GAD65 neurological autoimmunity

Long-term outcomes in antibody-negative autoimmune encephalitis: a retrospective study

BACKGROUND AND OBJECTIVE

Despite constituting one-third of suspected autoimmune encephalitis (AE) patients, antibody-negative cases without typical AE features are understudied. We aim to characterize the clinical phenotypes and long-term outcomes of "possible only" and "probable" AE cases.

METHODS

We conducted a retrospective analysis of adult patients evaluated at Mayo Clinic's Autoimmune Neurology Clinic (01/01/2006-12/31/2020), meeting diagnostic criteria for "possible only" or "probable but antibody-negative" AE, with ≥ 1 year of follow-up. All patients underwent neural antibody testing.

RESULTS

Among fifty-one patients, six had a change in diagnosis (non-autoimmune, 2) and were excluded from further analysis. Forty-five patients were analyzed [median age, 61 years (range 20-88); female, 21 (47%); median follow-up, 36 months (range 12-174)]. A nadir modified Rankin Scale (mRS) ≥ 3 was recorded in 41/45 (91%). CSF was inflammatory in 20/44 (45%) and MRI had encephalitic changes in 21/45 (47%). Unclassified neural-specific IgG staining on tissue-based assay was detected in five (11%). Two patients (4%) had paraneoplastic causation. Relapses (> 3 months from onset) were noted in 14 (31%). Memory dysfunction (69%), attention deficits (38%), and gait instability (29%) were the most frequent at the last follow-up. Most patients (76%) were independent at the last follow-up and only two required an assistive device to ambulate; 11 patients (24%) had poor neurological outcome (mRS ≥ 3). Higher mRS score and gait assistance requirement at 3 months were predictive of poor outcome (P ≤ 0.01).

DISCUSSION

Despite significant disability at initial disease stages, most antibody-negative AE patients regain independent functioning. Early functional status and gait assistance requirements may predict long-term prognosis.

Stiff-person syndrome and related disorders - diagnosis, mechanisms and therapies

Stiff-person syndrome (SPS) is the prototypical and most common autoimmune neuronal hyperexcitability disorder. It presents with stiffness in the limbs and axial muscles, stiff gait with uncontrolled falls, and episodic painful muscle spasms triggered by anxiety, task-specific phobias and startle responses, collectively leading to disability. Increased awareness of SPS among patients and physicians has created concerns about diagnosis, misdiagnosis and treatment. This Review addresses the evolving diagnostic challenges in SPS and overlapping glutamic acid decarboxylase (GAD) antibody spectrum disorders, highlighting the growing number of overdiagnoses and focusing on the progress made in our understanding of SPS pathophysiology, antibodies against GAD and other inhibitory synaptic antigens, and the fundamentals of neuronal hyperexcitability. It considers the role of impaired GABAergic or glycinergic inhibition in the cortex and at multiple levels in the neuraxis; the underlying autoimmunity and involvement of GAD antibodies; immunopathogenic mechanisms beyond antibodies, including environmental triggers; familial and immunogenetic susceptibility; and potential T cell cytotoxicity. Finally, the mechanistic rationale for target-specific therapeutic interventions is presented along with the available therapeutic approaches, including enhancers of GABA signalling drugs and immunotherapies.

Overview and Diagnostic Approach in Autoimmune Neurology

OBJECTIVE

The field of autoimmune neurology is rapidly evolving. This article reviews the epidemiology and pathophysiology as well as current approaches to clinical and paraclinical assessment, testing paradigms, and general principles of treatment.

LATEST DEVELOPMENTS

Improved recognition of autoimmune diagnoses among patients who have phenotypically diverse, subacute onset neurologic presentations is facilitated by disease-specific antibody biomarker discovery. These antibodies have varying associations with paraneoplastic causation (from no association to greater than 70% positive predictive value), immunotherapy responses, and outcomes. To simplify assessment in an increasingly complex discipline, neurologic phenotype-specific serum and CSF antibody evaluations are recommended. Clinical trials have led to the approval of monoclonal therapies for neuromyelitis optica spectrum disorder (NMOSD) and are underway for N-methyl-d-aspartate (NMDA) receptor and leucine-rich glioma inactivated protein 1 (LGI1) encephalitides.

ESSENTIAL POINTS

Autoimmune neurology is now a mainstream subspecialty, consisting of disorders with diverse presentations detectable using antibody testing of serum and CSF. Early and sustained immunotherapy (eg, corticosteroids, intravenous immunoglobulin [IVIg], plasma exchange) is recommended and may be supplemented by immune suppressants (eg, rituximab or cyclophosphamide) to sustain responses and optimize outcomes.

Stiff Person Syndrome and GAD Antibody-Spectrum Disorders

OBJECTIVE

Antibodies against glutamic acid decarboxylase (GAD), originally associated with stiff person syndrome (SPS), define the GAD antibody-spectrum disorders that also include cerebellar ataxia, autoimmune epilepsy, limbic encephalitis, progressive encephalomyelitis with rigidity and myoclonus (PERM), and eye movement disorders, all of which are characterized by autoimmune neuronal excitability. This article elaborates on the diagnostic criteria for SPS and SPS spectrum disorders, highlights disease mimics and misdiagnoses, describes the electrophysiologic mechanisms and underlying autoimmunity of stiffness and spasms, and provides a step-by-step therapeutic scheme.

LATEST DEVELOPMENTS

Very-high serum GAD antibody titers are diagnostic for GAD antibody-spectrum disorders and also predict the presence of GAD antibodies in the CSF, increased intrathecal synthesis, and reduced CSF γ-aminobutyric acid (GABA) levels. Low serum GAD antibody titers or the absence of antibodies generates diagnostic challenges that require careful distinction in patients with a variety of painful spasms and stiffness, including functional neurologic disorders. Antibodies against glycine receptors, first found in patients with PERM, are seen in 13% to 15% of patients with SPS, whereas amphiphysin and gephyrin antibodies, seen in 5% of patients with SPS spectrum disorders, predict a paraneoplastic association. GAD-IgG from different SPS spectrum disorders recognizes the same dominant GAD intracellular epitope and, although the pathogenicity is unclear, is an excellent diagnostic marker. The biological basis of muscle stiffness and spasms is related to autoimmune neuronal hyperexcitability caused by impaired reciprocal γ-aminobutyric acid-mediated (GABA-ergic) inhibition, which explains the therapeutic response to GABA-enhancing agents and immunotherapies.

ESSENTIAL POINTS

It is essential to distinguish SPS spectrum disorders from disease mimics to avoid both overdiagnoses and misdiagnoses, considering that SPS is treatable if managed correctly from the outset to prevent disease progression. A step-by-step, combination therapy of GABA-enhancing medications along with immunotherapies ensures prolonged clinical benefits.

Autoimmune-associated seizure disorders

With the discovery of an expanding number of neural autoantibodies, autoimmune etiologies of seizures have been increasingly recognized. Clinical phenotypes have been identified in association with specific underlying antibodies, allowing an earlier diagnosis. These phenotypes include faciobrachial dystonic seizures with LGI1 encephalitis, neuropsychiatric presentations associated with movement disorders and seizures in NMDA-receptor encephalitis, and chronic temporal lobe epilepsy in GAD65 neurologic autoimmunity. Prompt recognition of these disorders is important, as some of them are highly responsive to immunotherapy. The response to immunotherapy is highest in patients with encephalitis secondary to antibodies targeting cell surface synaptic antigens. However, the response is less effective in conditions involving antibodies binding intracellular antigens or in Rasmussen syndrome, which are predominantly mediated by cytotoxic T-cell processes that are associated with irreversible cellular destruction. Autoimmune encephalitides also may have a paraneoplastic etiology, further emphasizing the importance of recognizing these disorders. Finally, autoimmune processes and responses to novel immunotherapies have been reported in new-onset refractory status epilepticus (NORSE) and febrile infection-related epilepsy syndrome (FIRES), warranting their inclusion in any current review of autoimmune-associated seizure disorders.

