[Autoantibody diagnostics in neurology using native and recombinant antigenic substrates]

Autoimmune encephalitis in children and adolescents

Background

Autoimmune encephalitides with neural and glial antibodies have become an attractive field in neurology because the antibodies are syndrome-specific, explain the pathogenesis, indicate the likelihood of an underlying tumor, and often predict a good response to immunotherapy. The relevance and the management of antibody-associated encephalitides in the pediatric age group are to be discussed.

Main body

Subacutely evolving, complex neuropsychiatric conditions that are otherwise unexplained should raise the suspicion of autoimmune encephalitis. Determination of autoantibodies is the key diagnostic step. It is recommended to study cerebrospinal fluid and serum in parallel to yield highest diagnostic sensitivity and specificity. The most frequently found antibodies are those against the N-methyl-D-asparate receptor, an antigen on the neural cell surface. The second most frequent antibody is directed against glutamic acid decarboxylase 65 kDa, an intracellular protein, often found in chronic conditions with questionable inflammatory activity. Immunotherapy is the mainstay of treatment in autoimmune encephalitides. Steroids, apheresis and intravenous immunoglobulin are first-line interventions. Rituximab or cyclophosphamide are given as second-line treatments. Patients with surface antibodies usually respond well to immunotherapy whereas cases with antibodies against intracellular antigens most often do not.

Conclusion

With few exceptions, the experience in adult patients with autoimmune encephalitides can be applied to patients in the pediatric age range.

Encephalopathy Associated With Neurochondrin Autoantibodies

We determined the prevalence of autoantibodies against an extended number of established and novel neural antigens in children and adolescents with suspected autoimmune encephalitis, epilepsy, single seizures, or marked epileptiform activity in electroencephalography (EEG). Prospectively, 103 patients were recruited aged between 0 and 18 years and 104 controls. A panel of 35 autoantibodies against neural cell-surface and intracellular antigens was screened. Sixteen of 103 patients (15.5%) showed a positive result for 1 or more autoantibodies, compared to 6 of 104 controls (5.8%, P = .02). Neurochondrin was identified as a possible new target of autoantibodies in 3 patients within this cohort, but none in controls. The patients showed severe behavioral disturbances, memory and cognitive impairment, episodes of reduced responsiveness, but no seizures, and normal MRI. Clinical findings, course, and treatment response of these 3 patients are presented.

[Principles of autoimmune and paraneoplastic encephalitis]

The paraneoplastic and autoimmune encephalitides are now well-established entities. Detection of neural autoantibodies enables specific diagnoses, provides information on the underlying disease pathophysiology, immunological treatability and the likelihood of a tumor being the underlying cause. This is true for the "high ranking" neural antibodies that have been established in the context of circumscribed clinical images and in consideration of large control groups, have been found in the same way by other laboratories and they respond to immunotherapy. The immune reaction can be triggered by tumors and virus encephalitides, e.g. N‑methyl-D-aspartate (NMDA) receptor antibodies. In some cases a genetic predisposition has been shown. Some antibodies are formed peripherally, others intrathecally. The route of the antibodies into the brain can be via the blood-brain barrier or cerebrospinal fluid (CSF). In the brain itself, the antibodies lead to an internalization of antigenic receptors, such as NMDA and α‑amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, or to nerve-destroying activation of the classical complement cascade. In other conditions, cytotoxic T cells are at the core of the pathophysiology. For diagnostic purposes, the testing of CSF-serum pairs with broad spectrum antigen panels is recommended. Therapeutically, the aim is to suppress the production of pathogenic antibodies or even to eliminate them directly. A sequence of first-line treatment (steroids, intravenous immunoglobulins and/or apheresis) and second-line treatment (rituximab and/or cyclophosphamide) has been established.

Diagnosing autoimmune encephalitis based on clinical features and autoantibody findings

INTRODUCTION

Autoimmune encephalitides have been accepted as a reproducible and treatable new group of diseases. At present, there is concern that such diagnoses might be made too liberally. Areas covered: This article suggests how to make valid diagnoses. They should consist of three elements: the clinical syndrome, the associated antibody and the presumed cause or predisposition. Recently, an international consortium published formal clinical criteria for autoimmune encephalitides to enable diagnoses even if antibody testing is not (immediately) available and to prevent overinterpretation of questionable antibody results. Antibody testing has greatly benefitted from the introduction of cell-based assays for the demonstration of antibodies against surface antigens. Paraneoplastic or post-infectious situations, side effects of tumor therapies or genetic predispositions help to explain why a patient develops autoimmune encephalitis. Expert opinion: With the application of this three-fold diagnostic system, clinicians can counsel patients regarding therapy and prognosis, while researchers can form meaningful patient cohorts. An operationalization of criteria would be advantageous.

