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Introduction
- Follows an infection (viral) or vaccination
- Post infectious inflammatory immune-mediated process
- Focal neurologic deficits, headache, fever, altered consciousness
- Monophasic usually
- Can involve multiple sites in brain and spinal cord
- Full recovery in children apart from 10-30% which have residual deficit
- If episodes relapse in time or in place, consider multiple sclerosis as differential
- ADEM patients have no residual lesions on follow up, while MS patients show new lesions
Imaging
- Asymmetric areas of demyelination
- High signal in T2w images with swelling
- Subcortical white matter of both hemispheres
- Can sometimes involve cerebellum and spinal cord
- Cortex and deep grey matter can be involved but is less
- Free diffusion in all lesions
- Sometimes a more fulminant form can show hemorrhagic lesions
- Periventricular and callosal lesions favor MS
- Deep grey matter involvement favors ADEM more than MS
- Viral encephalitis tends to be cortical based and also shows diffusion restriction due to vasculitis
Differentials
- Apart from MS, consider autoantibody associated inflammatory demyelination like aquaporin-4 associated neuromyelitis optics spectrum disorders (NMSODs) and encephalomyelitis associated with myelin oligodendrocyte glycoprotein (MOG) autoantibody
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