Brain on fire: an imaging-based review of autoimmune encephalitis

Uncommon and Miscellaneous Inflammatory Disorders of the Brain and Spine

Inflammatory disorders of the brain and spine have a highly variable MRI appearance, often demonstrating significant overlap in imaging features. The resulting diagnostic dilemma is particularly challenging when considering the more uncommon neuroinflammatory entities. Diligent examination of the salient clinical presentation and signal alteration on imaging examination is necessary when considering neuroinflammation as a diagnostic possibility and may aid in raising suspicion for a particular neuroinflammatory entity. This article reviews a selection of uncommon and miscellaneous inflammatory disorders of the brain and spine to raise awareness of the clinical and imaging features that may assist in this challenging diagnostic task.

Autoimmune encephalitis: what the radiologist needs to know

Autoimmune encephalitis is a relatively novel nosological entity characterized by an immune-mediated damage of the central nervous system. While originally described as a paraneoplastic inflammatory phenomenon affecting limbic structures, numerous instances of non-paraneoplastic pathogenesis, as well as extra-limbic involvement, have been characterized. Given the wide spectrum of insidious clinical presentations ranging from cognitive impairment to psychiatric symptoms or seizures, it is crucial to raise awareness about this disease category. In fact, an early diagnosis can be dramatically beneficial for the prognosis both to achieve an early therapeutic intervention and to detect a potential underlying malignancy. In this scenario, the radiologist can be the first to pose the hypothesis of autoimmune encephalitis and refer the patient to a comprehensive diagnostic work-up - including clinical, serological, and neurophysiological assessments.In this article, we illustrate the main radiological characteristics of autoimmune encephalitis and its subtypes, including the typical limbic presentation, the features of extra-limbic involvement, and also peculiar imaging findings. In addition, we review the most relevant alternative diagnoses that should be considered, ranging from other encephalitides to neoplasms, vascular conditions, and post-seizure alterations. Finally, we discuss the most appropriate imaging diagnostic work-up, also proposing a suggested MRI protocol.

Microglial Activation Imaging Using 18F-DPA-714 PET/MRI for Detecting Autoimmune Encephalitis

Background Translocator protein (TSPO) PET has been used to visualize microglial activation in neuroinflammation and is a potential imaging tool for detecting autoimmune encephalitis (AIE). Purpose To compare the detection rate between TSPO radioligand fluorine 18 (18F) DPA-714 PET and conventional MRI and assess the relationship between 18F-DPA-714 uptake and clinical features in participants with AIE. Materials and Methods Healthy volunteers and patients with AIE were enrolled in this prospective study between December 2021 and April 2023. All participants underwent hybrid brain 18F-DPA-714 PET/MRI and antibody testing. Modified Rankin scale scoring and AIE-related symptoms were assessed in participants with AIE. Positive findings were defined as intensity of 18F-DPA-714 uptake above a threshold of the mean standardized uptake value ratio (SUVR) plus 2 SD inside the corresponding brain regions of healthy controls. The McNemar test was used to compare the positive detection rate between the two imaging modalities; the independent samples t test was used to compare continuous variables; and correlation with Bonferroni correction was used to assess the relationship between 18F-DPA-714 uptake and clinical features. Results A total of 25 participants with AIE (mean age, 39.24 years ± 19.03 [SD]) and 10 healthy controls (mean age, 28.70 years ± 5.14) were included. The positive detection rate of AIE was 72% (18 of 25) using 18F-DPA-714 PET compared to 44% (11 of 25) using conventional MRI, but the difference was not statistically significant (P = .065). Participants experiencing seizures exhibited significantly higher mean SUVR in the entire cortical region than those without seizures (1.23 ± 0.21 vs 1.15 ± 0.18; P = .003). Of the 13 participants with AIE who underwent follow-up PET/MRI, 11 (85%) demonstrated reduced uptake of 18F-DPA-714 accompanied by relief of symptoms after immunosuppressive treatment. Conclusion 18F-DPA-714 PET has potential value in supplementing MRI for AIE detection. Clinical trial registration no. NCT05293405 © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Zaharchuk in this issue.

Autoimmune encephalitis in a resource-limited public health setting: a case series analysis

BACKGROUND

 Autoimmune encephalitis (AE) consists of a group of acquired diseases that affect the central nervous system. A myriad of phenotypes may be present at the onset. Due to the heterogeneity of clinical presentations, it is difficult to achieve uniformity for the diagnostic and therapeutic processes and follow-up strategies.

