[Idiopathic CD4-positive lymphocytopenia-associated progressive multifocal leukoencephalopathy confirmed by brain biopsy following negative results of repeated CSF-JC-virus tests: a case report].

A 75-year-old man presented with dysarthria and left facial paralysis. Brain diffusion-weighted MRI revealed a high-signal intensity in the right precentral gyrus, and he was hospitalized under the diagnosis of cerebral infarction. His symptoms worsened and brain MRI findings were consistent with progressive multifocal leukoencephalopathy (PML). Cerebrospinal fluid (CSF) JC virus (JCV) was undetectable in the DNA polymerase chain reaction (PCR) test four times, but brain biopsy revealed typical PML histopathology. He had no human immunodeficiency virus infection and history of immunosuppressive treatment, but he was found to have CD4+ lymphocytopenia. He was treated with mefloquine and mirtazapine, and died 29 months after symptoms onset. In cases whose repeated DNA PCR results are negative for CSF JCV, brain biopsy may be useful for the diagnosis of PML.