'Medusa head ataxia': the expanding spectrum of Purkinje cell antibodies in autoimmune cerebellar ataxia. Part 3: Anti-Yo/CDR2, anti-Nb/AP3B2, PCA-2, anti-Tr/DNER, other antibodies, diagnostic pitfalls, summary and outlook

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.

Cerebellar degeneration in gluten ataxia is linked to microglial activation

Gluten sensitivity has long been recognized exclusively for its gastrointestinal involvement; however, more recent research provides evidence for the existence of neurological manifestations that can appear in combination with or independent of the small bowel manifestations. Amongst all neurological manifestations of gluten sensitivity, gluten ataxia is the most commonly occurring one, accounting for up to 40% of cases of idiopathic sporadic ataxia. However, despite its prevalence, its neuropathological basis is still poorly defined. Here, we provide a neuropathological characterization of gluten ataxia and compare the presence of neuroinflammatory markers glial fibrillary acidic protein, ionized calcium-binding adaptor molecule 1, major histocompatibility complex II and cluster of differentiation 68 in the central nervous system of four gluten ataxia cases to five ataxia controls and seven neurologically healthy controls. Our results demonstrate that severe cerebellar atrophy, cluster of differentiation 20+ and cluster of differentiation 8+ lymphocytic infiltration in the cerebellar grey and white matter and a significant upregulation of microglial immune activation in the cerebellar granular layer, molecular layer and cerebellar white matter are features of gluten ataxia, providing evidence for the involvement of both cellular and humoral immune-mediated processes in gluten ataxia pathogenesis.

Prognostic and relapsing factors of primary autoimmune cerebellar ataxia: a prospective cohort study

OBJECTIVE

The objective of this study was to investigate the factors influencing relapse and prognosis in patients with primary autoimmune cerebellar ataxia (PACA), an area previously not well understood.

METHODS

This prospective cohort study included patients who satisfied the modified diagnostic criteria of PACA. A modified Rankin scale score ≤ 2 at the last follow-up was defined as a favorable prognosis. Cox and Logistic regression were utilized to identify relapsing and prognostic factors, respectively.

RESULTS

A total of 68 patients were included and 35.3% were male. The median onset age was 42.9 years (IQR 22.1-54.0). Neuronal autoantibodies were detected in 33 (50.8%) patients. Of the 65 patients who received first-line immunotherapy, 55 (84.6%) were responsive and 10 (15.4%) were not. Responsiveness to first-line immunotherapy emerged as an independent factor for favorable prognosis (HR 16.762; 95% CI 2.877-97.655; p = 0.002), as did the absence of peripheral neuropathy/radiculopathy (HR 14.286; 95% CI 2.41-83.333; p = 0.003). Relapses occurred in 19 (27.9%) patients. Onset age ≤ 43 years (HR 5.245; 95% CI 1.499-18.35; p = 0.009), presence of peripheral neuropathy/radiculopathy (HR 4.280; 95% CI 1.622-11.298; p = 0.003) and elevated cerebrospinal fluid (CSF) protein concentration (HR 3.443; 95% CI 1.083-10.951; p = 0.036) were statistically significant relapsing factors.

CONCLUSION

This study identified younger onset age, presence of peripheral neuropathy/radiculopathy and elevated CSF protein concentration as relapsing factors, and absence of peripheral neuropathy/radiculopathy and responsiveness to first-line immunotherapy as independent factors for favorable prognosis in PACA patients. These findings may guide individualized treatment strategies and potentially improve patient outcomes.

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

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

Immunotherapies for the Effective Treatment of Primary Autoimmune Cerebellar Ataxia: a Case Series

Primary autoimmune cerebellar ataxia (PACA) is an idiopathic sporadic cerebellar ataxia that is thought to be immune-mediated but lacks biomarkers or a known cause. Here, we report two cases of immune-mediated cerebellar ataxia that responded favorably to immunotherapy, in which tissue-based indirect immunofluorescence test for serum or cerebrospinal fluid (CSF) samples yielded positive results. Case 1 was a 78-year-old man who presented with subacute progressive gait ataxia with truncal instability and dysarthria in response to steroids. Case 2 was a 62-year-old man who presented with relapses and remissions of acute progressive cerebellar ataxia occurring 1-2 times per year. Despite a favorable response to steroid treatment, he relapsed repeatedly in the absence of long-term immunosuppression. In the case of "idiopathic" cerebellar ataxia, immune-mediated causes should be investigated, and immunotherapy may have therapeutic effects.

Utility of Protein Microarrays for Detection of Classified and Novel Antibodies in Autoimmune Neurologic Disease

BACKGROUND AND OBJECTIVES

Neural antibodies are detected by tissue-based indirect immunofluorescence assay (IFA) in Mayo Clinic's Neuroimmunology Laboratory practice, but the process of characterizing and validating novel antibodies is lengthy. We report our assessment of human protein arrays.

METHODS

Assessment of arrays (81% human proteome coverage) was undertaken using diverse known positive samples (17 serum and 14 CSF). Samples from patients with novel neural antibodies were reflexed from IFA to arrays. Confirmatory assays were cell-based (CBA) or line blot. Epitope mapping was undertaken using phage display immunoprecipitation sequencing (PhiPSeq).

RESULTS

Control positive samples known to be reactive with linear epitopes of intracellular antigens (e.g., ANNA-1 [anti-Hu]) were readily identified by arrays in 20 of 21 samples. By contrast, 10 positive controls known to be enriched with antibodies against cell surface protein conformational epitopes (e.g., GluN1 subunit of NMDA-R) were indistinguishable from background signal. Three antibodies, previously characterized by other investigators (but unclassified in our laboratory), were unmasked in 4 patients using arrays (July-December 2022): Neurexin-3α, 1 patient; regulator of gene protein signaling (RGS)8, 1 patient; and seizure-related homolog like 2 (SEZ6L2), 2 patients. All were accompanied by previously reported phenotypes (encephalitis, 1; cerebellar ataxia, 3). Patient 1 had subacute onset of seizures and encephalopathy. Neurexin-3α ranked high in CSF (second ranked neural protein) but low in serum (660th overall). Neurexin-3α CBA was positive in both samples. Patient 2 presented with rapidly progressive cerebellar ataxia. RGS8 ranked the highest neural protein in available CSF sample by array (third overall). RGS8-specific line blot was positive. Patients 3 and 4 had rapidly progressive cerebellar ataxia. SEZ6L2 was the highest ranked neural antigen by arrays in all samples (CSF, 1, serum, 2; Patient 3, ranked 9th overall in CSF, 11th in serum; Patient 4, 6th overall in serum]). By PhIPSeq, diverse neurexin-3α epitopes (including cell surface) were detected in CSF from patient 1, but no SEZ6L2 peptides were detected for serum or CSF samples from Patient 3.

DISCUSSION

Individualized autoimmune neurologic diagnoses may be accelerated using protein arrays. They are optimal for detection of intracellular antigen-reactive antibodies, though certain cell surface-directed antibodies (neurexin-3α and SEZ6L2) may also be detected.

