PRES, posterior reversible leukoencephalopathy syndrome, hypertensive encephalopathy, reversible posterior cerebral oedema syndrome and hyperperfusion encephalopathy are all terms used to describe the same neuroradiology findings, which might be caused by a variety of totally different pathological processes. But, all those processes end up causing white matter oedema in a bilateral (usually posterior) distribution, which shines with an obvious increased signal intensity on an MRI T2-weighted image. The management for most of these conditions is the same (i.e. nothing specific) and the intensivist is invariably left in an unsatisfying position of the coma babysitter, waiting for this supposedly reversible condition to turn the corner so the patient can be extubated.
This condition has never come up in the first twenty or so years of the CICM Part II written exam until a relatively recent radiology question (Question 14.1 from the first paper of 2016). The college presented us with a T2-weighed MRI image which clearly demonstrated increased signal intensity in the posterior white matter. The history was given as "headache, confusion and blurred vision followed by a generalised tonic-clonic seizure" on the background of immunosuppression; the CSF was unremarkable. This was an ulcerative colitis patient who had been given infliximab recently, which is apparently a classical associatuion ( Zamvar et al, 2009). That time, 66% of the candidates were able to answer to a passing mark or better. PRES appeared again in Question 10 from the second paper of 2018, but this time with a full 10-mark SAQ asking for details about risk factors, clinical features, differential diagnoses, radiological findings and management.
Because this condition is something of an esoteric unicorn, the time-poor candidate is advised to steer clear of such magnum opus articles as the luxuriously detailed 2008 review by Walter Bartynski (Part 1 or Part 2). Something like the LITFL half-page or the Radiopedia entry will probably suffice. Otherwise, one risks joining this author in a swamp of unnecessary brain-cluttering detail. In any case, the Bartynski papers have been chopped up and boiled to form the summary below, which hopefully retains some of their educational value. Maximal attention was paid to the radiological features and risk factors, because this is what the college wanted in the answer to Question 14.1.
Say, you have an unconscious person. Under what circumstances can one decide to call their coma PRES? Well, there are actually no specific diagnostic criteria which must be met in order to make this diagnosis. Typically, there is a constellation of characteristic features:
The UpToDate authors courageously refuse to give us any guidance, "in the appropriate clinical setting, clinicians should recognize the neurologic syndrome... and order a brain MRI". A recent article by Fugate and Rabenstein (Lancet, 2015) offers a bunch of features which are compatible with the diagnosis, but nothing in the way of actual diagnostic criteria. Most authors struggle to define the syndrome, and it is still known by multiple synonyms (eg. hypertensive encephalopathy), but not everybody agrees that these are in fact synonyms (but rather separate radiologically similar conditions). In short, it's a mess.
The current "popular theory" for how this happens is the hypertension-failed autoregulation-hyperperfusion theory. It can be summarised in point form:
This theory is supported by the following observations:
The theory has the following major holes in it:
PRES is almost exclusive to significant systemic conditions. It is associated with something major going on in the rest of the body. Classical associations include the following list (borrowed from Bartynski's Table 1):
Biological processes commonly associated with PRES therefore include the following:
The UpToDate article gives an even larger list of "associated conditions", which adds the following:
Miscellaneous associations listed by Bartynski are also offered here as an interesting word salad
From UpToDate, a series of plausible differentials is:
This is probably relevant to the main thrust of Question 6 from the first paper of 2020, which basically asked "HSV encephalitis: how is this not PRES?". The specific answer called for "clinical manifestations, aetiology, treatment and complications". For the purpose of maintaining at least some semblance of attachment to exam relevance, the answer to this question is transformed into a table and presented below. The specific information regarding HSV encephalitis are derived from an excellent article by Bradshaw & Ventakesan (2016), which somehow happens to protrude through the Springer paywall.
|Pathophysiology / aetiology|
Historical features and symptoms
Features on examination
Historical features and symptoms
Features on examination
CSF biochemistry (Ellis, 2019)
Hypertensive complications (Fischer et al, 2017)
Persistent neurological sequelae are rare
Persisting epilepsy may occur
The images below were stolen from the 2012 article by Swarnalatha et al, where the PRES was associated with renal failure. These are the same T2 weighted MRI images which I used to replace the college's own pictures from Question 14.1 from the first paper of 2016.
MRI findings with different imaging sequences:
In case the reader is wondering whether it is valuable to commit this list of abbreviations to memory, they may refer to Question 2 from the first paper of 2019, where the MRI features of PRES were asked about (for 20% of the mark). The examiners complained of "poor knowledge in this area with many factual errors" which suggests that they absolutely did expect their trainees to have this information available for immediate recall.
Apart from waiting patiently until the condition resolves, what else can the intensivist realistically offer?