OBJECTIVES:To characterize the magnetic resonance imaging (MRI) lesion dynamics, comorbidities, predictors of relapse, and outcomes in anti-γ-aminobutyric acid type A receptor (GABAAR) encephalitis, and assess the utility of LIM-domain-only-protein 5 (LMO5) antibodies as tumor markers. METHODS:GABAAR antibodies were confirmed by 2 techniques in serum or cerebrospinal fluid. Long-term outcomes were defined as good (modified Rankin scale, mRS = 0-1) or poor (mRS 2-5) at ≥12 months. LMO5 antibodies were assessed by cell-based assays and Western blot. RESULTS:Thirty-three patients were identified (4 children, 29 adults; median age, 5.5 and 60 years; 61% male). Ten patients (10/32, 31%) had concurrent systemic autoimmunity. Adults presented with seizures and cognitive/behavioral symptoms, often with thymoma, gastrointestinal, or other tumors (18/33, 55%), whereas children frequently had seizures and ataxia with cerebellar MRI lesions. Multifocal T2/fluid-attenuated inversion recovery hyperintensities were present at onset in 23 of 31 (74%) or developed later in those with absent or single lesions. Lesions showed dynamic changes, suggesting ongoing inflammation even without clinical correlate. Relapses occurred in 17 of 31 (55%, all adults) and were associated with older age (p = 0.02) and lack of second-line immunotherapy (p = 0.02). Four patients (4/33, 12%) died. After a 32.5-month median follow-up, 9 of 20 (45%) had persistent cognitive deficits, and 6 of 20 (30%) had a poor outcome, which was associated with relapses (p = 0.04). LMO5 antibodies were absent in patients and controls. INTERPRETATION:Anti-GABAAR encephalitis shows age-dependent presentations, most commonly seizures. MRI reveals dynamic changes consistent with an ongoing "clinically silent" inflammation. Relapses and cognitive sequelae are common and associate with not receiving second-line immunotherapy. LMO5 antibodies lack tumor-predictive value. ANN NEUROL 2026;100:139-150.

BACKGROUND:In anti-NMDA receptor (NMDAR) encephalitis, delayed recovery and slow improvement makes it difficult to assess treatment refractoriness, leaving a knowledge gap about prolonged impaired consciousness. We aimed to assess treatment response, long-term outcomes, and their predictors in patients with NMDAR encephalitis and a prolonged vegetative state. METHODS:In this international retrospective cohort study, we included patients with NMDAR encephalitis from Jan 1, 2007 to Sept 30, 2024 who remained in a vegetative state (unresponsive wakefulness) for 9 months or longer in 21 hospitals across Austria, Brazil, Chile, China, Germany, Hong Kong, Japan, the Netherlands, Spain, Switzerland, and the USA. Data on disease presentation and long-term outcomes were collected via medical record review and a structured questionnaire sent to referring physicians. Outcomes were death, ability to follow commands, reaching a modified Rankin Scale (mRS) score of 2, or complete recovery (mRS 0 with return to premorbid activities). Competing risks analysis was used to assess survival and predictors of death, mRS score 2, and recovery. FINDINGS:45 patients were identified (38 female and seven male; median age 22 [IQR 19-31] years). The patients had impaired consciousness a median of 9 days after symptom onset (IQR 5-16). All 45 patients received first-line immunotherapy; 41 (91%) received second-line, and 18 (40%) received third-line immunotherapies. 21 (47%) of 45 patients had ovarian teratomas, which were removed in 20 patients. Median durations were: vegetative state 399 days (IQR 307-698); intensive care unit stay 275 days (189-354); mechanical ventilation 270 days (195-394); and hospitalisation 474 days (349-715). 13 (28%) patients were resuscitated from dysautonomic cardiac arrest. After a median of 5 years (IQR 3-7), 15 (33%) of 45 patients completely recovered (mRS score ≤1 and returned to all previous activities), 13 (29%) substantially improved (mRS score 2), 11 (24%) had mRS score 3-5, and six (13%) died. Five patients began command-following a median of 11 months (IQR 2-21) after last immunotherapy. Estimated cumulative incidence for reaching an mRS score of 2 was 66% at 5 years and 76% at 10 years, and for recovery was 32% at 5 years and 54% at 10 years. Teratomas were associated with a lower probability of reaching mRS score 2 (sub-distribution hazard ratio 0·39 [95% CI 0·18-0·84], p=0·0160), whereas older age (1·10 per year [1·04-1·23], p=0·0052) and higher NMDAR encephalitis 1-Year Functional Status (NEOS)2 score (1·51 [1·12-2·04], p=0·0072) were associated with increased mortality. INTERPRETATION:In people with NMDAR encephalitis and prolonged impairment of consciousness, full or substantial recovery was reached in approximately two-thirds of cases. Consequently, early assessment of treatment response or refractoriness might underestimate delayed improvement, prolonged therapy needs, or spontaneous recovery. Futility decisions should therefore be individualised with multidisciplinary input and based on extended follow-up. FUNDING:Instituto de Salud Carlos III and Fundació La Caixa.

