Acute disseminated encephalomyelitis (ADEM) is a monophasic acute inflammation and demyelination of white matter typically following a recent viral infection or vaccination.

Appearances vary from small punctate lesions to tumefactive regions, which have less mass effect than one would expect for their size, distributed in the supratentorial or infratentorial white matter. Compared to multiple sclerosis, involvement of the callososeptal interface is unusual. Lesions are usually bilateral but asymmetrical. Involvement of cerebral cortex, subcortical grey matter, especially the thalami.

Lumbar puncture and a multitude of other laboratory investigations were undertaken with no indicative findings.   This combined with the clinical history led to the presumptive diagnosis of ADEM.