Performance evaluation of a radioimmunoprecipitation assay for the detection of N-type voltage-gated calcium channel antibodies.

BACKGROUND: In this study, we assessed the performance characteristics of a laboratory-developed radioimmunoassay (RIA) to detect N-type voltage-gated calcium channel (N-VGCC) antibodies found in several autoimmune neurologic diseases. METHODS: Four hundred and forty-five (n = 445) sera were evaluated, including 156 sera (50 positive and 106 negative for N-VGCC antibodies) previously tested at Mayo Clinic Laboratories (MCL) and 289 controls (n = 187 disease and n = 102 healthy). Specimens were analyzed with the RIA using N-VGCC labeled with 125I-ω-conotoxin GVIA. The RIA was compared to the predicate MCL assay using a tiered positive predictive value (PPV) approach. Other performance characteristics evaluated included specificity, precision, interference, and stability. RESULTS: Qualitative inter-laboratory agreement based on tiered PPVs was 100% for results >1.00 nmol/L (71% PPV), 48% for results of 0.10-0.99 nmol/L (24% PPV) and 22% for results of 0.04-0.10 nmol/L (19% PPV). Negative results showed 90% agreement (n = 106). Specificity in controls positive for other neural autoantibodies and healthy controls were 87% and 100%, respectively. Acceptable results were observed for other performance characteristics. CONCLUSIONS: Inter-laboratory correlations demonstrate equivalence between assays with some discrepancies between low positive results. Collaborative efforts aimed at assessing the clinical spectrum associated with these antibodies and consensus for harmonizing test performance are required for optimal categorization of patients.

Autoimmune encephalitis with elevated N-type calcium channel antibodies as a multiple sclerosis mimic.

BACKGROUND: Voltage gated calcium channels (VGCC) are well-known targets for antibody-associated disease. Of the 5 VGCC subtypes, the most well-known is the P/Q subtype associated with Lambert-Eaton Myasthenic Syndrome (LEMS). However, this case focuses on the much less understood N-type calcium channel antibody. The objective of this case is to review the literature regarding the clinical significance of the N-type calcium channel antibody and its relationship to MS. METHODS: A 37-year old male presented with vertigo, paranoia, and tremor and had MRI changes suggestive of demyelinating disease. Evaluation revealed positive N-type calcium channel antibodies. Steroids dramatically improved symptoms and normalized antibodies. Years later recurrent symptoms were again associated with elevated antibodies. RESULTS AND CONCLUSION: This patient likely has autoimmune encephalitis associated with elevated N-type calcium channel antibodies. This case highlights the clinical significance of N-type calcium channel antibodies and the importance of correctly diagnosing patients with antibody mediated disease that may very well mimic more common neurologic diseases such as multiple sclerosis (MS).

Paraneoplastic cerebellar degeneration and lambert-eaton myasthenia in a patient with merkel cell carcinoma and voltage-gated calcium channel antibodies.

INTRODUCTION: Merkel cell carcinoma is a rare cutaneous, aggressive tumor. Although it shares many neuroendocrine features with small cell lung carcinoma, it has only occasionally been reported with paraneoplastic neurological syndromes. METHODS: A healthy 67-year-old man developed acute ataxia, vertigo, and nausea. Subsequently he also developed dysarthria, diplopia, xerostomia, fatigability and progressive anorexia. He underwent a full diagnostic workup and was found to have a high titer of voltage-gated calcium channel antibodies in serum and cerebrospinal fluid, neurophysiological findings compatible with Lambert-Eaton myasthenia and neurological signs compatible with cerebellar degeneration. RESULTS: A positron emission tomography study revealed a hypermetabolic lesion in the axilla, subsequently biopsied and consistent with Merkel cell carcinoma. CONCLUSIONS: In most previous reports, neurological symptoms preceded the Merkel cell carcinoma diagnosis, and the primary localization was in lymph nodes. This tumor should be considered in patients with paraneoplastic syndrome, and particularly Lambert-Eaton myasthenia after exclusion of small cell lung carcinoma. Muscle Nerve 56: 998-1000, 2017.

P/Q- and N-type calcium-channel antibodies: Oncological, neurological, and serological accompaniments.

