Posterior Leucoencephalopathy Syndrome

Synonyms include: Posterior reversible encephalopathy syndrome, PRES, reversible posterior cerebral oedema syndrome.

This is a rare "encephalopathic" condition, where the diagnosis depends on clinical and radiological features. It was first described as recently as 1996¹ although it is inconceivable that it did not occur before. It has been suggested that this is a new name for old syndromes.² The clinical symptoms are not enough to establish the diagnosis but MRI is often characteristic and essential to the diagnosis. Despite the name "leucoencephalopathy", lesions can occur in both white and grey areas.

Why the condition should have a predilection for the posterior part of the brain is unclear.³

It is rare but being recognised more often. Most of the literature is single or a few cases. It usually presents in adults but has been reported less often in children.⁴ There seems to be a breakdown of autoregulation⁵ and endothelial function, usually associated with very high blood pressure or certain drugs. The array of drugs implicated in this syndrome is growing but most cases are associated with hypertension or immunosuppression including cancer chemotherapy.

The underlying cause is often very high blood pressure leading to failure of autoregulation. Rapidly developing, fluctuating or intermittent hypertension is a particular risk. In a previously normotensive person it may develop at a mere 160/100 but it is more usual in those who have perhaps stopped treatment and BP surges to 220/120 or more.

It can also occur after carotid endarterectomy when the carotid baroreceptors fail.

Infection with sepsis and shock is being recognised more often as another aetiological factor.⁶

Clinical signs and symptoms are non-specific and may be acute or subacute.

• Headaches
• Altered mental state, lethargy and somnolence possible progressing to confusion and coma⁷
• Convulsions
• Blurred vision, hemianopia, visual neglect, hallucinations, cortical blindness
• There is often papilloedema, haemorrhages and exudates
• BP will be high

MRI shows predominantly posterior areas of oedema. Diffusion weighted sequences can differentiate between oedema from leaking capillaries and cell damage and hence can predict conversion to infarction and irreversible damage. There is symmetrical oedema of the posterior hemispheres.

These features may be seen on CT scan but MRI scan is clearer.

The presentation is often non-specific and it can easily be mistaken for other conditions:

• Stroke
• Sinus thrombosis
• Demyelination
• Vasculitis
• Encephalitis

• Hypertensive encephalopathy
• Eclampsia or severe pre-eclampsia
• Use of stimulant drugs that can raise BP including phenylephedrine, pseudoephedrine and even caffeine
• Abuse of cocaine and amphetamines
• Pheochromocytoma
• Haemolytic uraemic syndrome
• Blood transfusion

This list is far from exhaustive but high blood pressure is a common theme.

The following drugs are just some that have been implicated:

• Cyclosporin A
• Vincristine
• Tacrolimus
• Cisplatinum
• Interferon alpha
• Antiretroviral therapy
• Erythropoietin

The diagnosis needs to be made and the blood pressure brought down⁸ or sepsis treated.

If drugs are implicated they must be stopped.

• If it is caught in time it is reversible but if infarction has occurred there will be irreversible damage
• Delay in diagnosis gives a worse prognosis⁹
• The MRI scan is useful in giving prognosis¹⁰
• Recurrence can occur but is unusual¹¹