Comparative Study of Paraneoplastic and Nonparaneoplastic Autoimmune Encephalitis With GABABR Antibodies.

BACKGROUND AND OBJECTIVES: While patients with paraneoplastic autoimmune encephalitis (AE) with gamma-aminobutyric-acid B receptor antibodies (GABABR-AE) have poor functional outcomes and high mortality, the prognosis of nonparaneoplastic cases has not been well studied. METHODS: Patients with GABABR-AE from the French and the Dutch Paraneoplastic Neurologic Syndromes Reference Centers databases were retrospectively included and their data collected; the neurologic outcomes of paraneoplastic and nonparaneoplastic cases were compared. Immunoglobulin G (IgG) isotyping and human leukocyte antigen (HLA) genotyping were performed in patients with available samples. RESULTS: A total of 111 patients (44/111 [40%] women) were enrolled, including 84 of 111 (76%) paraneoplastic and 18 of 111 (16%) nonparaneoplastic cases (cancer status was undetermined for 9 patients). Patients presented with seizures (88/111 [79%]), cognitive impairment (54/111 [49%]), and/or behavioral disorders (34/111 [31%]), and 54 of 111 (50%) were admitted in intensive care unit (ICU). Nonparaneoplastic patients were significantly younger (median age 54 years [range 19-88] vs 67 years [range 50-85] for paraneoplastic cases, p < 0.001) and showed a different demographic distribution. Nonparaneoplastic patients more often had CSF pleocytosis (17/17 [100%] vs 58/78 [74%], p = 0.02), were almost never associated with KTCD16-abs (1/16 [6%] vs 61/70 [87%], p < 0.001), and were more frequently treated with second-line immunotherapy (11/18 [61%] vs 18/82 [22%], p = 0.003). However, no difference of IgG subclass or HLA association was observed, although sample size was small (10 and 26 patients, respectively). After treatment, neurologic outcome was favorable (mRS ≤2) for 13 of 16 (81%) nonparaneoplastic and 37 of 84 (48%) paraneoplastic cases (p = 0.03), while 3 of 18 (17%) and 42 of 83 (51%) patients had died at last follow-up (p = 0.008), respectively. Neurologic outcome no longer differed after adjustment for confounding factors but seemed to be negatively associated with increased age and ICU admission. A better survival was associated with nonparaneoplastic cases, a younger age, and the use of immunosuppressive drugs. DISCUSSION: Nonparaneoplastic GABABR-AE involved younger patients without associated KCTD16-abs and carried better neurologic and vital prognoses than paraneoplastic GABABR-AE, which might be due to a more intensive treatment strategy. A better understanding of immunologic mechanisms underlying both forms is needed.

HLA-DQB1*05 subtypes and not DRB1*10:01 mediates risk in anti-IgLON5 disease.

Anti-IgLON5 disease is a rare and likely underdiagnosed subtype of autoimmune encephalitis. The disease displays a heterogeneous phenotype that includes sleep, movement, and bulbar-associated dysfunction. Presence of IgLON5-antibodies in CSF/serum, together with a strong association with HLA-DRB1*10:01∼DQB1*05:01, support an autoimmune basis. In this study, a multicentric HLA study of 87 anti-IgLON5 patients revealed a stronger association with HLA-DQ than HLA-DR. Specifically, we identified a predisposing rank-wise association with HLA-DQA1*01:05∼DQB1*05:01, HLA-DQA1*01:01∼DQB1*05:01 and HLA-DQA1*01:04∼DQB1*05:03 in 85% of patients. HLA sequences and binding cores for these three DQ heterodimers were similar, unlike those of linked DRB1 alleles, supporting a causal link to HLA-DQ. This association was further reflected in an increasingly later age of onset across each genotype group, with a delay of up to 11 years, while HLA-DQ-dosage dependent effects were also suggested by reduced risk in the presence of non-predisposing DQ1 alleles. The functional relevance of the observed HLA-DQ molecules was studied with competition binding assays. These proof-of-concept experiments revealed preferential binding of IgLON5 in a post-translationally modified, but not native, state to all three risk-associated HLA-DQ receptors. Further, a deamidated peptide from the Ig2-domain of IgLON5 activated T cells in two patients, compared to one control carrying HLA-DQA1*01:05∼DQB1*05:01. Taken together, these data support a HLA-DQ-mediated T cell response to IgLON5 as a potentially key step in the initiation of autoimmunity in this disease.

Detection of High-Risk Paraneoplastic Antibodies against TRIM9 and TRIM67 Proteins.

