Postencephalitic epilepsy: Clinical characteristics and predictors

Summary Objective To describe the etiologies, clinical presentations, outcomes, and predictors of postencephalitic epilepsy (PE) in a large series of adult patients with acute encephalitis. Methods We conducted a retrospective review of patients diagnosed with acute encephalitis at Mayo Clinic, Rochester, between January 2000 and December 2012. The patients were categorized into two groups based on the presence or absence of PE at last follow-up. Multivariate logistic regression analysis was used to analyze factors associated with PE. Results We identified 198 consecutive patients (100 [50.5%] male and 98 [49.5%] female) with a median age of 58 years (range 41.8-69). Etiologies included viral infection (n = 95, 48%), autoimmune (n = 44, 22%), and unknown/others (n = 59, 30%). During hospitalization, seizures were seen in patients with autoimmune encephalitis (n = 24, 54.5%), unknown/others (n = 20, 33.9%), and viral encephalitis (n = 23, 24.2%). Interictal epileptiform discharges on electroencephalography (EEG) were present in 34 (54%), whereas periodic lateralized epileptiform discharges (PLEDs) and generalized periodic discharges (GPDs) were seen in 14 (41.2%) and 2 (5.9%) patients. Forty-six patients with seizures (70.8%) had fluid-attenuated inversion recovery (FLAIR)/T₂ abnormalities, 20 (31.3%) diffusion abnormalities, and 43 (66.2%) cortical involvement. Good outcome at discharge among patients with seizures was seen in 8/23 patients with viral etiology (34.8%), 10/24 patients with autoimmune encephalitis (45.5%), and 12/20 patients with unknown cause (60%). PE was present in 43 patients (29.9%). On multivariate regression analysis, the factors associated with PE were generalized seizures during hospitalization (p = 0.03), focal seizures (p ≤ 0.001), and the presence of FLAIR/T₂ abnormalities on brain magnetic resonance imaging (MRI) (p = 0.003). Significance The presence of seizures during hospitalization and an abnormal brain MRI are the strongest predictors of the development of PE. The etiology of encephalitis, presence of focal neurologic deficits, and interictal EEG abnormalities did not influence the development of PE.