[Progressive multifocal leukoencephalopathy with bilateral middle cerebellar peduncle lesions confirmed by repeated CSF-JC virus tests and coexistence of JC virus granule cell neuronopathy. Report of a case].

A 65 year-old woman with small lymphocytic leukemia presented with subacute cerebellar ataxia. Six months after rituximab chemotherapy, a cranial MRI revealed lesions in the bilateral middle cerebellar peduncles. Both cerebrospinal fluid (CSF) JC virus (JCV)-DNA PCR test on three occasions and brain biopsy were negative. CSF tests were repeated. The fourth test performed 6 months after the onset showed positive JCV-DNA, and a definite diagnosis of progressive multifocal leukoencephalopathy (PML) was made. Neuroimaging of cerebellar atrophy was considered to be coexistence of granule cell neuronopathy. Medication with mirtazapine and mefloquine was temporarily effective for several months. Little are known solitary bilateral MRI lesions of the middle cerebellar peduncle in PML. JCV-PCR test of CSF may be negative at an earlier stage of PML. Repeated CSF tests should be essential to confirming the diagnosis in such cases.