INTRODUCTION: Voltage-gated calcium-channel autoimmunity (VGCC-P/Q and VGCC-N types) occurs beyond Lambert-Eaton syndrome and lung cancer. METHODS: We reviewed records for 236 Mayo Clinic patients with VGCC antibodies found in evaluation for paraneoplastic neurological autoimmunity (generally without myasthenic syndromes). RESULTS: VGCC autoantibodies were detected in 3.4% of neurological patients, 1.7% of healthy controls, and 4% of neurologically asymptomatic lung cancer controls. Fifty neurological patients (21%) had ≥ 1 neoplasm, historically (46) or detected prospectively [small-cell lung carcinoma (2), breast adenocarcinoma (2), lymphoma (1), and suspected tonsillar carcinoma (1)]. Autoimmune neurological diagnosis frequencies (encephalopathy, ataxia, myelopathy, neuropathy, neuromuscular junction disorder, and myopathy) among patients with medium values (24%; 0.10-0.99 nmol/L) or low values (19%; 0.03-0.10 nmol/L) were fewer than among patients with antibody values exceeding 1.00 nmol/L (71%; P = 0.02 and 0.004, respectively). CONCLUSIONS: Among neuronal VGCC-autoantibody-seropositive patients, autoimmune neurological phenotypes and cancer types are diverse. Cautious interpretation of results (particularly medium and low values) is advised. Muscle Nerve, 2016 Muscle Nerve 54: 220-227, 2016.

Utility of Paraneoplastic Antibody Testing in the Diagnosis of Motor Neuron Disease.

OBJECTIVE: To evaluate the role of paraneoplastic autoantibody testing in the diagnosis of motor neuron disease (MND). BACKGROUND: There have been rare case reports of paraneoplastic MND that have prompted many physicians to test for paraneoplastic autoantibodies in patients with MND. Our study is the first to determine the utility of such testing. METHODS: Retrospective chart review of patients with MND from a tertiary referral center from 2007 to 2014. RESULTS: Of 316 patients with MND reviewed, 44% (n = 138) were evaluated by a Mayo Clinic paraneoplastic autoantibody panel. Of note, 73% of these patients (n = 101) were diagnosed with amyotrophic lateral sclerosis, fulfilling possible, probable, or definite revised El Escorial criteria. Of note, 9% of patients (13/138) of those who had paraneoplastic antibody testing performed were positive for at least 1 paraneoplastic antibody. Three patients had negative testing for malignancy. None had a different disease course than expected. CONCLUSIONS: Testing for paraneoplastic antibodies does not seem to change the diagnosis, management, or outcome in the setting of MND and is therefore of limited value.

Psychiatric Autoimmunity: N-Methyl-D-Aspartate Receptor IgG and Beyond.

BACKGROUND: Descriptions of psychiatric autoimmunity beyond N-methyl-D-aspartate (NMDA) receptor encephalitis are sparse. OBJECTIVE: To report the autoimmune psychiatric spectrum currently recognized in Mayo Clinic practice. METHODS: Medical record review, testing of stored serum and cerebrospinal fluid for IgGs reactive with synaptic receptors and ion channels, neuronal nuclear and cytoplasmic antigens (including glutamic acid decarboxylase 65-kDa isoform) and case-control comparison were conducted. Patients were categorized into group 1, all adult psychiatric inpatients tested for neural autoantibodies (2002-2011; n = 213), and group 2, all Mayo NMDA receptor IgG-positive patients (2009-2013; n = 13); healthy control subjects were also included (n = 173). RESULTS: In group 1, at least 1 serum autoantibody (but not NMDA receptor IgG) was detected in 36 of 213 psychiatric inpatients. In total, 12 patients were determined retrospectively to have high-likelihood autoimmune encephalitic diagnoses. The most commonly detected autoantibody specificities were voltage-gated potassium channel ([Kv1] VGKC) complex (6) and calcium channel (P/Q type or N type; 5). Symptoms seen were as follows: depressive (8), anxious (7), psychotic (7), disorganized (5), suicidal (3), manic (1) and catatonic (1). In group 2, among 13 NMDA receptor IgG-positive patients, 12 had encephalitis; their psychiatric symptoms were as follows: depressive (9), catatonic (9), disorganized (8), anxious (8), psychotic (7), manic (6), and suicidal (3). Catatonic symptoms were more common in the 12 NMDA receptor IgG-positive patients than in the 12 group 1 patients with high likelihood of encephalitis (p = 0.002). Antibody positivities were usually low positive in value among healthy controls (12 of 16 vs 3 of 12 group 1 encephalitis cases, p = 0.025). NMDA receptor IgG was not detected in any healthy control subject. CONCLUSIONS: A spectrum of psychiatric autoimmunity beyond NMDA-R IgG may be under-recognized. Diagnosis is facilitated by combining results of comprehensive psychiatric, laboratory, radiologic, and electrophysiologic evaluations.

