A novel non-rapid-eye movement and rapid-eye-movement parasomnia with sleep breathing disorder associated with antibodies to IgLON5: a case series, characterisation of the antigen, and post-mortem study

Atypical brain MRI findings in a patient with treatment responsive anti-IgLON5 disease

Anti-IgLON5 disease is a rare autoimmune neurological condition which was relatively recently described in the literature. This syndrome encompasses a range of clinical manifestations with most cases showing unremarkable findings on brain magnetic resonance imaging (MRI). Here, we report a case of a 61-year-old female patient with unique brain MRI features that, to the best of our knowledge, has not been reported in the literature before. Following treatment including immunotherapy, the patient experienced significant improvement clinically accompanied by radiological improvement on the follow-up imaging.

New knowledge on anti-IgLON5 disease

PURPOSE OF REVIEW

Anti-IgLON5 disease is characterized by a distinctive sleep disorder, associated with a heterogeneous spectrum of neurological symptoms. Initial autopsies showed a novel neuronal tauopathy predominantly located in the tegmentum of the brainstem. Recently, new diagnostic red flags, biomarkers predictors of response to immunotherapy, and novel insights into the autoimmune pathogenesis of the disease have been reported.

RECENT FINDINGS

Patients with diagnosis of neurodegenerative dementia, progressive supranuclear palsy (PSP) or with motor-neuron disease (MND)-like syndrome have been reported to have IgLON5 antibodies, which are the hallmark of anti-IgLON5 disease. Second, low levels of neurofilament light chain in serum and cerebrospinal fluid of patients at disease onset could be a predictor of immunotherapy response. Recent neuropathological studies indicate that the neuronal tau deposits occur late in the course of the disease. Moreover, IgLON5 antibodies induce cytoskeletal changes in cultured hippocampal neurons suggesting that the tauopathy could be secondary of the IgLON5 antibody effects.

SUMMARY

Anti-IgLON5 disease can mimic and should be considered in atypical presentations of MND, neurodegenerative dementia and PSP. Neurofilament light chain levels seem promising biomarker for disease prognosis. Finally, the neuropathological and in vitro experimental studies strengthen the autoimmune hypothesis of the disease.

Interest of rare autoantibodies in autoimmune encephalitis and paraneoplastic neurological syndromes: the utility (or futility) of rare antibody discovery

PURPOSE OF REVIEW

The increasing recognition and diagnosis of autoimmune encephalitis (AE) and paraneoplastic neurological syndromes (PNS) is partly due to neural autoantibody testing and discovery. The past two decades witnessed an exponential growth in the number of identified neural antibodies. This review aims to summarize recent rare antibody discoveries in the context of central nervous system (CNS) autoimmunity and evaluate the ongoing debate about their utility.

RECENT FINDINGS

In the last 5 years alone 15 novel neural autoantibody specificities were identified. These include rare neural antibody biomarkers of autoimmune encephalitis, cerebellar ataxia or other movement disorders, including multifocal presentations.

SUMMARY

Although the clinical applications of these rare antibody discoveries may be limited by the low number of positive cases, they still provide important diagnostic, prognostic, and therapeutic insights.

Mechanisms of autoimmune encephalitis

PURPOSE OF REVIEW

To provide an overview of the pathogenic mechanisms involved in autoimmune encephalitides mediated by antibodies against neuronal surface antigens, with a focus on NMDAR and LGI1 encephalitis.

RECENT FINDINGS

In antibody-mediated encephalitides, binding of IgG antibodies to neuronal surface antigens results in different pathogenic effects depending on the type of antibody, IgG subclass and epitope specificity. NMDAR IgG1 antibodies cause crosslinking and internalization of the target, synaptic and brain circuitry alterations, as well as alterations of NMDAR expressing oligodendrocytes, suggesting a link with white matter lesions observed in MRI studies. LGI1 IgG4 antibodies, instead, induce neuronal dysfunction by disrupting the interaction with cognate proteins and altering AMPAR-mediated signaling. In-vitro findings have been corroborated by memory and behavioral changes in animal models obtained by passive transfer of patients' antibodies or active immunization. These models have been fundamental to identify targets for innovative therapeutic strategies, aimed at counteracting or preventing antibody effects, such as the use of soluble ephrin-B2, NMDAR modulators (e.g., pregnenolone, SGE-301) or chimeric autoantibody receptor T cells (CAART) in models of NMDAR encephalitis.

SUMMARY

A deep understanding of the pathogenic mechanisms underlying antibody-mediated encephalitides is crucial for the development of new therapeutic approaches targeting brain autoimmunity.

Genetic predisposition to autoimmune encephalitis and paraneoplastic neurological syndromes

PURPOSE OF REVIEW

We summarize the recent discoveries on genetic predisposition to autoimmune encephalitis and paraneoplastic neurological syndromes (PNS), emphasizing clinical and pathophysiological implications.

RECENT FINDINGS

The human leukocyte antigen (HLA) is the most studied genetic factor in autoimmune encephalitis and PNS. The HLA haplotype 8.1, which is widely known to be related to systemic autoimmunity, has been only weakly associated with a few types of autoimmune encephalitis and PNS. However, the strongest and most specific associations have been reported in a subgroup of autoimmune encephalitis that comprises antileucine-rich glioma-inactivated 1 (LGI1) limbic encephalitis, associated with DRB1∗07 : 01 , anticontactin-associated protein-like 2 (CASPR2) limbic encephalitis, associated with DRB1∗11 : 01 , and anti-IgLON5 disease, associated with DRB1∗10 : 01∼DQA1∗01∼DQB1∗05 . Non-HLA genes have been poorly investigated so far in autoimmune encephalitis, mainly in those lacking HLA associations such as anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, with only a few genome-wide association studies (GWAS) reporting equivocal results principally limited by small sample size.

SUMMARY

Genetic predisposition seems to be driven mostly by HLA in a group of autoimmune encephalitis characterized by being nonparaneoplastic and having predominantly IgG4 autoantibodies. The contribution of non-HLA genes, especially in those diseases lacking known or strong HLA associations, will require large cohorts enabling GWAS to be powerful enough to render meaningful results.

The presence and clinical significance of autoantibodies in amyotrophic lateral sclerosis: a narrative review

Amyotrophic lateral sclerosis (ALS) is a debilitating and rapidly fatal neurodegenerative disease, which is characterized by the selective loss of the upper and lower motor neurons. The pathogenesis of ALS remains to be elucidated and has been connected to genetic, environmental and immune conditions. Evidence from clinical and experimental studies has suggested that the immune system played an important role in ALS pathophysiology. Autoantibodies are essential components of the immune system. Several autoantibodies directed at antigens associated with ALS pathogenesis have been identified in the serum and/or cerebrospinal fluid of ALS patients. The aim of this review is to summarize the presence and clinical significance of autoantibodies in ALS.

Upper airway manifestations of anti-IgLON5 disease: Otorhinolaryngological point of view

INTRODUCTION

Anti-IgLON5 disease is a recently described neurological disorder with multisystemic features. The disease is characterized by the presence of IgLON5 antibodies in serum and cerebrospinal fluid. Our objective is to describe in detail the otorhinolaryngological manifestations of this disease, which are frequent and may include dysphagia, dysarthria, vocal cord paralysis and laryngospasm.