OBJECTIVE

 To describe a series of patients diagnosed with AE in a resource-limited public hospital in southern Brazil and to analyze therapeutics and outcomes.

METHODS

 We retrospectively reviewed the electronic medical records of patients diagnosed with AE at the Hospital de Clínicas de Porto Alegre from 2014 to 2022. Data collected included clinical presentation, neuroimaging, cerebrospinal fluid testings, electroencephalogram, autoantibodies, treatments, outcomes, follow-up time, degree of neurological impairment, and mortality.

RESULTS

 Data from 17 patients were retrieved. Eleven cases were classified as definite AE and 6 as possible AE. Autoantibodies were identified in 9 patients. Timing for diagnosis was impacted by the high costs associated with autoantibody testing. Most patients became functionally dependent (82.4%) and most survivors remained with autoimmune-associated epilepsy (75%). Five patients died during hospitalization, and one after a 26-month of follow-up.

CONCLUSION

 In this resource-limited hospital, patients with AE had a worse clinical outcome than that previously described in the literature. Development of epilepsy during follow-up and mortality were greater, whilst functional outcome was inferior. Autoantibody testing was initially denied in most patients, which impacted the definitive diagnosis and the use of second-line therapies.

MR Imaging Findings in a Large Population of Autoimmune Encephalitis

BACKGROUND AND PURPOSE

Autoimmune encephalitis is a rare condition in which autoantibodies attack neuronal tissue, causing neuropsychiatric disturbances. This study sought to evaluate MR imaging findings associated with subtypes and categories of autoimmune encephalitis.

MATERIALS AND METHODS

Cases of autoimmune encephalitis with specific autoantibodies were identified from the medical record (2009-2019). Cases were excluded if no MR imaging of the brain was available, antibodies were associated with demyelinating disease, or >1 concurrent antibody was present. Demographics, CSF profile, antibody subtype and group (group 1 intracellular antigen or group 2 extracellular antigen), and MR imaging features at symptom onset were reviewed. Imaging and clinical features were compared across antibody groups using χ² and Wilcoxon rank-sum tests.

RESULTS

Eighty-five cases of autoimmune encephalitis constituting 16 distinct antibodies were reviewed. The most common antibodies were anti-N-methyl-D-aspartate (n = 41), anti-glutamic acid decarboxylase (n = 7), and anti-voltage-gated potassium channel (n = 6). Eighteen of 85 (21%) were group 1; and 67/85 (79%) were group 2. The median time between MR imaging and antibody diagnosis was 14 days (interquartile range, 4-26 days). MR imaging had normal findings in 33/85 (39%), and 20/33 (61%) patients with normal MRIs had anti-N-methyl-D-aspartate receptor antibodies. Signal abnormality was most common in the limbic system (28/85, 33%); 1/68 (1.5%) had susceptibility artifacts. Brainstem and cerebellar involvement were more common in group 1, while leptomeningeal enhancement was more common in group 2.

CONCLUSIONS

Sixty-one percent of patients with autoimmune encephalitis had abnormal brain MR imaging findings at symptom onset, most commonly involving the limbic system. Susceptibility artifact is rare and makes autoimmune encephalitis less likely as a diagnosis. Brainstem and cerebellar involvement were more common in group 1, while leptomeningeal enhancement was more common in group 2.

Approach to acute encephalitis in the intensive care unit

PURPOSE OF REVIEW

Recent years have seen a dramatic increase in the identification of autoimmune encephalitis (AE) and the emergence of new causes of infectious encephalitis (IE). However, management of these patients remains challenging, with many requiring care in intensive care units. Here, we describe recent advances in the diagnosis and management of acute encephalitis.

RECENT FINDINGS

Advances in the identification of clinical presentations, neuroimaging biomarkers, and electroencephalogram patterns have enabled more rapid diagnosis of encephalitis. Newer modalities such as meningitis/encephalitis multiplex PCR panels, metagenomic next-generation sequencing, and phage display-based assays are being evaluated in an effort to improve detection of autoantibodies and pathogens. Specific advances in the treatment of AE include establishment of a systematic approach to first-line therapies and the development of newer second-line modalities. The role of immunomodulation and its applications in IE are actively being investigated. In the ICU, particular attention to status epilepticus, cerebral edema, and dysautonomia may improve outcomes.

