Guidelines for treatment of immune-mediated cerebellar ataxias

A candidate projective neuron type of the cerebellar cortex: the synarmotic neuron

Previous studies on the granular layer of the cerebellar cortex have revealed a wide distribution of different subpopulations of less-known large neuron types, called "non-traditional large neurons", which are distributed in three different zones of the granular layer. These neuron types are mainly involved in the formation of intrinsiccircuits inside the cerebellar cortex. A subpopulation of these neuron types is represented by the synarmotic neuron, which could play a projective role within the cerebellar circuitry. The synarmotic neuron cell body map within the internal zone of the granular layer or in the subjacent white substance. Furthermore, the axon crosses the granular layer and runs in the subcortical white substance, to reenter in an adjacent granular layer, associating two cortico-cerebellar regions of the same folium or of different folia, or could project to the intrinsic cerebellar nuclei. Therefore, along with the Purkinje neuron, the traditional projective neuron type of the cerebellar cortex, the synarmotic neuron is candidate to represent the second projective neuron type of the cerebellar cortex. Studies of chemical neuroanatomy evidenced a predominant inhibitory GABAergic nature of the synarmotic neuron, suggesting that it may mediate an inhibitory GABAergic output of cerebellar cortex within cortico-cortical interconnections or in projections towards intrinsic cerebellar nuclei. On this basis, the present minireview mainly focuses on the morphofunctional and neurochemical data of the synarmotic neuron, and explores its potential involvement in some forms of cerebellar ataxias.

Consensus Paper: Latent Autoimmune Cerebellar Ataxia (LACA)

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

Overview of treatment strategies in paraneoplastic neurological syndromes

Treatment strategies in paraneoplastic neurological syndromes rely on the three pillars of tumor treatment, immunotherapy, and symptomatic treatment, the first one being by far the most important in the majority of patients and syndromes. Classically, antibodies against extracellular antigens are directly pathogenic, and patients with these syndromes are more responsive to immunomodulatory or immunosuppressive treatments than the ones with antibodies against intracellular targets. This chapter first discusses some general principles of tumor treatment and immunotherapy, followed by a closer look at specific treatment options for different clinical syndromes, focusing on symptomatic treatments.

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.

Immune-mediated ataxias: Guide to clinicians

Immune-mediated cerebellar ataxias were initially described as a clinical entity in the 1980s, and since then, an expanding body of evidence has contributed to our understanding of this topic. These ataxias encompass various etiologies, including postinfectious cerebellar ataxia, gluten ataxia, paraneoplastic cerebellar degeneration, opsoclonus-myoclonus-ataxia syndrome and primary autoimmune cerebellar ataxia. The increased permeability of the brain-blood barrier could potentially explain the vulnerability of the cerebellum to autoimmune processes. In this manuscript, our objective is to provide a comprehensive review of the most prevalent diseases within this group, emphasizing clinical indicators, pathogenesis, and current treatment approaches.

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.

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.

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.

Advances in the Pathogenesis of Auto-antibody-Induced Cerebellar Synaptopathies

The presence of auto-antibodies that target synaptic machinery proteins was documented recently in immune-mediated cerebellar ataxias. The autoantigens include glutamic acid decarboxylase 65 (GAD65), voltage-gated Ca²⁺ channel (VGCC), metabotropic glutamate receptor type 1 (mGluR1), and glutamate receptor delta (GluRdelta). GAD65 is involved in the synthesis, packaging, and release of GABA, whereas the other three play important roles in the induction of long-term depression (LTD). Thus, the auto-antibodies toward these synaptic molecules likely impair fundamental synaptic machineries involved in unique functions of the cerebellum, potentially leading to the development of cerebellar ataxias (CAs). This concept has been substantiated recently by a series of physiological studies. Anti-GAD65 antibody (Ab) acts on the terminals of inhibitory neurons that suppress GABA release, whereas anti-VGCC, anti-mGluR1, and anti-GluR Abs impair LTD induction. Notably, the mechanisms that link synaptic dysfunction with the manifestations of CAs can be explained by disruption of the "internal models." The latter can be divided into three levels. First, since chained inhibitory neurons shape the output signals through the mechanism of disinhibition/inhibition, impairments of GABA release and LTD distort the conversion process from the "internal model" to the output signals. Second, these antibodies impair the induction of synaptic plasticity, rebound potentiation, and LTD, on Purkinje cells, resulting in loss of restoration and compensation of the distorted "internal models." Finally, the cross-talk between glutamate and microglia/astrocytes could involve a positive feedback loop that accelerates excitotoxicity. This mini-review summarizes the pathophysiological mechanisms and aims to establish the basis of "auto-antibody-induced cerebellar synaptopathies."

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.

