Abstract
A 70-year-old woman with a human T-cell leukemia virus type 1 infection without any focal neurological symptoms showed age-related atherosclerotic changes in the white matter without any suspicious signal changes suggestive of progressive multifocal leukoencephalopathy (PML) based on the findings of MRI. Viral polymerase chain reaction (PCR) revealed 6,700 copies/mL of the JC virus genome in the cerebrospinal fluid (CSF). An immuno-pathological examination of the autopsied brain revealed JC virus capsid proteins, and in situ hybridization confirmed a JC virus infection, indicating that an active infection begins at the radiologically indistinguishable phase of PML. An early JC virus infection is probably associated with small, scattered demyelinating lesions around the cortico-medullary area of the cortex.