Reversible paraneoplastic limbic encephalitis associated with antibodies to the AMPA receptor

The bidirectional relationship of depression and disturbances in B cell homeostasis: Double trouble

Major depressive disorder (MDD) is a recurrent, persistent, and debilitating neuropsychiatric syndrome with an increasing morbidity and mortality, representing the leading cause of disability worldwide. The dysregulation of immune systems (including innate and adaptive immune systems) has been identified as one of the key contributing factors in the progression of MDD. As the main force of the humoral immunity, B cells have an essential role in the defense against infections, antitumor immunity and autoimmune diseases. Several recent studies have suggested an intriguing connection between disturbances in B cell homeostasis and the pathogenesis of MDD, however, the B-cell-dependent mechanism of MDD remains largely unexplored compared to other immune cells. In this review, we provide an overview of how B cell abnormality regulates the progression of MMD and the potential consequence of the disruption of B cell homeostasis in patients with MDD. Abnormalities of B-cell homeostasis not only promote susceptibility to MDD, but also lead to an increased risk of developing infection, malignancy and autoimmune diseases in patients with MDD. A better understanding of the contribution of B cells underlying MDD would provide opportunities for identification of more targeted treatment approaches and might provide an overall therapeutic benefit to improve the long-term outcomes of patients with MDD.

Thymoma-associated autoimmune encephalitis with myasthenia gravis: Case series and literature review

OBJECTIVES

This comprehensive review aimed to compile cases of patients with thymoma diagnosed with both autoimmune encephalitis (AE) and myasthenia gravis (MG), and describe their clinical characteristics.

METHODS

Clinical records of 3 AE patients in the first affiliated hospital of Sun Yat-sen University were reviewed. All of them were diagnosed with AE between 1 November 2021 and 1 March 2022, and clinical evidence about thymoma and MG was found. All published case reports were searched for comprehensive literature from January 1990 to June 2022.

RESULTS

A total of 18 cases diagnosed with thymoma-associated autoimmune encephalitis (TAAE) and thymoma-associated myasthenia gravis (TAMG) were included in this complication, wherein 3 cases were in the first affiliated hospital of Sun Yat-sen University and the other 15 were published case reports. 5/18 patients had alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antibody (AMPAR-Ab) in their serum and cerebrospinal fluid (CSF). All of them had positive anti-acetylcholine receptor antibody (AChR-Ab). And 12/18 patients showed a positive response to thymectomy and immunotherapy. Besides, thymoma recurrences were detected because of AE onset. And the shortest interval between operation and AE onset was 2 years in patients with thymoma recurrence.

CONCLUSIONS

There was no significant difference in the clinical manifestations between these patients and others with only TAMG or TAAE. TAAE was commonly associated with AMPAR2-Ab. Significantly, AE more commonly heralded thymoma recurrences than MG onset. And the intervals of thymectomy and MG or AE onset had different meanings for thymoma recurrence and prognoses of patients.

Anti-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor encephalitis developed after ovarian cancer cytoreduction surgery: a case report and literature review

BACKGROUND

Anti-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis, a rare subtype of autoimmune encephalitis (AE), is often found associated with tumors such as thymoma, lung cancer, ovarian tumors, and breast cancer, and the tumors were generally detected during the screening process after the encephalitis initiated. The tumor is considered a trigger of AE, but the mechanism remains unclear.

CASE PRESENTATION

A 53-year-old woman presented short-term memory loss two days after the primary cytoreduction for high-grade serous ovarian cancer (HGSOC, FIGO stage IC3). Cell-based assay found AMPAR CluA2 IgG positive in both serum (1:3.2) and cerebrospinal fluid (1:32). Moreover, mild AMPAR GluA1 and strong GluA2 expressions were also found positive in the paraffin sections of ovarian tumor tissue, indicating the ovarian cytoreduction surgery might stimulate the release of receptor antigens into the circulation system. The patient's condition deteriorated within two weeks, developing consciousness and autonomic dysfunction, leading to ICU admission. With oral steroids, intravenous immunoglobulin, plasmapheresis, and rituximab treatment, the patient's consciousness markedly improved after three months.

CONCLUSION

We presented the first case of anti-AMPAR encephalitis developed right after the primary cytoreduction of a patient with HGSOC and retrieved paraneoplastic anti-AMPAR encephalitis cases (n = 66). Gynecologists should pay attention to patients who develop cognitive dysfunction or psychiatric symptoms shortly after the ovarian tumor resection and always include AE in the differentiation diagnosis.

Patient characteristics and outcome in patients with anti-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis

OBJECTIVE

Anti-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis is a rare subtype of autoimmune encephalitis. We report patients diagnosed with anti-AMPAR encephalitis in western China, focusing on their clinical presentations, imaging results, treatment strategies, and prognosis.

METHODS

Data from patients diagnosed with anti-AMPAR encephalitis in the neurology center of West China Hospital from August 2018 to July 2021 were retrospectively collected and analyzed. Based on the diagnostic criteria of autoimmune encephalitis, nine cases were included.

RESULTS

Four patients (44%) were males, and the median age at presentation was 54 years (range, 25-85). Short-term memory loss was the most common initial symptom. Additional types of autoantibodies were identified in three patients. After presentation, four patients were found to have tumors: two with small cell lung cancer, one with ovarian teratoma, and one with thymoma. All patients accepted first-line immune therapy, and follow-up was available from 8 patients (median 20 weeks, range 4-78). At the last follow-up, three patients showed good outcomes (modified Rankin scale [mRS] 0-2; 37.5%). Five patients showed poor outcomes (mRS 3-6; 62.5%): two had minimal changes and remained hospitalized, two had residual severe cognitive impairments, and one patient died during follow-up. Outcomes were worse among patients with tumors. Finally, only one patient experienced relapse during follow-up.

CONCLUSION

Anti-AMPAR encephalitis should be considered in the differential diagnosis for middle- and senior-aged patients who present with predominantly acute or subacute short-term memory impairment. The long-term prognosis is correlated with the presence of a tumor.

