Contactin-associated protein-2 antibodies in non-paraneoplastic cerebellar ataxia

Paraneoplastic autoimmune neurologic disorders associated with thymoma

Thymoma is often associated with paraneoplastic neurologic diseases. Neural autoantibody testing is an important tool aiding diagnosis of thymoma and its autoimmune neurologic complications. Autoantibodies specific for muscle striational antigens and ion channels of the ligand-gated nicotinic acetylcholine receptor superfamily are the most prevalent biomarkers. The autoimmune neurologic disorders associating most commonly with thymoma are myasthenia gravis (MG), peripheral nerve hyperexcitability (neuromyotonia and Morvan syndrome), dysautonomia, and encephalitis. Patients presenting with these neurologic disorders should be screened for thymoma at diagnosis. Although they can cause profound disability, they usually respond to immunotherapy and treatment of the thymoma. Worsening of the neurologic disorder following surgical removal of a thymoma may herald tumor recurrence. Prompt recognition of paraneoplastic neurologic disorders is critical for patient management. A multidisciplinary approach is required for optimal management of neurologic autoimmunity associated with thymoma.

A retrospective study of autoimmune cerebellar ataxia over a 20-year period in a single institution

BACKGROUND

It is important to differentiate autoimmune cerebellar ataxia (ACA) from neurodegenerative CA, but this is sometimes difficult. We performed a retrospective study in a single institution in Japan over a 20-year period to reveal the clinical features of ACA.

METHODS

Patients with CA as the primary neurological symptom were enrolled from those admitted to the Department of Neurology, Hokkaido University Hospital between April 2002 and March 2022. ACA was diagnosed retrospectively according to the following criteria: (1) CA being the predominant symptom; (2) identification of cancer within 2 years of onset; (3) improvement in cerebellar symptoms following immunotherapy; and (4) ruling out alternative causes of CA. Patients fulfilling criteria (1), (2), and (4) were classified as paraneoplastic cerebellar degeneration (PCD), while those fulfilling (1), (3), and (4) were classified as non-PCD and enrolled as patients with ACA. Neurodegenerative diseases, e.g., multiple system atrophy (MSA), were confirmed retrospectively based on generally used diagnostic criteria and enrolled. Furthermore, the ACA diagnostic criteria proposed by Dalmau and Graus were applied retrospectively to the ACA patients to examine the validity of the diagnoses.

RESULTS

Among the 243 patients with CA, 13 were enrolled as ACA; five were PCD and eight were non-PCD. Eight of these cases met the proposed diagnostic criteria by Dalmau and Graus. MSA was the most prevalent disease among CA patients, with 93 cases. The incidence of cerebellar atrophy was significantly lower in ACA (3/13) than in MSA (92/92). Cerebrospinal fluid (CSF) pleocytosis was significantly more frequent in ACA than in MSA (4/13 vs. 2/55, respectively). However, there was no significant difference in the presence of oligoclonal bands, increased protein in CSF, and laterality differences in ataxia.

CONCLUSION

ACA was present in ~ 5% of Japanese CA patients. The absence of cerebellar atrophy, despite the presence of CA, strongly supports ACA over MSA. While CSF pleocytosis was observed more often in ACA, the positivity rate was only ~ 30%. Since ACA is treatable, further studies are needed to identify additional clinical features and accurate diagnostic biomarkers.

Anti-Homer-3 antibodies in cerebrospinal fluid and serum samples from a 58-year-old woman with subacute cerebellar degeneration and diffuse breast adenocarcinoma

Introduction

Subacute cerebellar ataxia combined with cerebrospinal fluid (CSF) pleocytosis is the result of an immune response that can occur due to viral infections, paraneoplastic diseases or autoimmune-mediated mechanisms. In the following we present the first description of a patient with anti-Homer-3 antibodies in serum and CSF who has been diagnosed with paraneoplastic subacute cerebellar degeneration due to a papillary adenocarcinoma of the breast.

Case presentation

A 58-year-old female was admitted to our clinical department because of increasing gait and visual disturbances starting nine months ago. The neurological examination revealed a downbeat nystagmus, oscillopsia, a severe standing and gait ataxia and a slight dysarthria. Cranial MRI showed no pathological findings. Examination of CSF showed a lymphocytic pleocytosis of 11 cells/µl and an intrathecal IgG synthesis of 26%. Initially, standard serological testing in serum and CSF did not indicate any autoimmune or paraneoplastic aetiology. However, an antigen-specific indirect immunofluorescence test (IIFT) revealed the presence of anti-Homer-3 antibodies (IgG) with a serum titer of 1: 32,000 and a titer of 1: 100 in CSF. Subsequent histological examination of a right axillary lymph node mass showed papillary adenocarcinoma cells. Breast MRI detected multiple bilateral lesions as a diffuse tumour manifestation indicative of adenocarcinoma of the breast. Treatment with high-dose methylprednisolone followed by five plasmaphereses and treatment with 4-aminopyridine resulted in a moderate decrease of the downbeat nystagmus and she was able to move independently with a wheeled walker after 3 weeks. The patient was subsequently treated with chemotherapy (epirubicin, cyclophosphamide) and two series of immunoglobulins (5 × 30 g each). This resulted in a moderate improvement of the cerebellar symptoms with a decrease of ataxia and disappearance of the downbeat nystagmus.

Conclusion

The presented case of anti-Homer-3 antibody-associated cerebellar degeneration is the first that is clearly associated with the detection of a tumour. Interestingly, the Homer-3 protein interaction partner metabotropic glutamate receptor subtype 1A (mGluR1A) is predominantly expressed in Purkinje cells where its function is essential for motor coordination and motor learning. Based on our findings, in subacute cerebellar degeneration, we recommend considering serological testing for anti-Homer-3 antibodies in serum and cerebrospinal fluid together with tumor screening.

Novelties in Autoimmune and Paraneoplastic Cerebellar Ataxias: Twenty Years of Progresses

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

Immune-Mediated Cerebellar Ataxia Associated With Neuronal Surface Antibodies

BACKGROUND

Immune-mediated cerebellar ataxias (IMCAs) are common in paraneoplastic cerebellar degeneration (PCD) but rarely occur in patients with neuronal surface antibodies (NSAbs). Although cerebellar ataxias (CAs) associated with anti-NMDAR and anti-CASPR2 have been reported in a few cases, they have never been studied systematically. This study aimed to analyze the characteristics of anti-NSAbs-associated CAs.

METHODS

A retrospective investigation was conducted to identify patients using the keywords IMCAs and NSAbs. We collected the clinical data of 14 patients diagnosed with anti-NSAbs-associated CAs.

RESULTS

The median age was 33 years (16-66), and the male-to-female ratio was 4:3. Nine were positive for NMDAR-Ab, two for LGI1-Ab, two for CASPR2-Ab, and one for AMPA2R-Ab. CAs were initial symptoms in three patients and presented during the first two months of the disease course (10 days on average) among the rest of the patients. After the immunotherapy, two cases were free from symptoms, and eight cases recovered satisfactorily (10/14, 71.4%). Compared with other causes of IMCAs, anti-NSAbs were more frequently associated with additional extra-cerebellar symptoms (85.7%), mostly seizures (78.6%) and mental abnormalities (64.3%). In the CSF analysis, pleocytosis was detected in ten patients (71.4%) and oligoclonal bands (OB) were observed in nine patients (64.3%). Moreover, compared with PCD and anti-GAD65-Ab-associated CAs, anti-NSAbs-associated CAs showed a better response to immunotherapy.

