Passively transferred Lambert-Eaton syndrome in mice receiving purified IgG

Small-cell lung cancer-associated autoantibodies: potential applications to cancer diagnosis, early detection, and therapy

Small-cell lung cancer (SCLC) is the most aggressive lung cancer subtype and lacks effective early detection methods and therapies. A number of rare paraneoplastic neurologic autoimmune diseases are strongly associated with SCLC. Most patients with such paraneoplastic syndromes harbor high titers of antibodies against neuronal proteins that are abnormally expressed in SCLC tumors. These autoantibodies may cross-react with the nervous system, possibly contributing to autoimmune disease development. Importantly, similar antibodies are present in many SCLC patients without autoimmune disease, albeit at lower titers. The timing of autoantibody development relative to cancer and the nature of the immune trigger remain to be elucidated. Here we review what is currently known about SCLC-associated autoantibodies, and describe a recently developed mouse model system of SCLC that appears to lend itself well to the study of the SCLC-associated immune response. We also discuss potential clinical applications for these autoantibodies, such as SCLC diagnosis, early detection, and therapy.

Paraneoplastic syndromes: an approach to diagnosis and treatment

Recent medical advances have improved the understanding, diagnosis, and treatment of paraneoplastic syndromes. These disorders arise from tumor secretion of hormones, peptides, or cytokines or from immune cross-reactivity between malignant and normal tissues. Paraneoplastic syndromes may affect diverse organ systems, most notably the endocrine, neurologic, dermatologic, rheumatologic, and hematologic systems. The most commonly associated malignancies include small cell lung cancer, breast cancer, gynecologic tumors, and hematologic malignancies. In some instances, the timely diagnosis of these conditions may lead to detection of an otherwise clinically occult tumor at an early and highly treatable stage. Because paraneoplastic syndromes often cause considerable morbidity, effective treatment can improve patient quality of life, enhance the delivery of cancer therapy, and prolong survival. Treatments include addressing the underlying malignancy, immunosuppression (for neurologic, dermatologic, and rheumatologic paraneoplastic syndromes), and correction of electrolyte and hormonal derangements (for endocrine paraneoplastic syndromes). This review focuses on the diagnosis and treatment of paraneoplastic syndromes, with emphasis on those most frequently encountered clinically. Initial literature searches for this review were conducted using PubMed and the keyword paraneoplastic in conjunction with keywords such as malignancy, SIADH, and limbic encephalitis, depending on the particular topic. Date limitations typically were not used, but preference was given to recent articles when possible.

Update on paraneoplastic neurological syndromes

PURPOSE OF REVIEW

To describe specificities and new advances in treatment of paraneoplastic neurological syndromes (PNS).

RECENT FINDINGS

PNS are defined as neurological syndromes of unknown cause that often antedate the diagnosis of an underlying cancer that is usually not clinically evident. The clinical signs of PNS are accurately described and 'classical' PNS have been established. Within the context of these syndromes, the concept of limbic encephalitis has evolved dramatically in the last 2 years due to the description of new auto-antibodies. The diagnosis and treatment of the associated cancer remains the key goal of the clinical management of PNS. However, the specific treatment of the neurological symptoms primarily depends on the immunological findings.

SUMMARY

There is increasing recognition of an extensive array of PNS and of several paraneoplastic antibodies as biological markers of these disorders. Basic immunological studies support the pathogenic role of some of these antibodies. Others are only markers of the disease.

Cancer-Induced, Immune-Mediated Ocular Degenerations

The means whereby vision can be lost from a disease located distant from the eye include autoimmunity, with sensitization resulting from extraocular stimuli, a process illustrated here by the immunologic confusion caused by cancers. The uncontrolled proliferation of malignancies commonly involves the expression of components of the central nervous system, but a damaging loss of tolerance is rare. When autoimmunity does develop, organ-specific antigens are more often involved than the more generalized and widely disseminated common neuronal components. A focus upon a single antigen is typical of the immune-mediated paraneoplasia, a collection of syndromes identified by unusual antibody reactions. This review provides an outline of the immunologic trail that led to the recognition of autoimmunity in paraneoplastic ocular degenerations, how specific antibody reactions aid in diagnosis, and the possibility of including antibodies in modes for sight-saving intervention. 'Those who do not know history are destined to repeat it'.

Paraneoplastic neurological syndromes: a review

BACKGROUND

Paraneoplastic neurologic syndromes (PNS) constitute a rare group of disorders resulting from damage to the nervous system in the setting of cancer physically unrelated to the tumor site. PNS are believed to result from an autoimmune attack of normal neuronal tissue, spurred by similar neuronal antigens ectopically expressed by tumor cells.

