Seven tesla MRI reveals amygdala and hippocampal subfield atrophy in dementia with Lewy bodies

The 7T-DLB study investigated whether atrophy of individual hippocampal and amygdala subfields is present in dementia with Lewy bodies (DLB) as well as in Alzheimer’s disease (AD) in which it has previously been established. MRI at standard clinical and research field strengths may have insufficient resolution to reveal the presence of atrophy in these regions in DLB; seven tesla MRI is ideally placed to examine subtle volumetric differences in these brain areas due to increased signal to noise ratio and tissue contrast. In this prospective, cross-sectional, seven tesla imaging study, 20 participants with probable DLB underwent MRI, clinical assessment, and cognitive testing, alongside a patient comparison group of 25 participants with probable AD, and 19 healthy controls. Scans were segmented using FreeSurfer automated pipelines. Hippocampal and amygdala subfield volumes were compared between diagnostic groups using a generalised linear model with age, sex, education, and total intracranial volume as covariates. Associations between volumes and cognition were examined using Kendall’s tau. Exploratory analyses investigated associations between subfield volumes and visual hallucinations scores, and in a sub-set of 41 participants (DLB=13, AD=17, controls=11), with plasma ptau-217 concentrations. Four (of 13) hippocampal subfields (molecular layer, subiculum, presubiculum, and entorhinal cortex) and five (of nine) amygdala subfields (accessory basal, central, medial and cortical nuclei, and anterior amygdaloid area) were significantly smaller in DLB compared to controls (pFDR<.05). In DLB, significant correlations between subfield volumes and Addenbrookes Cognitive Examination Scores were found for seven hippocampal subfields (Cornu Ammonis (CA)1, CA2/3, CA4, molecular layer, dentate gyrus, hippocampal amygdala transition area, and presubiculum), and five amygdala subfields (basal, accessory basal, central, cortical, and cortico-amygdala transition area) (all pFDR<.05). Exploratory analyses suggest that amygdala subfield volumes may be associated with visual hallucinations, though these provisional findings require replication. We conclude that structural seven tesla MRI reveals volumetric differences in individual hippocampal and amygdala subfields between DLB and controls, as well as between AD and controls where they have previously been described. Atrophy of individual subfields may potentially help explain the presence of cognitive and non-cognitive symptoms in DLB.