Clinical Characterization of Definite Autoimmune Limbic Encephalitis: A 30-case Series

Epilepsy, Immunity and Neuropsychiatric Disorders

Several studies have focused on the emerging role of immunity and inflammation in a wide range of neurological disorders. Autoimmune diseases involving central nervous system share well defined clinical features including epileptic seizures and additional neuropsychiatric symptoms, like cognitive and psychiatric disturbances. The growing evidence about the role of immunity in the pathophysiologic mechanisms underlying these conditions lead to the concept of autoimmune epilepsy. This relatively-new term has been introduced to highlight the etiological and prognostic implications of immunity in epileptogenesis. In this review, we aim to discuss the role of autoimmunity in epileptogenesis and its clinical, neurophysiological, neuroimaging and therapeutic implications. Moreover, we wish to address the close relationship between immunity and additional symptoms, particularly cognitive and psychiatric features, which deeply impact clinical outcomes in these patients. To assess these aspects, we first analyzed Rasmussen's encephalitis. Subsequently, we have covered autoimmune encephalitis, particularly those associated with autoantibodies against surface neuronal antigens, as these autoantibodies express a direct immune-mediated mechanism, different from those against intracellular antigens. Then, we discussed the connection between systemic immune disorders and neurological manifestations. This review aims to highlight the need to expand knowledge about the role of inflammation and autoimmunity in the pathophysiology of neurological disorders and the importance to early recognize these clinical entities. Indeed, early identification may result in faster recovery and a better prognosis.

OUP accepted manuscript

Objective

Autoimmune limbic encephalitis (ALE) is characterized by memory impairment, psychiatric symptoms, and epileptic seizures. Though, the neuropsychological profile of ALE is not yet well defined. However, there is some evidence that neuropsychological impairments might exceed those related to the limbic system and that different autoantibodies (AABs) are associated with distinguishable pattern of neuropsychological impairments. We provide a comprehensive presentation of neuropsychological performance of ALE in an immune therapy-naïve sample.

Methods

We retrospectively analyzed 69 immunotherapy-naïve ALE-patients (26 seropositive—[8 LGI1-, 4 CASPR2-, 2 GABA_B-R-, 3 Hu-, 4 GAD65-, 2 Ma2-, 2 unknown antigen, and 1 Yo-AABs] and 43 seronegative patients, mean age 56.0 years [21.9–78.2], mean disease duration 88 weeks [0–572]). Neuropsychological evaluations comprised of the domains memory, attention, praxis, executive functions, language, social cognition, and psychological symptoms. We compared these functions between seronegative −, seropositive patients with AABs against intracellular neural antigens and seropositive patients with AABs against surface membrane neural antigens.

Results

No effect of AAB group on neuropsychological performance could be detected. Overall, ALE predominantly presents with deficits in long-term memory and memory recognition, autobiographical-episodic memory loss, impairment of emotion recognition, and depressed mood. Furthermore, deficits in praxis of pantomimes and imitations, visuo-construction, and flexibility may occur.

Conclusion

ALE shows a wide spectrum of neuropsychological impairments, which might exceed the limbic system, with no evidence of differences between AAB groups. Neuropsychological assessment for diagnosing ALE should include long-term memory, memory recognition, autobiographical-episodic memory, emotion recognition, and a detailed investigation of depression.

Atypical Association of Autoimmune Limbic Encephalitis with Anti-NMDA Receptor Antibodies in a Young Male Patient: Clinical, Imaging, and Neuropsychological Characteristics

The spectrum of autoimmune encephalitis (AE) encompasses several entities characterized by a variable frequency of psychiatric symptoms, cognitive dysfunction, focal deficits, and seizures. Although patients with AE can be categorized in specific syndromes, overlapping manifestations are also common. Furthermore, atypical correlations between clinical phenotypes and autoantibody profiles could occur in rare cases. Here, we report the rare case of a young adult man attending due to new-onset seizures and a history of memory loss, autonomic disturbances, headache, behavioral changes, and visual and olfactory hallucinations. The patient was subjected to a complete diagnostic approach that included a comprehensive laboratory workup, neuropsychological testing, electroencephalogram, cerebrospinal fluid (CSF) analysis, brain MRI, and positron emission tomography/computed tomography scan that revealed a functional and structural compromise of the bilateral medial temporal lobes. Together with the clinical manifestations of the patient, these findings were compatible with the diagnosis of autoimmune limbic encephalitis (ALE). Strikingly, further analysis of the CSF showed autoantibodies against the N-methyl-D-aspartate (NMDA) receptor. We found very few cases of the co-occurrence of anti-NMDA receptor antibodies and nonparaneoplastic ALE in the literature, especially in male patients. Our report exemplifies the complicated differential diagnosis of ALE and adds clinical information of the association with anti-NMDA receptor antibodies.

Pitfalls and Caveats in Applying Chromogenic Immunostaining to Histopathological Diagnosis

Chromogenic immunohistochemistry (immunostaining using an enzyme-labeled probe) is an essential histochemical technique for analyzing pathogenesis and making a histopathological diagnosis in routine pathology services. In neoplastic lesions, immunohistochemistry allows the study of specific clinical and biological features such as histogenesis, behavioral characteristics, therapeutic targets, and prognostic biomarkers. The needs for appropriate and reproducible methods of immunostaining are prompted by technical development and refinement, commercial availability of a variety of antibodies, advanced applicability of immunohistochemical markers, accelerated analysis of clinicopathological correlations, progress in molecular targeted therapy, and the expectation of advanced histopathological diagnosis. However, immunostaining does have various pitfalls and caveats. Pathologists should learn from previous mistakes and failures and from results indicating false positivity and false negativity. The present review article describes various devices, technical hints, and trouble-shooting guides to keep in mind when performing immunostaining.

Neuropsychiatric Disorders Due to Limbic Encephalitis: Immunologic Aspect

Limbic encephalitis (LE) is a rare cause of encephalitis presenting as an acute and subacute onset of neuropsychiatric manifestations, particularly with memory deficits and confusion as core features, along with seizure occurrence, movement disorders, or autonomic dysfunctions. LE is caused by neuronal antibodies targeting the cellular surface, synaptic, and intracellular antigens, which alter the synaptic transmission, especially in the limbic area. Immunologic mechanisms involve antibodies, complements, or T-cell-mediated immune responses in different degree according to different autoantibodies. Sensitive cerebrospinal fluid markers of LE are unavailable, and radiographic findings may not reveal a typical mesiotemporal involvement at neurologic presentations; therefore, a high clinical index of suspicions is pivotal, and a neuronal antibody testing is necessary to make early diagnosis. Some patients have concomitant tumors, causing paraneoplastic LE; therefore, tumor survey and treatment are required in addition to immunotherapy. In this study, a review on the molecular and immunologic aspects of LE was conducted to gain awareness of its peculiarity, which we found quite different from our knowledge on traditional psychiatric illness.