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Published in final edited form as: J Neuroimmunol. 2025 Jun 30;406:578681. doi: 10.1016/j.jneuroim.2025.578681

N-type voltage-gated calcium channel antibody testing lacks diagnostic value in Lambert-Eaton myasthenic syndrome

Friederike A Arlt a,1, Masoud Majed b,a,2, Jack Wu a, Anastasia Zekeridou a,b, Shahar Shelly b,3, Vanda A Lennon a,b,c, Sean J Pittock a,b, Andrew McKeon a,b, Christopher J Klein a,b, Divyanshu Dubey a,b, John R Mills a,*
PMCID: PMC12477647  NIHMSID: NIHMS2110822  PMID: 40651295

Abstract

Introduction/aims:

Diagnostic evaluation for Lambert-Eaton myasthenic syndrome (LEMS) includes serological testing for voltage-gated calcium channel antibodies (VGCC-P/Q-type [VGCC-PQ] and VGCC-N-type [VGCC-N]). While VGCC-PQ antibodies are well-established biomarkers in LEMS, the clinical utility of VGCC-N antibody testing remains obscure. We aimed to determine the diagnostic value of VGCC-N antibody testing.

Methods:

A retrospective cross-sectional study was performed. The Mayo Clinic electronic medical record from 1995 to 2021 was reviewed for inclusion of patients fitting clinical electrodiagnostic criteria for LEMS, who were evaluated for serum VGCC antibodies (n = 123). Available sera were additionally tested for SOX1 antibodies (n = 68). Healthy adults were tested for VGCC-PQ and VGCC-N antibodies (n = 122). Clinical performance of each antibody test was evaluated statistically.

Results:

Among adult LEMS cases, 84.6 % (n = 99/117) tested positive for VGCC-PQ antibody while none of the healthy controls did. In contrast, 20.5 % (n = 24/117) were VGCC-N antibody positive, of which 95.8 % (n = 23/24) co-occurred with VGCC-PQ antibodies. The frequency of isolated VGCC-N antibody positivity was higher in controls than in LEMS (2.5 % [n = 3/122] vs. 0.9 % [n = 1/117]), and pediatric patients had no VGCC-N antibody reactivity. Neither VGCC-N antibody positivity nor titer was predictive of an associated small-cell lung cancer (SCLC-LEMS). By contrast, SOX1-IgG seropositivity associated significantly with SCLC-LEMS.

Discussion:

Inclusion of VGCC-N antibody testing does not improve diagnostic accuracy for LEMS, nor does it serve as a predictor of LEMS-associated cancers in contrast to SOX1-IgG testing. We recommend the exclusion of VGCC-N antibody testing given its non-specific disease associations and poor positive predictive value in LEMS screening.

Keywords: Lambert-Eaton myasthenic syndrome, Voltage-gated calcium channel antibody, P/Q-type voltage-gated calcium channel antibody, N-type voltage-gated calcium channel antibody, SOX1-IgG

1. Introduction

Lambert-Eaton myasthenic syndrome (LEMS) is a rare IgG-mediated presynaptic disorder of the neuromuscular junction with a prevalence of 2.6 to 3.4 per million (Titulaer et al., 2011a). Its clinical manifestations are weakness, muscle fatigability, predominantly affecting lower extremities, autonomic symptoms, and areflexia (Titulaer et al., 2011a; Abenroth et al., 2017). Its electromyographic hallmark is a low resting compound muscle action potential amplitude that facilitates during high frequency nerve stimulation or immediately following exercise (Titulaer et al., 2011a; Harper and Lennon, 2018). About 50–60 % of LEMS cases are paraneoplastic, most commonly with small-cell lung cancer (SCLC) (Titulaer et al., 2011b).

