Clinical meaning of significant intraindividual asymmetries in material-specific memory performance within the unimpaired range in 432 people with epilepsy

Material-specific memory deficits can provide lateralizing information regarding epileptogenic foci or structural lesions. Intraindividual performance asymmetries may occur despite overall unimpaired performance. This study investigates the clinical relevance of such asymmetries in people with epilepsy (PWE). We retrospectively analyzed data from 432 PWE who demonstrated unimpaired verbal and figural memory performance but exhibited significant intraindividual asymmetries in these domains, as determined by critical differences derived from co-normed data. Concordance between material-specific memory asymmetries and lateralization from MRI and EEG lateralization was evaluated using contingency tables and chi-square/Fisher's exact tests. Among 1,246 individuals with suspected epilepsy and unimpaired memory performance, 432 (34.7 %) with confirmed epilepsy diagnosis exhibited significant material-specific asymmetries. Of these, 367 (85.0 %) demonstrated a relative verbal memory superiority, and 65 (15.0 %) showed a figural memory superiority. Among PWE with lateralized temporal pathologies, Fisher's exact test showed a significant association between memory asymmetries and MRI lateralization, p = .036, V = .167. A chi-square test demonstrated no significant association between memory asymmetries and EEG lateralization, χ²(1) = 3.57, p = .059. No significant concordance emerged when temporal MRI and EEG findings were considered jointly, χ 2 (1) = 3.54, p = .060. The majority of PWE with significant intraindividual material-specific memory asymmetries within the unimpaired range exhibit verbal memory superiority. There is a statistically significant association of this performance asymmetry with MRI lateralization. In case of temporal pathologies, memory asymmetries clearly point to lateralized MRI pathologies, although the actual side cannot be reliably predicted due to putative reorganization processes.