🧠 Acute Disseminated Encephalomyelitis (ADEM) is a rare but important stroke mimic. It is an immune-mediated inflammatory demyelinating disease of the brain and spinal cord, usually monophasic, often following infection or vaccination. Most common in children, but can also affect adults.

📌 About

Major differential for acute stroke in younger patients.
Typically monophasic; relapses are uncommon compared with MS.
Mortality is around 2%, but fulminant cases may be fatal.
Pathology: perivenular demyelination with inflammation.

⚠️ Aetiology

Post-infectious (most common): measles, mumps, rubella, influenza, Mycoplasma, EBV, VZV.
Post-vaccination: rare, e.g. smallpox or rabies (historical context).
Declined markedly in incidence due to widespread immunisation programmes (e.g. MMR).
CSF may show raised myelin basic protein, indicating active demyelination.

🩺 Clinical Features

Prodrome: fever, headache, nausea, vomiting.
Neurological: seizures, meningism, ataxia, hemiparesis, encephalopathy → coma in severe cases.
Bilateral optic neuritis and transverse myelitis may occur.
More common in children, but adult cases do occur.

🔬 Investigations

CT head: May show diffuse cerebral oedema.
MRI brain: Large, often symmetrical lesions in basal ganglia, thalamus, and subcortical white matter. May also show oedema/haemorrhage.
CSF: Lymphocytic pleocytosis (WCC <300), raised protein. No oligoclonal bands → helps distinguish from MS.
Biopsy: Rarely required; shows perivenular demyelination.

🧾 Differentials

Multiple Sclerosis (MS)
Susac’s Syndrome
Progressive Multifocal Leukoencephalopathy (PML)
Viral encephalitis (esp. HSV)

💡 Key distinction from MS: ADEM is usually monophasic with diffuse, bilateral lesions and encephalopathy. MS is relapsing–remitting, often focal, and associated with CSF oligoclonal bands.

💊 Management

First-line: High-dose IV methylprednisolone (after excluding infection).
Second-line: IVIG or plasmapheresis if steroid-resistant. Rituximab for refractory disease.
Supportive: ICU care for severe cases; seizure control; manage raised ICP.
Rehabilitation: Neurorehab with physiotherapy and occupational therapy crucial for recovery.

📚 Further Reading

Acute Disseminated Encephalomyelitis: Current Understanding and Controversies

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Acute Disseminated Encephalomyelitis