Autoimmune Encephalitis overview
|
Autoimmune Encephalitis Microchapters |
|
Differentiating Autoimmune Encephalitis from Other Conditions |
|---|
|
Diagnosis |
|
Treatment |
|
Case Studies |
|
Autoimmune Encephalitis On the Web |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Julinka Auta Fernandes
Synonyms and keywords: Autoimmune encephalitides; neuronal autoantibodies; limbic encephalitis; antibody-negative autoimmune encephalitis.
Overview
Autoimmune encephalitis comprises immune-mediated inflammatory brain disorders that commonly cause evolving cognitive impairment, psychiatric or behavioral changes, seizures, and other neurological dysfunction. Anti-NMDA receptor encephalitis is one subtype. Some patients have no detectable neuronal antibody. Recognition relies on the clinical syndrome, appropriate investigations, and exclusion of competing diagnoses.[1]
Historical Perspective
Modern understanding of autoimmune encephalitis expanded with the identification of anti-NMDA receptor encephalitis in 2007, establishing a treatable neuronal-surface-antibody syndrome initially associated with teratoma.[2]
Syndrome-based diagnostic criteria published in 2016 enabled assessment before antibody results became available.[1]
Classification
Autoimmune encephalitis can be classified by antibody target, clinical phenotype, cancer association, and diagnostic certainty. Major immunological groups include:[3]
- Neuronal-surface or synaptic antibody-associated disease: examples include NMDAR, LGI1, CASPR2, AMPAR, GABA-A receptor, GABA-B receptor, and DPPX antibodies.
- Intracellular-antigen-associated disease: examples include Hu, Ma2, CRMP5, and GAD65 antibodies; cancer association and immunotherapy responsiveness differ between these entities.
- Antibody-negative disease: diagnosis requires an appropriate syndrome and fulfillment of applicable clinical criteria; a negative panel alone does not establish this category.
Clinical patterns include limbic, diffuse encephalitic, brainstem, and overlapping syndromes.[3]
Pathophysiology
Autoimmune encephalitis involves disturbed neuronal function and, in some subtypes, neuronal injury. In anti-NMDAR encephalitis, antibodies cross-link surface receptors and promote their internalization, disrupting synaptic signaling. Experimental evidence demonstrates that this receptor loss can reverse after antibody removal.[4]
In classical onconeural-antibody-associated syndromes, such as Hu-associated disease, antibodies chiefly identify an immune response in which cytotoxic T cells contribute substantially to neuronal damage.[5]
Causes
Autoimmune encephalitis may be non-paraneoplastic or associated with a tumor expressing neural antigens. Immune checkpoint inhibitor treatment can also trigger encephalitic autoimmunity. An identifiable external trigger is often absent.[5]
Autoimmune encephalitis can follow herpes simplex encephalitis. New psychiatric, cognitive, seizure, or movement symptoms after initial improvement warrant assessment for both post-infectious autoimmunity and recurrent infection.[6]
Differentiating Autoimmune Encephalitis from Other Conditions
Autoimmune encephalitis must be distinguished from infectious encephalitis, toxic or metabolic encephalopathy, primary psychiatric illness, seizure-related encephalopathy, neurodegenerative or prion disease, and structural or neoplastic disease, including CNS lymphoma. An isolated serum antibody result or apparent steroid response is insufficient to establish the diagnosis.[7]
Inflammatory and demyelinating disorders, including ADEM and MOG antibody-associated disease, can produce overlapping encephalitic presentations and require disease-specific assessment.[8]
Epidemiology and Demographics
Autoimmune encephalitis occurs in children and adults. In an Olmsted County, Minnesota, population study, estimated incidence was 0.8 per 100,000 person-years and prevalence was 13.7 per 100,000, comparable to infectious encephalitis in that population. These figures reflect the study's setting and case definitions rather than a universal worldwide rate; age and sex distributions vary with subtype.[9]
Risk Factors
Autoimmune encephalitis has subtype-specific associations rather than one universal risk profile. Certain tumors increase the likelihood of paraneoplastic disease, while many patients have no cancer. Age, sex, clinical phenotype, and antibody specificity help determine the relevant tumor risk.[5]
