• Herpes simplex virus is the commonest cause in adult population - responsible for 95% of cases
• Typically affects temporal and inferior frontal lobes

PC

• fever, headache, psychiatric symptoms, seizures, vomiting
• focal features e.g. aphasia
• peripheral lesions (e.g. cold sores) have no relation to presence of HSV encephalitis

Investigations

Labs:

• PCR for HSV

Imaging:

• MRI:
  • bilateral medial temporal and inferior frontal changes (e.g. petechial haemorrhages)
  • normal in one-third of patients

Special tests:

• CSF: lymphocytosis, elevated protein, CSF viral PCR (most useful test)
• EEG pattern: lateralised periodic discharges at 2 Hz

Management

Treatment of suspected encephalitis is empirical and should involve broad spectrum antimicrobial cover with 2g IV ceftriaxone BD and 10 mg/kg aciclovir TDS for two weeks.