What is Posterior Reversible Encephalopathy Syndrome (PRES)?
Posterior reversible encephalopathy syndrome (PRES) is an acute neurotoxic clinical-radiological syndrome characterized by vasogenic brain edema predominantly affecting the bilateral parieto-occipital regions, presenting with headache, altered consciousness, seizures, and visual disturbances that typically resolves completely with prompt treatment. 1, 2
Pathophysiology
- PRES results from disruption of the blood-brain barrier due to endothelial injury, most commonly triggered by abrupt blood pressure changes that overwhelm cerebral autoregulation, leading to extravasation of intravascular fluid and vasogenic edema in posterior brain regions 1, 3
- The posterior circulation is preferentially affected because it has less sympathetic innervation compared to anterior circulation, making it more vulnerable to hypertensive injury 1
Clinical Presentation
Neurological symptoms develop acutely or subacutely and include:
- Headache, nausea, and vomiting 4, 3
- Altered mental status ranging from confusion to coma 5, 2
- Seizures (common presenting feature) 5, 2
- Visual disturbances including blurred vision, visual field defects, and cortical blindness 2, 6
- Focal neurological deficits 5, 2
Common Triggering Factors
The most frequent precipitants include:
- Hypertensive crisis or accelerated hypertension 1, 4, 6
- Renal failure or impairment 1, 2, 4
- Immunosuppressive agents, particularly cyclosporine 1, 3
- Chemotherapy and high-dose antineoplastic therapy 1, 2
- Eclampsia or preeclampsia 2, 6
- Autoimmune diseases 1, 2
- Stem cell or solid organ transplantation 1
- Immune checkpoint inhibitors (anti-PD-1, anti-CTLA-4 combination therapy) 5
- Anti-TNF therapy such as infliximab 1
Diagnostic Imaging Features
MRI is the gold standard for diagnosis, showing:
- T2-weighted or FLAIR hyperintensities in bilateral parietal-occipital lobes, predominantly affecting white matter 1, 7
- Vasogenic edema pattern confirmed by diffusion-weighted imaging (DWI) with elevated apparent diffusion coefficient (ADC) values 7
- Atypical features may include anterior brain or brainstem involvement, cortical involvement, restricted diffusion, hemorrhage, or contrast enhancement 2, 3
CT scan limitations:
- May appear completely normal in early PRES due to low tissue contrast resolution 7
- Useful primarily to exclude intracranial hemorrhage when MRI is not immediately available 1, 7
Key Differential Diagnoses to Exclude
- Acute ischemic stroke in posterior circulation (shows restricted diffusion on DWI, unlike PRES) 7
- Infectious encephalitis (different enhancement patterns) 7
- Cerebral amyloid angiopathy-related inflammation 7
- Subarachnoid hemorrhage (when sulcal FLAIR hyperintensity present) 7
- Metabolic encephalopathies including uremic encephalopathy and hypoglycemia 7
Prognosis and Outcomes
- Complete spontaneous remission occurs in most cases without neurological sequelae when promptly recognized and treated 1, 2
- Poor prognostic factors include: altered sensorium, hypertensive etiology, hyperglycemia, longer time to control the causative factor, elevated C-reactive protein, coagulopathy, extensive cerebral edema, and hemorrhage on imaging 2
- Epilepsy is rare despite frequent acute seizures 2
- Permanent imaging abnormalities and residual neurological deficits can occur in severe cases with delayed recognition 2, 3
Critical Pitfalls to Avoid
- Failure to immediately discontinue the offending agent (immunosuppressants, chemotherapy, or other causative medications) can lead to prolonged illness and increased complications 1
- Missing concomitant conditions such as sepsis, electrolyte disturbances, or renal dysfunction that complicate management 1
- Delayed MRI imaging when CT appears normal but clinical suspicion remains high 7, 8
- Overly aggressive blood pressure reduction causing cerebral hypoperfusion 1