Rare Etiologies in Immune-Mediated Cerebellar Ataxias: Diagnostic Challenges

The cerebellum is particularly enriched in antigens and represents a vulnerable target to immune attacks. Immune-mediated cerebellar ataxias (IMCAs) have diverse etiologies, such as gluten ataxia (GA), post-infectious cerebellitis (PIC), Miller Fisher syndrome (MFS), paraneoplastic cerebellar degeneration (PCD), opsoclonus myoclonus syndrome (OMS), and anti-GAD ataxia. Apart from these well-established entities, cerebellar ataxia (CA) occurs also in association with autoimmunity against ion channels and related proteins, synaptic adhesion/organizing proteins, transmitter receptors, glial cells, as well as the brainstem antigens. Most of these conditions manifest diverse neurological clinical features, with CAs being one of the main clinical phenotypes. The term primary autoimmune cerebellar ataxia (PACA) refers to ataxic conditions suspected to be autoimmune even in the absence of specific well-characterized pathogenic antibody markers. We review advances in the field of IMCAs and propose a clinical approach for the understanding and diagnosis of IMCAs, focusing on rare etiologies which are likely underdiagnosed. The frontiers of PACA are discussed. The identification of rare immune ataxias is of importance since they are potentially treatable and may lead to a severe clinical syndrome in absence of early therapy.

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.

Case Report: Multisystem Autoimmune and Overlapping GAD65-Antibody-Associated Neurological Disorders With Beneficial Effect of Epilepsy Surgery and Rituximab Treatment

Glutamic acid decarboxylase (GAD) antibodies are associated with disabling conditions such as stiff person syndrome, temporal lobe epilepsy (TLE), limbic encephalitis, cerebellar ataxia (CA), and ocular movement disorders, which are usually chronic and difficult to treat. GAD-related TLE has poor response to anti-seizure medications and immune therapies, and epilepsy surgery is rarely successful. We report on a 47-year-old female with history of migraine, autoimmune thyroid disease, ankylosing spondylitis, and drug-resistant TLE. A video electroencephalography recorded frequent seizures with temporo-insular semiology, correlating to left temporal epileptiform activity and left mesiotemporal hyperintensity on magnetic resonance imaging. GAD autoimmunity was confirmed by very high GAD antibody titers in serum and cerebrospinal fluid. Steroids, immunoglobulins, and cyclophosphamide had no effect, and selective left amygdalectomy was performed based on very restricted hypermetabolism on positron-emission tomography. After transient seizure freedom, significant epilepsy improvement was observed in spite of memory decline. Transient worsening was noted 1 year later during diabetes mellitus manifestation and 5 years later during presentation of progressive CA, which stabilized on rituximab treatment. We believe this case illustrates the diversity and the frequent overlap of GAD-associated disorders, the need of early and aggressive immunotherapy in severe patients, as well as the possible benefit from epilepsy surgery in some GAD-TLE.

Rituximab Treatment and Long-term Outcome of Patients With Autoimmune Encephalitis: Real-world Evidence From the GENERATE Registry

BACKGROUND AND OBJECTIVES

To determine the real-world use of rituximab in autoimmune encephalitis (AE) and to correlate rituximab treatment with the long-term outcome.

METHODS

Patients with NMDA receptor (NMDAR)-AE, leucine-rich glioma-inactivated-1 (LGI1)- AE, contactin-associated protein-like-2 (CASPR2)-AE, or glutamic acid decarboxylase 65 (GAD65) disease from the GErman Network for Research on AuToimmune Encephalitis who had received at least 1 rituximab dose and a control cohort of non-rituximab-treated patients were analyzed retrospectively.

RESULTS

Of the 358 patients, 163 (46%) received rituximab (NMDAR-AE: 57%, CASPR2-AE: 44%, LGI1-AE: 43%, and GAD65 disease: 37%). Rituximab treatment was initiated significantly earlier in NMDAR- and LGI1-AE (median: 54 and 155 days from disease onset) compared with CASPR2-AE or GAD65 disease (median: 632 and 1,209 days). Modified Rankin Scale (mRS) scores improved significantly in patients with NMDAR-AE, both with and without rituximab treatment. Although being more severely affected at baseline, rituximab-treated patients with NMDAR-AE more frequently reached independent living (mRS score ≤2) (94% vs 88%). In LGI1-AE, rituximab-treated and nontreated patients improved, whereas in CASPR2-AE, only rituximab-treated patients improved significantly. No improvement was observed in patients with GAD65 disease. A significant reduction of the relapse rate was observed in rituximab-treated patients (5% vs 13%). Detection of NMDAR antibodies was significantly associated with mRS score improvement. A favorable outcome was also observed with early treatment initiation.

DISCUSSION

We provide real-world data on immunosuppressive treatments with a focus on rituximab treatment for patients with AE in Germany. We suggest that early and short-term rituximab therapy might be an effective and safe treatment option in most patients with NMDAR-, LGI1-, and CASPR2-AE.

CLASS OF EVIDENCE

This study provides Class IV evidence that rituximab is an effective treatment for some types of AE.

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.

