P/Q- & N-TYPE CALCIUM CHANNEL ANTIBODIES: ONCOLOGICAL, NEUROLOGICAL & SEROLOGICAL ACCOMPANIMENTS (2024)

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P/Q- & N-TYPE CALCIUM CHANNEL ANTIBODIES: ONCOLOGICAL, NEUROLOGICAL & SEROLOGICAL ACCOMPANIMENTS (1)

Link to Publisher's site

Muscle Nerve. Author manuscript; available in PMC 2017 Aug 1.

Published in final edited form as:

Muscle Nerve. 2016 Aug; 54(2): 220–227.

Published online 2016 Feb 8. doi:10.1002/mus.25027

PMCID: PMC4940238

NIHMSID: NIHMS751460

PMID: 26789908

Nicholas Zalewski, MD,1 Vanda A. Lennon, MD, PhD,1,2,3 Daniel H. Lachance, MD,1,2 Christopher J. Klein, MD,1,2 Sean J. Pittock, MD,1,2 and Andrew McKeon, MD1,2

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The publisher's final edited version of this article is available at Muscle Nerve

Associated Data

Supplementary Materials

Abstract

Introduction

Voltage-gated calcium channel-autoimmunity (VGCC-P/Q-type and VGCC-N-type) 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).

Discussion

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.

Keywords: Calcium channel, paraneoplastic, myasthenia, ataxia, neuropathy

INTRODUCTION

Voltage-gated calcium channels of P/Q-type (VGCC-P/Q) and N-type (VGCC-N) are targets of IgG-mediated motor nerve terminal autoimmunity in Lambert-Eaton syndrome (LES). Early supportive evidence included structural alterations of calcium channel-enriched presynaptic membranes in freeze-fracture electron microscopic images and disruption by LES patient serum of depolarization-dependent calcium influx in cultured small-cell carcinoma cells and murine motor nerve terminals.13 The snail-derived omega neurotoxins MVIIC and GVIA specifically antagonize P/Q- and N-type calcium channels, respectively.4,5 Radiolabeling of these high affinity peptide antagonists permitted development of radioimmunoassays for antibody detection.4,6,7 VGCC-P/Q antibodies are detectable in more than 90% of non-immunosuppressed patients with LES, and VGCC-N antibodies are detected in 73% of paraneoplastic cases (and 36% of non-paraneoplastic cases).6 A spectrum of VGCC-antibody-associated neurological disorders beyond LES has been supported by the Mayo Clinic Neuroimmunology Laboratory’s subsequent service serological experience of patients referred for paraneoplastic evaluation.6 Here we describe the frequency of VGCC-P/Q and VGCC-N antibody seropositivity in patients referred for paraneoplastic antibody evaluation on a service basis at the Mayo Clinic (not restricted to a neurological phenotype), as well as the frequency and spectrum of oncological, neurological, and serological accompaniments during a 24-month period. We also determined the frequency of neuronal VGCC-antibodies in serum of 2 control groups: healthy persons, and neurologically-asymptomatic patients with lung cancer.

PATIENTS & METHODS

The study was approved by the institutional review board of Mayo Clinic, Rochester, MN (IRB 14-5646). From July 1 2011 to June 30 2013, service paraneoplastic autoantibody evaluation of serum from 6842 patients seen at Mayo Clinic (Rochester Minnesota) yielded 236 positive results for VGCC-P/Q or VGCC-N antibody (3.4%).

Control subjects

Serum samples were available for: 1) 173 healthy residents of Olmsted County, Minnesota, who were of similar age and gender distribution to our patient referrals (collected in 2005), 97 were women (56%), and median age of serum draw was 52 years (range, 18–83 years); 2) 245 neurologically-asymptomatic patients with primary lung cancer [treatment-naïve, identified from the Mayo Clinic Epidemiology and Genetics of Lung Cancer Research registry, enrolled 1999 to 2005 (small-cell lung carcinoma, 35; adenocarcinoma, 70; squamous carcinoma, 70; other lung cancer types, 70)]8; 3) 202 patients consecutively referred for the paraneoplastic evaluation, but were seronegative (2004–2005).9

Clinical evaluation

N.Z. and A.M. reviewed the electronic medical record of all seropositive patients. This included history and examination findings, laboratory values, imaging findings, results of electrophysiological tests (electromyography, electroencephalography, and autonomic studies) and cerebrospinal (CSF) results. N.Z. and A.M. also confirmed the neurological diagnosis made by an evaluating Mayo Clinic neurologist.