LEMS diagnosis is based on electrophysiological and clinical findings but is often delayed, especially in patients lacking evidence of malignancy (Wirtz et al., 2002). The pathophysiology of LEMS is attributed to IgG antibodies binding to presynaptic voltage-gated calcium channels (VGCC) at the neuromuscular junction (Harper and Lennon, 2018). VGCC antibody seropositivity is considered confirmatory of LEMS (Titulaer et al., 2011b; Motomura et al., 1995; Lennon et al., 1995; Nakao et al., 2002; Lang et al., 2003). Historically, patients have been screened for two VGCC antibody subtypes, P/Q-type (VGCC-PQ) and N-type (VGCC-N). VGCC-PQ antibodies are detectable in approximately 90 % of electromyographically-confirmed LEMS patients (Lennon et al., 1995; Motomura et al., 1997). VGCC-N antibodies are detected in ~30 %, and primarily co-exist with VGCC-PQ antibodies (Motomura et al., 1997; Maddison et al., 2020a). Previous studies have demonstrated conflicting results regarding the utility of VGCC-N antibody testing and the relevance of isolated VGCC-N antibody seropositivity in diagnosing LEMS, particularly in the context of SCLC (Maddison et al., 2020a; Zalewski et al., 2016; Ebright et al., 2018). In this study, we investigate the clinical utility of antibody testing for VGCC-N in LEMS.

2. Methods

This retrospective cross-sectional study reviewed demographics, clinical, and electrophysiological data for 261 patients with suspected LEMS identified through the Mayo Data Explorer (evaluated at Mayo Clinic Rochester, between January 1995 and May 2021) who underwent concurrent clinical service serum-based VGCC-PQ (normal </=0.02 nmol/L) and VGCC-N (normal </=0.03 nmol/L) antibody testing using a clinically validated radioimmunoprecipitation assay (Apiwattanakul et al., 2010). LEMS diagnosis was confirmed for 123 patients by clinical electrodiagnostic criteria. Residual serum specimens (n = 68) were tested for SOX1 (SRY-box transcription factor 1) antibodies using a lineblot assay (Euroimmun, Lübeck, Germany; normal <11). All serological testing was performed in the Mayo Clinic Neuroimmunology Laboratory.

We evaluated serum samples from 122 presumably healthy adult subjects (lacking history of cancer, autoimmunity, or neurological symptoms) to determine the prevalence of VGCC-PQ and VGCC-N antibodies in the local population. Statistical analyses and figure illustrations were conducted using R (version 2024.04.2, the R Foundation for Statistical Computing, Vienna, Austria). Categorical variables were compared using Fisher’s exact tests. Continuous variables were compared between categorical groups using a Mann-Whitney U test or Kruskal-Wallis test for comparisons among more than two groups. Correlation between continuous variables was analyzed using the Pearson correlation test. A p-value <0.05 was considered statistically significant.

3. Results

3.1. LEMS patient population

Patient inclusion algorithm is shown in Figure 1 (Fig. 1). The final cohort included 123 patients who met clinical and electrophysiological criteria for LEMS diagnosis. The median age at symptom onset was 60 years (IQR: 51–68) for the adult population (n = 117/123), with 49.6 % females (Table 1). Six pediatric LEMS cases were identified (ages 11–16 years, all male); none had a cancer diagnosis (Supplementary Table 1).

Fig. 1. Flowchart of patients’ inclusion and subgroup stratification in the study.

Fig. 1.

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*Patients with suspected LEMS and VGCC antibody testing done in Mayo Clinic Laboratories. **LEMS diagnosis confirmed by clinical and electrophysiological criteria established by Titulaer et al. 2011 (Titulaer et al., 2011a), includes independent of VGCC antibody status. Red boxes indicate patients who were excluded from statistical analyses of cancer subgroups. LEMS: Lambert-Eaton myasthenic syndrome. SCLC: small-cell lung cancer. VGCC: voltage-gated calcium channel. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Table 1.

Adult LEMS patient characteristics.

