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Background and Objective: Despite constituting one-third of suspected autoimmune encephalitis (AE) patients, antibody-negative cases without typical AE features are understudied. We aim to characterize the clinical phenotypes and long-term outcomes of "possible only" and "probable" AE cases., Methods: We conducted a retrospective analysis of adult patients evaluated at Mayo Clinic's Autoimmune Neurology Clinic (01/01/2006-12/31/2020), meeting diagnostic criteria for "possible only" or "probable but antibody-negative" AE, with ≥ 1 year of follow-up. All patients underwent neural antibody testing., Results: Among fifty-one patients, six had a change in diagnosis (non-autoimmune, 2) and were excluded from further analysis. Forty-five patients were analyzed [median age, 61 years (range 20-88); female, 21 (47%); median follow-up, 36 months (range 12-174)]. A nadir modified Rankin Scale (mRS) ≥ 3 was recorded in 41/45 (91%). CSF was inflammatory in 20/44 (45%) and MRI had encephalitic changes in 21/45 (47%). Unclassified neural-specific IgG staining on tissue-based assay was detected in five (11%). Two patients (4%) had paraneoplastic causation. Relapses (> 3 months from onset) were noted in 14 (31%). Memory dysfunction (69%), attention deficits (38%), and gait instability (29%) were the most frequent at the last follow-up. Most patients (76%) were independent at the last follow-up and only two required an assistive device to ambulate; 11 patients (24%) had poor neurological outcome (mRS ≥ 3). Higher mRS score and gait assistance requirement at 3 months were predictive of poor outcome (P ≤ 0.01)., Discussion: Despite significant disability at initial disease stages, most antibody-negative AE patients regain independent functioning. Early functional status and gait assistance requirements may predict long-term prognosis., Competing Interests: Declarations. Conflict of interest: Georgios Mangioris and Emma Orozco report no disclosures. Divyanshu Dubey has consulted for UCB, Immunovant, Argenx, Arialys and Astellas pharmaceuticals. All compensations for consulting activities are paid directly to Mayo Clinic. He is a named inventor on filed patent that relates to KLHL11 as marker of autoimmunity and germ cell tumor. 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 & PR220430), David J. Tomassoni ALS Research Grant Program and UCB. Eoin P. Flanagan has served on advisory boards for Alexion, Genentech, Horizon Therapeutics and UCB. He has received research support from UCB. He has received speaker honoraria from Pharmacy Times. He received royalties from UpToDate. He is a site principal investigator in a randomized clinical trial of Rozanolixizumab for relapsing myelin oligodendrocyte glycoprotein antibody-associated disease run by UCB. He is a site principal investigator and a member of the steering committee for a clinical trial of satralizumab for relapsing myelin oligodendrocyte glycoprotein antibody-associated disease run by Roche/Genentech. He has received funding from the NIH (R01NS113828). He is a member of the medical advisory board of the MOG project. He is an editorial board member of Neurology, Neuroimmunology and Neuroinflammation, The Journal of the Neurological Sciences and Neuroimmunology Reports. A patent has been submitted on DACH1-IgG as a biomarker of paraneoplastic autoimmunity. Sean J. Pittock has received personal compensation for serving as a consultant for F. Hoffman-LaRoche AG, Genentech, Sage Therapeutics, Astellas and Arialis. He’s received personal compensation for serving on scientific advisory boards or data safety monitoring boards for F. Hoffman-LaRoche AG, Genentech, and UCB. His institution has received compensation for serving as a consultant for Astellas, Alexion/Astra Zeneca Rare Diseases, and Horizon/Amgen. All compensation is paid to Mayo Clinic. He has received research support from Alexion/Astra Zeneca Rare Diseases, Horizon/Amgen, F. Hoffman-LaRoche AG, Genentech and Adimmune. He has a patent, Patent# 8,889,102 (Application#12-678350, Neuromyelitis Optica Autoantibodies as a Marker for Neoplasia)—issued; a patent, Patent# 9,891,219B2 (Application#12-573942, Methods for Treating Neuromyelitis Optica (NMO) by Administration of Eculizumab to an individual that is Aquaporin-4 (AQP4)-IgG Autoantibody positive)-issued and from which he has received royalties. He is working as a consultant in the Mayo Clinic Neuroimmunology laboratory clinical service. He has patents issued for a variety of target antigens including MAP1B-IgGs, KLCHL11, SKOR2, and LUZP4 IgGs. Anastasia Zekeridou has patents submitted for Tenascin-R-IgG, PDE10A-IgG, CAMKV-IgG, and DACH1-IgG as biomarkers of paraneoplastic neurological autoimmunity. She has received research funding from Roche not relevant to this work and the Mayo Clinic Center for MS and Autoimmune Neurology. She’s consulted, without personal compensation, for Alexion Pharmaceuticals. Andrew McKeon reports research funding from National Institutes of Health (NIH: RO1NS126227, U01NS120901), patents issued for GFAP and MAP1B-IgGs and patents pending for CAMKV, PDE10A, Septins-5 and -7, and KLCHL11-IgGs, and has consulted for Janssen and Roche pharmaceuticals, without personal compensation. Ethical approval: This retrospective study was approved by the Mayo Clinic Institutional Review Board (IRB, 21-001297). Medical records of patients who consented to research review were included., (© 2024. Springer-Verlag GmbH Germany, part of Springer Nature.)

