Synopsis
Distinguish the usually monophasic encephalopathic demyelinating illness ADEM from infection, MS, MOG-associated disease and structural mimics, then deliver safe acute and recovery care.
- ADEM is an acute inflammatory demyelinating disorder that is commonest in children and often follows an infection; it is much less commonly the first diagnosis in an adult.
- Encephalopathy is a defining clinical feature: altered behaviour, irritability, drowsiness or reduced consciousness accompanies polyfocal neurological deficits.
- MRI usually shows large, bilateral, poorly demarcated T2 or FLAIR lesions in subcortical and central white matter, deep grey nuclei, brainstem, cerebellum or spinal cord.
- A preceding fever or viral illness does not prove ADEM, and active infectious encephalitis must be covered and investigated until sufficiently excluded.
- MOG-IgG is found in an important subgroup, especially children, and may predict optic neuritis, extensive myelitis or recurrence requiring a revised MOG-associated disease diagnosis.
- Typical MS more often lacks encephalopathy and shows small well-demarcated periventricular, juxtacortical or infratentorial lesions with dissemination in time.
- First-line treatment for a significant attack is commonly high-dose intravenous methylprednisolone; IV immunoglobulin or plasma exchange is used for severe inadequate response under specialist protocols.
- Most children improve substantially, but cognition, behaviour, fatigue, seizures, vision, movement and school participation require deliberate follow-up.
- New events after the expected monophasic period demand expert reconsideration of MOGAD, MS, NMOSD, recurrent ADEM, infection or a genetic or metabolic mimic.
- Vaccination history should be recorded without implying causation: infections are common antecedents and temporal association alone is not evidence that a vaccine caused the illness.
Key red flags
Days to weeks after a febrile illness, a child becomes unusually irritable, confused or sleepy and develops multifocal weakness, ataxia, cranial-nerve findings or seizures.
Deficits cannot be explained by one small lesion: combinations include hemiparesis, bilateral pyramidal signs, optic symptoms, cerebellar ataxia, brainstem dysfunction and an inflammatory cord syndrome.
Headache, repeated vomiting, papilloedema, hypertension with bradycardia, abnormal posturing or falling consciousness suggests life-threatening swelling and requires neurocritical escalation.
Fever, meningism, focal temporal seizures, rash, immunosuppression or travel and exposure risk sustain concern for viral, bacterial or other infection despite demyelinating MRI lesions.
Investigation priorities
Demonstrate the distribution and age of demyelinating lesions while excluding tumour, abscess, stroke, PRES and other structural encephalopathies.
Management branches
A child or adult has altered consciousness or behaviour with multifocal neurological signs.
- Stabilise airway, breathing and circulation, check glucose and electrolytes, treat seizures promptly and escalate signs of cerebral oedema or respiratory weakness to paediatric or adult critical care.
- Obtain urgent MRI and, when safe, CSF for microbiology and inflammation; give empiric aciclovir and antibacterial cover according to the encephalitis or meningitis pathway while infection remains credible.
- Document the preceding illness, medicines, vaccination timing, toxic exposures, immune status and detailed neurological pattern without assuming that temporal association supplies causation.
- Discuss early with a neuroinflammatory specialist and neuroradiologist because adult disease, atypical imaging or rapid worsening broadens the differential substantially.