Progressive Multifocal Leukoencephalopathy (PML)

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Background    Neuroimaging    Gross Pathology    Histopathology & Immunohistochemistry   Differential Diagnosis    Reference

BACKGROUND AND CLINICAL INFORMATION: Head

Clinical features:

Anatomic distribution of lesions: White matter of cerebrum, to a lesser extent, cerebellum, and brain stem.

Pathogenesis: Mechanism is not known but is associated with JC virus infection. Characterized by multifocal demyelination which grossly appear as gray foci in the white matter. Lesions may also be found in the gray matter.

NEUROIMAGING: Head

GROSS PATHOLOGY: Head

HISTOPATHOLOGY AND IMMUNOHISTOCHEMISTRY: Head  

Histology: multiple foci of demyelination with enlarged and bizzare astrocytes, which are often multinucletated and have multiple large processes. Lymphocytic infiltration can also be seen.

Eosinophilic or basophilic intranuclear inclusions are seen in atypical oligodendrocytes.

Virons are found profusely in oligodendrocytes, rarely in astrocytes, and never in neurons.

Demyelination is a prominent feature. However, destruction of axons, atypical for demyelinating diseases, is also seen in PML.

Frank necrosis with a phagocytic reaction indistinguishable from that seen in an infarct may be seen at the center of the lesions.

DIFFERENTIAL DIAGNOSIS: Head

REFERENCES: Head