From parasomnia to agrypnia excitata - An illustrative case on diagnostic approach

The diagnostic approach to sleep-related movements disorders is seldom discussed. We report a case of fatal familial insomnia who initially presented with persistent limb movements in sleep, which later progressed to a state of agrypnia excitata. Here, the evaluation of abnormal movements in sleep is discussed using a step-by-step diagnostic approach. Although no cure is available for fatal familial insomnia, prompt recognition of this condition is important to facilitate proper management, including the involvement of interdisciplinary neuropalliative care.

Bilateral Hypertrophic Olivary Degeneration as a Paraneoplastic Syndrome of a Poorly Differentiated Carcinoma of the Upper Gastrointestinal Tract: A Case Report and Literature Review

INTRODUCTION

Hypertrophic olivary degeneration (HOD) is a unique form of trans-synaptic neuronal degeneration within the dentato-rubro-olivary pathway which is manifested by the enlargement and hyperintensities of the inferior olivary nucleus in the brain magnetic resonance imaging.

CASE REPORT

We report a 53-year-old man admitted to our emergency department with a history of progressive ataxia and vertigo for 6 months before admission. Neurological examination revealed cerebellar dysfunction, and the brain magnetic resonance imaging showed bilateral HOD without an identifiable causative lesion within the brain or abnormal meningeal enhancement. Cerebrospinal fluid analysis showed mild lymphocytic pleocytosis, elevated protein, and negative cytology. Malignancy and paraneoplastic workup exhibited marked elevation of carbohydrate antigen 19-9 level and para-aortic lymphadenopathy. A histologic examination demonstrated the infiltration of lymph nodes by a malignant, poorly differentiated carcinomatous tumor that arises from the upper gastrointestinal tract. Considering the primary site of the tumor and HOD as a paraneoplastic effect of carcinoma, a FOLFIRINOX regimen, intravenous immunoglobulin, and pulse methylprednisolone were started. A follow-up imaging after 3 months depicted a significant resolution of HOD but the neurological status only mildly improved. The patient developed liver and adrenal metastasis over the following 6 months, culminating in his death.

CONCLUSION

This study strengthens a relationship between HOD and malignancy as a paraneoplastic syndrome and provides a new incentive for further researches to confirm this association.

Pathogenesis, diagnosis and treatment of paraneoplastic neurologic syndromes

Introduction: Paraneoplastic neurological syndromes (PNS) are a rare heterogeneous group of neurological diseases associated with tumors. These syndromes are the result of a cross-reactive immune response against antigens shared by the tumor and the nervous system. The discovery of an increasing number of autoantigens and the identification of tumoral factors leading to a substantial antitumoral immune response makes this topic highly innovative.Areas covered: This review covers the clinical, oncological, pathophysiological aspects of both immunological PNS groups. One is associated with autoantibodies against intracellular onconeural antibodies, which are highly specific for an underlying tumor, although the disease is mainly T-cell mediated. In contrast, PNS associated with pathogenic surface-binding/receptor autoantibodies, which are often responsive to immunosuppressive treatment, may manifest as paraneoplastic and non-paraneoplastic diseases. The most frequent tumors associated with PNS are (small cell) lung cancer, gynecological tumors, thymoma, lymphoma, and, in children, neuroblastoma. A special interest is given to PNS, induced by immune checkpoint-inhibitors (ICIs).Expert opinion: Research in PNS, including the group of ICI-induced PNS provide new insights in both the pathophysiology of PNS and tumor immune interactions and offers new treatment options for this group of severe neurological diseases.

Anti-Alpha-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor Encephalitis: A Review

Anti-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis, a rare subtype of autoimmune encephalitis, was first reported by Lai et al. The AMPAR antibodies target against extracellular epitopes of the GluA1 or GluA2 subunits of the receptor. AMPARs are expressed throughout the central nervous system, especially in the hippocampus and other limbic regions. Anti-AMPAR encephalitis was more common in middle-aged women and most patients had an acute or subacute onset. Limbic encephalitis, a classic syndrome of anti-AMPAR encephalitis, was clinically characterized by a subacute disturbance of short-term memory loss, confusion, abnormal behavior and seizure. Magnetic resonance imaging often showed T2/fluid-attenuated inversion-recovery hyperintensities in the bilateral medial temporal lobe. For suspected patients, paired serum and cerebrospinal fluid (CSF) testing with cell-based assay were recommended. CSF specimen was preferred given its higher sensitivity. Most patients with anti-AMPAR encephalitis were complicated with tumors, such as thymoma, small cell lung cancer, breast cancer, and ovarian cancer. First-line treatments included high-dose steroids, intravenous immunoglobulin and plasma exchange. Second-line treatments, including rituximab and cyclophosphamide, can be initiated in patients who were non-reactive to first-line treatment. Most patients with anti-AMPAR encephalitis showed a partial neurologic response to immunotherapy.

Clinical Review and Prognostic Analysis of α-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionate Receptor-Associated Encephalitis

Purpose: Autoimmune encephalitis (AE) is a heterogeneous neurological autoimmune disorder associated with cognitive and psychiatric symptoms. It can be divided into several subtypes based on autoantibodies. Anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor encephalitis (AMPAR-E) is one of the recently discovered AE subtypes, usually manifesting limbic encephalitis and with a good prognosis. Considering AMPAR-E has been described for the first time, only a few cases with similar antibodies have been reported clinically. We aimed to clarify the clinical course and prognosis of the disease in the light of previous reports. Patients and Methods: We collected data on the diagnosis and treatment of six cases of AMPAR-E, diagnosed at the Qilu Hospital of Shandong University in the past 5 years. We retrospectively analyzed the clinical characteristics of the patients and performed a follow-up of the disease. Results: The patients often presented with limbic encephalitis, which sometimes coexisted with tumors. In addition, immunotherapy had a significant effect on the disease. The clinical outcome was related to factors such as the age of onset, timing of treatment, and presence of tumors. Conclusion: In conclusion, specific antibody tests should be performed as early as possible in suspected cases. Clinicians should actively administer immunotherapy and the management of the co-tumor. In addition, repeat antibody tests and image examinations following discharge from the hospital guide the maintenance protocol of immunotherapy.

