Autoimmune Encephalitis electroencephalography
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Julinka Auta Fernandes
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Overview
In autoimmune encephalitis, electroencephalography (EEG) helps identify seizures, nonconvulsive status epilepticus, and focal or generalized cerebral dysfunction. Common abnormalities include background slowing and epileptiform discharges, but these are not specific for an autoimmune cause. A normal EEG does not exclude autoimmune encephalitis.[1][2]
The 2026 United Kingdom Joint Societies guidelines recommend considering EEG in all patients with suspected infectious or autoimmune encephalitis, ideally within 48–72 hours. Suspected ongoing seizures or status epilepticus require urgent assessment rather than waiting for this interval.[3]
Indications for EEG
In autoimmune encephalitis, EEG is particularly useful for:
- New seizures or recurrent episodes of impaired awareness.
- Unexplained confusion, fluctuating consciousness, or persistent reduced responsiveness.
- Persistent altered mental status after a clinical seizure.
- Subtle motor events or abnormal movements whose relationship to seizures is uncertain.
- Monitoring known electrographic seizures and response to treatment.
Repeat or prolonged recordings should be considered when the initial EEG is normal but the patient deteriorates or suspicion of intermittent seizures persists.[3][4]
EEG Findings in Autoimmune Encephalitis
Background and Epileptiform Abnormalities
In autoimmune encephalitis, EEG may demonstrate the following findings:
| Finding | Interpretation |
|---|---|
| Generalized background slowing | Supports diffuse cerebral dysfunction but is not specific for autoimmune inflammation. |
| Focal slowing, including temporal slowing | Suggests regional cerebral dysfunction and may support a limbic presentation in the appropriate clinical setting. |
| Focal or multifocal epileptiform discharges | Indicates epileptogenic potential; does not alone establish ongoing seizures or an autoimmune cause. |
| Electrographic seizures | May occur with subtle clinical signs or without an obvious clinical seizure. |
| Lateralized periodic discharges | May accompany autoimmune encephalitis, but require assessment of frequency, evolution, accompanying features, and clinical context. |
These findings should be interpreted by an experienced electroencephalographer. Standardized terminology distinguishes background abnormalities, periodic or rhythmic patterns, and electrographic or electroclinical seizures.[1][2][5]
Extreme Delta Brush
In autoimmune encephalitis, extreme delta brush is particularly associated with N-methyl-D-aspartate receptor (NMDAR) antibody encephalitis. It consists of rhythmic delta activity, approximately 1–3 hertz, with superimposed fast activity, typically in the beta range.[7]
The pattern occurs in only a subset of patients and is not unique to NMDAR antibody encephalitis. Its absence does not exclude that diagnosis, and its presence does not replace clinical assessment and appropriate antibody testing.[1]
Extreme delta brush has been associated with a prolonged and severe illness in observational cohorts. However, it should not be used alone to predict an individual's outcome. It must also be distinguished from medication-related fast activity and muscle artifact.[7]
Extreme delta brush is not automatically an electrographic seizure or status epilepticus. Its ictal significance requires assessment of evolution, clinical correlation, and the complete recording using accepted EEG criteria.[5]
LGI1 Antibody Encephalitis
In autoimmune encephalitis associated with leucine-rich glioma-inactivated protein 1 (LGI1) antibodies, EEG can show temporal slowing, epileptiform abnormalities, or subclinical seizures. However, patients with faciobrachial dystonic seizures (FBDS) may have no clear ictal change on a routine scalp EEG.[2]
A recording without an ictal scalp correlate should therefore not automatically invalidate clinically characteristic brief events. Video documentation and specialist assessment are helpful, while alternative explanations for the events must still be considered.[2]
Nonconvulsive Seizures and Status Epilepticus
In autoimmune encephalitis, electrographic seizures can contribute to confusion, reduced consciousness, or failure to recover after an apparent convulsion. Prolonged EEG can identify seizures that would otherwise be missed clinically.[4]
Periodic discharges or rhythmic slowing are not synonymous with status epilepticus. Some patterns lie on the ictal-interictal continuum, meaning they require clinical interpretation and may warrant additional evaluation or a treatment trial. Classification should follow accepted electrographic and electroclinical criteria rather than appearance alone.[5]
Continuous Video-EEG Monitoring
In autoimmune encephalitis, continuous EEG (cEEG) with synchronized video is particularly useful in critically ill patients with persistent altered consciousness, suspected nonconvulsive seizures, or ongoing status epilepticus. Video correlation can help distinguish seizures from dyskinesias and other nonepileptic movements.[4]
The American Clinical Neurophysiology Society consensus recommends at least 24 hours of recording for most critical-care indications, with shorter or longer monitoring selected according to the clinical question and initial findings. This is not a requirement for every stable patient with autoimmune encephalitis.[4]
Diagnostic Limitations and Follow-Up
In autoimmune encephalitis, EEG findings must be interpreted alongside the clinical syndrome and other investigations:
- Nonspecificity: slowing and epileptiform abnormalities also occur in infectious, toxic, metabolic, structural, and other neurological disorders.
