Acute Disseminated Encephalomyelitis (ADEM)
Summary
Acute disseminated encephalomyelitis (ADEM) is a monophasic inflammatory demyelinating disorder of the central nervous system. It typically affects children following viral infection or vaccination. Key distinguishing feature from MS is encephalopathy (confusion, altered consciousness). MRI shows multifocal "fluffy" white matter and deep grey matter lesions. Treatment is high-dose IV corticosteroids.
Key Facts
- Definition: Monophasic inflammatory demyelinating CNS disorder
- Age: Peak 5-8 years; rare in adults
- Trigger: Post-infectious (70-80%); post-vaccinal (5%)
- Key feature: Encephalopathy (distinguishes from MS)
- Prognosis: Good; 70-90% complete recovery
Clinical Pearls
Encephalopathy is Key: ADEM MUST have altered consciousness (confusion, drowsiness, coma). If no encephalopathy, consider MS instead.
"Fluffy Lesions": MRI shows large, bilateral, poorly-demarcated white matter lesions - unlike the discrete lesions of MS.
Monophasic: True ADEM is single event. If recurs, consider MP-ADEM or evolving MS.
Why This Matters Clinically
ADEM presents as acute encephalopathy with multifocal neurological signs. Early recognition enables prompt steroid treatment and excellent outcomes. Must be differentiated from MS (different prognosis and treatment implications).
Incidence
| Measure | Value |
|---|---|
| Incidence | 0.3-0.6 per 100,000/year |
| Paediatric | 0.4-0.8 per 100,000/year |
| Adult | Rare (<5% of cases) |
Demographics
| Factor | Details |
|---|---|
| Age | Peak 5-8 years; median 6-8 years |
| Sex | Slight male predominance (1.3:1) |
| Seasonality | Winter/Spring (post-URI) |
Risk Factors
| Factor | Notes |
|---|---|
| Recent viral infection | 70-80% have prodrome 1-4 weeks prior |
| Recent vaccination | Rare (especially historical vaccines) |
| Young age | Peak in childhood |
Mechanism of Disease
Step 1: Triggering Event
- Viral infection (measles, varicella, EBV, influenza, COVID-19)
- Rarely post-vaccination
Step 2: Immune Dysregulation
- Molecular mimicry: Viral antigens resemble myelin antigens
- Cross-reactive immune response
- T-cell and antibody-mediated attack on CNS myelin
Step 3: Perivenous Demyelination
- Inflammation around small vessels
- Perivascular demyelination (characteristic)
- White matter and deep grey matter affected
Step 4: Clinical Manifestations
- Multifocal neurological signs
- Encephalopathy (key distinguishing feature)
- Usually monophasic with good recovery
Pathological Features
| Finding | Description |
|---|---|
| Perivenous demyelination | Classic pattern |
| Inflammatory infiltrates | Lymphocytes, macrophages |
| Relative axonal sparing | Better than MS |
| Deep grey matter involvement | Thalamus, basal ganglia |
Prodrome
Core Features
| Feature | Description |
|---|---|
| Encephalopathy | Required for diagnosis; confusion, lethargy, coma |
| Multifocal signs | Polysymptomatic neurological deficits |
| Rapid onset | Hours to days |
Neurological Signs
| Sign | Frequency |
|---|---|
| Motor weakness (hemiparesis, quadriparesis) | 70-80% |
| Cerebellar signs (ataxia) | 50-60% |
| Cranial nerve palsies | 30-50% |
| Optic neuritis | 20-30% |
| Seizures | 20-35% |
| Spinal cord involvement (myelitis) | 20-30% |
| Speech disturbance | 20-30% |
Red Flags
[!CAUTION] Immediate Red Flags:
- Decreasing consciousness (GCS <12)
- Seizures (especially status)
- Respiratory compromise
- Rapid neurological deterioration
- Signs of raised intracranial pressure
General
- Fever (during prodrome)
- Signs of recent viral illness
- Altered mental status
Neurological Examination
| System | Findings |
|---|---|
| Mental status | Confusion, drowsiness, coma |
| Motor | Weakness (often asymmetric) |
| Reflexes | Hyperreflexia, Babinski positive |
| Cerebellar | Ataxia, dysmetria, dysarthria |
| Cranial nerves | Multiple palsies possible |
| Sensory | Variable sensory loss |
| Fundoscopy | Optic disc swelling (if optic neuritis) |
Examination for Complications
| Finding | Concern |
|---|---|
| Papilloedema | Raised ICP |
| Respiratory pattern changes | Brainstem involvement |
| Urinary retention | Spinal cord involvement |
Essential Investigations
| Test | Purpose | Findings in ADEM |
|---|---|---|
| MRI Brain + Spine | Gold standard | Large "fluffy" bilateral white matter lesions |
| CSF analysis | Rule out infection | Lymphocytic pleocytosis, elevated protein |
| Oligoclonal bands | MS differentiation | Usually ABSENT (vs MS) |
| MOG antibodies | MOG-AD association | Positive in 30-60% |
| AQP4 antibodies | Rule out NMOSD | Usually negative |
MRI Findings
| Feature | Description |
|---|---|
| White matter lesions | Large, bilateral, poorly-demarcated |
| Deep grey matter | Thalamus, basal ganglia involvement |
| Lesion appearance | "Fluffy" or "cloud-like" |
| Contrast enhancement | Variable |
| Spinal cord | Long segments possible |
CSF Findings
| Parameter | ADEM | MS |
