Cytomegalovirus-induced T-cell proliferation and the development of progressive multifocal leucoencephalopathy following bone marrow transplantation.

Progressive multifocal leucoencephalopathy (PML) is a rare disorder characterized by progressive demyelination within the brain. It is usually fatal and occurs when there are defects in cell-mediated immunity. We report a case of PML which developed following allogeneic bone marrow transplantation. It was preceded by the development of a persistent polyclonal expansion of large granular lymphocytes (LGLs) which appeared to rise as a consequence of cytomegalovirus infection.