CONCLUSION

IMCAs are rare and atypical in autoimmune encephalitis with neuronal surface antibodies. Compared with other forms of IMCAs, more symptoms of encephalopathy, a higher rate of pleocytosis and positive OB in CSF, and positive therapeutic effect were the key features of anti-NSAbs-associated CAs.

Diagnosis and Clinical Features in Autoimmune-Mediated Movement Disorders

Movement disorders are common manifestations in autoimmune-mediated encephalitis. This group of diseases is suspected to be triggered by infection or neoplasm. Certain phenotypes correlate with specific autoantibody-related neurological disorders, such as orofacial-lingual dyskinesia with N-methyl-D-aspartate receptor encephalitis and faciobrachial dystonic seizures with leucine-rich glioma-inactivated protein 1 encephalitis. Early diagnosis and treatment, especially for autoantibodies targeting neuronal surface antigens, can improve prognosis. In contrast, the presence of autoantibodies against intracellular neuronal agents warrants screening for underlying malignancy. However, early clinical diagnosis is challenging because these diseases can be misdiagnosed. In this article, we review the distinctive clinical phenotypes, magnetic resonance imaging findings, and current treatment options for autoimmune-mediated encephalitis.

Acute Cerebellar Inflammation and Related Ataxia: Mechanisms and Pathophysiology

The cerebellum governs motor coordination and motor learning. Infection with external microorganisms, such as viruses, bacteria, and fungi, induces the release and production of inflammatory mediators, which drive acute cerebellar inflammation. The clinical observation of acute cerebellitis is associated with the emergence of cerebellar ataxia. In our animal model of the acute inflammation of the cerebellar cortex, animals did not show any ataxia but hyperexcitability in the cerebellar cortex and depression-like behaviors. In contrast, animal models with neurodegeneration of the cerebellar Purkinje cells and hypoexcitability of the neurons show cerebellar ataxia. The suppression of the Ca2+-activated K+ channels in vivo is associated with a type of ataxia. Therefore, there is a gap in our interpretation between the very early phase of cerebellar inflammation and the emergence of cerebellar ataxia. In this review, we discuss the hypothesized scenario concerning the emergence of cerebellar ataxia. First, compared with genetically induced cerebellar ataxias, we introduce infection and inflammation in the cerebellum via aberrant immunity and glial responses. Especially, we focus on infections with cytomegalovirus, influenza virus, dengue virus, and SARS-CoV-2, potential relevance to mitochondrial DNA, and autoimmunity in infection. Second, we review neurophysiological modulation (intrinsic excitability, excitatory, and inhibitory synaptic transmission) by inflammatory mediators and aberrant immunity. Next, we discuss the cerebellar circuit dysfunction (presumably, via maintaining the homeostatic property). Lastly, we propose the mechanism of the cerebellar ataxia and possible treatments for the ataxia in the cerebellar inflammation.

Contemporary advances in antibody-mediated encephalitis: anti-LGI1 and anti-Caspr2 antibody (Ab)-mediated encephalitides

Encephalitides with antibodies directed against leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (Caspr2) represent two increasingly well characterised forms of autoimmune encephalitis. Both share overlapping and distinct clinical features, are mediated by autoantibodies directed against differing proteins complexed with voltage-gated potassium channels, with unique genetic predisposition identified to date. Herein we summarise disease mechanisms, clinical features, treatment considerations, prognostic factors and clinical outcomes regarding these disorders.

Clinical features and outcome of patients with autoimmune cerebellar ataxia evaluated with the Scale for the Assessment and Rating of Ataxia

BACKGROUND AND PURPOSE

This study was undertaken to assess the long-term outcome of patients with paraneoplastic and non paraneoplastic autoimmune cerebellar ataxia (ACA) using the Scale for the Assessment and Rating of Ataxia (SARA).

METHODS

Patients with subacute cerebellar ataxia admitted to our institution between September 2012 and April 2020 were prospectively recruited. Serum and/or cerebrospinal fluid was tested for neural autoantibodies by indirect immunofluorescence on mouse brain, cell-based assays, and radioimmunoassay. SARA and modified Rankin Scale (mRS) score were employed to assess patients' outcome.

RESULTS

Fifty-five patients were recruited, of whom 23 (42%) met the criteria for cerebellar ataxia of autoimmune etiology. Neural autoantibodies were detected in 22 of 23 patients (Yo-immunoglobulin G [IgG], n = 6; glutamic acid decarboxylase 65-IgG, n = 3; metabotropic glutamate receptor 1-IgG, n = 2; voltage-gated calcium channel P/Q type-IgG, n = 2; Hu-IgG, n = 1; glial fibrillary acidic protein-IgG, n = 1; IgG-binding unclassified antigens, n = 7). Thirteen patients were diagnosed with paraneoplastic cerebellar syndrome (PCS) and 10 with idiopathic ACA. All patients received immunotherapy. Median SARA score was higher in the PCS group at all time points (p = 0.0002), while it decreased significantly within the ACA group (p = 0.049) after immunotherapy. Patients with good outcome (mRS ≤ 2) had less neurological disability (SARA < 15) at disease nadir (p = 0.039) and presented less frequently with paraneoplastic neurological syndrome (p = 0.0028). The univariate linear regression model revealed a good correlation between mRS and SARA score both at disease onset (p < 0.0001) and at last follow-up (p < 0.0001). SARA score < 11 identified patients with good outcome.

CONCLUSIONS

Patients with idiopathic ACA significantly improved after immunotherapy. SARA score accurately reflects patients' clinical status and may be a suitable outcome measure for patients with ACA.

Limbic encephalitis

Limbic encephalitis (LE) is a clinical syndrome defined by subacutely evolving limbic signs and symptoms with structural and functional evidence of mediotemporal damage in the absence of a better explanation than an autoimmune (or paraneoplastic) cause. There are features common to all forms of LE. In recent years, antibody(ab)-defined subtypes have been established. They are distinct regarding underlying pathophysiologic processes, clinical and magnetic resonance imaging courses, cerebrospinal fluid signatures, treatment responsivity, and likelihood of a chronic course. With immunotherapy, LE with abs against surface antigens has a better outcome than LE with abs to intracellular antigens. Diagnostic and treatment challenges are, on the one hand, to avoid overlooking and undertreatment and, on the other hand, to avoid overdiagnoses and overtreatment. LE can be conceptualized as a model disease for the consequences of new onset mediotemporal damage by different mechanisms in adult life. It may be studied as an example of mediotemporal epileptogenesis.

Case Report: Prominent Brainstem Involvement in Two Patients With Anti-CASPR2 Antibody-Associated Autoimmune Encephalitis

Anti-contactin-associated protein-like 2 (CASPR2) antibody-associated autoimmune encephalitis is commonly characterized by limbic encephalitis with clinical symptoms of mental and behavior disorders, cognitive impairment, deterioration of memory, and epilepsy. The classical lesions reported are located at the medial temporal lobe or hippocampus, whereas prominent brainstem lesions have not been addressed to date. Herein, we reported two patients mimicking progressive brainstem infarction with severe neurological manifestations. On brain magnetic resonance imaging (MRI), prominent brainstem lesions were noted, although multifocal lesions were also shown in the juxtacortical and subcortical white matters, basal ganglia, hippocampus, and cerebellar hemisphere. Unexpectedly and interestingly, both cases had detectable CASPR2 antibodies in sera, and an exclusive IgG1 subclass was documented in the further analysis. They were treated effectively with aggressive immunosuppressive therapies including corticosteroids, intravenous immunoglobulin G, and rituximab, with the first case achieving a rapid remission and the other undergoing a slow but gradual improvement. To the best of our knowledge, this is the first report on prominent brainstem involvement with definite MRI lesions in anti-CASPR2 antibody-associated autoimmune encephalitis, which helps to expand the clinical spectrum of this rare autoimmune disease and update the lesion patterns in the CNS.