Patient characteristic Total adult n = 117 No tumor n = 73 SCLC n = 28 Other tumor n = 10
Demographics
 Female 58 (49.6) 37 (50.7) 14 (50.0) 4 (40.0)
 Age at onset 60 (51–68) 58 (42–65) 65 (60–71) 69 (63–73)
 Ever smoker 76 (64.9) 37 (50.7) 26 (92.9) 7 (70.0)
 Caucasian ethnicity 97 (82.9) 63 (86.3) 23 (82.1) 8 (80.0)
Diagnostic work up
 CT or PET imaging done 109 (93.2) 72 (98.6) 27 (96.4) 8 (80.0)
 Years from onset to first antibody testing 1 (0–3) 2(1–3) 0 (0–1) 0 (0–2)
Antibody status
 PQ+/N+ 23 (19.8) 11 (15.1) 7 (25.9) 4 (40.0)
 PQ+/N− 76 (64.9) 49 (67.1) 19 (67.9) 5 (50.0)
 Total PQ+ 99 (84.6) 60 (82.2) 26 (92.9) 9 (90.0)
 PQ−/N+ 1 (0.9) 1 (1.4) 0 (0.00) 0 (0.0)
 Total N+ 24 (20.5) 12 (16.4) 7 (25.0) 4 (40.0)
 PQ−/N− 17 (14.5) 12 (16.4) 2 (7.1) 1 (10.0)
 VGCC-PQ IgG titer (nmol/L) 0.33 (0.15–0.90) 0.30 (0.14–0.87) 0.42 (0.31–1.60) 0.16 (0.11–0.35)
 VGCC-N IgG titer (nmol/L) 0.14 (0.06–0.75) 0.16 (0.075–1.09) 0.14 (0.09–0.31) 0.19 (0.05–19.94)
 SOX1+ EL 7 (10.3) 1 (2.2) 5 (23.8) 0 (0.0)
 SOX1− EL 61 (89.7) 44 (97.8) 9 (64.3) 7 (100.0)
 PQ+/SOX1+ 5 (9.7) 0 (0.0) 5 (38.5) 0 (0.0)
 PQ+/SOX1− 49 (90.8) 35 (100.0) 8 (61.5) 6 (100.0)
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Demographics, diagnostic work up related to cancer, and autoantibody testing results, stratified by cancer status. Qualitative variables are presented as total numbers and frequencies (%). Quantitative variables are presented as median (interquartile range). Missing values <10 % except for SOX1 EL (n = 68). Patients with unknown cancer status (n = 6) were included in the total cohort. LEMS: Lambert-Eaton myasthenic syndrome, CT: chest computed tomography, PET: body positron emission tomography, PQ: VGCC P/Q-type antibodies, N: VGCC N-type antibodies, VGCC: voltage-gated calcium channel, IgG: immunoglobulin G, SOX1 EL: lineblot for SOX1 (SRY-box transcription factor 1 antibodies). + indicates positive antibody result, − indicates negative antibody result. On 6/117 adult LEMS patients, information on an existing cancer was not available accounting for discrepancies in the total number of patients in the cohort and the sum of patient numbers in the cancer subgroups.

Among the adult LEMS cases, 32.5 % (n = 38/117) were determined to be paraneoplastic due to co-existing or previously existing cancer; of those SCLC was diagnosed in 23.9 % (n = 28/117) and other malignancies were diagnosed in 8.5 % (n = 10/117; Supplementary Table 2). No tumor was diagnosed in 62.4 % (n = 73/117; NT-LEMS). Smoking history was strongly associated with SCLC-LEMS (92.9 % vs. 50.7 % in NT-LEMS; p < 0.001) but remained notably frequent even when a malignancy was not identified. Median age at neurological symptom onset was also higher in those with cancer (Table 1).

