Lambert-Eaton Myasthenic Syndrome Complicated by Anti-GABAB Receptor Encephalitis

A 74-year-old man experienced diplopia, generalized muscle weakness, and acute respiratory failure. He was diagnosed with Lambert-Eaton myasthenic syndrome (LEMS) and treated with immunotherapy, but no improvement was observed, and additional symptoms, including central apnea and hallucinations, appeared. Subsequent serum and cerebrospinal fluid (CSF) analyses confirmed the presence of GABAB receptor antibodies, indicating the coexistence of autoimmune encephalitis. Although there were no findings of malignancy, it is highly likely that occult small-cell lung carcinoma was present. When atypical symptoms occur in patients with LEMS, it is important to consider the possibility of concomitant autoimmune encephalitis.

[Lambert-Eaton Myasthenic Syndrome]

Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disorder that affects the neuromuscular junction, is characterized by proximal muscle weakness, reduction of tendon reflexes, and autonomic dysfunction. LEMS shows a prevalence of approximately 0.25-0.27 per 100,000 population. The characteristic muscle weakness observed in patients with LEMS is attributed to the role of pathogenic autoantibodies directed against voltage-gated calcium channels (VGCC) present on the presynaptic nerve terminal. Notably, 50-60% of patients with LEMS have an associated tumor, small-cell lung carcinoma (SCLC), which also expresses functional voltage-gated calcium channels (VGCC). The Japanese LEMS diagnostic criteria 2022 recommend documentation of typical electrophysiological abnormalities combined with myasthenic symptoms for accurate diagnosis. P/Q-type VGCC antibody positivity strongly supports the diagnosis. Treatment options are categorized as oncological treatment, immunotherapy, and symptomatic treatments. Effective treatment of the tumor can improve LEMS in patients with SCLC. Most patients benefit from 3,4-diaminopyridine administration for symptomatic treatment. A treatment algorithm is established by the clinical practice guidelines 2022.

[A case of myasthenia gravis with coexistence of anti-acetylcholine receptor antibodies and anti-P/Q-type VGCC antibodies]

A 79-year-old woman who presented ptosis and dysphagia were admitted to our hospital. Anti-acetylcholine receptor antibodies and anti-P/Q-type VGCC antibodies were both positive. Electrophysiological examination showed postsynaptic pattern which supported myasthenia gravis. She did not meet the diagnostic criteria for Lambert-Eaton myasthenic syndrome (LEMS). In cases which these antibodies coexist, careful electrophysiological evaluation is required for the diagnosis. In addition, although anti-P/Q-type VGCC antibodies have been specific to LEMS, patients with these antibodies represent various symptoms other than LEMS. Low and middle titer of the antibodies may be not specific to LEMS.

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.

Myasthenia gravis seronegative for acetylcholine receptor antibodies in South Korea: Autoantibody profiles and clinical features

Acquired myasthenia gravis (MG) is a prototype autoimmune disease of the neuromuscular junction, caused in most patients by autoantibodies to the muscle nicotinic acetylcholine receptor (AChR). There seem to be ethnic and regional differences in the frequency and clinical features of MG seronegative for the AChR antibody. This study aimed to describe the autoantibody profiles and clinical features of Korean patients with generalized MG seronegative for the AChR antibody. A total of 62 patients with a high index of clinical suspicion of seronegative generalized MG were identified from 18 centers, and we examined their sera for antibodies to clustered AChR, muscle-specific tyrosine kinase (MuSK), and low-density lipoprotein receptor-related protein 4 (LRP4) by cell-based assays (CBA) and to MuSK by radioimmunoprecipitation assay (RIPA). We also included 8 patients with ocular MG, 3 with Lambert-Eaton myasthenic syndrome, 5 with motor neuron disease, and 9 with other diagnoses as comparators for the serological testing. Antibodies were identified in 25/62 (40.3%) patients: 7 had antibodies to clustered AChR, 17 to MuSK, and 2 to LRP4. Three patients were double seropositive: 1 for MuSK and LRP4, and 2 for MuSK and clustered AChR. The patients with MuSK antibodies were mostly female (88.2%) and characterized by predominantly bulbar involvement (70%) and frequent myasthenic crises (58.3%). The patients with antibodies to clustered AChR, including 2 with ocular MG, tended to have a mild phenotype and good prognosis.

Myasthenia gravis and Lambert-Eaton myasthenic syndrome

PURPOSE OF REVIEW

This article reviews the clinical presentations, diagnostic findings, and treatment options for autoimmune myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome.

RECENT FINDINGS

Immunologic research is unraveling the immunopathology of MG and identifying targets for novel immune-based therapy of this condition. MG patients with antibodies to muscle-specific tyrosine kinase (MuSK) frequently present with symptoms and clinical findings that suggest nerve or muscle disease.

