement lasted for up to eight weeks.

AUTHORS' CONCLUSIONS

Limited but moderate to high quality evidence from randomised controlled trials showed that over days 3,4-diaminopyridine, or for up to 8 weeks IVIg, improved muscle strength scores and CMAP amplitudes in participants with Lambert-Eaton myasthenic syndrome. There are insufficient data at present to quantify this effect. Other possible treatments have not been tested in randomised controlled trials.

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.

3,4-Diaminopyridine is more effective than placebo in a randomized, double-blind, cross-over drug study in LEMS

The purpose of this study was to investigate the clinical and electrophysiological efficacy of 3,4-diaminopyridine (DAP) in patients with Lambert-Eaton myasthenic syndrome (LEMS) in a randomized, double-blind, cross-over drug trial. The diagnosis of LEMS was made based on the combination of fluctuating muscle weakness, diminished or absent reflexes, and more than 60% increment of the compound muscle action potential (CMAP) amplitude after brief exercise or 50-HZ stimulation on a repetitive nerve stimulation (RNS) test. Evaluations were done at baseline, with placebo, and with 3,4-DAP (up to 75-80 mg/day). Assignment of placebo or 3,4-DAP was done in a double-blinded manner. Measurements included subjective symptoms score, objective clinical measurements [LEMS classification, muscle strength score, quantitative myasthenia gravis (QMG) score] and RNS test and single-fiber electromyography (SFEMG). The differences between placebo and baseline values (placebo change) were compared with the differences between 3,4-DAP and baseline or placebo values (DAP change). Seven patients with LEMS (QMG score >9) participated in the study. One patient had major side-effects with 3,4-DAP and withdrew from the study. Statistically significant efficacy was noted with DAP change (N = 13) compared with placebo change (N = 7) according to the subjective symptoms score (P = 0.01), LEMS classification (P < 0.001), muscle strength score (P < 0.006), QMG score (P = 0.02), and CMAP (P = 0.03). For long-term treatment, 2 patients preferred 3,4-DAP, 1 chose guanidine hydrochloride, 1 preferred pyridostigmine, and 2 chose no treatment. A randomized, double-blind, cross-over drug trial of 3,4-DAP showed significant efficacy over placebo in patients with LEMS. As a long-term treatment, however, not all patients preferred this drug.

[A case of Lambert-Eaton myasthenic syndrome with small cell lung cancer, treated with 3,4-diaminopyridine]

A 77-year-old man was admitted to our hospital with muscle weakness and shortness of breath. Chest CT showed a mass in the left upper lobe, and electromyography showed waxing phenomenon with high-frequency repetitive stimulation. We diagnosed Lambert-Eaton myasthenic syndrome accompanying small cell lung cancer. He was treated with carboplatin and etoposide, and concurrent thoracic irradiation. Although, the tumor size decreased, his myasthenic symptoms remained. He started taking 3,4-diaminopyridine and his muscle weakness improved dramatically, and he was eventually able to walk finally. In some cases, anti-tumor therapies cannot improve the myasthenic symptoms. In such cases, 3,4-diaminopyridine could improve the quality of life, and should be approved in Japan.

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

Lambert-Eaton myasthenic syndrome is a rare, but reasonably well-understood, antibody-mediated autoimmune disease that is caused by serum auto-antibodies and results in muscle weakness and autonomic dysfunction. One half of the patients have an idiopathic form, the other half a tumour-associated form of the disease. Three randomised trials and a large number of smaller clinical studies have resulted in a number of drugs becoming available for the treatment of Lambert-Eaton myasthenic syndrome. Several drugs are available for the symptomatic treatment of the disease, including guanidine, aminopyridines or acetylcholinesterase inhibitors. Other therapies aim to deplete the serum autoantibodies or to suppress the immune system. For this purpose, immunomodulating strategies, such as intravenous immunoglobulins or plasmapheresis, or several immunosuppressive agents are available. Chemotherapy has successfully ameliorated the course of disease in Lambert-Eaton myasthenic syndrome patients with an underlying tumour.

Intravenous immunoglobulin use for neurologic diseases

Intravenous immunoglobulin (IVIG) has been used primarily for immune deficiency patients, and its greatest expansion is seen more and more in the treatment of autoimmune disorders, especially in neurology. The benefits of IVIG treatment include its availability in all treatment centers and its ease of administration in an outpatient setting. This article gives an overview of some autoimmune neurologic diseases and explores the clinical evidence supporting the use of IVIG.

