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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
- intravenous methyprednisolone or ACTH associated with clinical improvement
- shorten duration of symptoms and immediately halt further progression
- 2/3 of patients show a response
- plasmaphoresis and intravenous immunoglobulin reported to be associated
with dramatic improvement in some patient who do not respond to
corticosteroids
- cytotoxics have been used with success in some patients
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
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