Autoimmune Cerebellar Ataxia: Etiology and Clinical Characteristics of a Case Series from China

Autoimmune cerebellar ataxia (ACA) is an important and potentially treatable cause of sporadic cerebellar syndrome, but studies with large sample size are limited. This study reported a large ACA series in China and described its etiology and clinical characteristics. We reviewed all ACA patients from our hospital (2013-2021) and analyzed their clinical and paraclinical features, treatment, and outcome. ACA subtypes investigated included paraneoplastic cerebellar degeneration (PCD), primary autoimmune cerebellar ataxia (PACA), anti-glutamate decarboxylase (GAD)-associated cerebellar ataxia, opsoclonus-myoclonus syndrome (OMS), Miller Fisher syndrome (MFS), and ACA-associated with autoimmune encephalitis. A total of 127 patients were identified and 40.9% were male. The median onset age was 47.0 years. Gait ataxia was the most prevalent feature followed by limb ataxia, dizziness, and dysarthria/dysphagia. Extracerebellar manifestations included pyramidal signs (28.3%) and peripheral neuropathy/radiculopathy (15.0%). ACA subtypes were PCD (30.7%), PACA (37.8%), ACA associated with autoimmune encephalitis (12.6%), anti-GAD-associated ACA (8.7%), MFS (7.1%), and OMS (3.1%). Neuronal antibodies were positive in 67.7% of patients. Brain magnetic resonance imaging was unremarkable (55.7%) or showed atrophy (18.3%) or abnormal signal intensity (26.1%, most of which was extracerebellar). Although most patients received immunotherapy, the modified Rankin scale at last follow-up was ≤ 2 in only 47.3% patients. Thirteen patients died and 24 relapsed. Compared with PACA, PCD patients were older and had poorer outcome. This study illustrates the heterogeneity in the clinical features of ACA and suggests the importance of neuronal antibody testing in ACA diagnosis. PCD and PACA are the dominant ACA subtypes, and the former has a less favorable prognosis.

Therapy response in seronegative versus seropositive autoimmune encephalitis

Background

Autoimmune encephalitis (AE) might be seropositive or seronegative, depending on whether antibodies targeting well-characterized neuronal antigens can be detected or not. Since data on treatment efficacy in seronegative cases, are scarce, the main rationale of this study was to evaluate immunotherapy response in seronegative AE in comparison to seropositive cases.

Methods

An electronic database search retrospectively identified 150 AE patients, treated in our tertiary care university hospital between 2010 and 2020 with an AE. Therapy response was measured using both general impression and the modified Rankin Scale (mRS).

Results

Seventy-four AE patients (49.3%) were seronegative and 76 (50.7%) seropositive. These cases were followed up for a mean of 15.3 (standard deviation, SD, 24.9) and 24.3 months (SD 28.1), respectively. Both groups were largely similar on the basis of numerous clinical and paraclinical findings including cerebrospinal fluid, electroencephalography, magnetic resonance imaging, and 18-F-fluor-desoxy-glucose-positron-emmission-tomography pathologies. The majority of patients (80.4%) received at least one immunotherapy, which were glucocorticoids in most cases (76.4%). Therapy response on general impression was high with 49 (92.5%) of treated seronegative, and 57 (86.4%) of treated seropositive AE cases showing improvement following immunotherapies and not significantly different between both groups. Notably, the proportion of patients with a favorable neurological deficit (mRS 0-2) was twice as high during long-term follow-up as compared to baseline in both groups.

Conclusion

Since both, patients with seronegative and seropositive AE, substantially benefitted from immunotherapies, these should be considered in AE patients irrespective of their antibody results.

Anti-neurochondrin antibody as a biomarker in primary autoimmune cerebellar ataxia-a case report and review of the literature

BACKGROUND AND PURPOSE

Neuronal autoantibodies can support the diagnosis of primary autoimmune cerebellar ataxia (PACA). Knowledge of PACA is still sparce. This article aims to highlight the relevance of anti-neurochondrin antibodies and possible therapeutical consequences in people with PACA.

METHODS

This is a case presentation and literature review of PACA associated with anti-neurochondrin antibodies.

RESULTS

A 33-year-old man noticed reduced control of the right leg in May 2020. During his first clinic appointment at our institution in September 2021, he complained about gait imbalance, fine motor disorders, tremor, intermittent diplopia and slurred speech. He presented a pancerebellar syndrome with stance, gait and limb ataxia, scanning speech and oculomotor dysfunction. Within 3 months the symptoms progressed. An initial cerebral magnetic resonance imaging, June 2020, was normal, but follow-up imaging in October 2021 and July 2022 revealed marked cerebellar atrophy (29% volume loss). Cerebrospinal fluid analysis showed lymphocytic pleocytosis of 11 x 10³ /L (normal range 0-4) and oligoclonal bands type II. Anti-neurochondrin antibodies (immunoglobulin G) were detected in serum (1:10,000) and cerebrospinal fluid (1:320, by cell-based indirect immunofluorescence assay and immunoblot, analysed by the EUROIMMUN laboratory). After ruling out alternative causes and neoplasia, diagnosis of PACA was given and immunotherapy (steroids and cyclophosphamide) was started in January 2022. In March 2022 a stabilization of disease was observed.

CONCLUSION

Cerebellar ataxia associated with anti-neurochondrin antibodies has only been described in 19 cases; however, the number of unrecognized PACAs may be higher. As anti-neurochondrin antibodies target an intracellular antigen and exhibit a mainly cytotoxic T-cell-mediated pathogenesis, important therapeutic implications may result. Because of the severe and rapid clinical progression, aggressive immunotherapy was warranted. This case highlights the need for rapid diagnosis and therapy in PACA, as stabilization and even improvement of symptoms are attainable.

Septin-3 autoimmunity in patients with paraneoplastic cerebellar ataxia

BACKGROUND

Septins are cytoskeletal proteins with filament forming capabilities, which have multiple roles during cell division, cellular polarization, morphogenesis, and membrane trafficking. Autoantibodies against septin-5 are associated with non-paraneoplastic cerebellar ataxia, and autoantibodies against septin-7 with encephalopathy with prominent neuropsychiatric features. Here, we report on newly identified autoantibodies against septin-3 in patients with paraneoplastic cerebellar ataxia. We also propose a strategy for anti-septin autoantibody determination.

METHODS

Sera from three patients producing similar immunofluorescence staining patterns on cerebellar and hippocampal sections were subjected to immunoprecipitation followed by mass spectrometry. The identified candidate antigens, all of which were septins, were expressed recombinantly in HEK293 cells either individually, as complexes, or combinations missing individual septins, for use in recombinant cell-based indirect immunofluorescence assays (RC-IIFA). Specificity for septin-3 was further confirmed by tissue IIFA neutralization experiments. Finally, tumor tissue sections were analyzed immunohistochemically for septin-3 expression.

RESULTS

Immunoprecipitation with rat cerebellum lysate revealed septin-3, -5, -6, -7, and -11 as candidate target antigens. Sera of all three patients reacted with recombinant cells co-expressing septin-3/5/6/7/11, while none of 149 healthy control sera was similarly reactive. In RC-IIFAs the patient sera recognized only cells expressing septin-3, individually and in complexes. Incubation of patient sera with five different septin combinations, each missing one of the five septins, confirmed the autoantibodies' specificity for septin-3. The tissue IIFA reactivity of patient serum was abolished by pre-incubation with HEK293 cell lysates overexpressing the septin-3/5/6/7/11 complex or septin-3 alone, but not with HEK293 cell lysates overexpressing septin-5 as control. All three patients had cancers (2 × melanoma, 1 × small cell lung cancer), presented with progressive cerebellar syndromes, and responded poorly to immunotherapy. Expression of septin-3 was demonstrated in resected tumor tissue available from one patient.

