Reduction of P/Q-type calcium channels in the postmortem cerebellum of paraneoplastic cerebellar degeneration with Lambert-Eaton myasthenic syndrome

[Blood-brain barrier breakdown and autoimmune cerebellar ataxia]

Autoimmune cerebellar ataxia is a disease entity that affects the cerebellum and is induced by autoimmune mechanisms. The disease is classified into several etiologies, including gluten ataxia, anti-glutamate decarboxylase (GAD) ataxia, paraneoplastic cerebellar degeneration, primary autoimmune cerebellar ataxia and postinfectious cerebellar ataxia. The autoimmune response in the periphery cross-reacts with similar antigens in the cerebellum due to molecular mimicry. Breakdown of the blood‒brain barrier (BBB) could potentially explain the vulnerability of the cerebellum during the development of autoimmune cerebellar ataxia, as it gives rise to the entry of pathogenic autoantibodies or lymphocytes into the cerebellum. In this review, the maintenance of the BBB under normal conditions and the molecular basis of BBB disruption under pathological conditions are highlighted. Next, the pathomechanism of BBB breakdown in each subtype of autoimmune cerebellar ataxia is discussed. We recently identified glucose-regulated protein (GRP) 78 antibodies in paraneoplastic cerebellar degeneration and Lambert-Eaton myasthenic syndrome, and GRP78 antibodies induced by cross-reactivity with tumors can disrupt the BBB and penetrate anti-P/Q type voltage-gated calcium channel (VGCC) antibodies into the cerebellum, thus leading to cerebellar ataxia in this disease.

Paraneoplastic Cerebellar Degeneration Associated with Breast Cancer: A Case Report and a Narrative Review

Paraneoplastic neurological syndromes (PNSs) are an uncommon complication of cancer, affecting nearby 1/10,000 subjects with a tumour. PNSs can involve all the central and peripheral nervous systems, the muscular system, and the neuromuscular junction, causing extremely variable symptomatology. The diagnosis of the paraneoplastic disease usually precedes the clinical manifestations of cancer, making an immediate recognition of the pathology crucial to obtain a better prognosis. PNSs are autoimmune diseases caused by the expression of common antigens by the tumour and the nervous system. Specific antibodies can help clinicians diagnose them, but unfortunately, they are not always detectable. Immunosuppressive therapy and the treatment of cancer are the cornerstones of therapy for PNSs. This paper reports a case of PNSs associated with breast tumours and focuses on the most common paraneoplastic neurological syndromes. We report a case of a young female with a clinical syndrome of the occurrence of rigidity in the right lower limb with postural instability with walking supported and diplopia, with a final diagnosis of paraneoplastic cerebellar degeneration and seronegative rigid human syndrome associated with infiltrating ductal carcinoma of the breast.

Antibodies to neural cell surface and synaptic proteins in paraneoplastic neurologic syndromes

Among patients with paraneoplastic neurologic syndromes (PNS), emphasis has historically been placed on neural antibodies against intracellular proteins that have a strong association with malignancy. Because of the intracellular location of their antigenic targets, these antibodies are typically considered to be non-pathogenic surrogate markers of immune cell-mediated neural injury. Unfortunately, patients with these antibodies often have suboptimal response to immunotherapy and poor prognosis. Over the last two decades, however, dramatic advancements have been made in the discovery and clinical characterization of neural antibodies against extracellular targets. These antibodies are generally considered to be pathogenic, given their potential to directly alter antigen structure or function, and patients with these antibodies often respond favorably to prompt immunotherapy. These antibodies also associate with tumors and may thus occur as PNS, albeit more variably than neural antibodies against intracellular targets. The updated 2021 PNS diagnostic criteria, which classifies antibodies as high-risk, intermediate-risk, or lower-risk for an associated cancer, better clarifies how neural antibodies against extracellular targets relate to PNS. Using this recently created framework, the clinical presentations, ancillary test findings, oncologic associations, and treatment responses of syndromes associated with these antibodies are discussed.

Motor symptoms in nonparaneoplastic CNS disorders associated with neural antibodies

Motor symptoms are common, and sometimes predominant, in almost all nonparaneoplastic CNS disorders associated with neural antibodies. These CNS disorders can be classified into five groups: (1) Autoimmune encephalitis with antibodies against synaptic receptors, (2) cerebellar ataxias associated with neuronal antibodies that mostly target intracellular antigens. (3) Stiff-person syndrome and progressive encephalomyelitis with rigidity and myoclonus which have antibodies against glutamic acid decarboxylase and glycine receptor, respectively. Both diseases have in common the presence of predominant muscle stiffness and rigidity. (4) Three diseases associated with glial antibodies. Two present motor symptoms mainly due to the involvement of the spinal cord: neuromyelitis optica spectrum disorders with aquaporin-4 antibodies and myelin oligodendrocyte glycoprotein antibody-associated disease. The third disorder is the meningoencephalitis associated with glial fibrillar acidic protein antibodies which frequently also presents a myelopathy. (5) Two antibody-related diseases which are characterized by prominent sleep dysfunction: anti-IgLON5 disease, a disorder that frequently presents a variety of movement disorders, and Morvan syndrome associated with contactin-associated protein-like 2 antibodies and clinical manifestations of peripheral nerve hyperexcitability. In this chapter, we describe the main clinical features of these five groups with particular emphasis on the presence, frequency, and types of motor symptoms.

Unusual Association of Non-paraneoplastic Variant of Lambert-Eaton Myasthenic Syndrome with Predominant B-cell Inflammatory Myopathy

Introduction: Myasthenia gravis disease (MGD) and inflammatory myopathy (IM) are commonly reported in the literature and usually appear with thymic pathology. Lambert-Eton myasthenic syndrome (LEMS) associated with IM is extremely rare. Case Presentation: We report a 42-year-old female patient who presented with proximal muscle weakness of the upper and lower limbs, normal creatinine kinase (CK) level, and positive acetylcholine and voltage-gated calcium channel receptor antibodies. There were no oculobulbar symptoms and no history of thymoma, and the electrophysiological tests were unremarkable. Muscle biopsy revealed focal perimysial and perivascular inflammation, predominantly B-cell lymphocytes, in a non-necrotizing muscle. Conclusions: LEMS associated with IM, particularly B-cell inflammation, has never been reported in the absence of cancer history. Clinical investigations and myopathological features can help establish the diagnosis.

Lambert-Eaton Myasthenic Syndrome and Botulism

PURPOSE OF REVIEW

This article reviews the pathophysiology, epidemiology, clinical features, diagnosis, and treatment of Lambert-Eaton myasthenic syndrome (LEMS) and botulism, presynaptic disorders of neuromuscular transmission in which rapid diagnosis improves long-term outcomes.

RECENT FINDINGS

Therapy for LEMS has seen significant advances in recent years due to the approval of amifampridine-based compounds. LEMS is likely still underdiagnosed, particularly when no underlying malignancy is identified. Clinicians must have a strong suspicion for LEMS in any patient presenting with proximal weakness and autonomic dysfunction. Botulism is another rare disorder of presynaptic neuromuscular transmission that is most commonly associated with improper storage or preservation of food products. Over the past 2 decades, wound botulism has been increasingly reported among users of black tar heroin. A high degree of clinical suspicion and electrodiagnostic studies can be beneficial in distinguishing botulism from other acute neurologic disorders, and early involvement of state and federal health authorities may assist in confirming the diagnosis and obtaining treatment. When botulism is suspected, electrodiagnostic studies can provide clinical evidence of disordered neuromuscular transmission in advance of serologic confirmation, and providers should not wait for confirmation of the diagnosis to initiate treatment.

