Posterior Reversible Encephalopathy Syndrome (PRES) is an acute neurological condition characterized by brain dysfunction and specific changes visible on imaging. It is a syndrome, not a single disease, meaning it arises as a complication of an underlying medical problem. PRES is defined by the sudden onset of symptoms correlating with swelling (edema), typically in the back regions of the brain. The name highlights that the neurological deficits and imaging findings are usually reversible once the triggering cause is identified and treated.
The Neurological Mechanism of PRES
The physical changes defining PRES center on a disruption of the blood-brain barrier (BBB). The BBB normally regulates what substances pass from the bloodstream into the brain tissue. When compromised, it allows fluid, proteins, and plasma components to leak out of the blood vessels and accumulate in the brain.
This leakage creates vasogenic edema, the hallmark of PRES on a brain scan. The most accepted theory suggests that a rapid, severe rise in blood pressure overwhelms the brain’s ability to regulate its own blood flow (cerebral autoregulation). This leads to excessive pressure within the small blood vessels, damaging the delicate lining (endothelium) and forcing fluid out.
The condition is named “Posterior” because the back parts of the brain, specifically the parietal and occipital lobes, are most commonly affected. These posterior regions are thought to be particularly susceptible due to having less sympathetic nerve control compared to the front of the brain. Since the occipital lobes process vision, their involvement explains many of the syndrome’s typical visual symptoms.
Primary Causes and Associated Risk Factors
The most frequent trigger is an acute hypertensive crisis, where blood pressure rises rapidly and significantly, often exceeding a systolic pressure of 160 mmHg. This acute elevation is often more damaging than long-standing, controlled high blood pressure.
Many cases occur in pregnant individuals with pre-eclampsia or eclampsia, conditions involving new-onset high blood pressure and organ damage. Systemic illnesses affecting the blood vessels or immune system also increase risk, including severe kidney disease and autoimmune disorders like systemic lupus erythematosus.
Certain medications are implicated because they can directly damage the blood vessel lining. Immunosuppressive drugs (such as cyclosporine and tacrolimus, used after organ transplants) and specific chemotherapy agents are known to precipitate PRES. Patients with severe infections like sepsis or those undergoing cancer treatment are also at heightened risk.
Recognizing the Clinical Symptoms
The onset of PRES symptoms is typically rapid, developing over a few hours to several days. A sudden, severe headache is one of the most common complaints, often accompanied by confusion or an altered mental state. This encephalopathy can range from simple inattentiveness and drowsiness to profound confusion or even coma in severe presentations.
Visual disturbances are a defining characteristic. These changes can vary widely, from blurred or double vision to partial vision loss, and in some cases, complete cortical blindness. Seizures are another frequent symptom, occurring in a majority of patients, and may be the first sign prompting medical attention.
While these clinical features strongly suggest the diagnosis, they are not exclusive to PRES. The condition is confirmed by specialized brain imaging, most often Magnetic Resonance Imaging (MRI). The MRI reveals the characteristic pattern of vasogenic edema in the posterior brain regions.
Management and Expected Recovery
Treatment is primarily supportive and centers on immediately addressing the identified underlying cause. The most important intervention is the aggressive, yet controlled, reduction of severely high blood pressure. Physicians aim to gradually lower the blood pressure to prevent a sudden drop that could cause brain or organ ischemia, typically reducing it by no more than 20% to 25% in the first hour.
If the syndrome is linked to a medication, such as an immunosuppressant or chemotherapy agent, the drug is typically paused or the dosage is significantly reduced. Seizures are managed with standard anti-seizure medications to prevent further damage.
The prognosis is generally favorable. Most patients experience a complete resolution of their symptoms and the edema on follow-up imaging within days to weeks after the trigger is successfully managed. Full recovery is achieved in a high percentage of cases with prompt recognition and intervention. However, delayed treatment or complications like brain hemorrhage can lead to incomplete recovery or lasting neurological deficits.