Autoimmune Encephalitis other diagnostic studies
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Julinka Auta Fernandes
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Differentiating Autoimmune Encephalitis from Other Conditions |
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Autoimmune Encephalitis On the Web |
Overview
In autoimmune encephalitis, additional diagnostic studies are selected according to the clinical phenotype, unresolved differential diagnosis, and residual symptoms. They may characterize cognitive impairment, identify peripheral nerve involvement or sleep disorders, or investigate an alternative disease. No single additional study independently confirms or excludes autoimmune encephalitis.[1]
Core investigations are discussed in Laboratory Findings, Electroencephalography, and Magnetic Resonance Imaging. Additional testing should complement this assessment rather than substitute for it.
Other Diagnostic Studies
Neuropsychological Assessment
In autoimmune encephalitis, formal neuropsychological assessment can characterize difficulties involving memory, attention, executive function, processing speed, language, and other cognitive domains. It is particularly useful when persistent cognitive symptoms affect school, work, or independent daily activities.[2]
Brief tools such as the Montreal Cognitive Assessment or Mini-Mental State Examination may provide an initial screen, but should not automatically replace a detailed assessment. Testing should be selected for the patient's age, language, educational background, and ability to participate.[2]
Serial assessment can document recovery and guide rehabilitation. Interpretation should account for fatigue, mood, sleep, medication effects, and the severity of acute illness. A cognitive deficit is not specific for autoimmune encephalitis and does not independently demonstrate active inflammation or relapse.[3]
A 2026 nationwide Danish study incorporated both bedside cognitive tests and formal neuropsychological assessment into long-term evaluation, supporting the importance of assessing cognitive outcome alongside general functional recovery.[4]
Nerve Conduction Studies and Electromyography
In autoimmune encephalitis, nerve conduction studies and electromyography (EMG) are selective investigations when peripheral nerve or neuromuscular involvement is suspected. They are not routine tests for isolated encephalitis.
The 2024 Canadian consensus identifies potential usefulness in contactin-associated protein-like 2 (CASPR2) antibody encephalitis and related neurological syndromes, including Bickerstaff brainstem encephalitis and stiff person spectrum disorders.[1]
Clinical reasons for referral can include persistent muscle twitching, cramps, stiffness, or weakness suggesting an additional peripheral process. The protocol should be directed by the examination and suspected syndrome. An abnormal EMG characterizes neuromuscular involvement; it does not itself establish autoimmune brain inflammation.[1]
Polysomnography
In autoimmune encephalitis, polysomnography may help investigate persistent sleep disturbance, particularly when sleep-disordered breathing or unusual sleep-related events are suspected. The 2021 long-term management recommendations support polysomnographic evaluation of residual sleep disorders when appropriate.[3]
Sleep studies assess a complication or associated sleep disorder rather than independently diagnose encephalitis. Selection should follow specialist assessment; not every patient with insomnia requires polysomnography. Acute respiratory compromise requires immediate clinical assessment rather than waiting for an elective sleep study.[3]
Brain Biopsy
In autoimmune encephalitis, brain biopsy is not routinely required. Most patients with a typical presentation and compatible investigations can be assessed without tissue sampling. An initially normal brain scan or negative antibody testing is not, by itself, a reason for biopsy.[5]
Biopsy may be considered after multidisciplinary review when an atypical or progressive lesion raises substantial concern for an alternative diagnosis, such as lymphoma, another neoplasm, or an inflammatory mimic, and when tissue could change management.[5]
Inflammatory cells on biopsy are not specific for autoimmune encephalitis. The principal value of tissue sampling is often to identify or exclude another pathology; a nonspecific inflammatory result should not be treated as proof of an autoimmune cause.[1]
Other Tissue Sampling
In autoimmune encephalitis, tissue sampling of a detected extracranial lesion may be required to establish the nature of a suspected associated tumor or systemic disorder. The site and procedure should be selected with the relevant specialist. Confirmation of a tumor does not independently establish that the neurological syndrome is autoimmune or paraneoplastic.[5]
Interpretation and Limitations
In autoimmune encephalitis, additional studies should answer a defined clinical question:
- Neuropsychological testing characterizes cognitive impairment and recovery.
- Nerve conduction studies and EMG assess suspected peripheral involvement.
- Polysomnography evaluates selected sleep-related complications.
- Biopsy is reserved for situations where tissue diagnosis is likely to alter management.
Results must be interpreted with the clinical course and the core investigations. Additional studies should not be ordered indiscriminately or used to label nonspecific abnormalities as evidence of autoimmune encephalitis.[1][3]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 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 Galioto R, Grezmak T, Swetlik C, et al. Neuropsychological Testing in Autoimmune Encephalitis: A Scoping Review. Neurology: Neuroimmunology & Neuroinflammation. 2024;11(1):e200179. doi:10.1212/NXI.0000000000200179. PMID:37949665.
- ↑ 3.0 3.1 3.2 3.3 Abboud H, Probasco J, Irani SR, et al. Autoimmune encephalitis: proposed recommendations for symptomatic and long-term management. Journal of Neurology, Neurosurgery & Psychiatry. 2021;92(8):897–907. doi:10.1136/jnnp-2020-325302. PMID:33649021.
- ↑ Gaist TA, Lodahl LR, Thorup HA, et al. Long-Term Outcomes in Autoimmune Encephalitis: A Nationwide, Clinical Study in Denmark. Neurology: Neuroimmunology & Neuroinflammation. 2026;13(5):e200641. doi:10.1212/NXI.0000000000200641. PMID:42636416.
- ↑ 5.0 5.1 5.2 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.