Neurological Diseases and Prevalence of Antineuronal Antibodies in Patients with Autoimmune Polyendocrine Syndrome Type 1 - A National Cohort Study

Autoimmune polyendocrine syndrome type 1 (APS-1) is a rare monogenic disease caused by mutations in the autoimmune regulator gene. Although the disease-associated autoantibodies mostly target endocrine organs, autoantibodies from patients with APS-1 bind also to rat brain structures. The patients often have GAD65-antibodies, that can cause autoimmune encephalitis. However, neurological manifestations of APS-1 have not been systematically explored. We conducted a retrospective chart review on 44 Finnish patients with APS-1 (median age 38 years, 61% females) and collected all their neurological diagnoses. To assess the prevalence of serum antineuronal antibodies in APS-1, serum samples of 24 patients (median age 36 years, 63% females) were analyzed using a fixed cell-based assay. Of the 44 APS-1 patients, 10 (23%) had also received a diagnosis of a neurological disease. Of these neurological comorbidities, migraine (n = 7; 16%), central nervous system infections (n = 3; 7%), and epilepsy (n = 2; 5%) were the most prevalent. Other diagnoses recorded for single patients were axonal sensorimotor polyneuropathy, essential tremor, idiopathic intracranial hypertension, ischemic stroke, and trigeminal neuralgia. Serum antineuronal antibodies were detected in 42% of patients tested (10/24, 50% females, median age 42 years), GAD65 antibodies being the most common finding. Antibodies against glycine and aquaporin 4 were found in low titers. In four patients, relatively high titers of GAD65 antibodies without coexisting type 1 diabetes were found, but none presented with GAD65-encephalitis. Our study suggests an association between APS-1 and neurological disorders, the mechanisms of which are to be further investigated.

"Hot Cross Bun" Sign in a Patient with Glutamic Acid Decarboxylase 65-KDa Isoform Associated Cerebellar Ataxia: Case Report and Review of the Literature

The "hot cross bun" sign (HCBs) is a cruciform hyperintensity on T2-weighted imaging within the pons initially found in patients diagnosed as multiple system atrophy. However, recent findings have broadened the disease spectrum presented with HCBs. Here is a case report at an academic medical center. Cerebral magnetic resonance imaging (MRI), electroneuromyography, serum, and CSF analysis were performed. Literature is comprehensively reviewed. We investigated a woman presented with blurred speech and cerebellar ataxia. Her MRI showed the vertical line of HCBs 2 weeks after disease onset and gradually enhanced, presenting as an intact HCBs in a year. Glutamic acid decarboxylase 65-kDa isoform (GAD65) antibody IgG was detected in serum and CSF. The patient was diagnosed as GAD65 associated cerebellar ataxia and treated with corticosteroid and rituximab. We found 6 previously reported autoimmune cerebellar ataxia patients with HCBs. Anti-KLHL-11, anti-Homer-3, anti-Ri, and anti-Amphiphysin were associated. All patients had cerebellar ataxia with other neurological symptoms. Five patients were diagnosed with tumor. First-line immunotherapy including corticosteroid, intravenous immunoglobulin, and plasma exchange for most patients was unsatisfied. This case highlights the importance of considering GAD65 IgG evaluation in patients with progressive cerebellar syndrome and HCBs. Early diagnosis and therapy are challenging but imperative. Further studies are required in regard to therapeutic management.

Hippocampal sclerosis is associated with celiac disease type immunity in patients with drug-resistant temporal lobe epilepsy

BACKGROUND

A prior small-scale single center study suggested an association between celiac disease (CD)-type immunity and refractory temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS). The present study addresses this putative association in a large, well-characterized group of drug-resistant epilepsy (DRE) patients. These patients were grouped based on the spectrum of CD and gluten sensitivity-associated antibodies.

METHODS

In this cross-sectional study, 253 consecutive adult epilepsy patients (135 females, 118 males; age 16-76 years) were categorized into three groups: (i) CD-positive group with either prior diagnosis of CD or CD-specific TG2/EmA antibodies, (ii) AGA-positive group with antigliadin antibodies (AGA) but without CD, and (iii) CD/AGA-negative group without any gluten sensitivity-associated antibodies or CD. Clinical and immunological findings were then compared among the groups.

RESULTS

TLE with HS was more common in the CD-positive group compared to CD/AGA-negative group (31.8% versus 11.9%, P = 0.019). Autoimmune disorders were more common in the AGA-positive group than in the CD/AGA-negative group (P = 0.025). Considering HS lateralization; left lateralization was more common in CD-positive group compared to CD/AGA-negative group (71.4% versus 25%, P = 0.030). TG6 seropositivity did not differ among the groups (P > 0.05).

CONCLUSIONS

This study provides further evidence linking TLE with HS and CD-type autoimmunity suggesting that CD-type immune response to gluten can be one potential mechanism as a disease modifier leading to DRE and HS. Understanding these immunological factors is imperative for developing immunomodulatory or dietary treatments for DRE potentially preventing HS progression.

Prevention of MK-801-induced amnestic effect with combined activation of 5-HT1A and muscarinic receptors in mice

BACKGROUND

Muscarinic or 5-HT1A receptors are crucial in learning and memory processes, and their expression is evident in the brain areas involved in cognition. The administration of the activators of these receptors prevents the development of cognitive dysfunctions in animal models of schizophrenia induced by MK-801 (N-methyl-d-aspartate receptor antagonist) administration. GABAergic dysfunction is considered as one of the most important causes of MK-801-induced spatial learning deficits.

METHODS

Novel object recognition (NOR) and Morris water maze (MWM) tests were used to study the anti-amnestic effect of the biased 5-HT1A receptor agonist (F15599) alone or in combinations with VU0357017 (M1 receptor allosteric agonist), VU0152100 (M4 receptor positive allosteric modulator), and VU0238429 (M5 receptor positive allosteric modulator) on MK-801-induced dysfunctions. The compounds were administered for 5 consecutive days. Animals tested with the MWM underwent 5-day training. Western blotting was used to study the expressions of 5-HT1A receptors and the level of GAD65 in the frontal cortices (FCs) and hippocampi of the animals.

RESULTS

F15599 prevented the amnestic effect induced by MK-801 in the MWM at a dose of 0.1 mg/kg. The co-administration of the compound with muscarinic receptors activators had no synergistic effect. The additive effect of the combinations was evident in the prevention of declarative memory dysfunctions investigated in NOR. The administration of MK-801 impaired 5-HT1A expression in the hippocampi and decreased GAD65 levels in both the FCs and hippocampi. The administration of muscarinic ligands prevented these MK-801-induced deficits only in the hippocampi of MWM-trained animals. No effects of the compounds were observed in untrained mice.

CONCLUSION

Our results indicate that F15599 prevents schizophrenia-related spatial learning deficits in the MWM; however, the activity of the compound is not intensified with muscarinic receptors activators. In contrast, the combined administration of the ligands is effective in the NOR model of declarative memory. The muscarinic receptors activators reversed MK-801-induced 5-HT1A and GAD65 dysfunctions in the hippocampi of MWM-trained mice, but not in untrained mice.

Autoimmune central nervous system disorders: Antibody testing and its clinical utility

A rapidly expanding repertoire of neural antibody biomarkers exists for autoimmune central nervous system (CNS) disorders. Following clinical recognition of an autoimmune CNS disorder, the detection of a neural antibody facilitates diagnosis and informs prognosis and management. This review considers the phenotypes, diagnostic assay methodologies, and clinical utility of neural antibodies in autoimmune CNS disorders. Autoimmune CNS disorders may present with a diverse range of clinical features. Clinical phenotype should inform the neural antibodies selected for testing via the use of phenotype-specific panels. Both serum and cerebrospinal fluid (CSF) are preferred in the vast majority of cases but for some analytes either CSF (e.g. N-methyl-D-aspartate receptor [NMDA-R] IgG) or serum (e.g. aquaporin-4 [AQP4] IgG) specimens may be preferred. Screening using 2 methods is recommended for most analytes, particularly paraneoplastic antibodies. We utilize murine tissue-based indirect immunofluorescence assay (TIFA) with subsequent confirmatory protein-specific testing. The cellular location of the target antigen informs choice of confirmatory diagnostic assay (e.g. blot for intracellular antigens such as Hu; cell-based assay for cell surface targets such as leucine-rich glioma inactivated 1 [LGI1]). Titers of positive results have limited diagnostic utility with the exception of glutamic acid decarboxylase (GAD) 65 IgG autoimmunity, which is associated with neurological disease at higher values. While novel antibodies are typically discovered using established techniques such as TIFA and immunoprecipitation-mass spectrometry, more recent high-throughput molecular technologies (such as protein microarray and phage-display immunoprecipitation sequencing) may expedite the process of antibody discovery. Individual neural antibodies inform the clinician regarding the clinical associations, oncological risk stratification and tumor histology, the likely prognosis, and immunotherapy choice. In the era of neural antibody biomarkers for autoimmune CNS disorders, access to appropriate laboratory assays for neural antibodies is of critical importance in the diagnosis and management of these disorders.

