Characteristics of and risk factors for epilepsy after autoimmune and infectious encephalitis

Encephalitis is associated with significant morbidity including epilepsy. Data on post-encephalitic epilepsy (PEE) incidence and optimal management remain scarce. We prospectively investigated the frequency, characteristics, and risk factors of PEE after autoimmune encephalitis (AE) and infectious encephalitis (IE) in three Austrian tertiary care hospitals over ten years. We included patients ≥ 18 years diagnosed according to internationally recognized encephalitis algorithms or verification of well-characterized antineuronal autoantibodies (AE) or pathogens (IE). Epilepsy diagnosis followed International League Against Epilepsy criteria. All available clinical data were collected from electronic patient files. A prospective follow-up was conducted via structured interviews and clinical visits. Statistical analyses included Kaplan-Meier plots, correlation analyses, and regression models. Of 149 patients, 26 (17%) had AE, 108 (73%) IE, and 15 (10%) encephalitis of unknown etiology. Prospective follow-up was achieved in 74% of cases. Median follow-up was 2304 days (IQR 1433; 3274). Acute symptomatic seizures (ASS), acute symptomatic status epilepticus and PEE are significantly more frequent in AE than in IE (p < 0.001). Antiseizure medication (ASM) use persisted in 85% of AE and 30% of IE patients at last follow-up, despite only 12% meeting PEE criteria. In both types of encephalitis, we see a shift from focal-to-bilateral semiology. Difficult-to-treat seizures during initial hospitalization correlated with PEE risk (rho = 0.317; p < 0.001). Our study provides insights into PEE characteristics, management, and prognosis. It highlights the prevalence of ASM overuse in the wake of encephalitis and provides a prognostic tool assessing the individual PEE risk.