0:00

We've just described various vascular etiologies

0:04

for white matter disease that are

0:06

mediated through hypertension.

0:08

This leads to an additional entity known as

0:11

Posterior Reversible Encephalopathy Syndrome,

0:14

which we refer to as PRES.

0:17

So, PRES is mediated through

0:20

changes in blood pressure.

0:22

While initially, we thought that this was

0:24

secondary to hypertension

0:26

and severe hypertension,

0:27

what we've come to understand is that

0:29

fluctuations in the blood pressure

0:32

that may or may not represent hypertension,

0:35

can lead to PRES.

0:36

So, in other words,

0:37

if a patient who normally runs a blood pressure,

0:40

say, of 90 over 60,

0:43

subsequently has an episode

0:45

in which the blood pressure increases to 130 over 85,

0:49

even though it doesn't meet our standard

0:51

criteria of hypertension,

0:53

that fluctuation in the blood pressure can lead

0:56

to posterior reversible encephalopathy syndrome.

1:00

So, this was initially described in three conditions,

1:04

that fluctuations in the

1:05

blood pressure with hypertension,

1:07

eclampsia and preeclampsia,

1:09

with fluctuations of blood pressure

1:11

after birth or at the time of the birth,

1:15

as well as certain medications.

1:17

The classic medication was Cyclosporine.

1:20

We also see this with Tacrolimus,

1:22

but there are many, many medications now

1:25

associated with posterior reversible

1:28

encephalopathy syndrome, so-called PRES.

1:31

All of these seem to be mediated through

1:33

a dysfunction in vasoregulation

1:36

as the blood pressure change exceeds the ability

1:39

to vasoregulate and you get vasogenic

1:42

edema in the posterior white matter.

1:48

from the blood vessels into the interstitium

1:51

and the vasogenic edema.

1:53

You may see mild mass effect.

1:55

Now, the curious thing about posterior reversible

1:58

encephalopathy syndrome,

2:00

is that each of those specific terms

2:04

may not be seen with the entity.

2:06

In other words, we see sometimes PRES

2:08

that is not necessarily posterior,

2:10

but involves the anterior white matter.

2:12

We also see in 10% of cases

2:14

that the patients have infarctions

2:17

associated with the PRES,

2:19

and therefore, it is not reversible.

2:20

90% of the time, it's reversible.

2:23

10% of the time it's irreversible,

2:25

and you have actual infarctions.

2:27

And the E for encephalopathy

2:29

sometimes is relatively minor.

2:31

So, these are different examples

2:33

of patients who have PRES.

2:36

Here is a typical feature in which it's a

2:40

relatively symmetric process,

2:43

which extends to the deep white matter

2:45

in the subcortical region

2:47

and is involving the posterior aspect of the

2:50

white matter in the parietal occipital lobes.

2:53

Contrast that with this patient,

2:55

who has predominantly anterior involvement of

2:57

the frontal lobes.

2:58

Although you do see that

2:59

there is some involvement of the parietal lobes.

3:02

But by and large,

3:03

PRES is relatively symmetric from right to left.

3:08

10% of the cases will show contrast enhancement.

3:12

90% do not show contrast enhancement.

3:16

And as I said,

3:17

only 10% will show cytotoxic edema.

3:23

an ADC map which is showing bright signal

3:26

intensity. PRES, therefore,

3:29

no evidence of infarction. It's vasogenic edema,

3:32

not cytotoxic edema.

3:34

Those patients who have contrast enhancement,

3:38

those patients who have cytotoxic edema,

3:41

and sort of the 10% rule of PRES is the 10%

3:44

are hemorrhagic. Those patients do worse.

3:47

So if you have contrast enhancement,

3:50

if you have cytotoxic edema,

3:52

and if you have hemorrhage,

3:54

the prognosis is worse.

3:55

For more lasting clinical symptoms, however,

4:00

the typical feature of PRES

4:02

is that it is reversible.

4:04

So it does have resolution over the

4:07

course of weeks to a month.

4:10

Rarely,

4:11

you will have involvement of the gray matter,

4:16

which can occur in PRES.

4:18

And you may see mass effect associated

4:21

with PRES as well.

4:23

Women are affected more commonly than men,

4:25

but that is mediated through the cases in which

4:28

you have eclampsia and preeclampsia.

4:31

The etiologies of PRES have

4:33

been widely discussed.

4:35

You can see this in patients who are taking

4:38

cocaine and have wide fluctuations in the blood

4:41

pressure secondary to recreational drug use,

4:44

such as cocaine.

4:46

We also see it in patients who are on dialysis.

4:49

On dialysis, you may see,

4:51

because of the fluid changes,

4:53

wide fluctuations in the blood pressure,

4:55

which may also be seen with PRES.

4:57

You may see this with hepatic insufficiency

4:59

or hepato-renal syndrome.

5:01

You may see this with hemolytic uremia syndrome.

5:04

You may see this with lupus.

5:06

so there are many different causes of PRES

5:09

on the infectious etiologies.

5:11

We see it sometimes in patients who have sepsis,

5:13

and that's usually mediated through vascular

5:16

endothelial injury associated with the sepsis.

5:19

So the list of causes of PRES

5:22

is quite widespread.

5:23

Among the medications I mentioned were

5:25

cyclosporin as well as tacrolimus or FK 509.

5:30

However, almost,

5:31

there are very many chemotherapy agents,

5:34

Ara-C (ARa-C),

5:36

that have been associated with PRES.

5:39

This is what you want to see.

5:41

What you want to see is a patient who has PRES

5:44

that resolves completely. And again,

5:46

this occurs in about 90% of patients.

5:48

If you withdraw the medication,

5:51

if you monitor the blood pressure and

5:53

control the blood pressure swings,

5:55

if you treat the underlying disease,

5:57

such as sepsis, you will see complete reversal.

6:00

Of the disease.

6:01

And that is shown on the MRI scan.

6:04

Remember that the MRI scans tend to be

6:06

delayed versus the clinical response.

6:10

So when they withdraw the medications,

6:12

when they treat the blood pressure,

6:13

when they treat the infection,

6:15

that's leading to the sepsis,

6:17

the patients will respond clinically,

6:19

and the MRI scan might still show the signal

6:25

intensity abnormality in the

6:26

posterior white matter.

6:27

So the MRI is delayed in response compared

6:30

to the clinical response.