The well responsiveness of drug-resistant focal seizures in anti-AMPA2 receptor encephalitis to perampanel treatment

Anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor encephalitis is an anti-neuronal surface antigen autoimmune encephalitis and is relatively rare. Our study evaluated a patient who developed anti-AMPA2 receptor encephalitis with memory deficits and refractory focal seizures as paroxysmal jerking on right face as well as dystonic seizure on right hand. On this patient, the combination treatment of levetiracetam, carbamazepine, and clonazepam, monthly periodic intravenous immunoglobin and immunosuppressive therapies for 5 months was not effective for the focal seizures, while his memory loss was slightly improved. However, adjunctive perampanel treatment led to a rapid relief of seizures. Perampanel is suggested in seizures associated with anti-AMPA receptor encephalitis by directly attenuating nerve hyperexcitability caused by glutamate and Ca2+-permeable GluA4 subunit of AMPA receptors.

Anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor encephalitis: A case report

INTRODUCTION

: Anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) is a subtype of glutamate receptor that mediates most of the fast excitatory neurotransmission in the brain. Anti-AMPAR encephalitis is an autoimmune-mediated neurological disorder, frequently accompanied by the presence of neoplasms, comprising a spectrum of paraneoplastic syndrome.

PATIENT CONCERNS

A 56-year-old man was admitted for deterioration in memory and aberrant psychological behaviors, which lasted for at least 20 days.

DIAGNOSIS

The patient was diagnosed as anti-AMPAR encephalitis and 4 months later, he was diagnosed with small cell lung cancer.

INTERVENTIONS

Once diagnosis for anti-AMPAR encephalitis was confirmed, methylprednisolone was prescribed with initial dose 500 mg/d for 14 days until the patient returned to pre-illness state. Then he was discharged with oral treatment with corticosteroids. Following the diagnosis of small cell lung cancer, he received 5 rounds of chemotherapy, including carboplatin and etoposide.

OUTCOMES

After taken the prescription of Methylprednisolone for anti-AMPAR encephalitis, he returned to pre-illness state and was discharged. In April 21, 2017, after symptoms of respiratory system showed up, he was diagnosed with small cell lung cancer and he eventually died of respiratory failure.

CONCLUSION

Though progress has been made in recent years in diagnosis and treatment for autoimmune encephalitis, it is challenging to diagnose due to the similarity in clinical findings with other autoimmune or infectious encephalitis. In addition, it is necessary for these patients to regularly have tumor screening, considering AMPAR antibody encephalitis is closely associated with neoplasm, and the incidence of paraneoplastic syndrome is 63% to 70%.

Sleep disorders in autoimmune encephalitis

Sleep disorders in people with autoimmune encephalitis have received little attention, probably overshadowed by the presence of other neurological and psychiatric symptoms in this group of conditions. However, sleep disorders are frequent, often severe, and usually persist beyond the acute disease stage, interfering with patients' recovery and quality of life. Because autoimmune encephalitis can affect any brain network involved in sleep initiation and regulation, all types of sleep disorders can occur, with varying distinct associations, frequency, and intensity. Anti-IgLON5 and anti-NMDA receptor encephalitis exemplify two diseases in which sleep disorders are prominent. In anti-IgLON5 disease, sleep disorders were the core symptoms that led to the description of this disease, whereas in anti-NMDA receptor encephalitis, sleep disorders vary according to the disease stage along with other neuropsychiatric symptoms. Comprehensive, systematic, multicentre studies are needed to characterise sleep disorders and their mechanisms in autoimmune encephalitis.

Significance of Autoantibodies in Autoimmune Encephalitis in Relation to Antigen Localization: An Outline of Frequently Reported Autoantibodies with a Non-Systematic Review

Autoantibodies related to central nervous system (CNS) diseases propel research on paraneoplastic neurological syndrome (PNS). This syndrome develops autoantibodies in combination with certain neurological syndromes and cancers, such as anti-HuD antibodies in encephalomyelitis with small cell lung cancer and anti-Yo antibodies in cerebellar degeneration with gynecological cancer. These autoantibodies have roles in the diagnosis of neurological diseases and early detection of cancers that are usually occult. Most of these autoantibodies have no pathogenic roles in neuronal dysfunction directly. Instead, antigen-specific cytotoxic T lymphocytes are thought to have direct roles in neuronal damage. The recent discoveries of autoantibodies against neuronal synaptic receptors/channels produced in patients with autoimmune encephalomyelitis have highlighted insights into our understanding of the variable neurological symptoms in this disease. It has also improved our understanding of intractable epilepsy, atypical psychosis, and some demyelinating diseases that are ameliorated with immune therapies. The production and motility of these antibodies through the blood-brain barrier into the CNS remains unknown. Most of these recently identified autoantibodies bind to neuronal and glial cell surface synaptic receptors, potentially altering the synaptic signaling process. The clinical features differ among pathologies based on antibody targets. The investigation of these antibodies provides a deeper understanding of the background of neurological symptoms in addition to novel insights into their basic neuroscience.

Experimental Models of Neuroimmunological Disorders: A Review

Immune-mediated inflammatory diseases of the central nervous system (CNS) are a group of neurological disorders in which inflammation and/or demyelination are induced by cellular and humoral immune responses specific to CNS antigens. They include diseases such as multiple sclerosis (MS), neuromyelitis optica spectrum disorders (NMOSD), acute disseminated encephalomyelitis (ADEM) and anti-NMDA receptor encephalitis (NMDAR encephalitis). Over the years, many in vivo and in vitro models were used to study clinical, pathological, physiological and immunological features of these neuroimmunological disorders. Nevertheless, there are important aspects of human diseases that are not fully reproduced in the experimental models due to their technical limitations. In this review, we describe the preclinical models of neuroimmune disorders, and how they contributed to the understanding of these disorders and explore potential treatments. We also describe the purpose and limitation of each one, as well as the recent advances in this field.