Successful Autologous Hematopoietic Stem Cell Transplant in Glycine Receptor Antibody-Positive Stiff Person Syndrome: A Case Report

BACKGROUND AND OBJECTIVES

To describe a case of glycine receptor (GlyR) antibody-positive stiff person syndrome (SPS) treated with autologous hematopoietic stem cell transplant (aHSCT).

METHODS

This was a multicenter collaboration for the treatment of a single patient who underwent aHSCT as part of a clinical trial (NCT00716066). To objectively assess the response to transplantation, several clinical outcome measures were evaluated pretransplant and up to 18 months post-transplant, including modified Rankin Score (mRS), stiffness index, Hauser Ambulation Score (HAS), hypersensitivity index, timed 25-foot walk, and Montreal Cognitive Assessment.

RESULTS

After transplant, the patient achieved sustained clinical improvement evidenced across various clinical scales, including mRS, stiffness index, HAS, and 25-foot walk time.

DISCUSSION

aHSCT represents a promising treatment option for SPS, including for GlyR-positive patients. In addition, this case represents the need to validate and standardize best clinical outcome measures for patients with SPS.

CLASSIFICATION OF EVIDENCE

Class IV; this is a single observational study without controls.

Diabetic striatopathy and other acute onset de novo movement disorders in hyperglycemia

BACKGROUND AND AIMS

Acute onset de novo movement disorder is an increasingly recognized, yet undereported complication of diabetes. Hyperglycemia can give rise to a range of different movement disorders, hemichorea-hemiballism being the commonest. This article delves into the current knowledge about this condition, its diverse presentations, ongoing debates regarding its underlying mechanisms, disparities between clinical and radiological findings, and challenges related to its management.

METHODS

PubMed and Google Scholar were searched with the following key terms- "diabetes", "striatopathy", "hyperglycemia", "striatum", "basal ganglia", "movement disorder", "involuntary movement". Case reports, systematic reviews, meta-analysis, and narrative reviews published in English literature related to the topic of interest from January 1, 1950, to October 20, 2023, were retrieved. The references cited in the chosen articles were also examined, and those considered relevant were included in the review.

RESULTS

Diabetic striatopathy is the prototype of movement disorders associated with hyperglycemia with its characteristic neuroimaging feature (contralateral striatal hyperdensitity on computed tomography or hyperintensity on T1-weighted magnetic resonance imaging). Risk factors for diabetic striatopathy includes Asian ethnicity, female gender, prolonged poor glycemic control, and concurrent retinopathy. Several hypotheses have been proposed to explain the pathophysiology of movement disorders induced by hyperglycemia. These hypotheses are not mutually exclusive; instead, they represent interconnected pathways contributing to the development of this unique condition. While the most prominent clinical feature of diabetic striatopathy is a movement disorder, its phenotypic expression has been found to extend to other manifestations, including stroke, seizures, and cognitive and behavioral symptoms. Fortunately, the prognosis for diabetic striatopathy is generally excellent, with complete resolution achievable through the use of anti-hyperglycemic therapy alone or in combination with neuroleptic medications.

CONCLUSION

Hyperglycemia is the commonest cause of acute onset de novo movement disorders presenting to a range of medical specialists. So, it is of utmost importance that the physicians irrespective of their speciality remain aware of this clinical entity and check blood glucose at presentation before ordering any other investigations. Prompt clinical diagnosis of this condition and implementation of intensive glycemic control can yield significant benefits for patients.

Paraneoplastic movement disorders

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

Optimizing the diagnostic performance of neural antibody testing for paraneoplastic and autoimmune encephalitis in clinical practice

The detection of neural antibodies in patients with paraneoplastic and autoimmune encephalitis has majorly advanced the diagnosis and management of neural antibody-associated diseases. Although testing for these antibodies has historically been restricted to specialized centers, assay commercialization has made this testing available to clinical chemistry laboratories worldwide. This improved test accessibility has led to reduced turnaround time and expedited diagnosis, which are beneficial to patient care. However, as the utilization of these assays has increased, so too has the need to evaluate how they perform in the clinical setting. In this chapter, we discuss assays for neural antibody detection that are in routine use, draw attention to their limitations and provide strategies to help clinicians and laboratorians overcome them, all with the aim of optimizing neural antibody testing for paraneoplastic and autoimmune encephalitis in clinical practice.

Paraneoplastic neuropathies and peripheral nerve hyperexcitability disorders

Peripheral neuropathy is a common referral for patients to the neurologic clinics. Paraneoplastic neuropathies account for a small but high morbidity and mortality subgroup. Symptoms include weakness, sensory loss, sweating irregularity, blood pressure instability, severe constipation, and neuropathic pain. Neuropathy is the first presenting symptom of malignancy among many patients. The molecular and cellular oncogenic immune targets reside within cell bodies, axons, cytoplasms, or surface membranes of neural tissues. A more favorable immune treatment outcome occurs in those where the targets reside on the cell surface. Patients with antibodies binding cell surface antigens commonly have neural hyperexcitability with pain, cramps, fasciculations, and hyperhidrotic attacks (CASPR2, LGI1, and others). The antigenic targets are also commonly expressed in the central nervous system, with presenting symptoms being myelopathy, encephalopathy, and seizures with neuropathy, often masked. Pain and autonomic components typically relate to small nerve fiber involvement (nociceptive, adrenergic, enteric, and sudomotor), sometimes without nerve fiber loss but rather hyperexcitability. The specific antibodies discovered help direct cancer investigations. Among the primary axonal paraneoplastic neuropathies, pathognomonic clinical features do not exist, and testing for multiple antibodies simultaneously provides the best sensitivity in testing (AGNA1-SOX1; amphiphysin; ANNA-1-HU; ANNA-3-DACH1; CASPR2; CRMP5; LGI1; PCA2-MAP1B, and others). Performing confirmatory antibody testing using adjunct methods improves specificity. Antibody-mediated demyelinating paraneoplastic neuropathies are limited to MAG-IgM (IgM-MGUS, Waldenström's, and myeloma), with the others associated with cytokine elevations (VEGF, IL6) caused by osteosclerotic myeloma, plasmacytoma (POEMS), and rarely angiofollicular lymphoma (Castleman's). Paraneoplastic disorders have clinical overlap with other idiopathic antibody disorders, including IgG4 demyelinating nodopathies (NF155 and Contactin-1). This review summarizes the paraneoplastic neuropathies, including those with peripheral nerve hyperexcitability.

Case Report: Extraocular muscles paralysis associated with GAD65 antibody: a case series study

Objective

To explore the clinical manifestations of glutamic acid decarboxylase 65 (GAD65) antibody-positive patients with extraocular symptoms and the possible mechanism.

Method

Assays for the presence of GAD65 antibodies were performed on patients' serum and cerebral spinal fluid (CSF). The brain and ocular structures involved in eye movement were assessed via magnetic resonance imaging (MRI). Tests such as electromyography (EMG), particularly repetitive nerve stimulation (RNS), and neostigmine tests were utilized for differential diagnosis. Additionally, the interaction of GAD65 antibodies with muscle tissue was confirmed using immunofluorescence techniques.

Result

Each patient exhibited symptoms akin to extraocular myasthenia gravis (MG), with two individuals reporting diplopia and two experiencing ptosis. GAD65 antibodies were detected in either the serum or CSF, which were shown to bind with monkey cerebellum slides and mouse muscle slides. Neuroimaging of the brain and extraocular muscles via MRI showed no abnormalities, and all patients tested negative for the neostigmine test, RNS via EMG, and the presence of MG antibodies. However, thyroid-related antibodies were found to be abnormal in four of the patients.

Conclusion

Our results showed that GAD65 antibodies are not only associated with encephalitis, cerebellum ataxia or stiff-person syndrome caused by the decrease of GABAergic transmission but also diplopia and ptosis. Therefore, we should pay more attention to extraocular muscle paralysis patients without pathogenic antibodies directed against the components of neuromuscular junctions.

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.

