What is the treatment for viral encephalitis, specifically for a patient suspected of having herpes simplex virus (HSV) infection?

Treatment of Viral Encephalitis

Intravenous aciclovir at a dose of 10 mg/kg every 8 hours should be started immediately in all patients with suspected viral encephalitis, particularly when HSV infection is suspected, without waiting for confirmatory test results. 1, 2

Initial Management

• Start IV aciclovir within 6 hours of admission if:

  • Initial CSF and/or imaging findings suggest viral encephalitis
  • These results will not be available within 6 hours
  • The patient is very unwell or deteriorating 1

• Even if initial CSF microscopy or imaging is normal but clinical suspicion of HSV or VZV encephalitis remains, aciclovir should still be started promptly 1

• Dosing recommendations:

  • Adults and children >12 years: 10 mg/kg IV every 8 hours 2, 3
  • Dose reduction is necessary in patients with pre-existing renal impairment 1, 2

Duration of Treatment

• Standard treatment duration is 14-21 days for confirmed HSV encephalitis 1, 2
• Some experts recommend continuing treatment until CSF is negative for virus by PCR 1

Stopping Aciclovir Treatment

Aciclovir can be stopped in immunocompetent patients if:

1. An alternative diagnosis has been made, OR
2. HSV PCR in the CSF is negative on two occasions 24-48 hours apart, and MRI is not characteristic for HSV encephalitis, OR
3. HSV PCR in the CSF is negative once >72 hours after neurological symptom onset, with unaltered consciousness, normal MRI (performed >72 hours after symptom onset), and CSF <5 × 10^6/L white cells 1

Monitoring and Follow-up

• Regular renal function monitoring is essential during aciclovir treatment 2
• Consider repeat lumbar puncture at the end of treatment to confirm viral clearance 2
• Adequate hydration is crucial to prevent aciclovir-induced nephropathy 2

Role of Valaciclovir

• Oral aciclovir does not achieve adequate CSF levels
• Valaciclovir (the valine ester of aciclovir) has good oral bioavailability and may have a role in ongoing treatment, particularly in patients with HSV detectable in the CSF after 2-3 weeks of IV therapy 1
• High-dose valaciclovir (2 g three times daily) is being assessed for extended treatment 1

Role of Corticosteroids

• Corticosteroids should not be used routinely in patients with HSV encephalitis 1
• They may have a role under specialist supervision in patients with marked cerebral edema, brain shift, or raised intracranial pressure, but definitive data are lacking 1, 2

Common Pitfalls to Avoid

1. Delayed treatment initiation: Delays beyond 48 hours significantly worsen outcomes 2, 4
2. Stopping treatment based on a single negative CSF PCR: Initial CSF PCR can be negative in HSV encephalitis, especially if taken early (<72 hours after symptom onset) 1
3. Inadequate dosing: Using incorrect aciclovir dosage can lead to treatment failure 2
4. Failure to consider HSV in differential diagnosis: The most common reason for treatment delay is not considering HSV encephalitis despite suggestive clinical features 4

Special Considerations

• Brain biopsy has no role in the initial assessment of suspected viral encephalitis but may be considered if no diagnosis is made after the first week, especially with focal abnormalities on imaging 1
• Poor prognostic factors include advanced age, reduced consciousness, and delays of more than 48 hours between hospital admission and starting treatment 1, 2