BACKGROUND AND OBJECTIVES:Anti-IgLON5 disease is a progressive neurologic disorder characterized by sleep disturbances, gait instability, involuntary movements, and bulbar dysfunction. In long-standing cases, autopsy studies reveal a brainstem-predominant neuronal tauopathy. The disease is defined by antibodies against the neuronal adhesion molecule IgLON5 (IgLON5-abs), which reduce IgLON5 membrane clusters and disrupt the cytoskeleton in vitro. Our aim was to investigate whether these pathogenic effects occur in vivo through passive antibody transfer. METHODS:A passive transfer model was established by infusing CSF from patients with anti-IgLON5 disease or controls into the lateral ventricles of adult mice for 14 days via osmotic pumps. Motor and behavioral performance was evaluated using tests of coordination, sociability, anxiety-like behavior, and spatial memory. Mice were sacrificed at days 7, 18, and 30 for analysis of brain-bound human antibodies and quantification of total and synaptic IgLON5 clusters by confocal microscopy. Additional analyses included immunohistochemistry for phosphorylated tau, gliosis, and microglial activation. RESULTS:Mice receiving anti-IgLON5 CSF exhibited impaired motor coordination in the beam-walking and rotarod performance. Behavioral alterations included reduced social interaction, increased anxiety-like behavior, weight loss, and increased liquid intake. Human IgG deposition was predominantly localized in the hippocampus and periventricular regions, coinciding with a reduction in total and synaptic IgLON5 clusters whereas levels of the postsynaptic marker PSD95 remained unchanged. The reduction in IgLON5 clusters persisted through day 30. Microglial activation was consistently observed in affected regions, but tau pathology and gliosis were absent. DISCUSSION:This passive transfer model demonstrates that IgLON5 antibodies reduce neuronal membrane IgLON5 clusters, accompanied by microglial activation and motor and behavioral alterations. These results support a pathogenic role of IgLON5 antibodies in anti-IgLON5 disease.

