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Posterior reversible encephalopathy syndrome (PRES)

Learning objectives

  • Defining PRES and how to recognise it
  • Some understanding of aetiolgies
  • Clinical detection and Management


    Sporadic disease seen in children and adults.


    Dominant finding is seizures which are usually tonic-clonic. These are very common (over 90%) and patients nay even present with status epilepticus. Visual impairment due to occipital lobe involvement includes hemianopia and visual hallucinations and visual neglect, a dull bilateral headache and confusion and lethargy. Symptoms come on over 12-48 hours and resolve within a week, sometimes a little longer. Hypertension is common but may be secondary to PRES rather than a cause.


  • Bloods: There may be an increase in LDH, reduced platelets.
  • Imaging: The patient may just be labelled as 'epilepsy' unless MRI is done with typical findings. CT is only helpful in half the cases. The diagnosis is confirmed on MRI scan with the presence of bilateral hyperintensities on FLAIR predominantly in the parieto-occipital region but sometimes in frontal lobes, temporoccipital and cerebellum [Barynski WS 2008].Extensive lesions on T2 weighted imaging tend to have a worse prognosis [Covarrubias DJ et al. 2002]. The lesions are due to vasogenic oedema which can be distinguished by diffusion weighted imaging (DWI). MRI may demonstrate haemorrhage in about 20% which may be small microhaemorrhages or SAH. THe distribution resembles the brain watershed zones. DWI/ADC is helpful in showing cytotoxic infarction related changes rather than vasogenic oedema. RCVS is discussed above and should be considered but the history is quite different. Bilateral parieto-occipital lesions on MRI are not characteristic for RCVS. Vasculitis should be considered. Herpes simplex encephalitis. Status epilepticus is itself another cause of reversible MRI lesions but these are usually cortical and asymmetrical.
  • EEG is non-specific with diffuse slowing or focal δ waves. The differential is wide and includes a top of the basilar syndrome but seizures are very uncommon.

    Causes or Triggers of PRES with Comments
    Preeclampsia/eclampsiaNo difference in out come than with non pregnant PRES. Give IV Magnesium, Caesarean section
    Renal failureManage as usual
    Severe HypertensionKeep BP below 160 mmHG and avoid nitroglycerin
    Ciclosporin/Tacrolimus and othersWithin 2 weeks of drug starting. management is to withdraw therapy
    TransplantationWithin first month post transplantation
    AutoimmuneSLE, WG, SS, PAN
    InfectionSepsis syndrome with abnormal LFTs, Renal function, Multiorgan failure.
    Neuromyelitus optica suggests a defect in free water movement [Magaņa SM et al. 2009]


    As the name implies there is reversibility. Haemorrhage is possible. Recovery usually happens over several weeks. Repeat MRI after 10 days should show improvement. Blood pressure may be a primary or secondary phenomenon but BP control is advocated but not with nitroglycerin due to negative reports. Management is largely supportive. Seizures seem to burn out and so long term AEDs not needed. Recovery is the rule and outcomes excellent.

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