OBJECTIVE: Co-occurring anti-tripartite motif-containing protein 9 and 67 autoantibodies (TRIM9/67-IgG) have been reported in only a very few cases of paraneoplastic cerebellar syndrome. The value of these biomarkers and the most sensitive methods of TRIM9/67-IgG detection are not known. METHODS: We performed a retrospective, multicenter study to evaluate the cerebrospinal fluid and serum of candidate TRIM9/67-IgG cases by tissue-based immunofluorescence, peptide phage display immunoprecipitation sequencing, overexpression cell-based assay (CBA), and immunoblot. Cases in which TRIM9/67-IgG was detected by at least 2 assays were considered TRIM9/67-IgG positive. RESULTS: Among these cases (n = 13), CBA was the most sensitive (100%) and revealed that all cases had TRIM9 and TRIM67 autoantibodies. Of TRIM9/67-IgG cases with available clinical history, a subacute cerebellar syndrome was the most common presentation (n = 7/10), followed by encephalitis (n = 3/10). Of these 10 patients, 70% had comorbid cancer (7/10), 85% of whom (n = 6/7) had confirmed metastatic disease. All evaluable cancer biopsies expressed TRIM9 protein (n = 5/5), whose expression was elevated in the cancerous regions of the tissue in 4 of 5 cases. INTERPRETATION: TRIM9/67-IgG is a rare but likely high-risk paraneoplastic biomarker for which CBA appears to be the most sensitive diagnostic assay. ANN NEUROL 2023;94:1086-1101.

Different Genetic Signatures of Small-Cell Lung Cancer Characterize Anti-GABAB R and Anti-Hu Paraneoplastic Neurological Syndromes.

OBJECTIVE: Small-cell lung cancer (SCLC) is the malignancy most frequently associated with paraneoplastic neurological syndromes (PNS) and can trigger different antibody responses against intracellular (Hu) or neuronal surface (GABAB R) antigens. Our aim was to clarify whether the genomic and transcriptomic features of SCLC are different in patients with anti-GABAB R or anti-Hu PNS compared with SCLC without PNS. METHODS: A total of 76 SCLC tumor samples were collected: 34 anti-Hu, 14 anti-GABAB R, and 28 SCLC without PNS. The study consisted of 4 steps: (1) pathological confirmation; (2) next generation sequencing using a panel of 98 genes, including those encoding the autoantibodies targets ELAVL1-4, GABBR1-2, and KCTD16; (3) genome-wide copy number variation (CNV); and (4) whole-transcriptome RNA sequencing. RESULTS: CNV analysis revealed that patients with anti-GABAB R PNS commonly have a gain in chromosome 5q, which contains KCTD16, whereas anti-Hu and control patients often harbor a loss. No significantly different number of mutations regarding any onconeural genes was observed. Conversely, the transcriptomic profile of SCLC was different, and the differentially expressed genes allowed effective clustering of the samples into 3 groups, reflecting the antibody-based classification, with an overexpression of KCTD16 specific to anti-GABAB R PNS. Pathway analysis revealed that tumors of patients with anti-GABAB R encephalitis were enriched in B-cell signatures, as opposed to those of patients with anti-Hu, in which T-cell- and interferon-γ-related signatures were overexpressed. INTERPRETATION: SCLC genetic and transcriptomic features differentiate anti-GABAB R, anti-Hu, and non-PNS tumors. The role of KCTD16 appears to be pivotal in the tumor immune tolerance breakdown of anti-GABAB R PNS. ANN NEUROL 2023;94:1102-1115.

Early-Stage Contactin-Associated Protein-like 2 Limbic Encephalitis: Clues for Diagnosis.

BACKGROUND AND OBJECTIVES: Previous studies suggested that autoimmune limbic encephalitis with antibodies against contactin-associated protein-like 2 (CASPR2-encephalitis) is clinically heterogeneous and progresses slowly, preventing its early recognition. We aimed to describe the onset and progression of CASPR2-encephalitis and to assess long-term outcomes. METHODS: We retrospectively analyzed the medical records of all patients whose CSF tested positive for anti-CASPR2 antibodies in our center between 2006 and 2020. Standardized telephone interviews of all available patients and relatives were conducted, assessing long-term functional independence using the Functional Activity Questionnaire (FAQ) and quality of life using the 36-Item Short-Form Survey (SF36). RESULTS: Forty-eight patients were included (98% males; median age 64 years), and 35 participated in telephone interviews (73%). At onset, 81% had at least 1 neurologic symptom among the following: limbic (54%), peripheral nerve hyperexcitability (PNH; 21%), and/or cerebellar symptoms (17%). Most of the patients (75%) had initially symptoms of only one of these categories. Limbic symptoms at onset included mostly seizures (33%), while memory disturbances were less frequent (10%). PNH signs were mostly neuropathic pain (9/10 patients). Other symptoms seen at onset included asthenia (33%), mood disorders (25%), and insomnia (21%); 19% of patients did not show any limbic, peripheral, or cerebellar symptom at onset but only asthenia (15%), mood disorders (6%), weight loss (8%), dysautonomia (4%), and/or insomnia (2%). The peak of the disease was attained in median 16.7 months after onset. Over the study period (median follow-up, 58.8 months, range 10.6-189.1), 77% of patients developed ≥3 core CASPR2 symptoms and 42% fulfilled the diagnostic criteria for autoimmune limbic encephalitis, although all patients ultimately developed limbic symptoms. At the last visit, most interviewed patients (28/35 patients, 80%; median, 5 years after onset) had recovered functional independence (FAQ <9) while only the vitality subscore of the SF36 was lower than normative data (mean 49.9 vs 58.0, p = 0.0369). DISCUSSION: CASPR2-encephalitis has a progressive course and is highly heterogeneous at the early stage. In men older than 50 years, otherwise unexplained seizures, cerebellar ataxia, and/or neuropathic pain are suggestive of early-stage CASPR2-encephalitis, especially if they coincide with recent asthenia, mood disorders, or insomnia.

