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

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.