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Encephalitis: Brain Inflammation – Etiology, Presentation & Urgency

Encephalitis is inflammation of the brain parenchyma, distinct from meningitis (meningeal inflammation), though they often coexist (meningoencephalitis). It is a neurologic emergency.

Etiology

CategoryKey Pathogens
Viral (most common)HSV-1 (most common sporadic), VZV, enteroviruses, arboviruses (WNV, JEV, Zika), CMV, EBV, HHV-6, measles, rabies
AutoimmuneAnti-NMDA receptor, LGI1, CASPR2, GABA-B, AMPAR, DPPX (increasingly recognized)
BacterialListeria, Mycobacterium TB, Treponema, Borrelia, Rickettsia
Fungal/ParasiticCryptococcus, Coccidioides, Toxoplasma, Naegleria (PAM)
Post-infectious (ADEM)Demylination 1–4 wks post-viral/vaccine

Clinical Presentation

  • Altered mental status (confusion, lethargy, coma) – hallmark.
  • Fever, headache, seizures (focal or generalized).
  • Focal neurologic deficits (aphasia, hemiparesis, movement disorders).
  • Psychiatric features (psychosis, catatonia – esp. anti-NMDAR).
  • Brainstem signs (cranial nerve palsies, respiratory dysregulation).

Diagnostic Workup (Emergent)

  1. ABCs, IV access, seizure prophylaxis (levetiracetam).
  2. LP (if safe): Opening pressure, CSF cell count, protein, glucose, PCR panel (HSV, VZV, enterovirus), autoimmune panel, culture.
  3. MRI brain with contrast: T2/FLAIR hyperintensities (temporal lobes in HSV, limbic in anti-NMDAR).
  4. EEG: Focal slowing, epileptiform discharges, PLEDs (HSV).
  5. Blood: CBC, CMP, inflammatory markers, serologies, autoimmune panel.

Treatment (Time-Critical)

  • Empiric acyclovir 10 mg/kg IV q8h immediately (covers HSV/VZV) – do not delay for LP/MRI.
  • Add antibacterial/antifungal per risk factors.
  • Autoimmune: High-dose steroids ± IVIG ± plasma exchange ± rituximab.
  • ICU management: ICP monitoring, EEG, ventilation, nutrition.

Prognosis

  • HSV: Mortality ~20% with treatment; >70% without. Sequelae: memory deficits, epilepsy.
  • Autoimmune: Often responsive to immunotherapy; relapses possible.
  • Outcome correlates with time to treatment, etiology, age, immunocompetence.

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