Objective: To characterize the long-term outcomes of patients with "possible only" or "probable" autoimmune encephalitis (AE)., Background: Despite comprising one-third of AE cases, antibody-negative cases lacking typical AE-defining features are understudied., Design/methods: We conducted a retrospective analysis of adult patients evaluated at a tertiary center neuroimmunology practice from 2006 to 2020, meeting diagnostic criteria for "possible only" or "probable but antibody-negative" AE, with at least one year of follow-up. All patients underwent neural antibody testing., Results: Forty-five patients (median age, 61 years [range, 20-88]; female, 21 [47%]) were included, with a median follow-up of 36 months (range, 12-174). A change in diagnosis was noted in six additional patients, who were excluded from further analysis, with only two receiving a non-autoimmune diagnosis during follow-up. The majority (41/45 [91%]) presented with significant disability (modified Rankin Scale [mRS] ≥3) at baseline. CSF was inflammatory in 20/44 (45%) and MRI was abnormal in 21/45 (47%). Unclassified neural-specific IgG staining on tissue-based assay was detected in five (11%). Two cases (4%) had a paraneoplastic cause. The median time from onset to immunotherapy initiation was two months (range, 0-21), resulting in at least partial improvement in all 44 (98%) treated cases. Clinical relapses occurred in 14/45 (31%). At last follow-up, the most common symptoms were memory dysfunction (31/45 [69%]), attention deficits (17/45 [38%]), gait instability (13/45 [29%]), and visuospatial dysfunction (10/45 [22%]). Most patients achieved independence (median mRS, 2 [range, 0-6]); however, 11 patients had poor neurological outcome (mRS ≥3). Higher mRS score and gait assistance requirement at three months were predictive of poor outcome (P ≤0.01)., Conclusions: Despite significant disability at initial stages, patients with antibody-negative but clinically presumed AE show potential for improvement with immunotherapy, highlighting the importance of early intervention. Early functional status and gait assistance requirements may assist in predicting long-term prognosis.

Aicardi-Goutières syndrome (AGS) is a rare genetic early-onset progressive encephalopathy with variable clinical manifestations. The IFIH1 mutation has been confirmed to be responsible for type I interferon production and activation of the Janus kinase signaling pathway. We herein stress neurological observations and neuroimaging findings in a severe case report of an infant with AGS type 7 due to an IFIH1 mutation who was diagnosed in the first month of life. We also review neurological characteristics of IFIH1 mutations through recent literature., Competing Interests: None declared., (Thieme. All rights reserved.)

Immune-mediated cerebellar ataxias (IMCAs) represent a group of disorders in which the immune system targets mainly the cerebellum and related structures. We address fundamental questions on the diagnosis and immunological pathogenesis of IMCAs, as illuminated by recent advances in the field. Various types of IMCAs have been identified, including post-infectious cerebellitis, Miller Fisher syndrome, gluten ataxia, paraneoplastic cerebellar degeneration (PCD), opsoclonus and myoclonus syndrome, and anti-GAD ataxia. In some cases, identification of several well-characterized autoantibodies points to a specific etiology in IMCAs and leads to a firm diagnosis. In other cases, various autoantibodies have been reported, but their interpretation requires a careful consideration. Indeed, some autoantibodies have only been documented in a limited number of cases and the causal relationship is not established. In order to facilitate an early treatment and prevent irreversible lesions, new entities have been defined in recent years, such as primary autoimmune cerebellar ataxia (PACA) and latent autoimmune cerebellar ataxia (LACA). PACA is characterized by autoimmune features which do not align with traditional etiologies, while LACA corresponds to a prodromal stage. LACA does not imply the initiation of an immunotherapy but requires a close follow-up. Concurrently, accumulation of clinical data has led to intriguing hypotheses regarding the mechanisms of autoimmunity, such as a pathogenesis of autoimmunity against synapses (synaptopathies), and the vulnerability of the entire nervous system when the immunity targets ion channels and astrocytes. The development of PCD in patients treated with immune-checkpoint inhibitors suggests that molecular mimicry specifically determines the direction of autoimmunity, and that the strength of this response is modulated by co-signaling molecules that either enhance or dampen signals from the antigen-specific T cell receptor., (© 2024. Springer-Verlag GmbH Germany, part of Springer Nature.)

