Hippocampal subfield volumetry in corticobasal syndrome of diverse underlying pathologies

Multiple pathologies may underlie corticobasal syndrome (CBS), including Alzheimer's disease (AD). Typical amnestic AD is characterized by early selective hippocampal atrophy. The profile of hippocampal atrophy in AD patients presenting as CBS (CBS-AD), compared to CBS patients of non-AD pathologies (CBS-nAD) and amnestic AD patients, has not been studied.

To compare hippocampal subfield atrophy patterns between CBS-AD, CBS-nAD, typical amnestic AD patients, and control subjects.

Automated hippocampal subfield volumetry was performed via the hippocampal subfield segmentation pipeline of Freesurfer 6.0 on 3D T1-weighted images. CBS patients were classified as CBS-AD or CBS-nAD based on CSF AD biomarkers by applying the AT(N) classification system. Mean volumes of nine hippocampal subfields, head-body-tail segments, total hippocampus, and entorhinal and parahippocampal gyrus cortical thickness were measured.

Eighty-three subjects were included (CBS-AD: n = 14; CBS-nAD: n = 17; amnestic AD: n = 29; controls: n = 23). CBS-AD patients had greater whole hippocampal and hippocampal subfield atrophy compared to CBS-nAD. CBS-AD and amnestic AD patients did not differ in subfield volumes. CBS-nAD did not exhibit hippocampal atrophy compared to controls, with the exception of fimbria. (Cohen's d = 1.27; p = 0.038). Presubiculum (Cohen's d = 1.00; p = 0.002) and hippocampal body (Cohen's d = 0.95; p = 0.001) volumes exhibited the greatest differences between CBS-AD and CBS-nAD. Hippocampal subfield volume provided combined sensitivity and specificity < 80% for the discrimination of CBS-AD from CBS-nAD.

CBS-AD and amnestic AD patients exhibit comparable, and significantly greater hippocampal atrophy compared to CBS-nAD patients. Hippocampal subfield volumetry in CBS is indicative of an AD underlying pathology.