What is Posterior Reversible Encephalopathy Syndrome (PRES)?

What is Posterior Reversible Encephalopathy Syndrome (PRES)?

PRES is an acute neurotoxic syndrome characterized by reversible vasogenic edema predominantly affecting the bilateral parieto-occipital white matter, presenting with headache, altered consciousness, seizures, and visual disturbances, triggered by conditions that disrupt cerebral autoregulation and cause endothelial injury. 1

Pathophysiology

The syndrome results from disruption of the blood-brain barrier due to endothelial injury from abrupt blood pressure changes, leading to vasogenic edema 1. Two competing theories explain the mechanism:

• Breakthrough edema theory (more widely accepted): Severe hypertension exceeds cerebral autoregulation limits, causing breakthrough brain edema 2
• Vasoconstriction theory: Hypertension triggers cerebral autoregulatory vasoconstriction, leading to ischemia and subsequent brain edema 2

Vasoconstriction resulting in both vasogenic and cytotoxic edema is suspected to be responsible for both clinical symptoms and neuro-radiological findings 3.

Clinical Presentation

Core Neurological Symptoms

• Headache - one of the most common presenting symptoms 4, 5
• Altered consciousness/encephalopathy - ranging from confusion to coma 1, 4
• Seizures - frequently occur during acute phase, though chronic epilepsy is rare 1, 4
• Visual disturbances - including cortical blindness, visual field defects, or blurred vision 1, 4, 6
• Focal neurological deficits - may occur depending on affected brain regions 4

The clinical presentation is often nonspecific, making imaging essential for diagnosis 2.

Common Triggering Factors

High-Risk Clinical Contexts

• Pre-existing arterial hypertension - persistently elevated blood pressure remains the chief culprit 1, 3
• Renal impairment/failure - frequently associated with PRES development 1, 5
• Eclampsia - classic obstetric trigger requiring timely caesarean section 1, 3
• Immunosuppressive medications - particularly cyclosporine and other transplant-related drugs 1, 2
• High-dose antineoplastic therapy - chemotherapy agents can trigger PRES 1
• Allogenic stem-cell transplantation and solid organ transplantation 1
• Autoimmune diseases - including those treated with immunosuppressants 1, 5
• Anti-TNF therapy - infliximab has been reported to cause PRES in Crohn's disease patients 1

Diagnostic Imaging Features

Classic MRI Findings

• T2-weighted and FLAIR sequences show hyperintensities in bilateral parietal-occipital lobes, predominantly affecting white matter 1, 7
• Symmetrical white matter abnormalities suggestive of vasogenic edema 3
• MRI is the gold standard for diagnosis, preferred over CT 1, 7

Atypical Imaging Features

• Involvement of other brain regions beyond parieto-occipital areas 4
• Cortical involvement in addition to subcortical white matter 4
• Restricted diffusion on DWI sequences 4
• Hemorrhage or microhemorrhages 4
• Contrast enhancement 4

CT Imaging Role

• CT can be useful to exclude intracranial hemorrhage when MRI is not immediately feasible 1, 7
• Less sensitive than MRI for detecting subtle vasogenic edema 7

Prognosis and Outcomes

Favorable Outcomes

• Complete spontaneous remission occurs in most cases without sequelae when promptly recognized and managed 1
• Clinical and radiographic reversibility is common with appropriate treatment 4
• Early detection and management are key factors for rapid recovery and good outcomes 1, 5

Poor Prognostic Factors

• Altered sensorium at presentation 4
• Hypertensive etiology 4
• Hyperglycemia 4
• Longer time to control the causative factor 4
• Elevated C-reactive protein 4
• Coagulopathy 4
• Extensive cerebral edema on imaging 4
• Hemorrhage on imaging 4

Severe Complications

• Long-standing morbidity and mortality can occur in severe forms, though aggressive care has markedly reduced mortality and improved functional outcomes in malignant PRES 4
• Delayed recognition and management can result in severe and long-term neurological disability 6
• Patients with inadequate therapeutic support or delay in treatment may not have positive outcomes 3

Critical Diagnostic Pitfalls

• Failure to consider PRES in perioperative settings - can present as delayed emergence from anesthesia 6
• Missing the diagnosis due to nonspecific presentation - requires high index of suspicion in appropriate clinical contexts 2
• Relying on CT alone - may miss subtle findings that MRI would detect 1, 7
• Not obtaining follow-up imaging - documentation of reversibility is important for confirming diagnosis 2