The Epilepsy-Cog study: methods to establish a harmonized study of late-onset epilepsy in a meta-cohort of six population-based cohorts in the United States

ObjectivesWith the expected demographic shift toward those [≥]65 years of age in the United States, late-onset epilepsy (LOE) poses a significant public health issue, yet it has been historically understudied. We are undertaking an effort in the Epilepsy-Cog study to pool individual participant data from six US-based prospective cohort studies. In this paper, we outline the process for ascertaining epilepsy, harmonizing, and pooling individual participant data across the six cohorts. MethodsThe Epilepsy-Cog study includes individual participant data from six US-based longitudinal cohort studies: ARIC, CHS, MESA, NOMAS, REGARDS, and WHICAP. In all cohorts except NOMAS, prevalent and incident epilepsy were ascertained using Medicare claims-based algorithms. In NOMAS, epilepsy cases were identified through cohort-based reporting and medical record review. To perform cross-cohort harmonization of variables, we used the lowest common denominator approach, assigning response categories or value levels in common across all cohorts. ResultsFrom a total of 68,544 participants across six cohorts, 43,753 participants met eligibility criteria for Epilepsy-Cog. Among them, we identified 551 (1.3%) participants with prevalent epilepsy and 1,500 (3.4%) participants with incident epilepsy. We have harmonized demographic characteristics, health behaviors, vascular risk factors (VRFs), one genetic variable, medication use, subjective health status measures, incident events, and cause-of-death variables. ConclusionThe Epilepsy-Cog pooled cohort of 43,753 participants with and without epilepsy, combined with harmonized demographic, VRFs, and event data, offers a unique resource to yield new insights into LOE.