Toxic leukoencephalopathy is an alteration of cerebral white matter in which mylin sufferes the majortity of damage. This can be caused by a wide variety of toxins including chemotherapy, drugs of abuse (EtOH, coke, heroin), and carbon monoxide.  Similar finding can also be found with demyelinating diseases like multiple sclerosis, a variety of metabolic disorders, and cerebrovascular disease.
Cases have been published describing cocaine induced encephalopathy  as was the case in these images.
Acute Multiple sclerosis enhances with gadolinium while toxic leukoencephalopathy does not.
- Filley CM, Kleinschmidt-Demasters BK: Toxic Leukoencephalopathy. NEJM 345:425-432, 2001.
- Balamuthusamy S. MRI changes in cocaine induced toxic encephalopathy. www.priory.com/phych.htm, 2005