Detection of human herpesvirus 6 and JC virus in progressive multifocal leukoencephalopathy complicating follicular lymphoma

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Abstract
Progressive multifocal leukoencephalopathy (PML), a demyelinating infectious disease caused by JC virus (JCV), occurs almost exclusively in immunocompromised patients usually with malignant diseases. We report here a Japanese female with follicular lymphoma who subsequently developed PML. In addition to JCV, human herpesvirus 6 (HHV‐6) was detected in the affected brain lesions of the patient by polymerase chain reaction and by in situ hybridization. HHV‐6, recognized as a neurotropic virus, is known to be reactivated during immunosuppression and can cause fatal complications such as encephalitis/encephalopathy. It is likely that impaired immunity associated with lymphoma and the additional immunosuppression following cytopenia‐inducing chemotherapies predisposed the patient to reactivated HHV‐6 infection. Although it remains to be clarified whether HHV‐6 plays an important role as a co‐agent with JCV in causing demyelination of the brain, our observation alerts physicians to the possible association of HHV‐6 with the pathogenesis of PML. Am. J. Hematol. 67:200–205, 2001.