Predictive value of JC virus PCR in cerebrospinal fluid in the diagnosis of PML

Abstract Objective To assess the predictive value of JC virus (JCV) PCR in cerebrospinal fluid (CSF) in the diagnosis of progressive multifocal leukoencephalopathy (PML). Methods We conducted a retrospective database query to identify patients with positive CSF JCV PCR. Clinical features, final diagnosis and quantitative PCR results were obtained. Results A positive CSF JCV PCR had a PPV of 10.4% for the diagnosis of PML. A weakly positive PCR had a PPV of 1.6%, whereas a moderately to highly positive PCR had a PPV of 92.3%. A PPV of 0.0% was observed in immunocompetent patients and in patients without compatible clinical or radiological features. Conclusions A false-positive CSF JCV PCR is highly prevalent in our clinical practice. This test should be reserved for patients with a clinical suspicion of PML and the quantitative result of the PCR should be taken into account when making the diagnosis of PML.