Update in Autoimmune Movement Disorders: Newly Described Antigen Targets in Autoimmune and Paraneoplastic Cerebellar Ataxia

Movement disorders are a common feature of many antibody-associated neurological disorders. In fact, cerebellar ataxia is one of the most common manifestations of autoimmune neurological diseases. Some of the first autoantibodies identified against antigen targets include anti-neuronal nuclear antibody type 1 (ANNA-1 or anti-Hu) and Purkinje cell cytoplasmic antibody (PCA-1) also known as anti-Yo have been identified in paraneoplastic cerebellar degeneration. Historically these antibodies have been associated with an underlying malignancy; however, recently discovered antibodies can occur in the absence of cancer as well, resulting in the clinical syndrome of autoimmune cerebellar ataxia. The pace of discovery of new antibodies associated with autoimmune or paraneoplastic cerebellar ataxia has increased rapidly over the last few years, and pathogenesis and potential treatment options remains to be explored. Here we will review the literature on recently discovered antibodies associated with autoimmune and paraneoplastic cerebellar ataxia including adaptor protein-3B2 (AP3B2); inositol 1,4,5-trisphophate receptor type 1 (ITPR1); tripartite motif-containing (TRIM) proteins 9, 67, and 46; neurochondrin; neuronal intermediate filament light chain (NIF); septin 5; metabotropic glutamate receptor 2 (mGluR2); seizure-related 6 homolog like 2 (SEZ6L2) and homer-3 antibodies. We will review their clinical characteristics, imaging and CSF findings and treatment response. In addition, we will discuss two clinical case examples of autoimmune cerebellar ataxia.

Treatment of Primary Autoimmune Cerebellar Ataxia with Mycophenolate

Immune-mediated ataxias account for a substantial number of sporadic otherwise idiopathic ataxias. Despite some well-characterised entities such as paraneoplastic cerebellar degeneration where diagnostic markers exist, the majority of immune ataxias remained undiagnosed and untreated. We present here our experience in the treatment of suspected primary autoimmune cerebellar ataxia (PACA) using mycophenolate. All patients reported attend the Sheffield Ataxia Centre on a regular basis and had undergone extensive investigations, including genetic testing using next-generation sequencing, with other causes of ataxia excluded. The diagnosis of PACA was strongly suspected based on investigations, pattern of disease progression, and cerebellar involvement. Patients were treated with mycophenolate and monitored using MR spectroscopy of the cerebellar vermis. Thirty patients with PACA are reported here. Of these, 22 received mycophenolate (group 1). The remaining 8 were not on treatment (group 2-control group). Out of the 22 treated patients, 4 underwent serial MR spectroscopy prior to starting treatment and thus were used as controls making the total number of patients in the control group 12. The mean change of the MRS within the vermis (NAA/Cr area ratio) in the treatment group was + 0.144 ± 0.09 (improved) and in the untreated group - 0.155 ± 0.06 (deteriorated). The difference was significant. We also demonstrated a strong correlation between the spectroscopy and the SARA score. We have demonstrated the effectiveness of mycophenolate in the treatment of PACA. The results suggest that immune-mediated ataxias are potentially treatable, and that there is a need for early diagnosis to prevent permanent neurological deficit. The recently published diagnostic criteria for PACA would hopefully aid the diagnosis and treatment of this entity.

Transient Neurological Symptoms Preceding Cerebellar Ataxia with Glutamic Acid Decarboxylase Antibodies

A prompt diagnosis and treatment of patients with autoimmune cerebellar ataxia (CA) with antibodies against glutamic acid decarboxylase (GAD-Abs) may lead to a better prognosis. Herein, we report prodromal transient neurological symptoms that should raise clinical suspicion of CA with GAD-Abs. We initially identified a 70-year-old man who presented a first acute episode of vertigo, diplopia, and ataxia lasting 2 weeks. Two months later, he experienced a similar episode along with new-onset gaze-evoked nystagmus. After 4 months, downbeat nystagmus, left limb dysmetria, and gait ataxia progressively appeared, and an autoimmune CA was diagnosed based on the positivity of GAD-Abs in serum and cerebrospinal fluid (CSF). We searched retrospectively for similar presentations in a cohort of 31 patients diagnosed with CA and GAD-Abs. We found 11 (35.4%) patients (all women, median age 62 years; 8/11 [72.7%] with autoimmune comorbidities) with transient neurological symptoms antedating CA onset by a median of 3 months, including vertigo in 9 (81.8%; described as paroxysmal in 8) and fluctuating diplopia in 3 (27.3%) patients. The identification of transient neurological symptoms of unknown etiology, such as paroxysmal vertigo and fluctuating diplopia, should lead to GAD-Abs testing in serum and CSF, especially in patients with autoimmune comorbidities.

Recognition and management of rapid-onset gluten ataxias: case series

BACKGROUND

Most immune-mediated cerebellar ataxias, including those associated with gluten sensitivity (Gluten Ataxia), tend to present subacutely and usually progress gradually. Acute presentations with rapid progression outside the context of paraneoplastic cerebellar degeneration require prompt diagnosis and early access to disease-modifying immunotherapy in order to avert severe and permanent neurological disability.

CASE PRESENTATIONS

We describe three cases of rapid-onset Gluten Ataxia, an immune-mediated cerebellar ataxia due to gluten sensitivity. We detail their presentation, clinical and neuroimaging findings, and our treatment strategy with immunotherapy.

CONCLUSIONS

Our cases highlight the potential for immune-mediated cerebellar ataxias to present acutely, with rapid-onset symptoms and devastating neurological consequences. We caution against the diagnosis of 'post-infective cerebellitis' in adults, and advocate early consideration of an immune-mediated cerebellar ataxia and initiation of immunotherapy to prevent irreversible cerebellar damage.

