Autoimmune Encephalitis clinical diagnostic criteria
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Julinka Auta Fernandes
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Autoimmune Encephalitis Microchapters |
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Differentiating Autoimmune Encephalitis from Other Conditions |
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Diagnosis |
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Autoimmune Encephalitis On the Web |
Overview
Autoimmune encephalitis is classified as possible, probable, or definite according to the clinical syndrome and supporting evidence. The 2016 international criteria remain the basis of subsequent consensus guidance; these categories are not interchangeable.[1][2]
Assessment combines the history and examination with cerebrospinal fluid (CSF) analysis, magnetic resonance imaging (MRI), electroencephalography (EEG), and appropriately interpreted neural antibody tests. A possible diagnosis is an entry point for investigation, rather than confirmation of an autoimmune cause.[3]
Clinical Diagnostic Criteria
Possible autoimmune encephalitis in adults
All three requirements must be satisfied:[1][4]
- Symptoms progress over less than 3 months, involving short-term memory, mental status, or psychiatric function.
- At least one of the following is present:
- A new focal central nervous system (CNS) finding.
- Seizures that cannot be attributed to an established seizure disorder.
- CSF inflammation with more than 5 white blood cells/mm³.
- MRI abnormalities compatible with encephalitis.
- Other causes have been reasonably excluded.
Altered mental status includes impaired consciousness, lethargy, or a change in personality. Fever and antibody positivity are not required by this entry category.[1]
Definite autoimmune limbic encephalitis
The antibody-independent pathway requires all four findings:[5]
- A limbic syndrome developing over less than 3 months, with memory disturbance, seizures, or psychiatric changes.
- Bilateral medial temporal abnormalities on T2-weighted fluid-attenuated inversion recovery (FLAIR) MRI, largely confined to those regions.
- At least one supportive finding:
- CSF white blood cell count >5/mm³.
- Temporal epileptiform discharges or temporal slow-wave activity on EEG.
- Reasonable exclusion of competing diagnoses.
If one of the first three requirements is absent, definite autoimmune limbic encephalitis requires a relevant antibody against a neuronal surface, synaptic, or onconeural protein. Unilateral abnormalities or a normal MRI do not independently fulfill the antibody-independent imaging requirement.[5]
The original framework allowed medial temporal abnormalities on fluorodeoxyglucose positron emission tomography (FDG-PET) to support the imaging requirement. Contemporary Canadian guidance emphasizes that FDG-PET findings are nonspecific and must not establish the diagnosis alone.[5][2]
N-methyl-D-aspartate receptor antibody encephalitis
The following criteria apply to N-methyl-D-aspartate receptor (NMDAR) antibody encephalitis.[1]
Probable NMDAR antibody encephalitis
All three requirements apply:
- Within <3 months, development of at least four of six symptom groups:
- Psychiatric or behavioral abnormalities, or cognitive impairment.
- Speech disturbance, including pressured speech, reduced speech, or mutism.
- Seizures.
- Dyskinesias, rigidity, abnormal posturing, or another movement disorder.
- Reduced consciousness.
- Autonomic disturbance or central hypoventilation.
- At least one supportive investigation:
- EEG showing slowing, disorganization, epileptiform activity, or extreme delta brush.
- CSF pleocytosis or oligoclonal bands.
- Other disorders reasonably excluded.[1]
The framework also permits a probable diagnosis with three symptom groups and a systemic teratoma.[1]
Definite NMDAR antibody encephalitis
A definite diagnosis requires one or more of the six symptom groups, immunoglobulin G (IgG) antibodies targeting NMDAR subunit 1 (GluN1), and reasonable exclusion of alternatives. CSF testing is important; serum-only results can be misleading.[1]
Probable antibody-negative autoimmune encephalitis
All four requirements must be met:[1][6]
- Rapidly progressive memory, mental-status, or psychiatric disturbance over less than 3 months.
- Exclusion of a more specific, established autoimmune encephalitis syndrome.
- No well-characterized neural autoantibody in either serum or CSF, together with at least two of these three evidence categories:
- MRI findings suggestive of autoimmune encephalitis.
- Inflammatory CSF: pleocytosis, CSF-restricted oligoclonal bands, or an increased CSF IgG index.
- Brain biopsy demonstrating inflammatory infiltrates while excluding an alternative explanation, such as a tumor.
- Reasonable exclusion of other causes.
Two CSF abnormalities still represent one evidence category. EEG abnormalities are not an additional inflammatory category in this definition. A negative commercial antibody panel alone is insufficient to establish antibody-negative autoimmune encephalitis; the extent and methods of testing require review.[1][6] These criteria do not make brain biopsy a routine investigation.[2]
Children and Adolescents
Possible pediatric autoimmune encephalitis
The pediatric working-group framework is provisional and distinguishes neurological dysfunction from objective neuroinflammation.[7] Its clinical entry criteria, also incorporated into the 2024 Brazilian consensus, require all three of the following:[4]
- New neurological or psychiatric symptoms arising within 3 months in a previously healthy child.
- At least two of these features:
- Altered mental status or consciousness; encephalopathic slowing or epileptiform activity on EEG can substitute for this feature.
- Focal neurological deficits.
- Cognitive difficulty.
- Acute developmental regression.
- A movement disorder other than tics.
- Psychiatric symptoms.
- Seizures unexplained by a prior seizure disorder or another condition.
