ADEM: Acute Demyelinating Encephalomyelitis — The Brain Attack That Follows an Infection

Acute Disseminated Encephalomyelitis (ADEM) is a monophasic, immune-mediated inflammatory demyelinating disease of the central nervous system — meaning it typically occurs once (monophasic), is driven by a misdirected immune response, and attacks the myelin (white matter) of the brain and spinal cord. It most commonly occurs in children following a viral infection (measles, chickenpox, EBV, influenza — 1–3 weeks prior) or, rarely, following vaccination. ADEM is alarming in its presentation but responds dramatically to corticosteroids and carries a good prognosis in most cases.

Clinical Features

ADEM presents with: encephalopathy (altered level of consciousness, confusion, irritability) — a core feature that distinguishes it from multiple sclerosis; fever (at onset); multifocal neurological deficits — depending on which areas of the white matter are affected: hemiplegia, cerebellar ataxia, diplopia, optic neuritis, transverse myelitis; seizures (in up to 30% of paediatric cases); headache. The entire presentation develops rapidly, typically over days to 2 weeks.

MRI Features

Large, bilateral (often symmetric), poorly defined areas of T2/FLAIR hyperintensity in the white matter — typically involving subcortical white matter, basal ganglia, thalami, and brainstem. These large "fluffy" lesions contrasting with the smaller, well-defined, periventricular lesions of MS are an important distinguishing feature. Spinal cord involvement is common.

Treatment and Prognosis

High-dose IV methylprednisolone (20–30mg/kg/day for 3–5 days) produces dramatic improvement in most cases. IVIG or plasma exchange for non-responders. Prognosis: 70–90% of paediatric ADEM patients make full recovery. Some have residual deficits. A minority have relapsing disease — particularly MOG antibody-positive ADEM, which has a high relapse rate and requires maintenance immunosuppression. Sri Anand CNC, Chanda Nagar, Hyderabad. Call +91 90633 66983.