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.

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

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

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

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

Treatment-responsive primary autoimmune cerebellar ataxia in a patient with IgG and IgM anticerebellar antibodies

BACKGROUND AND PURPOSE

Primary autoimmune cerebellar ataxia (PACA) in the absence of another triggering disease represents an emerging category of neurological illness. We report such a case whose ataxia was markedly responsive to plasma exchange. We analyzed patient serum for the presence of IgM or IgG anticerebellar neuronal antibodies.

METHODS

Case presentation: rat cerebellar slice cultures incubated with patient sera were studied for IgG and IgM antibody uptake, intracellular binding, and neuronal death. Patient serum was evaluated for anti-myelin associated glycoprotein (anti-MAG) and associated anti-glycolipid antibodies.

RESULTS

Antibodies were taken up by viable cerebellar neurons and bound to intracellular antigens. Uptake and predominantly nuclear binding of IgG were seen in granule cells whereas cytoplasmic binding of IgM was observed predominantly in Purkinje cells. Intracellular antibody accumulation was not accompanied by neuronal death, consistent with the patient's excellent clinical response to plasma exchange. Anti-MAG or other associated anti-glycolipid antibodies were not detected.

CONCLUSIONS

PACA may be associated with both IgG and IgM antibodies reactive with cerebellar neuronal antigens. Our patient's response to plasma exchange supports a role for antineuronal antibodies in disease pathogenesis and emphasizes the need for rapid diagnosis and treatment.

Clinical Characteristics and Management of 50 Patients with Anti-GAD Ataxia: Gluten-Free Diet Has a Major Impact

The objective of this study is to report the clinical characteristics and treatment of patients with progressive cerebellar ataxia associated with anti-GAD antibodies. We performed a retrospective review of all patients with anti-GAD ataxia managed at the Sheffield Ataxia Centre over the last 25 years. We identified 50 patients (62% females) with anti-GAD ataxia. The prevalence was 2.5% amongst 2000 patients with progressive ataxia of various causes. Mean age at onset was 55 and mean duration 8 years. Gaze-evoked nystagmus was present in 26%, cerebellar dysarthria in 26%, limb ataxia in 44% and gait ataxia in 100%. Nine patients (18%) had severe, 12 (24%) moderate and 29 (58%) mild ataxia. Ninety percent of patients had a history of additional autoimmune diseases. Family history of autoimmune diseases was seen in 52%. Baseline MR spectroscopy of the vermis was abnormal at presentation in 72%. Thirty-five patients (70%) had serological evidence of gluten sensitivity. All 35 went on gluten-free diet (GFD). Eighteen (51%) improved, 13 (37%) stabilised, 3 have started the GFD too recently to draw conclusions and one deteriorated. Mycophenolate was used in 16 patients, 7 (44%) improved, 2 stabilised, 6 have started the medication too recently to draw conclusions and one did not tolerate the drug. There is considerable overlap between anti-GAD ataxia and gluten ataxia. For those patients with both, strict GFD alone can be an effective treatment. Patients with anti-GAD ataxia and no gluten sensitivity respond well to immunosuppression.

Advances in Therapies of Cerebellar Disorders: Immune-mediated Ataxias

The identification of an increasing number of immune mediated ataxias suggests that the cerebellum is often a target organ for autoimmune insults. The diagnosis of immune mediated ataxias is challenging as there is significant clinical overlap between immune mediated and other forms of ataxia. Furthermore the classification of immune mediated ataxias requires further clarification particularly for those ataxias where no specific antigenic trigger and associated antibodies have been identified. Recognition of immune mediated ataxias remains imperative as therapeutic interventions can be effective, although given the relative rarity of this entity, large-scale treatment trials may not be feasible. This review will discuss advances in therapies for immune mediated ataxias based on what is currently available in the literature.

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.

Clinical features and immunotherapy outcomes of anti-glutamic acid decarboxylase 65 antibody-associated neurological disorders

We described the clinical and neuroimaging characteristics of seven Chinese patients with anti-GAD65 antibody-associated neurological disorders of whom epileptic seizures were the initial and main symptoms. All patients were given immunotherapy and followed up monthly. The outcome demonstrates that immunotherapy is helpful for non-seizure manifestations of anti-GAD65-associated neurological autoimmunity and is less effective in the treatment of seizures, yet partial responses can still occur in the early stage. Taken together we suggest a trial with immunotherapy in all patients in the early stage of the disease, and in patients with non-epilepsy symptoms in the later stage.

Neurological Syndromes Associated with Anti-GAD Antibodies

Glutamic acid decarboxylase (GAD) is an intracellular enzyme whose physiologic function is the decarboxylation of glutamate to gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter within the central nervous system. GAD antibodies (Ab) have been associated with multiple neurological syndromes, including stiff-person syndrome, cerebellar ataxia, and limbic encephalitis, which are all considered to result from reduced GABAergic transmission. The pathogenic role of GAD Ab is still debated, and some evidence suggests that GAD autoimmunity might primarily be cell-mediated. Diagnosis relies on the detection of high titers of GAD Ab in serum and/or in the detection of GAD Ab in the cerebrospinal fluid. Due to the relative rarity of these syndromes, treatment schemes and predictors of response are poorly defined, highlighting the unmet need for multicentric prospective trials in this population. Here, we reviewed the main clinical characteristics of neurological syndromes associated with GAD Ab, focusing on pathophysiologic mechanisms.

