neurologic disorders
Progressive Multifocal Leukoencephalopathy (PML)
Diagnosis of PML
MRI Cerebrospinal fluid (CSF) testing for JC viral DNA Progressive multifocal leukoencephalopathy is suspected in patients with unexplained progressive brain dysfunction, particularly in those with depressed cell-mediated immunity. Provisional diagnosis of PML is made by contrast-enhanced MRI, which shows single or multiple white matter lesions on T2-weighted images. A contrast agent enhances, usually faintly and peripherally, 5 to 15% of lesions. CT may show low-density, nonenhancing lesions but is significantly less sensitive than MRI. CSF is analyzed for JC viral DNA using PCR; a positive result with compatible neuroimaging findings is nearly pathognomonic. Routine CSF analysis is usually normal. Serologic tests are not helpful. Stereotactic biopsy can provide a definitive diagnosis but is rarely warranted. 