Central nervous system herpes simplex and varicella zoster virus infections in natalizumab-treated patients.

We report on 20 natalizumab-treated patients with multiple sclerosis who developed laboratory-confirmed central nervous system (CNS) herpesvirus infections. In addition to progressive multifocal leukoencephalopathy, other CNS opportunistic infections have been rarely reported during natalizumab treatment. We encourage heightened awareness due to the risk for serious outcomes.