METHODS

In this study, we present a series of 9 patients with anti-IgLON5 disease and otolaryngological manifestations. Patients were evaluated between July 2012 and March 2022 by video-polysomnography, fiber-optic laryngoscopy, and functional endoscopic evaluation of swallowing.

RESULTS

The median age was 71 years, and 5 (56%) were female. Video-polysomnography showed a NREM/REM parasomnia in 6 patients (67%), obstructive sleep apnea in 8 (88%), stridor during sleep in 7 (78%) and central apneas in 1 (11%). Six out of the 9 patients (67%) presented episodes of acute respiratory failure that required mechanical ventilation, 6 had vocal fold palsy with 4 of them requiring tracheostomy (3 had to be performed on an emergency basis). Dysphagia occurred in 8 patients (89%). Prominent upper airway secretion and sialorrhea was also present in 3 cases.

CONCLUSION

The anti-IgLON5 disease exhibits extensive otolaryngological symptoms, mainly affecting the upper airway. These symptoms affect the quality of life and can be life-threatening. Prompt acute management is essential for stridor, dyspnea, and dysphagia. Given the potential severity of the symptoms and rarity of the disease, it is important for otolaryngologists to be familiar with anti-IgLON5 disease.

LEVEL OF EVIDENCE

Level 4.

Clinical analysis and literature review of two paediatric cases of anti-IgLON5 antibody-related encephalitis

Introduction

Anti-IgLON5 antibody-related encephalitis is a rare autoimmune disorder of the central nervous system, predominantly occurring in middle-aged elderly individuals, with paediatric cases being exceptionally rare. This study aims to enhance the understanding of paediatric anti-IgLON5 antibody-related encephalitis by summarising its clinical and therapeutic characteristics.

Method

A retrospective analysis was conducted on two paediatric patients diagnosed with anti-IgLON5 antibody-related encephalitis at Hunan Children's Hospital from August 2022 to November 2023. This involved reviewing their medical records and follow-up data, in addition to a literature review.

Results

The study involved two patients, one male and one female, aged between 2.5 and 9.6 years, both presenting with an acute/subacute course of illness. Clinically, both exhibited movement disorders (including dystonia, involuntary movements, and ataxia), cognitive impairments, sleep disturbances, and psychiatric symptoms. Patient 1 experienced epileptic seizures, while Patient 2 exhibited brainstem symptoms and abnormal eye movements. Neither patient showed autonomic dysfunction. Patient 1 had normal cerebrospinal fluid (CSF) and Brain MRI findings, whereas Patient 2 showed moderate leukocytosis and mild protein elevation in the CSF, and Brain MRI revealed symmetrical lesions in the basal ganglia and cerebellum. Oligoclonal bands in the CSF were positive in both cases. Both patients tested negative for HLA-DQB*05:01 and HLA-DRB*10:01. They received both first-line and second-line immunotherapies, with Patient 2 showing a poor response to treatment.

Discussion

Paediatric cases of anti-IgLON5 antibody-related encephalitis similarly present sleep disturbances as a core symptom, alongside various forms of movement disorders. Immunotherapy is partially effective. Compared to adult patients, these paediatric cases tend to exhibit more pronounced psychiatric symptoms, a more rapid onset, and more evident inflammatory changes in the CSF. The condition appears to have a limited association with HLA-DQB*05:01 and HLA-DRB*10:01 polymorphisms.

Phenotypic Insights Into Anti-IgLON5 Disease in IgLON5-Deficient Mice

BACKGROUND AND OBJECTIVES

Anti-IgLON5 disease is an autoimmune neurodegenerative disorder characterized by various phenotypes, notably sleep and movement disorders and tau pathology. Although the disease is known to be associated with the neuronal cell adhesion protein IgLON5, the physiologic function of IgLON5 remains elusive. There are conflicting views on whether autoantibodies cause loss of function, activation of IgLON5, or inflammation-associated neuronal damage, ultimately leading to the disease. We generated IgLON5 knockout (-/-) mice to investigate the functions of IgLON5 and elucidate the pathomechanism of anti-IgLON5 disease.

METHODS

IgLON5 knockout (-/-) mice underwent behavioral tests investigating motor function, psychiatric function (notably anxiety and depression), social and exploratory behaviors, spatial learning and memory, and sensory perception. Histologic analysis was conducted to investigate tau aggregation in mice with tauopathy.

RESULTS

IgLON5-/- mice had poorer performance in the wire hang and rotarod tests (which are tests for motor function) than wild-type mice. Moreover, IgLON5-/- mice exhibited decreased anxiety-like behavior and/or hyperactivity in behavior tests, including light/dark transition test and open field test. IgLON5-/- mice also exhibited poorer remote memory in the contextual fear conditioning test. However, neither sleeping disabilities assessed by EEG nor tau aggregation was detected in the knockout mice.

DISCUSSION

These results suggest that IgLON5 is associated with activity, anxiety, motor ability, and contextual fear memory. Comparing the various phenotypes of anti-IgLON5 disease, anti-IgLON5 disease might partially be associated with loss of function of IgLON5; however, other phenotypes, such as sleep disorders and tau aggregation, can be caused by gain of function of IgLON5 and/or neuronal damage due to inflammation. Further studies are needed to elucidate the role of IgLON5 in the pathogenesis of anti-IgLON5 diseases.

Autoimmune encephalitis: what the radiologist needs to know

Autoimmune encephalitis is a relatively novel nosological entity characterized by an immune-mediated damage of the central nervous system. While originally described as a paraneoplastic inflammatory phenomenon affecting limbic structures, numerous instances of non-paraneoplastic pathogenesis, as well as extra-limbic involvement, have been characterized. Given the wide spectrum of insidious clinical presentations ranging from cognitive impairment to psychiatric symptoms or seizures, it is crucial to raise awareness about this disease category. In fact, an early diagnosis can be dramatically beneficial for the prognosis both to achieve an early therapeutic intervention and to detect a potential underlying malignancy. In this scenario, the radiologist can be the first to pose the hypothesis of autoimmune encephalitis and refer the patient to a comprehensive diagnostic work-up - including clinical, serological, and neurophysiological assessments.In this article, we illustrate the main radiological characteristics of autoimmune encephalitis and its subtypes, including the typical limbic presentation, the features of extra-limbic involvement, and also peculiar imaging findings. In addition, we review the most relevant alternative diagnoses that should be considered, ranging from other encephalitides to neoplasms, vascular conditions, and post-seizure alterations. Finally, we discuss the most appropriate imaging diagnostic work-up, also proposing a suggested MRI protocol.

Recent advances in non-Huntington's disease choreas

INTRODUCTION

Chorea is primarily due to an imbalance of basal ganglia output pathways, often due to dysfunction or degeneration of the caudate nucleus and putamen, and can be due to many causes.

METHODS

We reviewed the recent literature to identify newly-recognized causes of chorea, including auto-immune, metabolic, and genetic. We also focused upon developments in mechanisms relating to underlying pathophysiology of certain genetic choreas and advances in therapeutics.

