Epidemiology

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Etiology

• Pathogen: herpes simplex virus
  • Neonates: both HSV-1 and HSV-2
    • Generalized necrotizing hemorrhagic encephalitis may especially occur with HSV-2 infection in neonates or immunocompromised patients (e.g., with HIV-AIDS), which can affect the insular cortex, brain stem, and cingulate gyri. HSV-2 primarily causes a benign course of viral meningitis in immunocompetent adults.
  • Adult: usually HSV-1
    • HSV-1 predominately affects the medial temporal lobes with or without inferolateral frontal lobe involvement.

Tip

HSV encephalitis is mainly caused by HSV-1, whereas HSV meningitis is typically caused by HSV-2.

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Pathophysiology

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Clinical features

Prodromal phase

• Duration: a few hours to days
• Nonspecific symptoms
  • Fever
    • Differ from ischemic stroke
  • Headache
  • Nausea and vomiting

Acute or subacute encephalopathy

• Focal neurological deficits (primarily affects the medial temporal lobe)
  • Altered sense of smell and loss of vision
  • Aphasia
  • Memory loss
  • Hemiparesis
  • Ataxia
  • Hyperreflexia
• Seizures (focal or generalized)
• Altered mental status (e.g., confusion, disorientation, lowered level of consciousness)

Tip

HSE may resemble bacterial meningitis, but the combination of altered mental status, seizures, and focal neurological deficits is more common for HSE!

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Diagnostics

Pathology

• Macroscopic: typical temporal lobe distribution with visible necrosis
• Microscopic
  • Hemorrhagic-necrotizing inflammation
  • Eosinophilic nuclear inclusions (Cowdry bodies)

Differential diagnostics

Feature	Meningitis	Meningo-encephalitis	Encephalitis
Fever, leukocytosis	Often	Often	Often
Meningeal irritation (e.g. Nuchal rigidity, photophobia)	Often	Often	No
Mental status alteration	Sometimes	Often	Nearly always
Seizure	Uncommon	More often than in meningitis	Often
Focal neurologic findings	Half of patients develop focal findings at some point during the disease course (usually later)	More often than in meningitis	Hallmark feature
Typical pathogens	Streptococcus pneumoniae, N. meningitidis, H. influenzae	HSV, VZV, Listeria spp.	HSV, VZV, Enteroviruses
*Focal neurologic findings include weakness, visual disturbance, aphasia, cerebellar findings, behavior chang

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Treatment

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