The horror autoinflammaticus derived from aberrant type I interferon secretion determines a special group of autoinflammatory diseases named interferonopathies. Diverse mechanisms involved in nucleic acids sensing, metabolizing or the lack of interferon signaling retro-control are responsible for the phenotypes associated to Aicardi-Goutières Syndrome (AGS), Proteasome-Associated Autoinflammatory Diseases (PRAAS), STING-Associated Vasculopathy with Infancy Onset (SAVI) and certain forms of monogenic Systemic lupus erythematosus (SLE). This review approaches interferonopathies from the basic immunogenetic concept to diagnosis and treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: This article discusses common principles in diagnosing and managing autoimmune neurologic conditions in children., Latest Developments: The key to improving outcomes in all patients with autoimmune neurologic diseases is making an early diagnosis, promptly initiating treatment, and identifying patients who will benefit from long-term maintenance treatment. Some neuroinflammatory syndromes can be diagnosed with an antibody biomarker (eg, aquaporin-4 antibodies, N-methyl-d-aspartate [NMDA] receptor antibodies), whereas others require clinical diagnostic criteria (eg, multiple sclerosis, opsoclonus-myoclonus syndrome). A proportion of children will be labeled as seronegative, and further investigations for other inflammatory or monogenetic etiologies need to be carried out in parallel with treating the central nervous system inflammation. Time to treatment and treatment escalation were shown to correlate with outcomes in many patients with these disorders. The choice and duration of treatment should be evaluated considering side effects and risks in the short and long terms. The presence of a highly inflammatory disease process in children supports the use of highly effective disease-modifying therapies in pediatrics., Essential Points: The phenotypes of pediatric autoimmune neurologic conditions may change across different age groups, as the brain is still actively developing. In general, the presentation in children is more inflammatory, but overall disability is lower, likely because of better neuroplasticity and repair. Convincing evidence has increasingly emerged to support the biological rationale that effective immunosuppressive therapies used in adult neuroimmunology are equally effective in children., (Copyright © 2024 American Academy of Neurology.)

Objective: Autoimmune neurologic disorders encompass a broad category of diseases characterized by immune system attack of the central, peripheral, or autonomic nervous systems. This article provides information on both acute and maintenance immunotherapy used to treat autoimmune neurologic disorders as well as a review of symptomatic management and special considerations when caring for patients with these diseases., Latest Developments: Over the past 20 years, more than 50 antibodies have been identified and associated with autoimmune neurologic disorders. Although advances in diagnostic testing have allowed for more rapid diagnosis, the therapeutic approach to these disorders has largely continued to rely on expert opinion, case series, and case reports. With US Food and Drug Administration (FDA) approval of biologic agents to treat neuromyelitis optica spectrum disorder (NMOSD) and myasthenia gravis as well as ongoing clinical trials for the treatment of autoimmune encephalitis, the landscape of immunotherapy options continues to expand. Consideration of the unique pathogenesis of individual autoimmune neurologic disorders as well as the mechanism of action of the diverse range of treatment options can help guide treatment decisions today while evidence from clinical trials informs new therapeutics in the future., Essential Points: Recognizing patients who have a clinical history and examination findings concerning for autoimmune neurologic disorders and conducting a thorough and directed imaging and laboratory evaluation aimed at ruling out mimics, identifying specific autoimmune syndromes, and screening for factors that may have an impact on immunotherapy choices early in the clinical course are essential to providing optimal care for these patients. Providers must consider immunotherapy, symptomatic treatment, and a multidisciplinary approach that addresses each patient's unique needs when treating patients with autoimmune neurologic disorders., (Copyright © 2024 American Academy of Neurology.)