SUMMARY

A targeted clinical history and a thorough neurologic examination with support from serologic and electrodiagnostic studies are key to early diagnosis of LEMS and botulism. Early diagnosis of both conditions creates opportunities for therapy and improves outcomes.

Cerebellar Ataxia With Anti-DNER Antibodies

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.

Paraneoplastic Cerebellar Degeneration With P/Q-VGCC vs Yo Autoantibodies

BACKGROUND AND OBJECTIVES

Paraneoplastic cerebellar degeneration (PCD) is characterized by a widespread loss of Purkinje cells (PCs) and may be associated with autoantibodies against intracellular antigens such as Yo or cell surface neuronal antigens such as the P/Q-type voltage-gated calcium channel (P/Q-VGCC). Although the intracellular location of the target antigen in anti-Yo-PCD supports a T cell-mediated pathology, the immune mechanisms in anti-P/Q-VGCC-PCD remain unclear. In this study, we compare neuropathologic characteristics of PCD with anti-P/Q-VGCC and anti-Yo autoantibodies in an archival autopsy cohort.

METHODS

We performed neuropathology, immunohistochemistry, and multiplex immunofluorescence on formalin-fixed and paraffin-embedded brain tissue of 1 anti-P/Q-VGCC, 2 anti-Yo-PCD autopsy cases and controls.

RESULTS

Anti-Yo-PCD revealed a diffuse and widespread PC loss together with microglial nodules with pSTAT1+ and CD8+granzymeB+ T cells and neuronal upregulation of major histocompatibility complex (MHC) Class I molecules. Some neurons showed a cytoplasmic immunoglobulin G (IgG) staining. In contrast, PC loss in anti-P/Q-VGCC-PCD was focal and predominantly affected the upper vermis, whereas caudal regions and lateral hemispheres were spared. Inflammation was characterized by scattered CD8+ T cells, single CD20+/CD79a+ B/plasma cells, and an IgG staining of the neuropil in the molecular layer of the cerebellar cortex and neuronal cytoplasms. No complement deposition or MHC-I upregulation was detected. Moreover, synaptophysin was reduced, and neuronal P/Q-VGCC was downregulated. In affected areas, axonal spheroids and the accumulation of amyloid precursor protein and glucose-regulated protein 78 in PCs indicate endoplasmatic reticulum stress and impairment of axonal transport. In both PCD types, calbindin expression was reduced or lost in the remaining PCs.

DISCUSSION

Anti-Yo-PCD showed characteristic features of a T cell-mediated pathology, whereas this was not observed in 1 case of anti-P/Q-VGCC-PCD. Our findings support a pathogenic role of anti-P/Q-VGCC autoantibodies in causing neuronal dysfunction, probably due to altered synaptic transmission resulting in calcium dysregulation and subsequent PC death. Because disease progression may lead to irreversible PC loss, anti-P/Q-VGCC-PCD patients could benefit from early oncologic and immunologic therapies.

A Breakdown of Immune Tolerance in the Cerebellum

Cerebellar dysfunction can be associated with ataxia, dysarthria, dysmetria, nystagmus and cognitive deficits. While cerebellar dysfunction can be caused by vascular, traumatic, metabolic, genetic, inflammatory, infectious, and neoplastic events, the cerebellum is also a frequent target of autoimmune attacks. The underlying cause for this vulnerability is unclear, but it may be a result of region-specific differences in blood–brain barrier permeability, the high concentration of neurons in the cerebellum and the presence of autoantigens on Purkinje cells. An autoimmune response targeting the cerebellum—or any structure in the CNS—is typically accompanied by an influx of peripheral immune cells to the brain. Under healthy conditions, the brain is protected from the periphery by the blood–brain barrier, blood–CSF barrier, and blood–leptomeningeal barrier. Entry of immune cells to the brain for immune surveillance occurs only at the blood-CSF barrier and is strictly controlled. A breakdown in the barrier permeability allows peripheral immune cells uncontrolled access to the CNS. Often—particularly in infectious diseases—the autoimmune response develops because of molecular mimicry between the trigger and a host protein. In this review, we discuss the immune surveillance of the CNS in health and disease and also discuss specific examples of autoimmunity affecting the cerebellum.

The Neuropathology of Autoimmune Ataxias

Autoimmune-mediated ataxia has been associated with paraneoplastic disease, gluten enteropathy, Hashimoto thyroiditis as well as autoimmune disorders without a known associated disease. There have been relatively few reports describing the neuropathology of these conditions. This review is an attempt to consolidate those reports and determine the ways in which autoimmune ataxias can be neuropathologically differentiated from hereditary or other sporadic ataxias. In most instances, particularly in paraneoplastic forms, the presence of inflammatory infiltrates is a strong indicator of autoimmune disease, but it was not a consistent finding in all reported cases. Therefore, clinical and laboratory findings are important for assessing an autoimmune mechanism. Such factors as rapid rate of clinical progression, presence of known autoantibodies or the presence of a malignant neoplasm or other autoimmune disease processes need to be considered, particularly in cases where inflammatory changes are minimal or absent and the pathology is largely confined to the cerebellum and its connections, where the disease can mimic hereditary or other sporadic ataxias.

Similarity and Diversity of Presynaptic Molecules at Neuromuscular Junctions and Central Synapses

Synaptic transmission is essential for controlling motor functions and maintaining brain functions such as walking, breathing, cognition, learning, and memory. Neurotransmitter release is regulated by presynaptic molecules assembled in active zones of presynaptic terminals. The size of presynaptic terminals varies, but the size of a single active zone and the types of presynaptic molecules are highly conserved among neuromuscular junctions (NMJs) and central synapses. Three parameters play an important role in the determination of neurotransmitter release properties at NMJs and central excitatory/inhibitory synapses: the number of presynaptic molecular clusters, the protein families of the presynaptic molecules, and the distance between presynaptic molecules and voltage-gated calcium channels. In addition, dysfunction of presynaptic molecules causes clinical symptoms such as motor and cognitive decline in patients with various neurological disorders and during aging. This review focuses on the molecular mechanisms responsible for the functional similarities and differences between excitatory and inhibitory synapses in the peripheral and central nervous systems, and summarizes recent findings regarding presynaptic molecules assembled in the active zone. Furthermore, we discuss the relationship between functional alterations of presynaptic molecules and dysfunction of NMJs or central synapses in diseases and during aging.

Update on Paraneoplastic Cerebellar Degeneration

Purpose of review: To provide an update on paraneoplastic cerebellar degeneration (PCD), the involved antibodies and tumors, as well as management strategies. Recent findings: PCD represents the second most common presentation of the recently established class of immune mediated cerebellar ataxias (IMCAs). Although rare in general, PCD is one of the most frequent paraneoplastic presentations and characterized clinically by a rapidly progressive cerebellar syndrome. In recent years, several antibodies have been described in association with the clinical syndrome related to PCD; their clinical significance, however, has yet to be determined. The 2021 updated diagnostic criteria for paraneoplastic neurologic symptoms help to establish the diagnosis of PCD, direct cancer screening, and to evaluate the presence of these newly identified antibodies. Recognition of the clinical syndrome and prompt identification of a specific antibody are essential for early detection of an underlying malignancy and initiation of an appropriate treatment, which represents the best opportunity to modulate the course of the disease. As clinical symptoms can precede tumor diagnosis by years, co-occurrence of specific symptoms and antibodies should prompt continuous surveillance of the patient. Summary: We provide an in-depth overview on PCD, summarize recent findings related to PCD, and highlight the transformed diagnostic approach.