Serological evaluation

VGCC antigens were solubilized in non-denaturing detergent (digitonin) from cerebral cortical membranes (porcine for VGCC-N; combined porcine and rabbit for VGCC-P/Q) and tagged by complexing with 125I–labeled ω-conopeptide GVIA or MVIIC, respectively. Antibodies were detected by radioimmunoprecipitation using goat anti-human immunoglobulin (IgG/IgM) as precipitant. Positive sera were re-evaluated in the course of this study comparing anti-human IgG/IgM and anti-human IgG as precipitants; values obtained were not significantly different from those originally obtained using a goat anti-human IgG/IgM precipitant, which are reported here. Results are expressed in terms of precipitated 125I-ω-conopeptide (nanomoles per liter of serum), after subtracting the value precipitated by healthy control sera, and repeating the assay with 125I-ω-conopeptide alone to eliminate false positive results.10

For antibody-positive patients, clinical/laboratory correlations were analyzed according to antibody value: high (VGCC-P/Q and VGCC-N, 1.00 nmol/L or greater), medium (VGCC-P/Q and VGCC-N, 0.10–0.99 nmol/L), and low (VGCC-P/Q, 0.03–0.09 nmol/L; VGCC-N, 0.04–0.09 nmol/L).8 Values of 0.00–0.02 nmol/L (VGCC-P/Q antibody) and 0.00–0.03 nmol/L (VGCC-N antibody) are considered normal. We compared the frequency of neurological diagnoses and cancers among patients and seronegative controls, and autoimmune diagnoses among antibody value groups using the Fisher exact test (P < 0.05 was considered significant).

All sera were evaluated additionally at time of clinical evaluation by: 1) standardized immunofluorescence assays for IgG autoantibodies of the following specificities: anti-neuronal nuclear (ANNA)-1, -2, -3; amphiphysin; Purkinje cell cytoplasmic -1, -2, and -Tr; collapsin response-mediator protein (CRMP)-5; anti-glial/neuronal nuclear (AGNA)-1; n-methyl-D-aspartate (NMDA) receptor (GluN1 subunit); a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid [AMPA receptor (GluA1 and GluA2)]; and gamma-aminobutyric acid (GABAB) receptor; 2) radioimmunoprecipitation assays for antibodies targeting neuronal voltage-gated potassium channel (VGKC)-complexes, muscle (α1) nicotinic acetylcholine receptor, and neuronal ganglionic (α3) acetylcholine receptor; and 3) enzyme-linked immunosorbent assay for striational antibodies. For the purpose of this study, we additionally performed cell-based assays using human embryonic kidney-293 cells transfected with appropriate expression plasmids to detect antibodies targeting NMDA receptor, AMPA receptor, and GABAB receptor (Euroimmun, Lübeck, Germany). Assays for muscle acetylcholine receptor modulating antibody, muscle-specific kinase (MuSK) antibody, leucine-rich-glioma-inactivated-1 (Lgi1) and contactin-associated protein-2 (CASPR2) IgGs, and glutamic acid decarboxylase 65-isoform (GAD65) antibody were not performed on all sera, but their detection frequencies are reported for patients tested.

RESULTS

Control subjects

Calcium channel antibodies were detected in 3 of 173 healthy control subjects (1.7%) and 10 of 245 neurologically asymptomatic patients with lung cancer (4%). Two healthy controls had VGCC-P/Q antibody (0.10 and 0.18 nmol/L), and 1 had VGCC-N antibody (0.05 nmol/L). Among the 10 lung cancer patients, 3 had VGCC-P/Q antibody (median value, 0.03 nmol/L; range, 0.03–0.52) and 8 had VGCC-N antibody (median, 0.05 nmol/L, range 0.04–0.13); 1 patient had both antibodies. Their carcinomas were squamous cell (4), non-small-cell, not otherwise specified (3), small-cell (2), and adenocarcinoma (1).

Neurological patients

One or both VGCC antibodies were detected in 236 of the 6842 patients tested (3.4%; VGCC-P/Q only, 142; VGCC-N only, 73; both, 21). None of neurological phenotype, autoimmune diagnosis, or cancer type could be predicted by calcium channel antibody profile (VGCC-P/Q, VGCC–N, or both). Fifty-two percent of the seropositive patients were women. Oncological, neurological, and serological accompaniments of seropositivity are summarized in Supplementary Table S1 (available online), and Tables 1 and ​and2,2, respectively. The median age at neurological symptom onset was 57 years (range 9–87 years). The median Mayo Clinic follow up period after initial evaluation was 7 months (range, 0 to 156 months).

