Autoimmune Encephalitis differential diagnosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Julinka Auta Fernandes
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Overview
Autoimmune encephalitis must be differentiated from other diseases that cause subacute memory loss, altered mental status, psychiatric symptoms, seizures, and movement disorders. Important alternatives include infectious encephalitis, epilepsy, toxic-metabolic encephalopathy, vascular disease, other inflammatory brain disorders, central nervous system (CNS) neoplasms, neurodegenerative disease, and primary psychiatric disorders.[1] Evaluation combines the clinical course, neurological examination, brain imaging, electroencephalography (EEG), cerebrospinal fluid (CSF) studies, and appropriately interpreted antibody testing. Investigations for supporting evidence and competing diagnoses proceed in parallel.[2]
Differentiating Autoimmune Encephalitis from other Diseases
Urgent exclusions
Autoimmune encephalitis assessment must promptly address infectious encephalitis, ongoing seizures, hypoglycemia, severe electrolyte disturbances, intoxication or withdrawal, and acute vascular disease. Suspected herpes encephalitis requires empiric antiviral treatment while investigations continue; antibody results should not delay this assessment.[3]
Differential diagnosis table
Autoimmune encephalitis has a broad differential diagnosis. The table below summarizes findings that help distinguish it from other conditions causing cognitive or behavioral change, seizures, altered consciousness, or focal neurological abnormalities. Urgent and treatable alternatives are presented first; the order does not imply a fixed prevalence ranking.
Abbreviations: central nervous system (CNS); cerebrospinal fluid (CSF); electroencephalography (EEG); magnetic resonance imaging (MRI); polymerase chain reaction (PCR); immunoglobulin G (IgG).
| Disease or diagnostic category | Similar features | Findings favoring the alternative diagnosis | Useful investigations and limitations |
|---|---|---|---|
| Autoimmune encephalitis: reference pattern | Subacute cognitive, behavioral, psychiatric, seizure, or movement disorder syndrome. | A compatible syndrome with supportive inflammatory findings or a clinically relevant neuronal antibody, after reasonable exclusion of alternatives. | MRI and CSF can be normal. Apply syndrome-specific criteria; no single test establishes all forms of autoimmune encephalitis.[1] |
| Herpes simplex encephalitis and other acute viral encephalitides | Fever, confusion, seizures, memory impairment, and temporal-lobe abnormalities. | An acute febrile course or compatible infectious exposure supports infection, but clinical and imaging overlap is substantial. | CSF viral PCR and exposure-directed testing. An early negative herpes simplex virus PCR does not exclude infection; repeat CSF testing when suspicion remains high.[3] |
| Other CNS infections | Encephalopathy, seizures, psychiatric changes, or inflammatory CSF. | Consider bacterial infection, tuberculosis, fungal infection, human immunodeficiency virus (HIV)-related disease, neurosyphilis, and opportunistic infection according to immune status, geography, and exposure. Low CSF glucose or a meningitic course warrants broader investigation. | CSF microbiology, antigen or molecular assays, cultures, and blood testing selected by context. A negative routine viral panel does not exclude these infections.[4] |
| Nonconvulsive status epilepticus, noninflammatory epilepsy, and postictal encephalopathy | Confusion, amnesia, behavioral change, and temporal MRI abnormalities. | An ictal or postictal course may explain the presentation without primary inflammation. | Urgent or prolonged EEG and reassessment after seizure control. Seizures can also result from autoimmune encephalitis, so identifying them does not settle the underlying cause.[5] |
| Toxic encephalopathy, medication effects, and substance withdrawal | Agitation, hallucinations, impaired consciousness, or seizures. | A temporal relationship to medication changes, intoxication, withdrawal, or exposure supports a toxic cause. | Medication and exposure history, targeted toxicology, and metabolic testing. Routine toxicology screens do not detect every substance.[5] |
| Metabolic, endocrine, or hypoxic encephalopathy | Delirium, cognitive dysfunction, abnormal movements, or seizures. | A relevant physiological disturbance, such as hypoglycemia, severe sodium disturbance, hepatic or renal failure, thyroid dysfunction, or hypoxia. | Glucose, electrolytes, renal and liver tests, oxygenation, and additional tests guided by the presentation. A metabolic abnormality may coexist with autoimmune encephalitis; hyponatremia can accompany leucine-rich glioma-inactivated 1 (LGI1) disease.[2] |
| Wernicke encephalopathy | Confusion, memory impairment, and gait disturbance. | Nutritional deficiency risk, ocular abnormalities, and cerebellar dysfunction. The complete classic triad need not be present. | Clinical assessment and supportive MRI; investigate nutritional risk. Suspected disease requires prompt thiamine treatment rather than waiting for confirmatory testing.[6] |
| Acute stroke, intracranial hemorrhage, or cerebral venous thrombosis | Altered consciousness, focal deficits, or seizures. | Abrupt onset and an arterial, hemorrhagic, or venous imaging pattern favor vascular disease. | Urgent brain imaging and arterial or venous imaging as indicated.[5] |
| Posterior reversible encephalopathy syndrome | Encephalopathy, seizures, headache, and visual disturbance. | Severe hypertension, renal disease, eclampsia, or a relevant drug exposure; MRI often demonstrates posterior-predominant vasogenic edema. | Blood pressure assessment, renal and exposure evaluation, and MRI. Distribution can be atypical and hypertension is not universal.[7] |