Parkinsonism in viral, paraneoplastic, and autoimmune diseases

Secondary parkinsonism, namely parkinsonism due to causes other than idiopathic neurodegeneration, may have multiple etiologies. Common secondary etiologies of parkinsonism such as drug-induced or vascular etiologies are well documented. Other secondary causes of parkinsonism such as infectious (mainly viral and prion-like diseases), autoimmune (systemic/drug-induced) and paraneoplastic etiologies are rare but are a topic of increasing interest. Older examples from the existing literature demonstrate the intricacies of viral infection from the last pandemic of the 20th century on the development of hypokinetic symptoms experienced in post-encephalitic patients. Viral and prion-like infections are only part of a complex interplay between the body's immune response and aberrant cell cycle perturbations leading to malignancy. In addition to the classic systemic autoimmune diseases (mainly systemic lupus erythematosus - SLE, and Sjögren syndrome), there have been new developments in the context of the current COVID-19 pandemic as well as more prominent use of immunotherapies such as immune checkpoint inhibitors in the treatment of solid tumors. Both of these developments have deepened our understanding of the underlying pathophysiologic process. Increased awareness and understanding of these rarer etiologies of parkinsonism is crucial to the modern diagnostic evaluation of a patient with parkinsonian symptoms as the potential treatment options may differ from the conventional levodopa-based therapeutic regimen of idiopathic Parkinson's disease. This review article aims to give an up-to-date review of the current literature on parkinsonian symptoms, their pathogenesis, diagnostic methods, and available treatment options. Many potential future directions in the field of parkinsonian conditions remain to be explored. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

Presynaptic Paraneoplastic Disorders of the Neuromuscular Junction: An Update

The neuromuscular junction (NMJ) is the target of a variety of immune-mediated disorders, usually classified as presynaptic and postsynaptic, according to the site of the antigenic target and consequently of the neuromuscular transmission alteration. Although less common than the classical autoimmune postsynaptic myasthenia gravis, presynaptic disorders are important to recognize due to the frequent association with cancer. Lambert Eaton myasthenic syndrome is due to a presynaptic failure to release acetylcholine, caused by antibodies to the presynaptic voltage-gated calcium channels. Acquired neuromyotonia is a condition characterized by nerve hyperexcitability often due to the presence of antibodies against proteins associated with voltage-gated potassium channels. This review will focus on the recent developments in the autoimmune presynaptic disorders of the NMJ.

Immune-Mediated Cerebellar Ataxias: Clinical Diagnosis and Treatment Based on Immunological and Physiological Mechanisms

Since the first description of immune-mediated cerebellar ataxias (IMCAs) by Charcot in 1868, several milestones have been reached in our understanding of this group of neurological disorders. IMCAs have diverse etiologies, such as gluten ataxia, postinfectious cerebellitis, paraneoplastic cerebellar degeneration, opsoclonus myoclonus syndrome, anti-GAD ataxia, and primary autoimmune cerebellar ataxia. The cerebellum, a vulnerable autoimmune target of the nervous system, has remarkable capacities (collectively known as the cerebellar reserve, closely linked to plasticity) to compensate and restore function following various pathological insults. Therefore, good prognosis is expected when immune-mediated therapeutic interventions are delivered during early stages when the cerebellar reserve can be preserved. However, some types of IMCAs show poor responses to immunotherapies, even if such therapies are introduced at an early stage. Thus, further research is needed to enhance our understanding of the autoimmune mechanisms underlying IMCAs, as such research could potentially lead to the development of more effective immunotherapies. We underscore the need to pursue the identification of robust biomarkers.

Cerebellar long-term depression and auto-immune target of auto-antibodies: the concept of LTDpathies

There is general agreement that auto-antibodies against ion channels and synaptic machinery proteins can induce limbic encephalitis. In immune-mediated cerebellar ataxias (IMCAs), various synaptic proteins, such as GAD65, voltage-gated Ca channel (VGCC), metabotropic glutamate receptor type 1 (mGluR1), and glutamate receptor delta (GluR delta) are auto-immune targets. Among them, the pathophysiological mechanisms underlying anti-VGCC, anti-mGluR1, and anti-GluR delta antibodies remain unclear. Despite divergent auto-immune and clinical profiles, these subtypes show common clinical features of good prognosis with no or mild cerebellar atrophy in non-paraneoplastic syndrome. The favorable prognosis reflects functional cerebellar disorders without neuronal death. Interestingly, these autoantigens are all involved in molecular cascades for induction of long-term depression (LTD) of synaptic transmissions between parallel fibers (PFs) and Purkinje cells (PCs), a crucial mechanism of synaptic plasticity in the cerebellum. We suggest that anti-VGCC, anti-mGluR1, and anti-GluR delta Abs-associated cerebellar ataxias share one common pathophysiological mechanism: a deregulation in PF-PC LTD, which results in impairment of restoration or maintenance of the internal model and triggers cerebellar ataxias. The novel concept of LTDpathies could lead to improvements in clinical management and treatment of cerebellar patients who show these antibodies.

Seizure-related 6 homolog like 2 autoimmunity: Neurologic syndrome and antibody effects

OBJECTIVE

To describe the clinical syndrome of 4 new patients with seizure-related 6 homolog like 2 antibodies (SEZ6L2-abs), study the antibody characteristics, and evaluate their effects on neuronal cultures.

METHODS

SEZ6L2-abs were initially identified in serum and CSF of a patient with cerebellar ataxia by immunohistochemistry on rat brain sections and immunoprecipitation from rat cerebellar neurons. We used a cell-based assay (CBA) of HEK293 cells transfected with SEZ6L2 to test the serum of 95 patients with unclassified neuropil antibodies, 331 with different neurologic disorders, and 10 healthy subjects. Additional studies included characterization of immunoglobulin G (IgG) subclasses and the effects of SEZ6L2-abs on cultures of rat hippocampal neurons.

RESULTS

In addition to the index patient, SEZ6L2-abs were identified by CBA in 3/95 patients with unclassified neuropil antibodies but in none of the 341 controls. The median age of the 4 patients was 62 years (range: 54-69 years), and 2 were female. Patients presented with subacute gait ataxia, dysarthria, and mild extrapyramidal symptoms. Initial brain MRI was normal, and CSF pleocytosis was found in only 1 patient. None improved with immunotherapy. SEZ6L2-abs recognized conformational epitopes. IgG4 SEZ6L2-abs were found in all 4 patients, and it was the predominant subclass in 2. SEZ6L2-abs did not alter the number of total or synaptic SEZ6L2 or the AMPA glutamate receptor 1 (GluA1) clusters on the surface of hippocampal neurons.

CONCLUSIONS

SEZ6L2-abs associate with a subacute cerebellar syndrome with frequent extrapyramidal symptoms. The potential pathogenic effect of the antibodies is not mediated by internalization of the antigen.