Table 1

Neurological Findings & Immunotherapy Responses

Neurological disorderTotal patients (N=236)Classified according to highest VGCC-P/Q or VGCC-N Ab valueBoth VGCC- P/Q and VGCC-N detected (N=21)Immunotherapy response
High (N=7)Medium (N=79)Low (N=150)No response (N=38)Modest response (N=22)Robust Response (N=9)
Peripheral neuropathy*61220399642
None49016330101
Cognitive4139295803
Miscellaneous37014231300
Dysautonomia1908110320
Parkinsonism110471200
Demyelinating disease110562111
Anterior horn cell disorders110291300
Radiculopathy100732200
Seizures100370101
Neuromuscular junction defect102530080
Cerebellar ataxia (non-demyelinating)92252320
Myopathy70520130
Brachial plexopathy40130011
Myelopathy (non-demyelinating)40400200
Dystonia30030000
Chorea10010100
Sensorineural hearing loss10010100
Stiff person syndrome10100010

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*EMG available in 55: length-dependent and primarily axonal sensorimotor (33), length-dependent mixed axonal and demyelinating (4), brachial plexopathy (4), sensorimotor demyelinating (2), sensory neuronopathy (2), severe, diffuse motor-predominant axonal polyradiculoneuropathy (1), multiple mononeuropathies (1), multiple subacute cranial neuropathies (1), multiple chronic cranial neuropathies (1), mild axonal neuropathy with fasciculations (1), severe chronic diffuse patchy polyradiculoneuropathy (1), sensorimotor polyradiculoneuropathy with demyelinating features (1), patchy primarily axonal polyradiculoneuropathy (1), and normal findings (2). Three patients were diagnosed with small fiber neuropathy only (normal EMG, 2; on clinical grounds alone, 1). Biopsied sural nerve tissue (2 patients) did not reveal inflammation.

Abbreviations: VGCC, voltage-gated calcium channel.

Table 2

Coexisting neural autoantibodies

AntibodyPatients (N=73)Median valueRange of positive valuesNormal rangeNeurological and cancer diagnoses
GAD65240.15 nmol/L0.03–3375 nmol/L≤ 0.02 nmol/LVarious
Striated muscle171: 4801:120–1:61440< 1: 120Various
AChR binding130.12 nmol/L0.03–28.0 nmol/L≤ 0.02 nmol/LVarious
VGKC-complex11*0.17 nmol/L0.03–1.74 nmol/L≤ 0.02 nmol/LVarious
Ganglionic AChR100.07 nmol/L0.03–0.20 nmol/L≤ 0.02 nmol/LVarious
AChR modulating645% loss28–94% loss≤ 20% lossVarious
ANNA-111: 122,880-≤ 1: 120Sensory neuronopathy, small-cell carcinoma
AGNA-111:1920-≤ 1: 120LES, small-cell carcinoma
NMDA receptor1CSF positive (CBA)--Encephalitis, none
GABAB receptor1Serum positive (CBA; CSF not available)--Chronic whole-body pain (nos); malignant thymoma
MuSK15.13 nmol/L-≤ 0.02 nmol/LMyasthenia gravis; none

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*One patient each was seropositive for Lgi1 and CASPR2 antibodies. The former had autoimmune encephalitis, the latter had autoimmune chorea.25

Abbreviations: AChR, acetylcholine receptor; AGNA, antiglial/neuronal nuclear antibody; ANNA, antineuronal nuclear antibody; CBA, cell-based assay; CSF, cerebrospinal fluid; GABA, gamma-aminobutyric acid; GAD65, glutamic acid decarboxylase, 65 kD isoform; MuSK, muscle-specific kinase; NMDA, n-methyl-D-aspartate; VGKC, voltage-gated potassium channel complex.

Oncological associations

Cancer occurred in 50 of 236 VGCC antibody seropositive neurological patients (21%, 46 had a history of cancer, and 6 had a new cancer found) and 34 of 202 seronegative controls (17%, all had a history of cancer only), P = 0.27. The neoplasms encountered among the patients are listed in Table S1 and are categorized according to antibody titer. Monoclonal gammopathy of undetermined significance and skin malignancies other than melanoma were excluded. One-fifth of the seropositive patients (50/236) had at least 1 neoplasm by history or detected following antibody detection (VGCC-P/Q antibody-positive only, 29; VGCC-N antibody-positive only, 15; dual antibody-positive, 6). A second cancer was found in 2 patients with past history of cancer.

Comprehensive cancer evaluation, performed in 123 patients [body computerized tomography (CT) scan, 105; positron-emission tomography (PET)-CT scan, 73] revealed imaging evidence of cancer in 6 patients (5%), a median of 3 months after autoantibody detection (range, 0–16 months), including small-cell lung carcinoma (2), breast adenocarcinoma (2), follicular lymphoma (1), and probable tonsillar carcinoma (1). One breast adenocarcinoma was discovered by routine diagnostic mammogram 13 months after the positive serology (body PET-CT scan had revealed no abnormality). The second patient’s breast adenocarcinoma was identified by routine screening mammography 16 months after the positive serology (with negative initial mammogram). The patient with tonsillar neoplasm suspected by PET-CT scan did not undergo recommended biopsy for confirmation and died within 2 months at another medical facility from undocumented cause.

