Acute encephalopathy
HSV-1 · Sporadic fatal encephalitis
MRIMedial temporal / insular / orbitofrontal; often hemorrhagic
CSF PCRSens 98% / spec 94%
TreatmentIV acyclovir 10 mg/kg q8h ×14–21 d
MortalityUntreated 70% → treated ~20%
Temporal lobe + fever + seizures? Start acyclovir now — an early negative PCR does NOT rule it out.
Key clinical features
- Asymmetric medial temporal / insular / orbitofrontal T2/FLAIR/DWI, often hemorrhagic
- Fever + AMS + focal seizures + behavioral change, aphasia
- Basal ganglia involvement makes classic HSV less likely → broaden the differential
- PCR can be NEGATIVE in the first 72h; up to 5% normal CSF early → repeat LP
- IV acyclovir 10 mg/kg q8h ×14–21 d empirically at first suspicion
- Hydrate + dose by ideal body weight to avoid crystalline nephropathy
◆ Signature clue
Post-HSV relapse (new dyskinesia/psychiatric change) → repeat HSV PCR AND send autoimmune (anti-NMDAR) antibodies — recurrent HSV must still be excluded.
Diagnosis
CSF HSV PCR (sens 98% / spec 94%); lymphocytic CSF with RBCs. Repeat LP if early PCR negative — normal CSF does not exclude it. MRI: medial temporal / insular / orbitofrontal.
Management
IV acyclovir empirically — do not wait for PCR. 10 mg/kg q8h ×14–21 d; hydrate + IBW dosing. Untreated mortality 70% → ~20% treated.