In this issue of JAMA Neurology, Wijburg and colleagues1 report on the association between progressive multifocal leukoencephalopathy (PML) lesion characteristics from magnetic resonance imaging (MRI) scans and the viral load of JC virus (JCV) DNA that is measured by quantitative polymerase chain reaction (qPCR). Among their conclusions is that the size of PML lesions identified using T2 and fluid-attenuated inversion recovery MRI images is positively correlated with the viral DNA load in the cerebrospinal fluid (CSF). At the extreme end of this phenotype, the authors observed that small lesions can be associated with the lack of detection of JCV DNA in the CSF. This suggests that among the patients with smaller, less classical MRI features, relied-on laboratory test results may not be immediately able to confirm a PML diagnosis. At first approximation, such conclusions seem axiomatic, smaller lesion, less virus. However, understanding how JCV infection causes lesions and what happens to the cell targets of the infection comprising those lesions is critical to contextualize these new findings.
Major EO. Progressive Multifocal Leukoencephalopathy Lesions and JC Virus: The Limits and Value of Imaging. JAMA Neurol. 2018;75(7):789–790. doi:10.1001/jamaneurol.2018.0004
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