An update on malignant tumor-related stiff person syndrome spectrum disorders: clinical mechanism, treatment, and outcomes

Stiff person syndrome (SPS) is a rare central nervous system disorder associated with malignancies. In this review, we retrieved information from PubMed, up until August 2023, using various search terms and their combinations, including SPS, stiff person syndrome spectrum disorders (SPSSDs), paraneoplastic, cancer, and malignant tumor. Data from peer-reviewed journals printed in English were organized to explain the possible relationships between different carcinomas and SPSSD subtypes, as well as related autoantigens. From literature searching, it was revealed that breast cancer was the most prevalent carcinoma linked to SPSSDs, followed by lung cancer and lymphoma. Furthermore, classic SPS was the most common SPSSD subtype, followed by stiff limb syndrome and progressive encephalomyelitis with rigidity and myoclonus. GAD65 was the most common autoantigen in patients with cancer and SPSSDs, followed by amphiphysin and GlyR. Patients with cancer subtypes might have multiple SPSSD subtypes, and conversely, patients with SPSSD subtypes might have multiple carcinoma subtypes. The first aim of this review was to highlight the complex nature of the relationships among cancers, autoantigens, and SPSSDs as new information in this field continues to be generated globally. The adoption of an open-minded approach to updating information on new cancer subtypes, autoantigens, and SPSSDs is recommended to renew our database. The second aim of this review was to discuss SPS animal models, which will help us to understand the mechanisms underlying the pathogenesis of SPS. In future, elucidating the relationship among cancers, autoantigens, and SPSSDs is critical for the early prediction of cancer and discovery of new therapeutic modalities.

Antineuronal Autoantibodies in the Cerebrospinal Fluid and Serum From 106 Patients With Recent-Onset Depression Compared With 106 Individually Matched Healthy Control Subjects

No large studies have investigated the prevalence of cerebrospinal fluid antineuronal autoantibodies in isolated depression. In this case-control study comparing 106 patients with isolated depression (ICD-10 code F32) with 106 healthy control subjects, cerebrospinal fluid and serum samples were tested for 7 immunoglobulin G autoantibodies using commercial fixed cell-based assays. To explore validity of methods, positive samples were retested twice by cell-based assays and once by tissue-based assays (monkey cerebellum). The prevalence of any of the antineuronal autoantibodies in cerebrospinal fluid was 0.0% in both groups and the seroprevalence was 0.9% in both groups, based on consistent findings in cell-based assays. However, all samples were negative by the tissue-based assay. Evaluation of antineuronal autoantibodies in cerebrospinal fluid cannot be recommended routinely for patients with isolated depression of moderate severity. Future studies of isolated depression should consider much larger sample sizes and evaluation of antineuronal autoantibodies using modalities other than commercial kits.

Neurological Manifestations of Glutamic Acid Decarboxylase Autoimmunity in Indian Patients

Objective

To study the neurological manifestations of glutamic acid decarboxylase (GAD 65) autoimmunity in Indian patients.

Methods

Retrospective study conducted in a tertiary care referral hospital in South India. Patients who tested positive for GAD 65 antibodies from February 2013 to July 2019 were included.

Results

We identified 922 patients who underwent GAD 65 testing, of which 81 tested positive (8.78%) [mean age 55.42 years (SD 17.39, range 9-86 years, median age 57 years)]. Males (n = 47) outnumbered the females (n = 34). All the GAD values measured were <5000 IU/ml. There were 34 cases (42%) of atypical parkinsonism (16/34, 47% fulfilled the diagnostic criteria for autoimmune atypical parkinsonism) in our series forming the most common group with GAD 65 positivity, followed by autoimmune encephalitis (8 cases, 9.88%). Men were more affected with atypical parkinsonism (22/34; 64.70%), stiff person syndrome (2/3; 66.66%), and neuropathy (4/7; 57.1%) while women were more with autoimmune encephalitis (6/8; 75%). Eighteen (22.6%) had underlying autoimmunity (three had type 1 diabetes mellitus). Six (7.4%) had underlying neoplasm. Thirty-three out of 43 patients responded to immunotherapy (76.74%). Five had spontaneous improvement.

Conclusion

Glutamic acid decarboxylase65 antibody values were much lower in our study population. Male-dominant autoimmunity was seen unlike that in Western literature. The most striking was the high preponderance of atypical parkinsonism in GAD 65-positive patients. We also found that GAD 65 positivity is a useful marker for a positive response to immunotherapy in suspected autoimmune neurological syndromes irrespective of their titers.

Clinical features and brain MRI volumetric changes in anti-mGluR5 encephalitis

BACKGROUND

Anti-metabotropic glutamate receptor 5 (mGluR5) encephalitis is a rare and under-recognized autoimmune encephalitis. This study is conducted to characterize its clinical and neuroimaging features.

METHODS

Twenty-nine patients with anti-mGluR5 encephalitis (15 new cases identified in this study and 14 previously reported cases) were included in this study and their clinical features were characterized. Brain MRI volumetric analysis using FreeSurfer software was performed in 9 new patients and compared with 25 healthy controls at both early (≤6 months of onset) and chronic (>1 year of onset) disease stages.

RESULTS

The common clinical manifestations of anti-mGluR5 encephalitis included cognitive deficits (n = 21, 72.4%), behavioral and mood disturbances (n = 20, 69%), seizures (n = 16, 55.2%), and sleep disorder (n = 13, 44.8%). Tumors were observed in 7 patients. Brain MRI T2/FLAIR signal hyperintensities were observed predominantly in mesiotemporal and subcortical regions in 75.9% patients. MRI volumetric analysis demonstrated significant amygdala enlargement in both early and chronic disease stages compared to healthy controls (P < 0.001). Twenty-six patients had complete or partial recovery, one remained stable, one died and one was lost to follow-up.

CONCLUSION

Our findings demonstrated that cognitive impairment, behavioral disturbance, seizures, and sleep disorder are the prominent clinical manifestations of anti-mGluR5 encephalitis. Most patients showed a good prognosis with full recovery, even in the paraneoplastic disease variants. The amygdala enlargement in the early and chronic disease stages is a distinct MRI feature, which exploratively offer a valuable perspective for the study of the disease processes.

Treating Epilepsy with Natural Products: Nonsense or Possibility?

Epilepsy is a neurological disease characterized by recurrent seizures that can lead to uncontrollable muscle twitching, changes in sensitivity to sensory perceptions, and disorders of consciousness. Although modern medicine has effective antiepileptic drugs, the need for accessible and cost-effective medication is urgent, and products derived from plants could offer a solution. For this review, we have focused on natural compounds that have shown anticonvulsant activity in in vivo models of epilepsy at relevant doses. In some cases, the effects have been confirmed by clinical data. The results of our search are summarized in tables according to their molecular targets. We have critically evaluated the data we present, identified the most promising therapeutic candidates, and discussed these in the text. Their perspectives are supported by both pharmacokinetic properties and potential interactions. This review is intended to serve as a basis for future research into epilepsy and related disorders.

Anti-glutamic acid decarboxylase antibody screening in first-episode psychosis

OBJECTIVE

The Royal Australian and New Zealand College of Psychiatrists recommends screening for a range of antibodies in first-episode psychosis, including anti-glutamic acid decarboxylase antibodies. Glutamic acid decarboxylase antibody-associated encephalitis occurs with high antibody titres and may cause cognitive dysfunction, seizures and psychiatric symptoms. However, glutamic acid decarboxylase antibodies are more frequently found in lower titre in association with other autoimmune disorders (such as diabetes mellitus type 1) and in healthy individuals. The utility of testing unselected populations of consumers with psychosis is unclear. The psychiatric manifestations of this disorder are also poorly described.

METHODS

First, systematic review of cohort and case-control studies that tested for IgG glutamic acid decarboxylase antibodies in psychiatric populations was conducted. Random-effects meta-analysis of odds ratio for antibody positivity in cases with psychosis and controls assessed prevalence. Second, literature review of all published cases and case series of glutamic acid decarboxylase antibody-associated limbic encephalitis was assessed for frequency and description of psychotic symptoms.

RESULTS

There were 17 studies, in which 2754 individuals with psychotic disorders were tested for glutamic acid decarboxylase IgG antibodies. Thirty-one consumers with psychosis (0.7%) had positive glutamic acid decarboxylase antibodies compared to 24 controls (1.0%), all at low titre and not fulfilling diagnostic criteria for autoimmune encephalitis. Meta-analysis found no significant difference in rates of glutamic acid decarboxylase antibody positivity (odds ratio = 1.8, 95% confidence interval: [0.90, 3.63]). Literature review found 321 cases of glutamic acid decarboxylase antibody-associated limbic encephalitis, with psychosis in 15 (4.3%) cases. Clinical screening would have identified all cases that presented to psychiatric services.

