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ADEM

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Acute disseminated encephalomyelitis (ADEM). Acute demyelinating disorder of central nervous system characterized by multi-focal white matter involvement.

Epidemiology

  • rare in developed countries. More common in developing countries where measles and other viral infections are more prevalent. Estimated to follow 1/1000 cases of measles

Aetiology

  • in developed countries most commonly follows non-specific upper respiratory tract infection
  • in developing countries most commonly follows common childhood illnesses (eg measles, chickenpox)
  • post immunization encephalomyelitis
    • most commonly associated with measles, mumps and rubella vaccination
      • incidence of ADEM following measles vaccination is 20 times lower than the incidence after measles infection

Clinical features

  • non-specific symptoms (eg fever, malaise, myalgia, headache, nausea and vomiting) often precede neurological features, begining 4-21 days after precipitating event
  • neurological features
    • focal or multi-focal
    • rapid onset over few days
    • early features:
      • encephalopathy: ranges from lethargy to coma
      • hemiparesis
      • cranial nerve palsies
      • paraparesis. Cord lesion often complete
    • meningism
    • ataxia
    • movement disorders
    • fits in severe cases
    • optic neuritis

Investigations

  • CSF
    • increased pressure
    • pleocytosis (up to 1000/ml). Usually lympohcytes. May be polymorphs in early states
    • raised protein (usually <1 mg/l). ± raised gammaglobulin, IgG, myelin basic protein
  • EEG
    • abnormalities common but non specific
  • CT
    • usually normal at onset
    • 5-14 days later becomes abnormal. Typical appearance is low attenuation, multifocal lesions in subcortical white matter
  • MRI
    • demyelinating lesions without mass effect scattered throughout white matter of posterior fossa and cerebral hemispheres. Appear as patchy areas of increased signal intensity on conventional T2-weighted images

Differential diagnosis

  • multiple sclerosis
    • difficult to distinguish from first episode of multiple sclerosis
    • clear-cut latent period between onset of non-specific symptoms and neurological features favours ADEM
  • antiphospholipid syndrome
    • both antiphospholipid syndrome and ADEM can present with transverse myelitis and optic neuritis
  • viral encephalitis
    • epidemic occurrence, absence of focal signs and persistence of systemic involvement more common
  • postmalarial neurological syndrome

Treatment

Prognosis

  • recovery can begin within days and on occasion complete resolution occurs within a few days
  • recovery over weeks to months is more usual
  • complete recovery in 50%
  • mortality 10-30%
  • poor prognosis associated with more severe symptoms and more abrupt onset

Further reading

Gorg RK. Acute disseminated encephalomyelitis. Postgrad Med J, 2003;79:11-17
Jurisdictional Blood Committee, for and on behalf of the Health Minister's Conference. Criteria for the Clinical Use of Intravenous Immunoglobulin in Australia. Canberra: Commonwealth of Australia; 2007



©Charles Gomersall, February, 2015 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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