Paraneoplastic Diseases of the Central Nervous System

Paraneoplastic neurological syndromes are nonmetastatic complications of malignancy secondary to immune-mediated neuronal dysfunction or death. Pathogenesis may occur from cell surface binding of antineuronal antibodies leading to dysfunction of the target protein, or from antibodies binding against intracellular antigens which ultimately leads to cell death. There are several classical neurological paraneoplastic phenotypes including subacute cerebellar degeneration, limbic encephalitis, encephalomyelitis, and dorsal sensory neuropathy. The patient’s clinical presentations may be suggestive to the treating clinician as to the specific underlying paraneoplastic antibody. Specific antibodies often correlate with the specific underlying tumor type, and malignancy screening is essential in all patients with paraneoplastic neurological disease. Prompt initiation of immunotherapy is essential in the treatment of patients with paraneoplastic neurological disease, often more effective in cell surface antibodies in comparison to intracellular antibodies, as is removal of the underlying tumor.

Limbic encephalitis associated with AMPA receptor and CRMP5 antibodies: A case report and literature review

AIMS

AMPA receptor (AMPAR) and CRMP5 antibodies are relatively uncommon in limbic encephalitis, and patients with both antibodies are rare. We recently treated such a patient, but the patient died after active treatment. To further understand this disease, we conducted a case report and literature review.

DISCUSSIONS

To date, five encephalitis patients, including our patient, have been found to be positive for AMPAR and CRMP5 antibodies. The male-to-female ratio of the reported cases is 4:1, and the age range is 26 and 62 years old. All five patients presented with various neuropsychiatric symptoms, including insomnia, abnormal behavior, seizures, extrapyramidal symptoms, and autonomic dysfunction. Four patients had tumors (three invasive thymomas and one suspected lymphoma), and three cases died within a short period of time. No tumor was detected in one of the patients during the follow-up period; however, after active treatment, the outcome was poor, and the patient developed cachexia. One patient had good response to immunotherapy and tumor therapy and successfully returned to work.

CONCLUSIONS

The prognosis of encephalitis associated with AMPAR and CRMP5 antibodies is worse than that of the encephalitis associated with AMPAR antibodies alone. The most likely cause is that this encephalitis is more likely to be accompanied by malignant tumors, leading to a poor prognosis. In addition, it may also be due to some synergistic mechanisms between the two antibodies. Further studies aimed at the prognosis of this type of encephalitis are warranted.

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

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

Clinical variants of limbic encephalitis

The clinical picture of immunomediator disorders of the central nervous system resulting from autoimmune or paraneoplastic processes is often represented by the limbic symptom complex or limbic encephalitis. The article gives a brief description of these conditions, allocated to a separate nosological group in 2007. The symptoms of limbic encephalitis include mental disorders and epileptic seizures of both convulsive and non-convulsive spectrum, up to epileptic status. Four clinical cases representative of different variants of limbic encephalitis are presented in this study, along with the discussion of epidemiology, differential diagnostics, and generally accepted patient management strategies. The diagnosis of limbic encephalitis was made on clinical grounds alone in three cases and on the presence of antibodies to N-Methyl-d-aspartic acid receptors in one case. A combination of glucocorticoid pulse therapy with prolonged use of valproic acid was successfully applied for the treatment of limbic encephalitis with non-convulsive epileptic status. Plasmapheresis was used for the treatment of limbic encephalitis with recurrent focal non-motor attacks with and without loss of consciousness, as well as for limbic encephalitis with focal motor attacks. Presented cases emphasize the need to increase the awareness of physicians of various specialties to autoimmune disorders of the nervous system. In addition, it highlights the necessity of complete diagnostic workup for a patient with impaired consciousness of unclear etiology.

Patient characteristics and outcome associations in AMPA receptor encephalitis

Antibody-mediated encephalitis defines a class of diseases wherein antibodies directed at cell-surface receptors are associated with behavioral and cognitive disturbances. One such recently described encephalitis is due to antibodies directed at alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR). This entity is exceptionally rare and its clinical phenotype incompletely described. We present findings from two cases of AMPAR encephalitis that exemplify variability in the disease spectrum, and summarize findings in published cases derived from a systematic literature review. When all patients are considered together, the presence of psychiatric symptoms at presentation portended a poor outcome and was associated with the presence of a tumor. Furthermore, we provide evidence to suggest that the topography of magnetic resonance imaging abnormalities in reported cases mirrors the distribution of AMPARs in the human brain. The potential for neurological improvement following immunomodulatory therapy together with the favorable outcome reported in most cases emphasizes the importance of testing for autoantibodies against neuronal cell-surface proteins, including AMPAR, in patients with clinical and neuroimaging findings suggestive of autoimmune encephalitis. Close attention to the clinical phenotype may inform the presence of malignancy and long-term prognosis.

Management of Autoimmune Encephalitis: An Observational Monocentric Study of 38 Patients

Over the last years the clinical picture of autoimmune encephalitis has gained importance in neurology. The broad field of symptoms and syndromes poses a great challenge in diagnosis for clinicians. Early diagnosis and the initiation of the appropriate treatment is the most relevant step in the management of the patients. Over the last years advances in neuroimmunology have elucidated pathophysiological basis and improved treatment concepts. In this monocentric study we compare demographics, diagnostics, treatment options and outcomes with knowledge from literature. We present 38 patients suffering from autoimmune encephalitis. Antibodies were detected against NMDAR and LGI1 in seven patients, against GAD in 6 patients) one patient had coexisting antibodies against GABA_A and GABA_B), against CASPR2, IGLON5, YO, Glycine in 3 patients, against Ma-2 in 2 patients, against CV2 and AMPAR in 1 patient; two patients were diagnosed with hashimoto encephalitis with antibodies against TPO/TG. First, we compare baseline data of patients who were consecutively diagnosed with autoimmune encephalitis from a retrospective view. Further, we discuss when to stop immunosuppressive therapy since how long treatment should be performed after clinical stabilization or an acute relapse is still a matter of debate. Our experiences are comparable with data from literature. However, in contrary to other experts in the field we stop treatment and monitor patients very closely after tumor removal and after rehabilitation from first attack.

