Progressive multifocal leukoencephalopathy (PML) is a rare infection caused by the John Cunningham virus (JC virus). The JC virus is present, but latent, in the majority of the population [Honce, Nagae & Nyberg, 2015]. Its activity is usually suppressed by the body’s immune system. In individuals with a compromised immune system, the virus may become re-activated, causing cell loss and destroying myelin-producing oligodendrocytes, resulting in severe demyelination and inflammation known as PML. Multiple sclerosis patients receiving immunosuppressant treatment have an increased risk of developing PML [Honce, Nagae & Nyberg, 2015].
MRI is a sensitive test to detect PML in asymptomatic cases [Wattjes et al, 2014]. Furthermore, as clinical manifestations of PML can be subtle, diagnosis can be delayed from days to months. In these cases, MRI may be a useful tool to offer patients, however interpretation requires specialist neuroradiology expertise. To diagnose PML, physicians should take into account the following factors: patients’ clinical symptoms, MRI findings, and CSF analysis. For final diagnosis CSF–PCR for JCV DNA should be used [Baldwin and Hogg, 2013].
Though PML can be fatal, close monitoring of high-risk individuals enables physicians to work with patients and the care team to make the best, informed treatment decisions.