Altered Cerebellar Response to Somatosensory Stimuli in the Cntnap2 Mouse Model of Autism

Atypical sensory processing is currently included within the diagnostic criteria of autism. The cerebellum is known to integrate sensory inputs of different modalities through its connectivity to the cerebral cortex. Interestingly, cerebellar malformations are among the most replicated features found in postmortem brain of individuals with autism. We studied sensory processing in the cerebellum in a mouse model of autism, knock-out (KO) for the Cntnap2 gene. Cntnap2 is widely expressed in Purkinje cells (PCs) and has been recently reported to regulate their morphology. Further, individuals with CNTNAP2 mutations display cerebellar malformations and CNTNAP2 antibodies are associated with a mild form of cerebellar ataxia. Previous studies in the Cntnap2 mouse model show an altered cerebellar sensory learning. However, a physiological analysis of cerebellar function has not been performed yet. We studied sensory evoked potentials in cerebellar Crus I/II region on electrical stimulation of the whisker pad in alert mice and found striking differences between wild-type and Cntnap2 KO mice. In addition, single-cell recordings identified alterations in both sensory-evoked and spontaneous firing patterns of PCs. These changes were accompanied by altered intrinsic properties and morphologic features of these neurons. Together, these results indicate that the Cntnap2 mouse model could provide novel insight into the pathophysiological mechanisms of autism core sensory deficits.

Meningioma preceding CASPR2 antibody limbic encephalitis with a stroke mimic: A case report

RATIONALE

Todd paralysis (a stroke-like presentation in some patients with epilepsy) caused by limbic encephalitis (LE) is not easily distinguished from acute ischemic stroke by clinicians in the emergency room.

PATIENT CONCERNS

We report a contactin-associated protein-like 2-antibody (CASPR2-Ab)-positive patient who presented with atypical LE.

DIAGNOSES

CASPR2-Ab-positive LE was the presumed diagnosis. Re-evaluation of cerebrospinal fluid (CSF) samples revealed autoantibodies targeting CASPR2 at an immunoglobulin G titer of 1:1. The clinical presentation of subacute onset seizures, abnormal electroencephalography, hypermetabolism on positron emission tomography, good immunotherapy response, and the presence of specific antibodies in serum supports a diagnosis of autoimmune LE.

INTERVENTION

The patient received glucocorticoids (1 g for 3 days and 500 mg for 3 days), immunoglobulin (25 g for 3 days), sodium valproate (1 g for 3 days), and clonazepam (1 mg for 3 days).

OUTCOMES

Remission of temporal lobe epilepsy symptoms and cognitive dysfunction was observed. Follow-up analysis of CSF and serological examination were not approved by the patient. His Mini-Mental State Examination score improved to 21/30. Stable remission of symptoms was achieved throughout the follow-up period of 50 days.

LESSONS

Autoimmune encephalitis (AE) should be considered in cases of late-onset epilepsy following meningioma peritumoral brain edema and resection. A diagnosis of AE should be considered in patients presenting with stroke-like symptoms if the magnetic resonance imaging abnormality does not match a known vascular territory. Early and correct diagnosis is crucial because immunotherapy is usually effective for this disease.

Clinical Profile and Treatment Response in Patients with CASPR2 Antibody-Associated Neurological Disease

Background:

The clinical spectrum of contactin-associated protein-like 2 (CASPR2) antibody-associated disease is wide and includes Morvan syndrome. Studies describing treatment and long-term outcome are limited.

Aims:

We report the clinical profile and emphasize response to treatment and long-term outcome in eight patients with CASPR2-antibody-associated disease.

Methods:

Clinical, radiological, electrophysiological, treatment, follow-up, and outcome data were collected by retrospective chart review.

Results:

Clinical manifestations included Morvan syndrome (n = 7) and limbic encephalitis (n = 1). None of the patients were positive for LGI1 antibody. Associated features included myasthenia (n = 1), thymoma (n = 1), and dermatological manifestations (n = 4). Patients were treated with intravenous methylprednisolone and plasma exchange during the acute symptomatic phase followed by pulsed intravenous methyl prednisolone to maintain remission. Mean-modified Rankin score at admission (pre-treatment), discharge, and last follow-up were 3.75, 2.5, and 0.42, respectively. One patient with underlying thymoma and myasthenic crisis died. The other seven patients were followed up for a mean duration of 19.71 months. All of them improved completely. Relapse occurred in one patient after 13 months but responded favorably to steroids.

Conclusion:

CASPR2 antibody-associated disease has favorable response to immunotherapy with complete improvement and good outcome. Underlying malignancy may be a marker for poor prognosis.

Anti-contactin-associated protein-like 2 antibody-associated cerebellar ataxia: A case report and literature review

The spectrum of anti-contactin-associated protein-like 2 (CASPR2) antibody-associated disease is expanding and the involvement of cerebellum was reported in the past few years. We report a 45-year-old male with chronically progressive cerebellar ataxia. CASPR2 antibodies were detected in his serum and cerebellar atrophy was observed on MRI. His symptoms improved prominently with steroids and intravenous immunoglobulins. 23 cases with CASPR2 antibodies and cerebellar ataxia were identified from previous publications. Most of patients showed acute or subacute onset with other typical presentations of anti-CASPR2 antibody-associated disease, such as limbic encephalitis. Immunotherapy was effective in the majority of patients.

Anti-LGI1, anti-GABABR, and Anti-CASPR2 encephalitides in Asia: A systematic review

AIM

We aim to review the literature to collate and describe features of encephalitides arising from autoantibodies against leucine-rich glioma-inactivated 1 (LGI1), gamma aminobutyric acid receptor (GABABR), and contactin-associated protein-like 2 (CASPR2) in Asian populations and compare them with findings of Western studies.

METHODS

Peer-reviewed articles published till 24 May 2020 were searched, and original, full-text studies from Asia with serum/CSF antibody-based diagnosis and at least 2 patients were selected. Twenty-four studies with 263 patients (139 anti-LGI1, 114 anti-GAGABR, and 10 anti-CASPR2) were included. Data were pooled to produce descriptive information on demographics, clinical characteristics, diagnostics, treatments, and outcome.

RESULTS

The mean age was 54.2 (anti-LGI1), 55.2 (anti-GABABR), and 47.7 years (anti-CASPR2), with an overall male predominance of 62.0%. Commonest clinical features across all types were seizures (87.5%), memory deficits (80.7%), psychiatric disturbances (75.9%), and altered consciousness (52.9%). Four anti-LGI1, 40 anti-GABABR, and 1 anti-CASPR2 patients had tumors. CSF, MRI, and EEG were abnormal in 33.3%, 54.1%, and 75% patients in anti-LGI1; 60.0%, 49.6%, and 85.7% in anti-GABABR; and 50%, 44.4%, and 100% in anti-CASPR2 patients, respectively. 95.6% patients received first-line therapy alone (steroids/IVIG/Plasma therapy), and 4.4% received second-line therapy (rituximab/cyclophosphamide). 91.7%, 63.6%, and 70% of patients had favorable outcomes (modified Rankin Score 0-2) with mortality rates at 2.5%, 23.2%, and 0% in the three types, respectively.

