HSV Encephalitis Treatment Protocol
Initiate intravenous acyclovir 10 mg/kg every 8 hours immediately upon clinical suspicion of HSV encephalitis, without waiting for confirmatory testing, and continue for 14-21 days. 1, 2
Immediate Treatment Initiation
Start acyclovir within 6 hours of admission if:
- Initial CSF or imaging suggests viral encephalitis
- Results will be delayed
- Patient is severely ill or deteriorating
- Clinical suspicion remains high even with normal initial studies 2
Early treatment is critical: Mortality drops to 8% when acyclovir is started within 4 days of symptom onset, compared to >70% without treatment. Delays beyond 2 days from hospital admission significantly worsen outcomes. 1, 2
Standard Dosing Protocol
Adults with normal renal function:
Neonates:
- Higher-dose acyclovir 20 mg/kg IV every 8 hours for 21 days has reduced mortality to 5% with better developmental outcomes 1
Renal impairment:
- Dose adjustment mandatory - acyclovir causes crystalluria and obstructive nephropathy in up to 20% of patients, typically after 4 days of therapy 2
Duration and Monitoring
Continue treatment for 14-21 days, then perform repeat lumbar puncture:
A negative CSF PCR at end of therapy correlates with better outcomes. Relapse rates reach 5-8% in adults and children when shorter courses (10 days) or standard doses are used, but relapses are not documented with higher doses (20 mg/kg) for 21 days in neonates. 1
Acyclovir-Resistant Cases
If CSF remains HSV PCR-positive despite adequate acyclovir therapy, consider acyclovir resistance and add foscarnet to the regimen. 3, 4
Adjunctive Corticosteroids - Controversial
Current guideline stance: Not officially recommended 1
However, one retrospective study of 45 patients showed worse outcomes in those NOT receiving corticosteroids. 1 The evidence remains insufficient for formal recommendation, though a European randomized trial is underway. 2
For VZV encephalitis specifically: Corticosteroids (e.g., prednisolone 60-80 mg daily for 3-5 days) are more commonly used due to the inflammatory/vasculitic component, particularly when vasculitis is present. 2
Weight-Based Considerations
Recent data suggests low-weight patients (<79 kg) may require higher absolute doses - minimum 2550 mg/day (850 mg every 8 hours) when renal function permits, as standard weight-based dosing may be insufficient. 5
Post-HSE Autoimmune Encephalitis
Critical pitfall: Nearly 30% of patients develop neurological relapses after initial HSE episode. 3
If relapse occurs with negative CSF HSV PCR:
- Consider autoimmune encephalitis (AE) post-HSE
- Test for anti-NMDA receptor antibodies (most common) and other neuronal antibodies
- Treat with first-line immunotherapy: corticosteroids, IVIG, or plasma exchange
- Escalate to rituximab or cyclophosphamide if needed 3
If relapse occurs with positive CSF HSV PCR:
- Suspect acyclovir resistance
- Add foscarnet 3
Prognostic Factors
Poor outcomes are independently predicted by:
- Age >30 years
- Glasgow Coma Score <6
- Symptom duration >4 days before treatment
- Simplified Acute Physiology Score ≥7 at admission
- Delay ≥2 days from admission to acyclovir initiation 1
Despite optimal acyclovir treatment, 18-month mortality remains 28%, with less than half of survivors returning to normal function. 1