Posterior Reversible Encephalopathy Syndrome

Posterior Reversible Encephalopathy Syndrome (PRES)

Posterior Reversible Encephalopathy Syndrome (PRES) is a clinicoradiological syndrome characterized by:

• Acute neurological symptoms
• Vasogenic cerebral edema (predominantly posterior circulation territory)
• Reversible changes on neuroimaging

It is not always posterior and not always reversible

• Frontal lobes may be involved
• Basal ganglia involvement possible
• Brainstem and cerebellar involvement possible
• Can even be unilateral

Pathophysiology 

Two major competing (but complementary) theories:

Failure of Cerebral Autoregulation (Hyperperfusion Theory)

When BP exceeds autoregulatory limits:

• Loss of arteriolar vasoconstriction
• Hyperperfusion
• Blood–brain barrier breakdown
• Extravasation of plasma → vasogenic edema

Posterior circulation more vulnerable because:

• Less sympathetic innervation
• Vertebrobasilar system less protected

Endothelial Dysfunction Theory (More accepted in ICU patients)

Seen in:

• Sepsis
• Cytotoxic drugs
• Eclampsia
• Transplant patients

Mechanism:

• Endothelial activation
• Capillary leakage
• Vasogenic edema
• Sometimes microthrombosis

Etiology & Risk Factors 

Clinical Presentation

Presentation  is acute or subacute (may evolve over 1-2 days).

Classic Tetrad

1. Headache (throbbing)-(~50%)
2. Seizures (~70%)(often generalized tonic–clonic)
3. Visual disturbances(~35%)
4. Altered sensorium/encephalopathy(~70%)

Imaging 

CT Brain(Not sensitive)

• May be normal early
• Hypodensities in posterior regions

MRI Brain(IOC)

• Bilateral symmetrical
• Parieto-occipital(~50%) white matter hyperintensity(MCA-PCA watershed area)
• T2-FLAIR hyperintensity-vasogenic edema(hallmark)
• No restricted diffusion (vasogenic, not cytotoxic)

DWI / ADC Pattern

• Vasogenic edema → ↑ ADC
• Cytotoxic edema → ↓ ADC (poor prognosis)

 Important  differentiation from ischemic stroke.

Atypical Imaging Patterns

• Frontal lobe involvement
• Basal ganglia involvement
• Brainstem involvement
• Hemorrhagic PRES (15–20%)
• Microhemorrhages (~40%)—GRE/SWI sequences

Differential Diagnosis

Management

Step 1: Control Blood Pressure

Goal:

• Reduce MAP by 20–25% in first hour
• Avoid rapid overcorrection

Preferred agents:

• Nicardipine infusion
• Labetalol infusion

Avoid:Nitroprusside (↑ ICP risk)

Step 2: Seizure Management

Follow status epilepticus protocol:

1. Benzodiazepines
2. Levetiracetam (preferred in ICU)
3. Valproate (avoid in liver failure)
4. Phenytoin (less preferred)

Long-term AED usually not required if reversible.

EEG in PRES

Maintain a low threshold for continuous EEG (cEEG) monitoring in any patient with PRES and altered mental status, particularly when:

• Mental status is fluctuating.
• Encephalopathy is disproportionate to MRI findings.
• There is suspicion of non-convulsive seizures or non-convulsive status epilepticus (NCSE).

Common EEG findings in PRES

• Diffuse theta slowing (most common finding).
• Focal sharp-wave discharges.
• Lateralized Periodic Discharges (LPDs), typically with a posterior predominance.
• Bilateral Independent Posterior Discharges (BIPDs).

Clinical pearl: Continuous EEG is valuable because electrographic seizures and NCSE are common in PRES and may be clinically silent, especially in critically ill patients.

Step 3: Remove Trigger

• Stop offending drug (tacrolimus, cyclosporine)
• Deliver fetus in eclampsia
• Treat sepsis aggressively
• Dialysis optimization in renal failure
• Treat hypomagnesemia aggressively.

 Step 4: ICP Control (if needed)

• Head elevation
• Osmotherapy (mannitol / hypertonic saline)
• Controlled ventilation if intubated

Complications

• Intracerebral hemorrhage
• Status epilepticus
• Brain herniation (rare)
• Persistent deficits (if delayed treatment)

 Is It Always Reversible?—>No.

Reversibility depends on:

• Early recognition
• Prompt BP control
• Removal of trigger
• Absence of cytotoxic edema

Poor prognostic markers:

• Diffusion restriction
• Brainstem involvement
• Severe hypertension
• Delayed management

Prognosis

• Most improve within 1 week
• Radiological resolution within weeks
• Mortality: ~5–15% in ICU cohorts
• Recurrence possible

PRES vs RCVS