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Acute Disseminated Encephalomyelitis (ADEM)


KEY FACTS

Terminology

  • Para-/postinfectious immune-mediated inflammatory disorder of white matter (WM)

    • Antibodies to pathogens exhibit cross-immunoreactivity with myelin basic protein

Imaging

  • Multifocal short-segment WM lesions with relatively little mass effect or vasogenic edema

    • Flame-shaped lesions with slight cord swelling

    • Dorsal white matter more voluminous

    • May see gray matter involvement

    • Variable enhancement, depending on stage of disease

    • May see nerve enhancement

  • Brain almost always involved

Top Differential Diagnoses

  • Inflammatory etiologies

    • Acquired demyelinating

      • –

        Multiple sclerosis

      • –

        Neuromyelitis optica

    • Parainfectious myelitis

    • Systemic autoimmune (vasculitis)

  • Noninflammatory mimics

    • Vascular malformation

    • Infarction, spinal cord

    • Tumor and cysts

  • Idiopathic acute transverse myelitis

Clinical Issues

  • Typically monophasic illness lasting from 2-4 weeks

    • Encephalopathy, paresis

  • Typically childhood or young adult

  • Rx: High-dose corticosteroids (acute)

Diagnostic Checklist

  • Delay between clinical onset, appearance of imaging findings common, so rescan if initial study is negative

Sagittal T1WI C+ MR shows linear enhancement along the dorsal surface of the midcervical cord
. Acutely, there is perivenous edema, demyelination, and infiltration with macrophages and lymphocytes, with relative axonal sparing. The late course of the disease is characterized by perivascular gliosis.

Axial T2WI MR depicts a hyperintense focus in the right hemicord
with minimal cord enlargement. ADEM is a postinfectious disease mediated by autoreactive cells or molecules.

Sagittal T2WI MR demonstrates a vague intramedullary focus of hyperintensity
. There is mild cord expansion.

Sagittal T1WI C+ MR illustrates an ovoid intramedullary focus of enhancement in the upper thoracic cord
.

TERMINOLOGY

Abbreviations

  • Acute disseminated encephalomyelitis (ADEM)

Definitions

  • Para-/postinfectious immune-mediated inflammatory disorder of white matter

IMAGING

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