Medial Temporal Lobe Volumes in Amnestic Mild Cognitive Impairment and Late-life Depression: Research Synthesis

There are important similarities and differences between the clinical presentation and prognosis of amnestic mild cognitive impairment (aMCI) and late-life depression (LLD). However, very little is known about the shared and distinct pathophysiological mechanisms between both conditions, even thought their frequent co-occurrence suggests a close association. In this research synthesis, we examined the extent of hippocampus (HC) and entorhinal cortex (ERC) atrophy as reported in 17 aMCI and 9 LLD studies. Total HC volume reduction was significant in almost 100% of aMCI and 50% of LLD studies when populations were compared to normal controls. Volume deficit for total and lateralized HC in LLD studies seemed fairly similar in terms of percentage to aMCI studies. Total ERC volume reduction was significant and larger than HC in all aMCI studies compared to normal controls. No LLD studies measured ERC volume. In general, exclusion criteria and demographic characteristics were fairly similar for most studies. However, imaging characteristics and segmentation protocols varied largely, which could impact the comparison of volume reductions in different studies. Future work investigating simultaneously both aMCI and LLD and using standardized imaging and segmentation protocol would be required to allow a better understanding of the association between aMCI and LLD.