HSV encephalitis and other viral encephalitis — Rapid

Synopsis

Recognise encephalitis from altered cognition, focal seizure and behavioural change, start intravenous aciclovir before confirmation, use MRI, EEG and repeat cerebrospinal-fluid PCR correctly, and prevent renal and neurological treatment harm.

Encephalitis means brain dysfunction with evidence of inflammation; meningism can coexist but altered cognition and focal features are decisive.
HSV-1 is the most important treatable sporadic cause in adults, often affecting temporal lobes and producing memory, language, behaviour or seizure symptoms.
Start aciclovir 10 mg/kg intravenously every 8 hours immediately, using protocol weight, hydration and renal adjustment.
Perform lumbar puncture when safe for cells, glucose, protein and HSV, VZV and selected pathogen PCR, without postponing aciclovir.
MRI is more sensitive than CT for temporal and limbic inflammation; EEG detects temporal periodic activity and non-convulsive seizures.
Repeat HSV PCR after 24 to 72 hours when an early negative result conflicts with a strong syndrome or characteristic MRI.
Treat proven HSV encephalitis for at least 14 days in immunocompetent adults and commonly 21 days in immune suppression, with repeat CSF before stopping when indicated.
Investigate autoimmune encephalitis, metabolic, toxic, epileptic and structural alternatives when virology is negative or recovery is atypical.

Key red flags

New focal seizure, temporal-lobe symptom or personality change with fever is HSV encephalitis until urgently assessed.

Falling consciousness, recurrent seizure or airway compromise requires critical care and continuous neurological monitoring.

A negative HSV PCR very early in illness does not exclude disease and should prompt repeat CSF when probability remains high.

Rising creatinine, myoclonus or worsening confusion during aciclovir can be crystal nephropathy or neurotoxicity as well as infection.

Temporal-lobe syndrome

Fever, memory failure, dysphasia, personality change, olfactory symptoms or focal seizure strongly supports HSV encephalitis.

VZV vasculitic disease

Recent zoster, cranial neuropathy, multifocal infarction or vascular headache raises VZV even without rash.

Non-convulsive status

Persistent reduced awareness, subtle twitching or fluctuating cognition can be ongoing seizure and requires urgent EEG.

Autoimmune mimic

Psychosis, dyskinesia, autonomic instability and seizures with negative infectious tests raises autoimmune encephalitis but does not justify early aciclovir omission.

Investigation priorities

CSF PCR and inflammatory profileFirst step

Detect HSV, VZV and selected viruses while characterising meningeal inflammation.

Management branches

ASSESSStart aciclovir on suspicion

Encephalitis is possible from altered mental status plus fever, seizure or focal findings.

Stabilise airway, breathing, circulation and glucose, treat convulsive seizure and obtain senior neurology and critical-care review.
Give intravenous aciclovir immediately with renal-adjusted dosing and continue ceftriaxone when bacterial meningitis remains plausible.
Perform lumbar puncture when safe and send sufficient CSF for bacterial and viral PCR, culture and later autoimmune testing.
Arrange urgent MRI and EEG; use CT only for immediate mass-effect or alternative emergencies, not as a gate before aciclovir.

Key medicines

Intravenous aciclovirGive aciclovir 10 mg/kg intravenously every 8 hours using protocol weight, renal adjustment and adequate hydration for suspected HSV encephalitis.Infuse appropriately, monitor creatinine and neurological state and consider crystal nephropathy or accumulation when renal function or cognition worsens.

Antiseizure treatmentUse the current emergency benzodiazepine and longer-acting antiseizure protocol for convulsive or electrographic seizures.Dose for organ function and interactions and use EEG to avoid both untreated non-convulsive status and unnecessary prolonged sedation.

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