Risk of epilepsy after traumatic brain injury: a nationwide Norwegian matched cohort study.

Background: Post-traumatic epilepsy (PTE) is a well-known complication of traumatic brain injury (TBI). Although several risk factors have been identified, prediction of PTE is difficult. Changing demographics and advances in TBI treatment may affect the risk of PTE. Our aim was to provide an up-to-date estimate of the incidence of PTE by linking multiple nationwide registers. Methods: Patients with TBI admitted to hospital 2015-2018 were identified in the Norwegian Trauma Registry and matched to trauma-free controls on sex and birth year according to a matched cohort design. They were followed up for epilepsy in nationwide registers 2015-2020. Cumulative incidence of epilepsy in TBI patients and controls was estimated taking competing risks into account. Analyses stratified by the Abbreviated Injury Scale (AIS) severity score, Glasgow Coma Scale score and age were conducted for the TBI group. Occurrence of PTE in different injury types was visualized using UpSet plots. Results: In total, 8,660 patients and 84,024 controls were included in the study. Of the patients, 3,029 (35%) had moderate to severe TBI. The cumulative incidence of epilepsy in the TBI group was 3.1% (95% Confidence Interval [CI] 2.8-3.5%) after 2 years and 4.0% (3.6-4.5%) after 5 years. Corresponding cumulative incidences in the control group were 0.2% (95% CI 0.2-0.3%) and 0.5% (0.5-0.6%). The highest incidence was observed in patients with severe TBI according to AIS (11.8% [95% CI 9.7-14.4%] after 2 years and 13.2% [10.8-16.0%] after 5 years) and in patients >40 years of age. Conclusion: Patients with TBI have significantly higher risk of developing epilepsy compared to population controls. However, PTE incidence following moderate-severe TBI was notably lower than what has been reported in several previously published studies.