BACKGROUND AND OBJECTIVES:Anti-IgLON5 disease is characterized by substantial clinical heterogeneity and variable outcomes. We investigated the associations of clinical features as well as serum neurofilament light chain (NfL), phosphorylated tau (p-tau), IgG4 levels, and the HLA-DRB110:01∼DQB105:01 haplotype with disease presentation and outcome. METHODS:This is a retrospective observational study of patients with anti-IgLON5 disease diagnosed in our laboratory with adequate clinical information and follow-up. Neurologic disability was evaluated with the modified Rankin Scale (mRS) and the anti-IgLON5 composite score (ICS). Serum NfL and p-tau181 levels were measured using a commercial single-molecule array (Simoa) assay and IgG4 levels by flow cytometry. Associations between biomarkers and baseline clinical features were assessed using Spearman rank correlation and linear regression analyses. Prognostic variables were evaluated using binary logistic and Cox proportional hazards regression models. RESULTS:We included 78 patients (median age 66 years, 55% male). Higher serum NfL levels correlated with clinical severity at diagnosis, as measured with the mRS (r = 0.438; p = 0.002) and ICS (r = 0.30; p = 0.029). Patients with the HLA-DRB1*10:01∼DQB1*05:01 haplotype more frequently presented with the bulbar or sleep phenotypes (24/41; 58%) compared with those without the haplotype (4/28; 14%; p = <0.001). Sixty-six patients received immunotherapy, and 14 (21%) showed clinical improvement at the last follow-up. In the multivariate Cox regression model, the neuromuscular phenotype was the only independent predictor of good outcome (mRS: 0-3; HR: 10.8; 95% CI 2.48-47.1; p = 0.002). Among the 30 patients who died (42%), the strongest independent predictor of mortality was the bulbar phenotype (HR: 2.59; 95% CI 1.08-6.21; p = 0.033), while serum NfL levels showed a significant but limited association (HR: 1.02; 95% CI 1.00-1.04; p = 0.02). DISCUSSION:Serum NfL levels correlate with neurologic disability, whereas the bulbar phenotype was the main risk factor of mortality, indicating that these patients should be closely monitored and considered for early interventions (i.e., tracheostomy) that may modify an otherwise poor prognosis.

Purpose of review This review describes the mechanisms of paraneoplastic neurological syndromes (PNS) and the recent advances underlying these. Recent findings This review covers advances in the understanding of the immunobiology of PNS. Specifically, evidence that PNS associated with antibodies against intracellular antigens are T-cell mediated processes, of interferon-γ signaling, major histocompatibility complex (MHC) class I upregulation, and granzyme mediated neuronal death. In contrast, PNS with antibodies against neuronal surface antigens are antibody-mediated and cause reversible neuronal dysfunction. Further, the perennial question of why only few patients develop these disorders is emerging from studies of tumor genomics and host HLA associations. Finally, immune checkpoint inhibitors have demonstrated the role of immune tolerance breakdown in the development of these disorders. Summary These advancements in understanding of mechanisms of PNS have several implications for clinical practice and research. For clinical practice, these findings may lead to prognostication of risk of PNS in cancer patients and potential novel therapeutic approaches. For research, these findings have important implications for understanding tumor immunology, and immune tolerance.

BACKGROUND AND OBJECTIVES:Although acute disseminated encephalomyelity (ADEM) can be myelin oligodendrocyte glycoprotein-IgG (MOG-IgG) positive or negative, it is unclear whether other MOG-antibody-associated disease (MOGAD)-like encephalitis syndromes occur without MOG-IgG. We aimed to define the frequency, clinico-radiologic features, outcomes, and antibody associations of such cases in children. METHODS:Prospective cohort study of children (<18 years) with encephalitis meeting clinico-radiologic MOGAD criteria, regardless of MOG-IgG status. Serum from all patients and CSF when available were tested by live cell-based assays (CBA-IIF, CBA-FACS) at 2 laboratories. Brain MRIs were centrally reviewed for MOGAD-like patterns (ADEM, cortical encephalitis, isolated/predominant central gray matter). Additional testing included CBAs for MOG-IgA, MOG-IgM, PLP1-IgG, glial fibrillary acidic protein-IgG, and AQP4-IgG, along with rat brain immunohistochemistry. RESULTS:Among 160 patients with MOGAD-like encephalitis, 120 were MOG-IgG positive and 40 negative (20 ADEM, 11 cortical encephalitis, 9 isolated/predominant central gray matter encephalitis). Clinical-radiologic features were broadly comparable between groups, including lesion distribution, frequency of associated longitudinally extensive transverse myelitis, lesion resolution, and functional outcomes. Relapses were more frequent in MOG-IgG-positive patients (22, 18% vs 1, 3%; p = 0.017). Immunohistochemistry revealed myelin immunostaining in 14 (12%) MOG-IgG-positive cases (CBA confirmed cross-reactivity with rodent MOG-epitopes) and 10 (25%) MOG-IgG-negative patients (no cross-reactivity with rodent MOG-epitopes); this included a fulminant case with autopsy showing perivenous demyelination and C4d complement deposition, suggesting autoantibodies against an unknown myelin antigen. MOG-IgA, MOG-IgM, or PLP1-IgG occurred in 36/111 (32%) MOG-IgG-positive and 7/37 (19%) MOG-IgG-negative cases, without clinical differences between groups. DISCUSSION:Children can develop the full spectrum of MOGAD-like encephalitis without MOG-IgG. Clinical features and immunotherapy response are similar to MOGAD, but relapses are uncommon.

