What is the treatment for herpes zoster (shingles) encephalitis?

Treatment of Herpes Zoster (Shingles) Encephalitis

Start intravenous acyclovir immediately at 10 mg/kg every 8 hours for adults and children with normal renal function, continuing for 14-21 days, as early treatment is critical for reducing mortality and neurological sequelae. 1, 2

Immediate Empirical Treatment

• Begin acyclovir within 6 hours of hospital admission for any patient with suspected encephalitis, even before diagnostic confirmation, as delays beyond 48 hours significantly worsen outcomes 1, 3
• The standard adult dose is 10 mg/kg intravenously every 8 hours for patients with normal renal function 1
• For neonates, use higher-dose acyclovir at 20 mg/kg intravenously every 8 hours for 21 days, which has reduced mortality to 5% 1, 3
• Reduce the dose in patients with pre-existing renal impairment to prevent crystalluria and obstructive nephropathy 1, 3

Treatment Duration and Monitoring

• Continue intravenous acyclovir for 14-21 days once VZV encephalitis is confirmed 1, 2
• Monitor renal function throughout treatment, as acyclovir-induced nephropathy can affect up to 20% of patients, typically after 4 days of IV therapy 2, 3
• Ensure adequate hydration during acyclovir administration to minimize nephrotoxicity risk 3
• Consider repeating lumbar puncture at the end of therapy to confirm CSF PCR negativity for VZV, particularly if clinical response is suboptimal 1, 2

Diagnostic Confirmation

• CSF PCR can detect varicella zoster virus DNA, though a negative test does not exclude the diagnosis 1
• CSF typically shows mononuclear pleocytosis, occasionally with low glucose concentration, and elevated protein in approximately half of patients 4, 5
• CSF VZV IgM antibodies may be present even when CSF PCR is negative, providing additional diagnostic support 1
• Brain imaging (MRI preferred over CT) may show hypodense lesions or be normal initially; SPECT scanning often reveals hypoperfusion, particularly in frontal areas 6

Adjunctive Corticosteroid Therapy

• Consider adding corticosteroids if VZV vasculopathy (stroke) is present, as there is evidence supporting their use in this specific context 1, 2
• The role of routine corticosteroids in VZV encephalitis without vasculopathy remains controversial and should be reserved for specialist supervision 1

Clinical Response and Prognosis

• Most patients show clinical improvement within 72 hours of starting acyclovir, with dramatic responses documented in case reports 7, 8
• The median duration from dermatomal lesion to encephalitis is 5 days in immunocompetent patients versus 15 days in immunosuppressed patients 4
• Common presenting symptoms include disturbances of mental function, ataxia, and nuchal rigidity in approximately one-third of cases 4
• Neuropsychological sequelae may include subcortical cognitive impairment with memory decline, slowed cognitive processing, and behavioral disinhibition, though these are generally less severe than HSV encephalitis 6
• Most surviving patients experience slow but eventual return to their prior cognitive status 5

Special Populations

• Immunosuppressed patients and those with disseminated zoster have increased risk of developing VZV encephalitis and may require longer treatment courses 4, 5
• Patients on dialysis who develop VZV encephalitis require dose adjustment but respond well to intravenous acyclovir 8
• Cranial zoster implies no or only slightly increased risk of encephalitis compared to other dermatomes 4

Critical Pitfalls to Avoid

• Never delay acyclovir beyond 48 hours waiting for diagnostic confirmation, as this is the single most important predictor of poor outcome 1, 3
• Do not rely on oral acyclovir for treatment of VZV encephalitis; intravenous administration is essential 8
• Do not stop acyclovir based solely on a single negative CSF PCR if clinical suspicion remains high, as PCR sensitivity varies 1
• Avoid inadequate hydration during treatment, which significantly increases nephropathy risk 3