Previous herpes simplex encephalitis is an important setting for secondary autoimmune encephalitis; antibody development after infection must be interpreted alongside new compatible symptoms.[6]
Screening
Autoimmune encephalitis testing should follow clinical suspicion. Nonspecific chronic symptoms or an incidental antibody result require careful reassessment because low pretest probability increases the risk of misdiagnosis.[7]
Natural History, Complications and Prognosis
Autoimmune encephalitis can progress to severe encephalopathy, status epilepticus, impaired consciousness, respiratory failure, autonomic instability, and death. Anti-NMDAR encephalitis illustrates how a severe acute illness can nevertheless be followed by substantial recovery. Early treatment and lower initial disease severity were associated with better outcomes in a large observational cohort; recovery sometimes continued beyond 18 months. These findings should not be treated as identical outcome estimates for every subtype.[10]
After the acute phase, autoimmune encephalitis may leave persistent cognitive, psychiatric, sleep, fatigue, and functional difficulties. Relapse risk and rehabilitation needs vary.[11]
Diagnosis
Diagnostic Study of Choice
Autoimmune encephalitis has no single universal confirmatory test. Evaluation integrates the clinical course with MRI, EEG, CSF analysis, and appropriately interpreted antibody testing. Discordant findings should prompt reconsideration of alternative diagnoses.[7]
Clinical Diagnostic Criteria
The 2016 criteria for possible autoimmune encephalitis require all three components:
- A new syndrome developing over less than three months, with impaired short-term memory, changed mental status, or psychiatric features.
- At least one supporting finding: a new focal neurological abnormality, otherwise-unexplained seizures, CSF leukocytes greater than 5/mm3, or MRI changes compatible with encephalitis.
- An evaluation that reasonably excludes competing causes.
These criteria identify a diagnostic possibility; more specific criteria are needed for probable or definite subtypes. Normal routine CSF or MRI findings do not independently exclude autoimmune encephalitis.[1]
Antibody-Negative Autoimmune Encephalitis
Antibody-negative autoimmune encephalitis requires careful application of established criteria, objective supporting findings, and exclusion of mimics. A compatible history with a negative commercial panel is insufficient by itself. Specialist review may identify a need for additional reference-laboratory testing or reconsideration of the diagnosis.[12]
For probable antibody-negative disease, the 2016 criteria require the subacute syndrome, exclusion of defined alternative autoimmune syndromes, negative recognized serum/CSF antibodies, and at least two of: suggestive MRI, inflammatory CSF, or inflammatory biopsy excluding other causes.[1]
History and Symptoms
Autoimmune encephalitis commonly presents with new memory impairment, confusion, personality or behavioral changes, psychiatric symptoms, and seizures. Anti-NMDAR disease may additionally involve speech reduction, catatonia, dyskinesias, autonomic disturbance, and hypoventilation. The sequence and combination of symptoms, rather than any single psychiatric symptom, are clinically important.[10]
In LGI1-associated autoimmune encephalitis, very brief recurrent faciobrachial dystonic seizures and hyponatremia are particularly useful clinical clues.[3]
Physical Examination
Autoimmune encephalitis examination should assess consciousness, orientation, memory, language, behavior, movement abnormalities, focal neurological deficits, and autonomic function. In children, developmental regression and loss of previously acquired language or other skills may be particularly informative. Examination findings must be interpreted against the patient's developmental baseline.[8]
Laboratory Findings
Autoimmune encephalitis investigations include CSF cell count, protein, glucose, oligoclonal bands or IgG index, and microbiological testing. Paired serum and CSF neuronal antibody testing improves diagnostic interpretation: CSF is especially important for NMDAR antibodies, while serum can be more sensitive for LGI1/CASPR2 antibodies. Blood testing addresses metabolic, infectious, and systemic inflammatory alternatives.[3]