CONCLUSION

Our findings suggest that these disorders present in Asian patients at a relatively young age often with features of seizures, memory deficits, and psychiatric disturbances and usually demonstrate a favorable clinical outcome.

Anti-CASPR2 clinical phenotypes correlate with HLA and immunological features

OBJECTIVE

Antibodies against contactin-associated protein-like 2 (CASPR2-Abs) have been described in acquired neuromyotonia, limbic encephalitis (LE) and Morvan syndrome (MoS). However, it is unknown whether these constitute one sole spectrum of diseases with the same immunopathogenesis or three distinct entities with different mechanisms.

METHODS

A cluster analysis of neurological symptoms was performed in a retrospective cohort of 56 CASPR2-Abs patients. In parallel, immunological features and human leucocyte antigen (HLA) were studied.

RESULTS

Cluster analysis distinguished patients with predominant limbic symptoms (n=29/56) from those with peripheral nerve hyperexcitability (PNH; n=27/56). In the limbic-prominent group, limbic features were either isolated (LE/-; 18/56, 32.1%), or combined with extralimbic symptoms (LE/+; 11/56, 19.6%). Those with PNH were separated in one group with severe PNH and extralimbic involvement (PNH/+; 16/56, 28.6%), resembling historical MoS descriptions; and one group with milder and usually isolated PNH (PNH/-; 11/56, 19.6%). LE/- and LE/+ patients shared immunogenetic characteristics demonstrating a homogeneous entity. HLA-DRB1*11:01 was carried more frequently than in healthy controls only by patients with LE (94.1% vs 18.3%; p=1.3×10^-10). Patients with LE also had serum titres (median 1:40 960) and rates of cerebrospinal fluid positivity (93.1%) higher than the other groups (p<0.05). Conversely, DRB1*11:01 association was absent in PNH/+ patients, but only they had malignant thymoma (87.5%), serum antibodies against leucine-rich glioma-inactivated 1 protein (66.7%) and against netrin-1 receptor deleted in colorectal carcinoma (53.8%), and myasthenia gravis (50.0%).

INTERPRETATION

Symptoms' distribution supports specific clinical phenotypes without overlap between LE and MoS. The distinct immunogenetic characteristics shared by all patients with LE and the particular oncological and autoimmune associations of MoS suggest two very different aetiopathogenesis.

Anti-CASPR2 antibody associated encephalitis with anosmia and demyelinating pseudotumor: A case report

A 20-year-old female presented with fine motor deficits and visual field defect was admitted to our hospital. CSF tests for autoimmune encephalitis antibodies and onconeuronal antibodies were unremarkable. MRI showed unilateral lesion involving left basal ganglia, external capsule, insula, hippocampus, and amygdala, which was considered to be demyelinating pseudotumor after surgical intervention. The patient's symptoms relieved so she didn't consent to immunotherapy. Two years and a half later our patient reported sudden anosmia. Reexamination by MRI demonstrated a new lesion. We then detected anti-CASPR2 antibodies in the patient's serum and gave her immunotherapy.

Caspr2 interacts with type 1 inositol 1,4,5-trisphosphate receptor in the developing cerebellum and regulates Purkinje cell morphology

Contactin-associated protein-like 2 (Caspr2) is a neurexin-like protein that has been associated with numerous neurological conditions. However, the specific functional roles that Caspr2 plays in the central nervous system and their underlying mechanisms remain incompletely understood. Here, we report on a functional role for Caspr2 in the developing cerebellum. Using a combination of confocal microscopy, biochemical analyses, and behavioral testing, we show that loss of Caspr2 in the Cntnap2-/- knockout mouse results in impaired Purkinje cell dendritic development, altered intracellular signaling, and motor coordination deficits. We also find that Caspr2 is highly enriched at synaptic specializations in the cerebellum. Using a proteomics approach, we identify type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) as a specific synaptic interaction partner of the Caspr2 extracellular domain in the molecular layer of the developing cerebellum. The interaction of the Caspr2 extracellular domain with IP3R1 inhibits IP3R1-mediated changes in cellular morphology. Together, our work defines a mechanism by which Caspr2 controls the development and function of the cerebellum and advances our understanding of how Caspr2 dysfunction might lead to specific brain disorders.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

Stop testing for autoantibodies to the VGKC-complex: only request LGI1 and CASPR2

Autoantibodies to leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein like-2 (CASPR2) are associated with clinically distinctive syndromes that are highly immunotherapy responsive, such as limbic encephalitis, faciobrachial dystonic seizures, Morvan’s syndrome and neuromyotonia. These autoantibodies target surface-exposed domains of LGI1 or CASPR2, and appear to be directly pathogenic. In contrast, voltage-gated potassium channel (VGKC) antibodies that lack LGI1 or CASPR2 reactivities (‘double-negative’) are common in healthy controls and have no consistent associations with distinct syndromes. These antibodies target intracellular epitopes and lack pathogenic potential. Moreover, the clinically important LGI1 and CASPR2 antibodies comprise only ~15% of VGKC-positive results, meaning that most VGKC-antibody positive results mislead rather than help. Further, initial VGKC testing misses some cases that have LGI1 and CASPR2 antibodies. These collective observations confirm that laboratories should stop testing for VGKC antibodies and instead, test only for LGI1 and CASPR2 antibodies. This change in practice will lead to significant patient benefit.

Immunological Bases of Paraneoplastic Cerebellar Degeneration and Therapeutic Implications

Paraneoplastic cerebellar degeneration (PCD) is a rare immune-mediated disease that develops mostly in the setting of neoplasia and offers a unique prospect to explore the interplay between tumor immunity and autoimmunity. In PCD, the deleterious adaptive immune response targets self-antigens aberrantly expressed by tumor cells, mostly gynecological cancers, and physiologically expressed by the Purkinje neurons of the cerebellum. Highly specific anti-neuronal antibodies in the serum and cerebrospinal fluid represent key diagnostic biomarkers of PCD. Some anti-neuronal antibodies such as anti-Yo autoantibodies (recognizing the CDR2/CDR2L proteins) are only associated with PCD. Other anti-neuronal antibodies, such as anti-Hu, anti-Ri, and anti-Ma2, are detected in patients with PCD or other types of paraneoplastic neurological manifestations. Importantly, these autoantibodies cannot transfer disease and evidence for a pathogenic role of autoreactive T cells is accumulating. However, the precise mechanisms responsible for disruption of self-tolerance to neuronal self-antigens in the cancer setting and the pathways involved in pathogenesis within the cerebellum remain to be fully deciphered. Although the occurrence of PCD is rare, the risk for such severe complication may increase with wider use of cancer immunotherapy, notably immune checkpoint blockade. Here, we review recent literature pertaining to the pathophysiology of PCD and propose an immune scheme underlying this disabling disease. Additionally, based on observations from patients' samples and on the pre-clinical model we recently developed, we discuss potential therapeutic strategies that could blunt this cerebellum-specific autoimmune disease.

Antibody-related movement disorders - a comprehensive review of phenotype-autoantibody correlations and a guide to testing

Background

Over the past decade increasing scientific progress in the field of autoantibody-mediated neurological diseases was achieved. Movement disorders are a frequent and often prominent feature in such diseases which are potentially treatable.

Main body

Antibody-mediated movement disorders encompass a large clinical spectrum of diverse neurologic disorders occurring either in isolation or accompanying more complex autoimmune encephalopathic diseases. Since autoimmune movement disorders can easily be misdiagnosed as neurodegenerative or metabolic conditions, appropriate immunotherapy can be delayed or even missed. Recognition of typical clinical patterns is important to reach the correct diagnosis.

