Progressive Multifocal Leukoencephalopathy versus Brain Metastasis in a Patient with Locally-Advanced Non-Small Cell Lung Cancer.

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease affecting the white matter of the brain. This condition is caused by the John Cunningham virus and leads to progressive neuropsychological deficits. Though the infection is typically seen in association with HIV or AIDS, other immune-compromised states may predispose patients as well. This report discusses a patient who developed PML following standard chemo-radiotherapy for non-small cell lung cancer in whom presentation was initially more convincing for brain metastasis; thus, highlighting the importance of accurate diagnosis of new brain lesions in this setting.