McKeon, Andrew

Objective To estimate the prevalence, incidence, and disease burden of autoimmune seizures and epilepsies in Olmsted County. Methods We conducted a retrospective, population‐based study using the Rochester Epidemiology Project (1996–2019). Age‐ and sex‐standardized rates (2019 United States standard population) per 100,000 were calculated with 95% confidence intervals (95% CIs). Temporal trends in incidence were assessed over 3 consecutive 8‐year intervals (1996–2003, 2004–2011, and 2012–2019) using Poisson regression to estimate rate ratios per period and trend. Disability‐adjusted life years (DALYs), years of life lost (YLL), and years lived with disability (YLD) and 95% uncertainty intervals (95% UIs) were estimated for 2019. Results Twenty‐three patients were identified between 1996 and 2019. In 2019, the standardized prevalence of all autoimmune seizures and epilepsies was 9.81 (95% CI, 5.59–15.21) per 100,000, including autoimmune‐associated epilepsy (AAE) 7.27 (3.74–11.95) and acute symptomatic seizures secondary to autoimmune encephalitis (ASSAE) 2.55 (0.69–5.60). From 1996 to 2019, the standardized incidence was 0.50 (0.29–0.77) per 100,000 person‐years overall, with AAE 0.36 (0.19–0.59) and ASSAE 0.15 (0.05–0.30). By period, the standardized incidence of all autoimmune seizures and epilepsies suggested a rising trend from 0.28 (95% CI, 0.06–0.68) in 1996 to 2003 to 0.60 (95% CI, 0.24–1.12) in 2004–2011, then plateaued at 0.53 (95% CI, 0.21–1.00) in 2012 to 2019 (rate ratio per 8‐year interval 1.30, 95% CI, 0.71–2.38), largely driven by the seropositive subgroup. The standardized DALY rate was 26.27 (95% Uncertainly intervals [UI], 5.30–67.09) per 100,000 (YLL 20.07 [0.00–60.21] and YLD 6.20 [5.06–7.39]). Interpretation Although autoimmune seizures and epilepsies remain rare, they result in a disproportionately high disease burden. ANN NEUROL 2026;100:74–83

ABSTRACT Objective We sought to characterize the sixth most common finding in our neuroimmunological laboratory practice (tissue assay‐observed unclassified neural antibodies [UNAs]), combining protein microarray and phage immunoprecipitation sequencing (PhIP‐Seq). Methods Patient specimens (258; 133 serums; 125 CSF) meeting UNA criteria were profiled; October 2022–September 2023. Top‐ranking candidate antigens were validated in silico, by dual‐staining confocal microscopy, and ≥ 1 protein‐specific assay. Clinical data were reviewed. Results Among 21 patients, 11 autoantibodies were characterized (serum, 19; CSF, all 9 available). Autoantigens were CACNA1I, 1; CAMK2B, 2; CLIP2, 1; FMN2, 2; MAP1A, 2; MAP2, 5; NECAB1, 1; SNAP91, 3; SRCIN1, 1; SYNJ1, 1; SYT3, 2. Analytical validation was by confocal TIIFA (all), western blot (10/10 available), and cell‐based assay (5/5 performed). Clinical accompaniments were: encephalitis, 6; brainstem encephalitis, 2; encephalomyelitis, 2; cerebellar ataxia, 2; longitudinally extensive transverse myelitis (LETM), 2; sensory neuronopathy, 1; peripheral neuropathy, 4, and movement disorders, 2. Inflammatory MRI abnormalities were identified in 5/16 patients (31%) with CNS disorders: T2 signal change (2), LETM (2), leptomeningeal enhancement (1). Seven of 8 (88%) had inflammatory CSF (pleocytosis, 5 [median 25.5 cells, range 7–294]; elevated IgG index/synthesis rate, 4; CSF‐exclusive oligoclonal bands, 4). Six had paraneoplastic causation (lung cancer, 2; other, 4); 3 were postinfectious (1 each of COVID‐19, HSV‐1, and post‐Group A streptococcal infection). Of 9 immunotherapy‐treated patients, 5 improved. Interpretation UNAs are partly accounted for by a repertoire of diverse mostly intracellular synaptic antigens. Their characterization is expedited by protein arrays and PhIPSeq. Further individual studies are needed to assess them as disease biomarkers.

