posterior reversible encephalopathy syndrome (PRES)

Introduction

a form of acute hypertensive encephalopathy usually associated with acute severe hypertension which usually resolves within 1-2 weeks of resolution of the hypertension but some may be left with neurologic impairment and in a minority it may result in death
thought to be due to failed autoregulation of the brain and/or endothelial dysfunction causing regional cerebral oedema - usually mainly posteriorly
may effect any age but most commonly occurs in middle age and is more common in women
many patients have significant co-morbidities
best detected on MRI scan

confluent vasogenic oedema in the watershed zones with relative sparing of temporal lobes

severe hypertension is usually present but may have occurred 24hrs or more earlier
constant mod-severe headache which is not respondent to simple analgesics
visual cortex symptoms may include:
- auras
- hallucinations
- hemianopia
- visual neglect
- cortical blindness
general CNS impairments such as:
- drowsiness or agitation
- confusion
- in severe cases, may progress to coma
- usually has brisk deep tendon reflexes and often positive Babinski signs are present
seizures may occur and may be the presenting feature, and may be recurrent
- these are usually generalised tonic clonic but may start from a focal seizure with an occipital lobe symptomatology including visual cortex symptoms as above

take bloods for FBE, U&E, LFTs, CRP, glucose, HCG (if not known to be pregnant or post-partum)
aggressive Mx of preeclampsia if this is the cause with MgSO4, etc - see pre-eclampsia and eclampsia and eclampsia
if not preeclampsia:
- control BP aiming to lower diastolic BP to 100-105 mmHg within first 2-6hrs but avoiding falls of more than 25% of initial value
  - too rapid a drop in BP may cause ischaemic stroke
  - consider iv labetalol
  - oral agents are NOT useful in the early Rx of this condition
- control seizures with benzodiazepines and phenytoin
- avoid corticosteroids as this may worsen the hypertension
- supportive care
- CT brain to exclude differentials (although is poor at excluding posterior circulation stroke)
  - is usually normal or non-specific although may show white matter hypodensitivities suggestive of PRES
- MRI brain is needed to demonstrate PRES in which case a MRA should also be done to exclude a posterior circulation stroke
  - MRI findings generally persist for days or even weeks after clinical resolution