Neurologic syndromes related to anti-GAD65: Clinical and serologic response to treatment

OBJECTIVE

Antibodies against glutamic acid decarboxylase 65 (anti-GAD65) are associated with a number of neurologic syndromes. However, their pathogenic role is controversial. Our objective was to describe clinical and paraclinical characteristics of anti-GAD65 patients and analyze their response to immunotherapy.

METHODS

Retrospectively, we studied patients (n = 56) with positive anti-GAD65 and any neurologic symptom. We tested serum and CSF with ELISA, immunohistochemistry, and cell-based assay. Accordingly, we set a cutoff value of 10,000 IU/mL in serum by ELISA to group patients into high-concentration (n = 36) and low-concentration (n = 20) groups. We compared clinical and immunologic features and analyzed response to immunotherapy.

RESULTS

Classical anti-GAD65-associated syndromes were seen in 34/36 patients with high concentration (94%): stiff-person syndrome (7), cerebellar ataxia (3), chronic epilepsy (9), limbic encephalitis (9), or an overlap of 2 or more of the former (6). Patients with low concentrations had a broad, heterogeneous symptom spectrum. Immunotherapy was effective in 19/27 treated patients (70%), although none of them completely recovered. Antibody concentration reduction occurred in 15/17 patients with available pre- and post-treatment samples (median reduction 69%; range 27%-99%), of which 14 improved clinically. The 2 patients with unchanged concentrations showed no clinical improvement. No differences in treatment responses were observed between specific syndromes.

CONCLUSION

Most patients with high anti-GAD65 concentrations (>10,000 IU/mL) showed some improvement after immunotherapy, unfortunately without complete recovery. Serum antibody concentrations' course might be useful to monitor response. In patients with low anti-GAD65 concentrations, especially in those without typical clinical phenotypes, diagnostic alternatives are more likely.

An Overview of the Current State and the Future of Ataxia Treatments

Cerebellar ataxia can be caused by a variety of disorders, including degenerative processes, autoimmune and paraneoplastic illness as well as by gene mutations inherited in autosomal dominant, autosomal recessive, or X-linked fashions. In this review, we highlight the treatments for cerebellar ataxia in a systematic way, to provide guidance for clinicians who treat patients with cerebellar ataxia. In addition, we review therapies currently under development for ataxia, which we feel is currently one of the most exciting fields in neurology.

Consensus Paper. Cerebellar Reserve: From Cerebellar Physiology to Cerebellar Disorders

Cerebellar reserve refers to the capacity of the cerebellum to compensate for tissue damage or loss of function resulting from many different etiologies. When the inciting event produces acute focal damage (e.g., stroke, trauma), impaired cerebellar function may be compensated for by other cerebellar areas or by extracerebellar structures (i.e., structural cerebellar reserve). In contrast, when pathological changes compromise cerebellar neuronal integrity gradually leading to cell death (e.g., metabolic and immune-mediated cerebellar ataxias, neurodegenerative ataxias), it is possible that the affected area itself can compensate for the slowly evolving cerebellar lesion (i.e., functional cerebellar reserve). Here, we examine cerebellar reserve from the perspective of the three cornerstones of clinical ataxiology: control of ocular movements, coordination of voluntary axial and appendicular movements, and cognitive functions. Current evidence indicates that cerebellar reserve is potentiated by environmental enrichment through the mechanisms of autophagy and synaptogenesis, suggesting that cerebellar reserve is not rigid or fixed, but exhibits plasticity potentiated by experience. These conclusions have therapeutic implications. During the period when cerebellar reserve is preserved, treatments should be directed at stopping disease progression and/or limiting the pathological process. Simultaneously, cerebellar reserve may be potentiated using multiple approaches. Potentiation of cerebellar reserve may lead to compensation and restoration of function in the setting of cerebellar diseases, and also in disorders primarily of the cerebral hemispheres by enhancing cerebellar mechanisms of action. It therefore appears that cerebellar reserve, and the underlying plasticity of cerebellar microcircuitry that enables it, may be of critical neurobiological importance to a wide range of neurological/neuropsychiatric conditions.

Acute cerebellar ataxia: differential diagnosis and clinical approach

Cerebellar ataxia is a common finding in neurological practice and has a wide variety of causes, ranging from the chronic and slowly-progressive cerebellar degenerations to the acute cerebellar lesions due to infarction, edema and hemorrhage, configuring a true neurological emergency. Acute cerebellar ataxia is a syndrome that occurs in less than 72 hours, in previously healthy subjects. Acute ataxia usually results in hospitalization and extensive laboratory investigation. Clinicians are often faced with decisions on the extent and timing of the initial screening tests, particularly to detect treatable causes. The main group of diseases that may cause acute ataxias discussed in this article are: stroke, infectious, toxic, immune-mediated, paraneoplastic, vitamin deficiency, structural lesions and metabolic diseases. This review focuses on the etiologic and diagnostic considerations for acute ataxia.