For NMDAR encephalitis, diagnostically relevant antibodies are IgG against the GluN1 subunit.[1]
Low-specificity findings, including thyroid antibodies or low-level serum neural antibodies, must not substitute for a compatible syndrome and adequate exclusion of mimics.[7]
Electrocardiogram
Autoimmune encephalitis-associated dysautonomia can cause heart-rate abnormalities. ECG and, when indicated, continuous cardiac monitoring evaluate complications rather than establish the encephalitis diagnosis.[11]
Chest X Ray
Autoimmune encephalitis has no characteristic chest X-ray finding. Chest radiography may address respiratory complications; it does not replace appropriate imaging for occult malignancy.[13]
CT Scan
Autoimmune encephalitis may have an unrevealing brain CT. CT can assess urgent structural alternatives when needed. Contrast-enhanced body CT commonly contributes to the initial adult malignancy search.[13]
MRI
Autoimmune encephalitis is evaluated with brain MRI. Limbic disease may show medial temporal T2/FLAIR hyperintensity; other subtypes can produce different patterns or normal imaging. A normal study does not exclude disease, and repeat MRI may be appropriate. Findings must be interpreted alongside infection, seizure-related changes, and other mimics.[13]
Echocardiography or Ultrasound
Autoimmune encephalitis is not diagnosed by echocardiography. Targeted ultrasound has a different role: pelvic or testicular imaging can investigate an associated neoplasm when indicated by phenotype and antibody findings.[13]
Other Imaging Findings
Autoimmune encephalitis assessment may include brain FDG-PET when suspicion remains high despite inconclusive conventional studies. Metabolic abnormalities are not diagnostic alone. Whole-body FDG-PET serves a separate, selected tumor-search role.[13]
Electroencephalography
Autoimmune encephalitis may produce EEG slowing or epileptiform abnormalities. In anti-NMDAR encephalitis, extreme delta brush is a recognized pattern, but its absence does not exclude disease and it is not a stand-alone diagnostic test. Prolonged EEG can help identify electrographic seizures.[14]
Other Diagnostic Studies
Autoimmune encephalitis rarely requires brain biopsy; its main value is investigating alternative pathology, such as neoplasm, when diagnostic uncertainty persists.[3]
Screening for an Associated Neoplasm
Adults newly diagnosed with autoimmune encephalitis should undergo an initial tumor search.[3]
Autoimmune encephalitis-associated tumor evaluation is guided by phenotype, antibody, age, and sex. Examples include ovarian teratoma in NMDAR-associated disease and lung cancer in selected paraneoplastic syndromes. Follow-up screening depends on risk. The 2021 PNS criteria recommend repeat screening every 4–6 months for two years when both a high-risk phenotype and high-risk antibody are present; this schedule is not universal for all autoimmune encephalitis.[5]
Pediatric Considerations
Autoimmune encephalitis in children requires pediatric-specific interpretation. Developmental regression, seizures, movement abnormalities, and behavioral change may dominate, while memory symptoms can be difficult to establish. Adult criteria should not be applied mechanically, and infectious, genetic, metabolic, and other inflammatory disorders must be considered.[8]
Treatment
Medical Therapy
Autoimmune encephalitis warrants prompt specialist-directed treatment after reasonable exclusion of alternative causes. Infection must be investigated urgently; empiric intravenous acyclovir is appropriate while HSV encephalitis remains a concern. Immunotherapy should not be delayed solely for antibody results. First-line options include high-dose corticosteroids, intravenous immunoglobulin, and plasma exchange, selected or combined according to severity and contraindications.[12]
Autoimmune encephalitis without adequate response requires reassessment and consideration of second-line treatment, commonly rituximab or cyclophosphamide. Choice and escalation timing depend on subtype, severity, and response, with specialist neuroimmunology input.[12]
Treatment evidence differs between subtypes. A small randomized trial supported IVIG for seizure reduction in LGI1/CASPR2-associated autoimmune epilepsy; its results should not be generalized to every encephalitis subtype or treatment comparison.[15]