SUMMARY

Early diagnosis and treatment have a marked effect on outcome in these diseases. In most cases, the diagnosis of MG or Lambert-Eaton myasthenic syndrome can be made from the history, supplemented with directed questions, and a physical examination designed to demonstrate variable weakness in affected muscle groups. Appropriate confirmatory tests almost always establish the diagnosis. Although several novel treatment modalities for MG are under investigation, currently available therapies produce substantial improvement in function and quality of life in most patients with this condition. Knowledge about the dosing, adverse effects, and costs of immunomodulatory therapies is essential for the effective management of patients with MG and Lambert-Eaton myasthenic syndrome.

Lambert-Eaton syndrome IgG inhibits transmitter release via P/Q Ca2+ channels

Objective:

To determine whether immunoglobulin G (IgG) from patients with Lambert-Eaton myasthenic syndrome (LEMS) decreases action potential–evoked synaptic vesicle exocytosis, and whether the effect is mediated by P/Q-type voltage-gated calcium channels (VGCCs).

Methods:

IgG was obtained from 4 patients with LEMS (3 males, 1 female), including 2 patients with lung malignancy. Antibodies against P/Q-type VGCCs were detected in all 4 patients, and against N-type VGCCs in 2. We incubated neuronal cultures with LEMS IgG and determined the size of the total recycling pool of synaptic vesicles and the rate of action potential–evoked exocytosis using fluorescence imaging of the amphiphilic dye SynaptoRed C1. Pooled IgG from healthy volunteers was used as a control. We repeated the experiments on synapses lacking P/Q-type calcium channels from a Cacna1a knockout mouse to determine whether these channels account for the pathogenic effect of LEMS IgG.

Results:

LEMS IgG had no effect on the total recycling pool size but significantly reduced the rate of action potential–evoked synaptic exocytosis in wild-type neurons when compared with neurons treated with control IgG. In contrast, LEMS IgG had no effect on the rate of synaptic vesicle exocytosis in neurons lacking P/Q-type channels.

Conclusions:

These data provide direct evidence that LEMS IgG inhibits neurotransmitter release by acting on P/Q-type VGCCs.

[Lambert-Eaton myasthenic syndrome, an immune pathology of neuromuscular junctions]

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder affecting neuromuscular junctions. LEMS has served as a model of paraneoplastic neurological syndromes and antitumoral immunity, shedding light on the pathological role of autoantibodies directed against synaptic targets. Autoantibodies associated with LEMS are directed against voltage-gated calcium channels (VGCC) present on nerve terminals of neuromuscular synapses. Anti-VGGC antibodies play a direct pathological role in LEMS by blocking VGCC and calcium entry during depolarisation. Nearly half of patients with LEMS have small-cell lung cancer (SCLC), which also expresses VGCC. Diagnosis of LEMS frequently permits early detection and treatment of SCLC Knowledge of this syndrome has led to the discovery of a broad range of cancerous and non cancerous antibody-mediated neurological syndromes, and led to the concept of autoimmune synaptopathies.

Antibodies to active zone protein ERC1 in Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is characterized by fluctuating muscle weakness and autonomic dysfunction. In 90% of the LEMS patients the disease is associated with auto-antibodies against the voltage-gated calcium channels (VGCC). Several auto-immune responses against other antigenic targets have been described to (co)-occur in LEMS patients. To identify new LEMS associated small cell lung cancer (SCLC) markers immunoprecipitation with a SCLC cell line was performed. We discovered strong immunoreactivity against the 120 kDa large ERC1 protein in one tumor-negative VGCC-positive LEMS patient. A recombinant ELISA assay and a cellular assay expressing GFP-tagged full length ERC1 were used to confirm the presence of auto-antibodies against ERC1 in this patient. Additional testing of 58 LEMS patients including 9 VGCC auto-antibody negative LEMS patients, 48 myasthenia gravis patients, 84 control patients with other diseases and 12 healthy controls revealed no other cases. ERC1 is therefore a new, but rare, antigen in LEMS.

[Autoantibody against the presynaptic P/Q-type voltage-gated calcium channel in Lambert-Eaton myasthenic syndrome]

Antibodies against the muscle acetylcholine receptor (AChR) were recognized as the cause of myasthenia gravis in the 1970s'. Since then, other neurological disorders associated with autoantibodies have been identified, each associated with an antibody against a ligand- or voltage-gated ion channel. Autoantibodies against P/Q-type voltage-gated calcium channels (VGCCs) are detected in patients with Lambert-Eaton myasthenic syndrome (LEMS). These antibodies interfere with the calcium-dependent release of acetylcholine from the presynaptic membrane. LEMS is an autoimmune disorder affecting the neuromuscular junction, and is characterized by proximal muscle weakness, reduction of tendon reflex, and autonomic dysfunction. Electrophysiological examinations show small-amplitude compound muscle action potentials and increments on rapid repetitive nerve stimulation. Fifty to sixty percent of LEMS patients present with tumors, mostly small cell lung carcinoma (SCLC), as a paraneoplastic syndrome. SCLC is a neuroendocrine tumor, which expresses neuronal VGCCs. Some patients present cerebellar ataxia, which is always accompanied by SCLC. These patients tend to show higher titers of VGCC antibodies than that by LEMS patients with no ataxia. The diagnosis can be confirmed by finding reduced compound muscle action potential amplitudes at rest that shows increments greater than 100% with repetitive nerve stimulation and antibody detection by using radioimmunoprecipitation assays. The treatment options are generally categorized as anti-tumor, immunomodulating, immunosuppressing, and symptomatic treatments. In cases with SCLC, effective treatment against the tumor can improve LEMS. Plasmapheresis and intravenous administration of high-dose immunoglobulins have a short effect. Prednisone, alone or in combination with immunosuppressants can achieve long-term control of the disorder.