Suppression of Peripheral Pain by Blockade of Voltage-Gated Calcium 2.2 Channels in Nociceptors Induces RANKL and Impairs Recovery From Inflammatory Arthritis in a Mouse Model.

OBJECTIVE: A hallmark of rheumatoid arthritis (RA) is the chronic pain that accompanies inflammation and joint deformation. Patients with RA rate pain relief as the highest priority; however, few studies have addressed the efficacy and safety of therapies directed specifically toward pain pathways. The ω-conotoxin MVIIA (ziconotide) is used in humans to alleviate persistent pain syndromes, because it specifically blocks the voltage-gated calcium 2.2 (CaV 2.2) channel, which mediates the release of neurotransmitters and proinflammatory mediators from peripheral nociceptor nerve terminals. The aims of this study were to investigate whether blockade of CaV 2.2 can suppress arthritis pain, and to examine the progression of induced arthritis during persistent CaV 2.2 blockade. METHODS: Transgenic mice expressing a membrane-tethered form of MVIIA under the control of a nociceptor-specific gene (MVIIA-transgenic mice) were used in the experiments. The mice were subjected to unilateral induction of joint inflammation using a combination of antigen and collagen. RESULTS: CaV 2.2 blockade mediated by tethered MVIIA effectively suppressed arthritis-induced pain; however, in contrast to their wild-type littermates, which ultimately regained use of their injured joint as inflammation subsided, MVIIA-transgenic mice showed continued inflammation, with up-regulation of the osteoclast activator RANKL and concomitant joint and bone destruction. CONCLUSION: Taken together, our results indicate that alleviation of peripheral pain by blockade of CaV 2.2- mediated calcium influx and signaling in nociceptor sensory neurons impairs recovery from induced arthritis and point to the potentially devastating effects of using CaV 2.2 channel blockers as analgesics during inflammation.

Small-cell lung cancer with voltage-gated calcium channel antibody-positive paraneoplastic limbic encephalitis: a case report.

INTRODUCTION: Paraneoplastic limbic encephalitis is a rare neurological syndrome and clinically characterized by cognitive dysfunction, memory impairment, seizures and psychiatric symptoms. Paraneoplastic limbic encephalitis is most frequently found in small-cell lung cancer, among various malignancies, and antineuronal antibodies are related to the autoimmune mechanism. We experienced a rare case of a patient with small-cell lung cancer with anti-voltage-gated calcium channel antibody-positive paraneoplastic limbic encephalitis. CASE PRESENTATION: A 61-year-old Japanese man with a history of smoking cigarettes presented with seizure, confusion and personality change in acute onset. Brain magnetic resonance imaging showed high signal intensity on T2-weighted image in his right temporal lobe, suggestive of limbic encephalitis. A mediastinoscopy of the lymph node revealed small-cell lung carcinoma, and he was staged as having limited stage disease. Antibodies against P/Q-type and N-type voltage-gated calcium channel were positive and Hu antibody was negative. He was started on chemotherapy of carboplatin plus etoposide with concurrent thoracic radiotherapy. Neurological symptoms were gradually improved after systemic chemotherapy. CONCLUSIONS: We should be alert to the potential of malignant neoplasms associated with paraneoplastic limbic encephalitis when we examine a patient with cancer with neurological disorders such as personality change, disorientation, unconsciousness and memory loss. A clinical marker such as voltage-gated calcium channel antibody may help our diagnosis in clinical practice.

N-type calcium channel antibody-mediated paraneoplastic limbic encephalitis: a diagnostic challenge.

