How are acute disseminated encephalomyelitis (ADEM) lesions differentiated from MS on MRI?

Updated: Nov 08, 2018
  • Author: J Nicholas Brenton, MD; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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ADEM lesions may contain areas of hemorrhage suggestive of HSV-2 encephalitis, changes never found in MS plaques.

Unusual MRI abnormalities that are found in young individuals suspected of having ADEM may help greatly in distinguishing ADEM from MS or other alternative diagnoses. ADEM gives rise to a much wider variety of appearances than MS. ADEM may produce large unilateral T2 bright lesions, some of which appear to have striking central cavitation. These lesions may suggest neoplasm, stroke, parasitism, abscess, or MS. Ring enhancement or mass effect sometimes found in ADEM may suggest abscess or tumor. [15] In rare cases, symmetrical, linear, posteriorly emphasized white matter changes on T2 weighting suggest leukodystrophy. Recognize that no changes on MRI are pathognomonic of ADEM or, for that matter, of demyelination.

Some patients with ADEM have normal findings on MRI on initial presentation that become abnormal and characteristic of ADEM if the study is repeated several weeks later. [16] This suggests that characteristic features may be missed because of sampling error, that normal findings on a scan do not exclude the ADEM diagnosis, and that the appearance of new lesions during the course of ADEM may not represent recrudescence of disease.

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