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Paraneoplastic neurological syndromes (PNSs) are rare complications of systemic cancers that can affect all parts of the central and/or peripheral nervous system. A body of experimental and clinical data has demonstrated that the pathogenesis of PNSs is immune-mediated. Nevertheless, the mechanisms leading to immune tolerance breakdown in these conditions remain to be elucidated. Despite their rarity, PNSs offer a unique perspective to understand the complex interplay between cancer immunity, effect of immune checkpoint inhibitors (ICIs), and mechanisms underlying the attack of neurons in antibody-mediated neurological disorders, with potentially relevant therapeutic implications. In particular, it is reported that ICI treatment can unleash PNSs and that the immunopathological features of PNS-related tumors are distinctive, showing prominent tumor-infiltrating lymphocytes and germinal center reactions. Intriguingly, similar pathological substrates have gained further attention as potential biomarkers of ICI-sensitivity and oncological prognosis. Moreover, the genetic analysis of PNS-associated tumors has revealed specific molecular signatures and mutations in genes encoding onconeural proteins, leading to the production of highly immunogenic neoantigens. Other than PNSs, autoimmune encephalitides (AEs) comprise a recently described group of disorders characterized by prominent neuropsychiatric symptoms, diverse antibody spectrum, and less tight association with cancer. Other triggering factors seem to be involved in AEs. Recent data have shed light on the importance of preceding infections (in particular, herpes simplex virus encephalitis) in inducing neurological autoimmune disorders in susceptible individuals (those with a selective deficiency in the innate immune system). In addition, in some AEs (e.g. LGI1-antibody encephalitis) an association with specific host-related factors [e.g., human leukocyte antigen (HLA)] was clearly demonstrated. We provide herein a comprehensive review of the most recent findings in the field of PNSs and AEs, with particular focus on their triggering factors and immunopathogenesis.

As the use of cancer immunotherapy with immune checkpoint inhibitors (ICIs) is expanding rapidly for the treatment of many tumor types, it is crucial that both neurologists and oncologists become familiar with the diagnosis and treatment of neurological immune-related adverse events (n-irAEs). These are rare complications, developing in their severe forms in only 1–3% of the patients, but are highly relevant due to their mortality and morbidity burden. The diagnosis of n-irAEs is—however—challenging, as many alternative diagnoses need to be considered in the complex scenario of a patient with advanced cancer developing neurological problems. A tailored diagnostic approach is advisable according to the presentation, clinical history, and known specificities of n-irAEs. Several patterns characterized by distinct clinical, immunological, and prognostic characteristics are beginning to emerge. For example, myasthenia gravis is more likely to develop after anti-programmed cell death protein 1 (PD-1) or anti-programmed cell death ligand 1 (PD-L1) treatment, while meningitis appears more frequently after anti-cytotoxic T lymphocyte antigen-4 (CTLA-4) therapy. Also, peripheral neuropathy and Guillain–Barré syndrome seem to be more common in patients with an underlying melanoma. Central nervous system disorders (CNS) are less frequent and are more often associated with lung cancer, and some of them (especially those with limbic encephalitis and positive onconeural antibodies) have a poor prognosis. Herein, we provide an update of the recent advances in the diagnosis and treatment of neurological toxicities related to ICI use, focusing on the exclusion of alternative diagnoses, diagnostic specificities, and treatment of n-irAEs.

To describe autoantibodies (Abs) against tripartite motif-containing (TRIM) protein 9 and 67 in two patients with paraneoplastic cerebellar degeneration (PCD) associated with lung adenocarcinoma. Abs were characterized using immunohistochemistry, Western blotting, cultures of murine cortical, and hippocampal neurons, immunoprecipitation, mass spectrometry, knockout mice for Trim9 and 67, and cell-based assay. Control samples included sera from 63 patients with small cell lung cancer without any paraneoplastic neurological syndrome, 36 patients with lung adenocarcinoma and PNS, CSF from 100 patients with autoimmune encephalitis, and CSF from 165 patients with neurodegenerative diseases. We found Abs targeting TRIM9 and TRIM67 at high concentration in the serum and the cerebrospinal fluid (CSF) of a 78-year-old woman and a 65-year-old man. Both developed subacute severe cerebellar ataxia. Brain magnetic resonance imaging found no abnormality and no cerebellar atrophy. Both had CSF inflammation with mild pleiocytosis and a few oligoclonal bands. We identified a pulmonary adenocarcinoma, confirming the paraneoplastic neurological syndrome in both patients. They received immunomodulatory and cancer treatments without improvement of cerebellar ataxia, even though both were in remission of their cancer (for more than 10 years in one patient). Anti-TRIM9 and anti-TRIM67 Abs were specific to these two patients. All control serum and CSF samples tested were negative for anti-TRIM9 and 67. Anti-TRIM9 and anti-TRIM67 Abs appeared to be specific biomarkers of PCD and should be added to the panel of antigens tested when this is suspected.

Objective To assess the long-term outcomes of patients with temporal lobe epilepsy and CSF anti-glutamate decarboxylase antibodies (GAD65-Abs). Methods We retrospectively analyzed the clinical records of 35 patients with temporal lobe epilepsy and CSF GAD65-Abs, collected from January 1993 to December 2016 and assessed cognitive impairment and seizure activity at last visit. Cognitive impairment was considered significant if impacting on daily life activities. Immunohistochemistry on rat brain slices and ELISA were used for antibody detection and titration. Results Median age was 30 years (range 2–63), 32/35 (91%) patients were female, and median follow-up was 68 months (range 7–232). At presentation, 20 patients had isolated temporal lobe epilepsy and 15 patients had other limbic symptoms, including anterograde amnesia ( n  = 10) and behavioral disturbances ( n  = 5). Progressive clinical deterioration over follow-up was reported in 28/35 patients (80%), including gradual increase of memory impairment ( n  = 25), and apparition of behavioral disturbances ( n  = 4) or mood disorders ( n  = 18). At last follow-up, 24/35 (69%) patients had cognitive disturbances with an impact on patient’s daily life activities, and 28/35 (80%) still had active seizures. Conclusion Most patients with temporal lobe epilepsy and CSF GAD65-Abs develop a chronic disease with progressive cognitive impairment and refractory epilepsy regardless of the presence of additional limbic symptoms at onset.

Major advances in our knowledge concerning autoimmune and paraneoplastic cerebellar ataxias have occurred in the last 20 years. The discovery of several neural antibodies represents an undeniable contribution to this field, especially those serving as good biomarkers of paraneoplastic neurological syndromes and those showing direct pathogenic effects. Yet, many patients still lack detectable or known antibodies, and also many antibodies have only been reported in few patients, which makes it difficult to define in detail their clinical value. Nevertheless, a notable progress has additionally been made in the clinical characterization of patients with the main neural antibodies, which, although typically present with a subacute pancerebellar syndrome, may also show either hyperacute or chronic onsets that complicate the differential diagnoses. However, prodromal and transient features could be useful clues for an early recognition, and extracerebellar involvement may also be highly indicative of the associated antibody. Moreover, important advances in our understanding of the pathogenesis of cerebellar ataxias include the description of antibody effects, especially those targeting cell-surface antigens, and first attempts to isolate antigen-specific T-cells. Furthermore, genetic predisposition seems relevant, although differently involved according to cancer association, with particular HLA observed in non-paraneoplastic cases and genetic abnormalities in the tumor cells in paraneoplastic ones. Finally, immune checkpoint inhibitors used as cancer immunotherapy may rarely induce cerebellar ataxias, but even this undesirable effect may in turn serve to shed some light on their physiopathology. Herein, we review the principal novelties of the last 20 years regarding autoimmune and paraneoplastic cerebellar ataxias.

ObjectiveTo report the clinical features and long-term outcome of 22 newly diagnosed paraneoplastic patients with GABAB receptor antibodies (GABABR-Abs).MethodsRetrospective clinical study of CSF-confirmed cases of GABABR-Abs encephalitis.ResultsWe 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).ConclusionParaneoplastic GABABR-Abs encephalitis is characterized by a stereotype presentation with an epilepsy phase before an encephalitic phase with dysautonomia. The functional prognosis is poor.

BackgroundPatients with leucine-rich glioma-inactivated 1 antibody (LGI1-Ab) encephalitis are typically elderly men that often carry human leucocyte antigen (HLA)-DRB1*07:01 (≈90%). Herein, we aimed to investigate whether patients with atypical demographic profiles or not carrying DRB1*07:01 have distinct clinical manifestations and outcome.MethodsRetrospective chart review of LGI1-Ab patients diagnosed at the French Reference Centre and three other European centres.ResultsAmong 238 patients included, median age at onset was 66 years (IQR: 60–73), 65% were male, 89% carried DRB1*07:01 and 10% DRB1*04:02, another known secondary HLA association. We identified three age groups (young, typical, old) based on percentiles of age distribution. Young (≤51 years) patients were less commonly male (35%, p=0.004), while faciobrachial dystonic seizures (FBDS; 65%, p=0.047) and hyponatraemia (64%, p=0.046) were more frequent in old (≥79 years) patients. Old patients experienced poor outcome (modified Rankin Scale [mRS] >2 at last follow-up) more frequently (64%, p<0.001). There were no significant differences between males and females. DRB1*07:01 non-carriers were younger (p=0.005) and less frequently male (47%, p=0.044), while non-carriers of both DRB1*07:01 and DRB1*04:02 experienced poor outcome more commonly (64%, p=0.005). Older age (adjusted OR: 1.08, 95% CI [1.02 to 1.14], p=0.008), higher mRS at nadir (4.22 [2.46–7.24], p<0.001) and DRB1*07:01 non-carrier status (8.39 [1.88–37.44], p=0.005) were independently associated with poor outcome. Moreover, older age (1.08 [1.04–1.11], p<0.001), FBDS (2.20 [1.17–4.13], p=0.014) and hyponatraemia (2.30 [1.22–4.34], p=0.010) were associated with severe encephalitis (mRS >3 at nadir).ConclusionsAge appears to be the main driver of clinical presentation, severity and outcome in LGI1-Ab encephalitis. Remarkably, DRB1*07:01 non-carriers are younger, more commonly female and experience poorer prognosis, reflecting a distinct pathophysiology.