Abstract Background To develop and validate a sensitive live cell-binding assay using flow cytometry to detect a3ß4-ganglionic nicotinic acetylcholine receptor (gnAChR) antibodies for diagnosis of autoimmune autonomic ganglionopathy (AAG, a subset of autoimmune autonomic neuropathies). The current radioimmunoprecipitation assay (RIPA) method has high false positive rate and utilizes radioactivity. Methods HEK293 cells were transiently transfected to express human a3ß4-gnAChR subunits, along with NACHO and RIC3 chaperons, and GFP for detection. Transfected cells were treated with 1mM nicotine liquid for 18-22 hours prior to lifting cells for flow cytometry. The IBI (IgG Binding Index) was then calculated as the median fluorescence intensity (MFI) of AF647 of the a3ß4-gnAChR subunits expressing cells divided by the MFI of the AF647 HEK293 expressing cells. Humanized AChR-specific monoclonal antibody (mAb03) was used as a single-point calibrator. The cut-off index (COI) ratio is calculated by dividing the IBI obtained from a sample by the established IBI cut-off value of the mAB03 calibrator set by the assay. A ratio >1 indicates a positive result, while a ratio below 1 is negative. The study tested sera from 83 Mayo Clinic patients suspected of having autoimmune autonomic ganglionopathy (AAG), with a total of 100 samples collected over several years (40 from patients with clinically confirmed AAG, and 60 from patients without AAG), all previously positive for a3-gnAChR antibodies by RIPA. Additionally, 130 control samples were included: 90 from healthy individuals, 22 with hypergammaglobulinemia, and 18 with systemic lupus erythematosus. Results Median RIPA a3ß4-gnAChR value among 40 AAG patient samples was 2.58 nmol/L (range, 0.06-29.1 nmol/L) and among 60 non-AAG patients was 0.14 nmol/L (range, 0.01-4.43 nmol/L). The mAB03 calibrator median IBI value across assays was 2.1 (range, 1.6-2.7). The COI ratio was calculated using the calibrated IBI values. Thirty-eight of 40 AAG patient samples were considered positive, resulting in median IBI of 3.10 (range, 1.29-6.71); sensitivity 95%. None of non-AAG patients and controls were considered positive; median IBI of 0.38 (range, 0.14-0.51); specificity 100%. The two negative AAG patient samples (IBI, 0.43 and 0.43) were from patients in remission (treated with immune suppressants), and had RIPA titers of 0.06 nmol/L and 0.74 nmol/L. Conclusion The a3ß4-gnAChR-IgG flow cytometry assay has high sensitivity and specificity for AAG-related a3-AChR antibodies. It was able to distinguish AAG patients from non-AAG patients and controls effectively. The flow cytometry assay’s cut-off index ratio effectively identifies AAG patients while remaining negative for non-AAG and control samples.