Conclusion

There is a growing number of newly discovered antibodies which can cause movement disorders. Several antibodies can cause distinctive phenotypes of movement disorders which are important to be aware of. Early diagnosis is important because immunotherapy can result in major improvement.In this review article we summarize the current knowledge of autoimmune movement disorders from a point of view focused on clinical syndromes. We discuss associated clinical phenomenology and antineuronal antibodies together with alternative etiologies with the aim of providing a diagnostic framework for clinicians considering underlying autoimmunity in patients with movement disorders.

Nonparaneoplastic autoimmune cerebellar ataxias

PURPOSE OF REVIEW

The current review develops the clinical presentations of nonparaneoplastic autoimmune cerebellar ataxia (ACA) and analyzes the association with autoantibodies.

RECENT FINDINGS

Emerging evidence suggests that autoimmunity is involved in a significant proportion of sporadic ataxia cases. Moreover, numerous autoantibodies have recently been described in association with sporadic cerebellar ataxia, improving diagnosis and patient categorization.

SUMMARY

Nonparaneoplastic ACA encompasses postinfectious acute cerebellar ataxia, opsoclonus-myoclonus-ataxia syndrome, and pure cerebellar ataxia with or without autoantibodies. There is still confusion about how to diagnose and classify the patients, and retrospective data suggest that these very rare entities are in fact largely underrecognized. Numerous autoantibodies have been found associated with sporadic ataxia, improving diagnosis accuracy, and patient categorization. However, although anti-glutamate decarboxylase isotype 65 (GAD65), anti-contactin-associated protein 2 (CASPR2), and anti metabotropic glutamate receptor (mGluR1) antibodies are well recognized biomarkers, many other autoantibodies have been described in very small numbers of patients and their specificity is unknown. Efficient biomarkers for ACA are still lacking and in many cases the diagnosis has to rely on a body of converging evidence.

Cerebrospinal Fluid Findings in Patients With Autoimmune Encephalitis-A Systematic Analysis

Autoimmune encephalitides (AIE) comprise a group of inflammatory diseases of the central nervous system (CNS), which can be further characterized by the presence of different antineuronal antibodies. Recently, a clinical approach for diagnostic criteria for the suspected diagnosis of AIE as well as definitive AIE were proposed. These are intended to guide physicians when to order the antineuronal antibody testing and/or facilitate early diagnosis even prior to the availability of the specific disease-confirming test results to facilitate prompt treatment. These diagnostic criteria also include the results of basic cerebrospinal fluid (CSF) analysis. However, the different antibody-defined AIE subtypes might be highly distinct with regard to their immune pathophysiology, e.g., the pre-dominance of specific IgG subclasses, IgG1, or IgG4, or frequency of paraneoplastic compared to idiopathic origin. Thus, it is conceivable that the results of basic CSF analysis might also be very different. However, this has not been explored systematically. Here, we systematically reviewed the literature about the 10 most important AIE subtypes, AIE with antibodies against NMDA, AMPA, glycine, GABAA, and GABAB receptors as well as DPPX, CASPR2, LGI1, IgLON5, or glutamate decarboxylase (GAD), with respect to the reported basic CSF findings comprising CSF leukocyte count, total protein, and the presence of oligoclonal bands (OCB) restricted to the CSF as a sensitive measure for intrathecal IgG synthesis. Our results indicate that these basic CSF findings are profoundly different among the 10 different AIE subtypes. Whereas, AIEs with antibodies against NMDA, GABAB, and AMPA receptors as well as DPPX show rather frequent inflammatory CSF changes, in AIEs with either CASPR2, LGI1, GABAA, or glycine receptor antibodies CSF findings were mostly normal. Two subtypes, AIEs defined by either GAD, or IgLON5 antibodies, did not fit into this general pattern. In AIE with GAD antibodies, positive OCBs in the absence of other changes were typical, while the CSF in IgLON5 antibody-positive AIE was characterized by elevated protein.

Behaviour and neuropathology in mice injected with human contactin-associated protein 2 antibodies

Serum antibodies that bind to the surface of neurons or glia are associated with a wide range of rare but treatable CNS diseases. In many, if not most instances, the serum levels are higher than CSF levels yet most of the reported attempts to reproduce the human disease in mice have used infusion of antibodies into the mouse cerebral ventricle(s) or intrathecal space. We used the intraperitoneal route and injected purified plasma IgG from either a CASPR2-antibody-positive patient (n = 10 mice) or healthy individual (n = 9 mice) daily for 8 days. Lipopolysaccharide was injected intraperitoneally on Day 3 to cause a temporary breach in the blood brain barrier. A wide range of baseline behaviours, including tests of locomotion, coordination, memory, anxiety and social interactions, were established before the injections and tested from Day 5 until Day 11. At termination, brain tissue was analysed for human IgG, CASPR2 and c-fos expression, lymphocyte infiltration, and neuronal, astrocytic and microglial markers. Mice exposed to CASPR2-IgG, compared with control-IgG injected mice, displayed reduced working memory during the continuous spontaneous alternation test with trends towards reduced short-term and long-term memories. In the open field tests, activities were not different from controls, but in the reciprocal social interaction test, CASPR2-IgG injected mice showed longer latency to start interacting, associated with more freezing behaviour and reduced non-social activities of rearing and grooming. At termination, neuropathology showed more IgG deposited in the brains of CASPR2-IgG injected mice, but a trend towards increased CASPR2 expression; these results were mirrored in short-term in vitro experiments where CASPR2-IgG binding to hippocampal neurons and to CASPR2-transfected HEK cells led to some internalization of the IgG, but with a trend towards higher surface CASPR2 expression. Despite these limited results, in the CASPR2-IgG injected mouse brains there was increased c-fos expression in the piriform-entorhinal cortex and hypothalamus, and a modest loss of Purkinje cells. There was also increased microglia density, morphological changes in both microglia and astrocytes and raised complement C3 expression on astrocytes, all consistent with glial activation. Patients with CASPR2 antibodies can present with a range of clinical features reflecting central, autonomic and peripheral dysfunction. Although the behavioural changes in mice were limited to social interactions and mild working-memory defects, the neuropathological features indicate potentially widespread effects of the antibodies on different brain regions.

Management of antibody-mediated autoimmune encephalitis in adults and children: literature review and consensus-based practical recommendations

Autoimmune encephalitis associated with antibodies against neuronal surface targets (NSAE) are rare but still underrecognized conditions that affect adult and pediatric patients. Clinical guidelines have recently been published with the aim of providing diagnostic clues regardless of antibody status. These syndromes are potentially treatable but the choice of treatment and its timing, as well as differential diagnoses, long-term management, and clinical and paraclinical follow-up, remain major challenges. In the absence of evidence-based guidelines, management of these conditions is commonly based on single-center expertise.Taking into account different published expert recommendations in addition to the multicenter experience of the Italian Working Group on Autoimmune Encephalitis, both widely accepted and critical aspects of diagnosis, management and particularly of immunotherapy for NSAE have been reviewed and are discussed.Finally, we provide consensus-based practical advice for managing hospitalization and follow-up of patients with NSAE.

Contactins in the central nervous system: role in health and disease

Contactins are a group of cell adhesion molecules that are mainly expressed in the brain and play pivotal roles in the organization of axonal domains, axonal guidance, neuritogenesis, neuronal development, synapse formation and plasticity, axo-glia interactions and neural regeneration. Contactins comprise a family of six members. Their absence leads to malformed axons and impaired nerve conduction. Contactin mediated protein complex formation is critical for the organization of the axon in early central nervous system development. Mutations and differential expression of contactins have been identified in neuro-developmental or neurological disorders. Taken together, contactins are extensively studied in the context of nervous system development. This review summarizes the physiological roles of all six members of the Contactin family in neurodevelopment as well as their involvement in neurological/neurodevelopmental disorders.

