Twelve-Month follow-up study of Fractional Anisotropy changes in Mild Cognitive Impairment compared to healthy elderly subjects

Background: Diffusion Tensor Imaging (DTI) demonstrates changes of white matter integrity in the very early stage of Alzheimer's disease (AD). Fractional anisotropy (FA) as a measurement of fiber tract integrity is reduced in patients with AD and patients with mild cognitive impairment (MCI) in intracortical projecting fiber tracts. However, most studies reported cross sectional data. In this study, we aimed to determine the changes of FA in MCI patients and healthy elderly subjects (HC) over 12 months follow-up. Methods: Thirteen MCI and 11 HC were enrolled. All subjects underwent neuropsychologcial testing and high resolution MRI and DTI scans at 3 Tesla at baseline and after 12 months of follow-up. We employed region of interest based measurements of FA in posterior cingulate gyrus (figure in upper row) and corpus callosum subregions (figure in lower row) including splenium and genu. ROI placement was guided by color coded fiber tract maps after coregistration of baseline and follow-up DTI maps. We used repeated measure analysis to determine the difference of FA between baseline and follow up. Results: There was no age difference between both groups. There was no significant decline of MMSE over time in MCI and HC groups. There was a significant decline of FA in corpus callosum genu in MCI patients (p < 0.016), but not in controls, and a decline of FA in splenium in both groups (p< 0.043). There was no significant decline of FA in posterior cingulate gyrus. Conclusions: There was significant decline of DTI based measures of white matter tract integrity in the corpus callosum of MCI patients and to a lesser extent in HC subjects. Contrary to our primary hypothesis, there was no decline of white matter integrity over time in the posterior cingulate gyrus. Future studies with longer follow up period and a larger number of subjects are required to confirm these findings.

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