SOX1 antibody-related paraneoplastic neurological syndromes: clinical correlates and assessment of laboratory diagnostic techniques.

OBJECTIVE: To describe the clinical associations of SOX1 antibodies (SOX1-Abs), determine the accuracy of various detection techniques, and propose laboratory criteria to identify definite paraneoplastic neurological syndromes (PNS) associated with SOX1-Abs. METHODS: Single-center, retrospective study of patients referred to the French Reference Center between 2009 and 2019 for confirmation of SOX1-Ab positivity, without concurrent neural antibodies. Patients were classified according to the updated diagnostic PNS criteria; biological samples were systematically retested with three distinct techniques (line blot, cell-based assay, indirect immunofluorescence). RESULTS: Among 77 patients with isolated SOX1-Ab positivity, 23 (29.9%) fulfilled the criteria for definite PNS; all of them had lung cancer (mostly small-cell) and presented mainly with Lambert-Eaton myasthenic syndrome (10/23) and rapidly progressive cerebellar ataxia (6/23). SOX1-Ab positivity varied depending on the laboratory methods which were used, and a single technique was not sufficient to draw conclusions about the PNS diagnosis. The combination of an antigen-specific test (line blot and/or cell-based assay) and immunofluorescence showed the highest accuracy (81.5%, 95% CI 70.0-90.1) in identifying definite PNS. Moreover, when the PNS-Care score was recalculated assigning three points at the laboratory-level only to patients with positive "antigenic-specific test + immunofluorescence" and 0 points to the remaining cases, a higher certainty for definite and non-PNS was achieved (from 41/77, 53.2%, to 60/77, 77.9%; p < 0.001). CONCLUSION: SOX1-Abs should be considered high-risk antibodies only when detected with a positive antigenic-specific test and immunofluorescence. Other laboratory results and clinical associations different from Lambert-Eaton myasthenic syndrome and rapidly progressive cerebellar ataxia should be carefully reassessed to rule out false positivity and alternative diagnoses.

Cerebellar Ataxia With Anti-DNER Antibodies: Outcomes and Immunologic Features.

BACKGROUND AND OBJECTIVES: There is no report on the long-term outcomes of ataxia with antibodies against Delta and Notch-like epidermal growth factor-related (DNER). We aimed to describe the clinical-immunologic features and long-term outcomes of patients with anti-DNER antibodies. METHODS: Patients tested positive for anti-DNER antibodies between 2000 and 2020 were identified retrospectively. In those with available samples, immunoglobulin G (IgG) subclass analysis, longitudinal cerebellum volumetry, human leukocyte antigen isotyping, and CSF proteomic analysis were performed. Rodent brain membrane fractionation and organotypic cerebellar slices were used to study DNER cell-surface expression and human IgG binding to the Purkinje cell surface. RESULTS: Twenty-eight patients were included (median age, 52 years, range 19-81): 23 of 28 (82.1%) were male and 23 of 28 (82.1%) had a hematologic malignancy. Most patients (27/28, 96.4%) had cerebellar ataxia; 16 of 28 (57.1%) had noncerebellar symptoms (cognitive impairment, neuropathy, and/or seizures), and 27 of 28 (96.4%) became moderately to severely disabled. Half of the patients (50%) improved, and 32.1% (9/28) had no or slight disability at the last visit (median, 26 months; range, 3-238). Good outcome significantly associated with younger age, milder clinical presentations, and less decrease of cerebellar gray matter volumes at follow-up. No human leukocyte antigen association was identified. Inflammation-related proteins were overexpressed in the patients' CSF. In the rodent brain, DNER was enriched in plasma membrane fractions. Patients' anti-DNER antibodies were predominantly IgG1/3 and bound live Purkinje cells in vitro. DISCUSSION: DNER ataxia is a treatable condition in which nearly a third of patients have a favorable outcome. DNER antibodies bind to the surface of Purkinje cells and are therefore potentially pathogenic, supporting the use of B-cell-targeting treatments.