The role of the laboratory in the expanding field of neuroimmunology: Autoantibodies to neural targets

Accelerated identification of autoantibodies associated with previously idiopathic neurological disease has provided insights into disease mechanisms, enhanced understanding of neurological function, and opportunities for improved therapeutic interventions. The role of the laboratory in the expanding field of neuroimmunology is critical as specific autoantibody identification provides guidance to clinicians in diagnosis, prognosis, tumor search strategies, and therapeutic interventions. The number of specific autoantibodies identified continues to increase and newer testing strategies increase efficiencies in the laboratory and availability to clinicians. The need for broadly targeted efficient testing is underscored by the variability in clinical presentation and tumor associations attributable to a specific autoantibody, and conversely the various autoantibody specificities that can be the cause of a given clinical presentation. While many of the antineural antibodies were first recognized in the setting of neoplastic disease, idiopathic autoimmune neurological disease in the absence of underlying tumor is increasingly recognized. Appropriation of therapeutic modalities used to treat autoimmune disease to treat these autoantibody mediated neurological diseases has improved patient outcomes. Interaction between clinicians and laboratorians is critical to our understanding of these diseases and optimization of the clinical benefits of our increasing knowledge in neuroimmunology.

Anti-AMPA receptor encephalitis associated with Medullary thyroid cancer

AMPA receptor (AMPAR) antibodies are a group of recently discovered antibodies which target the neuronal synaptic proteins causing B-cell (immune) mediated neuronal damage, resulting in various neurologic syndromes depending on the area of central nervous system involvement. These syndromes are mostly reversible if treated early. Tumour association has been reported in up to 60% of cases in the most recent case series with lung, breast, ovarian cancers and thymomas being the most commonly associated malignancies with these antibodies. We present here the first case of AMPAR encephalitis associated with medullary thyroid cancer. Our patient presented with cognitive dysfunction and behavioural changes over a period of 3 weeks, with a full recovery after starting immunotherapy, once the diagnosis of AMPAR limbic encephalitis was established. This case highlights the importance of early diagnosis and management of AMPAR encephalitis as these patients respond well to immunotherapy and can have an almost complete recovery.

Clinical Relapse of Anti-AMPAR Encephalitis Associated with Recurrence of Thymoma

We report a rare case of anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis presenting clinical relapse in association with recurrence of thymoma. Anti-AMPAR encephalitis is an autoimmune-mediated neurological disease, frequently accompanied by the presence of neoplasms, thus comprising the spectrum of paraneoplastic syndrome. A patient had been in remission for 34 months showed clinical relapse 3 months after the detection of recurrent thymoma. Clinical relapse of anti-AMPAR encephalitis after the recurrence of an initially detected neoplasm has not been previously reported. Our case therefore highlights the pathogenic relevance of specific tumor antigens as a trigger of anti-AMPAR antibody production and induction of the disease.

Neuronal Surface Autoantibodies in Neuropsychiatric Disorders: Are There Implications for Depression?

Autoimmune diseases are affecting around 7.6-9.4% of the general population. A number of central nervous system disorders, including encephalitis and severe psychiatric disorders, have been demonstrated to associate with specific neuronal surface autoantibodies (NSAbs). It has become clear that specific autoantibodies targeting neuronal surface antigens and ion channels could cause severe mental disturbances. A number of studies have focused or are currently investigating the presence of autoantibodies in specific mental conditions such as schizophrenia and bipolar disorders. However, less is known about other conditions such as depression. Depression is a psychiatric disorder with complex etiology and pathogenesis. The diagnosis criteria of depression are largely based on symptoms but not on the origin of the disease. The question which arises is whether in a subgroup of patients with depression, the symptoms might be caused by autoantibodies targeting membrane-associated antigens. Here, we describe how autoantibodies targeting membrane proteins and ion channels cause pathological effects. We discuss the physiology of these antigens and their role in relation to depression. Finally, we summarize a number of studies detecting NSAbs with a special focus on cohorts that include depression diagnosis and/or show depressive symptoms.

Prevalence and clinical characteristics of serum neuronal cell surface antibodies in first-episode psychosis: a case-control study

BACKGROUND

Psychosis is a common presenting feature in antibody-mediated encephalitis, for which prompt recognition and treatment usually leads to remission. We aimed to investigate whether people with circumscribed schizophrenia-like illnesses have such antibodies-especially antibodies against the N-methyl-D-aspartate receptor (NMDAR)-more commonly than do healthy controls.

METHODS

We recruited patients aged 14-35 years presenting to any of 35 mental health services sites across England with first-episode psychosis, less than 6 weeks of treatment with antipsychotic medication, and a score of 4 or more on at least one selected Positive and Negative Syndrome Scale (PANSS) item. Patients and controls provided venous blood samples. We completed standardised symptom rating scales (PANSS, ACE-III, GAF) at baseline, and tested serum samples for antibodies against NMDAR, LGI1, CASPR2, the GABAA receptor, and the AMPA receptor using live cell-based assays. Treating clinicians assessed outcomes of ICD diagnosis and functioning (GAF) at 6 months. We included healthy controls from the general population, recruited as part of another study in Cambridge, UK.

FINDINGS

Between Feb 1, 2013, and Aug 31, 2014, we enrolled 228 patients with first-episode psychosis and 105 healthy controls. 20 (9%) of 228 patients had serum antibodies against one or more of the neuronal cell surface antibodies compared with four (4%) of 105 controls (unadjusted odds ratio 2·4, 95% CI 0·8-7·3). These associations remained non-significant when adjusted for current cigarette smoking, alcohol consumption, and illicit drug use. Seven (3%) patients had NMDAR antibodies compared with no controls (p=0·0204). The other antibodies did not differ between groups. Antibody-positive patients had lower PANSS positive, PANSS total, and catatonia scores than did antibody-negative patients. Patients had comparable scores on other PANSS items, ACE-III, and GAF at baseline, with no difference in outcomes at 6 months.