SUMMARY

Substantial diagnostic delays still occur, with many cases left without an identified etiology. Antiviral therapies remain scarce, and optimal treatment regimens for AE still need to be clarified. Nevertheless, our understanding of diagnostic and therapeutic approaches to encephalitis is rapidly evolving.

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.

Increased formation of neutrophil extracellular traps in patients with anti-N-methyl-d-aspartate receptor encephalitis

Background

Neutrophil extracellular traps (NETs) have been found to play an important role in several nervous system diseases. However, their role in anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis remains unclear. The purpose of this study was to examine the possible role of NETs in anti-NMDAR encephalitis.

Materials and methods

Eleven patients with anti-NMDAR encephalitis and ten healthy participants were enrolled. Plasma NETs levels were detected using an immunofluorescence assay and enzyme-linked immunosorbent assay. Additionally, we examined 10 plasma cytokines in patients with anti-NMDAR encephalitis and analyzed the correlation between citrullinated histone 3 levels and cytokine release.

Results

Peripheral blood neutrophils from patients with anti-NMDAR encephalitis were more susceptible to NET generation. When compared with controls, cases of anti-NMDAR encephalitis showed elevated levels of IL-1 α, IL-6, IL-8, IL-13, MCP-1, and TNF-α (p < 0.05). Moreover, IL-6, IL-8, and TNF-α levels were positively correlated with H3Cit levels.

Conclusion

We provide evidence that NETs may play a role in anti-NMDAR encephalitis, providing clues for elucidation of the pathogenesis of this disease.

Critical care management of meningitis and encephalitis: an update

PURPOSE OF REVIEW

Meningitis and encephalitis represent severe neurological syndromes associated with encephalopathy, seizures, focal deficits, and neurological sequelae in survivors. We update on the critical care management of adult patients with severe meningitis and encephalitis.

RECENT FINDINGS

Large multicenter studies conducted in the adult population improved current knowledge on the epidemiology and outcomes of patients with severe meningitis and encephalitis. An early multimodal diagnostic workup (including CSF analysis, brain MRI, EEG, and serum studies) is mandatory for diagnosis and prognostication in those patients.New diagnostic methods, including multiplex PCR and next-generation sequencing techniques, allow for a faster differential diagnosis of infectious causes that may require specific antimicrobial therapy. Autoimmune causes of encephalitis, which may require urgent immunotherapy, are also increasingly recognized in the ICU setting. Although observational data suggest that early combined immunotherapy is associated with better neurological outcomes in patients with autoimmune encephalitis, randomized clinical trials have yet to be performed.

SUMMARY

Our review highlights the importance of an early multimodal approach for diagnosing severe meningitis and encephalitis. Randomized clinical trials are needed to identify pharmacological interventions that may improve patients' outcomes.

Role of Increased Syncytin-1 Expression in Pathogenesis of Anti-N-Methyl-d-Aspartate Receptor Encephalitis

PURPOSE

Syncytin-1 may play a role in several neuropsychiatric disorders, but its function in anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is unknown. The purpose of this study was to examine the possible mechanism of action of syncytin-1 in patients with anti-NMDAR encephalitis.

PATIENTS AND METHODS

Twenty patients with anti-NMDAR encephalitis and eight controls were recruited. The protein levels of syncytin-1 in serum were determined using an enzyme-linked immunosorbent assay, and the transcript levels of syncytin-1 were determined using real-time quantitative PCR. Flow cytometry was used for peripheral blood lymphocyte subset detection. Further, the relationship between syncytin-1 levels and clinical features of anti-NMDAR encephalitis and peripheral blood lymphocyte subsets was analyzed.

RESULTS

Compared with those in controls, higher syncytin-1 levels and percentage of B cells (CD3-CD19+) were observed in patients with anti-NMDAR encephalitis. Among anti-NMDAR encephalitis patients, the level of syncytin-1 positively correlated with the proportion of B cells and modified Rankin scale score at onset and after immunotherapy and negatively correlated with the proportion of CD3+ T cells.

CONCLUSION

An increased expression of Syncytin-1 is associated with the pathogenesis of anti-NMDAR encephalitis, providing evidence for elucidating the pathogenesis of the disease and suggesting novel therapeutic targets. Further, this study clarifies the role of syncytin-1 in neuroimmune disorders.