Human Leukocyte Antigen Association Study Reveals DRB1*04:02 Effects Additional to DRB1*07:01 in Anti-LGI1 Encephalitis.

BACKGROUND AND OBJECTIVES: To study human leukocyte antigen (HLA) allele associations in anti-leucine-rich glioma-inactivated 1 (LGI1) encephalitis. METHODS: A multiethnic cohort of 269 patients with anti-LGI1 encephalitis and 1,359 controls was included. Four-digit HLA sequencing and genome wide association single-nucleotide polymorphism typing imputation (0.99 concordance) were used for HLA typing. Significance of primary and secondary associations was tested using χ2, Fisher exact tests, or logistic regression with the control of population stratification covariates when applicable. RESULTS: DRB1*07:01 and DQA1*02:01, 2 alleles in strong linkage disequilibrium, were associated with the disease (90% vs 24%, OR = 27.8, p < 10e-50) across ethnicity independent of variation at DRB3 and DQB1, 2 flanking HLA loci. DRB1*07:01 homozygosity was associated with a doubling of risk (OR = 2.1, p = 0.010), suggesting causality. DRB1*07:01 negative subjects were younger (p = 0.003) and more frequently female (p = 0.015). Three patients with malignant thymomas did not carry DRB1*07:01, whereas patients with other tumors had high DRB1*07:01 frequency, suggesting that the presence of tumors other than thymomas may be coincidental and not causal. In both DRB1*07:01 heterozygous individuals and DRB1*07:01 negative subjects, DRB1*04:02 was associated with anti-LGI1 encephalitis, indicating an independent effect of this allele (OR = 6.85, p = 4.57 × 10-6 and OR = 8.93, p = 2.50 × 10-3, respectively). DRB1*04:02 was also independently associated with younger age at onset (ß = -6.68, p = 9.78 × 10-3). Major histocompatibility complex peptide-binding predictions using LGI1-derived peptides revealed divergent binding propensities for DRB1*04:02 and DRB1*07:01 alleles, suggesting independent pathogenic mechanisms. DISCUSSION: In addition to the established primary DRB1*07:01 association in anti-LGI1 encephalitis, we observe a secondary effect of DRB1*04:02 with lower age at onset. Our study provides evidence for secondary effects within HLA locus that correlate with clinical phenotypes in anti-LGI1 encephalitis.

Immunopathogenesis and proposed clinical score for identifying Kelch-like protein-11 encephalitis.

In this study, we report the clinical features of Kelch-like protein 11 antibody-associated paraneoplastic neurological syndrome, design and validate a clinical score to facilitate the identification of patients that should be tested for Kelch-like protein 11 antibodies, and examine in detail the nature of the immune response in both the brain and the tumour samples for a better characterization of the immunopathogenesis of this condition. The presence of Kelch-like protein 11 antibodies was retrospectively assessed in patients referred to the French Reference Center for paraneoplastic neurological syndrome and autoimmune encephalitis with (i) antibody-negative paraneoplastic neurological syndrome [limbic encephalitis (n = 105), cerebellar degeneration (n = 33)] and (ii) antibody-positive paraneoplastic neurological syndrome [Ma2-Ab encephalitis (n = 34), antibodies targeting N-methyl-D-aspartate receptor encephalitis with teratoma (n = 49)]. Additionally, since 1 January 2020, patients were prospectively screened for Kelch-like protein 11 antibodies as new usual clinical practice. Overall, Kelch-like protein 11 antibodies were detected in 11 patients [11/11, 100% were male; their median (range) age was 44 (35-79) years], 9 of them from the antibody-negative paraneoplastic neurological syndrome cohort, 1 from the antibody-positive (Ma2-Ab) cohort and 1 additional prospectively detected patient. All patients manifested a cerebellar syndrome, either isolated (4/11, 36%) or part of a multi-system neurological disorder (7/11, 64%). Additional core syndromes were limbic encephalitis (5/11, 45%) and myelitis (2/11, 18%). Severe weight loss (7/11, 64%) and hearing loss/tinnitus (5/11, 45%) were common. Rarer neurologic manifestations included hypersomnia and seizures (2/11, 18%). Two patients presented phenotypes resembling primary neurodegenerative disorders (progressive supranuclear palsy and flail arm syndrome, respectively). An associated cancer was found in 9/11 (82%) patients; it was most commonly (7/9, 78%) a spontaneously regressed ('burned-out') testicular germ cell tumour. A newly designed clinical score (MATCH score: male, ataxia, testicular cancer, hearing alterations) with a cut-off ≥4 successfully identified patients with Kelch-like protein 11 antibodies (sensitivity 78%, specificity 99%). Pathological findings (three testicular tumours, three lymph node metastases of testicular tumours, one brain biopsy) showed the presence of a T-cell inflammation with resulting anti-tumour immunity in the testis and one chronic, exhausted immune response-demonstrated by immune checkpoint expression-in the metastases and the brain. In conclusion, these findings suggest that Kelch-like protein 11 antibody paraneoplastic neurological syndrome is a homogeneous clinical syndrome and its detection can be facilitated using the MATCH score. The pathogenesis is probably T-cell mediated, but the stages of inflammation are different in the testis, metastases and the brain.