Movement disorders associated with neuronal antibodies

Movement disorders are one of the common clinical features of neurological disease associated with neuronal antibodies which is a group of potentially reversible disorder. They can present with hypokinetic or hyperkinetic types of involuntary movements and may have other associated neurological symptoms. The spectrum of abnormal movements associated with neuronal antibodies is widening. Some specific phenomenology of movement disorders are likely to give clue about the type of antibody, for instance, presence of paroxysmal dystonia (facio-brachial dystonic seizures) are a pointer toward presence of LGI-1 antibodies, and orofacial lingual dyskinesia is associated with NMDAR associated encephalitis. The presence of specific type of movement disorder allows high suspicion of testing of certain specific type of antibodies. In this review, we have discussed the various antibodies and the spectrum of movement disorder associated with them, highlighting if any distinct movement disorder allows the clinician to suspect type of antibody in a certain clinical context. We have also reviewed the treatment of the movement disorder associated with the neuronal antibodies. Physicians should have high index of suspicion of these disorders, as early institution of treatment options can lead to better outcome.

Inflammation and transcriptional responses of peripheral blood mononuclear cells in classic ataxia telangiectasia

INTRODUCTION

Classic ataxia telangiectasia (A-T) is an autosomal recessive disease characterized by early onset ataxia, immune deficiency, sino-pulmonary disease, lymphoid/solid malignancies and telangiectasias. Prior studies have suggested that chronic inflammation and premature aging may contribute to the development of malignancy and pulmonary disease in people with A-T. To further examine the link between A-T and inflammation, we hypothesized that subjects with classic A-T would have greater enrichment of inflammatory pathways in peripheral blood mononuclear cells (PBMCs) compared to non A-T age-matched controls. To test this hypothesis we used RNAseq as an unsupervised approach to identify biological processes altered in people with classic A-T.

METHODS

PBMCs were isolated from subjects with classic A-T and compared to non-A-T age-matched healthy controls. RNAseq with differential gene expression analyses was then performed. Selected genes were validated by RT-qPCR using cohorts of subjects consisting of classic A-T, mild A-T or non-A-T controls. Subjects with mild A-T were characterized by later onset/mild neurologic features and normal/near normal immune status.

RESULTS

RNAseq revealed 310 differentially expressed genes (DEGs) including genes involved in inflammation, immune regulation, and cancer. Using gene set enrichment analysis, A-T subjects were found to have biological processes enriched for inflammatory and malignancy pathways. In examining a cohort of A-T subjects in which baseline serum IL8 and IL6 levels were measured previously, an association was found between higher serum IL8 levels and higher likelihood of developing malignancy and/or death in a subsequent 4-6 year period.

CONCLUSION

RNAseq using PBMCs from subjects with classic A-T uncovered differential expression of immune response genes and biological processes associated with inflammation, immune regulation, and cancer. Follow-up of A-T subjects over a 4-6 year period revealed an association between higher baseline serum IL8 levels and malignancy/death. These findings support a role for inflammation as a contributing factor in A-T phenotypes.

Structural mapping of hot spots within human CASPR2 discoidin domain for autoantibody recognition

Accumulating evidence has showed that anti-CASPR2 autoantibodies occur in a long list of neurological immune disorders including limbic encephalitis (LE). Belonging to the well-known neurexin superfamily, CASPR2 has been suggested to be a central node in the molecular networks controlling neurodevelopment. Distinct from other subfamilies in the neurexin superfamily, the CASPR subfamily features a unique discoidin (Disc) domain. As revealed by our and others' recent studies, CASPR2 Disc domain bears a major epitope for autoantibodies. However, structural information on CASPR2 recognition by autoantibodies has been lacking. Here, we report the crystal structure of human CASPR2 Disc domain at a high resolution of 1.31 Å, which is the first atomic-resolution structure of the CASPR subfamily members. The Disc domain adopts a total β structure and folds into a distorted jellyroll-like barrel with a conserved disulfide-bond interlocking its N- and C-termini. Defined by four loops and located in one end of the barrel, the "loop-tip surface" is totally polar and easily available for protein docking. Based on structure-guided epitope prediction, we generated nine mutants and evaluated their binding to autoantibodies of cerebrospinal fluid from twelve patients with limbic encephalitis. The quadruple mutant G69N/A71S/S77N/D78R impaired CASPR2 binding to autoantibodies from eleven LE patients, which indicates that the loop L1 in the Disc domain bears hot spots for autoantibody interaction. Structural mapping of autoepitopes within human CASPR2 Disc domain sheds light on how autoantibodies could sequester CASPR2 ectodomain and antagonize its functionalities in the pathogenic processes.

LGI1, CASPR2 and related antibodies: a molecular evolution of the phenotypes

Recent biochemical observations have helped redefine antigenic components within the voltage-gated potassium channel (VGKC) complex. The related autoantibodies may be now divided into likely pathogenic entities, which target the extracellular domains of leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2), and species that target intracellular neuronal components and are likely non-pathogenic. This distinction has enhanced clinical practice as direct determination of LGI1 and CASPR2 antibodies offers optimal sensitivity and specificity. In this review, we describe and compare the clinical features associated with pathogenic LGI1 and CASPR2 antibodies, illustrate emerging laboratory techniques for antibody determination and describe the immunological mechanisms that may mediate antibody-induced pathology. We highlight marked clinical overlaps between patients with either LGI1 or CASPR2 antibodies that include frequent focal seizures, prominent amnesia, dysautonomia, neuromyotonia and neuropathic pain. Although occurring at differing rates, these commonalities are striking and only faciobrachial dystonic seizures reliably differentiate these two conditions. Furthermore, the coexistence of both LGI1 and CASPR2 antibodies in an individual occurs surprisingly frequently. Patients with either antibody respond well to immunotherapies, although systematic studies are required to determine the magnitude of the effect beyond placebo. Finally, data have suggested that CASPR2 and LGI1 modulation via genetic or autoimmune mechanisms may share common intermediate molecules. Taken together, the biochemical distinction of antigenic targets has led to important clinical advances for patient care. However, the striking syndrome similarities, coexistence of two otherwise rare antibodies and molecular insights suggest the VGKC complex may yet be a common functional effector of antibody action. Hence, we argue for a molecular evolution alongside a clinical and phenotypic re-evaluation.

Autoimmune encephalitis with anti-leucine-rich glioma-inactivated 1 or anti-contactin-associated protein-like 2 antibodies (formerly called voltage-gated potassium channel-complex antibodies)

PURPOSE OF REVIEW

Twenty years since the discovery of voltage-gated potassium channel (VGKC)-related autoimmunity; it is currently known that the antibodies are not directed at the VGKC itself but to two closely associated proteins, anti-leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (Caspr2). Antibodies to LGI1 and Caspr2 give well-described clinical phenotypes. Anti-LGI1 encephalitis patients mostly have limbic symptoms, and anti-Caspr2 patients have variable syndromes with both central and peripheral symptoms. A large group of patients with heterogeneous symptoms are VGKC positive but do not have antibodies against LGI1 or Caspr2. The clinical relevance of VGKC positivity in these 'double-negative' patients is questionable. This review focusses on these three essentially different subgroups.

