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  • Dr Hector Thomson


Updated: Nov 3, 2023

Dr Hector Thomson Emergency Registrar

Peer review: Dr Binula Wickramarachchi

While recent cases of Japanese Encephalitis have caught headlines, I recently stumbled across a disease I was embarrassed to say I had never heard of. My paediatric-trained colleagues all seemed to have heard of it, but I could scarcely find a mention in my ED textbooks, maybe because the diagnosis is never made downstairs and we call it viral meningitis pending a culture.

With a waiting room full of kids with viral URTIs, I now have a new disease to look out for along with PIMS-TS. Let me tell you about some more scary capital letters: ADEM.

So, what is ADEM?


ADEM is an autoimmune demyelinating disease of the central nervous system (CNS) which is monophasic (has a single occurrence) but multifocal in nature. So, lots of cool neurological signs but then they don’t go away; in contrast to MS, for example,  where they may fluctuate.

It's most commonly seen in children, though adults can also be affected. It was first described by Mr James Lukas, a surgeon in Leeds in the 18th Century, as "uncommon symptoms succeeding the measles".


All of the following are needed, along with reasonable exclusion of other possible neurological conditions:

  1. A first multifocal clinical CNS event of presumed inflammatory demyelinating cause

  2. Encephalopathy: stupor and/or lethargy or behavioural changes unexplained by fever, systemic illness or postictal symptoms

  3. An abnormal MRI brain during the acute phase (3 months)

  4. No new clinical or MRI findings >3 months after clinical onset


It isn’t clear what exactly causes ADEM but as with many autoimmune conditions, the current theory is that an infectious or environment trigger in a genetically susceptible child causes an autoimmune attack on the CNS resulting in demyelination.

The disease typically starts with an abrupt onset within a day to weeks after a viral infection (75%) or immunisation. Common viruses (Epstein-Barr, measles, mumps, rubella, and Coxsackie B) are the most common pathogens associated with postinfectious ADEM. COVID has been reported as a cause but a review this year only found 31 reported cases.

Bacterial triggers are rare and less than 5% of ADEM cases follow immunisation. These have most often been associated with the MMR vaccination.


The classic presentation is a 2-5 day prodrome where fever, nausea, vomiting, headache, and weakness may be present, followed by acute-onset, rapidly progressive encephalopathy and multifocal neurological symptoms.

Encephalopathy comprises change in behaviour and/or conscious state and can range from lethargy and irritability to coma.

A wide variety of neurological deficits can be manifested, determined mainly by the localization of lesions.  80% will have a motor deficit, 50-60% ataxia, and up to 50% will have a cranial nerve deficit with optic neuritis, often bilaterally.

Yes, that means you have to go find the tendon hammer and try and get those grumpy toddlers to walk for you!<