Argonaute Autoantibodies as Biomarkers in Autoimmune Neurologic Diseases.

OBJECTIVE: To identify and characterize autoantibodies (Abs) as novel biomarkers for an autoimmune context in patients with central and peripheral neurologic diseases. METHODS: Two distinct approaches (immunoprecipitation/mass spectrometry-based proteomics and protein microarrays) and patients' sera and CSF were used. The specificity of the identified target was confirmed by cell-based assay (CBA) in 856 control samples. RESULTS: Using the 2 methods as well as sera and CSF of patients with central and peripheral neurologic involvement, we identified Abs against the family of Argonaute proteins (mainly AGO1 and AGO2), which were already reported in systemic autoimmunity. AGO-Abs were mostly of immunoglobulin G 1 subclass and conformation dependent. Using CBA, AGO-Abs were detected in 21 patients with a high suspicion of autoimmune neurologic diseases (71.4% were women; median age 57 years) and only in 4/856 (0.5%) controls analyzed by CBA (1 diagnosed with small-cell lung cancer and the other 3 with Sjögren syndrome). Among the 21 neurologic patients identified, the main clinical presentations were sensory neuronopathy (8/21, 38.1%) and limbic encephalitis (6/21, 28.6%). Fourteen patients (66.7%) had autoimmune comorbidities and/or co-occurring Abs, whereas AGO-Abs were the only autoimmune biomarker for the remaining 7/21 (33.3%). Thirteen (61.9%) patients were treated with immunotherapy; 8/13 (61.5%) improved, and 3/13 (23.1%) remained stable, suggesting an efficacy of these treatments. CONCLUSIONS: AGO-Abs might be potential biomarkers of autoimmunity in patients with central and peripheral nonparaneoplastic neurologic diseases. In 7 patients, AGO-Abs were the only biomarkers; thus, their identification may be useful to suspect the autoimmune character of the neurologic disorder. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that AGO-Abs are more frequent in patients with autoimmune neurologic diseases than controls.

Distinctive clinical presentation and pathogenic specificities of anti-AK5 encephalitis.

Limbic encephalitis with antibodies against adenylate kinase 5 (AK5) has been difficult to characterize because of its rarity. In this study, we identified 10 new cases and reviewed 16 previously reported patients, investigating clinical features, IgG subclasses, human leucocyte antigen and CSF proteomic profiles. Patients with anti-AK5 limbic encephalitis were mostly male (20/26, 76.9%) with a median age of 66 years (range 48-94). The predominant symptom was severe episodic amnesia in all patients, and this was frequently associated with depression (17/25, 68.0%). Weight loss, asthenia and anorexia were also highly characteristic, being present in 11/25 (44.0%) patients. Although epilepsy was always lacking at disease onset, seizures developed later in a subset of patients (4/25, 16.0%). All patients presented CSF abnormalities, such as pleocytosis (18/25, 72.0%), oligoclonal bands (18/25, 72.0%) and increased Tau (11/14, 78.6%). Temporal lobe hyperintensities were almost always present at disease onset (23/26, 88.5%), evolving nearly invariably towards severe atrophy in subsequent MRIs (17/19, 89.5%). This finding was in line with a poor response to immunotherapy, with only 5/25 (20.0%) patients responding. IgG1 was the predominant subclass, being the most frequently detected and the one with the highest titres in nine CSF-serum paired samples. A temporal biopsy from one of our new cases showed massive lymphocytic infiltrates dominated by both CD4+ and CT8+ T cells, intense granzyme B expression and abundant macrophages/microglia. Human leucocyte antigen (HLA) analysis in 11 patients showed a striking association with HLA-B*08:01 [7/11, 63.6%; odds ratio (OR) = 13.4, 95% confidence interval (CI): 3.8-47.4], C*07:01 (8/11, 72.7%; OR = 11.0, 95% CI: 2.9-42.5), DRB1*03:01 (8/11, 72.7%; OR = 14.4, 95% CI: 3.7-55.7), DQB1*02:01 (8/11, 72.7%; OR = 13.5, 95% CI: 3.5-52.0) and DQA1*05:01 (8/11, 72.7%; OR = 14.4, 95% CI: 3.7-55.7) alleles, which formed the extended haplotype B8-C7-DR3-DQ2 in 6/11 (54.5%) patients (OR = 16.5, 95% CI: 4.8-57.1). Finally, we compared the CSF proteomic profile of five anti-AK5 patients with that of 40 control subjects and 10 cases with other more common non-paraneoplastic limbic encephalitis (five with antibodies against leucine-rich glioma inactivated 1 and five against contactin-associated protein-like 2), as well as 10 cases with paraneoplastic neurological syndromes (five with antibodies against Yo and five against Ma2). These comparisons revealed 31 and seven significantly upregulated proteins in anti-AK5 limbic encephalitis, respectively mapping to apoptosis pathways and innate/adaptive immune responses. These findings suggest that the clinical manifestations of anti-AK5 limbic encephalitis result from a distinct T cell-mediated pathogenesis, with major cytotoxicity-induced apoptosis leading to a prompt and aggressive neuronal loss, likely explaining the poor prognosis and response to immunotherapy.