INTERPRETATION

Some patients with first-episode psychosis had antibodies against NMDAR that might be relevant to their illness, but did not differ from patients without NMDAR antibodies in clinical characteristics. Our study suggests that the only way to detect patients with these potentially pathogenic antibodies is to screen all patients with first-episode psychosis at first presentation.

FUNDING

Medical Research Council.

Anti N-methyl-D-aspartate receptor encephalitis: a game-changer?

INTRODUCTION

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is an inflammatory disorder of the brain that has garnered significant interest within the medical and lay communities. There is a need for formal guidelines to assist physicians in identifying patients who should undergo testing for NMDAR encephalitis, recognizing the high potential for this potentially treatable disease to mimic more common disorders, and consequently remain undiagnosed.

AREAS COVERED

This review highlights the impact of the discovery of NMDAR encephalitis on the fields of neurology and psychiatry, and discusses the steps that are necessary to improve recognition and treatment of NMDAR encephalitis. Expert commentary: While much progress has been made in our understanding of NMDAR encephalitis, much work remains to be done to delineate the underlying disease mechanisms and their relevance to brain function.

NMDA Receptor Internalization by Autoantibodies: A Reversible Mechanism Underlying Psychosis?

Since the early 1990s it has been postulated that hypofunction of N-methyl-d-aspartate (NMDA) receptors in brain networks supporting perception and cognition underlies schizophrenic psychosis. Recently, NMDA receptor hypofunction was described in patients with psychotic manifestations who exhibited autoantibodies binding the GluN1 subunit of the receptor, and who improved when the level of these antibodies was lowered by immunomodulation. In this disorder, NMDA receptor antibodies decrease the availability of NMDA receptors by internalizing them. In this opinion article, we review this mechanism as well as data supporting or refuting the possibility that this disorder or similar autoimmune disorders affecting synaptic proteins, which are therefore treatable with immunomodulation, could account for some cases of idiopathic psychosis. We also suggest methodological approaches to clarify this issue.

Neuronal central nervous system syndromes probably mediated by autoantibodies

In the last few years, a rapidly growing number of autoantibodies targeting neuronal cell-surface antigens have been identified in patients presenting with neurological symptoms. Targeted antigens include ionotropic receptors such as N-methyl-d-aspartate receptor or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor, metabotropic receptors such as mGluR1 and mGluR5, and other synaptic proteins, some of them belonging to the voltage-gated potassium channel complex. Importantly, the cell-surface location of these antigens makes them vulnerable to direct antibody-mediated modulation. Some of these autoantibodies, generally targeting ionotropic channels or their partner proteins, define clinical syndromes resembling models of pharmacological or genetic disruption of the corresponding antigen, suggesting a direct pathogenic role of the associated autoantibodies. Moreover, the associated neurological symptoms are usually immunotherapy-responsive, further arguing for a pathogenic effect of the antibodies. Some studies have shown that some patients' antibodies may have structural and functional in vitro effects on the targeted antigens. Definite proof of the pathogenicity of these autoantibodies has been obtained for just a few through passive transfer experiments in animal models. In this review we present existing and converging evidence suggesting a pathogenic role of some autoantibodies directed against neuronal cell-surface antigens observed in patients with central nervous system disorders. We describe the main clinical symptoms characterizing the patients and discuss conflicting arguments regarding the pathogenicity of these antibodies.

Anti-NMDAR encephalitis and other glutamate and GABA receptor antibody encephalopathies

Over the last few year, antibodies to various central nervous system receptors, particularly the glutamate and γ-aminobutyric acid (GABA) receptors, have been found to be associated with autoimmune neurologic disorders. The receptors include the N-methyl-d-aspartate receptor (NMDAR), the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), the metabotropic glutamate receptors (mGluRs), and GABA type A and B receptors (respectively GABAAR and GABABR). Compared to the previously described paraneoplastic antibodies directed at intracellular targets, the patients with receptor antibodies are often younger, they less frequently have malignancies, and they respond better to immunotherapy. Many of the patients have limbic encephalitis with amnesia, disorientation, seizures, and psychological or psychiatric symptoms, but those with NMDAR antibodies usually develop a more widespread form of encephalitis, often leading to a decrease in consciousness and requirement for long-term intensive care treatment. The autoantibodies bind directly to the synaptic or extrasynaptic receptors on the membrane surface, and have direct effects on signal transduction in central synapses. These conditions are very important to recognize as the symptoms and complications can be fatal when not treated in time, whereas with immunotherapy many patients recover considerably.

Autoantibodies to central nervous system neuronal surface antigens: psychiatric symptoms and psychopharmacological implications

RATIONALE

Autoantibodies to central nervous system (CNS) neuronal surface antigens have been described in association with autoimmune encephalopathies which prominently feature psychiatric symptoms in addition to neurological symptoms. The potential role of these autoantibodies in primary psychiatric diseases such as schizophrenia or bipolar affective disorder is of increasing interest.

OBJECTIVES

We aimed to review the nature of psychiatric symptoms associated with neuronal surface autoantibodies, in the context of autoimmune encephalopathies as well as primary psychiatric disorders, and to review the mechanisms of action of these autoantibodies from a psychopharmacological perspective.

RESULTS

The functional effects of the autoantibodies on their target antigens are described; their clinical expression is at least in part mediated by their effects on neuronal receptor function, primarily at the synapse, usually resulting in receptor hypofunction. The psychiatric effects of the antibodies are related to known functions of the receptor target or its complexed proteins, with reference to supportive genetic and pharmacological evidence where relevant. Evidence for a causal role of these autoantibodies in primary psychiatric disease is increasing but remains controversial; relevant methodological controversies are outlined. Non-receptor-based mechanisms of autoantibody action, including neuroinflammatory mechanisms, and therapeutic implications are discussed.