[Long-term survival case of small-cell lung cancer with Lambert-Eaton myasthenic syndrome without anticancer therapy]

A 78-year-old man with complaints of appetite loss and weight loss visited our hospital in November 2006. Positron-emission tomography and computed tomography (PET/CT) showed swollen lymph nodes in the abdominal para-aorta, mediastinum and neck, with intense FDG accumulation. The pathological findings of the cervical lymph nodes revealed small-cell cancer. We diagnosed extensive small-cell lung cancer (SCLC), which occurred primarily in the left upper lobe. As subsequent CT revealed spontaneous shrinkage of the pulmonary nodule and swollen lymph nodes, the clinical course was monitored without anticancer therapy. In February 2007, progressive muscle weakness of the lower extremities developed. In July he was admitted with respiratory failure and required mechanical ventilation. Although we did not administer anticancer therapy due to his poor performance status, he survived for 30 months receiving mechanical ventilation, and the tumors continued to grow moderately. We diagnosed Lambert-Eaton myasthenic syndrome (LEMS) based on the clinical symptoms, the presence of anti-VGCC antibodies and waxing phenomenon on electromyography obtained in April 2009. Chemotherapy with amrubicin shrank the tumors, but his muscle weakness did not improve. Previous reports showed that a prognosis of SCLC with LEMS was better than that without LEMS. In this case, the tumors showed spontaneous regression without any anticancer therapy, and then increased moderately. The immune response was considered to have affected tumor growth.

[Lambert-Eaton myasthenic syndrome (LEMS)]

Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular disorder in which autoantibodies inhibit the presynaptic release of acetylcholine. Autoantibodies against P/Q-type voltage-gated calcium channels (VGCC) are detected in 85% of patients with LEMS. In addition, autoantibodies to synaptotagmin, an M1-type muscarinic acetylcholine receptor and SOX1 are also found in the sera of patients with LEMS. LEMS is closely associated with small cell lung cancer (SCLC) in 50-60% of patients. Patients with SCLC who have anti-VGCC antibodies have been reported to have a favorable prognosis. In contrast to paraneoplatic LEMS, other forms of LEMS may have an autoimmune aspect because of the established association between human leukocyte antigen and a family history of other autoimmune disorders in this condition. The clinical features of LEMS include proximal weakness, areflexia, ptosis, cerebellar ataxia and autonomic dysfunction. The findings of electrophysiological examination show that LEMS is characterized by compound muscle action potential potentials with a low amplitude and increment upon repetitive nerve stimulation at a high rate. Tumor removal is the primary treatment of LEMS. The efficacy of 3,4-diaminopyridine for the treatment of LEMS has also been established. Patients with LEMS require the immunotherapies such as plasma exchange and the administration of high doses of immunoglobulin and prednisolone.

[Recent advance in research for myasthenia gravis, in relation to various antibodies affecting synaptic structure and function]

Autoantibodies impair acetylcholine receptor (AChR) in myasthenia gravis (MG) and P/Q-type voltage-gated calcium channel (VGCC) in Lambert-Eaton myasthenic syndrome (LEMS). (1) Some of MG and LEMS patients are "seronegative" for respective antibodies or modified by antibodies that recognize other proteins than AChR and VGCC such as MuSK, AChR allosteric site, membrane Na+ channel and ryanodine receptor-1 (RyR1) in MG, and synaptotagmin-1 in LEMS. (2) Autoimmune responses affect the proteins participating in the mechanisms to compensate for synaptic disorders on the basis of presynaptic Ca2+ homeostasis provided by VGCC and non-VGCC (receptor-operated TRPCs): they act as enhancers of Ca(2+) -mediated ACh release via phospholipase C signaling pathways including M1-type presynaptic muscarinic AChR, neurotrophin receptor (TrkB), and fast-mode of synaptic vesicle recycling. (3) The pathophysiology contributive to contractile fatigue in MG includes RyR1 and also TRPC3. The TRPC3 also forms a complex with STIM1 and Orail to make up for Ca2+ after sarcoplasmic Ca2+ release. The prevalent detection of anti-TRPC3 antibodies in MG with thymoma could affect muscle contractile machineries in addition to anti-RyR1-induced affection. (4) When one faces "seronegative" MG, one should be cautious to conformation-specific antibodies and also congenital myasthenic syndromes.