Forty-six patients (19%) had a past history of 1 or more cancers of diverse histologic types and anatomic locations, including prostate adenocarcinoma (9), breast adenocarcinoma (8), cervical adenocarcinoma (4), lung small-cell carcinoma (3), bladder urothelial carcinoma (3), Hodgkin lymphoma (3), renal cell carcinoma (3), melanoma (3), colon adenocarcinoma (3), thyroid papillary carcinoma (2), non-Hodgkin lymphoma (1), lung squamous cell carcinoma (1), conjunctival spindle cell carcinoma (1), Waldenström macroglobulinemia (1), ovarian adenocarcinoma (1), vulval squamous cell carcinoma (1), gynecologic papillary serous adenocarcinoma (1), endometrial adenocarcinoma (1), lung adenocarcinoma (1), thymic carcinoma (1), multiple myeloma (1), adenocarcinoma of unknown primary (1), and myelofibrosis (1).

Neurological associations

Table 1 documents the frequency of neurological disorders. Definite or probable autoimmune diagnoses were assigned in 79 patients (35%) by the primary evaluating neurologist (53 and 26, respectively). In 6 patients the autoimmune disorder was multifocal, including LES (2, both had documented autonomic ganglionopathy in addition to the typical LES-associated dry mouth and constipation, and 1 had length-dependent somatic peripheral neuropathy), encephalomyelopathy (1), encephalomyeloradiculopathy (1), cerebellar ataxia and encephalopathy (1), and cerebellar ataxia with a prior history of myasthenia gravis (1). Forty-nine patients had neurological symptoms without objective findings and thus no neurological diagnosis. Thirteen patients were lost to follow up before final diagnostic classification. The following neurological disorders are described in rostro-caudal anatomic order. The comparative frequencies of neurological phenotypes among VGCC positive patients and 202 patient seronegative controls are documented in Supplementary Table S2. Dysautonomia, seizures, and neuromuscular junction disorders were more common among the VGCC antibody-positive patients.

Cortical disorders

Cognitive disorders (41) included autoimmune encephalopathy (14; 10 extra-limbic, 4 limbic), degenerative dementia (18), mild cognitive impairment (5), and cognitive disorder not otherwise specified (4). Ten patients had seizures in the setting of autoimmune encephalitis (4), autoimmune epilepsy (2), and seizures not otherwise specified (4).

Cerebellar ataxia

Nine of the 236 patients had a diagnosis of cerebellar ataxia (3.8%). We excluded from this category those patients whose ataxia was attributable to 1 or more radiologically-detectable cerebellar lesions consistent with stroke or classical multiple sclerosis. The median onset age was 59 years (range, 35–72 years); median follow up was 11 months (range, 1–48 months). Eight patients were VGCC-P/Q antibody-positive (median value, 0.10 nmol/L; range 0.07–4.16 nmol/L); 3 patients were VGCC-N antibody-positive (median value, 2.33 nmol/L, range, 0.05–6.08 nmol/L). Five patients in this group were assigned final diagnoses of autoimmune cerebellar ataxia, 3 patients with multiple system atrophy, cerebellar type (MSA-C, all had coexisting dysautonomia), and 1 with cerebellar ataxia of unknown cause. Follow up information was available for 4 of 5 patients with final diagnoses of autoimmune cerebellar ataxia. Two had a paraneoplastic cause and died from cancer within a median of 5 months, and 2 improved with treatment.

Other movement disorders

Eleven patients had parkinsonism (all had been assigned a neurodegenerative diagnosis), 3 had dystonia (2 in the context of degenerative parkinsonism and 1 with isolated jaw and tongue dystonia of unknown cause), 1 had paraneoplastic chorea, and 1 had stiff-person syndrome.

Demyelinating central nervous system (CNS) disorders

Eight of 11 patients had a classical multiple sclerosis (MS) phenotype [primary progressive MS (5); relapsing remitting MS (3)], and 3 had an atypical demyelinating disorder [periventricular encephalitis (2), mono-hemispheric subcortical encephalitis with transverse myelitis (1)]. Four patients had a non-demyelinating myelopathy, 2 autoimmune and 2 of unknown cause.

Miscellaneous CNS disorders

Nine patients had a headache disorder, 9 had a degenerative spine disease, 9 had a toxic-metabolic neurologic disorder, 8 had cerebrovascular disease, and 2 had a brain neoplasm.

