Isolated hippocampal sclerosis and focal dysplasia type IIIa: Comparative study of anatomo-electro-clinical profile and seizure outcome.

OBJECTIVE: Distinguishing drug-resistant temporal lobe epilepsy (TLE) caused by isolated hippocampal sclerosis (iHS) from focal cortical dysplasia type IIIa (FCD IIIa) remains a presurgical challenge. This study aimed to compare the clinical characteristics, electrophysiological data, and postsurgical seizure outcomes between these pathologies.

METHODS: We retrospectively analyzed a cohort of 50 consecutive TLE patients (mean duration of disease of 22 years) who underwent surgery. The histopathology confirmed either iHS (n = 22) or FCD IIIa (n = 28) and a minimum follow-up of 12 months. The groups were compared on complex presurgical data, surgery type, and outcome.

RESULTS: A history of febrile seizures (p = 0.02, OR = 4.7) was more frequent in the FCD IIIa group, which also had significantly lower intelligence quotient (IQ) scores in all domains. The mean total IQ score for FCD IIIa/iHS was 86/94 (p = 0.02); verbal IQ was 85/92 (p = 0.03); performance IQ was 89/98 (p = 0.02). The effect size was considered medium for all three (Cohen's d = 0.7, 0.63 and 0.68 respectively). Scalp EEG showed shorter seizures in FCD IIIa (p = 0.03), in SEEG, the temporal pole was more implanted in this group (p = 0.02, 50 % difference, OR = ∞). At a mean follow-up of 8.5 years, similar seizure-freedom rates was found between groups (82 % for FCD IIIa, 95 % for iHS; p = 0.48). Follow-up EEG and neuropsychological assessment at 6 months post-surgery showed no statistical differences.

SIGNIFICANCE: FCD IIIa and iHS exhibit several distinct electro-clinical features. The most important is a more impaired general cognitive profile associated with FCD IIIa, without differences in language or global memory.