[A case of the Lambert-Eaton syndrome of non-neoplastic origin. Ten-year follow-up]

A case is presented of a 34-year-old man who developed weakness of the proximal muscles of the extremities, particularly lower, slight myalgia, and vegetative symptoms (dryness in the mouth). Those symptoms progressed within a month. On examination weakness of the muscles of the extremities was found as well as weak tendon reflexes, slight atrophy of muscles of the arms and thighs and apokamnosis. Edrophonium test was slightly positive. Electrostimulation revealed changes typical of the Lambert-Eaton syndrome: low amplitude of the compound muscle action potential on single stimulus, decreasing amplitude of the subsequent responses to 3 Hz stimulation, marked facilitation on 30 Hz stimulation. Neoplastic etiology was excluded by chest X-ray and CT, as well as by bronchoscopy, abdominal and prostatic USG, and thyroid USG and scintigraphy. Antibodies to AChR were not found in the serum. The titre of the antibodies against voltage-gated calcium channels was highly positive which was decisive in the diagnosing of the Lambert-Eaton syndrome. The patient was treated with pyridostigmine, corticosteroids, cyclophosphamide and immunoglobulins. Ten years of follow-up have fully confirmed the diagnosis of a non-neoplastic Lambert-Eaton syndrome.

[Idiopathic Lambert-Eaton myasthenic syndrome: report of one case]

Lambert-Eaton myasthenic syndrome (LEMS) is an autoinmune idiopathic or paraneoplastic syndrome producing antibodies agaisnt presynaptic voltage calcium channels. The clinical features of patients with LEMS are muscle weakness and autonomic dysfunction. We report a 40 years old man with a four years history of proximal weakness, absent tendon reflexes and dry mouth. The diagnosis was confirmed by characteristic electromyographic findings, showing a low-amplitude muscle response that increased dramatically after activation. Circulating antibodies to voltage-gated calcium channel were present. The search for malignant tumors was negative. The patient was treated with prednisone and azathioprine and after four months, he was able to walk and signs of autonomic dysfunction started to subside.

[The use of intravenous immunglobulin in the treatment of autoimmune neuromuscular diseases]

Intravenous immunglobulin given in autoimmune neuromuscular disorders modulates the immune system by complex actions, including, 1. the modification of the expression and function of Fc receptors, 2. interference with the activation of the complement and the cytokine network, 3. neutralisation of antiidiotypic antibodies, 4. effects on the activation, differentiation and effector functions of the T and B cells. Controlled trials have shown that intravenous immunglobulin is effective as first-line therapy in patients with Guillain-Barré syndrome and multifocal motor neuropathy. In case of steroid resistance or coexisting diabetes mellitus, intravenous immunglobulin can be the first line therapy in chronic inflammatory demyelinating polyneuropathy as well. As an alternative therapy it can be a second-line choice in dermatomyositis, myasthenia gravis, Lambert-Eaton myasthenic syndrome, and stiff person syndrome. While it has a remarkably good safety record for long-term administration the following side effects have been observed: headache, skin rash, thromboembolic events and renal tubular necrosis. In some disorders, the appropriate dose and frequency of infusions that maintain a satisfactory therapeutic response is well defined on the basis of data of evidence-based medicine, whereas in others it still remains to be defined. For the analysis of pharmacoeconomical aspects and the mechanism(s) of response differences in the same disease categories, further studies are necessary.

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.

[Lambert-Eaton myasthenic syndrome with acute respiratory failure associated with small cell lung cancer]

HISTORY AND ADMISSION FINDINGS

A 53-year-old woman had suffered from progressive lower limb weakness for 8 weeks. She was not able to walk on her own. Two hours after admission endotracheal intubation and mechanical ventilation became necessary because of acute respiratory failure.

INVESTIGATIONS

Chest radiograph and computerized tomography showed a huge lesion originating from the lower lobe of the left lung with mediastinal infiltration. Histological examination of bronchoscopical-guided biopsy disclosed small cell lung cancer. Electrophysiological studies revealed an incremental response on high-rate stimulation in the repetitive nerve stimulation test. Autoantibodies to P/C-type voltage-gated calcium channels were detected. Further, laboratory test results revealed hyponatremia (100 mmol/l) and elevated ADH (11 pg/ml).

