Objective: The aim of this study was to assess the diagnostic utility of cerebrospinal fluid (CSF) myelin oligodendrocyte glycoprotein antibodies (MOG‐IgG) testing.Methods: We retrospectively identified patients for CSF MOG‐IgG testing from January 1, 1996, to May 1, 2023, at Mayo Clinic and other medical centers that sent CSF MOG‐IgG for testing including: controls, 282; serum MOG‐IgG positive MOG antibody‐associated disease (MOGAD), 74; serum MOG‐IgG negative high‐risk phenotypes, 73; serum false positive MOG‐IgG with alternative diagnoses, 18. A live cell‐based assay assessed CSF MOG‐IgG positivity (IgG‐binding‐index [IBI], ≥2.5) using multiple anti‐human secondary antibodies and end‐titers were calculated if sufficient sample volume. Correlation of CSF MOG‐IgG IBI and titer was assessed.Results: The pan‐IgG Fc‐specific secondary was optimal, yielding CSF MOG‐IgG sensitivity of 90% and specificity of 98% (Youden's index 0.88). CSF MOG‐IgG was positive in: 4/282 (1.4%) controls; 66/74 (89%) serum MOG‐IgG positive MOGAD patients; and 9/73 (12%) serum MOG‐IgG negative patients with high‐risk phenotypes. Serum negative but CSF positive MOG‐IgG accounted for 9/83 (11%) MOGAD patients, and all fulfilled 2023 MOGAD diagnostic criteria. Subgroup analysis of serum MOG‐IgG low‐positives revealed CSF MOG‐IgG positivity more in MOGAD (13/16[81%]) than other diseases with false positive serum MOG‐IgG (3/15[20%]) (p = 0.01). CSF MOG‐IgG IBI and CSF MOG‐IgG titer (both available in 29 samples) were correlated (Spearman's r = 0.64, p < 0.001).Interpretation: CSF MOG‐IgG testing has diagnostic utility in patients with a suspicious phenotype but negative serum MOG‐IgG, and those with low positive serum MOG‐IgG results and diagnostic uncertainty. These findings support a role for CSF MOG‐IgG testing in the appropriate clinical setting. ANN NEUROL 2024;96:34–45

Background and Objectives Neural antibodies are detected by tissue-based indirect immunofluorescence assay (IFA) in Mayo Clinic9s Neuroimmunology Laboratory practice, but the process of characterizing and validating novel antibodies is lengthy. We report our assessment of human protein arrays. Methods Assessment of arrays (81% human proteome coverage) was undertaken using diverse known positive samples (17 serum and 14 CSF). Samples from patients with novel neural antibodies were reflexed from IFA to arrays. Confirmatory assays were cell-based (CBA) or line blot. Epitope mapping was undertaken using phage display immunoprecipitation sequencing (PhiPSeq). Results Control positive samples known to be reactive with linear epitopes of intracellular antigens (e.g., ANNA-1 [anti-Hu]) were readily identified by arrays in 20 of 21 samples. By contrast, 10 positive controls known to be enriched with antibodies against cell surface protein conformational epitopes (e.g., GluN1 subunit of NMDA-R) were indistinguishable from background signal. Three antibodies, previously characterized by other investigators (but unclassified in our laboratory), were unmasked in 4 patients using arrays (July-December 2022): Neurexin-3α, 1 patient; regulator of gene protein signaling (RGS)8, 1 patient; and seizure-related homolog like 2 (SEZ6L2), 2 patients. All were accompanied by previously reported phenotypes (encephalitis, 1; cerebellar ataxia, 3). Patient 1 had subacute onset of seizures and encephalopathy. Neurexin-3α ranked high in CSF (second ranked neural protein) but low in serum (660th overall). Neurexin-3α CBA was positive in both samples. Patient 2 presented with rapidly progressive cerebellar ataxia. RGS8 ranked the highest neural protein in available CSF sample by array (third overall). RGS8-specific line blot was positive. Patients 3 and 4 had rapidly progressive cerebellar ataxia. SEZ6L2 was the highest ranked neural antigen by arrays in all samples (CSF, 1, serum, 2; Patient 3, ranked 9th overall in CSF, 11th in serum; Patient 4, 6th overall in serum]). By PhIPSeq, diverse neurexin-3α epitopes (including cell surface) were detected in CSF from patient 1, but no SEZ6L2 peptides were detected for serum or CSF samples from Patient 3. Discussion Individualized autoimmune neurologic diagnoses may be accelerated using protein arrays. They are optimal for detection of intracellular antigen-reactive antibodies, though certain cell surface-directed antibodies (neurexin-3α and SEZ6L2) may also be detected.