RECENT FINDINGS

The clinical phenotypes of anti-LGI1 encephalitis and anti-Caspr2 encephalitis have been described in more detail including data on treatment and long-term follow-up. A specific human leukocyte antigen (HLA) association was found in nontumor anti-LGI1 encephalitis, but not clearly in those with tumors. There has been increasing interest in the VGKC patients without LGI1/Caspr2 antibodies questioning its relevance in clinical practice.

SUMMARY

Anti-LGI1 encephalitis and anti-Caspr2 encephalitis are separate clinical entities. Early recognition and treatment is necessary and rewarding. The term VGKC-complex antibodies, lumping patients with anti-LGI1, anti-Caspr2 antibodies or lacking both, should be considered obsolete.

Movement disorders with neuronal antibodies: syndromic approach, genetic parallels and pathophysiology

Movement disorders are a prominent and common feature in many autoantibody-associated neurological diseases, a group of potentially treatable conditions that can mimic infectious, metabolic or neurodegenerative disease. Certain movement disorders are likely to associate with certain autoantibodies; for example, the characteristic dyskinesias, chorea and dystonia associated with NMDAR antibodies, stiff person spectrum disorders with GAD, glycine receptor, amphiphysin or DPPX antibodies, specific paroxysmal dystonias with LGI1 antibodies, and cerebellar ataxia with various anti-neuronal antibodies. There are also less-recognized movement disorder presentations of antibody-related disease, and a considerable overlap between the clinical phenotypes and the associated antibody spectra. In this review, we first describe the antibodies associated with each syndrome, highlight distinctive clinical or radiological 'red flags', and suggest a syndromic approach based on the predominant movement disorder presentation, age, and associated features. We then examine the underlying immunopathophysiology, which may guide treatment decisions in these neuroimmunological disorders, and highlight the exceptional interface between neuronal antibodies and neurodegeneration, such as the tauopathy associated with IgLON5 antibodies. Moreover, we elaborate the emerging pathophysiological parallels between genetic movement disorders and immunological conditions, with proteins being either affected by mutations or targeted by autoantibodies. Hereditary hyperekplexia, for example, is caused by mutations of the alpha subunit of the glycine receptor leading to an infantile-onset disorder with exaggerated startle and stiffness, whereas antibodies targeting glycine receptors can induce acquired hyperekplexia. The spectrum of such immunological and genetic analogies also includes cerebellar ataxias and some encephalopathies. Lastly, we discuss how these pathophysiological considerations could reflect on possible future directions regarding antigen-specific immunotherapies or targeting the pathophysiological cascades downstream of the antibody effects.

Expanding spectrum of contactin-associated protein 2 (CASPR2) autoimmunity-syndrome of parkinsonism and ataxia

Contactin-associated protein 2 (CASPR2) antibodies are originally associated with Morvan's syndrome and peripheral nerve hyper excitability. Our objective was to study retrospectively the clinical spectrum of CASPR2 antibody-positive patients in our hospital. This is a retrospective observational study. Patients treated at the Amrita Institute of Medical Sciences from May 2013 to April 2016, who were tested positive for CASPR2 antibodies, were included. A total of 1584 samples were tested in the neuroimmunology laboratory during the study period for voltage-gated potassium channel (VGKC) complex antibodies-leucine-rich glioma-inactivated protein 1 (LGI1) and CASPR2 antibodies. Thirty-four were positive for LGI1, 13 were positive for CASPR2, and 7 were for both (total 54-3.4% positivity). Of these 54 cases, 11 were treated in our hospital. Seven were positive for LGI1, three for CASPR2, and one for both. The patient who had both CASPR2 and LGI1 antibody positive had Morvan's syndrome. One patient with CASPR2 had neuromyotonia. The other patient was admitted with status epilepticus with a syndrome of parkinsonism and ataxia. The third patient had encephalopathy and myoclonus with a syndrome of parkinsonism and ataxia. Two of them underwent siddha treatment for other ailments prior to the onset of the disease for other ailments. Our short series shows the expanding spectrum of CASPR2 autoimmunity. Syndrome of parkinsonism and ataxia is an important manifestation of CASPR2 autoimmunity where we can offer a definitive treatment.

Autoimmune episodic ataxia in patients with anti-CASPR2 antibody-associated encephalitis

Objective:

To report paroxysmal episodes of cerebellar ataxia in a patient with anti–contactin-associated protein-like 2 (CASPR2) antibody-related autoimmune encephalitis and to search for similar paroxysmal ataxia in a cohort of patients with anti–CASPR2 antibody-associated autoimmune encephalitis.

Methods:

We report a patient with paroxysmal episodes of cerebellar ataxia observed during autoimmune encephalitis with anti-CASPR2 antibodies. In addition, clinical analysis was performed in a retrospective cohort of 37 patients with anti-CASPR2 antibodies to search for transient episodes of ataxia. Paroxysmal symptoms were further specified from the referral physicians, the patients, or their relatives.

Results:

A 61-year-old man with limbic encephalitis and anti-CASPR2 antibodies developed stereotyped paroxysmal episodes of cerebellar ataxia, including gait imbalance, dysarthria, and dysmetria, 1 month after the onset of the encephalitis. The ataxic episodes were specifically triggered by orthostatism and emotions. Both limbic symptoms and transient ataxic episodes resolved after treatment with steroids and IV cyclophosphamide. Among 37 other patients with anti-CASPR2 antibodies, we identified 5 additional cases with similar paroxysmal ataxic episodes that included gait imbalance (5 cases), slurred speech (3 cases), limb dysmetria (3 cases), and nystagmus (1 case). All had concomitant limbic encephalitis. Paroxysmal ataxia was not observed in patients with neuromyotonia or Morvan syndrome. Triggering factors (orthostatism or anger) were reported in 4 patients. Episodes resolved with immunomodulatory treatments in 4 patients and spontaneously in 1 case.

Conclusions:

Paroxysmal cerebellar ataxia must be added to the spectrum of the anti-CASPR2 antibody syndrome.

"Autoimmune Epilepsy": Encephalitis With Autoantibodies for Epileptologists

Autoimmune encephalitides may account for epilepsies of so far unknown cause. These "autoimmune epilepsies" may respond well to immunotherapy. More than a dozen autoantibodies have been found with this constellation; therefore, broad autoantibody testing of serum-CSF pairs offers the best diagnostic yield. Several particular features raise the suspicion of an autoimmune cause in otherwise unexplained seizure disorders.

Advances in Autoimmune Epilepsy Associated with Antibodies, Their Potential Pathogenic Molecular Mechanisms, and Current Recommended Immunotherapies

In this comprehensive article, we present an overview of some most common autoimmune antibodies believed to be potentially pathogenic for autoimmune epilepsies and elaborate their pathogenic mode of action in molecular levels based on the existing knowledge. Findings of the studies of immunemodulatory treatments for epilepsy are also discussed, and guidelines for immunotherapy are sorted out. We aim to summarize the emerging understanding of different pathogenic mechanisms of autoantibodies and clinical immunotherapy regimens to open up therapeutic possibilities for future optimum therapy. We conclude that early diagnosis of autoimmune epilepsy is of great significance, as early immune treatments have useful disease-modifying effects on some epilepsies and can facilitate the recovery.

Intracellular and non-neuronal targets of voltage-gated potassium channel complex antibodies

OBJECTIVES

Autoantibodies against the extracellular domains of the voltage-gated potassium channel (VGKC) complex proteins, leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-2 (CASPR2), are found in patients with limbic encephalitis, faciobrachial dystonic seizures, Morvan's syndrome and neuromyotonia. However, in routine testing, VGKC complex antibodies without LGI1 or CASPR2 reactivities (double-negative) are more common than LGI1 or CASPR2 specificities. Therefore, the target(s) and clinical associations of double-negative antibodies need to be determined.