3.2. Isolated VGCC-N antibody seropositivity is not disease-specific

VGCC-PQ antibodies were detected in 84.6 % (n = 99/117) of adult LEMS patients and 83.3 % (n = 5/6) of pediatric cases; VGCC-N and VGCC-PQ antibodies were both detected (PQ+/N+) in 20.5 % (n = 24/117) of adult cases but in no pediatric case. VGCC-PQ antibodies were not detected in any healthy control subject, but 2.5 % (n = 3/122) were seropositive for VGCC-N antibodies. One adult LEMS patient exhibited isolated VGCC-N antibody seropositivity (PQ−/N+, 0.11 nmol/L), and double seronegative cases occurred in 14.5 % (n = 17/117) of adults (Table 1) and one pediatric patient (Supplementary Table 1). The isolated PQ−/N+ case lacked evidence of cancer, was additionally GAD65 antibody-positive (0.17 nmol/L; normal ≤0.02 nmol/L) and presented with gait ataxia in addition to predominant lower extremity muscle weakness and hyporeflexia. Among the PQ−/N− cases, 58.8 % (n = 10/17) underwent longitudinal VGCC-N antibody testing, which confirmed persistent seronegative status.

VGCC-PQ antibody seropositivity was strongly associated with LEMS versus healthy controls (99/117 [84. 6 %] vs 0/122 [0 %]; p < 0.001). By contrast, isolated VGCC-N antibody seropositivity (N+/PQ−) was rare and not associated with LEMS (1/117 [0.9 %] vs 3/122 [2.5 %]; Fisher’s exact p = 0.61). VGCC-PQ antibody titers in adults (median: 0.33 nmol/L, IQR: 0.15–0.90) were higher than VGCC-N antibody titers (median: 0.14 nmol/L, IQR: 0.06–0.75, Fig. 1A). In PQ+/N+ patients, titers of both antibodies were highly correlated (r = 0.8, p < 0.001, Fig. 1B), and VGCC-N antibody positive serostatus was associated with higher VGCC-PQ antibody titers (median: 0.41 nmol/L, IQR: 0.14–1.54 in VGCC-N antibody positive patients vs. median: 0.23 nmol/L, IQR: 0.08–0.55 in VGCC-N antibody negative patients, p = 0.04). Median VGCC-PQ antibody titers in pediatric LEMS cases (median: 0.23 nmol/L, IQR: 0.10–1.60) were lower than in adult cases (median: 0.33 nmol/L, IQR: 0.15–0.90).

3.3. VGCC-N antibody serostatus in LEMS is not significantly associated with SCLC

VGCC-PQ antibodies were detected in 92.1 % (n = 35/38) of paraneoplastic LEMS cases, with VGCC-N antibodies co-existing in 28.9 % (n = 11/38). Among SCLC-LEMS cases, 92.9 % (n = 26/28) were positive, with VGCC-N antibodies co-existing in 25.0 % (n = 7/28). In the NT-LEMS cohort, 82.2 % (n = 60/73) were VGCC-PQ antibody positive and 15.1 % (n = 11/73) had a co-existing VGCC-N antibody. Double seronegative cases included 7.1 % (n = 2/28) of SCLC-LEMS, 10.0 % (n = 1/10) of other tumor-associated cases, and 16.4 % (n = 12/73) of NT-LEMS cases.

Neither VGCC-PQ nor VGCC-N antibody seropositivity was predictive of a cancer diagnosis (p = 0.44 and p = 0.16; Table 2A and 2B, respectively). Additionally, double seropositivity did not significantly correlate with higher cancer rates compared to VGCC-PQ antibody positivity alone (p = 0.18, Table 2C). SCLC patients had a trend toward higher VGCC-PQ antibody titers compared to patients with other cancers or non-cancer patients (Fig. 2C, median VGCC-PQ antibody titer of 0.30 nmol/L in NT-LEMS vs. 0.42 nmol/L in SCLC-LEMS vs. 0.16 nmol/L in LEMS patients with other cancers, p = 0.06). In contrast, VGCC-N antibody titers were similar across subgroups (Fig. 2D, median VGCC-N titer of 0.16 nmol/L in NT-LEMS vs. 0.14 nmol/L in SCLC-LEMS vs. 0.19 nmol/L in LEMS patients with other cancers, p = 0.72).