DIAGNOSIS, TREATMENT AND CLINICAL COURSE

These results led to the diagnosis of paraneoplastic Lambert-Eaton myasthenic syndrome (LEMS) with acute respiratory failure caused by small cell lung cancer. Additionally, SIADH (syndrome of inappropriate antidiuretic hormone secretion) was diagnosed as another paraneoplastic disease. Because of a prolonged weaning process resulting from inadequacy of mechanical ventilation, administration of intravenous immunoglobulins and chemotherapy with cisplatin and etoposide were undertaken. This made successful extubation possible after 7 days. In spite of all supportive treatment, clinical deterioration occurred. The patient died 27 days after the small cell lung cancer had been diagnosed.

CONCLUSION

The Lambert-Eaton myasthenic syndrome should be considered in cases of unexplained acute respiratory failure and clinical evidence of neoplastic disease.

Myasthenia gravis and myasthenic syndrome

Myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) are autoimmune ion channel disorders mediated by antibodies to postsynaptic acetylcholine receptors and presynaptic voltage-operated calcium channels, respectively. MG and LEMS are currently treated with corticosteroids and immunosuppressive drugs with a positive clinical outcome. Since both diseases are mediated by circulating autoantibodies, they are good candidates for immunomodulation by intravenous immunoglobulins (IVIG). Standardized controlled studies are lacking in this field, but there is general agreement that IVIG are effective. They can be used as an acute treatment to control temporarily the most severe forms of these diseases, as well as a chronic immunomodulating therapy in addition to standard pharmacological treatment. Several aspects of IVIG administration, cost benefit-analysis, and comparison to plasmapheresis are still needed.

Therapy in myasthenia gravis and Lambert-Eaton myasthenic syndrome

Myasthenia gravis (MG) is a heterogeneous disorder, a fact that needs to be kept in mind when considering treatment. Most patients benefit from pyridostigmine. In nonthymomatous ocular MG, prednisolone is often effective. Thymectomy is indicated for thymoma and is an option for acetylcholine receptor antibody-positive patients with generalized weakness developing under the age of 45 years. In older patients and in those failing to respond to thymectomy, prednisone alone or combined with azathioprine is the treatment of choice. Mycophenolate mofetil is an option in those intolerant of azathioprine. Lambert-Eaton myasthenic syndrome (LEMS) can exist in paraneoplastic (P-) and nonparaneoplastic (NP-) forms. Most patients benefit from 3,4-diaminopyridine. In P-LEMS, treatment of the tumor often results in neurological improvement. In both forms, prednisone alone is an option or combined with azathioprine in NP-LEMS. In both MG and LEMS, where weakness is severe, plasma exchange or intravenous immunoglobulin treatment may provide short-term benefit.

Use of intravenous immunoglobulin in Lambert-Eaton myasthenic syndrome

The authors report a case of a 65-year-old woman with small cell lung cancer who had profound, progressive lower extremity weakness, intermittent blurred vision, a dry mouth, and orthostatic hypotension. Results of laboratory and electrodiagnostic studies were consistent with the diagnosis of Lambert-Eaton myasthenic syndrome. The patient was treated with one course of intravenous immunoglobulin and had significant improvement.

Lambert-Eaton myasthenic syndrome in children

Lambert-Eaton myasthenic syndrome is a presynaptic disorder of neuromuscular transmission. It is characterized by muscle weakness, hyporeflexia, and autonomic dysfunction. It is most often associated with small cell carcinomas of the lung. Rare cases have been reported in children. We recently encountered two children with Lambert-Eaton myasthenic syndrome associated with antibodies to P/Q-type calcium channel but without evidence of neoplasms. Both patients showed prolonged and significant improvement following cyclosporin treatment. The diagnosis of Lambert-Eaton myasthenic syndrome should be considered in children with progressive weakness and a negative work-up for the usual causes. High-frequency repetitive nerve stimulation and P/Q-type calcium-channel antibodies may confirm the diagnosis.