Anterior horn cell disorders

Eleven patients had been assigned the diagnosis of anterior horn cell disorder, 10 typical amyotrophic lateral sclerosis of neurodegenerative type and 1 phenotypically unusual with insidiously progressive bulbar involvement in the context of a history of Sjögren syndrome.

Peripheral neuropathies

Peripheral neuropathy was diagnosed in 61 patients (26%), and in 38 (16%) this was the only neurological finding (Table 1). In 22 of the 61 patients (36%), the cause was deemed autoimmune. Forty patients were VGCC-P/Q antibody-positive (median value, 0.07; range 0.04–4.16), and 28 were VGCC-N antibody-positive (median value, 0.06 nmol/L; range, 0.04–6.08).

Autonomic neuropathy or dysautonomia was encountered in 19 patients. Their final diagnoses were MSA (5), LES (2), postural orthostatic tachycardia syndrome (2), or other diagnosis (10).

Neuromuscular Junction Disorder

Neuromuscular junction disorders were documented in 10 of the 236 seropositive patients (4.2%). LES was confirmed electrophysiologically in 6 patients (median VGCC-P/Q antibody value, 0.49 nmol/L; range, 0.17–1.84 nmol/L). None was VGCC-N antibody-positive. A neoplasm (small-cell lung carcinoma) was identified prospectively after antibody detection in1 patient, a smoker aged 43 years.

Serological, clinical and electrophysiological evidence supported a postsynaptic neuromuscular transmission defect in another 4 patients (median VGCC-P/Q antibody value, 0.07 nmol/L; range 0.05–0.10; none was VGCC-N antibody-positive). Two had coexisting muscle AChR binding antibody; 2 had muscle AChR modulating Ab, and 1 had MuSK antibody, Table 2. Myasthenic findings were generalized in 3 and extraocular muscle-restricted in 1. Tendon stretch reflexes were preserved in all. Compound muscle action potentials (CMAPs) were normal in all 3 who had nerve conduction testing. Responses to repetitive nerve stimulation were normal in 2 patients (1 with extraocular muscle-restricted weakness, the other with mild generalized weakness); 1 patient had a CMAP decrement (but not increment) and myopathic findings. Two of these 4 patients had a history of cancer (1 prostate adenocarcinoma and 1 metastatic gynecological serous adenocarcinoma).

Myopathies

Of 7 patients with diagnosis of myopathy, 3 had biopsy evidence of inflammation (varying patterns, but none diagnostically specific), 1 had necrotizing myopathy with minimal inflammatory reaction, and 3 were classified as non-autoimmune myopathy.

Clinical correlations according to antibody value

High values for VGCC-P/Q or VGCC-N antibody

Seven of the 236 patients had at least 1 VGCC antibody value exceeding 0.99 nmol/L, 3 of whom were positive for both antibodies. Five of those patients were assigned an autoimmune neurological diagnosis (71%, Tables S1 and 1): encephalopathy (3), LES (2), cerebellar ataxia (2), and peripheral neuropathy (2). One patient had a multifocal neurological disorder. Two patients had a history of cancer.

Medium values for VGCC-P/Q or VGCC-N antibody

Of the remaining 229 patients, 79 had at least 1 VGCC antibody value in the range of 0.10–0.99 nmol/L. Their assigned diagnoses were peripheral neuropathy (20), non-neurological disorder (16), cognitive disorder (9), autonomic neuropathy or dysautonomia (8), radiculopathy (7), neuromuscular junction disorder (5), myopathy (5), CNS demyelinating disease (5), myelopathy (4), parkinsonism (4), seizures (3), cerebellar ataxia (2), anterior horn cell disorder (2), brachial plexopathy (1), classic stiff-person syndrome (1), and miscellaneous neurological disorders (14). Nineteen of those patients (24%) had at least 1 autoimmune neurological diagnosis: encephalopathy or other cortical disorder (6), neuromuscular junction disorder (5), peripheral neuropathy (5), myopathy (3), or stiff-person syndrome (1). A malignancy was found in 4 patients following antibody detection.

Low values for VGCC-P/Q or VGCC-N antibody

In 150 patients the highest VGCC antibody value was in the range of 0.03–0.09 nmol/L. Their diagnoses included 1 or more of: peripheral neuropathy (39), non-neurological disorder (33), cognitive disorder (29), autonomic neuropathy or dysautonomia (11), anterior horn cell disorder (9), seizures (7), parkinsonism (7), CNS demyelinating disease (6), cerebellar ataxia (5), radiculopathy (3), brachial plexopathy (3), dystonia (3), neuromuscular junction disorder (3), myopathy (2), chorea (1), and miscellaneous CNS disorders (23). Twenty-nine patients (19%) had at least 1 autoimmune neurological diagnosis: peripheral neuropathy (15), encephalopathy or other cortical disorder (8), seizure disorder (5), neuromuscular junction disorder (3), ataxia (3), or another autoimmune neurological diagnosis (4). Cancer was found in 2 patients following antibody detection.

