Table 1.

Summary of diagnostic criteria for PML

Path to diagnosis	Diagnostic features	Diagnosisa
		Definite PML	Probable PML	Possible PML	Not PML
Neuropathological	Histopathological triad of demyelination, bizarre astrocytes, and enlarged oligodendroglial nuclei	Histopathological triad with detection of JCV protein and/or JCV DNA	Histopathological triad only	Detection of JCV protein only	No histopathological evidence of JCV infection
	JCV protein detected in focal brain lesions by immunohistochemistry or electron microscopy
	JCV DNA detected in focal brain lesions by in situ hybridization or PCR
Combined clinical, radiological and laboratory	Clinical: progressive neurological symptoms	JCV DNA detected in the CSF, and both imaging features and clinical features present	JCV DNA detected in the CSF and either imaging or clinical features present	Imaging and clinical features only, or only detection of JCV DNA in the CSF	Isolated clinical or imaging features
	Imaging: MRI features
	Laboratory: JCV DNA detected in the CSF by PCR

CSF, cerebrospinal fluid; JCV, JC virus; PCR, polymerase chain reaction; PML, progressive multifocal leukoencephalopathy. ^aCriteria are compiled from ref.⁶⁴.