RESULTS

Novel autoantibodies continue to be identified as causes of chorea. Both COVID-19 infection and vaccination are reported to result rarely in chorea, although in some cases causality is not clearly established. Advances in genetic testing continue to find more causes of chorea, and to expand the phenotype of known genetic disorders. Deep brain stimulation can be successful in certain circumstances.

CONCLUSION

Our understanding of mechanisms underlying this movement disorder continues to advance, however much remains to be elucidated.

Development of a Composite Score for the Clinical Assessment of Anti-IgLON5 Disease

BACKGROUND AND OBJECTIVES

To develop a composite score to assess the severity of the multiple symptoms present in anti-IgLON5 disease.

METHODS

The anti-IgLON5 disease composite score (ICS) was designed to evaluate 17 symptoms divided into 5 clinical domains (bulbar, sleep, movement disorders, cognition, and others). Each symptom was scored from 0 (absent/normal) to 3 or 6 (severe) depending on the contribution of the symptom to neurologic disability with a maximum ICS of 69. The ICS was tested in patients from 2 cohorts (Barcelona, Spain, and GENERATE, Germany) that included cases personally seen by the authors (internal) and patients whose ICS was obtained from information of questionnaires completed by the referring neurologists (external). Test-retest and interrater reliabilities of the ICS were assessed by the intraclass coefficient (ICC) and the correlation between the ICS and modified Rankin scale (mRS) with the nonparametric Spearman rank coefficient. The Wilcoxon signed rank test was used to compare the ICS at diagnosis of anti-IgLON5 disease and follow-up in a subset of patients with available clinical information.

RESULTS

A total of 86 patients (46 from Barcelona cohort; 40 from GENERATE cohort) were included. The median ICS was 15 (range 2-31). The ICS was higher in the Barcelona cohort than in the German cohort (18 vs 12, p < 0.001), due to higher partial scores in sleep and movement disorder domains. There were no significant differences in the ICS between internal and external patients (15 vs 14, p = 0.96). The ICS correlated with the mRS score (r = 0.429, p < 0.001). Test-retest and interrater reliabilities were excellent with an ICC of 0.997 (95% CI 0.992-0.999) and 0.973 (95% CI 0.925-0.990), respectively. ICS was retested during follow-up in 27 patients, and it was similar to that at diagnosis in 10 clinically stable patients (median ICS at diagnosis 11.5 vs 11.5 at follow-up; p = 1), higher in 8 patients who worsened (12.5 vs 18; p = 0.012), and lower in 9 patients who improved after immunotherapy (14 vs 10; p = 0.007).

DISCUSSION

The ICS is a valid method to assess the extension and severity of the different clinical manifestations of anti-IgLON5 disease.

Differentiating anti-IgLON5 disease and Lewy body dementia: a systematic review

BACKGROUND

Anti-IgLON5 disease is a rare but potentially reversible cause of cognitive impairment, sleep disturbances, dysautonomia, and movement disorders. It is an autoimmune encephalitis which, due to its insidious onset, could mimic neurodegenerative disorders, and multiple symptoms overlap with those seen in dementia with Lewy bodies (DLB). We hypothesized that the symptomatology and findings in patients with anti-IgLON5 disease overlapped with that of DLB.

OBJECTIVES

To assess the commonality of features in anti-IgLON5 disease and DLB and identify potential red flags for anti-IgLON5 disease in patients undergoing diagnostic evaluation for DLB.

METHODS

We searched in MEDLINE, Web of Science, and Embase from inception on December the 8th, 2022 with the search term "IgLON5". We performed a systematic review of case reports and case series of anti-IgLON5 disease, and two reviewers independently extracted data on symptoms and findings. Frequencies of symptoms were compared with consensus criteria for DLB.

RESULTS

We included 57 studies with 127 individual case reports of anti-IgLON5 disease (mean age 63 years at diagnosis, median symptom duration 2 years). Cognitive dysfunction was reported in 45% of cases, REM-sleep behavioral disorder in 15%, and 14% had parkinsonism. Respiratory insufficiency was reported in 37%, and bulbar symptoms in 67%.

CONCLUSIONS

We found a significant overlap between anti-IgLON5 disease and DLB. We propose that anti-IgLON5 disease should be considered in young patients with DLB with chorea, gaze palsy, early dysphagia, or prominent respiratory symptoms. Our study contributes to the emerging knowledge on symptoms and biomarkers in anti-IgLON5 disease.

Genetic forms of tauopathies: inherited causes and implications of Alzheimer's disease-like TAU pathology in primary and secondary tauopathies

Tauopathies are a heterogeneous group of neurologic diseases characterized by pathological axodendritic distribution, ectopic expression, and/or phosphorylation and aggregation of the microtubule-associated protein TAU, encoded by the gene MAPT. Neuronal dysfunction, dementia, and neurodegeneration are common features of these often detrimental diseases. A neurodegenerative disease is considered a primary tauopathy when MAPT mutations/haplotypes are its primary cause and/or TAU is the main pathological feature. In case TAU pathology is observed but superimposed by another pathological hallmark, the condition is classified as a secondary tauopathy. In some tauopathies (e.g. MAPT-associated frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Alzheimer's disease (AD)) TAU is recognized as a significant pathogenic driver of the disease. In many secondary tauopathies, including Parkinson's disease (PD) and Huntington's disease (HD), TAU is suggested to contribute to the development of dementia, but in others (e.g. Niemann-Pick disease (NPC)) TAU may only be a bystander. The genetic and pathological mechanisms underlying TAU pathology are often not fully understood. In this review, the genetic predispositions and variants associated with both primary and secondary tauopathies are examined in detail, assessing evidence for the role of TAU in these conditions. We highlight less common genetic forms of tauopathies to increase awareness for these disorders and the involvement of TAU in their pathology. This approach not only contributes to a deeper understanding of these conditions but may also lay the groundwork for potential TAU-based therapeutic interventions for various tauopathies.

MuSK Myasthenia Gravis-Potential Pathomechanisms and Treatment Directed against Specific Targets

Myasthenia gravis (MG) is an autoimmune disease in which autoantibodies target structures within the neuromuscular junction, affecting neuromuscular transmission. Muscle-specific tyrosine kinase receptor-associated MG (MuSK-MG) is a rare, often more severe, subtype of the disease with different pathogenesis and specific clinical features. It is characterized by a more severe clinical course, more frequent complications, and often inadequate response to treatment. Here, we review the current state of knowledge about potential pathomechanisms of the MuSK-MG and their therapeutic implications as well as ongoing research in this field, with reference to key points of immune-mediated processes involved in the background of myasthenia gravis.

Papillitis associated with IgLON5 autoimmunity: A novel clinical phenotype

OBJECTIVES

To describe papillitis as a clinical phenotype of IgLON5 autoimmunity.

METHODS

We retrospectively reviewed patients with IgLON5 autoimmunity who had optic neuropathy, optic neuritis, or optic disc edema. Sera from patients with recurrent papillitis were tested for IgLON5 antibodies.

RESULTS

We found two elderly males presenting with papillitis in the presence of IgLON5 antibodies. CSF pleocytosis was present and partial vision improvement occurred in one patient despite immunotherapy. Sera from 18 patients with recurrent papillitis were negative for IgLON5 antibodies.