Clinical and Prognostic Value of Immunogenetic Characteristics in Anti-LGI1 Encephalitis.

OBJECTIVE: Antibodies against leucine-rich glioma-inactivated 1 (LGI1-Abs) characterize a limbic encephalitis (LE) strongly associated with HLA-DRB1*07:01, although some patients lack LGI1-Abs in CSF or do not carry this allele. Whether they represent a different subtype of disease or have different prognoses is unclear. METHODS: Retrospective analysis of clinical features, IgG isotypes, and outcome according to LGI1-Ab CSF positivity and DRB1*07:01 in a cohort of anti-LGI1 LE patients. RESULTS: Patients with LGI1-Abs detected in both CSF and serum (105/134, 78%) were compared with those who were CSF negative (29/134, 22%). Both groups had similar clinical features and serum levels, but CSF-positive patients had shorter diagnostic delay, more frequently hyponatremia, inflammatory CSF, and abnormal MRI (p < 0.05). Human leukocyte antigen (HLA) genotyping was performed in 72/134 (54%) patients and 63/72 (88%) carried DRB1*07:01. Noncarriers (9/72, 12%) were younger, more commonly women, and had less frequently psychiatric and frontal symptoms (p < 0.05). No difference in IgG isotypes according to CSF positivity or HLA was found (p > 0.05). HLA and IgG isotypes were not associated with poor outcome (mRS >2 at last follow-up) in univariate analyses; CSF positivity was only identified as a poor outcome predictor in the multivariate analysis including the complete follow-up, whereas age and female sex also remained when just the first year was considered. CONCLUSIONS: LE without CSF LGI1-Abs is clinically indistinguishable and likely reflects just a lesser LGI1-Ab production. HLA association is sex and age biased and presents clinical particularities, suggesting subtle differences in the immune response. Long-term outcome depends mostly on demographic characteristics and the intensity of the intrathecal synthesis.

Clinical features, prognostic factors, and antibody effects in anti-mGluR1 encephalitis.

OBJECTIVE: To clinically characterize patients with anti-metabotropic glutamate receptor (mGluR) 1 encephalitis, to identify prognostic factors, and to study the immunoglobulin G (IgG) subclasses and effects of antibodies on neuronal mGluR1 clusters. METHODS: Clinical information on new and previously reported patients was reviewed. Antibodies to mGluR1 and IgG subclasses were determined with brain immunohistochemistry and cell-based assays, and their effects on mGluR1 clusters were studied on rat hippocampal neurons. RESULTS: Eleven new patients were identified (10 adults, 1 child);4 were female. In these and 19 previously reported cases (n = 30, median age 55 years), the main clinical manifestation was a subacute cerebellar syndrome that in 25 (86%) patients was associated with behavioral/cognitive changes or other neurologic symptoms. A tumor was found in 3 of 26 (11%). Brain MRI was abnormal in 7 of 19 (37%) at onset and showed cerebellar atrophy in 10 of 12 (83%) at follow-up. Twenty-five of 30 (83%) patients received immunotherapy. Follow-up was available for 25: 13 (52%) had clinical stabilization; 10 (40%) showed significant improvement; and 2 died. At the peak of the disease, patients with bad outcome at 2 years (modified Rankin Scale score > 2, n = 7) were more likely to have higher degree of initial disability, as reflected by a worse Scale for Assessment and Rating of Ataxia score, and more frequent need of assistance to walk. Antibodies to mGluR1 were mainly IgG1 and caused a significant decrease of mGluR1 clusters in cultured neurons. CONCLUSIONS: Anti-mGluR1 encephalitis manifests as a severe cerebellar syndrome, often resulting in long-term disability and cerebellar atrophy. The antibodies are pathogenic and cause significant decrease of mGluR1 clusters in cultured neurons.

