Herpes Simplex Encephalitis
A 22-year-old man has 4 days of fever, severe frontal headache, and progressive confusion. Yesterday he was unable to name familiar objects and had a brief episode of lip smacking with unresponsiveness. Lumbar puncture shows 380 cells/µL with 90 percent lymphocytes, protein 0.8 g/L, cerebrospinal fluid glucose 3.7 mmol/L with a normal serum glucose, and a negative Gram stain. Which of the following is the most appropriate intravenous treatment?
- A.Ceftriaxone, vancomycin, and dexamethasone
- B.Ceftriaxone and vancomycin
- C.Ceftriaxone alone
- D.AciclovirCorrect
Explanation
Fever with headache, altered mental status, and focal cortical features such as dysphasia and temporal lobe seizures defines encephalitis rather than simple meningitis, and herpes simplex virus type 1 is the commonest sporadic treatable cause. The cerebrospinal fluid supports it: a lymphocyte-predominant pleocytosis, mildly raised protein, a normal glucose ratio, and a negative Gram stain. Bacterial meningitis instead produces a neutrophil-predominant pleocytosis usually in the thousands, a very high protein, and a cerebrospinal fluid to serum glucose ratio below 0.4. Intravenous aciclovir 10 mg/kg every 8 hours must be started empirically the moment herpes encephalitis is suspected, because mortality falls from around 70 percent untreated to under 20 percent with early therapy, and delay of even 48 hours worsens neurological outcome. Diagnosis is confirmed by cerebrospinal fluid herpes simplex virus polymerase chain reaction, and MRI typically shows asymmetric temporal and inferior frontal lobe signal change. Ceftriaxone with vancomycin is the empirical regimen for bacterial meningitis, and dexamethasone before or with the first antibiotic dose reduces hearing loss and mortality in pneumococcal meningitis, but neither addresses a viral encephalitis. In practice many clinicians add empirical antibacterial cover until cultures and polymerase chain reaction return, but the single most appropriate and outcome-changing therapy in this presentation is aciclovir. Renal function should be monitored and adequate hydration maintained because aciclovir can crystallise in the tubules.
Why each option
- A.
- This is the empirical bacterial meningitis regimen with adjunctive dexamethasone; it does not treat the viral encephalitis suggested by the lymphocytic profile and focal cortical signs.
- B.
- Ceftriaxone plus vancomycin covers resistant pneumococcus and meningococcus but has no antiviral activity against herpes simplex virus.
- C.
- Ceftriaxone alone is inadequate even for empirical bacterial meningitis and does nothing for herpes encephalitis.
- D.
- Correct. Empirical intravenous aciclovir must be started immediately in suspected herpes simplex encephalitis, before polymerase chain reaction confirmation.
Reference: IDSA Practice Guidelines for the Management of Encephalitis; UpToDate 2025, Herpes simplex virus type 1 encephalitis
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