Data on the plasma exchange (PLEX) in myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) are limited. Herein, we evaluate outcomes after PLEX in MOGAD. This international multicenter retrospective cohort study included patients from 18 tertiary care centers in 6 countries. Inclusion criteria included fulfillment of the 2023 International MOGAD panel criteria, receipt of at least 3 sessions of PLEX, and follow-up of ≥3 months after PLEX. Patients with coexisting neuroinflammatory disorders were excluded. We assessed the frequency of complete recovery (CR), clinically significant improvement (CSI), visual acuity (VA), and Expanded Disability Status Scale (EDSS). Logistic regression analyses were performed to identify predictors of CR and CSI. Of 234 patients, 135 (58%) were female. The median (interquartile range [IQR]) age at attack was 34 (IQR 22-49) years, and 42 (17%) were children. In 165 of 243 (68%), the attack treated with PLEX was the first attack. Attack phenotypes included 161 optic neuritis (235 eyes), 77 myelitis, 24 acute disseminated encephalomyelitis, 15 brainstem/cerebellar, 3 cerebral-cortical encephalitis attack, and 1 cerebral polyfocal deficit-36 with >1 core phenotypes. A total of 239 (99%) attacks were also treated with corticosteroids and 32 (13%) with IV immunoglobulins. VA in optic neuritis improved from 20/400 (20/70-hand motion) to 20/20 (20/20-20/30), p < 0.001, and EDSS decreased from a median of 4.0 (3.0-6.5) to 1.0 (0.0-2.5), p < 0.001. Of 229 attacks without subsequent attacks within 3 months, 100 (44%) achieved CR and 213 (93%) CSI. The probability of CR was decreased with advanced age (adjusted odd ratio [95% CI] 0.97 [0.96-0.99] per year), higher EDSS worsening from baseline (0.66 [0.54-0.81] per 0.5 increment) and delayed PLEX (0.98 [0.96-0.99] per day). Advanced age (0.97 [0.96-0.99] per year) and delayed PLEX (0.95 [0.94-0.96] per day) decreased the probability of CSI. We observed favorable outcomes after PLEX in MOGAD attacks. However, advanced age and delayed initiation of PLEX were associated with a reduced probability of improvement. The absence of a control group limits our ability to differentiate PLEX effects from spontaneous recovery, prior corticosteroid response, or long-term immunotherapy. Future prospective studies are needed to assess the impact of PLEX on improvement. This study provides Class IV evidence that PLEX is associated with favorable clinical outcomes in patients with MOGAD.

Kelch-like protein-11 (KLHL11)-IgG is associated with rhombencephalitis and seminoma. It has not previously been described as a neurologic immune checkpoint inhibitor (ICI)-related adverse event (nirAE) or in association with esophageal adenocarcinoma. We describe a 61-year-old man with metastatic esophageal adenocarcinoma treated with folinic acid, fluorouracil, oxaliplatin (FOLFOX), and nivolumab, who subsequently developed diplopia, vertigo, and progressive gait ataxia after 8 weeks of treatment. Owing to a concern for ICI-associated myasthenia gravis, nivolumab was held and he was treated with prednisone and pyridostigmine. EMG showed no neuromuscular junction dysfunction, and acetylcholine-receptor antibodies were negative. Brain MRI was unrevealing. Murine brain tissue immunofluorescence assay revealed KLHL11-IgG in both serum and CSF, confirmed by cell-based assay. Tumor histopathology demonstrated poorly differentiated, highly proliferative adenocarcinoma with increased mitotic figures and cytoplasmic KLHL11 immunoreactivity. He was initiated on 6 months of cyclophosphamide in addition to FOLFOX for post-ICI-associated KLHL11-IgG rhombencephalitis. We report KLHL11-IgG rhombencephalitis associated with poorly differentiated esophageal cancer as a novel nirAE. Tumor staining revealed KLHL11 immunoreactivity, supporting a cancer-antigen-driven ICI-associated paraneoplastic syndrome. Recognition of novel nirAEs can expedite treatment and potentially prevent progressive neurologic disability.

Data regarding late adult-onset myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) are scant. This study sought to assess the frequency, characteristics, and outcome of late adult-onset MOGAD and identify differences from early adult-onset MOGAD. This retrospective, observational study included Mayo Clinic patients with MOGAD per 2023 diagnostic criteria and with onset age 50 years or older. Clinical, laboratory, radiologic, treatment, and outcome data were collected and compared between patients aged 50-59 years and those aged 60 years or older. Finally, the characteristics and outcome of patients with late adult-onset MOGAD (aged 50 or older) were compared with a reference group of patients with early adult-onset (aged 18-49) MOGAD (n = 141). There were 107 patients with late adult-onset MOGAD included, representing 25% of the MOGAD cohort (n = 436). The median age at onset was 59 years (range: 50-88), and 71 (66%) were female. Medical comorbidities were noted in 86 of 105 (83%). Optic neuritis was the most frequent onset attack (77/107, 72%), and the median Expanded Disability Status Scale (EDSS) score at nadir was 3 (range: 1-9). In 32 of 107 (30%), a potential trigger was noted, mostly infections. In 32 patients (30%), an alternative diagnosis was considered before MOGAD identification, most commonly giant cell arteritis (n = 15 [11 undergoing temporal artery biopsy]). By a median follow-up duration of 22 months (range: 0-306), 50 patients (47%) had a relapsing course, and preventive treatment was administered in 53 (50%). Medication side effects were common (41/107, 38%). No differences were observed in patients with MOGAD aged 50-59 years vs 60 years or older. Lastly, late adult-onset patients had more optic nerve involvement (p = 0.015; OR: 1.9; 95% CI 1.1-3.3), brainstem/cerebellar involvement (p = 0.008; OR: 3.4; 95% CI 1.1-3.3), and cognitive decline (p = 0.01; OR: 5.3; 95% CI 1.4-19.4) and less frequent myelitis (p < 0.001; OR: 0.4; 95% CI 0.2-0.7) vs those with early adult-onset MOGAD, but EDSS scores and frequency of a relapsing course were similar. Late adult-onset MOGAD accounts for one-quarter of patients with MOGAD. Optic neuritis is the dominant phenotype in this age group with MOGAD and is under-recognized and frequently misdiagnosed. Outcomes in late adult-onset MOGAD are similar to those in early adult-onset disease.