Table 2.

Association of LEMS patient subgroups and antibody status.

A
Antibody status No tumor SCLC Other tumor Fisher’s exact
PQ− 13 2 1
PQ+ 60 26 9 p = 0.44
B
Antibody status No tumor SCLC Other tumor Fisher’s exact
N− 61 21 6
N+ 12 7 4 p = 0.16
C
Antibody status No tumor SCLC Other tumor Fisher’s exact
PQ+/N− 49 19 5
PQ+/N+ 11 7 4 p = 0.18
D
Antibody status No tumor SCLC Other tumor Fisher’s exact
PQ+/SOX1− 35 8 6
PQ+/SOX1+ 0 5 0 p < 0.001
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Associated cancer was compared using Fisher’s Exact test between PQ+ and PQ− groups (A), between N+ and N− groups (B), between PQ+/N− and PQ+/N+ groups (C), and between PQ+/SOX1 + and PQ+/SOX1− groups (D). P: p-value. Statistical significance set at p < 0.05. SCLC: small-cell lung cancer. PQ: VGCC P/Q-type antibodies. N: VGCC N-type antibodies. VGCC: voltage-gated calcium channel. SOX1: lineblot for SOX1 (SRY-box transcription factor 1 antibodies). + indicates positive antibody result, − indicates negative antibody result.

Fig. 2. VGCC-P/Q-type and VGCC-N-type antibody titers in seropositive adult patients.

Fig. 2.

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A: VGCC-P/Q-type and -N-type antibody titers. B: Correlation of VGCC-P/Q-type and VGCC-N-type antibody concentrations (nmol/L) in double seropositive patients. C-D: VGCC-P/Q-type antibody titers (C) and VGCC-N-type antibody titers (D) stratified by cancer status. Blue dots represent antibody titers of LEMS patients without evidence of tumor (median VGCC-P/Q-type antibody titer, 0.30 nmol/L [IQR 0.14–0.87]; median VGCC-N-type antibody titer, 0.16 nmol/L [IQR: 0.075–1.09]), green dots represent antibody titers of patients with SCLC-LEMS (median VGCC-P/Q-type antibody titer, 0.42 nmol/L [IQR 0.31–1.60]; median VGCC-N-type antibody titer, 0.14 nmol/L [IQR: 0.09–0.31]) and red dots indicate titers of LEMS patients with tumors other than SCLC (median VGCC-P/Q-type antibody titer, 0.16 nmol/L [IQR 0.11–0.35]; median VGCC-N-type antibody titer, 0.19 nmol/L [IQR: 0.05–19.94]). Kruskal-Wallis test showed no statistically significant differences between the three groups for titer of either antibody, for VGCC-P/Q-type antibody positivity and cancer status (p = 0.06) or for VGCC-N-type antibody positivity and cancer status (p = 0.72). VGCC-PQ: VGCC-P/Q-type antibodies. VGCC-N: VGCC-N-type antibodies. VGCC: voltage-gated calcium channel. Titers are logarithmic scale. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3.4. SOX1 antibody testing distinguishes SCLC associated LEMS from non-paraneoplastic LEMS in adults

Given the limitations of VGCC antibody serostatus in distinguishing between paraneoplastic or SCLC-LEMS and NT-LEMS, we tested available sera for SOX1-IgGs, which are strongly associated with SCLC (Sabater et al., 2008; Titulaer et al., 2009). SOX1-IgG seropositivity was identified in only 10.3 % (n = 7/68) of all tested cases (Table 1), yet despite its rarity, it showed a significant association with underlying SCLC when comparing PQ+/SOX1+ to PQ+/SOX1− cases (p < 0.001, Table 2D). It is noteworthy that SOX1-IgGs were not detectable in either of the two PQ−/N− SCLC-LEMS cases.