Fundamental Mechanisms of Autoantibody-Induced Impairments on Ion Channels and Synapses in Immune-Mediated Cerebellar Ataxias

In the last years, different kinds of limbic encephalitis associated with autoantibodies against ion channels and synaptic receptors have been described. Many studies have demonstrated that such autoantibodies induce channel or receptor dysfunction. The same mechanism is discussed in immune-mediated cerebellar ataxias (IMCAs), but the pathogenesis has been less investigated. The aim of the present review is to evaluate what kind of cerebellar ion channels, their related proteins, and the synaptic machinery proteins that are preferably impaired by autoantibodies so as to develop cerebellar ataxias (CAs). The cerebellum predictively coordinates motor and cognitive functions through a continuous update of an internal model. These controls are relayed by cerebellum-specific functions such as precise neuronal discharges with potassium channels, synaptic plasticity through calcium signaling pathways coupled with voltage-gated calcium channels (VGCC) and metabotropic glutamate receptors 1 (mGluR1), a synaptic organization with glutamate receptor delta (GluRδ), and output signal formation through chained GABAergic neurons. Consistently, the association of CAs with anti-potassium channel-related proteins, anti-VGCC, anti-mGluR1, and GluRδ, and anti-glutamate decarboxylase 65 antibodies is observed in IMCAs. Despite ample distributions of AMPA and GABA receptors, however, CAs are rare in conditions with autoantibodies against these receptors. Notably, when the autoantibodies impair synaptic transmission, the autoimmune targets are commonly classified into three categories: release machinery proteins, synaptic adhesion molecules, and receptors. This physiopathological categorization impacts on both our understanding of the pathophysiology and clinical prognosis.

Paraneoplastic movement disorders: phenomenology, diagnosis, and treatment

Paraneoplastic syndromes include, by definition, any symptomatic and non-metastatic condition associated with a neoplasm. Paraneoplastic movement disorders are a heterogeneous group of syndromes encompassing both hyperkinetic and hypokinetic conditions, characterized by acute/sub-acute onset, rapidly progressive evolution, and multifocal localizations with several overlapping features. These movement disorders are immune-mediated, as shown by the rapid onset and by the presence of antineuronal antibodies in biological samples of patients, fundamental for the diagnosis. Antineuronal antibodies could be targeted against intracellular or neuronal surface antigens. Paraneoplastic movement disorders associated with anti-neuronal surface antigens antibodies respond more frequently to immunotherapy. The underlying tumors may be different, according to the clinical presentation, age, and gender of patients. Our search considered articles involving human subjects indexed in PubMed. Abstracts were independently reviewed for eligibility criteria by one author and validated by at least one additional author. In this review, we sought to critically reappraise the clinical features and the pathophysiological mechanisms of paraneoplastic movement disorders, focusing on diagnostic and therapeutic strategies. Our main aim is to make clinicians aware of paraneoplastic movement disorders, and to provide assistance in the early diagnosis and management of these rare but life-threatening conditions.

GRP78 antibodies damage the blood–brain barrier and relate to cerebellar degeneration in Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease of the neuromuscular junction caused by autoantibodies binding to P/Q-type voltage-gated calcium channels. Breakdown of the blood–brain barrier and diffusion of cerebellar granule/Purkinje cell-reactive autoantibodies into the CNS are critical for the pathogenesis of paraneoplastic cerebellar degeneration (PCD) with Lambert-Eaton myasthenic syndrome. We recently found evidence that glucose-regulated protein 78 (GRP78) autoantibodies in the plasma of patients with neuromyelitis optica promote the CNS access of AQP4 autoantibodies. In the present study, we investigated whether the GRP78 autoantibodies in PCD-LEMS IgG boost the brain uptake of cerebellar cell-reactive antibodies across the blood–brain barrier and facilitate cerebellar dysfunction. We first evaluated the effects of purified IgG from PCD-LEMS or PCD patients on the blood–brain barrier function in human brain microvascular endothelial cells using a high content imaging system with nuclear factor κB p65 and intracellular adhesion molecule 1 (ICAM1) immunostaining. Next, we identified GRP78 autoantibodies causing blood–brain barrier permeability in PCD-LEMS IgG by co-immunoprecipitation and the living cell-based antibody binding assays. Exposure of brain microvascular endothelial cells to IgG from PCD-LEMS patients induced nuclear factor κB p65 nuclear translocation, ICAM1 upregulation, reduced claudin-5 expression, increased permeability and increased autocrine IL-1β and IL-8 secretion; the IgG from patients with Lambert-Eaton myasthenic syndrome did not have these effects. We detected GRP78 autoantibodies in the IgG of LEMS-PCD (83.3%, n = 18), but observed fewer in patients with LEMS (6.6%, n = 15) and none were observed in the control subjects (n = 8). The depletion of GRP78 autoantibodies reduced the biological effect of LEMS-PCD IgG on brain microvascular endothelial cells. These findings suggest that GRP78 autoantibodies play a role beyond neuromyelitis optica and that they have direct implications in the phenotypic differences between PCD-LEMS and LEMS.

Clinical characteristics and long term follow-up of Lambert-Eaton myasthenia syndrome in patients with and without small cell lung cancer

In order to describe the clinical characteristics, treatment response and long-term follow up in Lambert-Eaton myasthenic syndrome (LEMS) patients with and without small cell lung cancer (SCLC) in East China, patients seen in Huashan Hospital from January 1997 to December 2017 were included. Clinical information was collected retrospectively and quantitative MG (QMG) score, manual muscle testing (MMT), activities of daily living (ADL) scale were evaluated when the patients were followed up. Of 50 patients, 23 (46%) were SCLC-LEMS and 20 (40%) were nontumor LEMS (NT-LEMS). The median onset age was 55.5 (18-86) years old and the gender ratio was about 1.8:1. It took less time to make the diagnosis (median time: 6 vs 22.5 months, p = 0.0003) and there were more patients with other paraneoplastic syndromes in SCLC-LEMS group than in NT-LEMS group (8/23 vs 0/20, p = 0.0042). Electrophysiologically, the peroneal compound motor action potential (CMAP) of rest showed difference between SCLC-LEMS and NT-LEMS (0.8 vs 1.6 mV, p = 0.0499). The median survival time of 19 SCLC-LEMS patients since the diagnosis of SCLC was 30 months. According to their survival time, SCLC patients with LEMS showed a more favorable prognosis than those without LEMS. In the time of follow-up, most NT-LEMS showed improvement or obtained status of CSR/PR/MM after immunosuppressive therapy and no significant difference in proportion of achieving CSR/PR/MM was found between SCLC-LEMS and NT-LEMS patients (0/5 vs 6/13, p = 0.114).

Immune-mediated Cerebellar Ataxias: Practical Guidelines and Therapeutic Challenges

Immune-mediated cerebellar ataxias (IMCAs), a clinical entity reported for the first time in the 1980s, include gluten ataxia (GA), paraneoplastic cerebellar degenerations (PCDs), antiglutamate decarboxylase 65 (GAD) antibody-associated cerebellar ataxia, post-infectious cerebellitis, and opsoclonus myoclonus syndrome (OMS). These IMCAs share common features with regard to therapeutic approaches. When certain factors trigger immune processes, elimination of the antigen( s) becomes a priority: e.g., gluten-free diet in GA and surgical excision of the primary tumor in PCDs. Furthermore, various immunotherapeutic modalities (e.g., steroids, immunoglobulins, plasmapheresis, immunosuppressants, rituximab) should be considered alone or in combination to prevent the progression of the IMCAs. There is no evidence of significant differences in terms of response and prognosis among the various types of immunotherapies. Treatment introduced at an early stage, when CAs or cerebellar atrophy is mild, is associated with better prognosis. Preservation of the "cerebellar reserve" is necessary for the improvement of CAs and resilience of the cerebellar networks. In this regard, we emphasize the therapeutic principle of "Time is Cerebellum" in IMCAs.