The overall positive predictive value for an autoimmune neurological diagnosis was 22%. Autoimmune neurological diagnoses were more common among patients with high antibody values (5/7) than among patients with medium values (19/79, P=0.02) or low values (29/150, P=0.004).

Coexisting autoantibodies

At least 1 other neural autoantibody was detected in 73 patients. Specificities included GAD65 (24), striated skeletal muscle (17), muscle AChR (binding antibody, 13; modulating antibody, 6), VGKC-complex (11), neuronal ganglionic AChR (10), AGNA-1 (1), NMDA receptor (1), GABAB receptor (1), ANNA-1 (1) and MuSK (1), Table 2. The GAD65 antibody value in 1 patient exceeded 20 nmol/L (3375 nmol/L); the neurological diagnosis was stiff-person syndrome. Non-organ-specific anti-nuclear antibody was noted in 19 patients, and smooth muscle antibody was noted in 1.

CSF Findings

CSF was tested in 75 patients. At least 1 abnormal value was recorded in 61 of the 75 patients (81%), most commonly an elevated protein (55 patients; median value of 58 mg/dL; range, 36–234). Thirteen had leukocytosis (median, 13 cells/μL; range, 6–43). Among those treated with immunotherapy, those with elevated CSF protein were not more likely to be responders (14 were responsive, 13 were not), but those with leukocytosis were responders (7 were responsive to immunotherapy, 0 were not).

Immunotherapies and outcomes among patients with suspected autoimmune diagnoses

Physician-documented symptomatic outcomes were available for 69 patients (29%) who received immunotherapy. Improvements were reported in 31 (mild to moderate, 22; robust, 9; Table 1). Some patients received more than 1 immunotherapy modality. Improvements were attributed to IV corticosteroids (10), oral corticosteroids (10), intravenous immune globulin (IVIg, 8), mycophenolate mofetil (4), azathioprine (2), plasma exchange (1), methotrexate (1), and rituximab (1).

DISCUSSION

We detected VGCC-P/Q or VGCC-N antibodies in 3.4% of patients who underwent comprehensive general serological evaluation for a neurological presentation which included neural-specific autoimmunity in the differential diagnosis. This study would have excluded most patients in whom LES was suspected clinically, because disease-specific testing can be ordered for LES. Previous reports have focused on LES, emphasizing lung carcinoma as the oncological association of VGCC antibodies, but VGCC-N and VGCC-P/Q antibodies were noted in an initial report in patients who presented with diverse paraneoplastic encephalomyeloneuropathies associated with adenocarcinomas of breast, ovary, colon, and other cancers.6 The cancer types we encountered in the study reported here were more diverse (most frequently adenocarcinomas). These sequentially tested patients from Mayo Clinic neurology practice exhibited autoimmune neurological phenotypes extending to every level of the nervous system, and included, in addition to some cases of classical LES: encephalopathies, cerebellar ataxias, myelopathies, and inflammatory neuropathies. Because frequency of cancer and most neurological phenotypes did not differ between cases and antibody negative controls, the significance VGCC-P/Q or VGCC-N antibodies must be interpreted in the context of other clinical and paraclinical findings.

We encountered diverse myasthenic syndromes, often paraneoplastic and reflecting the context in which testing was ordered. Six of 10 patients with a documented neuromuscular transmission defect unequivocally had LES, but 4 had clinical or electrophysiological findings that supported myasthenia gravis rather than LES. VGCC autoantibodies are rarely encountered in patients with myasthenia gravis except in paraneoplastic cases (other than thymoma).11 Conversely, muscle AChR or striational antibodies are encountered in ~5–10% of patients with LES.1214

As our laboratory has previously reported for the ganglionic α3 AChR and VGKC-complex antibodies, the neurological diagnostic specificity of seropositivity was directly proportional to the antibody level detected.8,15 Patients with high values (≥ 1.00 nmol/L) usually had an autoimmune diagnosis. Those with medium or low values had autoimmune neurological diagnoses in 19–24%, but a further 20% had no neurological diagnoses after extensive clinical and paraclinical testing. For the remaining 60%, a neurological diagnosis of alternative cause was established (often neurodegenerative), or the medical records contained insufficient data to determine a definitive neurological diagnosis.