[Paraneoplastic cerebellar degeneration and Lambert-Eaton myasthenic syndrome associated with anti P/Q-type voltage-gated calcium channel antibody in a patient with primary double lung cancer]

We report the case of a 50-year-old man with paraneoplastic cerebellar degeneration (PCD) and Lambert-Eaton myasthenic syndrome (LEMS) associated with primary double lung cancer. He developed acute progressive double vision, slurred speech, and gait disturbance. Neurological examination revealed diplopia, mild ptosis, bilateral horizontal gaze-evoked nystagmus, and cerebellar limb and truncal ataxia. The diffusion image of brain magnetic resonance imaging (MRI) revealed no abnormal findings in the cerebellum. On the basis of the diagnosis of acute cerebelitis, he was given methylprednisolone pulse therapy followed by oral prednisolone, which gradually improved his neurological signs and symptoms. The analysis of the possible etiology suggested that the PCD was induced by lung cancer, which led to ataxia. A chest computed tomography scan revealed mass lesions of irregular shape and unclear margins in the upper lobe of the right lung and a small nodule tumor in the upper lobe of the left lung. We performed transbronchial needle aspiration and detected the bronchioloalveolar carcinoma of the right lung. An electromyogram showed waxing phenomenon in the ulnar nerve at high-frequency (50Hz) stimulation. The serum levels of anti-P/Q-type voltage-gated calcium channel (VGCC) antibody were elavated in the patient. These findings confirmed that the pathogenesis of the condition of this patient to be associated with LEMS. His cerebellar symptoms were considered to be caused by the PCD, and the diplopia, ptosis, and hyporeflexia were attributed to LEMS. We performed upper left lobectomy with mediastinal lymphnode dissection via video-assisted thoracoscopic surgery. A histological study detected small cell carcinoma. A diagnosis of double primary lung cancer was made. Physicians need to be aware that patients may develop PCD and LEMS associated with anti-VGCC antibody caused by small cell lung cancer, and a mass survey should be conducted and careful examinations performed.

Monozygous twins with neuromuscular transmission defects at opposite sides of the motor endplate

Disorders affecting the postsynaptic side of the neuromuscular junction include autoimmune myasthenia gravis (MG) as well as some of the congenital myasthenic syndromes (CMS). Lambert-Eaton myasthenic syndrome (LEMS) is an acquired autoimmune neuromuscular disorder in which autoantibodies are directed against the presynaptic calcium channels. Here we describe two monozygous twin brothers: case 1 was diagnosed with an indeterminate form of acquired postsynaptic neuromuscular junction defect at age 32 and case 2 with LEMS at age 47. Case 1 presented clinically with mild generalized myasthenic weakness, neurophysiological examination revealed disturbed neuromuscular transmission along with probable myositis and serum analysis regarding antibodies against the acetylcholine receptor and muscle-specific tyrosine kinase was negative. Case 2 presented with proximal muscle fatigue accompanied by areflexia at rest and antibodies against the P/Q-type voltage-gated calcium channels were present. Neurophysiologically, case 2 had reduced baseline compound motor action potential amplitudes on neurography, decrement on low-frequency repetitive nerve stimulation (RNS) and pathological increment on high frequency RNS. To our knowledge this is the first case report of its kind and adds an intriguing contrast to the more common diagnosis of CMS in monozygous twins.

Paraneoplastic chronic demyelinating neuropathy and Lambert-Eaton myasthenic syndrome associated with multiple anti-neural antibodies and small-cell lung cancer

Lambert-Eaton myasthenic syndrome (LEMS) developed in a patient with presumed chronic inflammatory demyelinating polyneuropathy (CIDP) and negative chest CT. Since antibodies against both Hu and voltage-gated calcium channel (VGCC) were detected, repeated chest CT was performed, which eventually showed a pulmonary mass lesion. Biopsy revealed small cell lung cancer (SCLC) indicating the importance of repeated chest CT in LEMS even when an existing autoimmune-like disease and negative CT may suggest an autoimmune origin. This is the first report of paraneoplastic CIDP and LEMS associated with anti-Hu, anti-VGCC and SCLC.

Autoantibodies against M1 muscarinic acetylcholine receptor in myasthenic disorders

The Lambert-Eaton myasthenic syndrome (LEMS), often associated with small-cell lung carcinoma (SCLC), is a disorder of acetylcholine (ACh) release from motor nerve terminals. In most patients, it is caused by autoantibodies against the P/Q-type voltage-gated calcium channels (VGCC) that trigger ACh release. However, these antibodies are not detected in approximately 15% of clinically and electrophysiologically typical cases. The M1-type pre-synaptic muscarinic ACh receptor (M1 mAChR) modulates cholinergic neuromuscular transmission by linking to P/Q-type VGCC, and may partially compensate for the reduced calcium entry. Immunoblotting against solubilized human M1 mAChR, we detected autoantibodies in: (a) 14 of 20 (70%) anti-VGCC-positive LEMS patients; (b) all five anti-VGCC-negative LEMS patients, one of whose serum had previously passively transferred LEMS-type electrophysiological defects to mice; (c) all five LEMS patients with autonomic symptoms; (d) seven of 25 (28%) myasthenia gravis (MG) patients in whom increased ACh release partially compensates for post-synaptic defects; (e) none of 10 SCLC patients without LEMS. Although not proving primary pathogenicity of anti-M1 mAChR antibodies, the present results highlight their potential to affect synaptic compensatory mechanisms, more in LEMS than MG.

