Progressive multifocal leukoencephalopathy associated to natalizumab extended dosing regimen.

A risk for developing progressive multifocal leukoencephalopathy is a major barrier to natalizumab use. Extended dosing intervals have been proposed as a way to maintain therapeutic efficacy and reduce progressive multifocal leukoencephalopathy incidence. This is the first reported case of progressive multifocal leukoencephalopathy in a patient using an extended dosing regimen (300 mg/6 weeks). A close clinical and imaging monitoring allowed early detection, which is a major prognostic factor. A favorable outcome was seen with a therapy comprising plasma exchange therapy, mirtazapine, mefloquine and cidofovir. Further studies will be needed to assess the potential role of extended dosing intervals to improve prognosis in patients receiving natalizumab and also to measure its impact clinically and/or radiologically.