4. Discussion

In the present study, VGCC-PQ antibodies were common in both adult (84.6 %) and pediatric (83.3 %) LEMS cases. The frequency of VGCC-N antibodies in adult LEMS cases was 20.5 %, approximately 4-fold less than VGCC-PQ, and VGCC-N antibody was not detected in any pediatric LEMS case. Isolated VGCC-PQ antibody seropositivity was the most common serostatus (64.9 %) among adult LEMS cases, whereas isolated VGCC-N antibodies were rare (0.9 %) and more frequent in healthy adult controls (2.5 %). No healthy control was positive for VGCC-PQ antibodies. Neither VGCC-N antibody detection nor titer was predictive of underlying cancer and longitudinal VGCC-N antibody testing in PQ−/N− cases remained negative over time.

In our adult LEMS cohort the prevalence of VGCC-N antibodies (20.5 %) was lower than in previous reports (Lennon et al., 1995; Maddison et al., 2020a), but consistent with VGCC-N antibodies having significantly lower sensitivity for LEMS than VGCC-PQ antibodies (Lennon et al., 1995; Motomura et al., 1997; Zalewski et al., 2016). Isolated VGCC-N antibody positivity in this study had low specificity (2.5 % positivity in healthy adults) and likewise has been previously reported in patients without a paraneoplastic syndrome, in other neurological diseases such as amyotrophic lateral sclerosis or non-LEMS neurological autoimmunity, and in healthy people (Zalewski et al., 2016; Ebright et al., 2018). VGCC-PQ antibodies can also occur in non-LEMS patients (Zalewski et al., 2016), highlighting the need for more appropriate test utilization related to VGCC antibody testing in general. However, the diagnostic utility of VGCC-PQ antibody testing as a confirmatory assay in LEMS has been repeatedly shown (Titulaer et al., 2011a; Lennon et al., 1995). Considering the physiological and pathological functions of VGCC-N in dorsal roots and sympathetic and central nervous system synapses (Harper and Lennon, 2018; Simms and Zamponi, 2014), the non-specific clinical presentation of potential antibody-mediated VGCC-N dysfunction in contrast to VGCC-P/Q appears plausible (Harper and Lennon, 2018).

In the VGCC antibody testing populations at large reference laboratories, the pretest probability of LEMS is low due to the disproportionately high number of tests compared to the low prevalence of the disease (Titulaer et al., 2011a). This suggests that testing is being requested to rule-out rather than confirm a LEMS diagnosis. Further VGCC antibody testing has historically been included in large comprehensive antibody panels increasing the dilution of true positive cases in large test cohorts. The positive predictive value of VGCC-N antibody testing is therefore low. Its limited sensitivity and imperfect specificity potentially contribute to unnecessary clinical investigations and misdirected diagnoses.

Previous studies suggested VGCC-N type antibody testing can be useful in identifying patients with SCLC-LEMS (Maddison et al., 2020a; Martin-Moutot et al., 2008) where delayed diagnosis can be fatal. However, in the present work neither VGCC-N antibody positivity alone nor the combination with VGCC-PQ antibody serostatus were significantly associated with SCLC-LEMS. Further, VGCC-N antibody titers were not significantly elevated in SCLC-LEMS cases, and serial testing showed no occurrence of seroconversion. Our findings are at variance with a case series report of isolated VGCC-N antibody seropositivity in two SCLC-LEMS patients (Martin-Moutot et al., 2008) and a recent report that double VGCC-PQ and VGCC-N antibody seropositivity was associated with SCLC in 17/31 LEMS cases (Maddison et al., 2020a). This discrepancy in findings could relate to differences in patient population. Our study reflects a clinical service cohort at a tertiary medical center, where atypical presentations are more commonly encountered. Notably, the frequency of SCLC-LEMS (23.9 %) was lower in our cohort as compared to other studies. In addition to patient selection criteria, different assays for VGCC-N antibodies may have different diagnostic accuracies. Reported inter-laboratory performance studies indicate a high degree of variability, underscoring the clinical ambiguity of VGCC-N antibody testing (Lozier et al., 2021).