CONCLUSIONS

Septin-3 is a novel autoantibody target in patients with paraneoplastic cerebellar syndromes. Based on our findings, RC-IIFA with HEK293 cells expressing the septin-3/5/6/7/11 complex may serve as a screening tool to investigate anti-septin autoantibodies in serological samples with a characteristic staining pattern on neuronal tissue sections. Autoantibodies against individual septins can then be confirmed by RC-IIFA expressing single septins.

Ataxias: Hereditary, Acquired, and Reversible Etiologies

A variety of etiologies can cause cerebellar dysfunction, leading to ataxia symptoms. Therefore, the accurate diagnosis of the cause for cerebellar ataxia can be challenging. A step-wise investigation will reveal underlying causes, including nutritional, toxin, immune-mediated, genetic, and degenerative disorders. Recent advances in genetics have identified new genes for both autosomal dominant and autosomal recessive ataxias, and new therapies are on the horizon for targeting specific biological pathways. New diagnostic criteria for degenerative ataxias have been proposed, specifically for multiple system atrophy, which will have a broad impact on the future clinical research in ataxia. In this article, we aim to provide a review focus on symptoms, laboratory testing, neuroimaging, and genetic testing for the diagnosis of cerebellar ataxia causes, with a special emphasis on recent advances. Strategies for the management of cerebellar ataxia is also discussed.

Factors predisposing to humoral autoimmunity against brain-antigens in health and disease: Analysis of 49 autoantibodies in over 7000 subjects

BACKGROUND

Circulating autoantibodies (AB) against brain-antigens, often deemed pathological, receive increasing attention. We assessed predispositions and seroprevalence/characteristics of 49 AB in > 7000 individuals.

METHODS

Exploratory cross-sectional cohort study, investigating deeply phenotyped neuropsychiatric patients and healthy individuals of GRAS Data Collection for presence/characteristics of 49 brain-directed serum-AB. Predispositions were evaluated through GWAS of NMDAR1-AB carriers, analyses of immune check-point genotypes, APOE4 status, neurotrauma. Chi-square, Fisher's exact tests and logistic regression analyses were used.

RESULTS

Study of N = 7025 subjects (55.8 % male; 41 ± 16 years) revealed N = 1133 (16.13 %) carriers of any AB against 49 defined brain-antigens. Overall, age dependence of seroprevalence (OR = 1.018/year; 95 % CI [1.015-1.022]) emerged, but no disease association, neither general nor with neuropsychiatric subgroups. Males had higher AB seroprevalence (OR = 1.303; 95 % CI [1.144-1.486]). Immunoglobulin class (N for IgM:462; IgA:487; IgG:477) and titers were similar. Abundant were NMDAR1-AB (7.7 %). Low seroprevalence (1.25 %-0.02 %) was seen for most AB (e.g., amphiphysin, KCNA2, ARHGAP26, GFAP, CASPR2, MOG, Homer-3, KCNA1, GLRA1b, GAD65). Non-detectable were others. GWAS of NMDAR1-AB carriers revealed three genome-wide significant SNPs, two intergenic, one in TENM3, previously autoimmune disease-associated. Targeted analysis of immune check-point genotypes (CTLA4, PD1, PD-L1) uncovered effects on humoral anti-brain autoimmunity (OR = 1.55; 95 % CI [1.058-2.271]) and disease likelihood (OR = 1.43; 95 % CI [1.032-1.985]). APOE4 carriers (∼19 %) had lower seropositivity (OR = 0.766; 95 % CI [0.625-0.933]). Neurotrauma predisposed to NMDAR1-AB seroprevalence (IgM: OR = 1.599; 95 % CI [1.022-2.468]).

CONCLUSIONS

Humoral autoimmunity against brain-antigens, frequent across health and disease, is predicted by age, gender, genetic predisposition, and brain injury. Seroprevalence, immunoglobulin class, or titers do not predict disease.

Anti-Tr/DNER antibody-associated cerebellar ataxia: three rare cases report and literature review

BACKGROUND

To report three cases of autoimmune cerebellar ataxia related to anti-delta/notch-like epidermal growth factor-related receptor (Tr/DNER) antibodies.

CASE PRESENTATION

Patients with unknown cerebellar ataxia were screened with autoimmune cerebellar ataxia (ACA)-related antibody panel. The anti-Tr antibody was positive in three female patients in whom the onset ages were 43 years, 35 years and 43 years old. The antibody titres of serum and cerebrospinal fluid were all 1:32. Cerebral ataxia was the most prominent presentation. Mild cerebellar atrophy was found in one of the patients. Immunotherapy was effective in all three patients.

CONCLUSION

The Tr antibody is associated with autoimmune ataxia, and it has been suggested that the anti-Tr antibody should be tested in patients with cerebellar ataxia who are negative for routine ACA antibodies. Early immunotherapy may improve patient prognoses.

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.

Anti-Tr/DNER Antibody-Associated Cerebellar Ataxia: a Systematic Review

Rapidly progressive cerebellar ataxia is a classical paraneoplastic neurological syndrome associated with different autoantibodies and typical demographic characteristics, extracerebellar signs, tumor association, and prognosis. Anti-Tr/anti-Delta/Notch-like epidermal growth factor-related receptor (DNER) antibody is one of the associated antibodies. Given the rarity of this condition, our current knowledge is based on case reports and small case series. In order to improve our understanding of these conditions, we conducted a systematic review of the literature. Our study followed the PRISMA reporting guidelines. Studies of patients with the presence of anti-Tr/DNER antibodies in serum or cerebrospinal fluid (CSF) were included. We extract data information related to study characteristics, demographics, clinical symptoms, tumor association, neuroimaging, and cerebrospinal fluid analysis. Out of 131 records, we analyzed 17 papers, including a total of 85 patients with anti-Tr/DNER antibody-associated cerebellar ataxia. We confirmed that this disease occurred mostly in middle-aged males. Isolated cerebellar ataxia was the most common presentation. Extracerebellar features were rare (8%). Ninety-one percent of the patients presented an associated tumor, being Hodgkin lymphoma the most common. Abnormal neuroimaging patterns included cerebellar atrophy (19%) and cerebellar hypersignal (6%). Cerebrospinal fluid was inflammatory in 64% of the patients. Oncological response was complete in 88%, but neurological prognosis was poor with only 41% of the patients presenting significant neurological improvement at the last follow up. Anti-Tr/DNER antibodies should be tested in rapid progressive cerebellar ataxia. Oncological response is excellent; however, many patients do not improve from their cerebellar ataxia.

The Emerging Key Role of the mGluR1-PKCγ Signaling Pathway in the Pathogenesis of Spinocerebellar Ataxias: A Neurodevelopmental Viewpoint

Spinocerebellar ataxias (SCAs) are a heterogeneous group of autosomal dominantly inherited progressive disorders with degeneration and dysfunction of the cerebellum. Although different subtypes of SCAs are classified according to the disease-associated causative genes, the clinical syndrome of the ataxia is shared, pointing towards a possible convergent pathogenic pathway among SCAs. In this review, we summarize the role of SCA-associated gene function during cerebellar Purkinje cell development and discuss the relationship between SCA pathogenesis and neurodevelopment. We will summarize recent studies on molecules involved in SCA pathogenesis and will focus on the mGluR1-PKCγ signaling pathway evaluating the possibility that this might be a common pathway which contributes to these diseases.