CONCLUSION

Glutamic acid decarboxylase antibodies were uncommon in consumers with psychosis, with no significant difference in prevalence from controls and no cases of encephalitis identified. In cases with established glutamic acid decarboxylase antibody-associated limbic encephalitis, psychotic symptoms were uncommon and identifiable by clinical assessment. Targeted antibody testing guidelines should be further considered.

Case report: Autoimmune encephalitis with multiple auto-antibodies with reversible splenial lesion syndrome and bilateral ovarian teratoma

Background

Reversible splenial lesion syndrome (RESLES) is a spectrum of disease radiologically characterized by reversible lesions caused by multiple factors, primarily involving the splenium of the corpus callosum (SCC). The most common causes of RESLES include infection, antiepileptic drug use and withdrawal, and severe metabolic disorders. Nevertheless, cases of autoimmune encephalitis (AE) are uncommon.

Case presentation

A 26-year-old female computer programming engineer with no previous medical or psychiatric history reported to the psychiatric hospital due to a 3-day episode of irritability, babbling, limb stiffness, sleepwalking, hallucinations, and paroxysmal mania. Brain MRI revealed abnormal signals of the SCC. Lumbar puncture was performed and further testing for auto-antibodies was conducted in both the CSF and serum. CSF of the patient was positive for anti-NMDAR (titer of 1:3.2) antibodies, and serum was also positive for anti-NMDAR (titer of 1:32) as well as mGluR5 (titer of 1:10) antibodies. Enhanced CT of the pelvis showed an enlarged pelvic mass; bilateral ovarian teratomas (mature teratoma and immature teratoma) were evaluated, which were pathologically confirmed after transabdominal left adnexal resection, right ovarian biopsy, and ovarian cystectomy. The patient considerably improved after intravenous administration of steroids, immunoglobulin, oral prednisone, surgical treatment, and chemotherapy. A follow-up MRI revealed completely resolved lesions. During a 3-month follow-up, the patient experienced complete resolution of symptoms without any sign of recurrence and tumors. The titer of the anti-NMDAR antibody decreased to 1:10 in serum.

Conclusion

Herein, we report a rare case of AE with overlapping auto-antibodies, along with RESLES and bilateral ovarian teratomas. The current case provides the possibility of the concurrence of mGluR5 antibodies in anti-NMDAR encephalitis. However, the underlying mechanism remains elusive. Furthermore, we provide additional evidence that overlapping antibodies-related pathology may be one of the many causes of RESLES. Nonetheless, caution should be observed in interpreting the observation, considering that this is a single-case study.

Autoimmune-mediated encephalitis and mimics: A neuroimaging review

Autoimmune encephalitis is a category of autoantibody-mediated neurological disorders that often presents a diagnostic challenge due to its variable clinical and imaging findings. The purpose of this image-based review is to provide an overview of the major subtypes of autoimmune encephalitis and their associated autoantibodies, discuss their characteristic clinical and imaging features, and highlight several disease processes that may mimic imaging findings of autoimmune encephalitis. A literature search on autoimmune encephalitis was performed and publications from neuroradiology, neurology, and nuclear medicine literature were included. Cases from our institutional database that best exemplify major imaging features were presented.

Pediatric neuropsychiatric disorders with motor and nonmotor phenomena

The concept of pediatric autoimmune neuropsychiatric disorders associated with group A beta-hemolytic streptococcus (PANDAS) has become seminal since first introduced more than two decades ago. At the time of this writing, most neurologists, pediatricians, psychiatrists, and general pediatricians will probably have heard of this association or treated an affected child with PANDAS. The concept of an acute-onset, and typically self-limited, postinfectious autoimmune neuropsychiatric disorder resembling PANDAS manifesting vocal and motor tics and obsessive-compulsive disorder has broadened to other putative microbes and related endogenous and exogenous disease triggers. These disorders with common features of hypometabolism in the medial temporal lobe and hippocampus in brain 18fluorodeoxyglucose positron emission tomography fused to magnetic resonance imaging (FDG PET-MRI), form a spectrum: with the neuropsychiatric disorder Tourette syndrome and PANDAS with its well-defined etiopathogenesis at one end, and pediatric abrupt-onset neuropsychiatric syndrome (PANS), alone or associated with specific bacterial and viral pathogens, at the other end. The designation of PANS in the absence of a specific trigger, as an exclusionary diagnosis, reflects the current problem in nosology.

Autoimmune Encephalitis Misdiagnosis in Adults

Importance

Autoimmune encephalitis misdiagnosis can lead to harm.

Objective

To determine the diseases misdiagnosed as autoimmune encephalitis and potential reasons for misdiagnosis.

Design, Setting, and Participants

This retrospective multicenter study took place from January 1, 2014, to December 31, 2020, at autoimmune encephalitis subspecialty outpatient clinics including Mayo Clinic (n = 44), University of Oxford (n = 18), University of Texas Southwestern (n = 18), University of California, San Francisco (n = 17), University of Washington in St Louis (n = 6), and University of Utah (n = 4). Inclusion criteria were adults (age ≥18 years) with a prior autoimmune encephalitis diagnosis at a participating center or other medical facility and a subsequent alternative diagnosis at a participating center. A total of 393 patients were referred with an autoimmune encephalitis diagnosis, and of those, 286 patients with true autoimmune encephalitis were excluded.

Main Outcomes and Measures

Data were collected on clinical features, investigations, fulfillment of autoimmune encephalitis criteria, alternative diagnoses, potential contributors to misdiagnosis, and immunotherapy adverse reactions.

Results

A total of 107 patients were misdiagnosed with autoimmune encephalitis, and 77 (72%) did not fulfill diagnostic criteria for autoimmune encephalitis. The median (IQR) age was 48 (35.5-60.5) years and 65 (61%) were female. Correct diagnoses included functional neurologic disorder (27 [25%]), neurodegenerative disease (22 [20.5%]), primary psychiatric disease (19 [18%]), cognitive deficits from comorbidities (11 [10%]), cerebral neoplasm (10 [9.5%]), and other (18 [17%]). Onset was acute/subacute in 56 (52%) or insidious (>3 months) in 51 (48%). Magnetic resonance imaging of the brain was suggestive of encephalitis in 19 of 104 patients (18%) and cerebrospinal fluid (CSF) pleocytosis occurred in 16 of 84 patients (19%). Thyroid peroxidase antibodies were elevated in 24 of 62 patients (39%). Positive neural autoantibodies were more frequent in serum than CSF (48 of 105 [46%] vs 7 of 91 [8%]) and included 1 or more of GAD65 (n = 14), voltage-gated potassium channel complex (LGI1 and CASPR2 negative) (n = 10), N-methyl-d-aspartate receptor by cell-based assay only (n = 10; 6 negative in CSF), and other (n = 18). Adverse reactions from immunotherapies occurred in 17 of 84 patients (20%). Potential contributors to misdiagnosis included overinterpretation of positive serum antibodies (53 [50%]), misinterpretation of functional/psychiatric, or nonspecific cognitive dysfunction as encephalopathy (41 [38%]).

Conclusions and Relevance

When evaluating for autoimmune encephalitis, a broad differential diagnosis should be considered and misdiagnosis occurs in many settings including at specialized centers. In this study, red flags suggesting alternative diagnoses included an insidious onset, positive nonspecific serum antibody, and failure to fulfill autoimmune encephalitis diagnostic criteria. Autoimmune encephalitis misdiagnosis leads to morbidity from unnecessary immunotherapies and delayed treatment of the correct diagnosis.

Autoimmune meningoencephalitis associated with anti-glutamic acid decarboxylase antibody following COVID-19 infection: A case report

Anti-glutamic acid decarboxylase (Anti-GAD) are associated with various neurologic condition; but no meningitis has been reported with it, so far. Evidence demonstrates the associated of autoimmune meningoencephalitis with COVID-19 infection. Here, we report a 44-year-old female with progressive loss of consciousness with anti-GAD65 meningoencephalitis 1 month after COVID-19 infection.

