Posterior Reversible Encephalopathy Syndrome (PRES)

What happens in PRES

Normally, the brain's blood vessels keep blood flow steady despite changes in blood pressure (autoregulation). In PRES, this system fails:

• a sudden surge in blood pressure overwhelms autoregulation, especially in the back of the brain, which has less nerve control of its vessels
• or toxins, medicines or inflammation damage the vessel lining (endothelium)

Fluid leaks out of vessels into brain tissue (vasogenic edema). Because the damage is usually swelling rather than cell death, it can resolve fully.

Causes and triggers

• severe or rapidly rising blood pressure, including malignant hypertension
• preeclampsia and eclampsia: PRES is thought to underlie many eclamptic seizures; it can occur up to several weeks after delivery
• kidney failure and dialysis
• immunosuppressants: tacrolimus and cyclosporine, especially after organ transplant or bone marrow transplant
• cancer treatments: chemotherapy, bevacizumab and other targeted drugs
• autoimmune diseases: lupus, vasculitis
• sepsis
• other: high calcium or magnesium imbalance, blood transfusion, some recreational drugs

Symptoms

Symptoms usually develop over hours to days:

• headache: often severe, sometimes sudden
• seizures: occur in most patients; may be the first sign and can be repeated
• altered consciousness: confusion, agitation, drowsiness, rarely coma
• visual disturbances: blurred vision, visual field loss, hallucinations, or cortical blindness (eyes normal but the brain cannot process sight)
• nausea and vomiting
• less commonly, weakness or speech problems

Blood pressure is high in most, though PRES can occur with normal pressure when caused by drugs or toxins.

Diagnosis

• MRI of the brain: the key test. FLAIR sequences show bright areas of swelling, typically in the parietal and occipital lobes on both sides; other regions can be affected
• CT scan may be normal or show subtle changes; used first to exclude bleeding
• blood tests: kidney function, electrolytes, magnesium, drug levels (tacrolimus), autoimmune markers
• EEG for seizures or ongoing confusion
• exclusion of other causes: stroke, venous sinus thrombosis, infection (encephalitis), reversible cerebral vasoconstriction syndrome

Treatment

PRES is treated in hospital, often in intensive care.

• lower blood pressure gradually: usually by about 20 to 25 percent in the first hours with IV medicines; lowering it too fast can cause stroke
• control seizures with anti-seizure medicines
• remove or reduce the trigger: stop or change immunosuppressants or chemotherapy, treat sepsis, correct electrolytes
• in eclampsia: magnesium sulfate to prevent seizures, blood pressure control and delivery of the baby
• dialysis for kidney failure if needed

Outlook

Most people recover fully within days to 2 weeks, and MRI changes resolve. Complications occur in a minority: bleeding in the brain, stroke, persistent seizures or lasting vision and cognitive problems, more often when diagnosis or treatment is delayed. PRES can recur if the trigger returns, so long-term blood pressure control and medication review matter.

Frequently asked questions

What is PRES syndrome?

PRES is a condition where the brain swells, usually in the back regions, after blood vessels fail to handle very high blood pressure or are damaged by medicines or illness. It causes headaches, seizures, confusion and vision loss and is usually reversible with prompt treatment.

What causes posterior reversible encephalopathy syndrome?

Common causes are severe high blood pressure, preeclampsia and eclampsia, kidney failure, immune-suppressing drugs like tacrolimus, chemotherapy, sepsis and autoimmune diseases such as lupus.

Is PRES permanent?

Usually not. Most people recover completely within days to weeks once blood pressure is controlled and the trigger removed. A minority have lasting effects, particularly if there was bleeding, stroke or delayed treatment.

How is PRES diagnosed?

PRES is diagnosed with an MRI showing typical swelling patterns, mainly in the back of the brain, together with symptoms and a known trigger. Doctors also rule out stroke, bleeding, infection and other causes.

Can PRES happen after giving birth?

Yes. PRES can occur in pregnancy with preeclampsia or eclampsia and up to several weeks after delivery. Any severe headache, vision change or seizure after birth needs emergency care.