| Neuroleptic malignant syndrome, serotonin syndrome, and malignant catatonia | Fever, altered mental status, rigidity, and autonomic instability. | Dopamine-blocking drug exposure supports neuroleptic malignant syndrome; serotonergic exposure with hyperreflexia and myoclonus supports serotonin toxicity. Catatonia has several psychiatric and medical causes. | Drug history, neurological examination, creatine kinase, and evaluation for systemic complications. Catatonia can occur in autoimmune encephalitis and is not an etiological diagnosis by itself.[8] |
| Acute disseminated encephalomyelitis and myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease | Encephalopathy, seizures, and multifocal neurological deficits. | Multifocal demyelinating lesions, optic neuritis, or myelitis support a demyelinating syndrome. MOG antibody-associated disease can also cause cortical encephalitis with seizures. | Brain and, when indicated, spinal or optic-nerve MRI; phenotype-directed serum MOG-IgG cell-based testing. Interpret low-positive results within the diagnostic criteria.[9] |
| Multiple sclerosis and neuromyelitis optica spectrum disorder | Focal CNS symptoms and inflammatory MRI abnormalities; encephalopathic presentations can occur. | Characteristic demyelinating lesions, optic neuritis, myelitis, or area postrema symptoms favor the corresponding syndrome. | Apply the relevant diagnostic criteria and obtain appropriate CNS imaging; serum aquaporin-4 IgG testing is useful when neuromyelitis optica spectrum disorder is suspected.[9][10] |
| Neuropsychiatric systemic lupus erythematosus | Psychosis, seizures, cognitive dysfunction, or acute confusional state. | Established systemic disease, evidence of disease activity, or an antiphospholipid-associated vascular process may support attribution. | Systemic assessment, relevant serology, MRI, EEG, and CSF as indicated. Exclude infection, medication effects, and other causes before attributing symptoms to lupus.[11] |
| Primary angiitis of the CNS | Headache, cognitive change, seizures, and focal deficits. | Multifocal ischemic or hemorrhagic lesions and vascular abnormalities may favor vasculitis, although no MRI pattern is specific. | Specialist-directed vascular imaging and, in selected cases, biopsy. Normal angiography does not exclude small-vessel disease.[12] |
| Neurosarcoidosis | Cognitive dysfunction, seizures, or inflammatory CSF and MRI findings. | Compatible neurological involvement with evidence of systemic sarcoidosis supports consideration. | Search for accessible systemic disease and obtain tissue confirmation when feasible. Nonneural biopsy can support probable neurosarcoidosis; neural biopsy supports definite disease. Exclude infection and malignancy.[13] |
| CNS neoplasms, including glioma and primary CNS lymphoma | Subacute behavioral change, memory impairment, seizures, and temporal-lobe lesions. | Progressive lesion enlargement, mass effect, or pronounced enhancement should prompt reconsideration of a neoplasm.[14] | Contrast-enhanced MRI, selected CSF cytology or flow cytometry when safe, and tissue diagnosis when indicated. If lymphoma is suspected, coordinate biopsy before corticosteroids whenever clinically feasible because steroids can reduce diagnostic yield.[15] |
| Creutzfeldt-Jakob disease | Rapid cognitive decline, myoclonus, ataxia, or psychiatric change. | Cortical ribboning or characteristic striatal diffusion restriction supports a prion disorder in the appropriate syndrome. | CSF real-time quaking-induced conversion, diffusion MRI, and EEG. CSF 14-3-3 and total tau are neuronal injury markers and are not independently specific for prion disease.[16] |
| Other neurodegenerative disorders | Cognitive, behavioral, psychiatric, or movement abnormalities. | A progressive course and a recognizable Alzheimer, frontotemporal, or Lewy body phenotype favor neurodegeneration. | Longitudinal assessment, neuropsychology, imaging, and disease-specific biomarkers when appropriate. Time course alone is insufficient because some autoimmune syndromes evolve slowly.[17] |
| Primary psychiatric disorders | Psychosis, mood disturbance, agitation, or catatonia. | An isolated psychiatric syndrome without evolving neurological features or supporting investigations favors a primary psychiatric explanation. | Assess for cognitive decline, seizures, movement disorder, altered consciousness, or autonomic dysfunction that warrants neurological investigation. Neither psychiatric symptoms alone nor serum neuronal antibody positivity alone establishes autoimmune psychosis or encephalitis.[18] |
| Functional neurological or functional cognitive disorder | Seizure-like events, movement symptoms, or cognitive complaints. | Positive examination findings supporting a functional disorder, interpreted within the clinical history. | Specialist neurological and cognitive assessment. Normal MRI or CSF alone is insufficient to diagnose a functional disorder.[17] |
| Genetic, mitochondrial, or inherited metabolic disorders | Seizures, regression, psychiatric changes, or encephalopathy. | Pre-existing developmental difficulties, recurrent decompensation, family history, or multisystem findings should broaden the differential, especially in children. | Phenotype-directed metabolic and genetic assessment. These disorders should be considered alongside acquired inflammatory causes rather than excluded by a negative antibody panel.[19] |
Diagnostic pitfalls and overlapping disorders
Autoimmune encephalitis should be assessed using the complete clinical syndrome rather than an isolated abnormal test.
