ObjectiveThe contemporary diagnosis of paraneoplastic neurologic syndromes (PNSs) requires an increasing understanding of their clinical, immunologic, and oncologic heterogeneity. The 2004 PNS criteria are partially outdated due to advances in PNS research in the last 16 years leading to the identification of new phenotypes and antibodies that have transformed the diagnostic approach to PNS. Here, we propose updated diagnostic criteria for PNS.MethodsA panel of experts developed by consensus a modified set of diagnostic PNS criteria for clinical decision making and research purposes. The panel reappraised the 2004 criteria alongside new knowledge on PNS obtained from published and unpublished data generated by the different laboratories involved in the project.ResultsThe panel proposed to substitute “classical syndromes” with the term “high-risk phenotypes” for cancer and introduce the concept of “intermediate-risk phenotypes.” The term “onconeural antibody” was replaced by “high risk” (>70% associated with cancer) and “intermediate risk” (30%–70% associated with cancer) antibodies. The panel classified 3 levels of evidence for PNS: definite, probable, and possible. Each level can be reached by using the PNS-Care Score, which combines clinical phenotype, antibody type, the presence or absence of cancer, and time of follow-up. With the exception of opsoclonus-myoclonus, the diagnosis of definite PNS requires the presence of high- or intermediate-risk antibodies. Specific recommendations for similar syndromes triggered by immune checkpoint inhibitors are also provided.ConclusionsThe proposed criteria and recommendations should be used to enhance the clinical care of patients with PNS and to encourage standardization of research initiatives addressing PNS.

Objective:To define the clinical characteristics, management, and outcome of neurological immune-related adverse events (n-irAEs) of immune checkpoint inhibitors (ICIs).Methods:Systematic review of the literature following the PRISMA guidelines.Results:A total of 694 articles were identified. Two hundred fifty-six articles, with 428 individual patients, met the inclusion criteria. Reports regarding neuromuscular disorders (319/428, 75%) were more frequent than those on central nervous system (CNS) disorders (109/428, 25%). The most common n-irAEs reports were: myositis (136/428, 32%), Guillain-Barré syndrome and other peripheral neuropathies (94/428, 22%), myasthenic syndromes (58/428, 14%), encephalitis (56/428, 13%), cranial neuropathies (31/428, 7%), meningitis (13/428, 3%), CNS demyelinating diseases (8/428, 2%), and myelitis (7/428, 2%). Other CNS disorders were detected in 25/428 (6%) patients. Compared to the whole sample, myasthenic syndromes were significantly more Ab-positive (33/56, 59%; p<0.001). Anti-PD-1/PD-L1 were more frequent in myasthenic syndromes (50/58, 86%; p=0.005) and less common in meningitis (2/13, 15%; p<0.001) and cranial neuropathies (13/31, 42%; p=0.005).Anti-CTLA-4 ICIs were more frequent in meningitis (8/13, 62%; p<0.001) and less common in encephalitis (2/56, 4%; p=0.009) and myositis (12/136, 9%; p=0.01). Combination of different ICIs was more frequent in cranial neuropathies (12/31, 39%; p=0.005). Melanoma was more frequent in patients with peripheral neuropathies (64/94, 68%; p=0.003) and less common in encephalitis (19/56, 34%; p=0.001). The highest mortality rate was reached in myasthenic syndromes (28%).Conclusion:Considering the increasing use of ICI therapy in the forthcoming future, this information can be valuable in assisting neurologists and oncologists in early n-irAEs diagnosis and treatment.

ObjectiveTo 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.MethodsRetrospective nationwide study of all patients with Ma2-PNS developed during ICI treatment between 2017 and 2018.ResultsOur 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.ConclusionsWe 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.