REVIEW SUMMARY

The most common PNS are reviewed and also their association with specific onconeural antibodies, some directly pathogenic, others whose role in the disease process is less clear-cut. This diversity in pathogenesis is likely due to the relative role of humoral versus cellular immunity in PNS. Virtually any cancer may result in PNS but certain tumors, small cell lung cancer, gynecologic cancers (breast and ovarian), thymoma, and plasma cell tumors are more frequently encountered. In most instances, immunosuppressive therapy is unhelpful and outcome is poor.

CONCLUSIONS

PNS have diverse presentations, affecting both the central and peripheral nervous system and commonly, it is the PNS, not cancer that is the presenting symptom. Only subsequently, after onconeural antibodies are discovered or cancer is found, is PNS diagnosed. Neurologists should familiarize themselves with these rare syndromes and treatment principles, as rapid detection and treatment of the underlying tumor offer the best chance for recovery or prevention of further neurologic deterioration.

Paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes (PNS) can be defined as remote effects of cancer that are not caused by the tumor and its metastasis, or by infection, ischemia or metabolic disruptions. PNS are rare, affecting less than 1/10,000 patients with cancer. Only the Lambert-Eaton myasthenic syndrome is relatively frequent, occurring in about 1% of patients with small cell lung cancer. PNS can affect any part of the central and peripheral nervous system, the neuromuscular junction, and muscle. They can be isolated or occur in association. In most patients, the neurological disorder develops before the cancer becomes clinically overt and the patient is referred to the neurologist who has the charge of identifying a neurological disorder as paraneoplastic. PNS are usually severely disabling. The most common PNS are Lambert-Eaton myasthenic syndrome (LEMS), subacute cerebellar ataxia, limbic encephalitis (LE), opsoclonus-myoclonus (OM), retinopathies (cancer-associated retinopathy (CAR) and melanoma-associated retinopathy (MAR), Stiff-Person syndrome (SPS), chronic gastrointestinal pseudoobstruction (CGP), sensory neuronopathy (SSN), encephalomyelitis (EM) and dermatomyositis. PNS are caused by autoimmune processes triggered by the cancer and directed against antigens common to both the cancer and the nervous system, designated as onconeural antigens. Due to their high specificity (> 90%), the best way to diagnose a neurological disorder as paraneoplastic is to identify one of the well-characterized anti-onconeural protein antibodies in the patient's serum. In addition, as these antibodies are associated with a restricted range of cancers, they can guide the search for the underlying tumor at a stage when it is frequently not clinically overt. This is a critical point as, to date, the best way to stabilize PNS is to treat the cancer as soon as possible. Unfortunately, about one-third of patients do not have detectable antibodies and 5% to 10% have an atypical antibody that is not well-characterized. As PNS are believed to be immune-mediated, suppression of the immune response represents another treatment approach.

Onconeural antibodies are essential to diagnose paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes (PNS) can be defined as remote effects of cancer that are not caused by the tumor and its metastasis or by infection, ischemia or metabolic disruptions. In most patients, the neurological disorder develops before the cancer becomes clinically overt and the patient is referred to the neurologist who has the charge of identifying a neurological disorder as paraneoplastic. They are usually severely disabling. PNS are rare and are seen in less than 1% of patients with cancer. PNS depend on an autoimmune process triggered by cancer and directed to antigens common to both the cancer and the nervous system designated as onconeural antigens. Because of their high specificity (>90%), the best way to diagnose neurological disorders as paraneoplastic is to identify one of the well-characterized onconeural antibodies in the patient's serum. In addition, as these antibodies are associated with a restricted range of cancer, they permit orientating the search of the underlying tumor at a stage where it is frequently not clinically overt. This is a critical point, as today the best way to stabilize PNS is probably to treat the cancer as soon as possible. Unfortunately, about one-third of the patients do not have detectable antibodies and 5-10% have an atypical antibody that is not well characterized.

Advances in paraneoplastic neurological syndromes

PURPOSE OF REVIEW

To describe specificities and new advances in paraneoplastic neurologic syndromes (PNSs).

RECENT FINDINGS

Paraneoplastic neurologic syndromes are defined as neurologic syndromes of unknown cause that often antedate the diagnosis of an underlying, usually not clinically evident, cancer. In the last 2 decades, the discovery that many PNSs are associated with antibodies against neural antigens expressed by the tumor has suggested that some PNSs are immune-mediated. PNSs are rare and occur in less than 1% of patients with cancer. However, the diagnosis and treatment are important because the disability caused by the PNS is often severe, and the correct diagnosis usually leads to the discover of a small tumor with high chances of being cured.

SUMMARY

There is increasing recognition of an extensive variety of PNSs and of several paraneoplastic antibodies as clinical markers of these disorders. Basic immunologic studies support the pathogenic role of some of these antibodies, and basic molecular studies support the role of some antigens in neuronal degeneration and tumoral growth.

