Hippocampus and amygdala volume and morphology in neurodegenerative disorders with co-morbid epilepsy

Epilepsy is common in Alzheimer's disease (AD) and non-AD dementias. However, the neuroimaging correlates of epilepsy in dementias remain unexplored. We investigated mesial temporal morphology and volumes in AD (AD + Epi) and nonAD dementias (nonAD + Epi) with epilepsy.

Participants from 39 US Alzheimer's disease centers (9/2005-12/2021) were classified into dementia with epilepsy (AD + Epi, nonAD + Epi), dementia without epilepsy (AD-Epi, nonAD-Epi); and healthy controls. Dementia with epilepsy participants with available MRIs were matched to dementia without epilepsy and healthy controls by age, sex, and dementia type (AD versus non-AD). FreeSurfer segmented hippocampi and amygdalae. Point distribution models created via ShapeWorks quantified morphological differences in the left and right hippocampi and amygdalae. Hippocampal and amygdalar volumes were normalized to the total intracranial volume. Multivariate analysis of covariates (MANCOVA), adjusted for age, sex, intracranial volume, and dementia severity, identified statistically significant local morphological and normalized volume group differences.

A total of 703 participants (average age: 70.78 years, 391 (55.62 %) female) were included. AD-Epi and NonAD-Epi exhibited uniform hippocampal and amygdalar morphological atrophy bilaterally. In contrast, AD + Epi demonstrated morphological atrophy in the hippocampal bodies and tails bilaterally with sparing of the hippocampal heads, more pronounced inward deviations on mesial and lateral surfaces, and outward deviations in the middle hippocampal body bilaterally on the superior surface. NonAD + Epi showed significant morphological atrophy in the right hippocampal head, tail, and amygdala. No group volume differences were found.

We identified hippocampal body and tail atrophy in AD + Epi and right hippocampal head, tail, and amygdalar atrophy in nonAD + Epi. Different lateralized and region-specific patterns of limbic atrophy and dysmorphia highlight potential differences in the pathophysiology and the possible role of epilepsy in altering the trajectory of neurodegeneration in AD and nonAD.