Objective: This article focuses on the clinical features and diagnostic evaluations that accurately identify patients with ever-expanding forms of antibody-defined encephalitis. Forms of autoimmune encephalitis are more prevalent than infectious encephalitis and represent treatable neurologic syndromes for which early immunotherapies lead to the best outcomes., Latest Developments: A clinically driven approach to identifying many autoimmune encephalitis syndromes is feasible, given the typically distinctive features associated with each antibody. Patient demographics alongside the presence and nature of seizures, cognitive impairment, psychiatric disturbances, movement disorders, and peripheral features provide a valuable set of clinical tools to guide the detection and interpretation of highly specific antibodies. In turn, these clinical features in combination with serologic findings and selective paraclinical testing, direct the rationale for the administration of immunotherapies. Observational studies provide the mainstay of evidence guiding first- and second-line immunotherapy administration in autoimmune encephalitis and, whereas these typically result in some clinical improvements, almost all patients have residual neuropsychiatric deficits, and many experience clinical relapses. An improved pathophysiologic understanding and ongoing clinical trials can help to address these unmet medical needs., Essential Points: Antibodies against central nervous system proteins characterize various autoimmune encephalitis syndromes. The most common targets include leucine-rich glioma inactivated protein 1 (LGI1), N-methyl-d-aspartate (NMDA) receptors, contactin-associated proteinlike 2 (CASPR2), and glutamic acid decarboxylase 65 (GAD65). Each antibody-associated autoimmune encephalitis typically presents with a recognizable blend of clinical and investigation features, which help differentiate each from alternative diagnoses. The rapid expansion of recognized antibodies and some clinical overlaps support panel-based antibody testing. The clinical-serologic picture guides the immunotherapy regime and offers valuable prognostic information. Patient care should be delivered in conjunction with autoimmune encephalitis experts., (Copyright © 2024 American Academy of Neurology.)

With the discovery of an expanding number of neural autoantibodies, autoimmune etiologies of seizures have been increasingly recognized. Clinical phenotypes have been identified in association with specific underlying antibodies, allowing an earlier diagnosis. These phenotypes include faciobrachial dystonic seizures with LGI1 encephalitis, neuropsychiatric presentations associated with movement disorders and seizures in NMDA-receptor encephalitis, and chronic temporal lobe epilepsy in GAD65 neurologic autoimmunity. Prompt recognition of these disorders is important, as some of them are highly responsive to immunotherapy. The response to immunotherapy is highest in patients with encephalitis secondary to antibodies targeting cell surface synaptic antigens. However, the response is less effective in conditions involving antibodies binding intracellular antigens or in Rasmussen syndrome, which are predominantly mediated by cytotoxic T-cell processes that are associated with irreversible cellular destruction. Autoimmune encephalitides also may have a paraneoplastic etiology, further emphasizing the importance of recognizing these disorders. Finally, autoimmune processes and responses to novel immunotherapies have been reported in new-onset refractory status epilepticus (NORSE) and febrile infection-related epilepsy syndrome (FIRES), warranting their inclusion in any current review of autoimmune-associated seizure disorders., (© 2024 The Authors. Epileptic Disorders published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Background and Objectives: Aicardi Goutières syndrome (AGS) is type I interferonopathy characterized by severe neurologic impairment. Although many children with AGS demonstrate motor and expressive language deficits, the magnitude of receptive language impairment is uncharacterized. We sought to characterize cognitive function in AGS-affected children using assessment tools with reduced dependence on motor abilities and compare cognitive testing outcomes with overall severity and parental assessment of adaptive behavior., Methods: We performed a cross-sectional study. Children were recruited as part of the Myelin Disorders Biorepository Project at the Children's Hospital of Philadelphia. We included individuals with a confirmed diagnosis of AGS. We administered the Leiter International Performance Scale, third edition (Leiter-3), and the Vineland Adaptive Behavior Scale, third edition (VABS-3), in the context of research encounters. Motor skills were categorized by AGS Severity Scale mobility levels. Descriptive statistics and Spearman's rank correlation were used to compare assessments. Mann-Whitney and Kruskal-Wallis tests with correction with Dunn's multiple comparison test were used to compare test performance between mobility groups., Results: Cognitive and adaptive behavior performance was captured in 57 children. The mean age at encounters was 8.51 (SD 5.15) years. The median (IQR) Leiter-3 score was 51 (interquartile range [IQR] 60), with administration failure in 20 of 57 (35%) individuals. On the VABS-3, the Motor Domain (median 29, IQR 36.25) was more impacted than the Communication (median 50, IQR 52), Daily Living Skills (median 52, IQR 31), and Socialization (median 54, IQR 40) Domains ( p < 0.0001). The AGS Scale correlated with VABS-3 ( r = 0.86, p < 0.0001) and Leiter-3 ( r = 0.87, p < 0.0001). There was correlation between VABS-3 Domains and Leiter-3 ( r -range 0.83-0.97). Gross motor and fine motor categories, respectively, correlated with VABS-3 ( H = 39.37, p < 0.0001; U = 63, p < 0.0001) and Leiter-3 ( H = 40.43, p < 0.0001; U = 66, p < 0.0001). Within each gross motor and fine motor category of the AGS Scale, a subset of children scored within normal IQ range., Discussion: Parental assessment of function by the VABS-3 correlated with directly assessed performance measures. Our data underscore the potential value of VABS-3 and Leiter-3 as tools to assess psychometric function in AGS. With a deeper understanding of our patients' abilities, we can better guide clinicians and families to provide appropriate support and personalized interventions to empower children with leukodystrophies to maximize their communication and educational potential.