CONCLUSIONS

An analysis of the autoantibodies from a psychopharmacological perspective, as endogenous, bioactive, highly specific, receptor-targeting molecules, provides a valuable opportunity to understand the neurobiological basis of associated psychiatric symptoms. Potentially, new treatment strategies will emerge from the improving understanding of antibody-antigen interaction within the CNS.

Limbic encephalitis due to GABAB and AMPA receptor antibodies: a case series

BACKGROUND

Two novel antibodies (abs) directed to γ-aminobutyric acid B receptor (GABA(B)R) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) in patients with limbic encephalitis (LE) were first described by the Philadelphia/Barcelona groups and confirmed by the Mayo group. We present a novel series for further clinical and paraclinical refinement.

METHODS

Serum and cerebrospinal fluid samples from a diagnostic laboratory were selected if found to be positive for GABA(B)R or AMPAR abs within a broad antineuronal ab panel. Data were retrospectively compiled.

RESULTS

In 10 patients, we detected abs to GABA(B)R. Median age was 70 years. Five of them were diagnosed with small cell lung cancer (SCLC). Intrathecal GABA(B)R ab synthesis was found in all six patients with sufficient data available (median ab-index: 76.8). On MRI, we found bilateral mediotemporal and in two cases cortical abnormalities. EEG revealed encephalopathy, partly with epileptiform discharges. Five patients received immunotherapy, two patients tumour treatment and three both therapies. Three patients died, in five patients cognitive functions declined, one patient improved slightly and one patient fully recovered. AMPAR abs were detected in three patients with mnestic disturbances. Median age was 60.7 years. The only female patient was diagnosed with ovarian cancer. None of the patients had intrathecal ab synthesis. MRI findings showed bilateral mediotemporal abnormalities. EEG was normal in all patients. Two of the three immunologically treated patients improved, one patient stabilised on a low level.

DISCUSSION

GABA(B)R and AMPAR abs are well associated with LE. GABA(B)R abs lead to severe clinical, neuroradiological and EEG abnormalities with poorer outcome.

Limbic Encephalitis: Potential Impact of Adaptive Autoimmune Inflammation on Neuronal Circuits of the Amygdala

Limbic encephalitis is characterized by adaptive autoimmune inflammation of the gray matter structures of the limbic system. It has recently been identified as a major cause of temporal lobe epilepsy accompanied by progressive declarative – mainly episodic – ­memory disturbance as well as a variety of rather poorly defined emotional and behavioral changes. While autoimmune inflammation of the hippocampus is likely to be responsible for declarative memory disturbance, consequences of autoimmune inflammation of the amygdala are largely unknown. The amygdala is central for the generation of adequate homoeostatic behavioral responses to emotionally significant external stimuli following processing in a variety of parallel neuronal circuits. Here, we hypothesize that adaptive cellular and humoral autoimmunity may target and modulate distinct inhibitory or excitatory neuronal networks within the amygdala, and thereby strongly impact processing of emotional stimuli and corresponding behavioral responses. This may explain some of the rather poorly understood neuropsychiatric symptoms in limbic encephalitis.

Differences in epileptic symptoms depending on the type of autoimmune-mediated limbic encephalitis

Limbic encephalitis (LE) is an inflammatory disease of the central nervous system that is characterized by the selective involvement of limbic structures. The clinical manifestations of LE include the acute or sub-acute onset of recent memory disorders, mental disorders and seizures. Autoimmune-mediated LE is a major type of non-infectious LE; seizure is a hallmark of this type of LE. The treatment of epilepsy, which is a key factor that affects the prognosis of LE patients, warrants special attention. Understanding the characteristics of epilepsy caused by autoimmune-mediated LE and providing the appropriate treatment will help to improve patients' outcomes. In this article, we extensively review the literature related to autoimmune-mediated LE epidemiology, mechanisms, characteristics and seizure frequency and onset, and we discuss the possible diagnosis and treatment of this disease.

Encephalitis and AMPA receptor antibodies: Novel findings in a case series of 22 patients

OBJECTIVE

We report the clinical features, comorbidities, and outcome of 22 newly identified patients with antibodies to the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR).

METHODS

This was a retrospective review of patients diagnosed between May 2009 and March 2014. Immunologic techniques have been reported previously.

RESULTS

Patients' median age was 62 years (range 23-81; 14 female). Four syndromes were identified: 12 (55%) patients presented with distinctive limbic encephalitis (LE), 8 (36%) with limbic dysfunction along with multifocal/diffuse encephalopathy, one with LE preceded by motor deficits, and one with psychosis with bipolar features. Fourteen patients (64%) had a tumor demonstrated pathologically (5 lung, 4 thymoma, 2 breast, 2 ovarian teratoma) or radiologically (1 lung). Additional antibodies occurred in 7 patients (3 onconeuronal, 1 tumor-related, 2 cell surface, and 1 tumor-related and cell surface), all with neurologic symptoms or tumor reflecting the concurrent autoimmunity. Treatment and outcome were available from 21 patients (median follow-up 72 weeks, range 5-266): 5 had good response to immunotherapy and tumor therapy, 10 partial response, and 6 did not improve. Eventually 5 patients died; all had a tumor or additional paraneoplastic symptoms related to onconeuronal antibodies. Coexistence of onconeuronal antibodies predicted a poor outcome (p = 0.009).

CONCLUSION

Anti-AMPAR encephalitis usually manifests as LE, can present with other symptoms or psychosis, and is paraneoplastic in 64% of cases. Complete and impressive neurologic improvement can occur, but most patients have partial recovery. Screening for a tumor and onconeuronal antibodies is important because their detection influences outcome.