CONCLUSION

Papillitis could be a manifestation of IgLON5 disease, with or without accompanying cognitive, sleep, and movement disorders.

Atypical neurological manifestations in anti-IgLON5 disease: a case report

Anti-IgLON5 disease is a recently discovered autoimmune encephalopathy with sleep disorder as a hallmark in the majority of reported cases. Additional neurological manifestations include bulbar dysfunction, gait problems, movement disorders, oculomotor abnormalities, and hyperexcitability of the nervous system. At present, an increasing number of publications have dealt with the course and possible treatment options for anti-IgLON5 disease, and its clinical spectrum has expanded wider and more heterogeneous. Here, we report a case of a 66-year-old female with cognitive impairment accompanied by slow reaction, impaired memory, and decreased orientation. A positive cerebral MRI change and serum and cerebrospinal fluid (CSF) antibodies against IgLON5 were found during the diagnostic course. Subsequently the patient received immunotherapy and was generally in good health with no new symptoms during follow-up. Early testing for IgLON5 antibodies should be considered in patients with atypical neurological symptoms such as cognitive impairment, slow reaction, or decreased orientation. In clinical practice, immunotherapy should be considered in all cases of anti-IgLON5 encephalopathies.

IgLON5 deficiency produces behavioral alterations in a knockout mouse model

Background

Anti-IgLON5 disease is a neurological disorder characterized by autoantibodies against IgLON5 and pathological evidence of neurodegeneration. IgLON5 is a cell adhesion molecule of unknown function that is highly expressed in the brain. Our aim was to investigate the impact of IgLON5 loss-of-function in evaluating brain morphology, social behavior, and the development of symptoms observed in an IgLON5 knockout (IgLON5-KO) mouse model.

Methods

The IgLON5-KO mice were generated using CRISPR-Cas9 technology. Immunohistochemistry on fixed sagittal brain sections and Western blotting brain lysates were used to confirm IgLON5 silencing and to evaluate the presence of other cell surface proteins. Two- month-old IgLON5-KO and wild-type (WT) mice underwent a comprehensive battery of behavioral tests to assess 1) locomotion, 2) memory, 3) anxiety, 4) social interaction, and 5) depressive-like behavior. Brain sections were examined for the presence of anatomical abnormalities and deposits of hyperphosphorylated tau in young adult (2-month-old) and aged (22-month-old) mice.

Results

Mice did not develop neurological symptoms reminiscent of those seen in patients with anti-IgLON5 disease. Behavioral testing revealed that 2-month-old IgLON5-KO mice showed subtle alterations in motor coordination and balance. IgLON5-KO females exhibited hyperactivity during night and day. Males were observed to have depressive-like behavior and excessive nest-building behavior. Neuropathological studies did not reveal brain morphological alterations or hyperphosphorylated tau deposits.

Conclusion

IgLON5-KO mice showed subtle alterations in behavior and deficits in fine motor coordination but did not develop the clinical phenotype of anti-IgLON5 disease.

The psychiatric symptoms in anti-IgLON5 disease: Case report and literature review

Immunotherapy may be ineffective in the advanced stages of anti-IgLON5 disease with psychiatric symptoms. The psychiatric symptoms in advanced stages of anti-IgLON5 disease may be associated with neurodegeneration.

Paraneoplastic movement disorders

Paraneoplastic movement disorders are diverse autoimmune neurological illnesses occurring in the context of systemic cancer, either in isolation or as part of a multifocal neurological disease. Movement phenomena may be ataxic, hypokinetic (parkinsonian), or hyperkinetic (myoclonus, chorea, or other dyskinetic disorders). Some disorders mimic neurodegenerative or hereditary illnesses. The subacute onset and coexisting nonclassic features of paraneoplastic disorders aid distinction. Paraneoplastic autoantibodies provide further information regarding differentiating cancer association, disease course, and treatment responses. A woman with cerebellar ataxia could have metabotropic glutamate receptor 1 autoimmunity, in the setting of Hodgkin lymphoma, a mild neurological phenotype and response to immunotherapy. A different woman, also with cerebellar ataxia, could have Purkinje cytoplasmic antibody type 1 (anti-Yo), accompanying ovarian adenocarcinoma, a rapidly progressive phenotype and persistent disabling deficits despite immune therapy. The list of antibody biomarkers is growing year-on-year, each with its own ideal specimen type for detection (serum or CSF), accompanying neurological manifestations, cancer association, treatment response, and prognosis. Therefore, a profile-based approach to screening both serum and CSF is recommended. Immune therapy trials are generally undertaken, and include one or more of corticosteroids, IVIg, plasma exchange, rituximab, or cyclophosphamide. Symptomatic therapies can also be employed for hyperkinetic disorders.

PSP-Richardson syndrome mimics: An overview and pragmatic approach

Progressive supranuclear palsy-Richardson syndrome (PSP-RS) is a sporadic atypical parkinsonian syndrome with levodopa-unresponsive axial-predominant parkinsonism, early postural instability, vertical supranuclear gaze palsy, dysarthria, executive dysfunction and behavioural changes. PSP-RS can be mimicked by numbers of other disorders, generally known as PSP mimics, or PSP-like syndromes. Their aetiological spectrum includes neurodegenerative (mostly genetic), vascular, infectious and drug-induced illnesses as well as other causes. Based on the available data, we have tried to create a definition of PSP-RS mimics: a syndrome resembling PSP-RS with at least one of the following red flags: 1) positive family history; 2) onset before 45 years of age; 3) rapid or stepwise progression; 4) acute or subacute onset; 5) atypical symptoms and/or signs; 6) normal or atypical brain MRI; 7) history of HIV or untreated syphilis, aortal surgery or recent therapy with dopamine-blocking agents. We have suggested a short diagnostic algorithm leading to the identification of PSP-RS mimics and the recommended diagnostic work-up. The key point of the diagnostic process is the early identification and treatment of potentially treatable PSP-RS mimics.

Changing landscape in the field of paraneoplastic neurology: Personal perspectives over a 35-year career

Paraneoplastic neurologic syndromes are a group of rare disorders that have fascinated neurologists for more than a century. The discovery in the 1980s that many of these disorders occurred in association with antibodies against neuronal proteins revived the interest for these diseases. This chapter first traces the history of the paraneoplastic neurologic syndromes during the era that preceded the discovery of immune mechanisms and then reviews the immunologic period during which many of these syndromes were found to be associated with antibodies against intracellular onconeuronal proteins and pathogenic cytotoxic T-cell mechanisms. Alongside these developments, investigations on the antibody-mediated disorders of the peripheral nervous system, such as the myasthenic syndromes or neuromyotonia, provided suggestions for the study of the central nervous system (CNS) syndromes. These converging areas of research culminated with the groundbreaking discovery of a new category of CNS disorders mediated by antibodies against neuronal surface proteins or receptors. These disorders are not always paraneoplastic, and the understanding of these syndromes and mechanisms has changed the landscape of neurology and neurosciences.