Inositol 1,4,5-trisphosphate receptor type 1 autoantibody (ITPR1-IgG/anti-Sj)-associated autoimmune cerebellar ataxia, encephalitis and peripheral neuropathy: review of the literature

Background

In 2014, we first described novel autoantibodies to the inositol 1,4,5-trisphosphate receptor type 1 (ITPR1-IgG/anti-Sj) in patients with autoimmune cerebellar ataxia (ACA) in this journal. Here, we provide a review of the available literature on ITPR1-IgG/anti-Sj, covering clinical and paraclinical presentation, tumour association, serological findings, and immunopathogenesis.

Methods

Review of the peer-reviewed and PubMed-listed English language literature on ITPR1-IgG/anti-Sj. In addition, we provide an illustrative report on a new patient with ITPR1-IgG-associated encephalitis with cognitive decline and psychosis.

Results

So far, at least 31 patients with serum ITPR1-IgG/anti-Sj have been identified (clinical information available for 21). The most common manifestations were ACA, encephalopathy with seizures, myelopathy, and (radiculo)neuropathy, including autonomic neuropathy. In 45% of cases, an underlying tumour was present, making the condition a facultative paraneoplastic neurological disorder. The neurological syndrome preceded tumour diagnosis in all but one case. In most cases, immunotherapy had only moderate or no effect. The association of ITPR1-IgG/anti-Sj with manifestations other than ACA is corroborated by the case of a 48-year-old woman with high-titre ITPR1-IgG/anti-Sj antibodies and rapid cognitive decline, affecting memory, attention and executive function, and psychotic manifestations, including hallucinations, investigated here in detail. FDG-PET revealed right-temporal glucose hypermetabolism compatible with limbic encephalitis. Interestingly, ITPR1-IgG/anti-Sj mainly belonged to the IgG2 subclass in both serum and cerebrospinal fluid (CSF) in this and further patients, while it was predominantly IgG1 in other patients, including those with more severe outcome, and remained detectable over the entire course of disease. Immunotherapy with intravenous methylprednisolone, plasma exchange, and intravenous immunoglobulins, was repeatedly followed by partial or complete recovery. Long-term treatment with cyclophosphamide was paralleled by relative stabilization, although the patient noted clinical worsening at the end of each treatment cycle.

Conclusions

The spectrum of neurological manifestations associated with ITPR1 autoimmunity is broader than initially thought. Immunotherapy may be effective in some cases. Studies evaluating the frequency of ITPR1-IgG/anti-Sj in patients with cognitive decline and/or psychosis of unknown aetiology are warranted. Tumour screening is essential in patients presenting with ITPR1-IgG/anti-Sj.

Update in autoimmune and paraneoplastic myelopathies: Newly described antigen targets and antibody testing

Myelopathy is an increasingly recognized presentation of many antibody-mediated neuroinflammatory disorders. While specific features of certain autoimmune myelopathies such as aquaporin-4 antibody associated neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein associated disorder (MOGAD) are well-characterized, other less commonly seen antibody-associated myelopathies are not as well-defined. These include but are not limited to, Hu/ANNA1, anti-glial fibrillary acidic protein (GFAP), anti-CV2/collapsin response mediator protein (CRMP5), and amphiphysin. Here, we review the mentioned more common antibody mediated myelopathies as well those that as less common, followed by a review of differentials that may mimic these disorders.

Case report and literature analysis: Autoimmune cerebellar ataxia associated with homer-3 antibodies

Objective

We present a case of autoimmune cerebellar ataxia (ACA) associated with Homer protein homolog 3 (Homer-3) antibodies. Then, a review of the literature was conducted to summarize its clinical spectrum to improve clinicians' understanding of this rare entity.

Case presentation

A 25-year-old man suffered from the subacute onset of cerebellar ataxia and psychiatric symptoms with abnormalities in the cerebellum on initial brain MRI and Homer-3 antibodies titers of 1:100 in the serum. His neurological symptoms did not improve after intravenous methylprednisolone but significantly improved following plasma exchange with a modified Rankin Scale (mRS) score of 1. However, 5 months later, he experienced relapse during oral prednisone tapering with enhanced cerebellar lesions and obvious cerebellar atrophy on repeated MRI. Various immunomodulatory approaches, including corticosteroids and plasma exchange, were utilized with no improvement. Then rituximab was given for the first time to treat Homer-3 autoimmunity with partial improvement of symptoms. However, the patient remained profoundly disabled with an mRS score of 4.

Conclusion

ACA associated with Homer-3 antibodies may have a suboptimal response to corticosteroid therapy. More intense immunotherapy such as rituximab may contribute to the improvement of cerebellar syndrome. Relapsing courses and presentation of cerebellar atrophy may suggest a poor prognosis in this entity.

Autoantibody Encephalitis: Presentation, Diagnosis, and Management

Autoantibody encephalitis causes distinct clinical syndromes involving alterations in mentation, abnormal movements, seizures, psychiatric symptoms, sleep disruption, spasms, and neuromyotonia. The diagnoses can be confirmed by specific antibody tests, although some antibodies may be better detected in spinal fluid and others in serum. Each disorder conveys a risk of certain tumors which may inform diagnosis and be important for treatment. Autoantibodies to receptors and other neuronal membrane proteins are generally thought to be pathogenic and result in loss of function of the targets, so understanding the pharmacology of the receptors may inform our understanding of the syndromes. Patients may be profoundly ill but the syndromes usually respond to immune therapy, although there are differences in the types of immune therapy that are thought to be most effective for the various disorders.

Rho GTPase-activating protein 10 (ARHGAP10/GRAF2) is a novel autoantibody target in patients with autoimmune encephalitis

Background

In 2010, we described a novel immunoglobulin G (IgG) autoantibody (termed anti-Ca after the index case) targeting Rho GTPase-activating protein 26 (ARHGAP26, also termed GTPase regulator associated with focal adhesion kinase [GRAF], or oligophrenin-like protein 1 [OPHN1L]) in autoimmune cerebellar ataxia (ACA). Later, ARHGAP26-IgG/anti-Ca was reported in patients with limbic encephalitis/cognitive decline or peripheral neuropathy. In several of the reported cases, the syndrome was associated with cancer. ARHGAP10/GRAF2, which is expressed throughout the central nervous system, shares significant sequence homology with ARHGAP26/GRAF. Mutations in the ARHGAP10 gene have been linked to cognitive and psychiatric symptoms and schizophrenia.

Objective

To assess whether ARHGAP26-IgG/anti-Ca co-reacts with ARHGAP10.

Methods

Serological testing for ARHGAP10/GRAF2 autoantibodies by recombinant cell-based assays and isotype and IgG subclass analyses.