|---|---|---|
| Pleocytosis | Common (50-80%) | Uncommon |
| Protein | Elevated | Normal/mild ↑ |
| Oligoclonal bands | Usually absent | Present in >0% |
| Glucose | Normal | Normal |
Differential Investigations
| Test | To Exclude |
|---|---|
| Blood cultures | CNS infection |
| Viral PCR (CSF) | Viral encephalitis |
| HIV test | Opportunistic |
| Autoimmune panel | Vasculitis, SLE |
Acute Treatment
First-Line: High-Dose IV Corticosteroids
| Population | Dose | Duration |
|---|---|---|
| Children | IV Methylprednisolone 20-30 mg/kg/day (max 1g) | 3-5 days |
| Adults | IV Methylprednisolone 1g daily | 3-5 days |
| Oral taper | Prednisolone 1-2 mg/kg/day | Taper over 4-6 weeks |
Second-Line: Steroid-Refractory
| Treatment | Dose | Indication |
|---|---|---|
| IVIG | 2 g/kg over 2-5 days | Steroid non-response |
| Plasma exchange | 5-7 exchanges | Fulminant disease |
Supportive Care
- Seizure management (if present)
- Physiotherapy
- Respiratory support (if needed)
- Venous thromboembolism prophylaxis
- Stress ulcer prophylaxis
- Nutritional support
Monitoring
- Regular neurological observations
- GCS monitoring
- Watch for complications (raised ICP, status epilepticus)
Acute Complications
| Complication | Management |
|---|---|
| Seizures | Antiepileptic medications |
| Raised ICP | Dexamethasone, neurosurgery |
| Respiratory failure | Ventilatory support |
| Status epilepticus | ICU, aggressive AED therapy |
Long-Term Sequelae
| Outcome | Frequency |
|---|---|
| Complete recovery | 70-90% |
| Residual deficits | 10-30% |
| Cognitive impairment | 10-20% (especially young) |
| Epilepsy | 5-10% |
| Evolution to MS | 10-15% (especially if OCBs positive) |
Prognostic Factors
| Factor | Better Prognosis | Worse Prognosis |
|---|---|---|
| Age | Older children | Very young (<2y) |
| Presentation | Less severe | Fulminant, coma |
| MRI | Fewer lesions | Extensive involvement |
| OCBs | Absent | Present |
| MOG-Ab | Usually monophasic | May relapse |
Recovery
- Motor: Usually good recovery
- Cognitive: May have lasting deficits in young children
- Timing: Improvement within days to weeks of treatment
Follow-Up
- Repeat MRI at 3-6 months
- Monitor for new symptoms (MS evolution)
- Annual neurology review
- Educational support if cognitive issues
Key Guidelines
- IPMSSG Criteria (2012/2023) — International consensus for diagnosis
- UK Paediatric Neurology Guidelines — Management recommendations
Key Differentiating Features from MS
| Feature | ADEM | MS |
|---|---|---|
| Encephalopathy | Required | Absent |
| Episode | Monophasic | Relapsing-remitting |
| Age | Children | Young adults |
| MRI lesions | Large, fluffy, bilateral | Small, discrete, periventricular |
| OCBs | Usually absent | Present >0% |
| Deep grey matter | Common | Uncommon |
Evidence Strength
| Intervention | Level | Notes |
|---|---|---|
| IV Methylprednisolone | 2b | Observational studies |
| IVIG for refractory | 3 | Case series |
| Plasma exchange | 3 | Case series |
What is ADEM?
Acute disseminated encephalomyelitis (ADEM) is a condition where the immune system attacks the brain and spinal cord. This usually happens after a viral infection like a cold or flu.
What happens?
The body's immune system gets confused and attacks the protective covering of nerve fibres (myelin) in the brain. This causes inflammation and affects how the brain works.
What are the symptoms?
- Confusion or drowsiness
- Weakness in arms or legs
- Difficulty walking or balance problems
- Vision problems
- Seizures
How is it treated?
- Steroids: High-dose steroids through a drip reduce inflammation
- Hospital care: Your child will be monitored closely
- Rehabilitation: Physiotherapy helps recovery
What is the outcome?
- Most children (70-90%) recover completely
- Recovery usually happens over weeks to months
- Some children may have lasting mild problems with thinking or movement
- It usually happens only once
When to seek help
Return immediately if:
- Increasing drowsiness or confusion
- Seizures
- New weakness
- Difficulty breathing
Primary Guidelines
-
Krupp LB, Tardieu M, Amato MP, et al. International consensus criteria for pediatric MS and ADEM. Neurology. 2013;81(4):319-333. PMID: 23825173
-
Pohl D, Alper G, Van Haren K, et al. Acute disseminated encephalomyelitis: Updates on an inflammatory CNS syndrome. Neurology. 2016;87(9 Suppl 2):S38-S45. PMID: 27572859
Key Reviews
-
Tenembaum S, et al. Acute disseminated encephalomyelitis: a long-term follow-up study of 84 pediatric patients. Neurology. 2002;59(8):1224-1231. PMID: 12391351
-
Hynson JL, et al. Clinical and neuroradiologic features of acute disseminated encephalomyelitis in children. Neurology. 2001;56(10):1308-1312. PMID: 11376179
Further Resources
- MS Society UK: mssociety.org.uk
- Child Neurology Foundation: childneurologyfoundation.org
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. For suspected ADEM, seek urgent medical attention.