Autoimmune channelopathies in paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes and autoimmune encephalitides are immune neurological disorders occurring or not in association with a cancer. They are thought to be due to an autoimmune reaction against neuronal antigens ectopically expressed by the underlying tumour or by cross-reaction with an unknown infectious agent. In some instances, paraneoplastic neurological syndromes and autoimmune encephalitides are related to an antibody-induced dysfunction of ion channels, a situation that can be labelled as autoimmune channelopathies. Such functional alterations of ion channels are caused by the specific fixation of an autoantibody upon its target, implying that autoimmune channelopathies are usually highly responsive to immuno-modulatory treatments. Over the recent years, numerous autoantibodies corresponding to various neurological syndromes have been discovered and their mechanisms of action partially deciphered. Autoantibodies in neurological autoimmune channelopathies may target either directly ion channels or proteins associated to ion channels and induce channel dysfunction by various mechanisms generally leading to the reduction of synaptic expression of the considered channel. The discovery of those mechanisms of action has provided insights on the regulation of the synaptic expression of the altered channels as well as the putative roles of some of their functional subdomains. Interestingly, patients' autoantibodies themselves can be used as specific tools in order to study the functions of ion channels. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Neuronal surface antibody-mediated autoimmune encephalitis

In the past few years, many autoimmune encephalitides have been identified, with specific clinical syndromes and associated antibodies against neuronal surface antigens. There is compelling evidence that many of these antibodies are pathogenic and most of these encephalitides are highly responsive to immunotherapies. The clinical spectra of some of these antibody-mediated syndromes, especially those reported in only a few patients, are evolving. Others, such as anti-N-methyl-D-aspartate (NMDA) receptor encephalitis, are well characterized. Diagnosis involves recognizing the specific syndromes and identifying the antibody in a patient's cerebrospinal fluid (CSF) and/or serum. These syndromes are associated with variable abnormalities in CSF, magnetic resonance imaging, and electroencephalography. Treatment is often multidisciplinary and should be focused upon neutralizing the effects of antibodies and eliminating their source. Overlapping disorders have been noted, with some patients having more than one neurologic autoimmune disease. In other patients, viral infections such as herpes simplex virus encephalitis trigger robust antineuronal autoimmune responses.

Autoimmune encephalitis update

Cancer-associated immune-mediated disorders of the central nervous system are a heterogeneous group. These disorders include the classic paraneoplastic neurologic disorders and the more recently described autoimmune encephalitis associated with antibodies to neuronal cell-surface or synaptic receptors that occur with and without a cancer association. Autoimmune encephalitis is increasingly recognized as the cause of a variety of neuropsychiatric syndromes that can be severe and prolonged. In contrast to the classic paraneoplastic disorders that are poorly responsive to tumor treatment and immunotherapy, autoimmune encephalitis often responds to these treatments, and patients can have full or marked recoveries. As early treatment speeds recovery, reduces disability, and decreases relapses that can occur in about 20% of cases, it is important that the immune pathogenesis of these disorders is recognized.

Molecular and cellular mechanisms underlying anti-neuronal antibody mediated disorders of the central nervous system

Over the last decade multiple autoantigens located on the plasma membrane of neurons have been identified. Neuronal surface antigens include molecules directly involved in neurotransmission and excitability. Binding of the antibody to the antigen may directly alter the target protein's function, resulting in neurological disorders. The often striking reversibility of symptoms following early aggressive immunotherapy supports a pathogenic role for autoantibodies to neuronal surface antigens. In order to better understand and treat these neurologic disorders it is important to gain insight in the underlying mechanisms of antibody pathogenicity. In this review we discuss the clinical, circumstantial, in vitro and in vivo evidence for neuronal surface antibody pathogenicity and the possible underlying cellular and molecular mechanisms. This review shows that antibodies to neuronal surface antigens are often directed at conformational epitopes located in the extracellular domain of the antigen. The conformation of the epitope can be affected by specific posttranslational modifications. This may explain the distinct clinical phenotypes that are seen in patients with antibodies to antigens that are expressed throughout the brain. Furthermore, it is likely that there is a heterogeneous antibody population, consisting of different IgG subtypes and directed at multiple epitopes located in an immunogenic region. Binding of these antibodies may result in different pathophysiological mechanisms occurring in the same patient, together contributing to the clinical syndrome. Unraveling the predominant mechanism in each distinct antigen could provide clues for therapeutic interventions.

Antigenic and mechanistic characterization of anti-AMPA receptor encephalitis

Objective

Anti-AMPAR encephalitis is a recently discovered disorder characterized by the presence of antibodies in serum or cerebrospinal fluid against the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. Here, we examine the antigenic specificity of anti-AMPAR antibodies, screen for new patients, and evaluate functional effects of antibody treatment of neurons.

Methods

We developed a fusion protein (FP)-based western blotting test for anti-AMPAR encephalitis antibodies. Antibody specificity was also evaluated using immunocytochemistry of HEK293 cells expressing deletion mutants of AMPAR subunits. Purified patient immunoglobulin G (IgG) or AMPAR antibody-depleted IgG was applied to live neuronal cultures; amplitude and frequency of miniature excitatory postsynaptic currents (mEPSCs) were measured to evaluate functional effects of antibodies.

Results

Using both immunocytochemistry and FP western blots, we defined an antigenic region of the receptor in the bottom lobe of the amino terminal domain. Additionally, we used FPs to screen 70 individuals with neurologic symptoms of unknown cause and 44 patients with no neurologic symptoms or symptoms of known neuroimmunological origin for anti-AMPAR antibodies. Fifteen of the 70 individuals had anti-AMPAR antibodies, with broader antigenic reactivity patterns. Using purified IgG from an individual of the original cohort of anti-AMPAR encephalitis patients and a newly discovered patient, we found that application of IgG from either patient cohort caused an AMPAR antibody-dependent decrease in the amplitude and frequency of mEPSCs in cultured neurons.

Interpretation

These results indicate that anti-AMPAR antibodies are widespread and functionally relevant; given the robust response of patients to immunomodulation, this represents a significant treatable patient population.