What is the initial treatment for suspected viral encephalitis, particularly due to Herpes Simplex Virus (HSV)?

Initial Treatment for Suspected Viral Encephalitis (HSV)

Intravenous aciclovir (10 mg/kg every 8 hours) should be started immediately upon suspicion of HSV encephalitis, ideally within 6 hours of admission, without waiting for confirmation of HSV by PCR. 1, 2

Diagnostic and Treatment Algorithm

When to Start Treatment

• Start IV aciclovir if:
  • Initial CSF and/or imaging findings suggest viral encephalitis
  • Within 6 hours of admission if these results will not be available
  • If the patient is very unwell or deteriorating 1
  • Even if first CSF microscopy or imaging is normal but clinical suspicion remains high 1

Dosing Guidelines

• Adults and children >12 years: 10 mg/kg IV every 8 hours 1, 2, 3
• Children 3 months-12 years: 500 mg/m² IV every 8 hours 1, 2
• Dose adjustment: Required in patients with pre-existing renal impairment 1, 3

Duration of Treatment

• Proven HSV encephalitis: 14-21 days of IV aciclovir 1, 2
• Children aged 3 months-12 years: Minimum of 21 days due to higher relapse rates (up to 29%) 1, 2
• Repeat lumbar puncture at end of treatment to confirm CSF is negative for HSV by PCR 1, 2
• If CSF remains positive, continue aciclovir with weekly PCR until negative 1

When to Stop Empiric Treatment

Aciclovir can be discontinued in immunocompetent patients if:

1. An alternative diagnosis has been established, OR
2. HSV PCR in CSF is negative on two occasions 24-48 hours apart and MRI is not characteristic for HSV encephalitis, OR
3. HSV PCR in CSF is negative once >72 hours after symptom onset, with normal level of consciousness, normal MRI (performed >72 hours after symptom onset), and CSF white cell count <5 × 10⁶/L 1

Important Clinical Considerations

Monitoring During Treatment

• Monitor renal function regularly, especially after 4 days of therapy when risk of nephropathy increases 1, 2
• Maintain adequate hydration to reduce risk of crystalluria and obstructive nephropathy 1
• Watch for rare adverse events including hepatitis and encephalopathy 1

Prognostic Factors

• Poor outcomes associated with:
  • Advanced age
  • Reduced consciousness (low Glasgow Coma Score)
  • Delays >48 hours between hospital admission and starting treatment 1, 2

Common Pitfalls to Avoid

1. Delaying treatment: Do not wait for confirmation of diagnosis before starting aciclovir in suspected cases 1, 4
2. Incorrect dosing: Ensure appropriate weight-based dosing and adjust for renal impairment 5
3. Premature discontinuation: Inadequate treatment duration increases relapse risk, especially in children 1
4. Relying on oral aciclovir: Oral aciclovir does not achieve adequate CSF levels and should not be used for HSV encephalitis 2
5. Unnecessary CT scans: These can delay lumbar puncture and treatment initiation 5

Alternative Treatments

• Valacyclovir has been used in resource-limited settings or when IV access is difficult, but is not first-line therapy 6
• There is insufficient evidence to recommend routine use of corticosteroids in HSV encephalitis 1

HSV encephalitis is a medical emergency with high mortality if untreated. Early recognition and prompt initiation of IV aciclovir significantly improves outcomes and reduces mortality from over 70% to less than 20-30% 1, 7.