Objective: To delineate the clinical characteristics of antibody-negative autoimmune encephalitis (AE) and to investigate factors associated with long-term outcomes among antibody-negative AE., Methods: Patients diagnosed with antibody-negative AE were recruited from January 2016 to December 2022 at the Second Xiangya Hospital of Central South University. The study assessed the long-term outcomes of antibody-negative AE using the modified Rankin scale (mRS) and the Clinical Assessment Scale in Autoimmune Encephalitis (CASE). Predictors influencing long-term outcomes were subsequently analyzed. External validation of RAPID scores (refractory status epilepticus [RSE], age of onset ≥60 years, ANPRA [antibody-negative probable autoimmune encephalitis], infratentorial involvement, and delay of immunotherapy ≥1 month) was performed., Results: In total, 100 (47 females and 53 males) antibody-negative AE patients were enrolled in this study, with approximately 49 (49%) experiencing unfavorable long-term outcomes (mRS scores ≥3). Antibody-negative AE was subcategorized into ANPRA, autoimmune limbic encephalitis (LE), and acute disseminated encephalomyelitis (ADEM). Psychiatric symptoms were prevalent in LE and ANPRA subtypes, while weakness and gait instability/dystonia were predominant in the ADEM subtype. Higher peak CASE scores (odds ratio [OR] 1.846, 95% confidence interval [CI]: 1.163-2.930, p = 0.009) and initiating immunotherapy within 30 days (OR 0.210, 95% CI: 0.046-0.948, p = 0.042) were correlated with long-term outcomes. Receiver operating characteristic (ROC) analysis returned that the RAPID scores cutoff of 1.5 best discriminated the group with poor long-term outcomes (sensitivity 85.7%, specificity 56.9%)., Interpretation: The ANPRA subtype exhibited poorer long-term outcomes compared to LE and ADEM subtypes, and early immunotherapy was crucial for improving long-term outcomes in antibody-negative AE. The use of RAPID scoring could aid in guiding clinical decision making., (© 2024 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association.)

The clinical category of immune-mediated cerebellar ataxias (IMCAs) is now recognized after 3 decades of clinical and experimental research. The cerebellum gathers about 60% of neurons in the brain, is enriched in numerous plasticity mechanisms, and presents a large variety of antigens at the neuroglial level: ion channels and related proteins, synaptic adhesion/organizing proteins, transmitter receptors, and glial cells. Cerebellar circuitry is especially vulnerable to immune attacks. After the loss of immune tolerance, IMCAs present in an acute or subacute manner with various combinations of a vestibulocerebellar syndrome (VCS), a cerebellar motor syndrome (CMS), and a cerebellar cognitive affective syndrome/Schmahmann's syndrome (CCAS/SS). IMCAs include gluten ataxia (GA), post-infectious cerebellitis (PIC), Miller Fisher syndrome (MFS), paraneoplastic cerebellar degeneration (PCD), opsoclonus myoclonus syndrome (OMS), anti-glutamic acid decarboxylase (anti-GAD) ataxia, and glial fibrillary acidic protein (GFAP) astrocytopathy (GFAP-A). In addition, multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), Behçet disease, and collagen-vascular disorders may also present with cerebellar symptoms when lesions involve cerebellar afferences/efferences. Patients whose clinical profiles do not fit with IMCAs are now gathered in the group of primary autoimmune cerebellar ataxias (PACAs). Latent auto-immune cerebellar ataxia (LACA) refers to a clinical stage with a slow progressive course and a lack of obvious auto-immune background. At a pre-symptomatic stage, patients remain asymptomatic, whereas at the prodromal stage aspecific symptoms occur, announcing the symptomatic neuronal loss. LACA corresponds to a time-window where an intervention could lead to preservation of plasticity mechanisms. Patients may evolve from LACA to PACA and typical IMCAs, highlighting a continuum. Immune ataxias represent a model to elucidate the sequence of events leading to destruction of cerebellar neuronal reserve and develop novel strategies aiming to restore plasticity mechanisms., Competing Interests: The authors declare no conflict of interest. Mario Manto is serving as one of the Editorial Board members of this journal. We declare that Mario Manto had no involvement in the peer review of this article and has no access to information regarding its peer review. Full responsibility for the editorial process for this article was delegated to Gernot Riedel., (© 2024 The Author(s). Published by IMR Press.)