- Sampling limitations: a short recording may miss intermittent abnormalities.
- Confounding factors: sedatives, antiseizure medicines, sleep state, and artifact affect interpretation.
- Diagnostic criteria: temporal epileptic or slow-wave activity can support definite autoimmune limbic encephalitis when the other required criteria are met; EEG abnormalities alone do not establish that diagnosis.[9][5]
Repeat EEG should answer a defined question, such as whether new events are seizures or whether electrographic seizures have resolved. Serial findings should be compared with the examination, medication exposure, and clinical course rather than treated as a stand-alone measure of autoimmune disease activity.[3][4]
References
- ↑ 1.0 1.1 1.2 Hahn C, Budhram A, Alikhani K, et al. Canadian Consensus Guidelines for the Diagnosis and Treatment of Autoimmune Encephalitis in Adults. Canadian Journal of Neurological Sciences. 2024;51(6):734–754. doi:10.1017/cjn.2024.16. PMID:38312020.
- ↑ 2.0 2.1 2.2 2.3 Abboud H, Probasco JC, Irani S, et al. Autoimmune encephalitis: proposed best practice recommendations for diagnosis and acute management. Journal of Neurology, Neurosurgery & Psychiatry. 2021;92(7):757–768. doi:10.1136/jnnp-2020-325300. PMID:33649022.
- ↑ 3.0 3.1 3.2 Michael BD, Huang Y, McKeever S, et al. Management of suspected infectious and autoimmune encephalitis in adults – National Guidelines from the United Kingdom Joint Societies. Journal of Infection. Published online October 2026:106873. doi:10.1016/j.jinf.2026.106873. PMID:42863638.
- ↑ 4.0 4.1 4.2 4.3 4.4 Herman ST, Abend NS, Bleck TP, et al. Consensus statement on continuous EEG in critically ill adults and children, part I: indications. Journal of Clinical Neurophysiology. 2015;32(2):87–95. doi:10.1097/WNP.0000000000000166. PMID:25626778.
- ↑ 5.0 5.1 5.2 5.3 Hirsch LJ, Fong MWK, Leitinger M, et al. American Clinical Neurophysiology Society's Standardized Critical Care EEG Terminology: 2021 Version. Journal of Clinical Neurophysiology. 2021;38(1):1–29. doi:10.1097/WNP.0000000000000806. PMID:33475321.
- ↑ Krol LR. EEG Brainwaves.svg. Wikimedia Commons. December 3, 2020. Original work. CC0 public-domain dedication. Accessed November 6, 2026.
- ↑ 7.0 7.1 Schmitt SE, Pargeon K, Frechette ES, Hirsch LJ, Dalmau J, Friedman D. 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.
- ↑ Mizoguchi T, Hara M, Hirose S, Nakajima H. Extreme delta brush in anti-NMDAr encephalitis.png. Wikimedia Commons. Image dated February 15, 2022. Original article available at PubMed Central, PMC8885512. Creative Commons Attribution 4.0. Accessed November 6, 2026.
- ↑ Graus F, Titulaer MJ, Balu R, et al. A clinical approach to diagnosis of autoimmune encephalitis. Lancet Neurology. 2016;15(4):391–404. doi:10.1016/S1474-4422(15)00401-9. PMID:26906964.