In contrast to VGCC-N antibodies, SOX1-IgG seropositivity is useful in raising the likelihood of underlying SCLC in LEMS cases that are VGCC-PQ antibody positive (p < 0.001). Likewise, previous studies have supported additional testing for SOX1, SOX2, GABAb (gamma-aminobutyric acid type B receptor), and MAP1B (Microtubule-associated protein 1B) antibodies in adjuncts to diagnosing SCLC-LEMS (Sabater et al., 2008; Titulaer et al., 2009; Maddison et al., 2019; Gadoth et al., 2017). In the absence of VGCC-PQ positivity, SOX1-IgG detection did however not increase tumor identification in paraneoplastic LEMS patients (n = 3) leaving a serological diagnostic gap. SOX1-IgG was further overall less frequently detected than VGCC-PQ in SCLC-LEMS (26/28 vs 5/14). The lower reported test sensitivity of lineblot assays compared to other SOX1-IgG detection techniques might have impacted our test results (Ruiz-García et al., 2019). Of note, one of three double seronegative cases did not have SCLC but had bladder cancer 15 years prior to LEMS symptom onset. It is possible that the tumor and LEMS were coincidental occurrences. One of the two double seronegative SCLC-LEMS was CRMP5-IgG-positive (collapsin response-mediator protein 5) with the neuroretinitis and myeloradiculopathy that are classical CRMP5-IgG accompaniments. Established guidelines for cancer screening in LEMS patients at risk (Titulaer et al., 2011a) suggest antibody markers should only serve as an additional diagnostic tool while PET scans are standard of care for cancer detection (Titulaer et al., 2011a). Moreover, the clinical DELTA-P score (Dutch-English LEMS Tumor Association Prediction), which predicts the likelihood of SCLC in LEMS patients, is particularly useful in ambiguous cases such as seronegative LEMS (Titulaer et al., 2011b; Maddison et al., 2020b).

Our cohort included six pediatric LEMS patients, and the literature remains restricted to only a handful of small case series (≤ 5 patients each) (Wirtz et al., 2002; Tsao et al., 2002; Kostera-Pruszczyk et al., 2009; Morgan-Followell and de Los, 2013). Although VGCC-PQ antibodies have been detected sporadically in those reports, none has published paired VGCC-PQ- and VGCC-N antibody results, leaving the diagnostic yield of comprehensive VGCC testing in children undocumented (Morgan-Followell and de Los, 2013). VGCC-N antibodies were not detected in any of our six pediatric patients; five of the six were VGCC-PQ antibody-positive, reinforcing the lack of utility for VGCC-N antibody testing in suspected pediatric cases of LEMS.

Because VGCC-N antibodies were discovered before VGCC-PQ (Lennon and Lambert, 1989), it has been historically standard practice to include both VGCC antibody assessments in the serological evaluation of patients with suspected LEMS diagnosis. Our findings reinforce the need to exclude VGCC-N antibody testing from panel evaluations, particularly when used as a screening test, where it contributes more to diagnostic ambiguity than clarity.

4.1. Limitations

A limitation of our study is the retrospective data collection, with cases dating back to 1995, and the consequently lower number of samples available for SOX1 testing compared to VGCC-PQ and VGCC-N antibody testing. Further, we did not have demographic data such as smoking history on the control samples available limiting the possibility of comparing those to the LEMS cohort. The amount of SCLC LEMS was somewhat lower than in the literature presumably due to the patient selection at a tertiary medical center where patients with atypical presentations might be more frequently encountered.

5. Conclusion

VGCC-N antibody testing does not enhance diagnostic accuracy for LEMS and should be excluded from antibody test panels to prevent uncertainty in test interpretation. Testing for SOX1-IgGs, along with VGCC-PQ antibodies and VGCC-PQ titer determination, helps identify underlying SCLC.

