Amygdala microstructural changes in subjective cognitive decline: A diffusion kurtosis and neurite orientation dispersion and density imaging study

BackgroundPeople with subjective cognitive decline (SCD) are at increased risk of Alzheimer's disease. Prior research has suggested that amygdala volume may be more sensitive than hippocampal volume in detecting differences between SCD and age-matched controls, as well as in predicting SCD conversion to mild cognitive impairment. However, the microstructure underlying this volumetric change remains unclear.ObjectiveThis study evaluated amygdala microstructural differences in SCD versus control participants as well as associations between amygdala microstructure and volume, age, memory performance, anxiety, and depression using diffusion imaging.MethodsDiffusion tensor imaging, diffusion kurtosis imaging, and neurite orientation dispersion and density imaging were fit to diffusion MRI images. Group differences and correlations between diffusion metrics, age, memory, anxiety, and depression were assessed in 123 SCD versus 194 age-matched controls over age 55.ResultsIn the left amygdala, SCD participants had significantly lower fractional anisotropy (FA), lower kurtosis fractional anisotropy (KFA), and higher free water fraction (FWF). KFA was lower in the right amygdala in SCD. There were no significant group differences in the amygdala volume. Bilateral KFA negatively correlated with FWF, a marker of neuroinflammation and neurodegeneration. Left FA negatively correlated with orientation dispersion index, a marker of neuritic branching. Right KFA correlated with age only in SCD, while left FA correlated with anxiety only in controls.ConclusionsKFA is sensitive to group differences between SCD and controls in bilateral amygdala. KFA may reflect neuroinflammation and increased sensitivity to aging in the amygdala in SCD.