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The next entity to describe in this great parade

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of demyelinating disorders is progressive

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multifocal leukoencephalopathy, or PML.

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You can see that these have all long names,

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and that's why we tend to go with things

0:14

like ADEM and MS and MDEM and PML.

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A lot of short acronyms or the abbreviations.

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PML is an entity that is associated

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with the Papovavirus,

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the JC virus, that destroys oligodendrocytes,

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and hence leads to the white matter disease.

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It's typically found in immunocompromised hosts.

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And while initially this was a boon in the

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AIDS epidemic era, where we saw many,

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many cases of PML,

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it has subsequently transferred

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to those patients who are undergoing

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immunosuppressive therapies,

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such as organ transplants or chemotherapy for

0:59

cancer or lymphoma.

1:02

This is an entity that has usually

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little to no enhancement,

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but will favor the subcortical U fibers on MRI scan.

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It does have a posterior predilection,

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so we see it more commonly in the occipital lobes,

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as well as the parietal lobes,

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and you may also see it in the cerebellum

1:23

and brain stem.

1:25

This is a nice example of PML,

1:29

a typical stereotypical involvement

1:32

of the white matter.

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We notice that we have a confluent

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white matter lesion that is multifocal.

1:41

We're seeing it in the frontal lobe,

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as well as in the cerebellum.

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When we look at its extent,

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as opposed to something like multiple sclerosis,

1:55

it extends to the subcortical

1:59

U fibers in a confluent way.

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This is probably best demonstrated

2:03

here in the cerebellum,

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where you see it going all the way to the

2:07

periphery in sort of a claw-like fashion,

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not staying centrally that one would see

2:14

in other demyelinating disorders.

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On diffusion-weighted scan,

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it is not showing restricted diffusion.

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So less than 10% of cases of PML

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have restricted diffusion or decreased ADC,

2:31

and less than 10%

2:35

have gadolinium enhancement.

2:38

You see here that this lesion is not

2:40

showing gadolinium enhancement.

2:43

Less than 10% are hemorrhagic.

2:50

So, this is our stereotypical view of progressive

2:54

multifocal leukoencephalopathy.

2:56

I would like to draw in a little bit of white matter disease,

2:59

more in the parietal region

3:00

for that posterior predilection,

3:02

but in this case,

3:03

the patient's predominant involvement was

3:06

frontally in the supratentorial compartment,

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but out in the periphery of the cerebellum,

3:12

in the infratentorial compartment.