Results

26/31 serum samples (84%) from 9/12 (75%) ARHGAP26-IgG/anti-Ca-positive patients and 4/6 ARHGAP26-IgG/anti-Ca-positive CSF samples from four patients were positive also for ARHGAP10-IgG. ARHGAP10-IgG (termed anti-Ca2) remained detectable in the long-term (up to 109 months) and belonged mainly to the complement-activating IgG1 subclass. Median ARHGAP26-IgG/anti-Ca and median ARHGAP10-IgG/anti-Ca2 serum titres were 1:3200 and 1:1000, respectively, with extraordinarily high titres in some samples (ARHGAP26-IgG/anti-Ca: up to 1:1000,000; ARHGAP10-IgG: up to 1:32,000). ARHGAP26/anti-Ca serum titres exceeded those of ARHGAP10-IgG in all samples but one. A subset of patients was positive also for ARHGAP10-IgM and ARHGAP10-IgA. CSF/serum ratios and antibody index calculation suggested intrathecal production of ARHGAP26-IgG/anti-Ca and anti-ARHGAP10. Of 101 control samples, 100 were completely negative for ARHGAP10-IgG; a single control sample bound weakly (1:10) to the ARHGAP10-transfected cells.

Conclusions

We demonstrate that a substantial proportion of patients with ARHGAP26-IgG/anti-Ca-positive autoimmune encephalitis co-react with ARHGAP10. Further studies on the clinical and diagnostic implications of ARHGAP10-IgG/anti-Ca2 seropositivity in patients with autoimmune encephalitis are warranted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-022-11178-9.

Plasma lncRNA LOC338963 and mRNA AP3B2 are upregulated in paraneoplastic Lambert-Eaton myasthenic syndrome

INTRODUCTION/AIMS

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune neuromuscular junction disorder. Long noncoding RNA (lncRNA) can regulate the expression of mRNA and is involved in the development of autoimmune diseases, but few genetic studies are available. In this study we aimed to explore the lncRNA and mRNA changes of LEMS.

METHODS

Plasma lncRNA and mRNA expression profiles of three LEMS patients with small cell lung cancer (SCLC) and three matched healthy controls were analyzed by microarray. Differentially expressed lncRNAs and adjacent mRNAs were jointly analyzed, and candidates were verified by quantitative real-time polymerase chain reaction (qRT-PCR). The identified genes were subsequently evaluated in 9, 8, and 4 patients with paraneoplastic LEMS, nontumor LEMS, and SCLC, respectively. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to determine possible functions.

RESULTS

A total of 320 lncRNA and 168 mRNAs were differentially expressed in the three LEMS with SCLC and compared with healthy controls. Among these, lncRNA LOC338963 and its neighboring mRNA AP3B2 were upregulated jointly, which was confirmed by qRT-PCR. qRT-PCR revealed significant upregulation of the two genes in patients with paraneoplastic LEMS compared with nontumor LEMS or SCLC. GO analysis of AP3B2 identified the enrichment terms anterograde synaptic vesicle transport and establishment of synaptic vesicle localization. KEEG analysis showed that AP3B2 was enriched in lysosomal pathways.

DISCUSSION

LOC338963 and AP3B2 were upregulated in patients with paraneoplastic LEMS, suggesting their involvement in pathogenesis. These genes could be targets for exploring the pathomechanism of paraneoplastic LEMS.

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.

An Autoantigen Atlas From Human Lung HFL1 Cells Offers Clues to Neurological and Diverse Autoimmune Manifestations of COVID-19

COVID-19 is accompanied by a myriad of both transient and long-lasting autoimmune responses. Dermatan sulfate (DS), a glycosaminoglycan crucial for wound healing, has unique affinity for autoantigens (autoAgs) from apoptotic cells. DS-autoAg complexes are capable of stimulating autoreactive B cells and autoantibody production. We used DS-affinity proteomics to define the autoantigen-ome of lung fibroblasts and bioinformatics analyses to study the relationship between autoantigenic proteins and COVID-induced alterations. Using DS-affinity, we identified an autoantigen-ome of 408 proteins from human HFL1 cells, at least 231 of which are known autoAgs. Comparing with available COVID data, 352 proteins of the autoantigen-ome have thus far been found to be altered at protein or RNA levels in SARS-CoV-2 infection, 210 of which are known autoAgs. The COVID-altered proteins are significantly associated with RNA metabolism, translation, vesicles and vesicle transport, cell death, supramolecular fibrils, cytoskeleton, extracellular matrix, and interleukin signaling. They offer clues to neurological problems, fibrosis, smooth muscle dysfunction, and thrombosis. In particular, 150 altered proteins are related to the nervous system, including axon, myelin sheath, neuron projection, neuronal cell body, and olfactory bulb. An association with the melanosome is also identified. The findings from our study illustrate a connection between COVID infection and autoimmunity. The vast number of COVID-altered proteins with high intrinsic propensity to become autoAgs offers an explanation for the diverse autoimmune complications in COVID patients. The variety of autoAgs related to mRNA metabolism, translation, and vesicles suggests a need for long-term monitoring of autoimmunity in COVID. The COVID autoantigen atlas we are establishing provides a detailed molecular map for further investigation of autoimmune sequelae of the pandemic, such as “long COVID” syndrome.

A Breakdown of Immune Tolerance in the Cerebellum

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

Update on Paraneoplastic Cerebellar Degeneration

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

Neurological Autoimmunity Associated With Homer-3 Antibody: A Case Series From China

BACKGROUND AND OBJECTIVE

To present 6 new cases with Homer-3 antibodies that expand their clinical spectra and to evaluate the effect of immunotherapy.

METHODS

Patients with suspected autoimmune cerebellar disorder were tested for rare autoimmune cerebellar ataxia (ACA) antibodies (anti-Tr(DNER)/Zic4/ITPR1/Homer-3/NCDN/PKCγ/PCA-2/AP3B2/mGluR1/ATP1A3 antibodies) using both cell-based and tissue-based assays. Patients with positive serum or CSF results who were diagnosed with ACA were registered and followed up. This study reports and analyzes cases with Homer-3 antibodies.

RESULTS

Of the serum and CSF samples of 750 patients tested, 6 were positive for Homer-3 antibodies. All manifested subacute or insidious-onset cerebellar ataxia. Furthermore, 2 patients each exhibited encephalopathy, myeloradiculopathy, REM sleep behavior disorder, and autonomic dysfunction. Brain magnetic resonance images were normal (n = 1) or revealed cerebellar atrophy (n = 1), cerebellum and pons atrophy with the hot cross bun sign (n = 2), and bilateral cerebral abnormalities (n = 2). Definite leukocytosis was identified in the CSF of 2 patients, protein concentration elevation was observed in the CSF of 1 patient, and oligoclonal bands were present in 2 patients. All patients received immunotherapy, including corticosteroid, IV immunoglobulin, plasma exchange, and mycophenolate mofetil, after which the residual disability was still severe (modified Rankin Scale score ≥3 at the last follow-up in 4 patients and final Scale for the Assessment and Rating of Ataxia scores of 12-29), although 4 patients partially improved and 1 patient stabilized. The remaining 1 patient continued to deteriorate after repeated immunotherapy. Two patients relapsed.

DISCUSSION

Disorders associated with Homer-3 antibody can mimic multiple system atrophy with cerebellar features in both clinical and radiologic aspects. Accurate identification of autoimmune-mediated cases is critical. Timely, comprehensive immunotherapy is warranted, given the possibility of long-term clinical benefit.