Apheresis treatment in Lambert-Eaton myasthenic syndrome

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

Autoimmunity and neurological disease: antibody modulation of synaptic transmission

Over the past three decades, compelling evidence has emerged that the immune system can attack the nervous system with devastating consequences for human health. Either cell-mediated or humoral (antibody-mediated) autoimmune mechanisms may predominate in effecting a given disease, and either glia or neurons may fall under immune attack. A subset of these diseases has been particularly useful for understanding fundamental neuroscience as well as mechanisms of human disease. This subset involves humoral autoimmune attack on cell surface molecules subserving transmembrane signaling of excitable cells; special emphasis is placed here on proteins involved in synaptic transmission. We begin by reviewing the prototypic humoral autoimmune disease of synaptic transmission, myasthenia gravis. This provides a context for insights obtained from the study of diseases targeting molecules that regulate synaptic transmission at the neuromuscular junction and in the central nervous system. We also explore a disease where autoimmunity produces agonist antibodies acting at two distinct G-protein-coupled receptors. We conclude with an exploration of the vital issue of access of antibodies to targets within the central nervous system and the implications that such access may have in the pathogenesis of poorly understood idiopathic central nervous system diseases.

Paraneoplastic syndromes

Paraneoplastic syndromes (i.e. organ/tissue disorders associated with cancer) affecting the nervous system are thought to be the result of an autoimmune response triggered by specific cancer antigens. Several of these antigens have recently been identified and include the Hu, Yo and Ri proteins, with the Hu antigens being the best studied. Immunization of animals with HuD has been shown to retard the growth of HuD-positive neuroblastomas. In addition, the presence of anti-HuD antibody in humans with small-cell lung cancer predicts the slow growth of the tumor. The associated neurological disorders, however, limit the use of these and other antigens with similar characteristics in cancer vaccines.

Incidence of serum anti-P/O-type and anti-N-type calcium channel autoantibodies in the Lambert-Eaton myasthenic syndrome

The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease in which autoantibodies are directed against voltage-gated calcium channels (VGCCs) at presynaptic nerve terminals. We first demonstrated the presence of P/Q-type and N-type VGCCs in digitonin extracts prepared from human and rabbit cerebellum using the specific ligands 125I-omega-conotoxin MVIIC (125I-omega-CmTx) and 125I-omega-conotoxin GVIA (125I-omega-CgTx), respectively. We then tested sera from 72 LEMS patients' 25 with proven small cell lung cancer (SCLC) and 66 healthy or other neurological, SCLC or autoimmune disease controls in an immunoprecipitation assay using 125I-omega-CmTx-labelled (P/Q-type) VGCCs in human cerebellar extract. Sixty-six of 72 LEMS serum samples (91.7%) were positive for the presence of VGCC antibodies, as defined as a titre greater than 3 standard deviations above the mean for the healthy controls (n = 22). Rabbit cerebellar extract as antigen gave similar results (r = 0.94, P < 0.001, n = 30). By contrast, only 24/72 (33%) LEMS sera were positive in the assay for anti-N-type VGCC antibodies using 125I-omega-CgTx. All these 24 were also positive in the 125I-omega-CmTx assay. All healthy and disease control sera were negative in both assays. The anti-P/Q-type VGCC antibody titres did not correlate with an electrophysiological index of disease severity across individuals; however, longitudinal studies in a LEMS patient with SCLC receiving chemotherapy, and in a non-SCLC LEMS patient receiving immunosuppressive therapy showed an inverse relation between antibody titre and disease severity. These results support the view that anti-P/Q-type VGCC antibodies are implicated in the motor disorder in LEMS, and show that the omega-CmTx radioimmunoassay is a highly specific and sensitive means of detecting them.

Reduction of calcium currents by Lambert-Eaton syndrome sera: motoneurons are preferentially affected, and L-type currents are spared

Previous work has demonstrated that Lambert-Eaton syndrome (LES) antibodies reduce calcium currents in nonneuronal cells and neurons and reduce the amplitude of extracellularly recorded currents at mouse motor nerve terminals. We compared effects of LES sera on whole-cell currents of cultured nerve and muscle. LES sera more strongly reduced calcium currents in motoneurons than in sensory neurons. Motoneuronal potassium currents were unaffected. The sera minimally affected calcium currents in skeletal and cardiac muscle. In motoneurons, both low voltage-activated (LVA) and high voltage-activated (HVA) components of calcium current were decreased, demonstrating that the sera targeted more than one calcium channel type. The HVA current remaining in LES-treated motoneurons was little affected by micromolar omega-conotoxin MVIIC but was reduced > 70% by micromolar nimodipine. This pharmacological profile contrasts with untreated cells and suggest that LES sera primarily spare L-type currents in motoneurons.