Challenging Cases in Neurology: Neurologic Complications of COVID-19

Since the first reported cases of pneumonia in December 2019, coronavirus disease 2019 (COVID-19) has rapidly become recognized as a multisystem illness, with known effects on virtually every organ system. In particular, neurologic complications of COVID-19 have been reported since the beginning of the pandemic in both ambulatory patients with mild disease and critically ill patients. Although it remains unclear whether severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has the potential to directly invade the central nervous system, strokes and other neurovascular complications, sequelae of critical illness and metabolic derangements, parainfectious inflammatory disorders, and a poorly understood post-COVID syndrome have all been reported in patients with COVID-19. Here, we describe cases representing a diverse range of neurologic complications in patients infected with COVID-19.

Long-term Effectiveness of IVIg Maintenance Therapy in 36 Patients With GAD Antibody–Positive Stiff-Person Syndrome

Background and Objectives

IVIg has been the preferred immunotherapy in stiff-person syndrome (SPS) based on a 3-month controlled trial, but whether it is also effective in inducing long-term benefits or arresting disease progression is unknown. The information is needed because SPS is a progressively disabling disease and IVIg is liberally used as chronic therapy without efficacy data. The present study explores the long-term effects of IVIg in the largest cohort of well-characterized patients with SPS followed by the same clinicians over 10 years.

Methods

Data of 36 patients (32 glutamic acid decarboxylase [GAD] positive), diagnosed and treated with monthly maintenance IVIg by the same neurologists, were analyzed. Response was assessed by physician-observed changes, patients' reports of symptom improvement, modified Rankin Scale (mRS) scores, and dependency trials evaluating symptom recurrence after stopping IVIg, prolonging infusion frequency, decreasing monthly dose, or wearing-off effects in between doses. Clinically meaningful long-term response was defined by improved mRS scores, improvement in physician-assessed stiffness, balance and gait, and functional decline with dependency trials.

Results

Twenty-four of 36 (67%) patients had clinically meaningful response over a median 40-month period. Patients with improved mRS scores by 1–2 points manifested improved gait, posture, balance and decreased stiffness, spasms, and startle response; some patients using a wheelchair and those ambulating with devices walked unassisted. In 25% of responders, treatment benefit was sustained for a 40-month median period, but in 29.1%, it declined over a 39-month period; 12.5% exhibited a conditioning effect. Three of 5 patients with cerebellar GAD-SPS variant also improved over time. The 12 patients who did not respond the first 3 months remained unresponsive even if IVIg continued for several months.

Discussion

This is a large study in 36 patients with SPS demonstrating that monthly maintenance IVIg therapy offers long-term benefits in 67% of patients for a median 3.3-year period. Because 29.1% experienced diminishing benefit over time due to disease progression, the study highlights the need for more effective therapies.

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.

Diagnosis and Clinical Features in Autoimmune-Mediated Movement Disorders

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

Anti-GAD65 Antibody-Associated Autoimmune Encephalitis With Predominant Cerebellar Involvement Following Toripalimab Treatment: A Case Report of a Novel irAE of Toripalimab

Toripalimab (Junshi Bioscience Co., Ltd) is a new immune checkpoint inhibitor (ICI) that targets programmed cell death protein 1 (PD-1) in various cancers, including metastatic melanoma. No neurological immune-related adverse events (n-irAEs) of toripalimab have been reported, except for neuromuscular involvement. We report a case of a 63-year-old woman who presented with severe vertigo, vomiting, nystagmus, cerebellar ataxia, and cognitive impairment after toripalimab treatment for metastatic melanoma. Compared with the concomitant cognitive dysfunction and a pathological reflex involving the cerebral cortex, the signs and symptoms of cerebellar involvement were much more prominent. Anti-glutamic acid decarboxylase 65 (anti-GAD65) antibody was positive in both serum and cerebrospinal fluid (CSF). After intravenous immunoglobulin (IVIG) and methylprednisolone (IVMP) administration, the symptoms of vertigo and vomiting resolved, with cognitive impairment and cerebellar ataxia remaining. This is the first report of autoimmune encephalitis (AIE) as an n-irAE of toripalimab.

Are anti-glutamic acid decarboxylase 65-kDa isoform antibodies related to diabetes or brain tumor?

Background

Antibodies against the 65-kDa isoform of glutamic acid decarboxylase (GAD65) are biomarkers of autoimmune disorders and are more common in non-neurological autoimmune diseases than in neurological disorders. As for the central nervous system (CNS), it is well known that GAD65 is primarily associated with stiff-person syndrome, cerebellar ataxia, epilepsy, and paraneoplastic neurological syndrome. However, GAD65 antibodies have not been reported in patients with brain tumors.

Case presentation

This study presents the case of a 62-year-old man who manifested rapidly progressive dizziness with gradually worsening physical disturbance and unstable gait in the 2 months prior to consultation. Antibodies against GAD65 were detected in his serum. Brain magnetic resonance imaging (MRI) showed abnormal signals in the corpus callosum, the semi-oval center in both hemispheres, and the area below the frontal cortex, along with enhanced intracranial lesions in the same regions. Positron emission tomography–computed tomography (PET–CT) showed high metabolism in the corpus callosum, which protruded into both ventricles. Due to signs of malignancy, the patient was diagnosed with a malignant glioma.

Conclusions

This case raises awareness on the fact that anti-GAD65 antibodies may be associated with CNS neoplastic lesions. Early recognition of anti-GAD antibodies could be of great importance for the early diagnosis and targeted treatment of neoplastic lesions, and could lead to better prognosis.

Stiff-person Syndrome and GAD Antibody-spectrum Disorders: GABAergic Neuronal Excitability, Immunopathogenesis and Update on Antibody Therapies

Although antibodies against Glutamic Acid Decarboxylase (GAD) were originally associated with Stiff Person Syndrome (SPS), they now denote the "GAD antibody-spectrum disorders (GAD-SD)" that include Cerebellar Ataxia, Autoimmune Epilepsy, Limbic Encephalitis, PERM and eye movement disorder. In spite of the unique clinical phenotype that each of these disorders has, there is significant overlapping symptomatology characterized by autoimmune neuronal excitability. In addition to GAD, three other autoantibodies, against glycine receptors, amphiphysin and gephyrin, are less frequently or rarely associated with SPS-SD. Very high serum anti-GAD antibody titers are a key diagnostic feature for all GAD-SD, commonly associated with the presence of GAD antibodies in the CSF, a reduced CSF GABA level and increased anti-GAD-specific IgG intrathecal synthesis denoting stimulation of B-cell clones in the CNS. Because anti-GAD antibodies from the various hyperexcitability syndromes recognize the same dominant GAD epitope, the clinical heterogeneity among GAD-SD patients remains unexplained. The paper highlights the biologic basis of autoimmune hyperexcitability connected with the phenomenon of reciprocal inhibition as the fundamental mechanism of the patients' muscle stiffness and spasms; addresses the importance of high-GAD antibody titers in diagnosis, pinpointing the diagnostic challenges in patients with low-GAD titers or their distinction from functional disorders; and discusses whether high GAD-antibodies are disease markers or pathogenic in the context of their association with reduced GABA level in the brain and CSF. Finally, it focuses on therapies providing details on symptomatic GABA-enhancing drugs and the currently available immunotherapies in a step-by-step approach. The prospects of future immunotherapeutic options with antibody therapies are also summarized.

Autoimmune-Associated Seizures

PURPOSE OF REVIEW

This article focuses on the seizure manifestations and presentations of autoimmune-associated epilepsy and acute symptomatic seizures in autoimmune encephalitis. It discusses the specificity of the various central nervous system autoantibodies and clarifies when their presence can be considered indicative of an immune etiology. Finally, current recommendations regarding patient selection for autoimmune antibody evaluation are reviewed, and an approach to immunotherapy is provided.

RECENT FINDINGS

Although autoimmune seizures are caused by a heterogeneous group of autoantibodies, key features reported in the literature should alert clinicians to the possible diagnosis. In particular, seizure characteristics including frequency, timing, duration, and symptomatology can provide vital clues to help differentiate autoimmune-associated seizures from other causes of epilepsy. Diagnostic certainty also requires an understanding and integration of the spectrum of clinical and paraclinical presentations, and several scoring systems have been developed that may be useful to aid the identification of autoimmune seizures.

SUMMARY

Seizures due to autoimmune etiology are increasingly encountered in clinical practice. It is critical that clinicians recognize immune seizure etiologies early in their course given they are often responsive to immunotherapy but are usually resistant to antiseizure medications. Currently, however, it is unfortunately not uncommon for autoimmune-associated seizure disorders to remain undiagnosed, resulting in missed opportunities to administer effective therapies. Efforts to better understand autoimmune seizure manifestations and treatment strategies are ongoing.

