PML and lymphoma: It is plain to see that a direct supposed PML pathology cannot be established, since molecular tests are not infallible, imaging features are not directly accurate in all cases, symptomatology is not always illustrative, and also, various different underlying conditions (such as AIDS and lymphoma) or/and medications (like chemotherapy and natalizumab) can result in different pathology, thus all previous discussion on its pathology may be just speculation, and of course, it was discussed in the symptomatology section that various factors affect clinical manifestations and symptomatology.