Progressive multifocal leukoencephalopathy with concurrent Richter's syndrome

Progressive multifocal leukoencephalopathy (PML) is a demyelinating infecti ous disease caused by the JC virus. It was originally described in patients with chronic lymphocytic leukemia (CLL). Richter's syndrome, or transforma tion to large cell lymphoma, occurs in approximately 3% of patients with CL L, and carries a poor prognosis. We report a patient with documented PML an d concurrent Richter's transformation outside the central nervous system. B efore establishing a definitive diagnosis of PML, radiation therapy to the presumed lymphomatous brain lesion had been considered, raising the issue o f whether stereotactic brain biopsy should be considered in every patient i n a similar situation. Although this is likely a rare occurrence, patients with Richter's transformation documented at an extra-neural site and a brai n lesion may benefit from the establishment of an infectious diagnosis whic h would influence therapy.