Anti-CASPR2 clinical phenotypes correlate with HLA and immunological features.

OBJECTIVE: Antibodies against contactin-associated protein-like 2 (CASPR2-Abs) have been described in acquired neuromyotonia, limbic encephalitis (LE) and Morvan syndrome (MoS). However, it is unknown whether these constitute one sole spectrum of diseases with the same immunopathogenesis or three distinct entities with different mechanisms. METHODS: A cluster analysis of neurological symptoms was performed in a retrospective cohort of 56 CASPR2-Abs patients. In parallel, immunological features and human leucocyte antigen (HLA) were studied. RESULTS: Cluster analysis distinguished patients with predominant limbic symptoms (n=29/56) from those with peripheral nerve hyperexcitability (PNH; n=27/56). In the limbic-prominent group, limbic features were either isolated (LE/-; 18/56, 32.1%), or combined with extralimbic symptoms (LE/+; 11/56, 19.6%). Those with PNH were separated in one group with severe PNH and extralimbic involvement (PNH/+; 16/56, 28.6%), resembling historical MoS descriptions; and one group with milder and usually isolated PNH (PNH/-; 11/56, 19.6%). LE/- and LE/+ patients shared immunogenetic characteristics demonstrating a homogeneous entity. HLA-DRB1*11:01 was carried more frequently than in healthy controls only by patients with LE (94.1% vs 18.3%; p=1.3×10-10). Patients with LE also had serum titres (median 1:40 960) and rates of cerebrospinal fluid positivity (93.1%) higher than the other groups (p<0.05). Conversely, DRB1*11:01 association was absent in PNH/+ patients, but only they had malignant thymoma (87.5%), serum antibodies against leucine-rich glioma-inactivated 1 protein (66.7%) and against netrin-1 receptor deleted in colorectal carcinoma (53.8%), and myasthenia gravis (50.0%). INTERPRETATION: Symptoms' distribution supports specific clinical phenotypes without overlap between LE and MoS. The distinct immunogenetic characteristics shared by all patients with LE and the particular oncological and autoimmune associations of MoS suggest two very different aetiopathogenesis.

Transient Neurological Symptoms Preceding Cerebellar Ataxia with Glutamic Acid Decarboxylase Antibodies.

A prompt diagnosis and treatment of patients with autoimmune cerebellar ataxia (CA) with antibodies against glutamic acid decarboxylase (GAD-Abs) may lead to a better prognosis. Herein, we report prodromal transient neurological symptoms that should raise clinical suspicion of CA with GAD-Abs. We initially identified a 70-year-old man who presented a first acute episode of vertigo, diplopia, and ataxia lasting 2 weeks. Two months later, he experienced a similar episode along with new-onset gaze-evoked nystagmus. After 4 months, downbeat nystagmus, left limb dysmetria, and gait ataxia progressively appeared, and an autoimmune CA was diagnosed based on the positivity of GAD-Abs in serum and cerebrospinal fluid (CSF). We searched retrospectively for similar presentations in a cohort of 31 patients diagnosed with CA and GAD-Abs. We found 11 (35.4%) patients (all women, median age 62 years; 8/11 [72.7%] with autoimmune comorbidities) with transient neurological symptoms antedating CA onset by a median of 3 months, including vertigo in 9 (81.8%; described as paroxysmal in 8) and fluctuating diplopia in 3 (27.3%) patients. The identification of transient neurological symptoms of unknown etiology, such as paroxysmal vertigo and fluctuating diplopia, should lead to GAD-Abs testing in serum and CSF, especially in patients with autoimmune comorbidities.

Diagnostic yield of commercial immunodots to diagnose paraneoplastic neurologic syndromes.