Because of these limitations, we advise that the neurological and oncological significance of VGCC-P/Q or VGCC-N antibody positivities be interpreted in the clinical context of the individual patient. Additional clues to an autoimmune diagnosis include a subacute onset disorder with rapid progression without obvious alternative diagnostic explanation, the presence of a classic phenotype (such as LES), a personal or family history of 1 or more coexisting autoimmune diseases, an inflammatory spinal fluid, an inflammatory appearing MRI scan of brain or spine, and a coexisting neural antibody.16

Thirty percent of patients had coexisting neural autoantibodies that in some instances enhanced the neurological diagnostic specificity, for example NMDA-R antibody detected in a patient with encephalitis, and GAD65 antibody detected in a patient with classical stiff-person syndrome.17,18 Clues to an oncological diagnosis include a personal or family history of cancer and a smoking history. In other patients, the antibody profile had high specificity for cancer, for example ANNA-1 detected in a patient with small-cell carcinoma.19

In patients with isolated VGCC antibody findings with low suspicion for cancer based on the profile above, ensuring the patient is up-to-date (and continues to be) with age- and sex-appropriate cancer screening (breast exam, mammogram, pelvic exam, and colonoscopy) and a CT of chest (done 1 time only if normal) would likely suffice for cancer surveillance. A trial of immunotherapy could be considered in uncertain cases with objective neurological abnormalities, but it should not be undertaken in patients in whom an autoimmune diagnosis seems unlikely. False positivity may be encountered in patients with polyclonal hypergammaglobulinemia, including those who have received IVIg within the preceding 30 days.8

The VGKC-complex antibody radioimmunoassay, which is methodologically similar to the VGCC antibody assays employed in this study,20,21 has been determined to detect autoantibodies which target neuronal proteins that co-immunoprecipitate with detergent-solubilized VGKCs (namely, Lgi1 and Caspr2).22,23 Thus, it is conceivable that antibodies detected by the VGCC radioimmunoprecipitation assay might be directed at proteins interacting with VGCC-P/Q and VGCC-N proteins. A majority of patients with GABABR antibodies have coexisting VGCC-P/Q or VGCC-N antibodies (77%).24 In this study, only 1 patient with VGCC antibody had coexisting GABABR autoantibody, indicating the rarity of GABABR autoimmunity.

In summary, neuronal VGCC antibody-seropositive patients have diverse neurological presentations and cancer types. The cancers include squamous cell carcinomas, adenocarcinomas, and small-cell carcinomas. The neurological and oncological significance should be interpreted cautiously in the clinical context of the individual patient.

Supplementary Material

Supp Table S1

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Supp Table S2

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Abbreviations

AChRacetylcholine receptor
AGNAanti-glial/neuronal nuclear
AMAndrew McKeon
AMPAa-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid
ANNAanti-neuronal nuclear
CASPR2contactin-associated protein-2
CMAPcompound muscle action potential
CNScentral nervous system
CSFcerebrospinal fluid
CRMPcollapsin response-mediator protein
GAD65glutamic acid decarboxylase, 65 kDa isoform
GABAgamma-aminobutyric acid
Igimmune globulin
IVIgintravenous immune globulin
LESLambert-Eaton syndrome
Lgi1leucine-rich-glioma-inactivated-1
MSmultiple sclerosis
MSAmultiple system atrophy
MuSKmuscle-specific kinase
NMDAn-methyl- D-aspartate
VGCCvoltage-gated calcium channel
VGKCvoltage-gated potassium channel

Footnotes

This data were presented in part at the American Neurological Association, Chicago, IL, September 2015.

Disclosures

NZ, DHL, CK reports no disclosures

VL is named inventor on a patent relating to AQP4 as NMO antigen, and a pending patent related to AQP4 and cancer. Earnings to date from licensing this technology have exceeded the federal threshold for significant interest.

SP has received no royalties to date but may accrue revenue for patents relating to AQP4 antibodies for diagnosis of neuromyelitis optica and AQP4 autoantibody as a cancer marker. He receives research support from the Guthy-Jackson Charitable Foundation, Alexion Pharmaceuticals, Inc. and the National Institutes of Health (RO1 NS065829).

AM receives research support from Medimmune

References

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P/Q- & N-TYPE CALCIUM CHANNEL ANTIBODIES: ONCOLOGICAL, NEUROLOGICAL & SEROLOGICAL ACCOMPANIMENTS (2024)

FAQs

What is PQ type calcium channel antibody? ›

These antibodies generally reflect an immune response against cancer. P/Q-type calcium channel binding antibodies are found in 95% of nonimmunosuppressed patients with LES (100% of those with cancer) and in 20% of patients who have encephalomyeloneuropathies related to carcinoma of lung, breast, or ovary.

What is a Type N calcium channel antibody? ›

Voltage-Gated Calcium Channel (VGCC) Type N Antibody - N-type calcium channel antibodies are more highly associated with primary lung cancer than P/Q-type. One or all of the autoantibodies in the myasthenia gravis (MG)/LEMS evaluation can occur with neoplasia without evidence of neurological impairment.