Combination of structural MRI, functional MRI and brain PET-CT provide more diagnostic and prognostic value in patients of cerebellar ataxia associated with anti-Tr/DNER: a case report

Background

Brain magnetic resonance imaging (MRI) rarely reveals structural changes in patients with suspected anti-Tr/DNER encephalitis and thus provides very limited information. Here, we combined structural MRI, functional MRI, and positron emission tomography-computed tomography (PET-CT) findings to characterize this rare disorder in a patient.

Case presentation

A 43-year-old woman presented with progressive cerebellar ataxia, memory impairment, anxiety, and depression. Anti-Tr antibodies were detected in both her serum (1:10) and cerebrospinal fluid (1:10). A diagnosis of anti-Tr-positive autoimmune cerebellar ataxia was established. The patient’s symptoms were worse, but her brain MRI was normal. Meanwhile, voxel-based morphometry analysis showed bilateral reduced cerebellar volume, especially in the posterior lobe and uvula of the cerebellum and the middle of the left temporal lobe compared with 6 sex- and age-matched healthy subjects (6 females, 43 ± 2 years; p < 0.05). Using seed-based functional connectivity analysis, decreased connectivity between the posterior cingulate cortex/precuneus and left frontal lobe compared to the control group (p < 0.05) was detected. PET-CT revealed bilateral hypometabolism in the cerebellum and relative hypermetabolism in the cerebellar vermis and bilateral frontal lobe, but no malignant changes.

Conclusions

A combination of structural MRI, functional MRI, and brain PET-CT has higher diagnostic and prognostic value than conventional MRI in patients with suspected anti-Tr/DNER encephalitis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02403-5.

A Master Autoantigen-ome Links Alternative Splicing, Female Predilection, and COVID-19 to Autoimmune Diseases

Chronic and debilitating autoimmune sequelae pose a grave concern for the post-COVID-19 pandemic era. Based on our discovery that the glycosaminoglycan dermatan sulfate (DS) displays peculiar affinity to apoptotic cells and autoantigens (autoAgs) and that DS-autoAg complexes cooperatively stimulate autoreactive B1 cell responses, we compiled a database of 751 candidate autoAgs from six human cell types. At least 657 of these have been found to be affected by SARS-CoV-2 infection based on currently available multi-omic COVID data, and at least 400 are confirmed targets of autoantibodies in a wide array of autoimmune diseases and cancer. The autoantigen-ome is significantly associated with various processes in viral infections, such as translation, protein processing, and vesicle transport. Interestingly, the coding genes of autoAgs predominantly contain multiple exons with many possible alternative splicing variants, short transcripts, and short UTR lengths. These observations and the finding that numerous autoAgs involved in RNA-splicing showed altered expression in viral infections suggest that viruses exploit alternative splicing to reprogram host cell machinery to ensure viral replication and survival. While each cell type gives rise to a unique pool of autoAgs, 39 common autoAgs associated with cell stress and apoptosis were identified from all six cell types, with several being known markers of systemic autoimmune diseases. In particular, the common autoAg UBA1 that catalyzes the first step in ubiquitination is encoded by an X-chromosome escape gene. Given its essential function in apoptotic cell clearance and that X-inactivation escape tends to increase with aging, UBA1 dysfunction can therefore predispose aging women to autoimmune disorders. In summary, we propose a model of how viral infections lead to extensive molecular alterations and host cell death, autoimmune responses facilitated by autoAg-DS complexes, and ultimately autoimmune diseases. Overall, this master autoantigen-ome provides a molecular guide for investigating the myriad of autoimmune sequalae to COVID-19 and clues to the rare but reported adverse effects of the currently available COVID vaccines.

mGluR1 signaling in cerebellar Purkinje cells: Subcellular organization and involvement in cerebellar function and disease

The cerebellum is essential for the control, coordination, and learning of movements, and for certain aspects of cognitive function. Purkinje cells are the sole output neurons in the cerebellar cortex and therefore play crucial roles in the diverse functions of the cerebellum. The type 1 metabotropic glutamate receptor (mGluR1) is prominently enriched in Purkinje cells and triggers downstream signaling pathways that are required for functional and structural plasticity, and for synaptic responses. To understand how mGluR1 contributes to cerebellar functions, it is important to consider not only the operational properties of this receptor, but also its spatial organization and the molecular interactions that enable its proper functioning. In this review, we highlight how mGluR1 and its related signaling molecules are organized into tightly coupled microdomains to fulfill physiological functions. We also describe emerging evidence that altered mGluR1 signaling in Purkinje cells underlies cerebellar dysfunction in ataxias of human patients and mouse models.

Paraneoplastic Cerebellar Degeneration (PCD) associated with PCA-1 antibodies in established cancer patients

INTRODUCTION

Paraneoplastic cerebellar degeneration (PCD) is a rare set of neurological disorders arising from tumor-associated autoimmunity against antigens within the cerebellum. Anti-Purkinje cell cytoplasmic antibody 1 (PCA-1), or anti-Yo, is the most commonly linked antibody and is classically associated with breast and ovarian cancers.

METHODS

Medical records of patients at our institution who developed PCA-1 associated PCD were reviewed. Clinical information, including cancer history, cancer-directed treatment, and serum and CSF titers of PCA-1 antibody were extracted.

CASES

We report a series of cases of PCA-1 associated PCD in patients with known breast or ovarian cancer diagnosis not receiving immunotherapy. These cases highlight aspects of PCA-1 paraneoplastic syndrome such as triggering by cytotoxic chemotherapy or surgery, the possibility of tumor recurrence and the association with development of a second cancer.

DISCUSSION

Diagnosis of the syndrome requires neurological workup with lumbar puncture (LP) with cerebrospinal fluids (CSF) studies, serum and CSF paraneoplastic antibody panel, and neuroimaging. Inpatient admission for prompt workup and initiation of treatment is recommended. Treatment most commonly includes immunosuppression with corticosteroids, plasmapheresis, and/or intravenous immune globulin (IVIG); however, we postulate that other immune modulating treatments may warrant consideration.

CONCLUSION

These cases highlight the need for early recognition of the syndrome in patients receiving nonimmune based chemotherapy, for prompt workup and treatment.

Diagnostic Criteria for Primary Autoimmune Cerebellar Ataxia-Guidelines from an International Task Force on Immune-Mediated Cerebellar Ataxias

Aside from well-characterized immune-mediated ataxias with a clear trigger and/or association with specific neuronal antibodies, a large number of idiopathic ataxias are suspected to be immune mediated but remain undiagnosed due to lack of diagnostic biomarkers. Primary autoimmune cerebellar ataxia (PACA) is the term used to describe this later group. An International Task Force comprising experts in the field of immune ataxias was commissioned by the Society for Research on the Cerebellum and Ataxias (SRCA) in order to devise diagnostic criteria aiming to improve the diagnosis of PACA. The proposed diagnostic criteria for PACA are based on clinical (mode of onset, pattern of cerebellar involvement, presence of other autoimmune diseases), imaging findings (MRI and if available MR spectroscopy showing preferential, but not exclusive involvement of vermis) and laboratory investigations (CSF pleocytosis and/or CSF-restricted IgG oligoclonal bands) parameters. The aim is to enable clinicians to consider PACA when encountering a patient with progressive ataxia and no other diagnosis given that such consideration might have important therapeutic implications.