Unusual presentation of stiff-person syndrome in a patient with type 1 diabetes mellitus

Stiff-person syndrome (SPS) is a rare, autoimmune, neurological disorder that often occurs concurrently with other autoimmune disorders, such as type 1 diabetes mellitus, pernicious anaemia, vitiligo and Hashimoto's thyroiditis. It also can manifest as a paraneoplastic syndrome. Although SPS classically presents with truncal and appendicular stiffness and lumbar hyperlordosis, it can present focally in a single limb (termed stiff-limb syndrome). Here, we describe a woman with stiff-limb syndrome who initially presented with concerns about right foot swelling and pain. She also was positive for anti-GAD65 (anti-GAD2) antibodies. With treatment, she regained the ability to drive and ambulate without a walker, and she had a noted reduction in stimulus-induced spasms.

Pathophysiology and Clinical Management of Autoimmune Encephalitis-Associated Seizures

Seizures are a very common manifestation of autoimmune encephalitis (AE), ranging from 33% to 100% depending on the antigen, most often accompanied by other clinical features such as behavioral changes, movement disorders, memory deficits, autoimmune disturbances, and altered levels of consciousness. Unusual seizure frequency, resistance to antiepileptic treatment, and often, definitive response to immunotherapy emphasize the importance for neurologists to consider the probable etiology of immune disorders. Studies on pathogenic mechanisms of autoantibodies have improved the understanding of different pathophysiologies and clinical characteristics of different AE groups. In encephalitis with antibodies to neuronal extracellular antigens, autoantibodies play a direct role in disease pathogenesis. They have access to target antigens and can potentially alter the structure and function of antigens but induce relatively little neuronal death. Prompt immunotherapy is usually very effective, and long-term antiepileptic treatment may not be needed. In contrast, in encephalitis with antibodies against intracellular antigens, autoantibodies may not be directly pathogenic but serve as tumor markers. These autoantibodies cannot reach intracellular target antigens and are considered to result from a T-cell-mediated immune response against antigens released by apoptotic tumor cells, which contain nerve tissue or express neuronal proteins. Neuronal loss is frequently described and predominantly induced through cytotoxic T-cell mechanisms. They often exhibit an inadequate response to immunotherapy and require early tumor treatment. Long-term antiepileptic treatment is usually needed. In conclusion, each neural autoantibody can specifically precipitate seizures. Early proper management of these cases may help prevent neurological deterioration and manage the occurrence of seizures. Consequently, confirmation of the presence of neuronal autoantibodies is strongly recommended even in patients with confirmed AE, as they are not only essential in achieving a good outcome but also may provide evidence for underlying neoplasia.

Auto-destruction of the thyroid gland and coexisting glutamic acid decarboxylase mediated neurological disease in an adolescent: an unusual presentation of autoimmunity

OBJECTIVES

Hashimoto's thyroiditis (HT) is characterized by lymphocytic thyroid infiltration. Gradual thyroid failure can occur due to thyroid cell apoptosis. Rarely neurological autoimmunity due to glutamic acid decarboxylase (GAD) antigen can co exist with HT.

CASE PRESENTATION

A seven-year-old male presented with tiredness, weight loss, frequent falls, tachycardia, firm thyromegaly, and abnormal gait. Biochemical markers and thyroid ultrasound (TUS) showed autoimmune hyperthyroidism. Methimazole (MMI) was started and continued for 2.2 years. MRI brain was normal and neurological symptoms resolved. At nine years, he became hypothyroid and levothyroxine (LT4) was started. Serial TUS showed progressive thyroid atrophy. At 14.8 years, he developed epilepsy and fourth cranial nerve palsy, and diagnosed with GAD-65 central nervous system disease. At 15.3 years, TUS showed complete atrophy of right lobe with involuting left lobe volume.

CONCLUSIONS

This is an unusual form of atrophic thyroiditis (AT) with coexisting neurological autoimmunity. GAD-65 CNS autoimmunity should be considered in children with AT presenting with neurological signs.

Antibody Testing for Neurological Autoimmune Disorders: Evaluation of Best Practices at a Tertiary Referral Center

Background: Autoimmune neurology is a rapidly evolving field of study, where best practices for neurological antibody testing have yet to be determined. The growing number of options for antibody panel testing can create confusion amongst ordering clinicians and lead to ordering several concurrent panels (i.e., overlapping evaluations) or repeat panel evaluations. This study determined the frequency of these evaluations for autoimmune and paraneoplastic disorders and investigated how these practices informed clinical decision making and management.

Methods: This was a retrospective observational study of adult patients presenting to University of Texas Southwestern (UTSW) in 2017 with requests for antibody panels for autoimmune encephalitis and paraneoplastic disorders. Individuals with more than one panel requested were defined as either an overlapping evaluation (more than one panel requested within 14 days) or repeat evaluation (more than one panel requested 14 or more days apart). For those individuals with repeat panel testing, the proportion of panels with a change in antibody status or subsequent changes in clinical diagnosis and decision making were recorded.

Results: There was a total of 813 panels sent on 626 individuals. Twenty percent (126 individuals) had more than one panel requested. Only 10% of individuals had a matched serum and CSF evaluation. Forty-seven overlapping evaluations were performed in 46 (7.3%) of the individuals studied. Fifty-four (8.6%) individuals underwent 70 repeat evaluations encompassing 79 panels (9.7% of total panels ordered). Ten repeat evaluations showed a change in antibody status, of which only two were clinically significant. There was a single case where clinical management was affected by repeat autoantibody evaluation.

Conclusions: Ordering practices for suspected autoimmune encephalitis and paraneoplastic disorders are suboptimal with frequent overlapping antibody panel evaluations and non-paired serum/CSF samples at our center. Repeat autoantibody testing is a commonplace practice yet yielded novel information in only a minority of cases. These new results were, as a rule, clinically irrelevant and changed clinical decision making in <1% of cases. There is limited utility in these practice patterns. Future efforts should be directed at the development and standardization of neurological autoimmune and paraneoplastic autoantibody testing practice standards.

Autoimmune Neurology: The Need for Comprehensive Care

Autoimmune neurology is a rapidly developing specialty driven by an increasing recognition of autoimmunity as the cause for a broad set of neurologic disorders and ongoing discovery of new neural autoantibodies associated with recognizable clinical syndromes. The diversity of clinical presentations, unique pathophysiology, and the complexity of available treatments requires a dedicated multidisciplinary team to diagnose and manage patients. In this article, we focus on antibody-associated autoimmune encephalitis (AE) to illustrate broader themes applicable to the specialty. We discuss common diagnostic challenges including the utilization of clinical assessment tools along with the determination of the prognostic significance of certain autoantibodies, with a focus on implications for long-term management. A growing body of literature demonstrates the long-term cognitive, behavioral, and physical sequelae of AE. Dedicated resources are needed to effectively manage these patients. These resources may be best provided by experienced neurology clinics in partnership with other neurologic subspecialists, as well as psychiatrists, neuropsychologists, and physical medicine and rehabilitation providers.

Volumetric and shape analysis of the hippocampus in temporal lobe epilepsy with GAD65 antibodies compared with non-immune epilepsy

Glutamic acid decarboxylase 65 antibodies (anti-GAD65) have been found in patients with late-onset chronic temporal lobe epilepsy (TLE). No prior neuroimaging studies have addressed how they affect hippocampal volume and shape and how they relate to cognitive abnormalities. We aimed to investigate both brain structure and function in patients with isolated TLE and high anti-GAD65 levels (RIA ≥ 2000 U/ml) compared to 8 non-immune mesial TLE (niTLE) and 8 healthy controls (HC). Hippocampal subfield volume properties were correlated with the duration of the disease and cognitive test scores. The affected hippocampus of GAD-TLE patients showed no volume changes to matched HC whereas niTLE volumes were significantly smaller. Epilepsy duration in GAD-TLE patients correlated negatively with volumes in the presubiculum, subiculum, CA1, CA2-3, CA4, molecular layer and granule cell-molecular layer of the dentate nucleus. We found differences by advanced vertex-wise shape analysis in the anterior hippocampus of the left GAD-TLE compared to HC whereas left niTLE showed bilateral posterior hippocampus deformation. Verbal deficits were similar in GAD-TLE and niTLE but did not correlate to volume changes. These data might suggest a distinct expression of hippocampal structural and functional abnormalities based on the immune response.