General features, pathogenesis, and laboratory diagnostics of autoimmune encephalitis

Autoimmune encephalitis (AE) is a group of inflammatory conditions that can associate with the presence of antibodies directed to neuronal intracellular, or cell surface antigens. These disorders are increasingly recognized as an important differential diagnosis of infectious encephalitis and of other common neuropsychiatric conditions. Autoantibody diagnostics plays a pivotal role for accurate diagnosis of AE, which is of utmost importance for the prompt recognition and early treatment. Several AE subgroups can be identified, either according to the prominent clinical phenotype, presence of a concomitant tumor, or type of neuronal autoantibody, and recent diagnostic criteria have provided important insights into AE classification. Antibodies to neuronal intracellular antigens typically associate with paraneoplastic neurological syndromes and poor prognosis, whereas antibodies to synaptic/neuronal cell surface antigens characterize many AE subtypes that associate with tumors less frequently, and that are often immunotherapy-responsive. In addition to the general features of AE, we review current knowledge on the pathogenic mechanisms underlying these disorders, focusing mainly on the potential role of neuronal antibodies in the most frequent conditions, and highlight current theories and controversies. Then, we dissect the crucial aspects of the laboratory diagnostics of neuronal antibodies, which represents an actual challenge for both pathologists and neurologists. Indeed, this diagnostics entails technical difficulties, along with particularly interesting novel features and pitfalls. The novelties especially apply to the wide range of assays used, including specific tissue-based and cell-based assays. These assays can be developed in-house, usually in specialized laboratories, or are commercially available. They are widely used in clinical immunology and in clinical chemistry laboratories, with relevant differences in analytic performance. Indeed, several data indicate that in-house assays could perform better than commercial kits, notwithstanding that the former are based on non-standardized protocols. Moreover, they need expertise and laboratory facilities usually unavailable in clinical chemistry laboratories. Together with the data of the literature, we critically evaluate the analytical performance of the in-house vs commercial kit-based approach. Finally, we propose an algorithm aimed at integrating the present strategies of the laboratory diagnostics in AE for the best clinical management of patients with these disorders.

Pathophysiological Effects of Autoantibodies in Autoimmune Encephalitides

The heterogeneity of autoantibody targets in autoimmune encephalitides presents a challenge for understanding cellular and humoral pathophysiology, and the development of new treatment strategies. Thus, current treatment aims at autoantibody removal and immunosuppression, and is primarily based on data generated from other autoimmune neurological diseases and expert consensus. There are many subtypes of autoimmune encephalitides, which now entails both diseases with autoantibodies targeting extracellular antigens and classical paraneoplastic syndromes with autoantibodies targeting intracellular antigens. Here, we review the current knowledge of molecular and cellular effects of autoantibodies associated with autoimmune encephalitis, and evaluate the evidence behind the proposed pathophysiological mechanisms of autoantibodies in autoimmune encephalitis.

Progressive Ataxia and Palatal Tremor Is Not Associated with IgLON5 Antibodies: Results From Two Cases

Progressive ataxia and palatal tremor (PAPT) and anti-IgLON5 disease share possible clinical presentations. Furthermore, both have been associated to a tauopathy mainly affecting the brainstem. Nonetheless, anti-IgLON5 antibodies have never been tested in PAPT. We report on two PAPT cases without evidence of anti-IgLON5 antibodies in both CSF and serum. Despite common clinical and pathological characteristics, PAPT and IgLON5 disease are two distinct entities.

Autoimmune processes in neurological patients are much more common than presently suspected

Autoimmune encephalitides are seldom diseases. How rare they actually are, however, is not known. The low incidence combined with the problematic identification may dampen efforts of neurologists, to identify patients with unclear symptoms as suffering from autoimmune encephalitis. Here, we aim to obtain a better estimate, how many patients with autoimmune disorders should be expected among 100 inpatients in a conventional neurological department. From a total number of 2603 non-stroke patients attended in a 2-year period (2018-2019) 460 CSFs were obtained. From this collection 187 samples (40.7%, > 500 sections) could be analyzed with our immunocytochemical technique. Autoreactive antibodies were detected in 102 (55%) of these 187 CSF samples. Certainly, the presence of autoreactive antibodies does not necessarily indicate that the patient suffers from an autoimmune disease. Our data indicate that from roughly 2000 patients during 1 year about 125 patients with autoreactive CSF antibodies should be expected in a conventional neurological department. This represents the about 35-fold value of what is generally expected at present. Being aware of this high incidence may intensify the efforts of neurologist to identify patients with any type of autoimmune encephalitis. This will be beneficial for patients, because they often profit from immunomodulatory therapy. Interestingly, some CFSs from our patients react with the CA2 subdivision of the hippocampus. While long neglected, recent research places this area into an important position to influence hippocampal network physiology. Autoreactive antibodies in the CSF may disturb the function of CA2 neurons, thereby explaining some neuropsychiatric symptoms in patients with autoimmune encephalitides.

In Vivo Measurement of Tau Depositions in Anti-IgLON5 Disease Using [18F]PI-2620 PET

OBJECTIVES

Anti-IgLON5 disease is a recently discovered neurologic disorder combining autoimmunity and neurodegeneration. Core manifestations include sleep disorders, bulbar symptoms, gait abnormalities, and cognitive dysfunction, but other presentations have been reported. Hallmarks are autoantibodies targeting the neuronal surface protein IgLON5, a strong human leukocyte antigen system Class II association, and brainstem and hypothalamus-dominant tau deposits. The purpose of this cohort study was to visualize tau deposition in vivo with the second-generation tau-PET tracer.

METHODS

A cohort of 4 patients with anti-IgLON5 disease underwent a dynamic PET scan with [18F]PI-2620. One patient received a follow-up scan. Z-deviation maps and a 2-sample t test in comparison with healthy controls (n = 10) were performed. Antibody titers, neurofilament light chain, and disease duration were correlated with brainstem binding potentials.

RESULTS

Patients demonstrated increased [18F]PI2620 tau binding potentials in the pons, dorsal medulla, and cerebellum. The longitudinal scan after 28 months showed an increase of tracer uptake in the medulla despite immunotherapy. Higher antibody titers and neurofilament light chain correlated with higher tracer retention.

DISCUSSION

The results indicate that tau depositions in anti-IgLON5 disease can be visualized with [18F]PI-2620 and might correlate with the extent of disease. For validation, a larger longitudinal study is necessary.

Differential diagnosis of chorea (guidelines of the German Neurological Society)

INTRODUCTION

Choreiform movement disorders are characterized by involuntary, rapid, irregular, and unpredictable movements of the limbs, face, neck, and trunk. These movements often initially go unnoticed by the affected individuals and may blend together with seemingly intended, random motions. Choreiform movements can occur both at rest and during voluntary movements. They typically increase in intensity with stress and physical activity and essentially cease during deep sleep stages. In particularly in advanced stages of Huntington disease (HD), choreiform hyperkinesia occurs alongside with dystonic postures of the limbs or trunk before they typically decrease in intensity. The differential diagnosis of HD can be complex. Here, the authors aim to provide guidance for the diagnostic process. This guidance was prepared for the German Neurological Society (DGN) for German-speaking countries.