Anti-SOX1 Antibodies in Paraneoplastic Neurological Syndrome

Anti-Sry-like high mobility group box (SOX) 1 antibodies (abs) are partly characterized onconeural autoantibodies (autoabs) due to their correlation with neoplastic diseases. Anti-SOX1 abs are associated with various clinical manifestations, including Lambert-Eaton myasthenic syndrome (LEMS) and paraneoplastic cerebellar degeneration (PCD). However, the clinical characteristics of patients with anti-SOX1 abs have not been described in detail. This review systematically explores the reported patients with anti-SOX1 abs and analyzes these cases for demographic characteristics, clinical features, coexisting neuronal autoabs, neuroimaging findings, treatment, and clinical outcomes. In addition, considering that PCD is the most common paraneoplastic neurological syndrome and that the association between PCD and anti-SOX1 abs remains unclear, we focus on the presence of autoabs in relation to PCD and associated tumors. PCD-associated autoabs include various intracellular autoabs (e.g., anti-Hu, anti-Yo, anti-Ri, and anti-SOX1) and cell-surface autoabs (anti-P/Q-type voltage-gated calcium channel). Commonly involved tumors in PCD are small-cell lung cancer (SCLC), gynecological, and breast tumors. LEMS is the most common clinical symptom in patients with anti-SOX1 abs, followed by PCD, and multiple neuronal autoabs coexist in 47.1% of these patients. SCLC is still the predominant tumor in patients with anti-SOX1 abs, while non-SCLC is uncommon. No consistent imaging feature is found in patients with anti-SOX1 abs, and there is no consensus on either the therapy choice or therapeutic efficacy. In conclusion, the presence of anti-SOX1 abs alone is a potential predictor of an uncommon paraneoplastic neurological disorder, usually occurring in the setting of LEMS, PCD, and SCLC. The detection of anti-SOX1 abs contributes to an early diagnosis of underlying tumors, given the diversity of clinical symptoms and the absence of characteristic neuroimaging features.

Recent Advances in the Treatment of Cerebellar Disorders

Various etiopathologies affect the cerebellum, resulting in the development of cerebellar ataxias (CAs), a heterogeneous group of disorders characterized clinically by movement incoordination, affective dysregulation, and cognitive dysmetria. Recent progress in clinical and basic research has opened the door of the ‘‘era of therapy” of CAs. The therapeutic rationale of cerebellar diseases takes into account the capacity of the cerebellum to compensate for pathology and restoration, which is collectively termed cerebellar reserve. In general, treatments of CAs are classified into two categories: cause-cure treatments, aimed at arresting disease progression, and neuromodulation therapies, aimed at potentiating cerebellar reserve. Both forms of therapies should be introduced as soon as possible, at a time where cerebellar reserve is still preserved. Clinical studies have established evidence-based cause-cure treatments for metabolic and immune-mediated CAs. Elaborate protocols of rehabilitation and non-invasive cerebellar stimulation facilitate cerebellar reserve, leading to recovery in the case of controllable pathologies (metabolic and immune-mediated CAs) and delay of disease progression in the case of uncontrollable pathologies (degenerative CAs). Furthermore, recent advances in molecular biology have encouraged the development of new forms of therapies: the molecular targeting therapy, which manipulates impaired RNA or proteins, and the neurotransplantation therapy, which delays cell degeneration and facilitates compensatory functions. The present review focuses on the therapeutic rationales of these recently developed therapeutic modalities, highlighting the underlying pathogenesis.

Anti-GAD Antibodies and the Cerebellum: Where Do We Stand?

Anti-GAD65 antibodies (anti-GAD65 Abs) are associated with cerebellar ataxia (CA). The significance of anti-GAD65 Abs has been a focus of debates. Since GAD65 is intracellularly located and associated with type 1 diabetes mellitus and different clinical neurological phenotypes such as CA, stiff-person syndrome, and epilepsy, some researchers have argued that anti-GAD65 Abs have no pathogenic roles. On the other hand, recent physiological studies in vitro and in vivo have elucidated that binding of GAD65 by anti-GAD65 Abs elicits loss of GAD65 functions pertaining GABA release with an epitope dependence, leading to the development of CA. Internalization of autoantibodies has been also clarified. These studies provide substantial evidence of the pathogenesis of anti-GAD65 Abs in CA. We also discuss methodological problems in the identification of anti-GAD65 Abs.

Noninvasive Cerebellar Stimulation as a Complement Tool to Pharmacotherapy

BACKGROUND

Cerebellar ataxias represent a wide and heterogeneous group of diseases characterized by balance and coordination disturbance, dysarthria, dyssynergia and adyadococinesia, caused by a dysfunction in the cerebellum. In recent years there has been growing interest in discovering therapeutical strategy for specific forms of cerebellar ataxia. Together with pharmacological studies, there has been growing interest in non-invasive cerebellar stimulation techniques to improve ataxia and limb coordination. Both transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are non-invasive techniques to modulate cerebro and cerebellar cortex excitability using magnetic or electric fields.