Abstract Objectives γ‐Aminobutyric acid B receptor (GABA B R)‐IgG (immunoglobulin G) is an intermediate‐risk paraneoplastic autoantibody often associated with seizures. We aimed to assess the clinical and oncological features of GABA B R‐IgG autoimmune encephalitis (AE) and evaluate the performance of antibody testing. Methods Patients testing positive for GABA B R‐IgG in serum/cerebrospinal fluid (CSF) at Mayo Clinic Neuroimmunology Laboratory were identified. Archived sera were retested by cell‐based assay (CBA) at 1:100 and 1:200 dilutions. A live‐cell flow cytometry–based assay (LCFBA) was developed and validated using archived sera and CSF. True positivity included patients with classic presentations of GABA B R‐IgG AE or oncological explanations for antibody presence. Results Eighty‐six patients (median age 63 years; 43 female) presented with classic presentations of GABA B R‐IgG AE: encephalopathy with prominent seizures ( n = 55), status epilepticus ( n = 23), and rapidly progressive dementia ( n = 8). In addition, 44 patients (33%) had a false‐positive result for GABA B R‐IgG characterized by non‐specific symptoms/alternate diagnoses. Malignancy was identified in 78% of true‐positive patients, predominantly small cell lung carcinoma (SCLC). Testing serum at 1:100 dilution on CBA and using tissue immunofluorescence assay (IFA) in serum and CSF improved the identification of true‐positive patients ( p < 0.001). CBA at 1:100 dilution performed better than conventional CBA (at 1:10 dilution, p < 0.001) and tissue IFA ( p = 0.031). An in‐house LCFBA showed 100% sensitivity and specificity in CSF, performing similarly to conventional CBA ( p = 0.125) in CSF, but better than tissue IFA ( p = 0.031). Furthermore, serum LCFBA performed better than conventional CBA ( p = 0.022) and tissue IFA ( p = 0.006). LCFBA had the highest diagnostic accuracy and was closely followed by CBA at 1:100 dilution. Significance GABA B R‐IgG AE often presents as encephalopathy with seizures or status epilepticus in the context of an underlying SCLC. Multimodal evaluation using tissue IFA and fixed CBA at higher dilutions improves detection of true cases. LCFBA performs very well as a diagnostic test with very high sensitivity and specificity.

ABSTRACT Objectives To investigate the value of cytokine, chemokine, and neurofilament light chain (NfL) concentrations in predicting relapse risk, chronic epilepsy, and functional impairment in LGI1 autoimmune encephalitis (AE). Methods Cytokines/chemokines (IL‐1‐beta, IL‐2, IL‐4, IL‐5, IL‐6, IL‐8/CXCL8, IL‐10, IL‐12p70, IL‐13, IL‐17A, GM‐CSF, TNF‐alpha, IFN‐gamma, CXCL9, CXCL10, CXCL13, BAFF) and NfL concentrations were measured in CSF and paired serum from LGI1‐AE patients evaluated at Mayo Clinic (01/2015–02/2024), using a multiplex immunoassay system (ELLA, Bio‐Techne) and correlated with clinical outcomes. A laboratory‐based cohort of LGI1‐IgG‐positive patients and control cohorts, including patients with mixed non‐inflammatory disorders (MNID), Alzheimer's disease (AD), and temporal lobe epilepsy (TLE) were analyzed. Results Forty‐four patients with LGI1‐AE were included; 29 (66%) were male, with a median age of 68.5 years (range, 8–85). Median time from symptom onset to CSF sampling was eight months (IQR, 3–17); 19/42 (45%) experienced a clinical relapse and 27% developed chronic epilepsy. Serum IL‐6, serum and CSF IL‐8/CXCL8, and IL‐17A were higher in LGI1‐IgG positive patients than MNID ( p < 0.05). TLE cytokine/chemokine profiles were similar to LGI1 AE; AD patients had lower serum IL‐6 and CSF IL‐8/CXCL8 ( p = 0.04; p = 0.01), and higher serum IL‐17A and GM‐CSF ( p = 0.004; p = 0.01) than LGI1‐AE. Higher CSF IL‐6 and IL‐8/CXCL8 in LGI1‐AE associated with clinical relapse ( p < 0.05) and higher CSF NfL associated with chronic epilepsy ( p = 0.01). Conclusion Elevations in IL‐6, IL‐8/CXCL8, and IL‐17A were identified in this LGI1‐AE cohort. CSF IL‐6, IL‐8/CXCL8, and NfL levels are potential prognostic biomarkers for risk of relapse and chronic epilepsy in LGI1‐AE.