ADEM

Acute Disseminated Encephalomyelitis (ADEM)

Acute disseminated encephalomyelitis (ADEM) is a rare, but serious, immune-mediated disorder of the central nervous system. It is a monophasic (single-episode) demyelinating disease that typically occurs after a viral infection or, less commonly, a vaccination. ADEM is most common in children and is a key differential diagnosis for a new-onset neurological deficit in this age group.

Pathophysiology

ADEM is caused by an autoimmune response where the body’s immune system mistakenly attacks the myelin sheath—the fatty layer that insulates nerve fibres in the brain and spinal cord. The immune system is thought to “cross-react” with myelin proteins after exposure to an infectious agent (molecular mimicry). This widespread inflammation causes the neurological symptoms.

Clinical Presentation

The onset is typically acute or subacute, developing over a few days. The clinical features are highly variable and depend on the location and extent of the demyelination.

  • Preceding Illness: Most children have a viral-like illness (e.g., fever, cough, runny nose) 1-4 weeks before the onset of neurological symptoms.

  • Encephalopathy: This is the hallmark symptom and is required for a diagnosis of ADEM. The child presents with an altered level of consciousness, which can range from lethargy to coma.

  • Multifocal Neurological Deficits: This is a key feature that distinguishes ADEM from other conditions. Symptoms can include:

    • Motor: Hemiparesis (weakness on one side of the body), paraparesis, or quadriplegia.

    • Sensory: Numbness, tingling, or loss of sensation.

    • Cranial Nerves: Optic neuritis (pain on eye movement and visual loss) is common, as are facial nerve palsies.

    • Cerebellar: Ataxia and uncoordinated movements.

    • Seizures: These can occur in the acute phase.

Investigations

Prompt investigation is necessary to confirm the diagnosis and rule out other conditions.

  • Magnetic Resonance Imaging (MRI): A brain and spinal cord MRI is the most important diagnostic tool. It typically shows multiple, ill-defined, multifocal demyelinating lesions. The lesions are often large, bilateral, and asymmetrical. In contrast to multiple sclerosis (MS), they often spare the corpus callosum.

  • Lumbar Puncture (LP): Cerebrospinal fluid (CSF) analysis is usually performed. The CSF may show a mild pleocytosis (increased white blood cell count) and an elevated protein level. The absence of oligoclonal bands (OCB) in the CSF is a key finding that helps to differentiate ADEM from MS, where OCBs are typically present.

  • Blood Tests: These are generally non-specific but may be useful in ruling out other causes.

     

Management

The management of ADEM is focused on reducing the immune response and providing supportive care.

  • Immunomodulatory Therapy: High-dose intravenous corticosteroids (e.g., methylprednisolone) are the first-line treatment. This helps to reduce the inflammation.

  • Other Therapies: In severe cases that do not respond to steroids, intravenous immunoglobulin (IVIG) or plasma exchange may be used.

  • Supportive Care: This includes managing fever, pain, and seizures. Children with significant motor deficits may require physical and occupational therapy.

 

Prognosis

The prognosis for ADEM is generally good, with most children making a full recovery. However, a small percentage of children may be left with residual neurological deficits, and a small subset may have a recurrence or go on to develop MS. Long-term follow-up with a paediatric neurologist is therefore essential.