Posterior Reversible Encephalopathy Syndrome

      The posterior reversible encephalopathy syndrome (PRES) describes the combination of posterior cerebral involvement and brain dysfunction that occurs with this entity. Patients may present with headache, confusion, visual disturbance, and seizures. Several diseases and clinical conditions are associated with PRES, but the root cause seems to be acute or subacutely elevated blood pressure. Hypertension can occur with drug ingestion, chronic renal disease, autoimmune nephritis (systemic lupus erythematosus), Wegener's granulomatosis, acute renovascular hypertension, pheochromocytoma, preeclampsia and eclampsia, and immunosuppressant therapy.

      MRI reveals lesions with high signal intensity on FLAIR and T2 weighted nonenhanced images. There is a predilection for the posterior cerebral white matter, and in severe cases the adjacent gray matter can be involved. Extension into the frontal lobes is not uncommon, but isolated anterior white matter involvement is unusual. Contrast enhancement is patchy if present at all. The white matter lesions of PRES do not exhibit restricted diffusion. The white matter injury is largely reversible. At least, with correction of the hypertension, the MRI findings resolve within a few weeks and follow clinical recovery.

      Several immunosuppressive agents have been associated with PRES. The cyclosporins are the most widely used, and neurological complications occur in about 20 per cent of transplant patients receiving these agents. Cyclosporine has been shown to induce endothelial release of vasoactive mediators. Hypertension is present in 90% of patients, especially when combined with steroids. Although cyclo- sporine may have some direct neuro-toxicity on the myelin, symptoms and imaging are like those of hypertensive encephalopathy. White matter damage has also been reported with tacrolimus (FK 506), another commonly used immunosuppressant drug. Sudden changes in electrolyte or fluid balance can occur due to diarrhea, poly- or oliguria.  

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