Multiple pathophysiological mechanisms have been described according to the clinical setting where PRES takes place. In cases of hypertension, severe hypertension exceeding the limit of cerebral autoregulation leads to vasodilatation and plasma leakage into the interstitial space8
; this would occur preferentially in the posterior areas of the brain due to less prominent sympathetic innervation in the vertebrobasilar system.8
In cases of eclampsia, there is an excessive vasoconstriction in response to hypertension, with endothelial injury and cytotoxic edema.1,2,5,9,10
Immunosuppressive medications are thought to exert direct cytotoxic effects on the cerebral vasculature, and dialysis seems to reduce plasma urea and/or osmotically active solutes leading to fluid shifts into brain tissue.1,11
In our case, the recent dialysis onset and the high blood pressure could have been the cause of the syndrome. Despite this uncertainty, the VMR was clearly reduced initially and was normalised by day 10 (), supporting the suggestion that angioparesis is a main feature of PRES. Regardless of the pathophysiological mechanism, TCD/VMR constituted a rapidly available, inexpensive surrogate marker of improvement.
One potential limitation of this report could be related to the effect of antihypertensive treatment on the patient’s acute presentation, which could arguably have affected the VMR. However, there is supportive evidence that rapid blood pressure normalisation within 1–2 weeks may not exhaust vasomotor reserve12
; in addition, there are data to suggest that VMR may even improve with long term use of certain antihypertensives.13,14
We believe that TCD with VMR is a simple and practical method of monitoring the haemodynamic abnormalities in patients with PRES.
- Posterior reversible encephalopathy can occur in patients with normal blood pressure or only mild elevation.
- Transcranial Doppler with vasomotor reactivity study can be used to evaluate the brain arteries responsiveness to chemical stimuli.
- In our patient, the loss of vasomotor reactivity was associated with the radiological picture of PRES and its normalisation was associated with her clinical recovery.