Atrophy of hippocampal subfields as a diagnostic biomarker in alzheimer's disease patients and its differentiation from mild cognitive impairment disorders

Atrophy of hippocampal subfields is one of the diagnostic biomarkers of Alzheimer's disease, which has also been observed in many patients with mild cognitive impairment. There is still no clear understanding of the atrophy pattern of hippocampal subfields in Alzheimer's disease and its differentiation from mild cognitive impairment. In this cross-sectional study, hippocampal subfield atrophy in Alzheimer's patients were compared with patients with early (EMCI) and late (LMCI) cognitive impairment and the control group.

This was a cross-sectional study conducted from September 2021 to September 2022 in the radiology department of Tabriz Paramedical Faculty. MRI images of Alzheimer's patients, EMCI patients, LMCI patients, and normal controls (NCs) were obtained from the ADNI database. Different hippocampus subfields of hippocampal fissure, dentate gyrus head, dentate gyrus body, first cornu ammonis body, cornu ammonis head, subiculum body, and subiculum head were isolated using the hippocampus segmentation tool in FreeSurfer 7.0 software. The volume of all subfields was calculated bilaterally and normalized. The volume difference of each hippocampus subfield between the groups participating in the study and the pair volume difference between the groups was analyzed using the Kruskal-Wallis H Test and post-hoc Dunn's test. The P<0.05 was considered as the significance level.

The most significant volume difference between the four groups participating in the study was related to the whole hippocampus, DG body, subiculum body, and subiculum head subfields (P<0.0001). Also, when examining pairs, the most significant difference was observed between the NC/AD pair (P<0.0001) and the least significant difference between the pair of LMCI/AD group (P<0.05) and in the subfield subiculum body showing the progressive course of hippocampal subfield atrophy with cognitive progress towards Alzheimer's disease.

In most subfields of the hippocampus, a significant difference in atrophy can be seen, increasing the severity of atrophy as the disorder progresses toward Alzheimer's. Such findings can help guide future studies to improve diagnostic performance to identify individuals at high risk of Alzheimer's disease.