Lung cancer-induced blindness

Early investigations into the pathogenesis of vision loss in cancer patients noted the higher incidence with small cell carcinoma of the lung (SCCL), a neoplasia with suspected neuroendocrine origins [2-5,12,20,25,56,63,64]. The cause and effect relationship between the cancer and retinal deterioration was recognized, but the processes involved were not understood. Research eventually identified a sub-group of paraneoplastic retinopathy patients who exhibited indications of retinal hypersensitivity through their production of autoantibodies reactive with a single photoreceptor protein. The discovery of a small cell lung cancer culture actively expressing this same retinal autoantigen, provided tangible evidence to define a molecular basis for at least one type of paraneoplastic retinopathy. The identification of this immunologic anomaly illustrates how blindness can occur in some cancer patients, through the serendipitous initiation of ocular hypersensitivity, with vision loss developing as a cancer-induced autoimmune retinopathy.

Inhibition of calcium currents and exocytosis by Lambert-Eaton syndrome antibodies in human lung cancer cells

1. Human small-cell lung cancer (SCLC) cells are believed to express the antigens responsible for the production of pathological antibodies in the Lambert-Eaton syndrome (LES), a Ca2+ channel disorder in which quantal transmitter release from the motor nerve terminal is impaired. Whole-cell patch-clamp techniques were used to study the voltage-dependent Ca2+ channels expressed by H146 SCLC cells and the effects of LES antibodies on these channels. The types of Ca2+ channels were determined using biophysical properties and pharmacological sensitivity to several antagonists. 2. Whole-cell Ca2+ currents (ICa) in SCLC cells are sensitive to the dihydropyridine (DHP) nicardipine, omega-conotoxin GVIA (omega-CgTX GVIA) and omega-agatoxin IVA (omega-AgTX IVA). Nicardipine at 100 nM and 10 microM reduced ICa by 35 and 45% (n = 38 cells), respectively, while omega-CgTX GVIA (1 microM) inhibited ICa by 32% (n = 31). Application of omega-AgTX IVA at 50 and 100 nM to the cancer cells decreased ICa by 41 and 42%, respectively (n = 22). 3. Measurement of cell membrane capacitance (Cm) revealed that Ca(2+)-dependent exocytosis underlies the secretory activity of SCLC cells. Exocytosis, when induced by step depolarizing pulses and measured by increases in Cm, was markedly inhibited by nicardipine (10 microM) and omega-AgTX IVA (100 nM). In contrast, omega-CgTX GVIA (1 microM) was not as effective in altering increases in Cm. 4. From negative (-80 mV) and depolarized (-40 mV) holding potentials, both peak and plateau ICa were inhibited by the presence of LES antibodies (1 mg ml-1 IgG). LES serum also reduced depolarization-induced increases in Cm by 48% (n = 15). 5. To determine whether the LES antibodies are downregulating a specific type(s) of Ca2+ channel, nicardipine (10 microM), omega-CgTX GVIA (1 microM) or omega-AgTX IVA (100 nM) was applied to tumour cells that had been previously exposed to LES serum for 24 h. The most pronounced change was that omega-AgTX IVA was 38-84% less effective at reducing ICa after the IgG treatment. The effectiveness of nicardipine was diminished by 18% after incubation with the LES antibodies, whereas the omega-CgTX GVIA was seen to be more effective. These results suggest that LES IgG downregulates P-type Ca2+ channels and, possibly, to a lesser extent L-type channels. 6. In view of recent evidence that P-type Ca2+ channels mediate cholinergic transmitter release at the mammalian neuromuscular junction (NMJ), the expression of P-type Ca2+ channels in the SCLC cells and the reactivity of LES IgG with these channels support the hypothesis that P-type Ca2+ channels in these cancer cells may trigger the autoantibody production in this disorder. The antibodies so produced are implicated in the functional impairment of the Ca2+ channels characteristic of LES.

The difference in shape of spontaneous and uniquantal evoked synaptic potentials in frog muscle

1. Spontaneous and stimulation-induced uniquantal synaptic activity at the frog cutaneous pectoris muscle, treated with neostigmine, was recorded by focal extracellular microelectrodes. A monoexponential curve was fitted to the decay of each synaptic response. 2. A highly significant positive relationship was found between the amplitude and the decay time constant of spontaneous extracellular miniature endplate potentials (MEPPs(o)), whereas the relationship displayed by evoked uniquantal extracellular endplate potentials (EPPs(o)) was only slightly greater than zero. 3. The difference did not stem from changes in the muscle membrane conductance or from inclusion of outstanding MEPPs(o) formed as a result of the block of acetylcholinesterase. 4. The dependence of the rise time on the amplitude was also stronger in MEPPs(o) than in EPPs(o). 5. In the absence of neostigmine, MEPPs(o) exhibited a positive correlation between decay time constant and amplitude, while EPPs(o) did not show such a correlation. 6. In view of previously published models of transmitter release, it is suggested that spontaneous secretion of quanta occurs both within and outside the active zones facing postsynaptic areas of variable receptor density.