OBJECTIVE: To investigate the diagnostic yield of commercial immunodots to detect onconeural antibodies associated with paraneoplastic neurologic syndromes (PNSs), we analyzed the proportion of confirmed positive results using alternative techniques. METHODS: Sera (n = 5,300) of patients with suspected PNS were tested by PNS+2 blot (Ravo Diagnostika; January 2016-May 2017) or EUROLINE PNS 12 Ag (Euroimmun; July 2017-November 2018). Positive samples were further explored by in-house indirect immunofluorescence and a third in-house technique (Western blot or cell-based assay) using recombinant protein. Those found negative by these 2 techniques were considered as nonconfirmed. We analyzed the relationship between band intensity and final confirmation. Clinical data were collected for all confirmed results and nonconfirmed EUROLINE immunodots. RESULTS: PNS+2 blot was positive in 128/1,658 (7.7%) sera and confirmed in 47/128 (36.7%). EUROLINE was positive in 186/3,626 (5.1%) and confirmed in 56/186 (30.1%). Confirmation was highly variable among the antibodies tested, from 7.2% (PNS+2 blot) and 5.8% (EUROLINE) for anti-Yo to 88.2% (PNS+2 blot) and 65.0% (EUROLINE) for anti-Hu. None of the 27 weak positive sera by EUROLINE was confirmed. Band intensity in confirmed cases was variable among the antibodies from strong positive for all anti-Yo (n = 3) and anti-Hu (n = 11) to positive (n = 19) or strong positive (n = 9) for anti-SOX1. Among patients with a nonconfirmed EUROLINE result and available clinical information, all had an alternative diagnosis, and only 6.7% had cancer. CONCLUSIONS: Immunodots may be useful for PNS screening, but a threshold should be established for each antibody, and clinical information and confirmation by other techniques are essential. CLASSIFICATION OF EVIDENCE: The study provides Class IV evidence that immunodot assays for onconeural antibodies accurately identify patients with paraneoplastic neurologic syndromes.

Increased frequency of anti-Ma2 encephalitis associated with immune checkpoint inhibitors.

OBJECTIVE: To report the induction of anti-Ma2 antibody-associated paraneoplastic neurologic syndrome (Ma2-PNS) in 6 patients after treatment with immune checkpoint inhibitors (ICIs). We also analyzed (1) patient clinical features compared with a cohort of 44 patients who developed Ma2-PNS without receiving ICI treatment and (2) the frequency of neuronal antibody detection before and after ICI implementation. METHODS: Retrospective nationwide study of all patients with Ma2-PNS developed during ICI treatment between 2017 and 2018. RESULTS: Our series of patients included 5 men and 1 woman (median age, 63 years). The patients were receiving nivolumab (n = 3), pembrolizumab (n = 2), or a combination of nivolumab and ipilimumab (n = 1) for treatment of neoplasms that included lung (n = 4) and kidney (n = 1) cancers and pleural mesothelioma (n = 1). Clinical syndromes comprised a combination of limbic encephalitis and diencephalitis (n = 3), isolated limbic encephalitis (n = 2), and a syndrome characterized by ophthalmoplegia and head drop (n = 1). No significant clinical difference was observed between our 6 patients and the overall cohort of Ma2-PNS cases. Post-ICI Ma2-PNS accounted for 35% of the total 17 Ma2-PNS diagnosed in our center over the 2017-2018 biennium. Eight cases had been detected in the preceding biennium 2015-2016, corresponding to a 112% increase of Ma2-PNS frequency since the implementation of ICIs in France. Despite ICI withdrawal and immunotherapy, 4/6 patients died, and the remaining 2 showed a moderate to severe disability. CONCLUSIONS: We show a clear association between ICI use and increased diagnosis of Ma2-PNS. Physicians need to be aware that ICIs can trigger Ma2-PNS because clinical presentation can be challenging.

Isolated seizures are a common early feature of paraneoplastic anti-GABAB receptor encephalitis.

OBJECTIVE: To report the clinical features and long-term outcome of 22 newly diagnosed paraneoplastic patients with GABAB receptor antibodies (GABABR-Abs). METHODS: Retrospective clinical study of CSF-confirmed cases of GABABR-Abs encephalitis. RESULTS: We identified 22 patients (4 female) with GABABR-Abs, with a median age of 64 years (range 55-85). All were paraneoplastic: 20 small-cell lung cancer, one malignant thymoma, and one uncharacterized lung mass. The most frequent first symptom was the isolated recurrent seizures without cognitive inter-ictal impairment in 17 patients (77%). In the other, three presented the first behavioral disorders and two presented de novo status epilepticus (SE). After a median delay of 10 days (range 1-30), the recurrent seizures' phase was followed by an encephalitic phase characterized by confusion in 100% of cases and SE in 81% (n = 17), with 53% (n = 9) non-convulsive SE. Dysautonomic episodes were frequent (36%, n = 8, bradycardia and central apnea) and killed three patients. CSF study was abnormal in 95% of the cases (n = 21). At the encephalitic phase, MRI showed a temporal FLAIR hypersignal in 73% (n = 16) of the cases. First-line immunotherapy was initiated after a median delay of 26 days (range 6-65) from disease onset, and a partial response was observed in 10 out of 20 patients (50%). There was no complete response. Two years after onset, a massive anterograde amnesia affected all still alive patients. Nine patients died from cancer progression (median survival: 1.2 years). CONCLUSION: Paraneoplastic GABABR-Abs encephalitis is characterized by a stereotype presentation with an epilepsy phase before an encephalitic phase with dysautonomia. The functional prognosis is poor.