Objectives Ma/Ma2-associated neurologic autoimmunity is characterized by CNS involvement. However, isolated peripheral nervous system (PNS) presentations have been rarely reported. We aimed to describe the frequency and syndromes of patients with Ma/Ma2 antibodies and isolated PNS involvement.Methods We performed a nested case series within multicenter cohorts of patients with Ma/Ma2-associated neurologic syndromes, confirmed by tissue-based assay and line-blot. Patients with isolated PNS presentations were included.Results Among 212 patients with Ma/Ma2 antibody-associated neurologic syndromes, 7 (3%) presented with isolated PNS involvement (median age, 68 years; 4/7 female). PNS syndromes included sensory neuronopathy (3 patients), myeloradiculopathy (1), radiculoplexopathy (1), motor neuronopathy (1), and multiple mononeuropathy. All patients were anti-Ma2-positive, whereas Ma antibodies (reactive against Ma1 and Ma2 proteins) were detected in 2 (33%)/6 tested patients. An associated cancer was identified in 6 (86%)/7 patients: pleural mesothelioma; oral squamous cell; testicular, lung, and breast cancer; and B-cell lymphoma. Five patients received immunotherapy, cancer treatment, or both. After a median follow-up of 23 months, symptoms improved or stabilized in 3 patients and progressed in 4.Discussion Isolated PNS involvement is a rare manifestation of Ma/Ma2 associated autoimmunity. Ma/Ma2 antibody testing should be considered in neuronopathies and unexplained non-length-dependent neuropathies.

Anti-IgLON5 disease is an autoimmune encephalitis that presents with a heterogenous clinical phenotype, including sleep disorders, movement abnormalities and bulbar involvement. It is characterized by autoantibodies against IgLON5, 85% association with HLA-DQB1*05:∼ and a brainstem-dominant tauopathy. Cellular and murine models report pathogenic effects of the autoantibodies, and neurodegenerative factors suggest progressive atrophy as a common sequela. However, evidence from in vivo patient data and long-term follow-up is limited, and the degree of progression remains elusive. In this multicentre study, clinical and brain MRI data were collected from 127 patients across 12 countries to investigate the relationships between clinical presentations and the development of distinct brain atrophy patterns. Our data show that most patients develop a complex multisystem phenotype as the disease progresses; however, neuromuscular manifestations rarely emerge at later disease stages. By comparison to healthy controls, this disease presents with severe substructure-specific atrophy, especially affecting the hypothalamus, brainstem, accumbens and basal ganglia, which, in age-independent analyses, show significant ventricular enlargement and also suggest progression of brainstem atrophy over the disease course. Moreover, the focality of atrophy was functionally linked to specific symptoms, with more severe involvement of the basal ganglia in patients with movement disorders, and greater atrophy in the hippocampus and thalamus in patients with cognitive impairment. Taken together, our results provide evidence of distinct atrophy patterns in anti-IgLON5 disease, which closely mirror sites of pathophysiologic processes, including autoantibody binding and tau deposition. Our data emphasize the brainstem as the pathophysiological hub of the disease and provide normative data for the incorporation of atrophy measurements into routine clinical assessments and future treatment studies to monitor disease trajectory and evaluate future treatment strategies.