- Reasonable exclusion of alternative explanations, including other causes of CNS inflammation.
Further pediatric classification
The pediatric categories use the clinical presentation, exclusion of mimics, antibody findings, and evidence of neuroinflammation together:[7]
| Category | Supporting evidence |
|---|---|
| Probable antibody-negative pediatric autoimmune encephalitis | Compatible clinical findings, negative neural antibody testing, and at least one abnormal investigation demonstrating neuroinflammation, such as inflammatory CSF, supportive MRI, or inflammatory brain pathology. |
| Definite antibody-positive pediatric autoimmune encephalitis | A compatible presentation and a well-characterized, clinically relevant neural antibody. When the antibody is detected in CSF, separate inflammatory evidence is not required. With serum-only antibody detection, at least one additional investigation must demonstrate neuroinflammation. |
EEG abnormalities can support neurological dysfunction but do not count as objective neuroinflammation in this pediatric framework. Pre-existing developmental or psychiatric difficulties do not make autoimmune encephalitis impossible, but require particular attention to genetic, metabolic, and other alternatives.[7]
Interpretation and Diagnostic Pitfalls
- Exclude mimics throughout assessment: Infection, seizure-related abnormalities, toxic or metabolic encephalopathy, neoplasm, and primary psychiatric illness can resemble autoimmune encephalitis. Herpes simplex virus (HSV) encephalitis is an important treatable alternative; an early negative CSF polymerase chain reaction (PCR) test may require repetition when suspicion remains high.[8]
- Interpret antibodies with the phenotype: A positive result does not automatically establish causation. Unexpected or discordant results warrant specialist and laboratory review, including confirmatory testing when appropriate.[6]
- Normal investigations are not a universal exclusion: Routine CSF or MRI may be normal in antibody-associated disease. Nevertheless, the additional objective findings specified above remain necessary when applying the antibody-negative criteria.[2]
- Do not use nonspecific markers as confirmation: Thyroid antibodies and voltage-gated potassium channel (VGKC)-complex antibodies without an identified relevant antigen do not establish autoimmune encephalitis. Improvement with corticosteroids is also insufficient by itself to confirm the diagnosis.[8][6]
- Recognize the limits of the framework: Some antibody-associated syndromes fall outside the typical subacute presentation. Demyelinating presentations, acute disseminated encephalomyelitis (ADEM), and Bickerstaff brainstem encephalitis require their own syndrome-specific assessment. The historical Hashimoto encephalopathy label should not be assigned merely because thyroid antibodies are present.[2][8]
Patients who meet only possible criteria after a complete evaluation, or whose findings remain inconsistent, require specialist reassessment before the diagnostic label or treatment is escalated.[2]
Related Microchapters
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Graus F, Titulaer MJ, Balu R; et al. (2016). "A clinical approach to diagnosis of autoimmune encephalitis". The Lancet Neurology. 15 (4): 391–404. doi:10.1016/S1474-4422(15)00401-9. PMID 26906964.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Hahn C, Budhram A, Alikhani K; et al. (2024). "Canadian Consensus Guidelines for the Diagnosis and Treatment of Autoimmune Encephalitis in Adults". Canadian Journal of Neurological Sciences. 51 (6): 734–754. doi:10.1017/cjn.2024.16. PMID 38312020 Check
|pmid=value (help). - ↑ van Steenhoven RW, de Vries JM, Bruijstens AL; et al. (2023). "Mimics of Autoimmune Encephalitis: Validation of the 2016 Clinical Autoimmune Encephalitis Criteria". Neurology: Neuroimmunology & Neuroinflammation. 10 (6): e200148. doi:10.1212/NXI.0000000000200148. PMID 37582614 Check
|pmid=value (help). - ↑ 4.0 4.1 Dutra LA, Silva PVC, Ferreira JHF; et al. (2024). "Brazilian consensus recommendations on the diagnosis and treatment of autoimmune encephalitis in the adult and pediatric populations". Arquivos de Neuro-Psiquiatria. 82 (7). doi:10.1055/s-0044-1788586. PMID 39089672 Check
|pmid=value (help). - ↑ 5.0 5.1 5.2 Budhram A, Leung A, Nicolle MW, Burneo JG (2019). "Diagnosing autoimmune limbic encephalitis". CMAJ. 191 (19): E529–E534. doi:10.1503/cmaj.181548. PMID 31085562.
- ↑ 6.0 6.1 6.2 6.3 Dalmau J, Graus F (2023). "Diagnostic criteria for autoimmune encephalitis: utility and pitfalls for antibody-negative disease". The Lancet Neurology. 22 (6): 529–540. doi:10.1016/S1474-4422(23)00083-2. PMID 37210100 Check
|pmid=value (help). - ↑ 7.0 7.1 7.2 Cellucci T, Van Mater H, Graus F; et al. (2020). "Clinical approach to the diagnosis of autoimmune encephalitis in the pediatric patient". Neurology: Neuroimmunology & Neuroinflammation. 7 (2): e663. doi:10.1212/NXI.0000000000000663. PMID 31953309.
- ↑ 8.0 8.1 8.2 Michael BD, Huang Y, McKeever S; et al. (2026). "Management of suspected infectious and autoimmune encephalitis in adults – National Guidelines from the United Kingdom Joint Societies". Journal of Infection: 106873. doi:10.1016/j.jinf.2026.106873. PMID 42863638 Check
|pmid=value (help).