Aicardi-Goutières syndrome is a genetic inflammatory disorder resulting in dispersed neurologic dysfunction. Despite a recognition of overall motor impairment, fine and visual motor skills are undercharacterized. We hypothesize that there is a spectrum of fine and visual motor skills in the Aicardi-Goutières syndrome population as captured by a standard outcome measure, the Peabody Developmental Motor Scales (PDMS-2), which will be proportional to overall disease severity.In a cohort of 74 subjects, the Peabody Developmental Motor Scales-2 grasping and visual-motor integration subtests were administered concurrently with the Aicardi-Goutières syndrome Severity Scale (severe [range 0-3], moderate [range 4-8], and attenuated [range 9-11]). The cohort was also compared by genotype and performance as defined by raw scores. The distribution of Peabody Developmental Motor Scales-2 scores within a genotype was assessed by interquartile ranges (IQRs).Peabody Developmental Motor Scales-2 grasping and visual-motor integration performance was the least variable in the TREX1 -cohort (IQR: 10.00-12.00) versus the SAMHD1 and IFIH1 cohorts (IQR: 51.00-132.00 and 48.50-134.00, respectively). Neurologic severity highly correlated with both fine and visual motor skills (Spearman correlation: r  = 0.87, 0.91, respectively). A floor effect (lowest 10% of possible scores) was observed within the severe cohort (n = 32/35), whereas a ceiling effect (top 10%) was observed in the attenuated cohort (n = 13/17).This study characterized the spectrum of fine and visual motor function in the Aicardi-Goutières syndrome population, which correlated with overall neurologic dysfunction. The Peabody Developmental Motor Scales-2 grasping and visual-motor integration showed promise as potential assessment tools in moderate and attenuated Aicardi-Goutières syndrome cohorts. A better understanding of fine and visual motor function in this population will benefit clinical care and clinical trial design., Competing Interests: Declaration of Conflicting InterestsThe authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: AV receives grants and in-kind support for research from Eli Lilly, Gilead, Takeda, Illumina, Biogen, Homology, Ionis, Passage Bio, and Orchard Therapeutics and serves on the scientific advisory boards of the European Leukodystrophy Association and the United Leukodystrophy Foundation, as well as in an unpaid capacity for Takeda, Ionis, Biogen, and Illumina. LAA is a consultant for Takeda, Biogen, and Orchard Therapeutics.

Background and Objectives: Despite detection of autoantibodies, anti-IgLON5 disease was historically considered a tau-associated neurodegenerative disease, with limited treatment options and detrimental consequences for the patients. Observations in increasing case numbers hint toward underlying inflammatory mechanisms that, early detection provided, open a valuable window of opportunity for therapeutic intervention. We aimed to further substantiate this view by studying the CSF of patients with anti-IgLON5., Methods: We identified 11 patients with anti-IgLON5 from our database and compared clinical, MRI, and CSF findings with a cohort of 20 patients with progressive supranuclear palsy (PSP) (as a noninflammatory tauopathy) and 22 patients with functional neurologic disorder., Results: Patients with anti-IgLON5 show inflammatory changes in routine CSF analysis, an increase in B-lymphocyte frequency, and the presence of plasma cells in comparison to the PSP-control group and functional neurologic disease controls. Patients with intrathecal plasma cells showed a clinical response to rituximab., Discussion: Our findings indicate the importance of inflammatory mechanisms, in particular in early and acute anti-IgLON5 cases, which may support the use of immune-suppressive treatments in these cases. The main limitation of the study is the small number of cases due to the rarity of the disease., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)