[A retrospective study of the effects of 3,4-diaminopyridine treatment in Lambert-Eaton myasthenic syndrome]

In this independent clinical study, we analyzed retrospectively the clinical features of 9 cases (6 male and 3 female) of Lambert-Eaton myasthenic syndrome that were administered 3,4-diaminopyridine (3,4-DAP). Four cases showed no cancer and 5 cases had small cell lung carcinoma. Seven cases were positive for anti voltage-gated calcium channel antibodies. Activities of daily living (ADL) were improved by 3,4-DAP in 8 cases that showed mainly weakness of the extremities, but did not improve ADL in 1 case with cerebellar ataxia of paraneoplastic cerebellar degeneration (PCD). Seven cases showed autonomic symptoms, and 6 cases were improved with 3,4-DAP. The maintenance dose varied widely among individuals, with a single dose ranging from 10 to 40 mg. Each patient was prescribed a maintenance dose 3 to 7 times a day. The daily dosage ranged from 36 to 100 mg. Two cases showed adverse effects to the treatment. Of those 2 cases, 1 case treated at 45 mg/day discontinued treatment, but another case treated at 100 mg/day reduced the dosage and continued treatment. The administration period was 1 to 149 months. Three cases have continued 3,4-DAP for more than 10 years. Four cases have discontinued 3,4-DAP, with 2 cases discontinuing due to death, 1 case discontinuing due to progression of cancer, and 1 case discontinuing due to an adverse reaction. Our results suggest that 3,4-DAP treatment is effective for weakness and autonomic symptoms, but may be ineffective for ataxia of PCD. Treatment with 3,4-DAP can be tolerated for a long period, but the optimal dosage varies widely among individuals.

Paraneoplastic Cerebellar Degeneration and Lambert-Eaton Myasthenic Syndrome Associated with Neuroendocrine Carcinoma of the Oropharynx

Paraneoplastic cerebellar degeneration and Lambert-Eaton myasthenic syndrome (PCD-LEMS) are usually associated with small-cell lung carcinoma (SCLC). PCD-LEMS with extrapulmonary non-SCLC tumors; however, has not been previously reported. A 78-year-old man presented with dysarthria, dysphagia, staggering gait, and lower extremity muscle fatigue. He was diagnosed with PCD-LEMS associated with neuroendocrine carcinoma of the oropharynx, based on the histological findings of the biopsy, the existence of antibodies against P/Q-type voltage-gated calcium channels, and an incremental response of the compound muscle action potentials during repetitive nerve stimulation tests. Thus, PCD-LEMS should be included in the differential diagnosis of neurological dysfunction, even in extrapulmonary non-SCLC patients.

Immune-mediated ataxias

Immune-mediated cerebellar ataxia (CA) comprises a group of rare diseases that are still incompletely described, and are probably underdiagnosed. Both acute and progressive progressions are possible. Different syndromes have been identified, including CA associated with anti-GAD antibodies, the cerebellar type of Hashimoto encephalopathy, primary autoimmune CA, gluten ataxia, opsoclonus-myoclonus syndrome, and paraneoplastic cerebellar degenerations. Most of these syndromes are associated with autoantibodies targeting neuronal antigens. Additionally, autoimmune CA can be triggered by infections, especially in children, and in rare cases occur in the context of an autoimmune multisystem disease, such as systemic lupus erythematosus, sarcoidosis, or Behçet disease. A careful workup is needed to distinguish autoimmune CA from other causes. In adults, a paraneoplastic origin must be ruled out, especially in cases with subacute onset. Neurologic outcome in adults is frequently poor, and optimal therapeutic strategies remain ill defined. The outcome in children is in general good, but children with a poor recovery are on record. The precise pathophysiologic mechanisms even in the presence of detectable autoantibodies are still largely unknown. Further research is needed on both the clinical and mechanistic aspects of immune-mediated CA, and to determine optimal therapeutic strategies.

Calcium channel autoimmunity: Cerebellar ataxia and lambert-eaton syndrome coexisting

INTRODUCTION

Neuronal calcium channel antibodies are a biomarker of Lambert-Eaton syndrome (LES) and cerebellar ataxia. We have encountered several patients with LES and cerebellar ataxia coexisting, and we sought to further define this association.

METHODS

We reviewed records of patients at our institution with a diagnosis of "Lambert-Eaton syndrome" and "cerebellar ataxia."

RESULTS

Seventeen patients were identified with LES and ataxia. Presenting symptoms were weakness (8), concurrent weakness and ataxia (4), ataxia (4), and other (1). Nine patients had small-cell lung carcinoma, 3 of whom had survival greater than 100 months. Immunotherapy responses were best among patients without cancer. Nine of 17 (53%) patients were alive at last follow-up (median survival 62 months; range, 8-240).

DISCUSSION

Calcium channel autoimmunity should be considered in patients with coexisting cerebellar ataxia and myasthenic weakness. Affected patients may survive small-cell carcinoma or have immunotherapy-responsive neurological symptoms. Muscle Nerve, 2018.

Autoantibodies to Synaptic Receptors and Neuronal Cell Surface Proteins in Autoimmune Diseases of the Central Nervous System

Investigations in the last 10 years have revealed a new category of neurological diseases mediated by antibodies against cell surface and synaptic proteins. There are currently 16 such diseases all characterized by autoantibodies against neuronal proteins involved in synaptic signaling and plasticity. In clinical practice these findings have changed the diagnostic and treatment approach to potentially lethal, but now treatable, neurological and psychiatric syndromes previously considered idiopathic or not even suspected to be immune-mediated. Studies show that patients' antibodies can impair the surface dynamics of the target receptors eliminating them from synapses (e.g., NMDA receptor), block the function of the antigens without changing their synaptic density (e.g., GABAb receptor), interfere with synaptic protein-protein interactions (LGI1, Caspr2), alter synapse formation (e.g., neurexin-3α), or by unclear mechanisms associate to a new form of tauopathy (IgLON5). Here we first trace the process of discovery of these diseases, describing the triggers and symptoms related to each autoantigen, and then review in detail the structural and functional alterations caused by the autoantibodies with special emphasis in those (NMDA receptor, amphiphysin) that have been modeled in animals.

Voltage-Gated P/Q-Type Calcium Channel Antibodies Associated With Cerebellar Degeneration

BACKGROUND

Paraneoplastic cerebellar degeneration is a rare neurological condition characterized by diffuse cerebellar dysfunction and magnetic resonance imaging evidence of progressive cerebellar atrophy. It has been associated with several autoantibodies and malignancies in adults. To date, only six cases have been described in male children.

PATIENT DESCRIPTION

We describe an eight-year-old girl with a prodrome of abdominal pain and vomiting followed by acute onset diplopia, dysarthria, dysmetria, and ataxia. She was found to have cerebellar degeneration in association with P/Q-type calcium channel antibodies.

CONCLUSION

This is the first child with documented paraneoplastic cerebellar degeneration in association with P/Q-type calcium channel antibodies.

Neuronal central nervous system syndromes probably mediated by autoantibodies

In the last few years, a rapidly growing number of autoantibodies targeting neuronal cell-surface antigens have been identified in patients presenting with neurological symptoms. Targeted antigens include ionotropic receptors such as N-methyl-d-aspartate receptor or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor, metabotropic receptors such as mGluR1 and mGluR5, and other synaptic proteins, some of them belonging to the voltage-gated potassium channel complex. Importantly, the cell-surface location of these antigens makes them vulnerable to direct antibody-mediated modulation. Some of these autoantibodies, generally targeting ionotropic channels or their partner proteins, define clinical syndromes resembling models of pharmacological or genetic disruption of the corresponding antigen, suggesting a direct pathogenic role of the associated autoantibodies. Moreover, the associated neurological symptoms are usually immunotherapy-responsive, further arguing for a pathogenic effect of the antibodies. Some studies have shown that some patients' antibodies may have structural and functional in vitro effects on the targeted antigens. Definite proof of the pathogenicity of these autoantibodies has been obtained for just a few through passive transfer experiments in animal models. In this review we present existing and converging evidence suggesting a pathogenic role of some autoantibodies directed against neuronal cell-surface antigens observed in patients with central nervous system disorders. We describe the main clinical symptoms characterizing the patients and discuss conflicting arguments regarding the pathogenicity of these antibodies.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Autoantibodies to central nervous system neuronal surface antigens: psychiatric symptoms and psychopharmacological implications

RATIONALE

Autoantibodies to central nervous system (CNS) neuronal surface antigens have been described in association with autoimmune encephalopathies which prominently feature psychiatric symptoms in addition to neurological symptoms. The potential role of these autoantibodies in primary psychiatric diseases such as schizophrenia or bipolar affective disorder is of increasing interest.