Cerebellar ataxia and myeloradiculopathy associated with AP3B2 antibody: a case report and literature review

BACKGROUND

AP3B2 is one of the subunits of vesicle coat protein AP3 and is specifically expressed in central nervous system neurons. AP3B2 antibody has been reported in patients with autoimmune cerebellar ataxia and various extracerebellar symptoms. However, there have been few reports on its clinical features and treatment response.

METHODS

We report a 47-year-old man with AP3B2 antibody who presented with insidious-onset paresthesia and gait disturbance. His serum and cerebrospinal fluid (CSF) showed reactivity with the cytoplasm of Purkinje cells and granular layer synapses comparable to the reported specific pattern of anti-AP3B2 IgG, and this was confirmed by a cell-based assay. His symptoms improved after the administration of intravenous immunoglobulin, and oral prednisone and mycophenolate mofetil. Extensive examination and long-term follow-up showed no evidence of malignancy. A literature review was included to emphasize the neurological syndrome associated with this rare autoantibody.

RESULTS

Eleven cases with AP3B2 antibody, including our patient, were identified. The diversity of symptoms, including cerebellar and sensory ataxia, paresthesia, and weakness, was in line with the extensive binding of AP3B2 antibody to the spinal cord gray matter, dorsal root ganglia, cerebellar cortex, and nucleus. In the CSF, half of patients had elevated white blood cell counts, increased protein concentrations, or CSF-specific oligoclonal bands. All previous cases had subacute onsets and no improvement was noted after immunotherapy.

CONCLUSION

Our case indicated that disorders associated with AP3B2 antibody can also start insidiously. Immunotherapy is warranted given the possibility of clinical improvement.

An autoantigen profile of human A549 lung cells reveals viral and host etiologic molecular attributes of autoimmunity in COVID-19

We aim to establish a comprehensive COVID-19 autoantigen atlas in order to understand autoimmune diseases caused by SARS-CoV-2 infection. Based on the unique affinity between dermatan sulfate and autoantigens, we identified 348 proteins from human lung A549 cells, of which 198 are known targets of autoantibodies. Comparison with current COVID data identified 291 proteins that are altered at protein or transcript level in SARS-CoV-2 infection, with 191 being known autoantigens. These known and putative autoantigens are significantly associated with viral replication and trafficking processes, including gene expression, ribonucleoprotein biogenesis, mRNA metabolism, translation, vesicle and vesicle-mediated transport, and apoptosis. They are also associated with cytoskeleton, platelet degranulation, IL-12 signaling, and smooth muscle contraction. Host proteins that interact with and that are perturbed by viral proteins are a major source of autoantigens. Orf3 induces the largest number of protein alterations, Orf9 affects the mitochondrial ribosome, and they and E, M, N, and Nsp proteins affect protein localization to membrane, immune responses, and apoptosis. Phosphorylation and ubiquitination alterations by viral infection define major molecular changes in autoantigen origination. This study provides a large list of autoantigens as well as new targets for future investigation, e.g., UBA1, UCHL1, USP7, CDK11A, PRKDC, PLD3, PSAT1, RAB1A, SLC2A1, platelet activating factor acetylhydrolase, and mitochondrial ribosomal proteins. This study illustrates how viral infection can modify host cellular proteins extensively, yield diverse autoantigens, and trigger a myriad of autoimmune sequelae. Our work provides a rich resource for studies into “long COVID” and related autoimmune sequelae.

An Autoantigen Profile of Human A549 Lung Cells Reveals Viral and Host Etiologic Molecular Attributes of Autoimmunity in COVID-19

We aim to establish a comprehensive COVID-19 autoantigen atlas in order to understand autoimmune diseases caused by SARS-CoV-2 infection. Based on the unique affinity between dermatan sulfate and autoantigens, we identified 348 proteins from human lung A549 cells, of which 198 are known targets of autoantibodies. Comparison with current COVID data identified 291 proteins that are altered at protein or transcript level in SARS-CoV-2 infection, with 191 being known autoantigens. These known and putative autoantigens are significantly associated with viral replication and trafficking processes, including gene expression, ribonucleoprotein biogenesis, mRNA metabolism, translation, vesicle and vesicle-mediated transport, and apoptosis. They are also associated with cytoskeleton, platelet degranulation, IL-12 signaling, and smooth muscle contraction. Host proteins that interact with and that are perturbed by viral proteins are a major source of autoantigens. Orf3 induces the largest number of protein alterations, Orf9 affects the mitochondrial ribosome, and they and E, M, N, and Nsp proteins affect protein localization to membrane, immune responses, and apoptosis. Phosphorylation and ubiquitination alterations by viral infection define major molecular changes in autoantigen origination. This study provides a large list of autoantigens as well as new targets for future investigation, e.g., UBA1, UCHL1, USP7, CDK11A, PRKDC, PLD3, PSAT1, RAB1A, SLC2A1, platelet activating factor acetylhydrolase, and mitochondrial ribosomal proteins. This study illustrates how viral infection can modify host cellular proteins extensively, yield diverse autoantigens, and trigger a myriad of autoimmune sequelae.

Indirect immunofluorescent assay as an aid in the diagnosis of suspected immune mediated ataxias

BACKGROUND AND PURPOSE

Immune mediated cerebellar ataxias account for a substantial proportion of all progressive ataxias. A diagnostic serological test is not always available. This is particularly problematic in Primary Autoimmune Cerebellar Ataxia, hence the necessity for diagnostic criteria recently devised and published by an International Task Force. We present our experience in the use of a commercially available indirect immunofluorescence assay, intended to be used for the detection of antibodies associated with paraneoplastic neurological syndromes.

METHODS

Retrospective review of patients with ataxia who underwent serological testing using this assay as part of their diagnostic evaluation. We were interested in 3 groups: suspected immune mediated ataxias, genetically confirmed ataxias and patients with cerebellar variant of multi-system atrophy (MSA-C). The indirect immunofluorescence assay was performed using commercially available monkey cerebellum slides and anti-human IgG FITC conjugated antiserum.

RESULTS

A total of 300 patients that had this test and fitted into one of these 3 groups (immune ataxias 190, genetic ataxias 60, MSA-C 50) were identified. The prevalence of positive immunofluorescence but negative immunoblot was 172/190 (91%) in the suspected immune ataxia group, 3/60 (5%) in the genetic group and 2/50 (4%) in the MSA-C group. The difference between the first and the other groups was significant χ² (1, N = 291) = 64.2, p < 00001.

CONCLUSIONS

This report demonstrates that a commercially available immunofluorescence assay can be used to provide additional diagnostic aid for suspected immune mediated ataxias and in particular Primary Autoimmune Cerebellar Ataxia where no diagnostic marker exists.