METHODS

Here we aim to review the most relevant studies regarding the application of TMS and tDCS for the treatment of cerebellar ataxia.

CONCLUSION

As pharmacological strategies were shown to be effective in specific forms of cerebellar ataxia and are not devoid of collateral effects, non-invasive stimulation may represent a promising strategy to improve residual cerebellar circuits functioning and a complement tool to pharmacotherapy.

Immune-mediated Cerebellar Ataxias: Practical Guidelines and Therapeutic Challenges

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

Serum antigliadin antibodies in cerebellar ataxias: a systematic review and meta-analysis

BACKGROUND

Gluten sensitivity refers to prominent immunological responses to gluten, usually in conjunction with elevated levels of serum antigliadin antibody (AGA). The association between AGA and cerebellar ataxias has been inconsistently reported.

METHODS

We performed a systematic literature search and a meta-analysis to study the weighted pooled OR of idiopathic cerebellar ataxia (IDCA) cases to controls or to hereditary ataxia (HA) for AGA seropositivity using fixed effect model.

RESULTS

Eleven studies were included, with a total of 847 IDCA cases, 1654 controls and 445 HA cases. IDCA cases had fourfold higher odds than controls (OR 4.28, 95% CI 3.10 to 5.90) and twofold higher odds than HA cases (OR 2.23, 95% CI 1.45 to 3.44) of having AGA seropositivity. Sensitivity analysis excluding the most weighted study, which accounted for 69% of the total weight, still showed similar associations (IDCA vs controls, OR 3.18, 95% CI 1.79 to 5.67 and IDCA vs HA, OR 1.72, 95% CI 1.03 to 2.86, respectively). The subgroup analysis showed that, when compared with controls, IDCA cases of both East Asian and Western countries had approximately threefold to fourfold higher odds to have AGA seropositivity (OR 3.41, 95% CI 1.67 to 6.97 and OR 4.53, 95% CI 3.16 to 6.49, respectively), suggesting the lack of ethnic heterogeneity. The odds of AGA seropositivity for HA cases was not significantly higher than controls (OR 1.41, 95% CI 0.82 to 2.44).

CONCLUSION

Our study indicates the association between AGA and IDCA, across different geographic regions.

Cerebellar Ataxia With Extreme Photophobia Associated With Anti-SOX1 Antibodies

Anti-SOX1 antibodies are associated with diverse neurological syndromes, targeting both the central (paraneoplastic cerebellar degeneration) and peripheral nervous systems (Lambert Eaton myasthenic syndrome, paraneoplastic neuropathy). Although the pathogenic role of these antibodies remains unclear, their strong association with underlying neoplastic disease (mainly small-cell lung cancer) has designated them as onconeural antibodies. Here, we present a case of cerebellar ataxia with marked photophobia, with severe atrophy of the cerebellum and brain stem, associated with anti-SOX1 antibodies without evidence of an underlying malignancy. Although anti-SOX1-associated cerebellar syndrome is infrequent, investigation of these antibodies should be considered as a part of the diagnostic algorithm if more common causes have been ruled out. Extensive brain stem lesions causing disruption of the trigeminal pathway and its connections with the pretectal area might explain the underlying mechanism of the associated photophobia. Early recognition of anti-SOX1 antibodies, exclusion of underlying neoplasm, and prompt initiation of immunotherapy are essential to achieve a better outcome.

Stiff person syndrome with Anti-GAD65 antibodies within the national veterans affairs health administration

INTRODUCTION

Stiff person syndrome (SPS) is a neurological disorder characterized by muscle rigidity primarily in the truncal muscles, commonly associated with autoantibodies to the glutamic acid-decarboxylase 65 kD receptor (GAD65). There is limited epidemiological information on patients with SPS.

METHODS

We performed a retrospective case review using the National United States Veterans Affairs Health Administration electronic medical record system. We analyzed prevalence, demographics, disease characteristics, and treatment outcomes in SPS patients who were anti-GAD65 antibody positive.

RESULTS

Fifteen patients met our criteria. Point prevalence was 2.06 per million, and period prevalence was 2.71 per million. Men to women ratio was 14:1. All patients benefitted from treatment with symptomatic antispasmodic agents. Ten of 15 patients received intravenous immunoglobulin, with a majority demonstrating stable or improved modified Rankin scores.

DISCUSSION

This investigation was a large North American epidemiological study of SPS with predominantly male patients. Symptomatic therapy was beneficial for most patients, with less clear sustained benefit of immunotherapy. Muscle Nerve 58:801-804, 2018.

