“…While JCV-specific antibodies are present in 50%-90% of the adult population worldwide, PML is an exceedingly rare complication with an incidence of 0.2-4.4 cases per 100,000 individuals in the general population [ 1 , 6 , 9 , 10 ]. Asymptomatic primary infection with JCV occurs in childhood and may subsequently reactivate from sites of latency and undergo sequential genomic rearrangements, spreading to the central nervous system in immunocompromised individuals [ 2 , 5 , 8 , 9 ]. The American Academy of Neurology (AAN) Neuroinfectious Disease Section developed the criteria for the diagnosis of PML which may be confirmed by either (1) the typical neuropathologic histopathologic triad of demyelination, bizarre astrocytes, and enlarged oligodendroglial nuclei as well as the presence of JCV or (2) clinical and radiographic findings consistent with PML and not better explained by other disorders as well as the JCV by polymerase chain reaction (PCR) in the cerebrospinal fluid (CSF) [ 1 , 6 , 9 - 11 ].…”