Progressive multifocal leukoencephalopathy (PML)
General description
Progressive multifocal leukoencephalopathy (PML) is a demyelinating disorder caused by the reactivation of the JC virus, which is acquired as an asymptomatic infection in many children and young adults. The reactivation of the virus is associated with immunosuppressive therapy, malignancies such as chronic myeloid leukemia, malignant lymphoma, or plasma cell neoplasm, and immunodeficiency states, such as HIV infection. Additionally, the use of monoclonal antibody drugs, including natalizumab and rituximab, can also increase the risk of developing PML.
Clinical manifestation
The clinical manifestations of progressive multifocal leukoencephalopathy (PML) typically include muscle weakness, sensory deficits, hemianopia, cognitive dysfunction, aphasia, and gait disturbances, with these symptoms often progressing over the course of several weeks.
Cerebral white matter lesion
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CerebrumParietal lobeCerebral white matterSubcortical white matter
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CerebrumFrontal lobeCerebral white matterSubcortical white matter
A characteristic neuroimaging finding in PML is the presence of bilateral, asymmetric subcortical white matter T2WI/FLAIR hyperintensities. The white matter lesions typically involve the parietal and frontal lobes, while the cerebral cortex and periventricular white matter are typically preserved.
In PML, T1WI hypointensity in the white matter lesions is a distinguishing characteristic, which helps differentiate it from HIV encephalopathy. Diffusion restriction is observed peripherally in the lesion, suggesting that the leading edge of the lesion is actively involved.
Cerebellar involvement
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CerebrumCerebral white matter
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Middle cerebellar peduncle
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Brainstem
In PML, the cerebellar white matter is initially involved, with subsequent progression to the middle cerebellar peduncles and tegmentum of the pons, potentially leading to clinical manifestations such as abducens nerve palsy or facial nerve palsy.
SWI and T2*WI hypointensity in U-fiber
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CerebrumFrontal lobeCerebral white matterSubcortical white matterU-fiber
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CerebrumParietal lobeCerebral white matterSubcortical white matterU-fiber
PML occasionally shows linear hypointensity in SWI and T2*WI along subcortiacl U-fiber.