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Progressive Multifocal Leukoencephalopathy (PML)


KEY FACTS

Terminology

  • Progressive multifocal leukoencephalopathy (PML)

  • Subacute opportunistic infection caused by DNA virus JC polyomavirus (JCV)

  • JCV infects oligodendrocytes, causes demyelination in immunocompromised patients

  • Associated with immunosuppression, often AIDS

    • Organ transplant, cancer, chemotherapy, myeloproliferative disease, and steroid treatment

    • Reported in treatment for multiple sclerosis and in rheumatic diseases

Imaging

  • Multifocal T2-hyperintense demyelinating plaques involve subcortical white matter (WM), extend to deep WM; gray matter often spared until late stage

  • Characteristic involvement of subcortical U fibers

  • Generally no contrast enhancement or mass effect

  • Late: Confluent WM disease, cystic changes

  • Propensity for frontal and parietooccipital region, thalamus

    • May involve brainstem and cerebellum

  • May be solitary, multifocal, or widespread confluent

Top Differential Diagnoses

  • HIV encephalitis

  • Acute disseminated encephalomyelitis

  • Acquired CMV

  • Immune reconstitution inflammatory syndrome

Clinical Issues

  • Without treatment (plasma exchange): Poor prognosis, death in 2.5-4.0 months

    • HAART reported to improve survival

  • Associated with natalizumab treatment

Diagnostic Checklist

  • Test for JCV before treatment with high-risk medications

  • New multifocal WM lesions in AIDS or patient on high-risk medication? Consider PML!

Axial FLAIR MR in an AIDS patient who was somnolent at presentation shows scalloped hyperintensity in the left frontoparietal white matter
. There is involvement of the subcortical U fibers
, characteristic of PML. Note involvement of the corpus callosum
but lack of mass effect.

Axial DWI in an HIV patient with very low CD4(+) counts and PML demonstrates central core of low signal
surrounded by rim of higher signal
. Appearance of PML on DWI varies with disease stage.

Axial FLAIR MR in a patient with multiple sclerosis on natalizumab and developed PML demonstrates infiltrating hyperintensity involving the right temporal, parietal, and occipital white matter
as well as the splenium
.

Axial T1C+ MR in the same patient shows white matter hypointensity
with very faint enhancement at the margins
. Monoclonal antibody therapy (like natalizumab) used in a wide spectrum of immunologic diseases may depress the immune system and predispose the patient to PML.

TERMINOLOGY

Abbreviations

  • Progressive multifocal leukoencephalopathy (PML)

Definitions

  • Subacute opportunistic infection caused by DNA virus JC polyomavirus (JCV)

IMAGING

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