[Progressive Multifocal Leukoencephalopathy with Inflammatory Reactions].

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disorder caused by reactivation of the JC virus associated with impaired host immunity. However, PML may occur even without an evident cause of immunosuppression. In such cases, JC virus DNA in cerebrospinal fluid (CSF) may not be detectable with polymerase chain reactions (PCR), and a brain biopsy may be performed. Pathology may exhibit marked inflammatory reactions around the JC virus-infected cells, although typical intranuclear viral inclusions would rarely be seen. Atypical inflammation in patients with PML likely an indication of the host's immune-response against the virus. this is usually observed in those with relatively-mild immunosuppression with favorable prognosis. Here, we describe cases of PML that exhibited inflammatory reactions; a recent topic, PML with immune reconstruction inflammatory syndrome (IRIS), will also be discussed.