PRES

Posterior Reversible Encephalopathy Syndrome (PRES) is a clinico-radiographic syndrome characterized by vasogenic edema predominantly in the posterior (occipital/parietal) white matter. Pathophysiology: failure of cerebral autoregulation leads to blood-brain barrier breakdown and vasogenic edema.

• Severe hypertension -most common trigger. Exceeds upper limit of autoregulation.
• Eclampsia / pre-eclampsia -one of the most important causes in young women
• Immunosuppressants -tacrolimus, cyclosporine (calcineurin inhibitors) -common in transplant patients
• Chemotherapy -especially VEGF inhibitors (bevacizumab)
• Autoimmune disease -SLE, TTP, thrombotic microangiopathy
• Renal failure -especially with fluid overload and hypertension

Classic features: seizures (most common presenting symptom, 60-75%), headache (50%), visual disturbances (cortical blindness, blurry vision, visual field defects -33%), altered mental status (28%), and hypertension (often severe). Typically acute/subacute onset over hours to days.

• TREAT THE CAUSE -this is the most important step:
  • Hypertensive emergency: lower BP gradually (IV antihypertensives -nicardipine, labetalol)
  • Eclampsia: magnesium sulfate + delivery
  • Drug-induced: discontinue offending agent (tacrolimus, cyclosporine, chemotherapy)
• Seizure management: Benzodiazepines for acute seizures. Levetiracetam (Keppra) for prophylaxis/maintenance (fewer drug interactions than phenytoin in transplant patients).
• BP control: Target 25% reduction in MAP over first few hours. Avoid precipitous drops (risk of ischemia). IV nicardipine or labetalol preferred.
• Usually REVERSIBLE if treated promptly -clinical and radiographic improvement typically within days to weeks. Delayed treatment can lead to permanent infarction, hemorrhage, and death.

• MRI brain (with FLAIR) -study of choice. Shows bilateral, symmetric white matter edema in posterior regions (occipital/parietal lobes). FLAIR and T2 sequences show hyperintense signal. DWI helps distinguish vasogenic (PRES) from cytotoxic (stroke) edema.
• CT head -less sensitive, may appear normal early. Can show low-density areas in posterior regions. Rule out hemorrhage.
• BP -often severely elevated (but PRES can occur at normal BPs, especially drug-induced)
• BMP -renal function, electrolytes
• CBC, LDH, peripheral smear, haptoglobin -rule out TTP/HUS if thrombocytopenia present
• Urine protein/Cr ratio -if pregnant or postpartum (pre-eclampsia workup)
• Drug levels -tacrolimus, cyclosporine trough levels if applicable
• LP -typically not needed. CSF may show mild protein elevation. Mainly to rule out meningitis/encephalitis if diagnosis uncertain.

• Blood pressure -continuous arterial line or frequent NIBP. Target 25% MAP reduction over first hours, then gradually normalize.
• Neurologic exam -serial neuro checks q1-2h. Document mental status, vision, motor function.
• Repeat MRI -in 1-2 weeks to confirm radiographic resolution. If not improving, reconsider diagnosis.
• Seizure monitoring -consider continuous EEG if altered mental status persists or recurrent seizures.
• Drug levels -if calcineurin inhibitor-related, check trough levels and hold/reduce dose until resolution.
• Urine output and renal function -especially if pre-eclampsia or renal failure is the trigger.