Ferretti F, et al. - Given the diagnostic significance of polyomavirus JC (John Cunningham; JCV)-DNA detection in cerebrospinal fluid (CSF) in progressive multifocal leukoencephalopathy (PML), researchers investigated the clinical significance of plasma JCV-DNA via retrospectively analyzing plasma samples from PML patients that were drawn close to disease onset and from controls without PML. Observations suggested that in cases where CSF is unavailable or JCV-DNA is not detectable in CSF, testing JCV-DNA in plasma might complement PML diagnosis. In addition, findings suggested the utility JCV-DNA plasma levels as a marker of disease progression in both human immunodeficiency virus-negative and combination antiretroviral therapy-treated HIV-positive PML patients.