Neurology · MU Sofia

49. Herpetic encephalitis

Explains herpetic encephalitis as an acute, severe viral infection, mainly by HSV-1, that causes necrotising, haemorrhagic damage to the temporal and frontal lobes. It goes through aetiology, how the virus spreads, clinical features including psychiatric and focal signs, examination findings, CSF and MRI and EEG findings, differential diagnosis, urgent acyclovir treatment and prognosis.

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Topic 49 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 284 words (2 min of reading), with 15 flashcards.

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  1. Herpetical encephalitis

Herpetical encephalitis

Definition: Herpetic encephalitis is an acute, severe viral encephalitis caused mainly by Herpes simplex virus type 1 (HSV-1), characterized by necrotizing inflammation of the brain, especially the temporal and frontal lobes.

Etiology

  • HSV-1 (most common in adults)
  • HSV-2 (more in neonates or immunocompromised)

Pathogenesis

  • Primary infection or viral reactivation
  • Virus spreads via trigeminal or olfactory pathways
  • Predilection for: Temporal lobe. Limbic system
  • Causes hemorrhagic necrosis of brain tissue

Clinical Features

A. Acute onset: High fever. Severe headache. Malaise

B. Encephalitic syndrome (key triad)

  • Altered mental status (confusion → coma)
  • Seizures (often focal or generalized)
  • Focal neurological deficits

C. Characteristic psychiatric & cognitive symptoms: Behavioral changes. Memory impairment (especially short-term memory). Hallucinations / psychosis

D. Focal neurological signs: Aphasia (dominant temporal lobe). Hemiparesis. Cranial nerve involvement (less common)

Examination Findings: Reduced level of consciousness. Fever.Focal cortical signs (aphasia, hemiparesis). Signs of increased intracranial pressure may appear. Possible meningeal irritation (meningoencephalitis)

CSF Findings: ↑ opening pressure (mild–moderate). Clear or slightly bloody CSF. ↑ lymphocytes. Mild ↑ protein. Normal glucose

  • Important clue: RBCs in CSF (hemorrhagic necrosis) → strongly suggests HSV encephalitis

Neuroimaging

  • MRI (gold standard): Temporal lobe hyperintensity. Hemorrhagic necrosis. Edema in limbic structures hippocampus, amygdala, and cingulate gyrus

EEG Findings: Periodic lateralized epileptiform discharges (PLEDs), especially temporal region

Differential Diagnosis

1. Other viral encephalitis: Less focal (no strong temporal lobe predilection)

2. Brain abscess: Ring-enhancing lesion on imaging

3. Stroke: Sudden onset, no fever, no CSF inflammation

4. Bacterial meningitis: Prominent meningeal signs, neutrophilic CSF

Treatment (URGENT)

  • First-line: Acyclovir IV (start immediately, do not wait for confirmation)
  • Supportive care: ICU monitoring. Control seizures (antiepileptics). Manage intracranial pressure

Prognosis: High mortality if untreated. Early treatment significantly improves outcome

  • Survivors may have: Memory deficits. Epilepsy. Personality changes

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