Editing Progressive multifocal leukoencephalopathy (section)

==Diagnosis==
PML is diagnosed in a patient with a progressive course of the disease, finding JC virus [[DNA]] in [[cerebrospinal fluid|spinal fluid]] together with consistent white-matter lesions on brain [[magnetic resonance imaging]] (MRI); alternatively, a brain [[biopsy]] is diagnostic<ref name=NIH/> when the typical histopathology of demyelination, bizarre astrocytes, and enlarged oligodendroglial nuclei are present, coupled with techniques showing the presence of JC virus.<ref name=AAN>{{cite journal|author1=Berger JR|author2=Aksamit AJ|author3=Clifford DB|title=PML diagnostic criteria: consensus statement from the AAN Neuroinfectious Disease Section|journal=Neurology|date=9 April 2013|volume=80|issue=15|pages=1430–8|doi=10.1212/WNL.0b013e31828c2fa1|pmid=23568998|display-authors=etal|pmc=3662270}}</ref>

Characteristic evidence of PML on brain [[CT scan]] images are multifocal, non[[Radiocontrast agent|contrast]] enhancing hypodense lesions without [[mass effect (medicine)|mass effect]], but MRI is far more sensitive than CT.<ref name=AAN/> The most common area of involvement is the cortical white matter of [[frontal lobe|frontal]] and [[parietal lobe|parieto]] [[occipital lobe]]s, but lesions may occur anywhere in the brain, such as the [[basal ganglia]], [[external capsule]], and [[posterior cranial fossa]] structures such as the brain stem and cerebellum.<ref name=AAN/>
Although typically multifocal, natalizumab-associated PML is often monofocal, predominantly in the frontal lobe.<ref name=AAN/>