METHODS

Sera (n=1131) from several clinically defined cohorts were tested for IgG radioimmunoprecipitation of radioiodinated α-dendrotoxin (¹²⁵I-αDTX)-labelled VGKC complexes from mammalian brain extracts. Positive samples were systematically tested for live hippocampal neuron reactivity, IgG precipitation of ¹²⁵I-αDTX and ¹²⁵I-αDTX-labelled Kv1 subunits, and by cell-based assays which expressed Kv1 subunits, LGI1 and CASPR2.

RESULTS

VGKC complex antibodies were found in 162 of 1131 (14%) sera. 90 of these (56%) had antibodies targeting the extracellular domains of LGI1 or CASPR2. Of the remaining 72 double-negative sera, 10 (14%) immunoprecipitated ¹²⁵I-αDTX itself, and 27 (38%) bound to solubilised co-expressed Kv1.1/1.2/1.6 subunits and/or Kv1.2 subunits alone, at levels proportionate to VGKC complex antibody levels (r=0.57, p=0.0017). The sera with LGI1 and CASPR2 antibodies immunoprecipitated neither preparation. None of the 27 Kv1-precipitating samples bound live hippocampal neurons or Kv1 extracellular domains, but 16 (59%) bound to permeabilised Kv1-expressing human embryonic kidney 293T cells. These intracellular Kv1 antibodies mainly associated with non-immune disease aetiologies, poor longitudinal clinical-serological correlations and a limited immunotherapy response.

CONCLUSIONS

Double-negative VGKC complex antibodies are often directed against cytosolic epitopes of Kv1 subunits and occasionally against non-mammalian αDTX. These antibodies should no longer be classified as neuronal-surface antibodies. They consequently lack pathogenic potential and do not in themselves support the use of immunotherapies.

Netrin-1 receptor antibodies in thymoma-associated neuromyotonia with myasthenia gravis

OBJECTIVE

To identify cell-surface antibodies in patients with neuromyotonia and to describe the main clinical implications.

METHODS

Sera of 3 patients with thymoma-associated neuromyotonia and myasthenia gravis were used to immunoprecipitate and characterize neuronal cell-surface antigens using reported techniques. The clinical significance of antibodies against precipitated proteins was assessed with sera of 98 patients (neuromyotonia 46, myasthenia gravis 52, thymoma 42; 33 of them with overlapping syndromes) and 219 controls (other neurologic diseases, cancer, and healthy volunteers).

RESULTS

Immunoprecipitation studies identified 3 targets, including the Netrin-1 receptors DCC (deleted in colorectal carcinoma) and UNC5A (uncoordinated-5A) as well as Caspr2 (contactin-associated protein-like 2). Cell-based assays with these antigens showed that among the indicated patients, 9 had antibodies against Netrin-1 receptors (7 with additional Caspr2 antibodies) and 5 had isolated Caspr2 antibodies. Only one of the 219 controls had isolated Caspr2 antibodies with relapsing myelitis episodes. Among patients with neuromyotonia and/or myasthenia gravis, the presence of Netrin-1 receptor or Caspr2 antibodies predicted thymoma (p < 0.05). Coexisting Caspr2 and Netrin-1 receptor antibodies were associated with concurrent thymoma, myasthenia gravis, and neuromyotonia, often with Morvan syndrome (p = 0.009). Expression of DCC, UNC5A, and Caspr2 proteins was demonstrated in paraffin-embedded thymoma samples (3) and normal thymus.

CONCLUSIONS

Antibodies against Netrin-1 receptors (DCC and UNC5a) and Caspr2 often coexist and associate with thymoma in patients with neuromyotonia and myasthenia gravis.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that antibodies against Netrin-1 receptors can identify patients with thymoma (sensitivity 21.4%, specificity 100%).

Voltage-gated potassium channel-complex autoimmunity and associated clinical syndromes

Voltage-gated potassium channel (VGKC)-complex antibodies are defined by the radioimmunoprecipitation of Kv1 potassium channel subunits from brain tissue extracts and were initially discovered in patients with peripheral nerve hyperexcitability (PNH). Subsequently, they were found in patients with PNH plus psychosis, insomnia, and dysautonomia, collectively termed Morvan's syndrome (MoS), and in a limbic encephalopathy (LE) with prominent amnesia and frequent seizures. Most recently, they have been described in patients with pure epilepsies, especially in patients with the novel and distinctive semiology termed faciobrachial dystonic seizures (FBDS). In each of these conditions, there is a close correlation between clinical measures and antibody levels. The VGKC-complex is a group of proteins that are strongly associated in situ and after extraction in mild detergent. Two major targets of the autoantibodies are leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein 2 (CASPR2). The patients with PNH or MoS are most likely to have CASPR2 antibodies, whereas LGI1 antibodies are found characteristically in patients with FBDS and LE. Crucially, each of these conditions has a good response to immunotherapies, often corticosteroids and plasma exchange, although optimal regimes require further study. VGKC-complex antibodies have also been described in neuropathic pain syndromes, chronic epilepsies, a polyradiculopathy in porcine abattoir workers, and some children with status epilepticus. Increasingly, however, the antigenic targets in these patients are not defined and in some cases the antibodies may be secondary rather than the primary cause. Future serologic studies should define all the antigenic components of the VGKC-complex, and further inform mechanisms of antibody pathogenicity and related inflammation.

Neurochondrin is a neuronal target antigen in autoimmune cerebellar degeneration

OBJECTIVE

To report on a novel neuronal target antigen in 3 patients with autoimmune cerebellar degeneration.

METHODS

Three patients with subacute to chronic cerebellar ataxia and controls underwent detailed clinical and neuropsychological assessment together with quantitative high-resolution structural MRI. Sera and CSF were subjected to comprehensive autoantibody screening by indirect immunofluorescence assay (IFA) and immunoblot. Immunoprecipitation with lysates of hippocampus and cerebellum combined with mass spectrometric analysis was used to identify the autoantigen, which was verified by recombinant expression in HEK293 cells and use in several immunoassays. Multiparameter flow cytometry was performed on peripheral blood and CSF, and peripheral blood was subjected to T-cell receptor spectratyping.

RESULTS

Patients presented with a subacute to chronic cerebellar and brainstem syndrome. MRI was consistent with cortical and cerebellar gray matter atrophy associated with subsequent neuroaxonal degeneration. IFA screening revealed strong immunoglobulin G1 reactivity in sera and CSF with hippocampal and cerebellar molecular and granular layers, but not with a panel of 30 recombinantly expressed established neural autoantigens. Neurochondrin was subsequently identified as the target antigen, verified by IFA and immunoblot with HEK293 cells expressing human neurochondrin as well as the ability of recombinant neurochondrin to neutralize the autoantibodies' tissue reaction. Immune phenotyping revealed intrathecal accumulation and activation of B and T cells during the acute but not chronic phase of the disease. T-cell receptor spectratyping suggested an antigen-specific T-cell response accompanying the formation of antineurochondrin autoantibodies. No such neurochondrin reactivity was found in control cohorts of various neural autoantibody-associated neurologic syndromes, relapsing-remitting multiple sclerosis, cerebellar type of multiple system atrophy, hereditary cerebellar ataxias, other neurologic disorders, or healthy donors.

CONCLUSION

Neurochondrin is a neuronal target antigen in autoimmune cerebellar degeneration.