Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease which results from the JC virus infecting oligodendrocytes. It is considered the most common clinical manifestation of JC virus infection in the brain. Although often in those with AIDS, it can occur in any patient with an immunocompromised status.

Multifocal T2 high signal foci representing areas of demyelination are characteristic with both the subcortical and deep white matter is involved with a preponderance for the subcortical U fibers. PML has a propensity for the frontal and parieto-occipital regions as well as the thalamus and basal ganglia.

This case illustrates the rapidity (progressiveness) of the disease.