Cerebrospinal fluid and serum JC virus antibody detection in multiple sclerosis patients treated with natalizumab.

Progressive multifocal leukoencephalopathy (PML) is a complication of natalizumab treatment. In order to identify natalizumab-treated patients at risk of developing PML, we assayed for anti-JC virus (JCV) antibody levels in cerebrospinal fluid (CSF). Serial CSF antibody levels were obtained, with 4 patients showing increases in anti-JCV levels indicating possibly viral activation. In patients with both CSF and serum antibody levels, a comparison showed only a moderate Spearman Rank Correlation Coefficient of 0.38. Our data suggests that serum anti-JCV antibody testing alone may not suffice in identifying at-risk patients because of the lack of uniform correlation with CSF titers.