Electrophysiological differences in seropositive and seronegative Lambert-Eaton myasthenic syndrome

In order to determine whether there is any difference between voltage-gated calcium-channel antibody (VGCC-Ab)-positive and -negative groups in Lambert-Eaton myasthenic syndrome (LEMS), we compared the clinical and electrophysiological features between 13 patients with VGCC-Ab and 6 VGCC-Ab-negative patients. No obvious difference was observed in the various clinical features or findings on single-fiber electromyography between seropositive and seronegative cases. In seropositive cases, the compound muscle action potential (CMAP) amplitude was lower but the increment on post-exercise facilitation (PEF) and high-rate stimulation (HRS) was significantly higher than in the seronegative group, indicating that the repetitive nerve stimulation (RNS) test in the seropositive group is more typical of LEMS and more severe. A 100% increment as the diagnostic criterion in the routine RNS test was satisfied in all seropositive cases but in only three seronegative cases, whereas a 60% increment as the diagnostic criterion was found in all seronegative cases. The classic triad (low CMAP amplitude, decrement at low rate of stimulation, and increment at PEF or HRS) of RNS is rare, adding to the difficulty in diagnosing LEMS in the seronegative group, and making a 60% increment criterion more critical for the diagnosis of this disorder.

Immunology of disorders of neuromuscular transmission

The neuromuscular junction (NMJ) is a prototype synapse and myasthenia gravis is the prototypic antibody-mediated disorder. There are now three other disorders of neuromuscular transmission caused by antibodies to other essential components of the NMJ. Antibodies to the muscle-specific kinase, MuSK, are defining a new form of myasthenia that can be associated with muscle atrophy. Antibodies to voltage-gated calcium channels are responsible for muscle weakness and autonomic dysfunction in the Lambert Eaton myasthenic syndrome. Antibodies to voltage-gated potassium channels are found in patients with a range of disorders affecting the NMJ, the autonomic system or the central nervous system. The pathogenic mechanisms probably depend on the IgG subclass of the antibodies and are only partly shared between the diseases.

Phoneutria nigriventer ω-Phonetoxin IIA: A new tool for anti-calcium channel autoantibody assays in Lambert–Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a neurological autoimmune disease in which downregulation of voltage-gated calcium channels (VGCCs) leads to reduced acetylcholine release from motoneuron terminals. 70% of cases are paraneoplastic and rapid diagnosis of LEMS can result in early detection of the underlying tumor. Serological assays based on the capacity of autoantibodies to precipitate VGCCs labeled with radioligands provide valuable data. We have established a novel assay using the spider venom peptide 125I-omega-Phonetoxin IIA (125I-omegaPtxIIA). 125I-omegaPtxIIA labeled recombinant Cav2.1 and Cav2.2 channels and endogenous VGCCs in rat brain membranes. Autoantibodies that immunoprecipitate a 125I-omegaPtxIIA/channel complex were detected in 26/31 (84%) LEMS patients. The patients that were seropositive in the 125I-omegaPtxIIA assay corresponded precisely to the population that was positive for Cav2.1 and/or Cav2.2 antibodies detected using two different omega-conotoxins. Thus, the 125I-omegaPtxIIA assay detects a broader spectrum of autoantibody specificities than current omega-conotoxin-based assays.

[Lambert-Eatone myastenic syndrome]

A detailed comparative analysis of neurologic symptoms in 45 patients with Lambert-Eatone myastenic syndrome (LEMS) and 42 patients with generalized myasthenia allowed us to single out clinical patterns facilitating disease diagnosis and differentiation. There were no clinical differences in patients having LEMS with or without paraneoplastic process. Electromyography study revealed the presence of typical phenomena: a reduced amplitude of compound muscle action potential and incremental response at 40-Hz stimulation. The compound muscle action potential tripled after 20 s of maximal voluntary contraction. Sera from 89% of patients with LEMS contained IgG antibodies that immunoprecipitate a radiolabeled complex of a selective antagonist of P/Q type voltage-gated calcium channels. The degree of inhibition of calcium influx by patient's IgG correlated with the reduction in amplitude of the resting compound muscle action potential.

P/Q-type calcium channel antibodies, Lambert-Eaton myasthenic syndrome and survival in small cell lung cancer

To assess the survival impact of the presence of P/Q-type calcium channel antibodies in patients with small cell lung carcinoma (SCLC), we examined the frequency of the antibodies and Lambert-Eaton myasthenic syndrome (LEMS) in 148 consecutive patients with SCLC, and in 30 patients with paraneoplastic cerebellar degeneration and SCLC, and studied their relation with survival. In both series, only patients with LEMS had a remarkably long survival, whereas presence of the antibodies without LEMS did not result in a better prognosis.

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

OBJECTIVE

To report the clinical, electrophysiological, and immunological findings in one patient with MG and LEMS overlap syndrome (myasthenia gravis and Lambert-Eaton myasthenic syndrome).