Calcium channel autoantibodies in myasthenic syndrome and small cell lung cancer

Lambert-Eaton myasthenic syndrome (LEMS) is one of the neurologic paraneoplastic syndromes often found in patients with lung cancer. It is characterized by a generalized deficit of neurotransmitter release. Patients with small cell lung cancer (SCLC) in particular may develop LEMS, and SCLC is very often detected in patients affected by LEMS. LEMS is an autoimmune disease, and autoantibodies that interfere with neurotransmitter release by binding to presynaptic voltage-operated calcium channels (VOCCs) have been found in sera of patients with LEMS. Both human neuronal and SCLC cell lines express omega-conotoxin-sensitive VOCCs, and autoantibodies from patients affected by LEMS can precipitate these channels. We have now screened a large population of patients and control subjects in order to define the specificity and sensitivity of the anti-VOCC antibody assay. We have tested sera from 52 patients with LEMS with and without SCLC; 32 sera from patients with SCLC without LEMS, 31 from patients with non-SCLC, 34 from patients with inflammatory lung diseases, 17 from patients with other neurologic disorders, and 48 from healthy control subjects. We have found that a positive result with this radioimmunoassay is highly specific for LEMS, with or without SCLC, when the antibody titer is higher than 14.21 pM. Anti-VOCC antibodies have also been found in about 40% of patients with SCLC without LEMS, but they were absent in all the other populations tested. We can conclude that this serologic assay is a very useful aid in the diagnosis of LEMS, and it might be useful also for the early diagnosis of SCLC.

Specificity of Lambert-Eaton myasthenic syndrome immunoglobulin for nerve terminal calcium channels

Lambert-Eaton Myasthenic Syndrome (LEMS) is a presynaptic, neuromuscular disorder characterized by impaired nerve-evoked release of ACh. Repetitive nerve stimulation, which increases the probability of quantal release, improves the transmission defect. An autoantibody to Ca2+ channels of presynaptic motor nerve terminals is thought to mediate the pathogenesis of this disease. The goal of the present study was to examine the specificity of LEMS autoantibodies for nerve terminal Ca2+ channels as compared to other voltage-sensitive ion channels in nerve terminals, and to determine if non-specific membrane damage contributed to the pathogenesis of LEMS. The ion channel specificity of LEMS autoantibody was assessed by comparing the ability of acute application of IgG isolated from the plasma of a patient with LEMS to reduce depolarization-dependent uptake of 45Ca2+ and 22Na+ into or efflux of 86Rb+ from rat forebrain synaptosomes. The clinical diagnosis of LEMS was confirmed electrophysiologically by treatment of mice for 30 days with plasma (1.5 ml/day) taken from this patient. Characteristic reduction of quantal content elicited at 1 Hz and facilitation at 20 Hz was observed in mice treated with LEMS plasma compared to those treated with control plasma. One s, K(+)-stimulated 45Ca2+ uptake was inhibited 36.5 +/- 14.5% and 44.5 +/- 9.8% by acute application of 2 and 4 mg/ml LEMS IgG, respectively; IgG from patients with small cell carcinoma of the lung (SCC) had no effect on 45Ca2+ entry. The same concentrations of LEMS IgG affected neither voltage-dependent uptake of 22Na+ into veratridine-depolarized synaptosomes nor 86Rb+ efflux from K(+)-depolarized synaptosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Lambert-Eaton syndrome: antigen-antibody interaction and calcium current inhibition in chromaffin cells

Plasma and IgG obtained from 10 Lambert-Eaton myasthenic syndrome (LES) patients (5 with carcinoma, 5 without associated cancer), 6 healthy subjects, and 1 patient with small-cell lung cancer (SCLC) were examined in their ability to recognize chromaffin cell antigens on Western blots. The pattern of antigen recognition was compared with the magnitude of inhibition of voltage-dependent calcium and sodium currents recorded with the patch-clamp technique from chromaffin cells. Eight of the 11 patients with LES and/or SCLC recognized plasma membrane proteins and 9 of the patients' IgG interacted with cytoplasmic antigens with no apparent pattern of antigen recognition between patients. Also, there was no obvious band pattern distinguishing patients with LES from those with LES and concurrent SCLC. Eighty percent of the LES patients' antibodies were capable of reducing the calcium current (ICa) in chromaffin cells. One of the novel findings of this study is that 30% of the patients had produced antibodies which were able to inhibit both calcium and sodium currents (INa). The heterogeneous response of the IgG on the Western blots does not appear to correlate with the efficacy of reducing the inward currents.

