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  • Dr Hector Thomson

ACUTE DISSEMINATED ENCEPHALOMYELITIS (ADEM)

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?


ACUTE DISSEMINATED ENCEPHALOMYELITIS (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".

CRITERIA FOR DIAGNOSIS


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

CAUSE


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.

PRESENTATION

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!<