METHODS

Evaluation of clinical, electrophysiological, and immunological findings in one patient with this disease.

RESULTS

A female patient with pernicious anemia had clinical findings of ptosis, diplopia, proximal leg weakness, areflexia and a positive edrophonium test as well as the classic patterns initially of MG and later of LEMS on successive repetitive nerve stimulation (RNS) tests. Immunologically she demonstrated positive acetylcholine receptor antibody (ACh-ab) and positive N-type voltage-gated calcium-channel antibody (VGCC-ab) titers.

CONCLUSIONS

Among five reported cases combining the features of MG and LEMS and having positive AChR- and VGCC-ab titers, our patient provides the most convincing clinical, electrophysiological, and immunological evidence for the existence of MG and LEMS overlap syndrome.

SIGNIFICANCE

MG and LEMS overlap syndrome is a distinct entity.

Recent advance in immunological tests in paraneoplastic neurological syndrome

Paraneoplastic neurological syndromes are uncommon, however; their diagnosis is of major practical importance. Any portion of the nervous system may be involved in paraneoplastic syndromes. There is increasing evidence that the pathogenesis of many paraneoplastic neurological syndromes appears to be an immune reaction against antigen shared by the cancer and the nervous system. The identification of antibodies in the serum or cerebrospinal fluid in the central nervous system of paraneoplastic syndrome patient confirms the clinical diagnosis of paraneoplastic syndrome, and allows early identification of an underlying tumor at a stage when it is localized and more amenable to treatment. Cancer therapy (surgery, radiotherapy, chemotherapy) seems to be the most efficient treatment for the paraneoplastic neurological symptoms. Immunomodulatory therapy (intravenous immunoglobulin, plasmapheresis, immunosuppression) can halt or even reverse the neurological syndrome. The recent advances in understanding of the autoimmune pathology of these disorders should lead to more effective treatment options.

HLA and smoking in prediction and prognosis of small cell lung cancer in autoimmune Lambert–Eaton myasthenic syndrome

Patients with small cell lung cancer (SCLC) survive longer if they have the antibody-mediated Lambert-Eaton myasthenic syndrome (LEMS), making this autoimmune disorder a prototype disease for studying cancer immunosurveillance. Patients with nontumor LEMS (NT-LEMS) never develop SCLC but are otherwise indistinguishable clinically. Therefore, we have compared immunogenetic factors in SCLC-LEMS and NT-LEMS and studied their role in the pathogenesis of LEMS and survival from SCLC. In 48 British and 29 Dutch Caucasian LEMS patients, we studied clinical symptoms, antibody titers, HLA types and alleles at six nearby located microsatellite loci. Highly significant associations were found in NT-LEMS, which appeared strongest with HLA-B8, but also involved HLA-DQ2, -DR3 and six flanking microsatellite alleles. SCLC-LEMS patients were not different from controls. Smoking was a strong predictor of SCLC. In contrast, HLA-B8 positivity correlated with a decreased risk of SCLC even among the smokers. Moreover, in SCLC-LEMS patients, HLA-B8 positivity correlated with prolonged survival after LEMS onset. We propose that two distinct immunopathogenetic routes can lead to one clinically and serologically indistinguishable autoimmune myasthenic syndrome. HLA-DR3-B8 is strongly associated with LEMS in nontumor patients only. In other LEMS patients, SCLC apparently provides a powerful autoimmunogenic stimulus that overrides HLA restrictions in breaking tolerance to calcium channels. Moreover, negativity for HLA-B8 combined with smoking behavior points more strongly to an underlying SCLC and predicts a worse prognosis in SCLC-LEMS patients.

Presynaptic effects of immunoglobulin G from patients with Lambert-Eaton myasthenic syndrome: Their neutralization by intravenous immunoglobulins

Intravenous immunoglobulin (IVIg) treatment improves muscle strength in Lambert-Eaton myasthenic syndrome (LEMS), but its specific mode of action is unknown. We have delineated its mode of action on neuromuscular blocking properties of LEMS IgG. The effect of sera and purified IgG from six patients with LEMS on evoked quantal release was investigated after direct application to the motor nerve terminal by the perfused macro-patch-clamp electrode in mouse hemidiaphragms. The effect of LEMS IgG was analyzed alone and after coincubation with different concentrations of IVIg or its Fab fragments. All LEMS sera and purified LEMS IgG fractions taken before IVIg treatment inhibited evoked quantal release in a dose-dependent manner. When LEMS IgG was coincubated with a therapeutic IVIg preparation, presynaptic inhibitory activity of LEMS IgG was diminished in a dose-dependent fashion. Monovalent Fab fragments were as effective in neutralizing the activity of LEMS IgG as whole IVIg. These direct neutralizing effects of IVIg may explain its therapeutic efficacy.