OBJECTIVES

We aimed to review the nature of psychiatric symptoms associated with neuronal surface autoantibodies, in the context of autoimmune encephalopathies as well as primary psychiatric disorders, and to review the mechanisms of action of these autoantibodies from a psychopharmacological perspective.

RESULTS

The functional effects of the autoantibodies on their target antigens are described; their clinical expression is at least in part mediated by their effects on neuronal receptor function, primarily at the synapse, usually resulting in receptor hypofunction. The psychiatric effects of the antibodies are related to known functions of the receptor target or its complexed proteins, with reference to supportive genetic and pharmacological evidence where relevant. Evidence for a causal role of these autoantibodies in primary psychiatric disease is increasing but remains controversial; relevant methodological controversies are outlined. Non-receptor-based mechanisms of autoantibody action, including neuroinflammatory mechanisms, and therapeutic implications are discussed.

CONCLUSIONS

An analysis of the autoantibodies from a psychopharmacological perspective, as endogenous, bioactive, highly specific, receptor-targeting molecules, provides a valuable opportunity to understand the neurobiological basis of associated psychiatric symptoms. Potentially, new treatment strategies will emerge from the improving understanding of antibody-antigen interaction within the CNS.

Neurologic autoimmunity: mechanisms revealed by animal models

Over the last decade, neurologic autoimmunity has become a major consideration in the diagnosis and management of patients with many neurologic presentations. The nature of the associated antibodies and their targets has led to appreciation of the importance of the accessibility of the target antigen to antibodies, and a partial understanding of the different mechanisms that can follow antibody binding. This chapter will first describe the basic principles of autoimmune inflammation and tissue damage in the central and peripheral nervous system, and will then demonstrate what has been learnt about neurologic autoimmunity from circumstantial clinical evidence and from passive, active, and occasionally spontaneous or genetic animal models. It will cover neurologic autoimmune diseases ranging from disorders of neuromuscular transmission, peripheral and ganglionic neuropathy, to diseases of the central nervous system, where autoantibodies are either pathogenic and cause destruction or changes in function of their targets, where they are harmless bystanders of T-cell-mediated tissue damage, or are not involved at all. Finally, this chapter will summarize the relevance of current animal models for studying the different neurologic autoimmune diseases, and it will identify aspects where future animal models need to be improved to better reflect the disease reality experienced by affected patients, e.g., the chronicity or the relapsing/remitting nature of their disease.

'Medusa head ataxia': the expanding spectrum of Purkinje cell antibodies in autoimmune cerebellar ataxia. Part 2: Anti-PKC-gamma, anti-GluR-delta2, anti-Ca/ARHGAP26 and anti-VGCC

Serological testing for anti-neural autoantibodies is important in patients presenting with idiopathic cerebellar ataxia, since these autoantibodies may indicate cancer, determine treatment and predict prognosis. While some of them target nuclear antigens present in all or most CNS neurons (e.g. anti-Hu, anti-Ri), others more specifically target antigens present in the cytoplasm or plasma membrane of Purkinje cells (PC). In this series of articles, we provide a detailed review of the clinical and paraclinical features, oncological, therapeutic and prognostic implications, pathogenetic relevance, and differential laboratory diagnosis of the 12 most common PC autoantibodies (often referred to as 'Medusa head antibodies' due their characteristic somatodendritic binding pattern when tested by immunohistochemistry). To assist immunologists and neurologists in diagnosing these disorders, typical high-resolution immunohistochemical images of all 12 reactivities are presented, diagnostic pitfalls discussed and all currently available assays reviewed. Of note, most of these antibodies target antigens involved in the mGluR1/calcium pathway essential for PC function and survival. Many of the antigens also play a role in spinocerebellar ataxia. Part 1 focuses on anti-metabotropic glutamate receptor 1-, anti-Homer protein homolog 3-, anti-Sj/inositol 1,4,5-trisphosphate receptor- and anti-carbonic anhydrase-related protein VIII-associated autoimmune cerebellar ataxia (ACA); part 2 covers anti-protein kinase C gamma-, anti-glutamate receptor delta-2-, anti-Ca/RhoGTPase-activating protein 26- and anti-voltage-gated calcium channel-associated ACA; and part 3 reviews the current knowledge on anti-Tr/delta notch-like epidermal growth factor-related receptor-, anti-Nb/AP3B2-, anti-Yo/cerebellar degeneration-related protein 2- and Purkinje cell antibody 2-associated ACA, discusses differential diagnostic aspects, and provides a summary and outlook.

Autoimmune channelopathies in paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes and autoimmune encephalitides are immune neurological disorders occurring or not in association with a cancer. They are thought to be due to an autoimmune reaction against neuronal antigens ectopically expressed by the underlying tumour or by cross-reaction with an unknown infectious agent. In some instances, paraneoplastic neurological syndromes and autoimmune encephalitides are related to an antibody-induced dysfunction of ion channels, a situation that can be labelled as autoimmune channelopathies. Such functional alterations of ion channels are caused by the specific fixation of an autoantibody upon its target, implying that autoimmune channelopathies are usually highly responsive to immuno-modulatory treatments. Over the recent years, numerous autoantibodies corresponding to various neurological syndromes have been discovered and their mechanisms of action partially deciphered. Autoantibodies in neurological autoimmune channelopathies may target either directly ion channels or proteins associated to ion channels and induce channel dysfunction by various mechanisms generally leading to the reduction of synaptic expression of the considered channel. The discovery of those mechanisms of action has provided insights on the regulation of the synaptic expression of the altered channels as well as the putative roles of some of their functional subdomains. Interestingly, patients' autoantibodies themselves can be used as specific tools in order to study the functions of ion channels. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Molecular and cellular mechanisms underlying anti-neuronal antibody mediated disorders of the central nervous system

Over the last decade multiple autoantigens located on the plasma membrane of neurons have been identified. Neuronal surface antigens include molecules directly involved in neurotransmission and excitability. Binding of the antibody to the antigen may directly alter the target protein's function, resulting in neurological disorders. The often striking reversibility of symptoms following early aggressive immunotherapy supports a pathogenic role for autoantibodies to neuronal surface antigens. In order to better understand and treat these neurologic disorders it is important to gain insight in the underlying mechanisms of antibody pathogenicity. In this review we discuss the clinical, circumstantial, in vitro and in vivo evidence for neuronal surface antibody pathogenicity and the possible underlying cellular and molecular mechanisms. This review shows that antibodies to neuronal surface antigens are often directed at conformational epitopes located in the extracellular domain of the antigen. The conformation of the epitope can be affected by specific posttranslational modifications. This may explain the distinct clinical phenotypes that are seen in patients with antibodies to antigens that are expressed throughout the brain. Furthermore, it is likely that there is a heterogeneous antibody population, consisting of different IgG subtypes and directed at multiple epitopes located in an immunogenic region. Binding of these antibodies may result in different pathophysiological mechanisms occurring in the same patient, together contributing to the clinical syndrome. Unraveling the predominant mechanism in each distinct antigen could provide clues for therapeutic interventions.