[Quantitative evaluation of the effect of 3,4-diaminopyridine in a patient with Lambert-Eaton myasthenic syndrome using dynamic dynamometry]

We reported a 72-year-old woman with Lambert-Eaton myasthenic syndrome. The chief complaint was weakness and atrophy of the thigh muscles, which prevented her from climbing stairs even with a handrail. Sensory and autonomic function was normal without amblygeustia. There was no malignancy found, and her serum anti-V/Q type voltage-gated calcium channel antibody was negative. Administration of 3,4-diaminopyridine (DAP), known to accelerate acetylcholine release, was very effective and she became able to climb stairs without a handrail. For evaluation of the therapeutic effect of DAP, the initial compound muscle action potential (ICMAP) on evoked electromyogram has been recommended because it provides highly sensitive and reproducible results. Unfortunately this method is usually applied to several particular distal muscles for technical reasons. In the present case, evaluation of the quadriceps femoris muscle was most important because it was most responsible for her disability. We attempted to measure the angular velocity and the angular acceleration on knee extension movement using dynamic dynamometry. The angular velocity improved from 124 to 162 deg/sec and the angular acceleration from 220 to 390 deg/sec2. The results were more sensitive and more relevant to her demonstrable ADL improvement than grasping power increase and ICMAP improvement recorded at the distal muscles.

Long term outcome in Lambert-Eaton myasthenic syndrome without lung cancer

OBJECTIVES

To determine the prognosis in patients with Lambert-Eaton myasthenic syndrome (LEMS) without small cell lung cancer (SCLC), and to analyse longitudinal clinical, electrophysiological, and immunological data on each patient to establish prognostic factors for long term outcome.

METHODS

The retrospective and part prospective study of 47 patients with LEMS was undertaken from data recorded during visits to a specialist neuromuscular clinic. Serial measurements of muscle strength score in shoulder abduction, elbow extension and hip flexion, compound muscle action potential (CMAP) amplitude, and postcontraction increment in abductor digiti minimi (ADM), and anti-P/Q-type voltage gated calcium channel (VGCC) antibody titre were made at each visit.

RESULTS

Muscle strength scores were improved in 88% of patients after a median duration of immunosuppressive treatment of 6 years (range 1.3 to 17 years); anti-VGCC antibody titres fell in 52% after treatment; and mean resting CMAP amplitude improved from 2.7 mV initially to 8.8 mV after 2 years of treatment p<0.001). Initial pretreatment anti-VGCC antibody titre did not correlate significantly with either CMAP amplitude, CMAP increment, or clinical score: from serial measurements made during follow up, significant correlation between antibody titre and CMAP amplitude was seen in only two patients. Sustained clinical remission was achieved by 20 (43%) of whom only four remained in remission without the need for immunosuppression. Using a Cox proportional hazards model, the only independent predictor of sustained clinical remission was initial pretreatment clinical score (p=0.03). Lymphoma presented in three patients during the study.

CONCLUSIONS

The prognosis in patients with LEMS without SCLC is favourable, although patients often need significant doses of immunosuppressive treatment to remain clinically stable. Only initial clinical muscle strength measurements and not anti-VGCC antibody titres or electrophysiological recordings are predictive of long term outcome.

Lambert-Eaton myasthenic syndrome: electrodiagnostic findings and response to treatment

The authors reviewed the incidence of cancer, repetitive nerve stimulation findings, and response to treatment in 73 patients with Lambert-Eaton myasthenic syndrome. Thirty-one patients (42%) had lung cancer, 29 small cell. Doubling of the compound motor action potential amplitude in three tested distal muscles was seen in only 41% of patients. Treatment with 3, 4-diaminopyridine produced moderate to marked self-reported functional improvement in 79% of the 53 treated patients.

Lambert-Eaton myasthenic syndrome associated with idiopathic thrombocytopenic purpura and diffuse panbronchiolitis: long-term remission after a course of intravenous immunoglobulin combined with low-dose prednisolone

We report a case of Lambert-Eaton myasthenic syndrome (LEMS) associated with idiopathic thrombocytopenic purpura (ITP) and diffuse panbronchiolitis (DPB). An extensive search for malignancy yielded negative results. Interestingly, ITP and DPB developed simultaneously when the patient suffered from myasthenic symptoms. This is the first report in the Japanese or English literature of an association of LEMS, ITP, and DPB. The use of cholinesterase blocker alone did not improve the myasthenic symptoms, and the symptoms and signs relapsed with the tapering of prednisolone (PSL) dosage. However, after administration of immunoglobulin (IVIG) (0.4 g/kg/day x 5 days), low-dose PSL (20 mg/day) alleviated the LEMS and ITP, and the diseases have remained in remission for 8 months without additional IVIG. We suspect that there is a synergistic relationship between IVIG and PSL.