- Possible autoimmune encephalitis is an entry point for evaluation: It is not equivalent to a confirmed autoimmune diagnosis, and mimics may meet these initial criteria.[14]
- Antibody results require clinical correlation: Thyroid peroxidase antibodies, low-specificity serum findings, and voltage-gated potassium channel complex antibodies without LGI1 or contactin-associated protein-like 2 (CASPR2) specificity can mislead. Immunotherapy response alone does not confirm the diagnosis.[17]
- Normal investigations do not independently exclude disease: Normal MRI or routine CSF can occur in autoimmune encephalitis. Conversely, temporal MRI abnormalities and EEG slowing are not specific.[1]
- Negative antibody testing does not establish seronegative disease: Antibody-negative autoimmune encephalitis requires appropriate clinical criteria, supporting findings, and exclusion of alternatives. Paired serum and CSF testing should be selected and interpreted according to the suspected antibody syndrome.[2]
- Some inflammatory disorders are related or overlapping: glial fibrillary acidic protein (GFAP) astrocytopathy, neuro-Behçet disease, and chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS) can enter the differential according to the anatomical syndrome and MRI pattern. Demyelinating disease and neuronal autoimmune encephalitis may coexist.[5][1]
- Deterioration after herpes encephalitis has more than one explanation: Distinguish persistent or recurrent infection from a subsequent autoimmune syndrome, often involving N-methyl-D-aspartate receptor (NMDAR) antibodies.[20]
Pediatric considerations
Autoimmune encephalitis in children requires age-appropriate assessment of developmental regression, cognition, behavior, seizures, and movement abnormalities. Adult criteria should not be applied uncritically. Consider genetic, metabolic, neurodevelopmental, infectious, and demyelinating alternatives, particularly when the history predates the apparent acute illness.[19]
References
- ↑ 1.0 1.1 1.2 1.3 Graus F, Titulaer MJ, Balu R, et al. (2016). "A clinical approach to diagnosis of autoimmune encephalitis". Lancet Neurol. 15 (4): 391–404. doi:10.1016/S1474-4422(15)00401-9. PMID 26906964.
- ↑ 2.0 2.1 2.2 Hahn C, Budhram A, Alikhani K, et al. (2024). "Canadian Consensus Guidelines for the Diagnosis and Treatment of Autoimmune Encephalitis in Adults". Can J Neurol Sci. 51 (6): 734–754. doi:10.1017/cjn.2024.16. PMID 38312020 Check
|pmid=value (help). - ↑ 3.0 3.1 Michael BD, Huang Y, McKeever S, et al. (2026-10). "Management of suspected infectious and autoimmune encephalitis in adults – National Guidelines from the United Kingdom Joint Societies". J Infect: 106873. doi:10.1016/j.jinf.2026.106873. PMID 42863638 Check
|pmid=value (help). Check date values in:|date=(help) - ↑ Venkatesan A, Tunkel AR, Bloch KC, et al. (2013). "Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the international encephalitis consortium". Clin Infect Dis. 57 (8): 1114–1128. doi:10.1093/cid/cit458. PMID 23861361.
- ↑ 5.0 5.1 5.2 5.3 Abboud H, Probasco JC, Irani S, et al. (2021). "Autoimmune encephalitis: proposed best practice recommendations for diagnosis and acute management". J Neurol Neurosurg Psychiatry. 92 (7): 757–768. doi:10.1136/jnnp-2020-325300. PMID 33649022 Check
|pmid=value (help). - ↑ Galvin R, Bråthen G, Ivashynka A, et al. (2010). "EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy". Eur J Neurol. 17 (12): 1408–1418. doi:10.1111/j.1468-1331.2010.03153.x. PMID 20642790.
