Anti-mGluR1 encephalitis: Case illustration and systematic review

Neuronal antibodies in nonparaneoplastic autoimmune cerebellar ataxias

PURPOSE OF REVIEW

To describe relevant advances in nonparaneoplastic autoimmune cerebellar ataxias (ACA) with neuronal antibodies.

RECENT FINDINGS

Apart from metabotropic glutamate receptor 1(mGluR1) antibodies, in recent years, the number of neuronal antibodies against surface antigens in ACA has increased with the description of glutamate kainate receptor subunit 2 (GluK2) antibodies in young patients with cerebellitis. Around 20% of patients with contactin-associated protein-like 2 (CASPR2) encephalitis also present prominent cerebellar ataxia. However, isolate cerebellar ataxia is unusual (<4%). Outcome in patients with neuronal antibodies against surface antigens remains suboptimal despite the cerebellar ataxia probably is antibody-mediated.Concerning neuronal antibodies against intracellular antigens, up to 25% of patients with glutamic acid decarboxylase (GAD) antibodies present transient episodes of vertigo or diplopia that antedate the development of the ACA. There is in-vitro evidence that septin-5 is partially exposed to the membrane and the antibodies may interfere with septin-5 function. The clinical significance of the remaining antibodies against intracellular antigens remains unclear.

SUMMARY

The number of antibodies against surface antigens is increasing in ACA, but the response to the immunotherapy remains suboptimal. More studies are needed to clarify the role of most of the antibodies against intracellular antigens described in these patients.

Cerebellar encephalitis associated with anti-mGluR1 antibodies: a case report and comprehensive literature review

Anti-metabotropic glutamate receptor 1 encephalitis is an uncommon autoimmune condition characterized by a subacute onset of cerebellar syndrome. Frequently, it also manifests as sleep disorders and cognitive or behavioral changes. While immunotherapy is the primary treatment approach, the disease remains poorly understood. Herein, we present a case of anti-metabotropic glutamate receptor 1 encephalitis, highlighting its primary cerebellar syndrome manifestation. The first magnetic resonance imaging scan showed no obvious abnormality. Lumbar puncture showed increased cerebrospinal fluid pressure, increased white blood cell count and protein level. The next-generation sequencing of cerebrospinal fluid showed Epstein-Barr virus infection, and the patient was diagnosed with viral cerebellar encephalitis. However, antiviral therapy was ineffective. Finally, anti-metabotropic glutamate receptor 1 was measured at 1:1,000, and the patient was definitely diagnosed with anti-metabotropic glutamate receptor 1 encephalitis. Therefore, clinicians should pay attention to such diseases to avoid misdiagnosis.

Pathophysiological Effects of Autoantibodies in Autoimmune Encephalitides

The heterogeneity of autoantibody targets in autoimmune encephalitides presents a challenge for understanding cellular and humoral pathophysiology, and the development of new treatment strategies. Thus, current treatment aims at autoantibody removal and immunosuppression, and is primarily based on data generated from other autoimmune neurological diseases and expert consensus. There are many subtypes of autoimmune encephalitides, which now entails both diseases with autoantibodies targeting extracellular antigens and classical paraneoplastic syndromes with autoantibodies targeting intracellular antigens. Here, we review the current knowledge of molecular and cellular effects of autoantibodies associated with autoimmune encephalitis, and evaluate the evidence behind the proposed pathophysiological mechanisms of autoantibodies in autoimmune encephalitis.

Anti-NMDA and Anti-AMPA Receptor Antibodies in Central Disorders: Preclinical Approaches to Assess Their Pathological Role and Translatability to Clinic

Autoantibodies against NMDA and AMPA receptors have been identified in the central nervous system of patients suffering from brain disorders characterized by neurological and psychiatric symptoms. It has been demonstrated that these autoantibodies can affect the functions and/or the expression of the targeted receptors, altering synaptic communication. The importance to clarify, in preclinical models, the molecular mechanisms involved in the autoantibody-mediated effects has emerged in order to understand their pathogenic role in central disorders, but also to propose new therapeutic approaches for preventing the deleterious central consequences. In this review, we describe some of the available preclinical literature concerning the impact of antibodies recognizing NMDA and AMPA receptors in neurons. This review discusses the cellular events that would support the detrimental roles of the autoantibodies, also illustrating some contrasting findings that in our opinion deserve attention and further investigations before translating the preclinical observations to clinic.