Meningo-encephalitis encephalitis, acute viral

A86

DESCRIPTION

A number of viruses cause infection of the brain and meninges. Herpes simplex is the most important because it is treatable. A high mortality and morbidity is associated with untreated herpes meningo-encephalitis.

Complications include:

  • increased intracranial pressure,
  • permanent neurological deficits,
  • cerebral oedema,
  • seizures,
  • blindness,
  • deafness,
  • inappropriate antidiuretic hormone (ADH) secretion.

Clinical Features

  • Severe headache, fever, nausea, vomiting, lethargy and abnormal behaviour.
  • Alteration in level of consciousness, i.e. drowsiness, confusion, stupor or coma.
  • Generalised and/or focal convulsions.
  • Focal neurological deficits.
  • Abnormal movements i.e. basal ganglia involvement.
  • Cranial nerve palsies (brainstem involvement), loss of sphincter control, paresis of limbs and segmental sensory loss (spinal cord involvement).
  • Some patients may have signs of meningeal irritation.
  • Herpes encephalitis may have an acute and fulminant course. It can result from primary infection or reactivation.
  • Herpetic skin lesions are usually NOT present in children with HSV encephalitis.

Investigations

  • Laboratory tests are important in excluding bacterial, fungal or TB meningitis.
  • CSF & blood for HSV PCR if the diagnosis is suspected.
  • CSF, may be normal or reveal:
    • mildly raised protein,
    • normal glucose level, and
    • mild pleocytosis, mostly lymphocytes.
    • Red cells are commonly observed with herpes encephalitis.
    • CT Brain, if focal signs or seizures, unexplained reduced level of consciousness, status epilepticus, diagnostic uncertainty
      - may reveal oedema
    • Herpes simplex preferentially involves the temporal lobes and orbital surfaces of the frontal lobes.
    • CT findings may only be apparent after 3–5 days.
  • EEG, if focal or prolonged seizures, diagnostic uncertainty, suspected non-convulsive seizures.
    • May demonstrate changes suggestive of herpes encephalitis.

GENERAL AND SUPPORTIVE MEASURES

  • Admit to high or intensive care unit, if appropriate.
  • Monitor, where indicated:
    • neurological status,
    • respiration,
    • heart rate,
    • body temperature,
    • blood pressure,
    • electrolytes,
    • haematocrit,
    • blood glucose,
    • acid-base status,
    • blood gases,
    • fluid balance, i.e. hydration,
    • serum and urine osmolarity.
  • Ensure adequate nutrition, nasogastric feeding if necessary.
  • If enteral feeding is not possible, give maintenance intravenous fluids.

MEDICINE TREATMENT

If herpes simplex virus or varicella zoster virus encephalitis suspected:

  • Aciclovir, IV, 8 hourly administered over 1 hour.
    If 0–12 years of age: 20mg/kg/dose.
    If > 12 years of age: 10mg/kg/dose.
    • Herpes simplex: 14 days.
    • Varicella: 7 days.
    • If an alternative diagnosis is made and CSF PCR is negative, stop acyclovir.

Note: CSF PCR may be negative in the first 3 days of illness.

Acute convulsions

See Status epilepticus (convulsive) .

Provide adequate analgesia see Pain control .

Raised intracranial pressure or cerebral oedema

Elevate head of bed ± 30°.
Maintain PaCO₂ at 4–5 kPa; intubate and ventilate, if necessary.
Avoid fluid overload.

  • Mannitol, IV, 250 mg/kg administered over 30–60 minutes.
    • Do not repeat without consulting a paediatrician.

REFERRAL

  • Deterioration of clinical condition despite adequate treatment.
  • Meningo-encephalitis with complications or loss of consciousness.