Neurologic complications of lung cancer

Neurologic complications of lung cancer are a frequent cause of morbidity and mortality. Tumor metastasis to the brain parenchyma is the single most common neurologic complication of lung cancer, of any histologic subtype. The goal of radiation therapy and in some cases surgical resection for patients with brain metastases is to improve or maintain neurologic function, and to achieve local control of the brain lesion(s). Metastasis of lung cancer to the spinal epidural space requires urgent evaluation and treatment. Early diagnosis and modern surgical and radiotherapy techniques improve neurologic outcome for most patients. Leptomeningeal metastasis is a less common but ominous occurrence in patients with lung cancer. Lung carcinomas can also occasionally metastasize to the brachial plexus, skull base, dura, or pituitary. Paraneoplastic neurologic disorders are uncommon but important complications of lung carcinoma, and are generally the presenting feature of the tumor. Paraneoplastic disorders are believed to be caused by an autoimmune humoral or cellular attack against shared "onconeural" antigens. The most frequent paraneoplastic disorders in patients with lung cancer are Lambert-Eaton myasthenic syndrome, and multifocal paraneoplastic encephalomyelitis, both mainly occurring in association with small-cell lung carcinoma. There is a variety of other paraneoplastic disorders affecting the central and peripheral nervous systems. Some affected patients have a good neurologic outcome, while others are left with severe permanent neurologic disability.

Paraneoplastic disorders of the central and peripheral nervous systems

Paraneoplatic neurologic syndromes (PNS) have been seminally defined as acute or subacute neurological syndromes resulting from nervous system dysfunction that is remote from the site of a malignant neoplasm or its metastases. However, in respect to our current understanding of their pathogenesis we may redefine these disorders as cancer-related dysimmune neurologic syndromes. We first deal with the epidemiology and the pathogenesis of PNS, then the different classic PNS are reviewed with clinical features according to the associated onconeuronal antibodies. Finally, therapeutic approaches are discussed.

Non-paraneoplastic voltage-gated calcium channels antibody-mediated cerebellar ataxia responsive to IVIG treatment

Non-paraneoplastic cerebellar ataxia associated with voltage-gated calcium channel (VGCC) antibodies is a rare entity with only few cases reported in literature. We describe a 60 year-old man with subacute cerebellar ataxia and subclinical Lambert-Eaton myasthenic syndrome (LEMS) in whom VGCC antibodies were detected at high titer in serum and cerebrospinal fluid. Screening for underlying malignancies was negative. Intravenous immunoglobulin treatment led to the improvement of clinical picture and reduction of serum antibody titer over a 13-month follow-up period. We emphasize that VGCC antibodies should be included in the diagnostic work-up of patients with subacute cerebellar ataxia and that treatment with IVIG can improve the clinical picture and prevent disability.

Intrathecal injection of P/Q type voltage-gated calcium channel antibodies from paraneoplastic cerebellar degeneration cause ataxia in mice

The role of antibodies against the P/Q type voltage-gated calcium channels (VGCC-ab) in the pathogenesis of paraneoplastic cerebellar degeneration (PCD) and lung cancer is unclear. We evaluated in mice the effect of intrathecal injection of IgG purified from serum of a patient with both PCD and Lambert-Eaton myasthenic syndrome (LEMS), and from another patient with isolated LEMS. Mice injected with PCD/LEMS IgG developed marked, reversible ataxia compared with those injected with LEMS or control IgG. These findings suggest that P/Q-type VGCC-ab may play a role in the pathogenesis of ataxia in patients with PCD and SCLC.

Paraneoplastic neurological syndromes: general treatment overview

OPINION STATEMENT

Major recent discoveries have bringing out a revised definition of paraneoplastic neurological syndromes (PNS), bringing out the concept of antibody-mediated neurological disorders, triggered or not by cancer. Classification of these diseases is not based anymore on the clinical pattern or an underlying tumor, but on the location of the targeted antigens. Indeed, evolution, response to treatment, and pathophysiology are radically different according to the associated antibodies. In some patients with newly described antibodies targeting cell-surface antigens, humoral immunity seems to play a direct role and a dramatic improvement is observed with immunomodulator treatments. In these patients, an associated tumor is less frequent. Conversely, patients with antibodies directed against intracellular targets are, in most cases, characterized by a high degree of irreversible neuronal death mediated by cytotoxic T-cells and do not improve after immunomodulator treatments. In these patients, an associated tumor is highly frequent and must be cured as soon as possible. A third group of patients can be identified with anti-GAD65 and anti-Amphiphysin antibodies. In patients with these antibodies, the efficiency of immunomodulator treatments is less clear as well as the type of immune response that could be a mix between humoral and cellular. In this last group, the antigen is intracellular, but patients may improve with immunomodulator treatments and associated tumors are rare. Thus, identification of associated antibodies should be prompt and the treatment guided according the identified antibody. Mainstream of treatment include the quest of a tumor and its cure. Immunotherapy must be promptly initiated, targeting humoral, or cellular immune response, or both, according to the associated antibodies. Furthermore, in some situations such as Lambert-Eaton Myasthenic Syndromes and Stiff-Person Syndromes, symptomatic drugs can be useful to control the symptoms.

[Synchronous appearance and improvement with anticancer chemotherapy of paraneoplastic cerebellar degeneration and Lambert-Eaton myasthenic syndrome complicated with small cell lung cancer]

A 62-year-old man who had suffered from instability of gait and double vision for two months was admitted to our hospital because of weakness of the extremities and ataxia of the extremities and trunk. Chest X-rays and CT scans showed enlargement of the left hilar lymph nodes and a nodular shadow in the left lung. Transbronchial biopsy revealed small cell lung cancer. We diagnosed the patient with two conditions: paraneoplastic cerebellar degeneration (PCD), based on cerebellar ataxia, the presence of Hu antineuronal antibodies, and the absence of cerebellar atrophy and malignancy; and Lambert-Eaton myasthenic syndrome (LEMS), based on weakness of the extremities, the presence of P/Q-type voltage-gated calcium channel antibodies, and waxing in the evoked electromyogram. Anticancer chemoradiation therapy that was started within three months of symptom onset resulted in reductions in size of the hilar lymph nodes and the nodule. Concurrently, cerebellar ataxia, weakness of the extremities, and double vision all disappeared. Anticancer chemotherapy is effective against LEMS while usually less effective against PCD. Early commencement of anticancer chemotherapy is recommended for the treatment of PCD with LEMS.

A pilot study on neurological manifestations and antibodies against antigens in children with hematological and other cancers

BACKGROUND

Paraneoplastic neurological syndromes (PNS) are most commonly recognized in adults with cancer and can often be identified by the presence of serum antibodies to neuronal proteins that are also expressed by the associated tumor. In children: (a) little emphasis is given to the possibility of paraneoplastic neurological involvement; and (b) few studies investigated the presence of anti-neuronal antibodies.

OBJECTIVE

To run a pilot study on the spectrum of PNS and presence of antibodies to neural antigens in children with malignancies.

METHODS

23 children (7 boys; 16 girls, aged 4 months to 16 years) with hematological or other cancers were examined for neurological manifestations and for antibodies to the neuronal antigens that are frequently detected in adult patients with PNS.