Time Is Cerebellum

The cerebellum characteristically has the capacity to compensate for and restore lost functions. These compensatory/restorative properties are explained by an abundant synaptic plasticity and the convergence of multimodal central and peripheral signals. In addition, extra-cerebellar structures contribute also to the recovery after a cerebellar injury. Clinically, some patients show remarkable improvement of severe ataxic symptoms associated with trauma, stroke, metabolism, or immune-mediated cerebellar ataxia (IMCA, e.g., multiple sclerosis, paraneoplastic cerebellar degeneration, gluten ataxia, anti-GAD65 antibody-associated cerebellar ataxia). However, extension of a cerebellar lesion can impact upon the fourth ventricle or the brainstem, either by direct or indirect mechanisms, leading to serious complications. Moreover, cerebellar reserve itself is affected by advanced cell loss and, at some point of disease progression, deficits become irreversible. Such phase transition from a treatable/restorable state (the reserve is still sufficient) to an untreatable state (the reserve is severely affected) is a loss of therapeutic opportunity, highlighting the need for early treatment during the restorable stage. Based on the motto of "Time is Brain," a warning that stresses the importance of early therapeutic intervention in ischemic diseases, we propose "Time is Cerebellum" as a principle in the management of patients with cerebellar diseases, especially immune ataxias whose complexity often delay the therapeutic intervention. Indeed, this concept should not be restricted to ischemic cerebellar diseases. We argue that every effort should be made to reduce the diagnostic delay and to initiate early therapy to avoid the risk of transition from a treatable state to an irreversible condition and an associated accumulation of disability. The myriad of disorders affecting the cerebellum is a challenging factor that may contribute to irreversible disability if the window of therapeutic opportunity is missed.

Acute Cerebellar Ataxia Associated with Anti-glutamic Acid Decarboxylase Antibodies Mimicking Miller Fisher Syndrome

We herein report the case of a 53-year-old man with cerebellar ataxia with anti-glutamic acid decarboxylase antibody (GAD-Ab) who mimicked Miller Fisher syndrome (MFS). He developed ophthalmoplegia, diplopia, and gait ataxia for one week. The serum and cerebrospinal fluid GAD-Ab titers were greatly increased, and the GAD-Ab index suggesting intrathecal antibody synthesis was elevated, while GQ1b-Ab was negative. After steroid pulse therapy and following prednisolone, his symptoms dramatically improved over the course of 11 months with the simultaneous decline of GAD-Ab titers. This case indicates that cerebellar ataxia with GAD-Ab can present with acute neurological findings mimicking MFS, and that steroid therapy has an excellent therapeutic effect.

The neuropathology of the adult cerebellum

This chapter summarizes the neuropathologic features of nonneoplastic disorders of the adult cerebellum. Gait ataxia and extremity dysmetria are clinical manifestations of diseases that interrupt the complex cerebellar circuitry between the neurons of the cerebellar cortex, the cerebellar nuclei (especially the dentate nuclei), and the inferior olivary nuclei. The cerebellum is a prominent target of several sporadic and hereditary neurodegenerative diseases, including multiple system atrophy, spinocerebellar ataxia, and Friedreich ataxia. Purkinje cells display selective vulnerability to hypoxia but a surprising resistance to hypoglycemia. A classic toxin that damages the cerebellar cortex is methylmercury, but the most common injurious agent to Purkinje cells is ethanol. Many drugs cause ataxia, but doubts continue about phenytoin. Ischemic lesions of the cerebellum due to arterial thrombosis or embolism cause a spectrum of symptoms and signs, depending on the territory involved. Large hemorrhages have an unfavorable prognosis because they displace critical brainstem structures or penetrate into the fourth ventricle. Fungal infections and toxoplasmosis of the cerebellum, and cerebellar progressive multifocal leukoencephalopathy, have become rarer because of improved control of the acquired immunodeficiency syndrome. Ataxia is a prominent feature of prion disease. Adult-onset Niemann-Pick type C1 disease and Kufs disease may have a predominantly ataxic clinical phenotype. The adult cerebellum is also vulnerable to several leukodystrophies. A rare but widely recognized complication of cancer is paraneoplastic cerebellar degeneration.

Immune-mediated ataxias

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

Treatment of Cerebellar Ataxia in the Context of Systemic Diseases

Purpose of review The purpose of this review is to assess the evidence behind treatment regimens for cerebellar ataxias occurring in the context of systemic disease. We will address systemic conditions which are associated with specific involvement of the cerebellum (rather than widespread nervous system involvement) and those conditions for which some degree of evidence of treatment response exists.

Recent findings We have divided systemic disorders affecting the cerebellum into systemic immunological disorders, endocrine and metabolic disorders and paraneoplastic. Recent studies have increased understanding of the range of cerebellar disorders associated with a systemic immunological condition. The identification of newer pathogenic antibodies has improved diagnosis in conditions which would have previously been labelled as idiopathic. However, their rarity and phenotypic variability makes defining optimal immunomodulatory treatment regimens challenging. There is some evidence for beneficial effects of immunomodulation, particularly in anti-GAD ataxia and Hashimoto’s encephalopathy, although, at this time, specific treatment regimens cannot be defined. Immune-mediated paraneoplastic cerebellar disorders show response to therapy dependent, to some extent, on the underlying pathogenic antibody. Much is still to be understood concerning treatment regimens for the ataxic manifestations of metabolic disorders, notably alcohol-induced cerebellar injury, which are common and which are associated with significant disability.

Summary Despite their rarity, cerebellar ataxias occurring in the context of systemic disease cause significant morbidity and better therapies are required to improve outcomes associated with these conditions.