Enteric neuronal autoantibodies in pseudoobstruction with small-cell lung carcinoma

Severe gastrointestinal dysmotility is a newly recognized paraneoplastic syndrome that occurs with small-cell lung carcinoma. Thirty-four patients with small-cell carcinoma, of whom 5 had chronic intestinal pseudoobstruction and 29 had no digestive symptoms, were studied serologically. Four of the 5 patients with gut dysmotility had immunoglobulin G antibodies reactive with neurons of the myenteric and submucosal plexuses of jejunum and stomach in an indirect immunofluorescence assay. Antibodies of this type were not found in any of the 29 patients who had no gut dysmotility, nor were they found in patients with chronic idiopathic intestinal pseudoobstruction (n = 8), ovarian cancer (n = 20), or epilepsy (n = 4) or in normal subjects (n = 9). In 4 of the patients with paraneoplastic pseudoobstruction, antibodies in highly diluted serum (1:4000-1:8000) bound selectively to nuclei and cytoplasm of neuronal elements in the gut. This novel autoantibody activity suggests that intestinal pseudoobstruction occurring in patients with small-cell carcinoma may have an autoimmune basis. From a clinical standpoint, serological testing offers a simple means for determining which patients with gut dysmotility syndromes may have associated small-cell carcinoma, thereby enabling earlier diagnosis and treatment of the tumor.

Acetylcholine release at identified nerve terminals in the organ-cultured frog neuromuscular preparation

1. The frog cutaneous pectoris neuromuscular preparation was maintained in organ culture for a few days, at either 24 or 14 degrees C. The synaptic activity of identified nerve terminals was repeatedly examined in order to describe the sequence and time course of changes from normal synaptic activity to a complete synaptic silence. 2. We found that the 'transient stage' (stage II, according to Ko, 1981) consists of at least three distinct periods each characterized by a unique trend of change in synaptic activity. The initial change involved a simultaneous decay of both spontaneous and nerve stimulation-evoked release of acetylcholine (sub-stage II1). Subsequently, the frequency of spontaneous miniature endplate potentials (MEPPs) increased gradually, while the evoked release continued its monotonous decay (sub-stage II2). During the third sub-stage spontaneous MEPPs, but no evoked endplate potentials (EPPs), were observed (sub-stage II3). 3. Statistical properties of acetylcholine release in still-transmitting junctions at sub-stage II2 and in non-transmitting junctions at sub-stage II3 were investigated. MEPPs with skewed amplitude histograms and bursting behaviour were evident at both sub-stages. However, the incidence and the extent of these distortions were higher in the non-transmitting junctions. 4. An inverse relation between the quantal content of evoked release and the rate of spontaneous secretion was found in the transmitting junctions. 5. These results suggest that some of the deterioration of synaptic activity in organ culture is caused by an impairment of the release process itself. Possible cellular mechanisms are discussed.

Edrophonium responsiveness not necessarily diagnostic of myasthenia gravis

Uneqivocally positive edrophonium tests, both clinically and electrophysiologically, were observed in a classic case of the Lambert-Eaton myasthenic syndrome. A review of the literature revealed that a positive edrophonium response has been reported in a majority of cases of myasthenia gravis (MG) and overlap myasthenic syndrome and in some cases of the Lambert-Eaton myasthenic syndrome, botulism, congenital myasthenic syndrome, drug-induced myasthenic syndrome, the Guillain-Barre syndrome, and amyotrophic lateral sclerosis. From this, we conclude that an unequivocally positive edrophonium test alone is not necessarily diagnostic of MG and that the diagnosis of MG should be based on the clinical features together with edrophonium-responsiveness and other laboratory findings.

Autoantibodies bind solubilized calcium channel-omega-conotoxin complexes from small cell lung carcinoma: a diagnostic aid for Lambert-Eaton myasthenic syndrome

Serum autoantibodies found by radioimmunoassay in 27 of 52 patients with the Lambert-Eaton myasthenic syndrome (LES) bound specifically to a soluble omega-conotoxin binding component of a voltage-gated Ca2+ channel (VGCC) complex extracted from small cell lung carcinoma (SCC). These antibodies were not found in 43 control patients with other neurologic diseases, including myasthenia gravis, peripheral neuropathies, and amyotrophic lateral sclerosis, or in 9 patients with endocrine autoimmunity, but they were found in 2 of 21 control patients with SCC without a history of LES, 1 of whom had severe autonomic neuropathy. Seropositivity was more frequent in patients with LES who had evidence of a primary lung cancer (76%) than in those with other neoplasms or without evidence of cancer (30%). Antigens extracted from SCC tumor lines derived from patients with and without LES and from a human neuroblastoma line yielded results that were highly correlated. A control extract of colonic carcinoma (derived from a patient with LES) yielded negative results. The data implicate a tumor-associated VGCC as the autoimmunizing stimulus in a subset of patients with LES and provide the first direct evidence that the VGCC complex in SCC is a target for some LES antibodies. The serologic test described should be a useful aid in diagnosing LES.