[Myoclonus as a movement disorder]

Myoclonus is often a diagnostic and therapeutic challenge due to its broad phenomenological variability and limited therapeutic options. This article gives a short survey and characterizes in detail two common types of myoclonus, cortical myoclonus and reticular reflex myoclonus. Clinical testing and electrophysiological investigations provide relevant local diagnostic indications for the generating structure(s). Such indications would influence not only the strategies of neuroimaging and laboratory investigations aimed at clarifying the underlying cause but also the selection of drugs to suppress myoclonus.

Frequencies of neuronal autoantibodies in healthy controls: Estimation of disease specificity

OBJECTIVE

To provide an extensive overview on the prevalence of antibodies against neuronal surfaces (neuronal surface antibody [NSAb]) in healthy participants and disease controls.

METHODS

We searched the PubMed database (1974 to October 2016) for studies that analyzed frequencies of 22 different NSAbs in serum or CSF and included controls. Antibody prevalence was calculated for patients with NSAb-mediated disease and controls, including healthy participants, and those with neurologic and nonneurologic diseases. Different assays for antibody detection were compared.

RESULTS

In 309 articles, 743,299 antibody tests for 22 NSAbs were performed, including 30,485 tests for 19 NSAbs in healthy controls (HCs). Of these, 26,423 (86.7%) were tested with current standard methods, usually cell-based assays. Prevalence was very low in HCs (mean 0.23%, absent for 9/19 antibodies), and test numbers ranged from 21 to 3,065 per antibody. One study reported >1,000 healthy participants, and the others contained 21-274 samples. CSF samples were virtually not available from HCs. NSAb prevalence was considerably higher (1.5%) in 69,850 disease controls, i.e., patients not initially suspected to have NSAb-mediated diseases. Antibody determination in controls using nonstandard assays (such as ELISA) resulted in 6% positivity.

CONCLUSIONS

NSAbs are rarely found in healthy participants, particularly with standard detection methods, suggesting high disease specificity and supporting their diagnostic usefulness. Conversely, positive titers in atypical patients might point to the still expanding phenotypic spectrum. Future studies should include more CSF samples, data from HCs, and experimental evidence for antibody pathogenicity.

Multiparametric serological testing in autoimmune encephalitis using computer-aided immunofluorescence microscopy (CAIFM)

Autoantibodies against neuronal cell surface antigens are tightly associated with immunotherapy-responsive autoimmune encephalitis, and a considerable number of corresponding autoantigens has been identified in recent years. Most patients initially present with overlapping symptoms, and a broad range of autoantibodies has to be considered to establish the correct diagnosis and initiate treatment as soon as possible to prevent irreversible and sometimes even life-threatening damage to the brain. Recombinant cell-based immunofluorescence allows to authentically present fragile membrane-associated surface antigens and, in combination with multiparametric analysis in the form of biochip mosaics, has turned out to be highly beneficial for parallel and prompt determination of anti-neuronal autoantibodies and comprehensive differential diagnostics. For the evaluation of recombinant cell-based IIFT, a semi-automated novel function was introduced into an established platform for computer-aided immunofluorescence microscopy. The system facilitates the microscopic analysis of the tests and supports the laboratory personnel in the rapid issuance of diagnostic findings, which is of major importance for autoimmune encephalitis patients since timely initiation of treatment may lead to their full recovery.

Antineuronal antibodies against neurotransmitter receptors and synaptic proteins in schizophrenia: current knowledge and clinical implications

When Eugen Bleuler coined the term 'schizophrenia' he believed that various causes of illness may underlie this disease. Currently, neurodevelopmental abnormalities and consecutive impairments in dopaminergic and glutamatergic neurotransmission are considered as major causes of schizophrenia. However, there are various indications for involvement of immune processes, at least in subgroups of patients. Circulating antineuronal antibodies provide a promising link between the well-described disturbances in neurotransmission and the immune hypothesis of schizophrenia. This review summarizes important studies that have examined the role of glutamate, dopamine, acetylcholine and serotonin receptor autoantibodies, and other antineuronal antibodies against synaptic proteins in the serum of patients diagnosed with schizophrenia. Currently, it is not known whether the presence of antineuronal antibodies in blood should be considered as a causal or disease-modulating factor in schizophrenia. Due to emerging evidence regarding the important role of the blood-brain barrier, combined testing of serum and cerebrospinal fluid is likely to be more appropriate to answer this question than pure serum analyses. We suggest implementation of such testing in first-onset and treatment-resistant patients as part of the diagnostic process. In addition, future clinical trials should evaluate if immunotherapy (e.g. cortisone pulse therapy, intravenous immunoglobulins, plasmapheresis, rituximab, or cyclophosphamide) is helpful in cases with a neuroinflammatory component.