Also, the diagnosis of PML histopathology supposes it as: (i) definite, if classic histopathologic triad and tissue PCR test for JCPyV and immunohistochemistry/electron microscopy are all positive or even if only the last one or only the positivity in viral DNA is absent, (ii) probable, if there is positivity in classic histopathologic triad but the others are absent (iii) possible, if immunohistochemistry/electron microscopy is positive but the others are absent, and (iv) negative for PML/not PML, if all are negative and a DNA test is not performed, as seen in Table 2 [9]. This evidence concerns the gene PML and progressive multifocal leukoencephalopathy.