Immunological features of neurological paraneoplastic syndromes

Neurological paraneoplastic syndromes are a rare group of disorders that occur in 1-2% of people with malignancy. They are usually caused by an immune response, triggered by and directed against a tumour, that cross-reacts with protein expressed by the peripheral or central nervous system. Any part of the nervous system can be affected and patients often develop severe and permanent disability. Diagnosis can be difficult as in two-thirds of patients the neurological problems appear up to 5 years before the tumour manifests. However, certain of these syndromes are often associated with specific serum autoantibodies that can be useful both in diagnosis of the neurological syndrome and in focusing the search for a particular tumour. Thus, these antibodies can allow earlier identification and treatment of cancer and, potentially, a reduction in morbidity and mortality. It was only in the 1980s that the first anti-neuronal autoantibodies were characterized and their associations with clinical syndromes and tumours defined. Further antibodies have been isolated over the past 20 years and novel pathogenic mechanisms for several syndromes have been recognized. For example, voltage-gate ion channels seem to be a common target for autoantibodies involved in peripheral nerve diseases such as the Lambert-Eaton myasthenic syndrome and neuromyotonia (Isaacs' syndrome). However, the place of most paraneoplastic antibodies in the pathogenesis of central syndromes is yet to be fully elucidated.

Lambert-Eaton myasthenic syndrome as an autoimmune calcium channelopathy

Lambert-Eaton myasthenic syndrome, often associated with small-cell lung carcinoma, is a disease of neuromuscular transmission in which antibodies directed against voltage-gated calcium channel (VGCC)(P/Q-type) in the motor nerve terminal play a crucial role in causing a deficient quantal release of acetylcholine. The motor nerve terminal and carcinoma cell may share a common antigen. The study using synthetic peptides and recombinant protein specified the extracellular S5-S6 linker regions in 3 of 4 domains as immunodominant sites in the molecular structure of P/Q-type VGCC alpha1 subunit. Also, the study by use of peptides and recombinant protein corresponding to synaptotagmin I suggested that in this functionally VGCC-associated presynaptic protein, the segment which exposes extracellularly during exocytosis can be immunogenic for the syndrome.

Lambert-Eaton myasthenic syndrome. Clinical and electrophysiological findings in seven cases

We report the clinical and electrophysiological findings in seven patients with Lambert-Eaton myasthenic syndrome (LEMS). All patients were males aged 40-73 years old. Six presented proximal muscle weakness and one both proximal and distal. The tendon reflexes were absent in four patients, depressed in two and normal in one patient. Three patients presented ophthalmic and four autonomic symptoms. The syndrome was diagnosed 3-12 months after the onset of symptoms in six patients and 4 years later in one. Acetylcholine receptor antibodies were negative in all patients. Voltage-gated calcium channel antibodies (VGCC) were measured in five patients and were positive in four. All patients had low compound muscle action potential (CMAP) at rest, a decrement in CMAP amplitude of 20-47% at 3 Hz repetitive nerve stimulation, and an increment of 200-700% at 40 Hz. In three patients the syndrome was associated with histologically verified small-cell lung cancer (SCLC). In the younger patient (40 years old), a lymph node biopsy performed nine years before the diagnosis of LEMS, had shown an atypical microcellular cancer of undetermined origin, which was treated with chemotherapy. LEMS 9 years after the diagnosis of cancer has not been described previously. The fifth patient had a two years history of bladder cancer (grade II). Three years after the diagnosis of LEMS he presented chronic lymphogenic leukemia. No malignancy was found in the remaining 2 patients.

Dosage et spécificité d’autoanticorps anti-canaux calcium dans le syndrome myasthénique de Lambert-Eaton

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune channelopathy in which patients produce autoantibodies directed against voltage-gated calcium channels. Autoantibodies down-regulate calcium channels resulting in reduced transmitter release, which in turn leads to muscular weakness and autonomic dysfunction. LEMS is paraneoplastic in 60-70% of patients, most frequently associated with small cell lung carcinoma (SCLC). SCLC lines express many neuronal and neuroendocrine proteins including neuronal calcium channels of the Cav2 family (P/Q and N-type channels). It is thus likely that the paraneoplastic form of LEMS is the consequence of an anti-tumoral immune response and the production of antibodies that cross-react with identical or homologous antigens in nerve terminals. Neurological symptoms generally appear several Months before detection of the tumor. Consequently correct diagnosis of LEMS is crucial as it can allow early treatment of a particularly aggressive carcinoma. Based on published studies, our laboratory has set-up serological assays for LEMS autoantibodies as an aid to diagnosis. Calcium channels in detergent extracts of rat brain or cerebellum membranes were labeled with radioligands specific for N-type (125I-omega conotoxin GVIA) or P/Q-type (125I-omega conotoxin MVIIC) calcium channels. Autoantibodies that immunoprecipitate the ligand/channel complex can thus be titrated. Analysis of 31 LEMS sera revealed the presence of anti-N type channel antibodies in 58% and anti-P/Q type channel antibodies in 74% of patients with titres ranging from 90 to 2950 pM. Only 5 patients were seronegative in both tests, thus a combination of the two assays reliably detected autoantibodies in 26/31 (84%) patients.

