Table 2.

Investigations in autoimmune encephalitis

Investigation	Expected results in autoimmune encephalitis	Notes
EEG	Focal or diffuse slow activity +/− foci of epileptic activity (subclinical seizures)11
	Extreme delta brush pattern more specific and associated with worse outcome and increased likelihood of ICU admission33
MRI	Unilateral or bilateral hippocampal MRI FLAIR-T2 hyperintensities (typical of limbic encephalitis)5	Not a sensitive investigation, even when marked neurological component.34 More useful for excluding other diagnoses (dementia, demyelinating conditions, vasculitis, tumour, etc) particularly in the elderly where these pathologies are more common.
	Transient contrast enhancement in medial temporal lobe(s) (especially in paraneoplastic encephalitis)5
18F-FDG-PET	Medial temporal lobe hypermetabolism35	May be more sensitive than MRI but lower specificity.36
CSF	Pleocytosis (6–14 cells/µL) (may be earlier sign)37	CSF antibodies are more relevant than serum (higher sensitivity and specificity, better correlation to clinical course with treatment)21
	Oligoclonal bands (may be later sign)37
	Specific autoantibodies
Whole body PET/CT+/−US testes/ovaries	To look for a tumour if a paraneoplastic process suspected
ANA	Non-specific marker of systemic inflammation

ANA, antinuclear antibodies; FDG-PET, fluorodeoxyglucose positron emission tomography; FLAIR2, fluid attunated inversion recovery/T2 weighted; ICU, intensive care unit; US, ultrasound.