Atypical progressive multifocal leukoencephalopathy with plasma-cell infiltrates.

In rare cases of progressive multifocal leukoencephalopathy (PML) the lesions are atypical in that the characteristic alteration of oligodendrocytic nuclei is infrequent or absent, and the demyelinated foci contain mononuclear inflammatory infiltrates including numerous plasma cells. Otherwise these cases, both as to the topographic features of the lesions, and the background of chronic lymphoproliferative or myeloproliferative disease or immunosuppressive treatment, conform to the usual pattern. In the case here reported, that of a 54-year-old man receiving immunosuppressive drugs for chronic polymyositis, electron microscopy showed papovavirions in astrocytic nuclei and fluorescent antibody studies indicated that these represented JC virus. In this and the 3 previously reported similar cases of atypical PML, the neurologic illness was less devastating than generally occurs in classic PML. Possibly these cases represent instances of unusually strong host-resistance against the disease.