Progressive Multifocal Leukoencephalopathy (PML)

Epidemiology and Etiology:

· Viral encephalopathy

· JC polyomavirus

· Preferentially effects oligodendrocytes

· Immunosuppressed (almost invariably)

· Likely reactivated from previous exposure

· 65% of normal people have been exposed by age 14y

Common sites:

· Subcortical

· Brainstem

· Cerebellum

· Spinal cord occasionally

Gross features:

· Multifocal extensive white matter lesions

Histologic features:

· Patches of irregular, ill-defined white matter destruction

· Demyelination, reduced number of axons

· Lipid-laden macrophages at the centre

· Enlarged oligodendrocyte nuclei at the periphery

· Glassy amphophilic nuclear inclusion replacing chromatin

· Bizarre giant astrocytes maybe

· Irregular, hyperchromatic, sometimes multiple nuclei

· Reactive fibrillary astrocytes

Immunophenotype:

Marker:	Sensitivity:	Specificity:
JC virus

Molecular features:

·

Other features:

·

References:

· Kumar V, Fausto N, Abbas A. Robbins & Cotran Pathologic Basis of Disease, Seventh Edition. 7th ed. Saunders; 2004.