Herpes Simplex Encephalitis — Management Pathway

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] Suspected HSV encephalitis?
   Fever + altered consciousness + focal signs/seizures — suspected HSV encephalitis? (The most common cause of sporadic fatal encephalitis, HSV-1 involving the medial temporal/inferior frontal lobes. Fever + headache → altered consciousness (common) + focal deficit/seizures/behavioral change (this combination suggests HSV encephalitis, distinct from bacterial meningitis). LP CSF: lymphocytic pleocytosis, raised protein, may have red cells; HSV PCR is the gold standard (but can be false-negative within 72 h); MRI temporal lobe lesions (first-line, may be normal early).)
   • Suspected HSV encephalitis → Suspected HSV encephalitis → immediate acyclovir
   • Does not fit → Does not fit
2. [End] Does not fit
   Differentiate bacterial/other viral meningoencephalitis, autoimmune encephalitis, metabolic/toxic encephalopathy, stroke, etc., and work up accordingly (LP, imaging, EEG); altered consciousness + fever still warrants a low threshold for empiric antiviral + antibacterial therapy until excluded.
3. [End] Suspected HSV encephalitis → immediate acyclovir
   Once suspected, start empiric IV acyclovir 10 mg/kg q8h immediately, do not wait for LP/imaging/PCR (delay worsens outcome/increases mortality). Complete LP (HSV PCR) + MRI; if the initial PCR is negative but suspicion is high, continue acyclovir and repeat PCR at 3–7 days. Course 14–21 days, with adequate hydration (to prevent acyclovir nephrotoxicity); empiric antibiotics until bacterial meningitis is excluded; control seizures, manage raised ICP/cerebral edema; neurology/infectious disease consult.

Source guidelines & references

• Herpes simplex encephalitis (AMBOSS; IDSA/international encephalitis consensus)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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