An Autoantigen Atlas from Human Lung HFL1 Cells Offers Clues to Neurological and Diverse Autoimmune Manifestations of COVID-19

COVID-19 is accompanied by a myriad of both transient and long-lasting autoimmune responses. Dermatan sulfate (DS), a glycosaminoglycan crucial for wound healing, has unique affinity for autoantigens (autoAgs) from apoptotic cells. DS-autoAg complexes are capable of stimulating autoreactive B cells and autoantibody production. Using DS affinity, we identified an autoantigenome of 408 proteins from human fetal lung fibroblast HFL11 cells, at least 231 of which are known autoAgs. Comparing with available COVID data, 352 proteins of the autoantigenome have thus far been found to be altered at protein or RNA levels in SARS-Cov-2 infection, 210 of which are known autoAgs. The COVID-altered proteins are significantly associated with RNA metabolism, translation, vesicles and vesicle transport, cell death, supramolecular fibrils, cytoskeleton, extracellular matrix, and interleukin signaling. They offer clues to neurological problems, fibrosis, smooth muscle dysfunction, and thrombosis. In particular, 150 altered proteins are related to the nervous system, including axon, myelin sheath, neuron projection, neuronal cell body, and olfactory bulb. An association with the melanosome is also identified. The findings from our study illustrate a strong connection between viral infection and autoimmunity. The vast number of COVID-altered proteins with propensity to become autoAgs offers an explanation for the diverse autoimmune complications in COVID patients. The variety of autoAgs related to mRNA metabolism, translation, and vesicles raises concerns about potential adverse effects of mRNA vaccines. The COVID autoantigen atlas we are establishing provides a detailed molecular map for further investigation of autoimmune sequelae of the pandemic.

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

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

Imaging Review of Paraneoplastic Neurologic Syndromes

Paraneoplastic syndromes are systemic reactions to neoplasms mediated by immunologic or hormonal mechanisms. The most well-recognized paraneoplastic neurologic syndrome, both clinically and on imaging, is limbic encephalitis. However, numerous additional clinically described syndromes affect the brain, spinal cord, and peripheral nerves. Many of these syndromes can have imaging findings that, though less well described, are important in making the correct diagnosis. Moreover, imaging in these syndromes frequently mimics more common pathology, which can be a diagnostic challenge for radiologists. Our goal is to review the imaging findings of paraneoplastic neurologic syndromes, including less well-known entities and atypical presentations of common entities. Specifically, we discuss limbic encephalitis, paraneoplastic cerebellar degeneration, paraneoplastic brain stem encephalitis, cranial neuropathy, myelitis, and polyneuropathy. We also demonstrate common diagnostic pitfalls that can be encountered when imaging these patients.

Antinuclear antibodies (ANA) patterns in paraneoplastic cerebellar degeneration during the course of disease and treatment protocols - A case report

Paraneoplastic cerebellar degeneration (PCD) is a rare disease that is triggered by an abnormal immune response to a malignant tumor by cross-reaction of antibodies. The low prevalence of this condition has not allowed for large-scale randomized controlled trials. Suspecting a paraneoplastic syndrome followed by rapid diagnosis is crucial before the symptoms irreversibely progress. Indirect immunofluorescence (IIF) with HEp-2 ​cells is currently the most widely used screening technique for the detection of a wide range of nuclear and cytoplasmatic autoantibodies. Here, we present a case of a female Caucasian patient, 61 years of age, who started having sudden symptoms of PCD starting April 2016 that progressed through the course of 10 months before the final diagnosis. Assuming that antinuclear antibodies (ANA) testing could give rise to suspicion of an underlying malignancy but also to an underlying autoimmune etiology of PCD, we followed the ANA patterns of the patient during the course of disease and treatment protocols. A total of four ANA follow ups were done on serum dilution 1:100 and all showed weak positive results on hepatic cells and a mix of similar patterns that, through the course of time, differed slightly on HEp-2 ​cells. Finding positive antinuclear or anticytoplasmic auto-antibodies might guide toward an extensive and useless search for a systemic autoimmune disease ignoring the possibility of searching for paraneoplastic-specific antibodies. An unspecified mix of patterns should not be ignored and might, through further research, show to be more valuable in the ANA screening than is the case now. Weak positive results should not mislead into thinking that there is no overall effect on health, since quite the opposite was the case here. In our example, neither the tumor response to treatment, neurological presentation nor the immunological treatment had a strong effect on the ANA patterns which remained almost identical throughout the course of disease and treatment. Ultrastructural and molecular events in the pathogenesis of the disease could have caused certain minor changes in the pattern but are not of clinical value at the moment and further research is needed.

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

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

Neurochondrin neurological autoimmunity

Objectives

To describe the neurologic spectrum and treatment outcomes for neurochondrin-IgG positive cases identified serologically in the Mayo Clinic Neuroimmunology Laboratory.

Methods

Archived serum and CSF specimens previously scored positive for IgGs that stained mouse hippocampal tissue in a nonuniform synaptic pattern by immunofluorescence assay (89 among 616,025 screened, 1993–2019) were reevaluated. Antibody characterization experiments revealed specificity for neurochondrin, confirmed by recombinant protein assays.

Results

IgG in serum (9) or CSF (4) from 8 patients yielded identical neuron-restricted CNS patterns, most pronounced in hippocampus (stratum lucidum in particular), cerebellum (Purkinje cells and molecular layer), and amygdala. All were neurochondrin-IgG positive. Five were women; median symptom onset age was 43 years (range, 30–69). Of 7 with clinical data, 6 presented with rapidly progressive cerebellar ataxia, brainstem signs, or both; 1 had isolated unexplained psychosis 1 year prior. Five of 6 had cerebellar signs, 4 with additional brainstem symptoms or signs (eye movement abnormalities, 3; dysphagia, 2; nausea and vomiting, 1). One patient with brainstem signs (vocal cord paralysis and VII nerve palsy) had accompanying myelopathy (longitudinally extensive abnormality on MRI; aquaporin-4-IgG and myelin oligodendrocyte glycoprotein-IgG negative). The 7th patient had small fiber neuropathy only. Just 1 of 7 had contemporaneous cancer (uterine). Six patients with ataxia or brainstem signs received immunotherapy, but just 1 remained ambulatory. At last follow-up, 5 had MRI evidence of severe cerebellar atrophy.

Conclusion

In our series, neurochondrin autoimmunity was usually accompanied by a nonparaneoplastic rapidly progressive rhombencephalitis with poor neurologic outcomes. Other phenotypes and occasional paraneoplastic causes may occur.

Neurologic Autoimmunity in the Era of Checkpoint Inhibitor Cancer Immunotherapy

Neurologic autoimmune disorders in the context of systemic cancer reflect antitumor immune responses against onconeural proteins that are autoantigens in the nervous system. These responses observe basic principles of cancer immunity and are highly pertinent to oncological practice since the introduction of immune checkpoint inhibitor cancer therapy. The patient's autoantibody profile is consistent with the antigenic composition of the underlying malignancy. A major determinant of the pathogenic outcome is the anatomic and subcellular location of the autoantigen. IgGs targeting plasma membrane proteins (eg, muscle acetylcholine receptor -IgG in patients with paraneoplastic myasthenia gravis) have pathogenic potential. However, IgGs specific for intracellular antigens (eg, antineuronal nuclear antibody 1 [anti-Hu] associated with sensory neuronopathy and small cell lung cancer) are surrogate markers for CD8⁺ T lymphocytes targeting peptides derived from nuclear or cytoplasmic proteins. In an inflammatory milieu, those peptides translocate to neural plasma membranes as major histocompatibility complex class I protein complexes. Paraneoplastic neurologic autoimmunity can affect any level of the neuraxis and may be mistaken for cancer progression. Importantly, these disorders generally respond favorably to early-initiated immunotherapy and cancer treatment. Small cell lung cancer and thymoma are commonly associated with neurologic autoimmunity, but in the context of checkpoint inhibitor therapy, other malignancy associations are increasingly recognized.