Clinical Character of CASPR2 Autoimmune Encephalitis: A Multiple Center Retrospective Study

Objective

To examine the clinical characteristics of autoimmune encephalitis associated with the contactin-associated protein-2 (CASPR2) antibody.

Materials and Methods

Medical records of all patients diagnosed with CASPR2 antibody-associated encephalitis were retrospectively analysed. Data regarding demographic features, neurological symptoms and signs, laboratory tests, imaging results, treatments, and prognosis were collected.

Results

A total of 25 patients aged from 3 to 79 years old were enrolled in this study, with a median age of 43. Eight of 25 (32%) were female, and 17 of 25 (68%) were male. The median age of symptom onset was 42 years old with the course of disease from onset to hospital admission ranging from 2 days to 6 months (median was 17 days). Six patients (6/25) had fever as an onset symptom. During the course of disease, cognitive disturbance was the most common symptom, which was observed in 17 patients (17/25) in total. Eight patients (8/25) met the criteria for limbic encephalitis. Epileptic seizure occurred in six of these eight patients. Four patients (4/25) were diagnosed as Morvan syndrome. All patients were positive for anti-CASPR2 antibody in the serum (1:10-1:300). In six patients, antibodies were detected both in the blood and CSF (1:32-1:100). White blood cell (WBC) counts in the CSF were elevated in eight patients (8/25). The concentration of proteins in CSF increased in 10 patients (ranging from 480 to 1,337.6 mg/dl), decreased in seven patients (ranging from 23.2 to 130.5 mg/dl) and remained at a normal range in the other eight patients (ranging from 150 to 450 mg/dl). Abnormal electroencephalogram (EEG) activities included slow background activity and epileptic patterns. Abnormal signals in the bilateral hippocampus were detected by magnetic resonance imaging (MRI) in three patients presenting cognitive disturbance. In one patient who had limbic encephalitis, increased metabolism of bilateral basal ganglia and the mesial temporal lobe was revealed by PET-CT. Eleven of 15 patients receiving immunotherapy experienced varying degrees of improvement. Relapse occurred in four of 25 patients (4/25) after 2 months.

Conclusion

CASPR-antibody-mediated autoimmune encephalitis is characterized by diverse clinical manifestations. The most prominent conclusion revealed by this retrospective analysis is the involvement of both central and peripheral nerve systems, as well as a lower relapse rate, a good response to immunotherapy, and favorable short-term prognosis after treatment was also demonstrated. Besides, additional work is necessary to evaluate the long-term prognosis.

Case Report: Autoimmune Encephalitis Associated With Anti-glutamic Acid Decarboxylase Antibodies: A Pediatric Case Series

Background: Antibodies against glutamic acid decarboxylase (GAD) are associated with various neurologic conditions described in patients, including stiff person syndrome, cerebellar ataxia, refractory epilepsy, and limbic and extralimbic encephalitis. There have been some case reports and investigations regarding anti-GAD65 antibody-associated encephalitis in adult populations, but pediatric cases are rare. We retrospectively analyzed the clinical data of three anti-GAD65 antibody-positive patients to explore the diversity and clinical features of anti-GAD65 antibody-associated pediatric autoimmune encephalitis.

Methods: The clinical data of a series of three patients positive for anti-GAD65 antibody were retrospectively analyzed. GAD65 antibodies were determined in serum and CSF using a cell-based assay.

Results: All three patients were female, and the onset ages were 4 years and 9 months, 6 years, and 16 years old. Their clinical phenotypes included autoimmune limbic encephalitis, extralimbic encephalitis, and encephalitis combining limbic and extralimbic encephalitis. The clinical symptoms included seizures, memory deficits, drowsiness, dysautonomia, and headache. All patients had abnormal carinal MRI and EEG. All patients received immunotherapy and had transiently good responsiveness, but one patient then experienced relapse. In follow-up, one patient with extralimbic encephalitis recovered completely, while two patients with limbic involvement had poor outcomes with refractory focal epilepsy.

Conclusion: In addition to limbic encephalitis, extralimbic encephalitis is also an important phenotype in patients who are positive for anti-GAD65 antibodies. Early diagnosis and immunotherapy can improve the symptoms. However, patients with limbic encephalitis often have refractory epilepsy in the chronic phase and have a poor long-term outcome.

A Diagnostic Dilemma of Antiglutamic Acid Decarboxylase 65 (Anti-GAD 65) and Mycoplasma Pneumoniae Antibodies in a Girl Presenting with Acute-Onset Obsessive-Compulsive Disorder

Acute-onset obsessive-compulsive disorder can be challenging, especially when triggered by an underlying disease process. Clinicians often turn to Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS), but it is important to consider a broad differential in these patients. We present a case of a 9-year-old girl with acute-onset obsessive-compulsive behavior likely triggered by a post-infectious phenomenon that ultimately resolved following treatment with plasmapheresis.

GAD antibody-spectrum disorders: progress in clinical phenotypes, immunopathogenesis and therapeutic interventions

Antibodies against glutamic acid decarboxylase (GAD), originally linked to stiff person syndrome (SPS), now denote the "GAD antibody-spectrum disorders" (GAD-SD) that also include autoimmune epilepsy, limbic encephalitis, cerebellar ataxia and nystagmus with overlapping symptomatology highlighting autoimmune neuronal excitability disorders. The reasons for the clinical heterogeneity among GAD-antibody associated syndromes remain still unsettled, implicating variable susceptibility of GABAergic neurons to anti-GAD or other still unidentified autoantibodies. Although anti-GAD antibody titers do not correlate with clinical severity, very high serum titers, often associated with intrathecal synthesis of anti-GAD-specific IgG, point to in-situ effects of GAD or related autoantibodies within the central nervous system. It remains, however, uncertain what drives these antibodies, why they persist and whether they are disease markers or have pathogenic potential. The review, focused on these concerns, describes the widened clinical manifestations and overlapping features of all GAD-SD; addresses the importance of GAD antibody titers and potential significance of GAD epitopes; summarizes the biologic basis of autoimmune hyperexcitability; highlights the electrophysiological basis of reciprocal inhibition in muscle stiffness; and provides practical guidelines on symptomatic therapies with gamma-aminobutyric acid-enhancing drugs or various immunotherapies.

Autoantibodies Targeting Intracellular and Extracellular Proteins in Autoimmunity

Detecting autoantibodies provides foundational information for the diagnosis of most autoimmune diseases. An important pathophysiological distinction is whether autoantibodies are directed against extracellular or intracellular proteins. Autoantibodies targeting extracellular domains of proteins, such as membrane receptors, channels or secreted molecules are often directly pathogenic, whereby autoantibody binding to the autoantigen disrupts the normal function of a critical protein or pathway, and/or triggers antibody-dependent cell surface complement killing. By comparison, autoantibodies directed against intracellular proteins are recognized as useful diagnostic biomarkers of abnormal autoimmune activity, but the link between antigenicity and pathogenicity is less straightforward. Because intracellular autoantigens are generally inaccessible to autoantibody binding, for the most part, they do not directly contribute to pathogenesis. In a few diseases, autoantibodies to intracellular targets cause damage indirectly by immune complex formation, immune activation, and other processes. In this review, the general features of and differences between autoimmune diseases segregated on the basis of intracellular or extracellular autoantigens are explored using over twenty examples. Expression profiles of autoantigens in relation to the tissues targeted by autoimmune disease and the temporal appearance of autoantibodies before clinical diagnosis often correlate with whether the respective autoantibodies mostly recognize either intracellular or extracellular autoantigens. In addition, current therapeutic strategies are discussed from this vantage point. One drug, rituximab, depletes CD20+ B-cells and is highly effective for autoimmune disorders associated with autoantibodies against extracellular autoantigens. In contrast, diseases associated with autoantibodies directed predominately against intracellular autoantigens show much more complex immune cell involvement, such as T-cell mediated tissue damage, and require different strategies for optimal therapeutic benefit. Understanding the clinical ramifications of autoimmunity derived by autoantibodies against either intracellular or extracellular autoantigens, or a spectrum of both, has practical implications for guiding drug development, generating monitoring tools, stratification of patient interventions, and designing trials based on predictive autoantibody profiles for autoimmune diseases.