What is a P and Q type calcium channel? ›

P/Q-type calcium channels are high-voltage-gated calcium channels contributing to vesicle release at synaptic terminals. A number of neurological diseases have been attributed to malfunctioning of P/Q channels, including ataxia, migraine and Alzheimer's disease.

What is N-type calcium channel pain? ›

In the pain pathway, N-type calcium channels serve to regulate pain signals sent from the peripheral nervous system to Central Nervous System. Although many N-type calcium channels blockers are known, most potent and selective belong to the family of conotoxins.

What neurological diseases are voltage gated calcium channel antibodies related to? ›

Voltage gated calcium channel (VGCC) antibodies are generally associated with Lambert-Eaton myasthenic syndrome. However the presence of this antibody has been associated with paraneoplastic as well as non-paraneoplastic cerebellar degeneration.

What is the N-type calcium channel? ›

In the periphery, N-type calcium channels are essential for the release of neurotransmitters from nociceptors in neurons of the dorsal horn of the spinal cord [4]. Furthermore, N-type calcium channels control the release of adrenaline from postganglionic sympathetic neurons [5–8].

What blood test shows Lambert Eaton syndrome? ›

Testing for LEMS includes: Blood test. A blood test can reveal if you have anti-calcium channel antibodies. About 85% of people with LEMS have these antibodies in their blood.

Where are P type calcium channels located? ›

They are found at axon terminals, as well as in somatodendritic areas of neurons within the central and peripheral nervous system. P-type calcium channels are also critical to vesicle release, specifically neurotransmitters and hormones at synaptic terminals of excitatory and inhibitory synapses.

What is the function of the calcium channel? ›

Calcium channels are the structural components of cardiac cells that provide a mechanism to modulate the force of contraction. One of the ways that this occurs is through beta-adrenergic receptor (b-AR) stimulation to cause a positive inotropic response that is regulated by protein kinase A (PKA).

What are the two types of calcium channels? ›

In cardiac tissues, the two types of calcium channels are the L type and the T type. L-type channels are found in all cardiac cells and T-type are expressed in Purkinje cells, pacemaker and atrial cells. Both these types of channels contribute to atrioventricular conduction as well as pacemaker activity.

What will a calcium channel allow? ›

Calcium channels located in the plasma membrane enable the entry of Ca2+ due to the existence of the concentration gradient of Ca2+ across the plasma membrane (the difference between the intracellular and extracellular side).

What are P type channels? ›

P-type calcium channels are activated by high-voltage, and can be found at presynaptic terminals. These channels are composed of α1 (CaV2.1), α2δ, and β subunits. P-type calcium channels can be found throughout the nervous system and in the heart.

What is the calcium channel in nerve pain? ›

Northwestern Medicine investigators have discovered that specific calcium channels help regulate sex differences in the functioning of immune cells for neuroinflammation and overall neuropathic pain, according to findings published in Science Advances.

What is an N-type calcium channel blocker drug? ›

Ziconotide (Prialt)

It is derived from the venom of a marine snail (genus Conus). Ziconotide blocks calcium influx into N-type calcium channels in the dorsal horn laminae of the spinal cord, thus preventing afferent conduction of nerve signals.

What is calcium channel in medical terms? ›

Calcium channel blockers (CCBs), also known as calcium channel antagonists, have been approved by the US Food and Drug Administration (FDA) and are widely used to treat various conditions such as hypertension, coronary heart disease, and chronic stable angina.

What does a positive VGCC antibody test mean? ›

Antibodies against VGCC P/Q are graded as Intermediate-risk antibodies with an frequency of 50% (LEMS ; nearly 90% for rapidly progressive cerebellar syndrome) of underlying cancer and a positive result yield 2 points PNS score, according to Updated Diagnostic Criteria for Paraneoplastic Neurologic Syndromes.

What are the different types of calcium channel receptors? ›

Voltage-gated calcium channels are grouped into three families: High-voltage activated dihydropyridine-sensitive (L-type, Cav1. x) channels; High-voltage activated dihydropyridine-insensitive (Cav2. x) channels; Low-voltage-activated (T-type, Cav3. x) channels (Alexander et al., 2015a).

What are P-type voltage-gated calcium channels? ›

The P-type calcium channel is a type of voltage-dependent calcium channel. Similar to many other high-voltage-gated calcium channels, the α1 subunit determines most of the channel's properties. The 'P' signifies cerebellar Purkinje cells, referring to the channel's initial site of discovery.

What is the normal range for VGCC antibodies? ›

Values of 0.00–0.02 nmol/L (VGCC-P/Q antibody) and 0.00–0.03 nmol/L (VGCC-N antibody) are considered normal.

References

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