A 20 year-old man with a history of heroin abuse developed confusion and weakness. Within a few days, he was abulic and mute. Bilateral upper motor neuron signs were present.

In this case, the diffuse white matter disease (i.e., leukoencephalopathy) resulted from the toxic effect of inhaling heated heroin vapor ("chasing the dragon"). In this situation, MRI shows diffuse, symmetrical white matter hyperintensities. A similar pattern of white matter changes can be seen following cranial irradiation or chemotherapy agents, or as a consequence of rare inherited disorders of white matter (i.e., leukodystrophies).