RECOMMENDATIONS

Hereditary (inherited) and non-hereditary (non-inherited) forms of chorea can be distinguished. Therefore, the family history is crucial. However, even in conditions with autosomal-dominant transmission such as HD, unremarkable family histories do not necessarily rule out a hereditary form (e.g., in cases of early deceased or unknown parents, uncertainties in familial relationships, as well as in offspring of parents with CAG repeats in the expandable range (27-35 CAG repeats) which may display expansions into the pathogenic range).

CONCLUSIONS

The differential diagnosis of chorea can be challenging. This guidance prepared for the German Neurological Society (DGN) reflects the state of the art as of 2023.

Evaluation and treatment approaches for neurological post-acute sequelae of COVID-19: A consensus statement and scoping review from the global COVID-19 neuro research coalition

Post-acute neurological sequelae of COVID-19 affect millions of people worldwide, yet little data is available to guide treatment strategies for the most common symptoms. We conducted a scoping review of PubMed/Medline from 1/1/2020-4/1/2023 to identify studies addressing diagnosis and treatment of the most common post-acute neurological sequelae of COVID-19 including: cognitive impairment, sleep disorders, headache, dizziness/lightheadedness, fatigue, weakness, numbness/pain, anxiety, depression and post-traumatic stress disorder. Utilizing the available literature and international disease-specific society guidelines, we constructed symptom-based differential diagnoses, evaluation and management paradigms. This pragmatic, evidence-based consensus document may serve as a guide for a holistic approach to post-COVID neurological care and will complement future clinical trials by outlining best practices in the evaluation and treatment of post-acute neurological signs/symptoms.

REM Behavior Disorder: Implications for PD Therapeutics

PURPOSE

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia that occurs during REM sleep, characterized by REM sleep without atonia (RSWA) and dream enactment behavior (DEB). RBD is associated with several diseases and medications but most notably is a prodromal feature of synucleinopathies, including Parkinson's disease (PD). This article reviews RBD, its treatments, and implications for PD therapeutics.

RECENT FINDINGS

Recent research recognizes RBD as a prodromal marker of PD, resulting in expansion of basic science and clinical investigations of RBD. Current basic science research investigates the pathophysiology of RBD and explores animal models to allow therapeutic development. Clinical research has focused on natural history observation, as well as potential RBD treatments and their impact on sleep and phenoconversion to neurodegenerative disease. RBD serves as a fresh access point to develop both neuroprotective and symptomatic therapies in PD. These types of investigations are novel and will benefit from the more established basic science infrastructure to develop new interventions.

Trigeminal Nerve Involvement in Bulbar-Onset Anti-IgLON5 Disease

OBJECTIVES

Anti-IgLON5 disease (IgLON5-D) may present with a bulbar-onset motor neuron disease-like phenotype, mimicking bulbar-onset amyotrophic lateral sclerosis. Recognition of their distinctive clinical and paraclinical features may help for differential diagnosis. We report 2 cases of atypical trigeminal neuropathy in bulbar-onset IgLON5-D.

METHODS

Trigeminal nerve involvement was assessed using comprehensive clinical, laboratory, electrophysiologic, and MRI workup.

RESULTS

Both patients were referred for progressive dysphagia, sialorrhea, and hoarseness. They were treated with bilevel positive airway pressure for nocturnal hypoventilation. Patient 1 complained of continuous facial burning pain with allodynia, exacerbated by mastication and prolonged speech. Patient 2 reported no facial pain. Anti-IgLON5 autoantibodies (IgLON5-Abs) were positive in serum for both patients and CSF for patient 1. Cerebral MRI revealed bilateral T2 fluid-attenuated inversion recovery (FLAIR) hyperintensity and enlargement of trigeminal nerves without gadolinium enhancement in both patients. Needle myography showed fasciculations in masseter muscles. Blink-reflex study confirmed bilateral trigeminal neuropathy only in patient 2. Cortical laser-evoked potentials showed a bilateral small-fiber dysfunction in the trigeminal nerve ophthalmic branch in patient 1.

DISCUSSION

In case of progressive atypical bulbar symptoms, the presence of a trigeminal neuropathy or trigeminal nerve abnormalities on MRI should encourage the testing of IgLON5-Abs in serum and CSF.

Mimics of Autoimmune Encephalitis: Validation of the 2016 Clinical Autoimmune Encephalitis Criteria

BACKGROUND AND OBJECTIVES

The clinical criteria for autoimmune encephalitis (AE) were proposed by Graus et al. in 2016. In this study, the AE criteria were validated in the real world, and common AE mimics were described. In addition, criteria for probable anti-LGI1 encephalitis were proposed and validated.

METHODS

In this retrospective cohort study, patients referred to our national referral center with suspicion of AE and specific neuroinflammatory disorders with similar clinical presentations were included from July 2016 to December 2019. Exclusion criteria were pure cerebellar or peripheral nerve system disorders. All patients were evaluated according to the AE criteria.

RESULTS

In total, 239 patients were included (56% female; median age 42 years, range 1-85). AE was diagnosed in 104 patients (44%) and AE mimics in 109 patients (46%). The most common AE mimics and misdiagnoses were neuroinflammatory CNS disorders (26%), psychiatric disorders (19%), epilepsy with a noninflammatory cause (13%), CNS infections (7%), neurodegenerative diseases (7%), and CNS neoplasms (6%). Common confounding factors were mesiotemporal lesions on brain MRI (17%) and false-positive antibodies in serum (12%). Additional mesiotemporal features (involvement extralimbic structures, enhancement, diffusion restriction) were observed more frequently in AE mimics compared with AE (61% vs 24%; p = 0.005). AE criteria showed the following sensitivity and specificity: possible AE, 83% (95% CI 74-89) and 27% (95% CI 20-36); definite autoimmune limbic encephalitis (LE), 10% (95% CI 5-17) and 98% (95% CI 94-100); and probable anti-NMDAR encephalitis, 50% (95% CI 26-74) and 96% (95% CI 92-98), respectively. Specificity of the criteria for probable seronegative AE was 99% (95% CI 96-100). The newly proposed criteria for probable anti-LGI1 encephalitis showed a sensitivity of 66% (95% CI 47-81) and specificity of 96% (95% CI 93-98).

DISCUSSION

AE mimics occur frequently. Common pitfalls in AE misdiagnosis are mesiotemporal lesions (predominantly with atypical features) and false-positive serum antibodies. As expected, the specificity of the criteria for possible AE is low because these criteria represent the minimal requirements for entry in the diagnostic algorithm for AE. Criteria for probable AE (-LGI1, -NMDAR, seronegative) and definite autoimmune LE are applicable for decisions on immunotherapy in early disease stage, as specificity is high.