Background and Objectives Detecting neural surface antibodies (NSAbs) is essential for diagnosing autoimmune encephalitis. The recommended diagnostic strategy involves initial screening with tissue-based assays (TBAs), followed by confirmation with cell-based assays (CBAs). While specialized centers use in-house TBAs, many clinical laboratories depend on commercial TBAs, whose accuracy is yet to be fully assessed. Methods We selected 92 CSF and 99 serum samples from patients with autoimmune encephalitis and NSAbs confirmed by in-house TBAs and CBAs (20 samples each for AMPAR, GABA(A)R, GABA(B)R, IgLON5, LGI1, NMDAR, and CASPR2; 19 for mGluR5; 17 for DPPX; and 15 for mGluR1 antibodies), along with 50 CSF and 50 serum samples from negative controls. We assessed the performance of a commercial indirect immunofluorescence (IIF)-TBA (EUROIMMUN). Slides were evaluated as "positive" or "negative" by 2 experienced investigators and 2 less experienced raters. Discordant results were re-evaluated through interrater discussion and assessed using Cohen's kappa. Results The experienced raters agreed on 94% (133/142) of CSF and 88% (131/149) of serum classifications (Cohen's kappa = 0.87 and 0.75, respectively, p < 0.001). Among CSF samples, 75% (106/142) were correctly identified while 19% (27/142) were misclassified (13 false positives, 14 false negatives). Among serum samples, 66% (98/149) were correctly identified while 22% (33/149) were misclassified (11 false positives, 22 false negatives). The poorest performance was seen in detecting NMDAR, GABA(A)R, and mGluR5 Abs, which were not identified in 5 of 10, 6 of 10, and 5 of 9 serum samples and in 4 of 10, 5 of 10, and 5 of 10 CSF samples, respectively. The overall sensitivity of the commercial IIF-TBA was 84% for CSF and 76% for serum while the specificity was 72% for CSF and 73% for serum. Less experienced raters correctly identified 69% (98/142) of CSF samples and 73% (109/149) of serum samples and misclassified 13% (18/142) of CSF samples and 11% (16/149) of serum samples, and 18% (26/142) of CSF samples and 16% (24/149) of serum samples remained discordant. Discussion The diagnostic performance of EUROIMMUN IIF-TBA in detecting NSAbs in autoimmune encephalitis is suboptimal. NMDAR antibodies, among the most common NSAbs, can be missed in 50% of cases. This commercial TBA should not be used alone as a screening method nor as a confirmatory technique for NSAbs.

BACKGROUND AND OBJECTIVES:The aim of this study was to describe the clinical features and long-term outcome of patients with glycine receptor (GlyR) antibody-mediated progressive encephalomyelitis with rigidity and myoclonus (PERM), a disease commonly included under the term of stiff-person spectrum disorders (SPSDs). METHODS:We conducted a retrospective analysis of patients with PERM and GlyR antibodies diagnosed in our laboratory and a systematic literature review (following Preferred Reporting Items for Systematic Reviews and Meta-Analyses [PRISMA] 2020 reporting guideline) of previously reported patients with sufficient clinical information and ≥12 months of follow-up. Neurologic disability was measured with the modified Rankin Scale (mRS). Relapses were defined as any event occurring >6 months after the first episode that required immunotherapy. RESULTS:Forty-one patients were identified, 22 from our database and 19 from the literature. The median age was 58 years (IQR: 43-66 years), and 36 (88%) were male and 5 female. The median time from symptom onset to admission was 2 weeks (IQR: 1-4 weeks). Predominant presentations included brainstem symptoms, mainly dysphagia and trismus, in 23 patients (56%); muscle stiffness and myoclonus in 9 (22%); dysesthesias or pruritus in 7 (17%); and cacosmia with dysgeusia in 2 (5%). Five patients (12%) never developed muscle stiffness. The median (range) mRS score at nadir was 5 (3-5). All patients received immunotherapy. Eleven patients died, 8 from complications of PERM. There were 12 relapses in 10 (28%) of 36 patients who lived >6 months. All relapses responded to immunotherapy. The functional status at the last visit, median time 24 months (IQR: 18-72 months), was good (mRS score <3) in 23 (70%) of the 33 patients who did not die from PERM. Age (HR: 1.06; 95% CI 1.01-1.11; p = 0.019) and admission to the intensive care unit (HR: 5.26; 95% CI 1.41-19.57, p = 0.013) were independent predictors of bad outcome (mRS score ≥3). DISCUSSION:GlyR antibody-mediated PERM is a rapidly progressive and severe disease that predominantly affects men and frequently presents with brainstem involvement. Its distinct demographic and clinical features suggest that it should be considered separately from SPSDs, which typically follows a chronic course and is more commonly associated with glutamic acid decarboxylase antibodies.

