USMLE Prep - Medical Reference Library

Posterior Reversible Encephalopathy Syndrome (PRES) — Triggers, MRI, and BP/Seizure Control

System: Neurology • Reviewed: Sep 1, 2025 • Step 1Step 2Step 3

Synopsis:

Headache, encephalopathy, visual symptoms, and seizures in the setting of acute BP fluctuation, cytotoxic therapy, autoimmune disease, or eclampsia. MRI shows posterior‑predominant vasogenic edema. Treat by removing the trigger, controlled BP reduction, magnesium in eclampsia, and antiepileptics; most cases improve within days to weeks.

Key Points

  • Confirm diagnosis early with highest‑yield tests (and do not let testing delay time‑critical therapy).
  • Use explicit hemodynamic, respiratory, and neurologic targets to guide escalation.
  • Document disposition criteria, follow‑up, and patient education before discharge.

Algorithm

  1. Stabilize ABCs; treat seizures (benzodiazepine → levetiracetam).
  2. Obtain MRI brain with FLAIR/DWI; consider MRV if CVST suspected.
  3. Identify and stop the trigger (calcineurin inhibitors, cytotoxics).
  4. Control BP (goal ~25% MAP reduction over 24–48 h; avoid rapid drops).
  5. If eclampsia → magnesium sulfate; expedite obstetric management.
  6. Correct precipitants (renal failure, autoimmune flare).
  7. ICU vs ward based on mental status and BP control needs.
  8. Follow neurologic exam; repeat MRI if atypical course or deficits persist.
  9. Plan antiepileptic taper over weeks if seizures controlled and MRI resolves.

Clinical Synopsis & Reasoning

Headache, encephalopathy, visual symptoms, and seizures in the setting of acute BP fluctuation, cytotoxic therapy, autoimmune disease, or eclampsia. MRI shows posterior‑predominant vasogenic edema. Treat by removing the trigger, controlled BP reduction, magnesium in eclampsia, and antiepileptics; most cases improve within days to weeks.


Treatment Strategy & Disposition

Stabilize ABCs. Initiate guideline‑concordant first‑line therapy with precise dosing and continuous monitoring. Escalate to advanced or procedural interventions when predefined failure criteria are met. Define ICU, step‑down, and ward disposition triggers explicitly, and arrange specialty consultation early.


Epidemiology / Risk Factors

  • Risk varies by comorbidity and precipitating factors

Investigations

TestRole / RationaleTypical FindingsNotes
CBCAnemia/leukocytosisContext‑specificTrend response
BMPElectrolytes/renalDerangements commonRenal dosing/monitoring
Condition‑specific imagingPer topicDiagnostic hallmarkDo not delay with red flags
MRI brain with FLAIR/DWIDiagnosisPosterior‑predominant vasogenic edemaRule out infarct/hemorrhage
Lumbar puncture (selected)Exclude infection/autoimmuneMild protein elevationNot routinely required

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Nicardipine/ClevidipineDHP CCBMinutesControlled BP reductionAvoid precipitous drops
LevetiracetamSV2A modulatorHoursSeizure controlSomnolence
Magnesium sulfate (eclampsia)Vasodilator/anticonvulsantMinutesPre‑eclampsia/eclampsiaMonitor reflexes/respiration

Prognosis / Complications

  • Outcome depends on timeliness of diagnosis and definitive therapy

Patient Education / Counseling

  • Explain red flags, adherence, and the follow‑up plan; provide written instructions.

References

  1. See bibliography — Link