Supplementary Material

Supplementary material

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jneuroim.2025.578681.

Acknowledgments

We thank Aaron Cepress for his sharing his expertise and assistance with sample testing.

Footnotes

Declaration of competing interest

Friederike A. Arlt reports no relevant disclosures. Masoud Majed reports no relevant disclosures. Jack Wu reports no relevant disclosures. Anastasia Zekeridou reports research funding from Roche/Genentech and patents submitted for DACH1-IgG, Tenascin-R-IgG, CAMKV-IgG and PDE10A-IgG as biomarkers of neurological autoimmunity. Shelley Shahar reports no relevant disclosures. Vanda A. Lennon reports no pertinent disclosures.

Sean J. Pittock reports grants, personal fees, and non-financial support from Alexion Pharmaceuticals; grants, personal fees, and non-financial support from Amgen; and personal fees for consulting from Genentech, Roche, UCB, and Arialys. He has two patents issued (8,889,102; application 12–678,350; Neuromyelitis Optica Autoantibodies as a Marker for Neoplasia; and 9891219B2; application 12–573,942; Methods for Treating Neuromyelitis Optica [NMO] by Administration of Eculizumab to an individual that is Aquaporin-4 [AQP4]-IgG Autoantibody positive) for which he has received royalties. He also has patents pending for IgGs to the following proteins as biomarkers of autoimmune neurological disorders: septin-5, kelch-like protein 11, LUZP4, PDE10A, and MAP1B.

Andrew McKeon reports patents issued for GFAP and MAP1B-IgGs and patents pending for Septins-5 and -7, and KLHL11-IgGs, and has consulted for Janssen and Roche pharmaceuticals, without personal compensation. AM reports research funding from National Institutes of Health (NIH: RO1NS126227, U01NS120901).

Christopher J. Klein reports no relevant disclosures.

Divyanshu Dubey reports has served on the clinical advisory board for UCB, Argenx, and Arialys Pharmaceuticals, with all compensation for consulting activities being paid directly to Mayo Clinic. He is a named inventor on a filed patent that relates to KLHL11 as a marker of autoimmunity and germ cell tumor. Additionally, he has patents pending for LUZP4-IgG, cavin-4-IgG, and SKOR2-IgG as markers of neurological autoimmunity. He has received funding from the DOD (CA210208 [germ cell tumor], PR220430 [inflammatory neuropathy], and AL240239 [ALS]), the David J. Tomassoni ALS Research Grant Program, and UCB.

John R. Mills reports grant support from Werfen Diagnostics. He has patents issued related to the measurement of immunoglobulins by mass spectrometry for which he receives royalties. He also has patents pending for LUZP4-IgG, Cavin-4-IgG, and SKOR2-IgG as markers of neurological autoimmunity.

Study participants’ consent

All participants gave written informed consent to participate in the study.

CRediT authorship contribution statement

Friederike A. Arlt: Writing – original draft, Visualization, Conceptualization. Masoud Majed: Writing – original draft, Visualization, Conceptualization. Jack Wu: Writing – review & editing, Investigation. Anastasia Zekeridou: Writing – review & editing, Investigation. Shahar Shelly: Writing – review & editing, Investigation. Vanda A. Lennon: Writing – review & editing, Investigation. Sean J. Pittock: Writing – review & editing, Investigation. Andrew McKeon: Writing – review & editing, Investigation. Christopher J. Klein: Writing – review & editing, Investigation. Divyanshu Dubey: Writing – review & editing, Investigation, Conceptualization. John R. Mills: Writing – review & editing, Supervision, Project administration, Conceptualization.

Data availability

Anonymized data are available upon reasonable request from the principal investigator and corresponding author (mills.john2@mayo.edu).

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary material
NIHMS2110822-supplement-Supplementary_material.docx (18.6KB, docx)

Data Availability Statement

Anonymized data are available upon reasonable request from the principal investigator and corresponding author (mills.john2@mayo.edu).

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