Analysis of inflammatory markers and tau deposits in an autopsy series of nine patients with anti-IgLON5 disease

Anti-IgLON5 disease is a rare neurological, probably autoimmune, disorder associated in many cases with a specific tauopathy. Only a few post-mortem neuropathological studies have been reported so far. Little is known about the pathogenic mechanisms that result in neurodegeneration. We investigated the neuropathology of anti-IgLON5 disease and characterized cellular and humoral inflammation. We included nine cases (six of them previously published). Median age of patients was 71 years (53-82 years), the median disease duration was 6 years (0.5-13 years), and the female to male ratio was 5:4. Six cases with a median disease duration of 9 years presented a prominent tauopathy. Five of them had a classical anti-IgLON5-related brainstem tauopathy and another presented a prominent neuronal and glial 4-repeat tauopathy, consistent with progressive supranuclear palsy (PSP). Three cases with short disease duration (median 1.25 years) only showed a primary age-related neurofibrillary pathology. Inflammatory infiltrates of T and B cells were mild to moderate and did not significantly differ between anti-IgLON5 disease cases with or without tauopathy. In contrast, we found an extensive neuropil deposition of IgG4 in the tegmentum of the brainstem, olivary nucleus, and cerebellar cortex that was most prominent in two patients with short disease duration without the typical IgLON5-related tauopathy. The IgG4 deposits were particularly prominent in the cerebellar cortex and in these regions accompanied by mild IgG1 deposits. Activated complement deposition (C9neo) was absent. Our study indicates that IgLON5-related tau pathology occurs in later disease stages and may also present a PSP-phenotype with exclusively 4-repeat neuronal and glial tau pathology. The prominent deposition of anti-IgLON5 IgG4 at predilection sites for tau pathology suggests that anti-IgLON5 antibodies precede the tau pathology. Early start of immunotherapy might prevent irreversible neuronal damage and progression of the disease, at least in a subgroup of patients.

[Parkinson's and Alzheimer's disease as system-wide neurodegenerative disorders]

BACKGROUND

Parkinson's and Alzheimer's disease (PD/AD) are characterized by cellular pathological changes that precede clinical manifestation and symptom onset by decades (prodromal period) as well as by a heterogeneity of clinical symptoms. Both diseases are recognized as system-wide diseases with organ-transgressing dysregulation and involvement of immunological and neuroinflammatory mechanisms facilitating pathological protein aggregation and neurodegeneration.

OBJECTIVES

Overview of natural course, phenotypes and classification of PD/AD with a focus on underlying (system-wide) immunological and neuroinflammatory mechanisms.

METHODS

Literature research and consideration of expert opinions.

RESULTS

The accumulation of misfolded proteins such as amyloid‑β and synuclein in the course of neurodegenerative processes forms the basis of the current biological classifications, understanding of course and subtypes. Protein aggregation in PD/AD induces an innate immune response by activating microglia and the release of inflammatory mediators such as cytokines and chemokines and leading to further spread of neurodegeneration and accumulation of intracellular neurofibrillary tangles (NFTs). There is also growing evidence that adaptive immune responses involving auto-antibodies or auto-antigen-specific T‑/B-cell reactions involving tau, amyloid‑β or synuclein might be involved in the disease progression or subtypes of PD/AD.

CONCLUSIONS

Both innate and adaptive immune responses seem to be substantially involved in the pathological cascade leading to neurodegeneration in PD/AD and may contribute to disease progression and clinical subtypes. Thus, future targeted interventions should not only focus on protein aggregation but also on neuroinflammatory and immunological mechanisms.

Scoring sleep in neurodegenerative diseases: A pilot study in the synucleinopathies

BACKGROUND

Neurodegenerative diseases often alter sleep architecture, complicating the application of the standard sleep scoring rules. There are no recommendations to overcome this problem. Our aim was to develop a scoring method that incorporates the stages previously applied in dementia with Lewy Bodies (DLB), anti-IgLON5 disease, and fatal insomnia, and to test it in patients with alpha-synucleinopathies.

METHODS

Video-polysomnographies (VPSG) of nine patients (DLB:3, Parkinson's disease (PD):3, and multiple system atrophy (MSA):3) selected for their difficulty in applying standard rules were scored independently by two authors, using additional Sleep/Wake stages. These included Abnormal Wake, Subwake, Undifferentiated NREM sleep (UNREM), Poorly structured N2 (P-S N2) and abnormal REM sleep including REM without atonia (RWA), REM without low-amplitude, mixed-frequency EEG activity (RWL) and REM without rapid eye movements (RWR).

RESULTS

Patients (4 females) had a median age of 74 (range 63-85). Six patients (all with PD or DLB) had abnormal EEG awake and Subwake stage. UNREM sleep was present in all patients, typically at sleep onset, and was the most common sleep stage in five. P-S N2 was recorded only in the three patients with MSA. Periods of normal and abnormal NREM coexisted in three patients. RWA was the predominant REM subtype, RWR occurred mainly in patients with MSA and RWL in those with DLB. Six patients had brief REM episodes into NREM sleep which we termed "Encapsulated RBD".

CONCLUSION

Our scoring system allows an accurate description of the complex sleep-wake changes in patients with alpha-synucleinopathies.

Sleep Disturbances in Autoimmune Neurological Diseases

PURPOSE OF REVIEW

To summarize the current evidence on the associations between autoimmune neurological diseases (e.g., multiple sclerosis, myasthenia gravis) and sleep disturbances (e.g., insomnia, parasomnias), as well as to review the main characteristics of sleep disorders with an immune-related pathophysiology (e.g., narcolepsy, anti-IgLON5 disease).

RECENT FINDINGS

An immune-mediated damage of the areas in the central nervous system that control sleep and wake functions (e.g., hypothalamus, brainstem) can lead to sleep disorders and sleep symptoms. Sleep disturbances are the reason to seek for medical attention in certain neuroimmunological conditions (e.g., narcolepsy, anti-IgLON5 disease) where sleep-related alterations are the main clinical feature. The assessment of sleep-related symptomatology and disorders should be included in the routine evaluation of patients with autoimmune neurological diseases. Clinicians should be aware of the typical clinical presentation of certain neuroimmunological disorders mainly affecting sleep.

The Role of IgLON Cell Adhesion Molecules in Neurodegenerative Diseases

In the brain, cell adhesion molecules (CAMs) are critical for neurite outgrowth, axonal fasciculation, neuronal survival and migration, and synapse formation and maintenance. Among CAMs, the IgLON family comprises five members: Opioid Binding Protein/Cell Adhesion Molecule Like (OPCML or OBCAM), Limbic System Associated Membrane Protein (LSAMP), neurotrimin (NTM), Neuronal Growth Regulator 1 (NEGR1), and IgLON5. IgLONs exhibit three N-terminal C2 immunoglobulin domains; several glycosylation sites; and a glycosylphosphatidylinositol anchoring to the membrane. Interactions as homo- or heterodimers in cis and in trans, as well as binding to other molecules, appear critical for their functions. Shedding by metalloproteases generates soluble factors interacting with cellular receptors and activating signal transduction. The aim of this review was to analyse the available data implicating a role for IgLONs in neuropsychiatric disorders. Starting from the identification of a pathological role for antibodies against IgLON5 in an autoimmune neurodegenerative disease with a poorly understood mechanism of action, accumulating evidence links IgLONs to neuropsychiatric disorders, albeit with still undefined mechanisms which will require future thorough investigations.

Sleep Disorders Associated with Neurodegenerative Diseases

Sleep disturbances are common in various neurological pathologies, including amyotrophic lateral sclerosis (ALS), multiple system atrophy (MSA), hereditary ataxias, Huntington's disease (HD), progressive supranuclear palsy (PSP), and dementia with Lewy bodies (DLB). This article reviews the prevalence and characteristics of sleep disorders in these conditions, highlighting their impact on patients' quality of life and disease progression. Sleep-related breathing disorders, insomnia, restless legs syndrome (RLS), periodic limb movement syndrome (PLMS), and rapid eye movement sleep behavior disorder (RBD) are among the common sleep disturbances reported. Both pharmacological and non-pharmacological interventions play crucial roles in managing sleep disturbances and enhancing overall patient care.

