Gray matter atrophy patterns of mild cognitive impairment subtypes

Mild cognitive impairment (MCI) is a heterogeneous neurocognitive disorder that can be classified into various subtypes. The present study aims to examine the gray matter (GM) atrophy patterns of MCI subtypes in comparison with a cognitively healthy group. Participants, including 135 MCI subjects and 120 cognitively healthy controls, were drawn from the Sydney Memory and Ageing Study. The MCI subjects were first categorized into amnestic (aMCI) and non-amnestic (naMCI) subtypes, which were then divided into single-domain (aMCI-SD and naMCI-SD) and multiple-domain subtypes (aMCI-MD and naMCI-MD). Furthermore, naMCI-SD was divided into three subgroups (language, processing speed, and executive function) according to individual cognitive impairment. Voxel-wise GM volumes were then compared between MCI subtypes and controls. The aMCI group had significantly lower GM volumes in the bilateral hippocampi and temporal cortices than the controls. This was mainly due to GM reduction of aMCI-MD but not aMCI-SD, as the latter did not show any significant GM reduction. GM reduction of naMCI and its two subdivisions was shown in widespread brain regions compared to controls. GM volumes of the multiple-domain subtypes (aMCI-MD and naMCI-MD) were lower than their single-domain counterparts (aMCI-SD and naMCI-SD) in the frontal and temporal lobes, respectively. Moreover, the language subgroup of naMCI-SD showed GM reduction in the frontal and temporal lobes compared to controls. MCI subtypes displayed specific patterns of GM atrophy that appear to be related to their various clinical presentations, which implies that underlying mechanisms of MCI subtypes are different.