- ↑ Fugate JE, Claassen DO, Cloft HJ, et al. (2010). "Posterior reversible encephalopathy syndrome: associated clinical and radiologic findings". Mayo Clin Proc. 85 (5): 427–432. doi:10.4065/mcp.2009.0590. PMID 20435835.
- ↑ Rogers JP, Oldham MA, Fricchione G, et al. (2023). "Evidence-based consensus guidelines for the management of catatonia: Recommendations from the British Association for Psychopharmacology". J Psychopharmacol. 37 (4): 327–369. doi:10.1177/02698811231158232. PMID 37039129 Check
|pmid=value (help). - ↑ 9.0 9.1 Banwell B, Bennett JL, Marignier R, et al. (2023). "Diagnosis of myelin oligodendrocyte glycoprotein antibody-associated disease: International MOGAD Panel proposed criteria". Lancet Neurol. 22 (3): 268–282. doi:10.1016/S1474-4422(22)00431-8. PMID 36706773 Check
|pmid=value (help). - ↑ Wingerchuk DM, Banwell B, Bennett JL, et al. (2015). "International consensus diagnostic criteria for neuromyelitis optica spectrum disorders". Neurology. 85 (2): 177–189. doi:10.1212/WNL.0000000000001729. PMID 26092914.
- ↑ Bertsias GK, Ioannidis J, Aringer M, et al. (2010). "EULAR recommendations for the management of systemic lupus erythematosus with neuropsychiatric manifestations: report of a task force of the EULAR standing committee for clinical affairs". Ann Rheum Dis. 69 (12): 2074–2082. doi:10.1136/ard.2010.130476. PMID 20724309. Vancouver style error: initials (help)
- ↑ Pascarella R, Antonenko K, Boulouis G, et al. (2023). "European Stroke Organisation (ESO) guidelines on Primary Angiitis of the Central Nervous System (PACNS)". Eur Stroke J. 8 (4): 842–879. doi:10.1177/23969873231190431. PMID 37903069 Check
|pmid=value (help). - ↑ Stern BJ, Royal W 3rd, Gelfand JM, et al. (2018). "Definition and Consensus Diagnostic Criteria for Neurosarcoidosis: From the Neurosarcoidosis Consortium Consensus Group". JAMA Neurol. 75 (12): 1546–1553. doi:10.1001/jamaneurol.2018.2295. PMID 30167654.
- ↑ 14.0 14.1 Van Steenhoven RW, de Vries JM, Bruijstens AL, et al. (2023). "Mimics of Autoimmune Encephalitis: Validation of the 2016 Clinical Autoimmune Encephalitis Criteria". Neurol Neuroimmunol Neuroinflamm. 10 (6): e200148. doi:10.1212/NXI.0000000000200148. PMID 37582614 Check
|pmid=value (help). - ↑ Ferreri A, Illerhaus G, Doorduijn JK, et al. (2024). "Primary central nervous system lymphomas: EHA–ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up". Ann Oncol. 35 (6): 491–507. doi:10.1016/j.annonc.2023.11.010. Vancouver style error: initials (help)
- ↑ Hermann P, Appleby B, Brandel JP, et al. (2021). "Biomarkers and diagnostic guidelines for sporadic Creutzfeldt-Jakob disease". Lancet Neurol. 20 (3): 235–246. doi:10.1016/S1474-4422(20)30477-4. PMID 33609480 Check
|pmid=value (help). - ↑ 17.0 17.1 17.2 Flanagan EP, Geschwind MD, et al. (2023). "Autoimmune Encephalitis Misdiagnosis in Adults". JAMA Neurol. 80 (1): 30–39. doi:10.1001/jamaneurol.2022.4251.
- ↑ Pollak TA, et al. (2020). "Autoimmune psychosis: an international consensus on an approach to the diagnosis and management of psychosis of suspected autoimmune origin". Lancet Psychiatry. 7 (1): 93–108. doi:10.1016/S2215-0366(19)30290-1. PMID 31669058.
- ↑ 19.0 19.1 Cellucci T, Van Mater H, Graus F, et al. (2020). "Clinical approach to the diagnosis of autoimmune encephalitis in the pediatric patient". Neurol Neuroimmunol Neuroinflamm. 7 (2): e663. doi:10.1212/NXI.0000000000000663. PMID 31953309.
- ↑ Armangue T, Spatola M, Vlagea A, et al. (2018). "Frequency, symptoms, risk factors, and outcomes of autoimmune encephalitis after herpes simplex encephalitis: a prospective observational study and retrospective analysis". Lancet Neurol. 17 (9): 760–772. doi:10.1016/S1474-4422(18)30244-8. PMID 30049614.