Diffuse large B cell lymphoma secondary to JC virus in progressive multifocal leukoencephalopathy.

We present the case of a 43-year-old-man with a past medical history of HIV with recently initiated HAART and existing PML that presented with altered mental status. The initial diagnosis was deemed to be PML-IRIS; however, neuroimaging brought into question this diagnosis. Flow cytometry performed from the cerebrospinal fluid revealed diffuse large B cell lymphoma. JC virus may act in an oncogenic role similarly to EBV and predispose to CNS lymphomas. Patients with PML caused by JC virus may develop secondary malignancies.