Detecting neural surface antibodies (NSAbs) is essential for diagnosing autoimmune encephalitis. The recommended diagnostic strategy involves initial screening with tissue-based assays (TBAs), followed by confirmation with cell-based assays (CBAs). While specialized centers use in-house TBAs, many clinical laboratories depend on commercial TBAs, whose accuracy is yet to be fully assessed. We selected 92 CSF and 99 serum samples from patients with autoimmune encephalitis and NSAbs confirmed by in-house TBAs and CBAs (20 samples each for AMPAR, GABAAR, GABABR, IgLON5, LGI1, NMDAR, and CASPR2; 19 for mGluR5; 17 for DPPX; and 15 for mGluR1 antibodies), along with 50 CSF and 50 serum samples from negative controls. We assessed the performance of a commercial indirect immunofluorescence (IIF)-TBA (EUROIMMUN). Slides were evaluated as "positive" or "negative" by 2 experienced investigators and 2 less experienced raters. Discordant results were re-evaluated through interrater discussion and assessed using Cohen's kappa. The experienced raters agreed on 94% (133/142) of CSF and 88% (131/149) of serum classifications (Cohen's kappa = 0.87 and 0.75, respectively, p < 0.001). Among CSF samples, 75% (106/142) were correctly identified while 19% (27/142) were misclassified (13 false positives, 14 false negatives). Among serum samples, 66% (98/149) were correctly identified while 22% (33/149) were misclassified (11 false positives, 22 false negatives). The poorest performance was seen in detecting NMDAR, GABAAR, and mGluR5 Abs, which were not identified in 5 of 10, 6 of 10, and 5 of 9 serum samples and in 4 of 10, 5 of 10, and 5 of 10 CSF samples, respectively. The overall sensitivity of the commercial IIF-TBA was 84% for CSF and 76% for serum while the specificity was 72% for CSF and 73% for serum. Less experienced raters correctly identified 69% (98/142) of CSF samples and 73% (109/149) of serum samples and misclassified 13% (18/142) of CSF samples and 11% (16/149) of serum samples, and 18% (26/142) of CSF samples and 16% (24/149) of serum samples remained discordant. The diagnostic performance of EUROIMMUN IIF-TBA in detecting NSAbs in autoimmune encephalitis is suboptimal. NMDAR antibodies, among the most common NSAbs, can be missed in 50% of cases. This commercial TBA should not be used alone as a screening method nor as a confirmatory technique for NSAbs.

We report a patient with tremor and cerebellar syndrome for whom screening by immunochemistry and later immunoblot confirmation did not disclose other antibodies, except for anti-diacylglycerol lipase alpha (DAGLA). Other etiologies for a cerebellar syndrome were ruled out. Clinical improvement following cancer therapy supports a paraneoplastic origin.

Antibodies directed against the enzyme diacylglycerol lipase alpha (DAGLA) have been recently discovered to cause a severe autoimmune cerebellar syndrome. We report a patient with DAGLA antibodies with prominent tremor and ataxia occurring in the context of a malignant melanoma, indicating that these antibodies may also occur in paraneoplastic cerebellar degeneration.