Acute Disseminated Encephalomyelitis
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Direct answer
Acute disseminated encephalomyelitis is an immune-mediated, post-infectious demyelination of the brain and spinal cord, usually appearing a few weeks after a viral infection or vaccination. MRI shows multifocal, large and poorly demarcated white matter lesions, and high-dose intravenous methylprednisolone is the standard first treatment. The illness is typically monophasic, which helps separate it from multiple sclerosis.
What you must remember
- Trigger: a preceding viral infection such as measles, varicella or influenza, or a recent vaccination.
- Clinical picture: fever, headache and drowsiness or encephalopathy, with multifocal signs such as hemiparesis, ataxia, optic neuritis or cranial nerve palsies.
- MRI pattern: multifocal, bilateral, large lesions in white matter, often with thalamic and basal ganglia involvement.
- CSF findings: mild pleocytosis or normal results, with oligoclonal bands usually absent.
- First-line treatment: high-dose intravenous methylprednisolone for three to five days, followed by an oral taper in many regimens.
- Refractory disease: plasma exchange or intravenous immunoglobulin when steroids fail.
- Fulminant variant: acute haemorrhagic leukoencephalitis, with haemorrhage within lesions and a high risk of death.
A diagnostic pathway from fever to MRI
A child who develops drowsiness and limb weakness after a viral illness needs a structured approach. The steps below separate acute disseminated encephalomyelitis from infective encephalitis and from the first attack of multiple sclerosis.
- Recognise the context: note a viral illness or vaccination typically a few weeks earlier, with encephalopathy and multifocal deficits. This pattern points towards a post-infectious cause.
- Image the brain: contrast MRI shows multifocal, bilateral lesions, and spinal MRI is added when cord signs are present. The imaging pattern is the key discriminating test.
- Examine the CSF: look for mild lymphocytic pleocytosis, absent oligoclonal bands and a normal glucose level. Send PCR for herpes simplex virus to exclude a treatable infection.
- Exclude mimics: herpes simplex encephalitis, the first episode of multiple sclerosis, neuromyelitis optica and metabolic disease must be considered before the diagnosis is accepted.
- Start steroids: give high-dose intravenous methylprednisolone once herpes encephalitis is reasonably excluded. Early treatment limits the duration of deficits.
- Escalate if needed: plasma exchange or intravenous immunoglobulin is added when there is no clinical improvement after steroids.
- Follow up: repeat MRI and review neurodevelopment over months. Any recurrence prompts reconsideration of multiphasic disease.
Where the exam tries to catch you
Acute disseminated encephalomyelitis questions often hinge on one discriminating feature.
- Trap: expecting oligoclonal bands to confirm acute disseminated encephalomyelitis Correct: their absence supports this diagnosis, whereas oligoclonal bands are typical of multiple sclerosis.
- Trap: labelling every post-vaccine demyelination as acute disseminated encephalomyelitis Correct: the diagnosis needs encephalopathy and a characteristic MRI, and mimics must be excluded first.
- Trap: starting steroids without excluding herpes simplex encephalitis Correct: herpes encephalitis needs aciclovir and can be fatal if an untreated infection is masked by steroids.
- Trap: calling a first episode with large lesions multiple sclerosis Correct: a monophasic course with large, poorly demarcated lesions and encephalopathy favours acute disseminated encephalomyelitis.
Frequently asked questions
How long after an infection does acute disseminated encephalomyelitis usually begin?
Acute disseminated encephalomyelitis usually begins a few weeks after a viral infection or vaccination, rather than during the acute illness itself. This delay is an important clue that the disease is post-infectious rather than direct viral invasion of the brain.
Which MRI features favour acute disseminated encephalomyelitis?
MRI features favouring acute disseminated encephalomyelitis are multifocal, bilateral, large and poorly demarcated white matter lesions, often with thalamic or basal ganglia involvement. Periventricular ovoid lesions are more typical of multiple sclerosis, so their pattern helps in the differential.
How is acute disseminated encephalomyelitis treated in children?
Acute disseminated encephalomyelitis is treated first with high-dose intravenous methylprednisolone for three to five days, usually followed by an oral steroid taper. Plasma exchange or intravenous immunoglobulin is reserved for children who do not respond to steroids.
How does acute disseminated encephalomyelitis differ from multiple sclerosis in children?
Acute disseminated encephalomyelitis is usually a single monophasic episode with encephalopathy and large lesions. Multiple sclerosis involves recurrent episodes separated in time and space, and its CSF commonly shows oligoclonal bands.
What is acute haemorrhagic leukoencephalitis?
Acute haemorrhagic leukoencephalitis is a fulminant variant of acute disseminated encephalomyelitis in which the lesions show haemorrhage. It carries a high risk of death or severe disability, so it is usually treated aggressively from the outset.