ObjectiveTo describe the spectrum and outcome of central nervous system complications associated with immune checkpoint inhibitors (CNS-ICI).MethodsPatients with CNS-ICI were identified and their characteristics compared with ICI-related peripheral neuropathy (PN-ICI).ResultsWe identified 19 patients with CNS-ICI. The patients were receiving nivolumab (n=8), pembrolizumab (n=6), a combination of ipilimumab-nivolumab (n=3), ipilimumab-durvalumab (n=1), or atezolizumab (n=1). Underlying malignancies included non-small-cell lung cancer (n=8), melanoma (n=3), and other less common tumours (n=8). Neurological phenotypes were limbic encephalitis (n=8), meningoencephalitis (n=4) and cerebellitis (n=4). Two patients developed isolated confusion and one parkinsonism. Associated autoantibodies included onconeural (Ma2, n=7; Hu, n=1), astrocytic (glial fibrillar acidic protein, n=2) and neuronal surface (contactin-associated protein-like 2, n=1) specificities. ICIs were withheld and corticosteroid treatment was given in all cases. Five patients received intravenous immunoglobulin, two rituximab, one plasmapheresis and one infliximab. Overall, six patients died. Readministration of ICI was attempted in three patients, without further relapses. Non-small-cell lung cancer was significantly more frequent in patients with CNS-ICI (p<0.01), while melanoma and ipilimumab treatment were more common in PN-ICI (p<0.01 and p=0.01). Conversely, CNS-ICI cases were more frequently antibody-positive than PN-ICI (p<0.01) and showed a strong trend towards poorer outcome (p=0.053).ConclusionThree main clinical phenotypes characterise CNS complications of ICIs, each with distinct immunological background, disease course and response to treatment. Other clinical manifestations (including parkinsonism and steroid-responsive confusion) are also possible. Underlying cancers, antibody prevalence and outcome appear different from those of patients with PN-ICI.

Objectives:To report the clinical, biological, imaging features, and the clinical course of a French cohort of patients with glial fibrillar acidic protein (GFAP) autoantibodies.Methods:We retrospectively included all patients tested positive for GFAP antibodies in the cerebrospinal fluid, by immunohistochemistry and confirmed by cell-based assay using cells expressing human GFAPα, since 2017, from two French referral centers.Results:We identified 46 patients with GFAP antibodies. Median age at onset was 43 years, and 65% were men. Infectious prodromal symptoms were found in 82%. Other auto-immune diseases were found in 22% of patients, and coexisting neural autoantibodies in 11%. Tumors were present in 24%, and T cell dysfunction in 23%. The most frequent presentation was subacute meningoencephalitis (85%) with cerebellar dysfunction in 57% of cases. Other clinical presentation included myelitis (30%), visual (35%) and peripheral nervous system involvement (24%). MRI showed perivascular radial enhancement in 32%, periventricular T2 hyperintensity in 41%, brainstem involvement in 31%, leptomeningeal enhancement in 26%, and reversible splenial lesions in 4 cases. 33/40 patients had a monophasic course, associated to a good outcome at last follow-up (Rankin Score≤2: 89%), despite a severe clinical presentation. Adult and pediatric features are similar. Thirty-two patients were treated with immunotherapy. 11/22 patients showed negative conversion of GFAP antibodies.Interpretation:GFAP auto-immunity is mainly associated with acute/subacute meningoencephalomyelitis with prodromal symptoms, for which tumors and T cell dysfunction are frequent triggers. The majority of patients followed a monophasic course with a good outcome.

Objective:To clinically characterize patients with anti-metabotropic glutamate receptor (mGluR)1 encephalitis, identify prognostic factors, and study the IgG subclasses and effects of antibodies on neuronal mGluR1 clusters.Methods:Clinical information of 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 females. In these and 19 previously reported cases (n=30, median age 55) the main clinical manifestation was a subacute cerebellar syndrome that in 25 (86%) patients was associated with behavioral/cognitive changes or other neurological symptoms. A tumor was found in 3/26 (11%). Brain MRI was abnormal in 7/19 (37%) at onset and showed cerebellar atrophy in 10/12 (83%) at follow-up. Twenty-five/30 (83%) patients received immunotherapy. Follow-up was available from 25: 13 (52%) had clinical stabilization, 10 (40%) significant improvement, and 2 died. At the peak of the disease, patients with bad outcome (mRS>2, n=7) were more likely to have higher degree of initial disability, as reflected by a worse SARA (Scale for Assessment and Rating of Ataxia) score, and the 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.