Progressive multifocal leukoencephalopathy: serial high-b-value diffusion-weighted MR imaging and apparent diffusion coefficient measurements to assess response to highly active antiretroviral therapy.

A patient with human immunodeficiency virus-related posterior fossa progressive multifocal leukoencephalopathy had serial diffusion-weighted imaging using b-values of 1000 and 3000 before and during highly active antiretroviral therapy (HAART). High-b-value images provided a superior definition of the leading edge of the lesion and additional information about the integrity of white matter tracts. Following HAART, there was a marked reduction of lesional apparent diffusion coefficient and reconstitution of anisotropy in the affected middle cerebellar peduncle.