HSV Encephalitis
System: CNS Infections · Parent MOC: MOC - Diseases by System
One-Sentence Definition
HSV encephalitis is life-threatening inflammation of the brain parenchyma caused most often by HSV-1 (and sometimes HSV-2), diagnosed by CSF PCR and treated with urgent antiviral therapy.
Clinical Presentation
- Fever, headache, altered behavior, focal deficits, seizures
- Temporal lobe predilection (HSV-1) — personality change, aphasia, olfactory hallucinations
- Can mimic stroke, psychiatric illness, other encephalitides
Pathogens
| Agent | Notes |
|---|---|
| HSV (usually HSV-1) | Leading sporadic viral encephalitis in immunocompetent adults |
| Mimics | VZV, enteroviruses, arboviruses, autoimmunity |
Pathogenesis
- Reactivation or primary spread to CNS; neuronal infection → necrosis/inflammation
- Delayed treatment ↑ morbidity/mortality
Diagnosis
| Step | Test | Note |
|---|---|---|
| Urgent | CSF PCR for HSV | High sensitivity/specificity early |
| Support | MRI (temporal changes) | Supports but does not replace PCR |
| Adjunct | CSF cell count/protein, EEG | Lymphocytic pleocytosis |
| Avoid delay | Start acyclovir while awaiting PCR if suspicion high | Do not wait for MRI |
Treatment Principles
- IV acyclovir promptly — duration per guidelines/response
- Supportive ICU care; seizure control
- Treat until PCR negative / clinical course per protocol
Prevention
- No routine vaccine for HSV; prevention is recognition + early treatment
Differential / Pitfalls
- Bacterial Meningitis (meningeal > parenchymal)
- Autoimmune encephalitis — may need immunotherapy if HSV PCR negative
- False-negative early PCR — repeat if strong suspicion
Related
Active Recall
- Why start acyclovir before PCR returns?
- Classic anatomic predilection of HSV-1 encephalitis?
- Most important confirmatory test?