PRES/Hypertensive Encephalopathy: Definition and Clinical Manifestations
Posterior reversible encephalopathy syndrome (PRES) is a specific manifestation of hypertensive encephalopathy characterized by reversible white matter lesions predominantly in the posterior brain regions, occurring when markedly elevated blood pressure overwhelms cerebral autoregulation, leading to vasogenic edema that is fully reversible with timely recognition and blood pressure control 1.
Pathophysiology
The underlying mechanism involves failure of cerebral autoregulation when blood pressure rises rapidly and severely. The posterior brain regions are particularly vulnerable because sympathetic innervation is less pronounced in these areas, providing less effective dampening of blood pressure oscillations 1. This leads to:
- Disruption of the blood-brain barrier due to endothelial injury from abrupt blood pressure changes 2
- Vasogenic edema formation, predominantly affecting white matter over gray matter 2
- Cerebral edema, microscopic hemorrhages, and infarctions as histopathological changes 1
Critical point: There is no specific blood pressure threshold—the rate of blood pressure increase is more important than the absolute value in determining whether hypertensive encephalopathy/PRES develops 1.
Clinical Manifestations
Primary Symptoms
Patients present with acute neurological deficits including 2, 3:
- Seizures (occur in 60-90% of cases, particularly in younger patients) 4, 5
- Visual disturbances ranging from blurred vision to cortical blindness 1, 5
- Headache 1, 2, 5
- Altered consciousness (from confusion and lethargy to coma) 2, 1, 3
Additional Features
- Somnolence and lethargy preceding loss of consciousness 1
- Tonic-clonic seizures 1
- Nausea and vomiting 5
- Focal neurological lesions are rare and should raise suspicion for intracranial hemorrhage or ischemic stroke instead 1
Diagnostic Imaging
MRI is the diagnostic modality of choice 1, 4:
- T2-weighted or FLAIR sequences show increased signal intensity representing vasogenic edema 1
- Bilateral parietal-occipital lobe involvement is characteristic, predominantly affecting white matter 2
- Atypical patterns are frequently observed 4
CT is useful primarily to exclude intracranial hemorrhage but may miss subtle findings 1.
Risk Factors and Precipitants
Beyond severe hypertension, consider 1, 2:
- Renal impairment and chronic kidney disease 2, 6, 7
- Immunosuppressive agents (cyclosporin, tacrolimus) 1, 2
- Autoimmune diseases 2
- High-dose antineoplastic therapy 2
- Stem-cell or solid organ transplantation 2
- Obstructive sleep apnea 6
- Drugs: steroids, NSAIDs, sympathomimetics, cocaine, anti-angiogenic therapy 1
Prognosis and Complications
PRES is usually reversible with appropriate management within 2 weeks 2. However:
- Mortality ranges from 10-19% 4
- 40-44% experience persistent neurological deficits or residual radiologic lesions 4
- Delayed diagnosis and treatment may lead to permanent neurological deficits, cerebral infarction, or death 4, 6, 8
- Seizures in PRES carry increased risk of developing epilepsy, more so than post-stroke seizures 5
Common Pitfalls
- Misdiagnosis due to overlap with stroke, encephalitis, and other acute neurological syndromes is common 4
- Assuming a specific blood pressure threshold exists—focus on the rate of rise and clinical context 1
- Failing to consider PRES in normotensive patients—it can develop without significant blood pressure elevation in certain contexts 8
- Not investigating secondary causes of hypertension, particularly renovascular disease in patients with solitary kidneys 7