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Encephalitis

Definition:

  • Encephalitis is an inflammation of the brain parenchyma, often caused by a viral infection or, less commonly, by a non-infectious inflammatory process.

Epidemiology:

  • Occurs worldwide with varying etiologies based on geographical regions.
  • Affects all ages, but incidence is higher in children, the elderly, and immunocompromised individuals.

Etiology:

  1. Infectious Encephalitis:
    • Viral infections are the most common cause (e.g., herpes simplex virus (HSV), varicella-zoster virus, enteroviruses, arboviruses like West Nile virus).
    • Bacterial, fungal, and parasitic infections are less common.
  2. Autoimmune Encephalitis:
    • Associated with immune-mediated processes.
    • Examples include anti-NMDA receptor encephalitis.

Pathophysiology:

  • Infection or autoimmune response leads to brain inflammation, neuronal damage, cerebral edema, and in severe cases, increased intracranial pressure.

Clinical Features:

  • Fever, headache, altered mental status (ranging from mild confusion to coma).
  • Seizures, focal neurological deficits, movement disorders.
  • Symptoms of meningitis (neck stiffness, photophobia) may also be present.

Diagnosis:

  • Lumbar puncture and CSF analysis: Elevated white cells, elevated protein, normal to low glucose.
  • PCR of CSF for viral pathogens.
  • EEG, MRI or CT scan to assess brain inflammation and exclude other causes.
  • Autoimmune encephalitis requires specific antibody testing.

Management:

  • Antiviral therapy (e.g., acyclovir for suspected HSV encephalitis) should be initiated promptly, often before the diagnosis is confirmed.
  • Supportive care: Management of seizures, intracranial pressure, hydration, and nutritional support.
  • Immunosuppressive therapy for autoimmune encephalitis.
  • Rehabilitation services for residual neurological deficits.

Prognosis:

  • Highly variable, depending on the etiology and promptness of treatment.
  • HSV encephalitis can be fatal if untreated, but treatment significantly reduces mortality and morbidity.

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