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Acute Disseminated Encephalomyelitis (ADEM)
Overview
- Acute disseminated encephalomyelitis (ADEM) is essentially the monophasic, pediatric counterpart to MS.
- It typically involves a single (monophasic) disseminated attack of CNS demyelination (however ADEM can be multi-phasic: two or more attacks).
- White matter hyperintensities are typically scattered (disseminated) asymmetrically throughout the brain.
ADEM vs MS
It's helpful to learn ADEM in the context of MS. On the basis of a single event, ADEM can be hard to differentiate from MS, so let's focus on the key differences in their presentations.
- ADEM typically occurs in the pediatric population (5 – 8 y.o.), whereas the age of onset of MS is typically 20 – 50 y.o.
- It often occurs in the setting a viral illness.
- Note that although it’s commonly quoted that vaccines increase the risk of ADEM (especially the MMR vaccine), there is considerable argument about the true risk that vaccines confer in causing ADEM.
- In ADEM, there is often encephalopathy (or behavioral disturbance) and multifocal symptoms at onset (vs MS where encephalopathy is uncommon attacks are typically to specific modalities).
- It's easy to understand the genesis of the encephalopathy and diffuse presentation when we consider the widespread disease burden at onset.
- In ADEM, there is simultaneous lesion enhancement, since the lesions typically occur at/around the same time (in MS there is typically isolated lesion enhancement, admixed with non-enhancing lesions).
- In ADEM, is not uncommon for there to be basal ganglia involvement in ADEM (this would be categorically bizarre for MS).
References
- See the Non-MS White Matter Disorders tutorial.