HSV Encephalitis
Introduction And Etiology
- Herpes simplex virus encephalitis represents a life-threatening neurological emergency and remains the most frequent cause of sporadic, fatal encephalitis in pediatric and adult populations globally.
- Without prompt antiviral administration, mortality approaches 75%, and survivors frequently experience severe long-term neurological sequelae.
- In older children and adults, the disease is almost exclusively caused by HSV type 1.
- In neonates, the condition frequently results from vertical transmission, with HSV type 2 accounting for approximately 70% of cases, while the remainder are caused by HSV type 1.
Pathophysiology
- The virus enters via mucosal surfaces or abraded skin, replicates locally, and transports retrogradely along axons to sensory ganglia, such as the trigeminal ganglia, to establish latency.
- Central nervous system invasion results from either primary infection or reactivation of latent virus, which travels along olfactory or trigeminal nerves directly into the brain.
- The infection induces acute, necrotizing inflammation with a distinct predilection for the temporal and frontal lobes, alongside the limbic system.
- Extensive tissue necrosis, hemorrhage, and cerebral edema ensue rapidly.
- Microscopic evaluation typically reveals perivascular lymphocytic cuffing and characteristic intranuclear inclusion bodies.
- In neonates, an immature immune system permits hematogenous dissemination or direct neuronal spread, frequently causing diffuse global encephalitis rather than isolated focal temporal involvement.
Clinical Manifestations
| Patient Group | Key Clinical Features |
|---|---|
| Older Children And Adults | • Presentation features a prodrome of fever, malaise, headache, and nausea. • Neurological signs encompass altered consciousness, focal or generalized seizures, and focal deficits including aphasia, hemiparesis, or ataxia. • Limbic involvement triggers prominent personality changes, psychosis, memory loss, anosmia, and gustatory hallucinations. |
| Neonates | • Symptoms classically emerge between 8 and 17 days of life, frequently mimicking bacterial sepsis or meningitis. • Systemic features include temperature instability, lethargy, poor feeding, and vomiting. • Neurological signs manifest as seizures, bulging fontanelle, and altered muscle tone. • Skin vesicles are notably absent in approximately 40% of cases presenting with central nervous system disease. |
Diagnostic Evaluation
| Diagnostic Modality | Characteristic Findings |
|---|---|
| Polymerase Chain Reaction | Cerebrospinal fluid PCR for HSV DNA serves as the definitive diagnostic method of choice, exhibiting high sensitivity and specificity. It becomes positive within 24 hours of symptom onset. |
| Cerebrospinal Fluid Analysis | Lumbar puncture classically reveals mononuclear pleocytosis, moderately elevated protein, and normal or mildly decreased glucose. The presence of red blood cells in a non-traumatic tap is a classic hallmark reflecting hemorrhagic necrosis. |
| Neuroimaging | Magnetic Resonance Imaging is the preferred modality, frequently demonstrating asymmetric high-intensity signals on T2 and FLAIR sequences within the temporal and frontal lobes. |
| Electroencephalogram | Testing may reveal characteristic periodic lateralized epileptiform discharges originating from the temporal regions. |
Management Protocol
Antiviral Therapy
- Intravenous Acyclovir must be initiated immediately and empirically upon clinical suspicion, prior to definitive diagnostic confirmation.
- Neonatal Dosing: Administer 60 mg/kg/day intravenously, divided every 8 hours, for a minimum duration of 21 days. High-dose therapy significantly improves neurodevelopmental survival.
- Pediatric Dosing: For infants, children, and adolescents, administer 30 mg/kg/day intravenously, divided every 8 hours, for a duration of 14 to 21 days.
- Acyclovir precipitates in renal tubules, necessitating rigorous patient hydration and close monitoring of renal function to prevent obstructive nephropathy.
- Neutropenia may occur, demanding twice-weekly absolute neutrophil count monitoring during treatment.
Management Of Resistant Strains
- Antiviral resistance, typically mediated by viral thymidine kinase gene mutations, necessitates alternative therapy utilizing Foscarnet or Cidofovir.
- These alternative agents possess higher nephrotoxicity, demanding meticulous electrolyte and renal function monitoring.
Supportive Care
- Promptly manage seizures utilizing anticonvulsants such as levetiracetam or fosphenytoin to prevent further brain injury.
- Manage cerebral edema and raised intracranial pressure by elevating the head of the bed and administering hyperosmolar therapy, such as mannitol or hypertonic saline.
- Strictly monitor fluid balance to manage the high risk of concurrent Syndrome of Inappropriate Antidiuretic Hormone secretion.
Neonatal Suppressive Therapy
- Following the initial 21-day intravenous course, neonates require prolonged oral suppressive therapy to improve neurodevelopmental outcomes and prevent cutaneous recurrences.
- Administer oral Acyclovir at a dose of 300 mg/m² per dose three times daily for a complete duration of 6 months.