BACKGROUND: The etiology of encephalitis presents a diagnostic challenge and often remains a mystery. However, current technological advances using antibodies can enable a definitive diagnosis in cases that would previously have been suspected to be idiopathic or viral encephalitis. Our objective is to show that tonsil neuroendocrine carcinoma can present initially as limbic encephalitis mediated by N-type calcium channel antibodies and to highlight the diagnostic confusion before cancer detection. METHODS: We report a rare case of neuroendocrine cancer presenting as limbic encephalopathy, Lambert-Eaton myasthenic syndrome and neuropathy. The patient was diagnosed and treated at The University of Texas MD Anderson Cancer Center in November 2011. RESULTS: Paraneoplastic limbic encephalitis was diagnosed based on clinical presentation of seizures, short-term memory loss, retrograde amnesia, disorientation, distractibility, and abulia; on the exclusion of brain metastases, CNS infection, stroke, metabolic or nutritional deficits, or medication-related events; and on CSF results with inflammatory findings and an abnormal electroencephalography study that showed seizure activity in the left temporal lobe. Serum paraneoplastic panel was positive for P/Q-type calcium channel antibody and N-type calcium channel antibody. Magnetic resonance imaging of brain was unremarkable. CONCLUSION: This case highlights limbic encephalitis as an atypical presentation of neuroendocrine cancer. It also illustrates how treatment of the underlying cancer can reverse limbic encephalitis and Lambert-Eaton myasthenic syndrome in a neuroendocrine carcinoma patient even before the paraneoplastic panel becomes negative.

Presence of paraneoplastic antibodies in non-carcinomatous patients with neurological involvements of unknown cause.

BACKGROUND: Paraneoplastic antibodies (PAs) play a crucial role in the diagnostic approach of paraneoplastic neurological syndrome (PNS). We clarified the frequency and the clinical profile of PA-positive non-carcinomatous patients with neurological involvements of unknown cause. METHODS: PAs were analyzed in sera of 222 consecutive non-carcinomatous patients (122 men and 100 women) defined as acute or subacute onset of unknown-causative symptoms involving the neuromuscular junction, the central and/or the peripheral nervous system between 2006 and 2009. PAs contained antineuronal nuclear autoantibody type 1, 2, 3, Purkinje cell cytoplasmic autoantibody type 1, 2, anti-Tr, amphiphysin, CRMP-5, P/Q-type, N-type voltage-gated calcium channels (VGCC), voltage-gated potassium channel complex (VGKCC) and neuronal acetylcholine receptor (nAChR) antibodies. PA-seropositive patients received detailed examination of carcinoma in the whole body for the following 2 years. RESULTS: Nine patients were PA-positive. VGKCC antibodies were found in four patients, P/Q-type VGCC antibodies in two, N-type VGCC antibodies in two and nAChR antibodies in one. Neurological features revealed limbic encephalitis in four patients, sensorimotor neuropathy in three and Lambert-Eaton myasthenic syndrome in two. One year later, 2 patients developed myelodysplastic syndrome and lung adenocarcinoma (one patient each). CONCLUSION: We conclude that PA-seropositive frequency is 4.1% in non-carcinomatous neurological patients at examination. VGKCC, P/Q-type and N-type VGCC, and nAChR antibodies have benefits for screening non-carcinomatous PNS patients with acute or subacute neurological deficits of unknown cause.

VGCC antibody-positive paraneoplastic cerebellar degeneration presenting with positioning vertigo.

A 70-year-old woman developed paraneoplastic cerebellar degeneration (PCD) due to P/Q-type and N-type voltage-gated calcium channel antibodies and small cell lung cancer, the main clinical manifestations of which were severe positioning vertigo and vomiting. Loss of the visual suppression of caloric nystagmus, spontaneous downbeat nystagmus, periodic alternating nystagmus, and positioning vertigo in our patient most probably corresponds to the cerebellar flocculus/paraflocculus lesion caused by PCD.

[Lambert-Eaton myasthenic syndrome associated with pulmonary squamous cell carcinoma and circulating anti-P/Q-type voltage-gated calcium channel antibody].

We report a 64-year-old man diagnosed with Lambert-Eaton myasthenic syndrome (LEMS) associated with pulmonary squamous cell carcinoma. Circulating anti-P/Q-type voltage-gated calcium channel (VGCC) antibody was detected, and the patient was treated with 3,4-diaminopyridine. At age 61, chest radiograph revealed a tumor shadow in the right upper lung field. This was surgically removed, and a histological diagnosis of moderately differentiated pulmonary squamous cell carcinoma was obtained. After about 1 year, mediastinal metastasis was detected and 5-FU was administered. Eight months later, metastasis was noted in the left frontal hemisphere, and radiosurgical therapy was performed. The brain tumor gradually shrank but generalized fatigue, thirst, and gait disturbance developed after 4 months. A diagnosis of LEMS was made on the basis of neurological findings including proximal muscle weakness and absent tendon reflexes; autonomic symptoms (thirst, constipation, and impotence); characteristic electromyographic findings; and circulating anti-P/Q-type VGCC antibody. He has been treated with 3,4-diaminopyridine at a dose of 30 mg/day, resulting in marked improvement in symptoms but little change in electromyographic findings. The present case is very rare and suggests that anti-P/Q-type VGCC antibody may be involved in the mechanism of LEMS associated with pulmonary squamous cell carcinoma.