Effect of 3,4-diaminopyridine on the time course of decay of compound muscle action potential augmentation in the Lambert-Eaton myasthenic syndrome

3,4-Diaminopyridine (3,4-DAP) is known to be beneficial in the symptomatic treatment of the Lambert-Eaton myasthenic syndrome (LEMS). The effects of 3,4-DAP on the decay of postexercise augmentation were observed in 6 patients with LEMS. After 10 s maximal voluntary contraction, the amplitude of the compound muscle action potential (CMAP) recorded from abductor digiti minimi decayed exponentially after an initial rise. The rate of decay in CMAP amplitude was increased after treatment with 3,4-DAP, suggesting that this drug has an effect on the efflux of calcium ions from the presynaptic nerve terminal.

Distribution of electrophysiological abnormality in Lambert-Eaton myasthenic syndrome

OBJECTIVE

To assess the distribution of electrophysiological abnormality in Lambert-Eaton myasthenic syndrome (LEMS) to identify the most sensitive muscle to use in routine examination.

METHODS

Surface recorded compound muscle action potential (CMAP) amplitudes were made from abductor digiti minimi, abductor pollicis brevis, anconeus, biceps brachii, and trapezius in 10 patients with LEMS. The effect of 3,4-diaminopyridine (3,4-DAP) was recorded in each muscle in nine patients. CMAP amplitudes were measured at rest and immediately after 10 seconds maximal voluntary contraction in each muscle. Values were compared with results obtained from 12 healthy controls.

RESULTS

Resting CMAP amplitudes were reduced in at least one muscle in all patients compared with controls, most markedly in abductor digiti minimi and anconeus. The administration of 3,4-DAP resulted in significantly improved resting CMAP amplitudes in trapezius only. After maximal voluntary muscle contraction, characteristic increments in CMAP amplitude of over 100% above resting values were seen in abductor digiti minimi and abductor pollicis brevis in seven patients, anconeus and biceps brachii in five patients. No patient had this level of increment in trapezius.

CONCLUSION

Despite predominantly proximal limb weakness seen clinically in patients with LEMS, the most sensitive muscles for detecting characteristic electrophysiological abnormalities of low resting CMAP amplitude and increment of over 100% after 10 seconds maximal voluntary contraction are abductor digiti minimi, abductor pollicis brevis, and anconeus.

Low-dose guanidine and pyridostigmine: relatively safe and effective long-term symptomatic therapy in Lambert-Eaton myasthenic syndrome

Guanidine hydrochloride is known to be highly effective in the symptomatic treatment of the Lambert-Eaton myasthenic syndrome (LEMS). However, because of its potentially dangerous side reactions of hematologic abnormalities and renal insufficiency, 3,4-diaminopyridine, which is not readily available in the United States, is recommended as the preferred drug for LEMS. We used low-dose guanidine and pyridostigmine combination therapy in 9 patients with LEMS and analyzed its long-term safety and effectiveness. In all patients, a liberal amount of pyridostigmine was used, while daily guanidine dose was kept below 1000 mg a day, and guanidine was given between pyridostigmine dosings. This combination therapy was used for 3-102 months (mean: 34.1 months) and improved clinical status in all patients. Although guanidine had to be discontinued due to severe gastrointestinal symptoms in 3 cases, no serious side reactions such as bone marrow suppressions or signs of renal insufficiency developed in any case. Thus, we conclude that low-dose guanidine therapy is relatively safe and effective for long-term symptomatic treatment of LEMS when it is combined with pyridostigmine.

Stimulated single-fiber electromyography in Lambert-Eaton myasthenic syndrome before and after 3,4-diaminopyridine

A patient with LEMS unrelated to cancer was studied by stimulated single-fiber electromyography (SFEMG) before and 3 months after the onset of therapy with 3,4-diaminopyridine. All end-plates showed a progressive reduction in blockings and jitter with the increase in stimulation rate. Treatment significantly corrected this feature, but the overall pattern of frequency-improved jitter remained. Such widespread finding is rare but diagnostic for Lambert-Eaton myasthenic syndrome. Stimulated SFEMG can be used to monitor therapy in such patients.