Symptomatic and Supportive Therapy
Autoimmune encephalitis management also addresses seizures, agitation or psychosis, sleep problems, movement disorders, dysautonomia, nutrition, and immobility-related complications. Medication choices require attention to adverse effects and interactions.[11]
Interventions
Severe autoimmune encephalitis may require intensive care, airway protection, mechanical ventilation, and autonomic support. Plasma exchange is an immunotherapeutic intervention, rather than a diagnostic procedure.[16]
Surgery
Autoimmune encephalitis associated with an identifiable tumor requires prompt consideration of tumor-directed treatment alongside immunotherapy. Resection of an associated ovarian teratoma is an important example; surgery treats the associated neoplasm rather than removing inflamed brain tissue.[2]
Pediatric Treatment Considerations
For pediatric NMDAR-antibody encephalitis, international consensus recommends corticosteroids, with IVIG or plasma exchange added in severe disease. Rituximab is generally preferred over cyclophosphamide when second-line therapy is needed. Escalation may be considered around two weeks after first-line initiation in refractory cases; treatment duration and maintenance are individualized. These recommendations concern this specific pediatric subtype.[16]
Rehabilitation
Autoimmune encephalitis recovery may require physical, occupational, speech, and neuropsychological rehabilitation. Follow-up should address cognition, mood, fatigue, daily function, and supported return to education or work.[11]
Prevention
Primary Prevention
Autoimmune encephalitis has no established disease-specific primary prevention strategy. Routine prophylactic immunotherapy is not recommended for otherwise healthy individuals.[11]
Secondary Prevention
Autoimmune encephalitis relapse prevention is individualized. Maintenance immunotherapy is considered in selected relapsing or high-risk cases, alongside surveillance for associated tumors when indicated. New symptoms require assessment for relapse, residual impairment, infection, and treatment complications.[11]
Cost-Effectiveness of Therapy
Autoimmune encephalitis economic evidence is context dependent. A US decision model suggested that routine antibody screening in first-episode psychosis might be cost-effective under some assumptions, but substantial uncertainty remained. This does not establish universal screening or prove the comparative cost-effectiveness of individual immunotherapies.[17]
Future or Investigational Therapies
Autoimmune encephalitis research includes randomized evaluation of targeted therapies and more sensitive measures of recovery. The published CIELO protocol describes a trial of satralizumab in NMDAR- or LGI1-antibody-positive disease; a trial protocol establishes the study design rather than treatment efficacy.[18]
For refractory autoimmune encephalitis, agents such as tocilizumab or bortezomib have limited supporting evidence and require specialist multidisciplinary consideration rather than routine first-line use.[12]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Graus F, Titulaer MJ, Balu R, et al. A clinical approach to diagnosis of autoimmune encephalitis. Lancet Neurol. 2016;15(4):391–404. doi:10.1016/S1474-4422(15)00401-9. PMID:26906964.
- ↑ 2.0 2.1 Dalmau J, Tüzün E, Wu HY, et al. Paraneoplastic anti-N-methyl-D-aspartate receptor encephalitis associated with ovarian teratoma. Ann Neurol. 2007;61(1):25–36. doi:10.1002/ana.21050. PMID:17262855.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Hahn C, Budhram A, Alikhani K, et al. Canadian Consensus Guidelines for the Diagnosis and Treatment of Autoimmune Encephalitis in Adults. Can J Neurol Sci. 2024;51(6):734–754. doi:10.1017/cjn.2024.16. PMID:38312020.
- ↑ Hughes EG, Peng X, Gleichman AJ, et al. Cellular and synaptic mechanisms of anti-NMDA receptor encephalitis. J Neurosci. 2010;30(17):5866–5875. doi:10.1523/JNEUROSCI.0167-10.2010. PMID:20427647.
- ↑ 5.0 5.1 5.2 5.3 Graus F, Vogrig A, Muñiz-Castrillo S, et al. Updated Diagnostic Criteria for Paraneoplastic Neurologic Syndromes. Neurol Neuroimmunol Neuroinflamm. 2021;8(4):e1014. doi:10.1212/NXI.0000000000001014. PMID:34006622.