Complicated paraneoplastic neurological syndromes: a report of two patients with small cell or non-small cell lung cancer

Paraneoplastic neurological syndromes are frequently associated in patients with small cell lung cancer (SCLC) and antineuronal antibodies are involved in the autoimmune mechanism. Multiple syndromes are sometimes complicated in a single patient with SCLC. However, little is known about non-SCLC-associated neurological manifestations. We report two patients with complicated paraneoplastic neurological syndromes. Patient 1 showed paraneoplastic limbic encephalitis (PLE), paraneoplastic sensory neuropathy (PSN) and Lambert-Eaton myasthenic syndrome (LEMS) associated with SCLC. Patient 2 developed opsoclonus-ataxia and probable PLE associated with non-SCLC. Analysis of various antineuronal antibodies revealed that anti-Hu and P/Q-type voltage-gated calcium channel (VGCC) antibodies were positive in Patient 1 but any antibodies were not in Patient 2. Brain MRI demonstrated high intensity signals in temporal lobes particularly on fluid-attenuated inversion recovery (FLAIR) or diffusion-weighted images. These findings suggest that complicated paraneoplastic neurological syndromes occur in non-SCLC as well as SCLC and that unidentified antineuronal autoantibodies may underlie the pathophysiology.

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.

Pathogenic Autoantibodies in the Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular transmission in which antibodies are directed against voltage-gated calcium channels (VGCCs). We studied the action of LEMS immunoglobulin G (IgG) on cloned human VGCCs stably transfected into human embryonic kidney cells (HEK293). All LEMS IgGs tested bound to the surface of the P/Q-type VGCC cell line and caused a significant reduction in whole-cell calcium currents in these cells. By contrast, only 2 out of 6 IgGs bound extracellularly to the N-type VGCC cell line, and none of the LEMS IgGs tested was able to reduce whole-cell calcium currents in these cells. We used this apparent specificity of LEMS IgG for the P/Q-type VGCC to investigate the action of these IgGs on model systems where a number of different VGCC populations exist in equilibrium. LEMS IgG caused a significant downregulation in the omega-agatoxin IVA-sensitive P/Q-type VGCCs of cultured rat cerebellar neurons, but this was accompanied by a concomitant rise in the "resistant" R-type VGCCs. By using the passive transfer model of LEMS, similar results were observed at the mouse neuromuscular junction, where a significant reduction in P/Q-type VGCCs was paralleled by an increase in L- and R-type VGCCs. These results demonstrate an unexpected plasticity in the expression of VGCCs in mammalian neurons and may represent a mechanism by which the pathogenic effects of LEMS IgG are reduced.

High innate production of interleukin-10 and tumor necrosis factor-alpha contributes to susceptibility for non-paraneoplastic Lambert-Eaton myasthenic syndrome

Non-paraneoplastic Lambert-Eaton myasthenic syndrome (LEMS) is an antibody-mediated autoimmune disorder, in which genetically determined interleukin-10 (Il-10) and tumor necrosis factor-alpha (TNF-alpha) could play a role in the susceptibility for the disease. Therefore, we analyzed the production of Il-10 and TNF-alpha after whole-blood stimulation in first-degree family members of patients with LEMS without malignancy, as a measure of innate production in the patients. Thirty-six first-degree family members of 10 patients and 80 healthy controls were studied. Both Il-10 (p=0.037) and TNF-alpha (p=0.0016) production were increased in the family members, but had no relation with the severity of LEMS or HLA-B8DR3 carriership. Our findings suggest that high innate production of Il-10 and TNF-alpha is a susceptibility factor for non-paraneoplastic LEMS.

Lambert-Eaton Myasthenic syndrome in a child with an autoimmune phenotype

We report on a child with a family history of autoimmune defects, who presented at the age of 3(1/2) years with alopecia and Graves disease. He subsequently developed vitiligo and psoriasis. At 9(1/2) years, he developed an autoimmune form of Lambert-Eaton Myasthenic syndrome (LEMS) with a significant elevation of glutamic acid decarboxylase (GAD) autoantibodies. Shortly thereafter he developed chronic urticaria. HLA associations were present for Graves disease, vitiligo, psoriasis, and IgA deficiency. There was also evidence of autoimmunity involving the pancreatic islet cells and gastric parietal cells.

Autoantibodies to ion channels at the neuromuscular junction

Autoantibodies directed against voltage- or ligand-gated ion channels and their associated proteins at the neuromuscular junction give rise to a family of neurological autoimmune diseases. Antibodies to acetylcholine receptors or muscle-specific kinase present on the postsynaptic muscle membrane are associated with different forms of myasthenia gravis (MG). Antibodies to the presynaptic voltage-gated potassium and calcium channels are responsible for acquired neuromyotonia and Lambert-Eaton myasthenic syndrome (LEMS), respectively. The patients respond to immunotherapies and their plasma can transfer defects in neuromuscular transmission to mice, indicating that these are antibody-mediated conditions. In a small proportion of cases, ion channel antibodies have also been implicated in neurological dysfunction in the central nervous system. In these conditions, a proportion of the patients have an underlying tumour, thymoma in both MG and neuromyotonia and small cell lung carcinoma in LEMS, emphasising the putative role of autoimmunity to tumour antigens as a cause of neurological disease.