Acute Disseminated Encephalomyelitis (ADEM)


a.k.a. Acute dissemniated leukoencephalitis a.k.a. Acute postinfectious/post-vaccinial perivenous encephalitis, a.k.a. acute demyelinating encephalomyelitis,


Clinical  features plus MRI and supportive tests

Clinical features:

Encephalopathy, focal findings may occur. Often follows an infectious illness or exposure to new antigen to medication

Findings on Investigations:


  • T2: preferred. High signal intensities (large patchy) in white matter in the brain (subcortical & deep, may extend to ventricles) +/-spinal cord and deep grey nuclei. May or may not enhance with gadolinium.

CT: some areas of hypoattenuation in the white matter and deep grey nuclei

  • Protein: mildly elevated 0.5-1.5 g/L (50-150 mg/dL)
  • WCC: lymphocytic pleocytosis usually
  • IgG index: usually normal
  • Myelin basic protein: high


Gross: small lesions in the white matter
Microscopically: perivenous lymphocytes, macrophages & plasma cells. Perivenous demyelination, with relatively spared axons. Usually no inflammation around the arteries. Meningeal inflammatory infiltrates occur.

Acute hemorrhagic leukoencephalitis of Hurst a.k.a Acute hemorrhageic encephalomyelitis AHEM, variant:

Pathology; Grossly, disseminated foci of hemorrhage in the white matter of the cerebral hemispheres, corpus callosum, pons & cerebellum
Microscopically, fibrinoid necrosis of blood veins. Perivenous necrosis, surrounded by hemorrhages. Perivenous mononuclear cells and neutrophils. Some demyelination and axonal loss.

Investigations to consider:

LP for CSF analysis
Viral screen:

  • Measles, paramyxovirus, varicella, rubella, and Epstein-Barr virus
  • Mycoplasma pneumoniae serology & cold agglutinins



  • Corticosteroids
  • IVIG
  • Plasma exchange

Related articles: