Encephalitis

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Encephalitis is an acute inflammation of the brain parenchyma, most commonly caused by viral infections, leading to neurological dysfunction and systemic symptoms.

Aetiology

Encephalitis can be caused by infectious or autoimmune processes.

1. Infectious Causes (Most Common):

  • Viral: herpes simplex virus (HSV-1 most common), varicella-zoster virus (VZV), enteroviruses, cytomegalovirus (CMV) (in immunocompromised patients), and arboviruses.
  • Bacterial: rare, but can occur in secondary bacterial meningitis.
  • Fungal: cryptococcus in immunocompromised individuals.
  • Parasitic: toxoplasma gondii in HIV/AIDS patients.

2. Autoimmune Causes:

  • Autoimmune encephalitis (e.g., anti-NMDA receptor encephalitis).
  • Paraneoplastic encephalitis (associated with malignancies).

Pathophysiology

  • Viral or immune mediated invasion leads to inflammation of brain tissue.
  • Neuronal damage results in cognitive, motor, and behavioural dysfunction.
  • Cerebral oedema may cause raised intracranial pressure (ICP), leading to altered consciousness.

Risk factors

  • Recent viral illness or immunosuppression (HIV, chemotherapy, transplant patients).
  • Travel history (exposure to arboviruses or endemic infections).
  • Neonates and older adults (weaker immune systems).
  • Autoimmune conditions.

Signs and symptoms

Encephalitis presents with a combination of systemic and neurological features.

Systemic Symptoms:

  • Fever.
  • Headache.
  • Generalised malaise.

Neurological Symptoms:

  • Altered mental status: confusion, drowsiness, coma.
  • Seizures: focal or generalised.
  • Focal neurological deficits: weakness, speech impairment.
  • Behavioural changes: hallucinations, agitation (especially in HSV-1 encephalitis).

Signs of Raised ICP:

  • Nausea, vomiting.
  • Papilloedema (on fundoscopy).
  • Bradycardia and hypertension (Cushing’s triad in severe cases).

Investigations

  • Urgent CT or MRI brain: excludes space-occupying lesions before lumbar puncture.
  • Lumbar puncture (LP): CSF analysis shows lymphocytic pleocytosis, elevated protein, and normal/low glucose.
  • CSF PCR for HSV and VZV: confirms viral cause (gold standard for HSV encephalitis).
  • EEG: may show diffuse slowing or periodic lateralised epileptiform discharges (PLEDs) in HSV encephalitis.
  • Blood tests: FBC (leukocytosis), CRP, blood cultures.
  • Autoimmune screen: if autoimmune encephalitis is suspected.

Management

1. Empirical Antiviral Therapy (Start Immediately While Awaiting Results):

  • IV Aciclovir: for example, 10 mg/kg every 8 hours for 14–21 days (HSV/VZV encephalitis).

2. Supportive Care:

  • Admit to a high dependency unit if there is altered consciousness.
  • Monitor for seizures and give benzodiazepines if needed.
  • IV fluids, nutritional support.

3. Management of Complications:

  • Seizure control: IV lorazepam followed by antiepileptic drugs.
  • Raised ICP: head elevation, IV mannitol if severe.
  • Autoimmune encephalitis: consider IV steroids, plasma exchange, or IV immunoglobulin (IVIG).

4. Long-Term Follow-Up:

  • Repeat MRI to assess residual damage.
  • Neurorehabilitation if cognitive impairment persists.
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