Immune checkpoint inhibitors (ICI), i.e., anti-PD1/PDL1 and anti-CTLA-4, have reshaped the prognosis of many cancers. Increased use of ICI has led to the onset of new adverse events. Neurological immune-related adverse events are rare, heterogenous, and potentially life-threatening. Chronic intestinal pseudo-obstruction (CIPO) is an immune-related autonomic plexus neuropathy that may be caused by infiltration of the myenteric plexus by CD8 + T cells. It is a rare and potentially fatal side effect that can be difficult to diagnose early because of initial nonspecific clinical presentation including vomiting, nausea, diarrhea, and constipation. Some rare cases have been described in the literature reporting a frequent resistance to corticosteroids making it necessary to use other immunosuppressive therapy. Vedolizumab is an antibody (Ab) blocking integrin α4-β7 used to treat inflammatory bowel disease. We report the first three cases of ICI-induced CIPO-treated with vedolizumab after corticosteroid failure, with very limited benefits (only one patient with transitory improvement). Based on our results in three cases, vedolizumab does not currently appear to be a therapeutic option. Earlier administration with a standardized dose and frequency schedule may provide better outcomes.

The primary cause of neurological syndromes with antibodies against glutamic acid decarboxylase 65 (GAD65-Ab) is unknown, but genetic predisposition may exist as it is suggested by the co-occurrence in patients and their relatives of other organ-specific autoimmune diseases, notably type 1 diabetes mellitus (T1DM), and by the reports of a few familial cases. We analyzed the human leukocyte antigen (HLA) in 32 unrelated patients and compared them to an ethnically matched sample of 137 healthy controls. Four-digit resolution HLA alleles were imputed from available Genome Wide Association data, and full HLA next-generation sequencing-based typing was also performed. HLA DQA1*05:01–DQB1*02:01–DRB1*03:01 was the most frequent class II haplotype in patients (13/32, 41%). DQB1*02:01 was the only allele found to be significantly more common in patients than in controls (20/137, 15%, corrected p  = 0.03, OR 3.96, 95% CI [1.54–10.09]). There was also a trend towards more frequent DQA1*05:01 among patients compared to controls (22/137, 16%; corrected p  = 0.05, OR 3.54, 95% CI [1.40–8.91]) and towards a protective effect of DQB1*03:01 (2/32, 6% in patients vs. 42/137, 31% in control group; corrected p  = 0.05, OR 0.15, 95% CI [0.02–0.65]). There was no significant demographic or clinical difference between DQ2 and non-DQ2 carriers ( p  > 0.05). Taken together, these findings suggest a primary DQ effect on GAD65-Ab neurological diseases, partially shared with other systemic organ-specific autoimmune diseases such as T1DM. However, it is likely that other non-HLA loci are involved in the genetic predisposition of GAD65-Ab neurological syndromes.

Immune-mediated cerebellar ataxias (IMCAs) have diverse etiologies. Patients with IMCAs develop cerebellar symptoms, characterized mainly by gait ataxia, showing an acute or subacute clinical course. We present a novel concept of latent autoimmune cerebellar ataxia (LACA), analogous to latent autoimmune diabetes in adults (LADA). LADA is a slowly progressive form of autoimmune diabetes where patients are often initially diagnosed with type 2 diabetes. The sole biomarker (serum anti-GAD antibody) is not always present or can fluctuate. However, the disease progresses to pancreatic beta-cell failure and insulin dependency within about 5 years. Due to the unclear autoimmune profile, clinicians often struggle to reach an early diagnosis during the period when insulin production is not severely compromised. LACA is also characterized by a slowly progressive course, lack of obvious autoimmune background, and difficulties in reaching a diagnosis in the absence of clear markers for IMCAs. The authors discuss two aspects of LACA: ( 1 ) the not manifestly evident autoimmunity and ( 2 ) the prodromal stage of IMCA’s characterized by a period of partial neuronal dysfunction where non-specific symptoms may occur. In order to achieve an early intervention and prevent cell death in the cerebellum, identification of the time-window before irreversible neuronal loss is critical. LACA occurs during this time-window when possible preservation of neural plasticity exists. Efforts should be devoted to the early identification of biological, neurophysiological, neuropsychological, morphological (brain morphometry), and multimodal biomarkers allowing early diagnosis and therapeutic intervention and to avoid irreversible neuronal loss.