Failure of cidofovir therapy in progressive multifocal leukoencephalopathy unrelated to human immunodeficiency virus.

We describe the first reported human immunodeficiency virus (HIV)-seronegative patient treated with cidofovir for progressive multifocal leukoencephalopathy (PML). Marked clinical and radiological progression of PML occurred during cidofovir therapy. The improvement observed during cidofovir therapy of HIV-infected patients may be due to the effect of concomitant antiretroviral therapy rather than cidofovir.