Purified Serum IgG from a Patient with Anti-IgLON5 Antibody Cause Long-Term Movement Disorders with Impaired Dopaminergic Pathways in Mice

Background: Anti-IgLON5 disease is a rare autoimmune disease of the central nervous system. It typically manifests as a chronic condition, characterized by cognitive impairments, movement disorders, and sleep disorders. The mechanisms underlying movement disorders in this disease remain poorly understood due to a lack of research. Furthermore, this disease exhibits both neuroimmune and neurodegenerative characteristics. The objective of this study is to explore the underlying mechanisms of movement disorders caused by anti-IgLON5 antibodies for the first time. Methods: Antibodies were purified from the serum of a confirmed patient of anti-IgLON5 disease. The passive transfer animal models were employed, where antibodies were continuously injected into the substantia nigra pars compacta (SNc) of the mouse midbrain using stereotactic injection to explore the mechanism of movement disorder. The effects of anti-IgLON5 antibodies on dopaminergic neurons in the SNc and neurodegeneration were examined through immunohistochemistry. Changes in neurotransmitter levels in the basal ganglia were assessed using high-performance liquid chromatography. Additionally, RNA-seq was employed to identify the differentially expressed genes associated with the short-term and long-term effects of anti-IgLON5 antibody on the SNc. Results: Mice injected with anti-IgLON5 antibodies in the SNc exhibited persistent movement impairments for up to 3 months. One week after antibody injection, the number of TH neurons significantly decreased compared to the control group, accompanied by reduced projection fibers in the basal ganglia and decreased dopamine levels. After 3 months of antibody injection, an increase in phosphorylated Tau was observed in the SNc of the midbrain. Additionally, long-term sustained activation of microglia was detected in the SNc. The differentially expressed genes of long-term effects of IgLON5 antibodies were different from their short-term effects on the SNc. Conclusion: Purified serum IgG from a patient with anti-IgLON5 antibodies can cause long-term movement disorder in mice. The movement disorders appear to be linked to the impaired dopaminergic pathway, and the increased p-Tau showed neurodegenerative changes induced by the anti-IgLON5 antibody.

Unveiled central hypoventilation after tracheotomy in anti-IgLON5 disease: a case report

Anti-IgLON5 disease is a recently described entity that has been associated with neurological symptoms and sleep disturbances including sleep breathing disorders. Sleep stridor as well as obstructive and less often central sleep apnea have been reported but rarely needing ventilation on tracheotomy. We report the case of a patient in whom obstructive sleep apnea with secondary development of dysphagia and recurrent aspiration pneumonia led to the diagnosis of anti-IgLON 5 disease. Acute respiratory failure due to laryngospasm required intubation and eventually tracheotomy. Yet hypoventilation persisted, and polysomnography demonstrated central sleep apnea alternating with sleep-related tachypnea. Nocturnal ventilation was thus reintroduced. The association of obstructive sleep apnea with dysphagia is a potential red flag for anti-IgLON5 disease, which remains an overlooked diagnosis. Breathing disorders can be complex in this context, with a mixed obstructive and central pattern whose central component can be unveiled after tracheotomy. This highlights the importance of closely monitoring sleep and respiration even after tracheotomy.

CITATION

Tankéré P, Le Cam P, Folliet L, et al. Unveiled central hypoventilation after tracheotomy in anti-IgLON5 disease: a case report. J Clin Sleep Med. 2023;19(9):1701-1704.

Antibodies Associated With Autoimmune Encephalitis in Patients With Presumed Neurodegenerative Dementia

BACKGROUND & OBJECTIVES

Autoimmune encephalitis (AIE) may present with prominent cognitive disturbances without overt inflammatory changes in MRI and CSF. Identification of these neurodegenerative dementia diagnosis mimics is important because patients generally respond to immunotherapy. The objective of this study was to determine the frequency of neuronal antibodies in patients with presumed neurodegenerative dementia and describe the clinical characteristics of the patients with neuronal antibodies.

METHODS

In this retrospective cohort study, 920 patients were included with neurodegenerative dementia diagnosis from established cohorts at 2 large Dutch academic memory clinics. In total, 1,398 samples were tested (both CSF and serum in 478 patients) using immunohistochemistry (IHC), cell-based assays (CBA), and live hippocampal cell cultures (LN). To ascertain specificity and prevent false positive results, samples had to test positive by at least 2 different research techniques. Clinical data were retrieved from patient files.

RESULTS

Neuronal antibodies were detected in 7 patients (0.8%), including anti-IgLON5 (n = 3), anti-LGI1 (n = 2), anti-DPPX, and anti-NMDAR. Clinical symptoms atypical for neurodegenerative diseases were identified in all 7 and included subacute deterioration (n = 3), myoclonus (n = 2), a history of autoimmune disease (n = 2), a fluctuating disease course (n = 1), and epileptic seizures (n = 1). In this cohort, no patients with antibodies fulfilled the criteria for rapidly progressive dementia (RPD), yet a subacute deterioration was reported in 3 patients later in the disease course. Brain MRI of none of the patients demonstrated abnormalities suggestive for AIE. CSF pleocytosis was found in 1 patient, considered as an atypical sign for neurodegenerative diseases. Compared with patients without neuronal antibodies (4 per antibody-positive patient), atypical clinical signs for neurodegenerative diseases were seen more frequently among the patients with antibodies (100% vs 21%, p = 0.0003), especially a subacute deterioration or fluctuating course (57% vs 7%, p = 0.009).

DISCUSSION

A small, but clinically relevant proportion of patients suspected to have neurodegenerative dementias have neuronal antibodies indicative of AIE and might benefit from immunotherapy. In patients with atypical signs for neurodegenerative diseases, clinicians should consider neuronal antibody testing. Physicians should keep in mind the clinical phenotype and confirmation of positive test results to avoid false positive results and administration of potential harmful therapy for the wrong indication.

Autoimmune encephalitis: recent clinical and biological advances

In 2015, we wrote a review in The Journal of Neurology summarizing the field of autoantibody-associated neurological diseases. Now, in 2023, we present an update of the subject which reflects the rapid expansion and refinement of associated clinical phenotypes, further autoantibody discoveries, and a more detailed understanding of immunological and neurobiological pathophysiological pathways which mediate these diseases. Increasing awareness around distinctive aspects of their clinical phenotypes has been a key driver in providing clinicians with a better understanding as to how these diseases are best recognized. In clinical practice, this recognition supports the administration of often effective immunotherapies, making these diseases 'not to miss' conditions. In parallel, there is a need to accurately assess patient responses to these drugs, another area of growing interest. Feeding into clinical care are the basic biological underpinnings of the diseases, which offer clear pathways to improved therapies toward enhanced patient outcomes. In this update, we aim to integrate the clinical diagnostic pathway with advances in patient management and biology to provide a cohesive view on how to care for these patients in 2023, and the future.