Lambert-eaton myasthenic syndrome differential reactivity of tumor versus non-tumor patients to subunits of the voltage-gated calcium channel.

OBJECTIVE: Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease in which the transmission across the neuromuscular junction is disturbed by autoantibodies directed against the presynaptic P/Q-type voltage-gated calcium channels (VGCC). LEMS is paraneoplastic (T-LEMS) in about 60% of patients mostly associated with a small cellular lung carcinoma (SCLC), but occurs spontaneously without a tumor in 40% (NT-LEMS). In most cases neurologic symptoms appear before tumor diagnosis, but there is as yet no clear specific serologic marker to distinguish between NT- and T-LEMS. METHODS: To see whether antibodies from patients with NT- and T-LEMS differentially recognize antigenic sites of the alpha 1A subunit of P/Q-type VGCC, we studied serum samples from 22 T-LEMS and 24 NT-LEMS patients. Sera reactivity was tested by Western blot analysis to recombinant proteins corresponding to the extracellular S5-S6 linker region of three out of four domains forming the alpha 1 subunit of P/Q-type VGCC. RESULTS: Sera from 9/24 (37,5%) NT-LEMS patients, but only 1/22 (4,6%) T-LEMS patients recognized domain IV (p=0,011). Seroreactivity to domains I and III was similar for NT-LEMS and T-LEMS patients (domain I: 8%/14%; domain III: 46%/41%, not significant). CONCLUSIONS: These data suggest that an antibody response to domain IV is more common in LEMS without tumor than in paraneoplastic LEMS. This may have implications for diagnostic workup in LEMS patients without previously established diagnosis of a tumor. Additionally this could point towards a differential autoimmune pathogenesis between T-LEMS and NT-LEMS.

Distinct evolution of calcium channel antibody types in Lambert-Eaton myasthenic syndrome.

To determine whether titers of anti-P/Q type and anti-N type calcium channel antibodies provide distinct information, both types of assay were performed during follow-up of 7 patients with Lambert-Eaton myasthenic syndrome (LEMS). In 4 patients with both antibody responses, titers evolved independently and often in an inverse relationship. Two patients with squamous cell lung carcinoma (SqCLC) produced anti-N type channel antibodies, but no detectable anti-P/Q channel responses. These results suggest that anti-N channel autoantibodies constitute an immune response distinct from the anti-P/Q type channel specificity and can also correlate with clinical evolution. Consequently combined assays may provide more comprehensive information during follow-up of LEMS.

[P/Q-type voltage-dependent calcium channels in neurological disease]. / Canales de calcio dependientes de voltaje de tipo P/Q en neurología.

INTRODUCTION: Voltage-dependent calcium channels (VDCC) are hetero-multimeric complexes that mediate calcium influx into cells in response to changes in membrane potential. The alpha1A subunit, encoded by the CACNA1A gene, is the pore-forming structure specific to the neuronal P/Q-type voltage-dependent calcium channels (P/QCC), present exclusively in neurons. The ancillary subunits beta, alpha2delta and gamma, which are common to other VDCC, modulate alpha1A activity. P/QCC are involved in neuronal plasticity and survival, and mediate fast neurotransmission in the central and peripheral nervous system. Their highest levels of expression are found in the Purkinje cell layer of the cerebellum and in the hippocampus. METHODS: Congenital and acquired disturbances of the P/QCCs lay behind some neurological diseases, such as spinocerebellar ataxia type 6, episodic ataxia type 2 and paraneoplastic cerebellar degeneration; familial hemiplegic migraine; generalized convulsive epilepsy, generalized absence epilepsy and myasthenic syndrome of Lambert-Eaton. CONCLUSION: In this article, the structure and modulation of normal P/QCCs, and the neurological diseases caused by disturbances in these are reviewed. Electrophysiological characterization of mutated P/QCCs has yielded decreased calcium conductance in every case, compared with wild type channels. Research about calcium channelopathies should clarify how altered channel function produces disease and lead to new treatments for these conditions.

Phoneutria nigriventer omega-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.

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.

[Dosage and specificity of anti-calcium channel antibodies in Lambert-Eaton myasthenic syndrome]. / 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.