Progressive multifocal leukoencephalopathy associated with isolated CD8+ T-lymphocyte deficiency mimicking tumefactive MS.

Progressive multifocal leukoencephalopathy (PML) is a severe demyelinating disease of the central nervous system (CNS) caused by lytic infection of oligodendrocytes by the polyomavirus JC (JCV). PML has classically been described in individuals with profound cellular immunosuppression. While some case reports have documented PML in individuals with minimal or occult immunosuppression, such cases are very rare and their pathogenesis is not well understood. We report a unique case of a 74 year-old woman who developed PML clinically mimicking tumefactive multiple sclerosis in the context of an idiopathic isolated CD8+ T-lymphocytopenia. Her course subsequently stabilized, concomitant to the development of a cellular immune response directed against JCV. We review the current literature of related cases and discuss the pathogenesis and implications of this rare presentation.