Specificity of calcium channel autoantibodies in Lambert-Eaton myasthenic syndrome

Autoantibodies that interfere with neurotransmitter release by affecting the function of voltage-operated calcium channels (VOCCs) have been found in patients with Lambert-Eaton myasthenic syndrome (LES). To find out the nature of the antigen to which these autoantibodies bind, tests were done with omega-conotoxin, which blocks some types of VOCCs. LES antibodies were able to immunoprecipitate VOCCs prepared from the human neuronal cell line IMR32 which were pre-labelled with the specific VOCC ligand omega-conotoxin. LES autoantibodies are also able to specifically down-regulate the expression of VOCCs in IMR32 cells. A new radioimmunoassay for the quantitative detection of LES antibodies was developed and found to be of value in distinguishing LES patients from patients with myasthenia gravis and some other neurological disorders.

Lambert-Eaton myasthenic syndrome: immunoglobulin G inhibition of Ca2+ flux in tumor cells correlates with disease severity

We compared the effects of Lambert-Eaton myasthenic syndrome (LEMS) immunoglobulin G (IgG) obtained from patients with and without small-cell lung carcinoma (SCLC) on voltage-gated (K+-stimulated) 45Ca2+ flux in cell lines derived from a human SCLC (MAR10) and from a rat pheochromocytoma (PC12) and related these to electromyographic indexes of clinical severity. Control IgG was obtained from patients with other neurological disorders or healthy individuals. Inhibition of Ca2+ flux by LEMS IgG was time and dose dependent. The flux was significantly reduced in MAR10 cells grown in either SCLC-LEMS IgG (0.38 nmol/10(6) cells; p less than 0.001) or non-SCLC-LEMS IgG (0.35 nmol/10(6) cells; p less than 0.001), compared with that in MAR10 cells grown in control IgG (0.7 nmol/10(6) cells). Similar significant reductions were also observed in PC12 cells. The reduction in amplitude of the resting compound muscle action potential in the LEMS patients correlated positively (r = 0.70; p = 0.007) with the inhibition of Ca2+ flux in MAR10 cells by their IgG. These results strongly support the view that IgG autoantibodies that can inhibit Ca2+ flux in SCLC cells are responsible for the disorder of transmitter release at motor nerves in SCLC-associated LEMS.

Transient Lambert-Eaton myasthenic syndrome associated with systemic lupus erythematosus

We present a patient who developed the Lambert-Eaton myasthenic syndrome (LEMS) in association with systemic lupus erythematosus (SLE). Severe proximal weakness with electrodiagnostic evidence of LEMS developed over 2 days during an exacerbation of cutaneous manifestations (bullous pemphigoid) associated with SLE. Following an increase in the daily dose of prednisone, there was complete clinical restitution of strength within 2 weeks and a slower resolution of electrodiagnostic abnormalities over 6 months. Marked serologic abnormalities were present at the onset and showed improvement over 6-8 months. LEMS had been infrequently described in association with SLE. The immunologic features of both SLE and LEMS suggest a linkage between the two diseases in this patient. We hypothesize that increased antibodies associated with exacerbation of SLE cross reacted with the neuromuscular junction membrane to produce LEMS.

Circulating antineuronal antibodies in small cell lung cancer

Antibodies directed against neuronal cells were found in the serum of 10 out of 27 patients with small cell lung cancer (SCLC) by means of an indirect immunofluorescent test. Positive staining was found either in nuclei of neurons with sparing of nucleoli or in the cytoplasm only. Antibodies belonged to IgG or IgM. A comparison with a control group of 60 patients yielded a high specificity of the circulating antibodies for SCLC. Contrary to recent reports, we were not able to confirm an association between the existence of circulating antibodies against neurons and the incidence of neurologic paraneoplastic disorders.

Selected IgG rapidly induces Lambert-Eaton myasthenic syndrome in mice: complement independence and EMG abnormalities

Antibodies in individual patients with the Lambert-Eaton myasthenic syndrome (LES) differ in their reactivity with mouse motor nerve terminals. Of 26 LES patients' sera injected a single time into mice, 3 caused a highly significant reduction in stimulus-dependent quantal release (m) of acetylcholine (ACh) (to 6, 33, and 42 quanta per impulse at 1 Hz, respectively; mean for 10 control sera, 100 quanta at 1 Hz). The most potent serum (LES-A) was fully effective in mice deficient in complement component C5 and in mice depleted of complement components C3----C9 by cobra venom factor. A single i.v. injection of serum reduced m in direct proportion to log dose. Responses to K+ depolarization and increasing concentrations of Ca2+ were like those observed in human LES. With LES-A serum, or its IgG, m was reduced near maximally in 1 day and plateaued in 3-4 days. Recovery began after day 8; m was in the normal range by day 20-30. Electromyographic (EMG) abnormalities were not seen until m fell below 40 quanta per impulse at 1 Hz. Below 10 quanta, clinical signs of weakness appeared, and the EMG abnormalities were those classically associated with LES: a marked reduction of compound muscle action potential to a single nerve stimulus in rested muscle, a further decrement during stimulation at slow rates, but marked facilitation during rapid repetitive stimulation.

