Cumulative electroconvulsive therapy sessions and focal epilepsy: A nationwide cohort study in Japan.

objectiveElectroconvulsive therapy (ECT) is widely used for severe psychiatric disorders, yet concerns remain regarding possible epileptogenic effects associated with prolonged or repeated exposure. We examined the association between cumulative ECT sessions and focal epilepsy in a nationwide Japanese cohort.

methodsWe conducted a retrospective cohort study using a nationwide claims database including 3733 patients who received ECT between 2008 and 2025. For analyses of incident focal epilepsy, patients with a prior diagnosis of epilepsy before the first ECT session were excluded from the at-risk population. New-onset focal epilepsy was defined as a G40.2 diagnosis recorded after ECT initiation. Person-time accrued from the first ECT session to epilepsy diagnosis or last follow-up. Multivariable logistic regression assessed the association between cumulative ECT sessions and focal epilepsy, adjusting for age, sex, and psychiatric diagnoses. An exploratory time-varying Cox model evaluated cumulative exposure as a time-dependent variable.

resultsAmong 3733 patients (mean age 56.9 years; 66.4% female), 96 (2.6%) developed focal epilepsy, corresponding to an incidence of 3748 per 100 000 person-years. A cumulative exposure pattern was observed, with diagnosis rates exceeding 5% among patients receiving ≥ 50 sessions and peaking at 9.1% in the 80-89 session group. Each additional ECT session was associated with higher odds of focal epilepsy (β = 0.0099, p = 0.004). Age, sex, and psychiatric diagnoses were not significant predictors. In exploratory time-varying analysis, reaching ≥ 50 sessions was associated with increased hazard, although event numbers were limited. Latency to diagnosis ranged from weeks to over 4000 days. Following epilepsy diagnosis, 70.8% discontinued ECT and 98.0% received antiseizure medication. SIGNIFICANCE: In this nationwide cohort, greater cumulative ECT exposure was associated with focal epilepsy diagnosis. While causality cannot be established, these findings support consideration of careful neurological monitoring during prolonged ECT courses. PLAIN LANGUAGE SUMMARY: Electroconvulsive therapy (ECT) is an effective treatment for severe mental illnesses. However, its long-term neurological effects are not fully understood. We analyzed nationwide data from 3733 patients in Japan who received ECT and examined whether repeated treatments were associated with new diagnoses of focal epilepsy. Ninety-six patients (2.6%) were diagnosed with focal epilepsy after starting ECT. The likelihood of diagnosis was higher among patients who received more ECT sessions, particularly those undergoing prolonged courses. Although this study cannot determine whether ECT directly causes epilepsy, our findings suggest that careful neurological monitoring may be considered during extended treatment.