RESULTS

Ten of the 23 children had neurological symptoms (and/or positive antibodies): in 6/10 neurological manifestations could be explained by tumor invasion or chemotoxicity or were probably incidental; a child with neuroblastoma developed opsoclonus-myoclonus syndrome without detectable anti-neuronal antibodies; antibodies to a Tr-like cerebellar antigen [associated to no neurological signs and later enuresis], to voltage-gated potassium channels [associated to sensory signs] and to glutamic acid decarboxylase [associated to multifocal myoclonus] were found in one child each. Results were compared with age- and sex-matched control groups.

CONCLUSION

These results suggest that PNS, though surprisingly not so uncommon in children, may be associated with immune responses to distinct neuronal antigens. Further work is needed to determine whether screening for new antibodies to neuronal antigens could be a useful aid in the diagnosis and prognosis of neurological syndromes in children.

Pathogenic and physiological autoantibodies in the central nervous system

In this article, we review the current knowledge on pathological and physiological autoantibodies directed toward structures in the central nervous system (CNS) with an emphasis on their regulation and origin. Pathological autoantibodies in the CNS that are associated with autoimmunity often lead to severe neurological deficits via inflammatory processes such as encephalitis. In some instances, however, autoantibodies function as a marker for diagnostic purposes without contributing to the pathological process and/or disease progression. The existence of naturally occurring physiological autoantibodies has been known for a long time, and their role in maintaining homeostasis is well established. Within the brain, naturally occurring autoantibodies targeting aggregated proteins have been detected and might be promising candidates for new therapeutic approaches for neurodegenerative disorders. Further evidence has demonstrated the existence of naturally occurring antibodies targeting antigens on neurons and oligodendrocytes that promote axonal outgrowth and remyelination. The numerous actions of physiological autoantibodies as well as their regulation and origin are summarized in this review.

[The pathophysiology and treatment of autoimmune neuromuscular junction diseases]

The neuromuscular junction lacks the protection of the blood-nerve barrier and is vulnerable to antibody-mediated disorders. Myasthenia gravis (MG) is caused by the failure of neuromuscular transmission mediated by autoantibodies against acetylcholine receptors (AChR) and muscle-specific receptor tyrosine kinase (MuSK)/LDL-receptor related protein 4 which are AChR-associated transmembrane post-synaptic proteins involved in AChR aggregation. The seropositivity rates for AChR positive and MuSK positive MG in Japan are 80-85% and 5-10%/less than 1%,respectively. The incidence of late-onset MG, defined as onset after age 50 years, has been increasing worldwide. A nationwide epidemiological survey in Japan also revealed that the rates of late-onset MG had increased from 20% in 1987 to 42% in 2006. In 2010, a guideline for standard treatments of late-onset MG was published by the Japanese Society of Neurological Therapeutics. Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease of the neuromuscular junction and approximately 60% of LEMS patients have a tumor, mostly small cell lung cancer (SCLC), as a paraneoplastic neurological syndrome. The clinical pictures of Japanese LEMS patients are as follows; male dominant sex ratio (3 : 1), mean age 62 years (17-80 years), 61% of LEMS have SCLC, and the remaining are without cancer. In less than 10% of cases there are signs of cerebellar dysfunctions (paraneoplastic cerebellar degeneration with LEMS; PCD-LEMS) as well, often associated with SCLC. Most patients benefit from 3, 4-diaminopyridine plus pyridostigmine. In paraneoplastic LEMS, treatment of the tumor often results in neurological improvement. In non-paraneoplastic LEMS, prednisone alone or combined with immunosuppressants are treatment options. In both MG and LEMS, where weakness is severe, plasma exchange or intravenous immunoglobulin treatment may provide short-term benefit.

Paraneoplastic and non-paraneoplastic autoimmunity to neurons in the central nervous system

Autoimmune central nervous system (CNS) inflammation occurs both in a paraneoplastic and non-paraneoplastic context. In a widening spectrum of clinical disorders, the underlying adaptive (auto) immune response targets neurons with a divergent role for cellular and humoral disease mechanisms: (1) in encephalitis associated with antibodies to intracellular neuronal antigens, neuronal antigen-specific CD8⁺ T cells seemingly account for irreversible progressive neuronal cell death and neurological decline with poor response to immunotherapy. However, a pathogenic effect of humoral immune mechanisms is also debated. (2) In encephalitis associated with antibodies to synaptic and extrasynaptic neuronal cell surface antigens, potentially reversible antibody-mediated disturbance of synaptic transmission and neuronal excitability occurs in the absence of excessive neuronal damage and accounts for a good response to immunotherapy. However, a pathogenic effect of cellular immune mechanisms is also debated. We provide an overview of entities, clinical hallmarks, imaging features, characteristic laboratory, electrophysiological, cerebrospinal fluid and neuropathological findings, cellular and molecular disease mechanisms as well as therapeutic options in these two broad categories of inflammatory CNS disorders.

Autoimmune channelopathies of the nervous system

Ion channels are complex transmembrane proteins that orchestrate the electrical signals necessary for normal function of excitable tissues, including the central nervous system, peripheral nerve, and both skeletal and cardiac muscle. Progress in molecular biology has allowed cloning and expression of genes that encode channel proteins, while comparable advances in biophysics, including patch-clamp electrophysiology and related techniques, have made the functional assessment of expressed proteins at the level of single channel molecules possible. The role of ion channel defects in the pathogenesis of numerous disorders has become increasingly apparent over the last two decades. Neurological channelopathies are frequently genetically determined but may also be acquired through autoimmune mechanisms. All of these autoimmune conditions can arise as paraneoplastic syndromes or independent from malignancies. The pathogenicity of autoantibodies to ion channels has been demonstrated in most of these conditions, and patients may respond well to immunotherapies that reduce the levels of the pathogenic autoantibodies. Autoimmune channelopathies may have a good prognosis, especially if diagnosed and treated early, and if they are non-paraneoplastic. This review focuses on clinical, pathophysiologic and therapeutic aspects of autoimmune ion channel disorders of the nervous system.

Paraneoplastic Neurologic Disorders: A Brief Overview

Immune-mediated paraneoplastic neurologic disorders (PND) may affect any part of the nervous system, and can mimic many non-cancer associated disorders. The availability of diagnostic tests based on the presence of specific anti-neuronal antibodies facilitates diagnosis and can suggest treatment strategies. Once thought to be poorly responsive to therapies, it is now recognized that there is a subgroup of PND, mostly associated with antibodies to antigens on the neuronal cell surface that are highly treatment responsive. For all PND, identification and treatment of the underlying tumor is the most effective step in the potential control or stabilization of the neurological disorder.

Neuronal autoantigens--pathogenesis, associated disorders and antibody testing

The discovery of disorders that are associated with antibodies to neuronal cell-surface proteins has led to a paradigm shift in our understanding of CNS autoimmunity. These disorders can occur in patients with or without cancer-often children or young adults who develop psychosis, catatonic or autistic features, memory problems, abnormal movements, or seizures that were previously considered idiopathic. The autoantigens in such cases have crucial roles in synaptic transmission, plasticity and peripheral nerve excitability. Patients can be comatose or encephalopathic for months and yet fully recover with supportive care and immunotherapy. By contrast, disorders in which the antibodies target intracellular antigens, and in which T-cell-mediated irreversible neuronal degeneration occurs, show a considerably poorer response to treatment. In this article, we review the various targets of neuronal antibodies, focusing predominantly on autoantigens located on the cell surface or synapses-namely, N-methyl-D-aspartate receptors, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, γ-aminobutyric acid receptors, leucine-rich glioma-inactivated protein 1, contactin-associated protein-like 2, and metabotropic glutamate receptors. We also provide an algorithm to identify and assess antibodies that bind to cell-surface and synaptic antigens.