Lambert-Eaton myasthenic syndrome: the lack of short-term in vitro effects of serum factors on neuromuscular transmission

Serum was obtained from 7 patients with the Lambert-Eaton myasthenic syndrome (LES), 3 patients with small-cell carcinoma of the lung (SCCL), and 9 healthy control subjects. Serum samples were applied in vitro to the rat neuromuscular junction (for 1-3 h for control LES sera; 4 h for SCCL sera), following which the pre- and postjunctional physiological effects of serum factors were studied in the presence of 10 mM [Mg2+]o. All sera produced a marked reduction in the frequency of spontaneous miniature end-plate potentials (MEPPs), while causing slight to moderate changes in MEPP amplitude. There were no consistent changes in the quantum content of the impulse-evoked end-plate potentials, though the serum from one LES patient significantly and reversibly inhibited the evoked quantal release. No significant effect was found when a human intercostal muscle was exposed to serum from another LES patient for 2 h. Therefore, when applied in vitro on a short-term basis, the putative LES autoantibodies do not consistently react with voltage-dependent calcium channels in the motor nerve terminal and thus fail to reproduce the physiologic abnormality of the syndrome. We suggest that the pathogenic IgG molecules may require more than 3h of incubation in order to gain access to, and inhibit the function of, the prejunctional Ca2+ channels.

IgG from patients with Lambert-Eaton syndrome blocks voltage-dependent calcium channels

Lambert-Eaton syndrome, an autoimmune disorder frequently associated with small-cell carcinoma of the lung, is characterized by impaired evoked release of acetylcholine from the motor nerve terminal. Immunoglobulin G (IgG) antibodies from patients with the syndrome, applied to bovine adrenal chromaffin cells, reduced the voltage-dependent calcium channel currents by about 40 percent. When calcium was administered directly into the cytoplasm, however, the IgG-treated cells exhibited normal exocytotic secretion, as assayed by membrane capacitance measurement. Measurement with the fluorescent calcium indicator fura-2 indicated that the IgG treatment reduced potassium-stimulated increase in free intracellular calcium concentration. The pathogenic IgG modified neither kinetics of calcium channel activation nor elementary channel activity, suggesting that a reduction in the number of functional calcium channels underlies the IgG-induced effect. Therefore, Lambert-Eaton syndrome IgG reacts with voltage-dependent calcium channels and blocks their function, a phenomenon that can account for the presynaptic impairment characteristic of this disorder.

Immunoglobulins of Lambert-Eaton myasthenic syndrome inhibit rat pituitary hormone release

We speculated that IgG from patients with Lambert-Eaton myasthenic syndrome (LES) would inhibit calcium-dependent hormone secretion in rat anterior pituitary (AP) cells. Primary cultures of normal AP cells were continuously exposed to crude IgG from an LES patient or from healthy control subjects, and the incubation media were assayed for prolactin (PRL) or growth hormone (GH). The LES IgG caused a time- and concentration-dependent reduction of PRL and GH release compared with control IgG over 0.5 to 48 hours using concentrations of 0.01 to 4.0 mg/ml. The calcium-channel activator maitotoxin stimulated 45Ca2+ uptake and PRL release from AP cells under control conditions, and the LES IgG significantly reduced both actions of maitotoxin. Thus LES IgG appears to modulate an AP antigenic site, perhaps representing an integral component of voltage-gated calcium channels that may share properties with similar presynaptic elements at the neuromuscular junction.

Antineuronal antibodies in small cell lung carcinoma--a significance for paraneoplastic syndromes?

In recent years a cause-effect relationship between the existence of circulating antineuronal antibodies (CANA) and neurological paraneoplastic syndromes has been described by several authors suggesting specifity of such antibodies for paraneoplastic syndromes. The present study is a systematic approach to elucidate the significance of CANA in tumor patients. Forty patients with biopsy-proven small cell cancer of the lung (SCLC) were compared to 70 non-SCLC patients and 20 controls in respect to clinical and neurophysiological findings. CANA were found in 17 patients with SCLC. However, only one of these patients with SCLC and positive CANA displayed a sensory neuropathy of the Denny-Brown type, which appeared to be unrelated to CANA titers and oncological course. Contrary to recent reports, we were not able to confirm an association between the existence of CANA and an increased incidence of paraneoplastic neurological syndromes. These data suggest that the antineuronal antibodies appear to be specific for SCLC, but are not necessarily related to paraneoplastic neurological syndromes.