- ↑ 6.0 6.1 Armangue T, et al. Frequency, symptoms, risk factors, and outcomes of autoimmune encephalitis after herpes simplex encephalitis: a prospective observational study and retrospective analysis. Lancet Neurol. 2018;17(9):760–772. doi:10.1016/S1474-4422(18)30244-8. PMID:30049614.
- ↑ 7.0 7.1 7.2 7.3 Flanagan EP, Geschwind MD, Lopez-Chiriboga AS, et al. Autoimmune Encephalitis Misdiagnosis in Adults. JAMA Neurol. 2023;80(1):30–39. doi:10.1001/jamaneurol.2022.4251. PMID:36441519.
- ↑ 8.0 8.1 8.2 Cellucci T, Van Mater H, Graus F, et al. Clinical approach to the diagnosis of autoimmune encephalitis in the pediatric patient. Neurol Neuroimmunol Neuroinflamm. 2020;7(2):e663. doi:10.1212/NXI.0000000000000663. PMID:31953309.
- ↑ Dubey D, Pittock SJ, Kelly CR, et al. Autoimmune encephalitis epidemiology and a comparison to infectious encephalitis. Ann Neurol. 2018;83(1):166–177. doi:10.1002/ana.25131. PMID:29293273.
- ↑ 10.0 10.1 Titulaer MJ, McCracken L, Gabilondo I, et al. Treatment and prognostic factors for long-term outcome in patients with anti-NMDA receptor encephalitis: an observational cohort study. Lancet Neurol. 2013;12(2):157–165. doi:10.1016/S1474-4422(12)70310-1. PMID:23290630.
- ↑ 11.0 11.1 11.2 11.3 11.4 11.5 Abboud H, Probasco J, Irani SR, et al.; Autoimmune Encephalitis Alliance Clinicians Network. Autoimmune encephalitis: proposed recommendations for symptomatic and long-term management. J Neurol Neurosurg Psychiatry. 2021;92(8):897–907. doi:10.1136/jnnp-2020-325302. PMID:33649021.
- ↑ 12.0 12.1 12.2 12.3 Michael BD, et al. Management of suspected infectious and autoimmune encephalitis in adults – National Guidelines from the United Kingdom Joint Societies. J Infect. Published online October 2026:106873. doi:10.1016/j.jinf.2026.106873. PMID:42863638.
- ↑ 13.0 13.1 13.2 13.3 13.4 Abboud H, Probasco JC, Irani S, et al.; Autoimmune Encephalitis Alliance Clinicians Network. Autoimmune encephalitis: proposed best practice recommendations for diagnosis and acute management. J Neurol Neurosurg Psychiatry. 2021;92(7):757–768. doi:10.1136/jnnp-2020-325300. PMID:33649022.
- ↑ Schmitt SE, et al. Extreme delta brush: a unique EEG pattern in adults with anti-NMDA receptor encephalitis. Neurology. 2012;79(11):1094–1100. doi:10.1212/WNL.0b013e3182698cd8. PMID:22933737.
- ↑ Dubey D, et al. Randomized Placebo-Controlled Trial of Intravenous Immunoglobulin in Autoimmune LGI1/CASPR2 Epilepsy. Ann Neurol. 2020;87(2):313–323. doi:10.1002/ana.25655. PMID:31782181.
- ↑ 16.0 16.1 Nosadini M, Thomas T, Eyre M, et al. International Consensus Recommendations for the Treatment of Pediatric NMDAR Antibody Encephalitis. Neurol Neuroimmunol Neuroinflamm. 2021;8(5):e1052. doi:10.1212/NXI.0000000000001052. PMID:34301820.
- ↑ Ross EL, Becker JE, Linnoila JJ, Soeteman DI. Cost-Effectiveness of Routine Screening for Autoimmune Encephalitis in Patients With First-Episode Psychosis in the United States. J Clin Psychiatry. 2021;82(1):19m13168. PMID:33211912.
- ↑ Lee ST, Abboud H, Irani SR, et al. Innovation and optimization in autoimmune encephalitis trials: the design and rationale ... (CIELO). Front Neurol. 2024;15:1437913. doi:10.3389/fneur.2024.1437913. PMID:39193150.