Seizure outcomes of posterior reversible encephalopathy syndrome and correlations with electroencephalographic changes

Rationale: Seizures are among the most common clinical presentations of posterior reversible encephalopathy syndrome (PRES). This syndrome has rarely been reported to cause chronic epilepsy or persistent cortical dysfunction. The prognostic value of EEG findings during PRES is unknown. We retrospectively evaluated EEG characteristics in patients with PRES in a single medical center. We also evaluated the long-term outcome regarding seizure occurrence beyond the acute phase in these patients. Methods: We searched a radiology database at the University of Minnesota from 1997 to 2012 to identify patients with clinically and radiologically diagnosed PRES. Among the patients with PRES, we reviewed MRI images, EEG findings, clinical manifestations including seizure occurrences, and clinical outcomes beyond the acute phase. Results: Seventy-five patients were included in the study. Fifty-eight out of seventy-five (77.3%) patients with PRES had seizures. A total of 48 EEG studies were performed in 38 patients. Generalized slowing was the most common EEG pattern. Among the 38 patients who had EEGs, 37 (97.3%) patients had diffuse or focal slowing of the background, and 11 (28.9%) patients had IEDs. Four out of seventy-five (5.3%) patients had seizures later than one month beyond their hospitalization for PRES. None of these 4 patients had seizures before the episode of PRES. Two patients developed chronic epilepsy, with seizures occurring later than one year after the PRES. Conclusion: Most patients who had seizures or who had epileptiform activities in EEG during PRES did not subsequently develop chronic epilepsy. No patient developed chronic epilepsy in the absence of clinical seizures during PRES. Posterior reversible encephalopathy syndrome may infrequently be associated with subsequent development of symptomatic epilepsy.