O3‐01‐03: A Diffusion Tensor MRI study of patients with Mild cognitive impairment and Alzheimer's disease with a two‐year clinical follow up

Previous diffusion tensor (DT) MRI studies, which assessed the predictive value of structural brain changes for conversion to Alzheimer's disease (AD), limited their analysis to the medial temporal lobe (MTL). To date, no prospective studies have considered the prognostic value of brain DT MRI measures beyond the MTL. Aims of this study were to assess whether brain changes detected by DT MRI can improve the understanding of structural damage in AD, and are associated with different risks of conversion to AD in amnestic mild cognitive impairment (aMCI). Twenty-one aMCI, 21 AD, and 20 healthy subjects underwent conventional and DT MRI at baseline. All subjects were clinically followed up over two years; at the end of follow up, aMCI were grouped into converters to AD (aMCI-C) and nonconverters (aMCI-NC). Mean diffusivity (MD) and fractional anisotropy (FA) were obtained from total grey (GM) and white matter (WM), and from several GM and WM regions of interest (ROIs). A significant trend of worsening with a trajectory “normal/aMCI/AD” was demonstrated for the total GM and WM damage, as well as for diffusivity abnormalities in ROIs, mainly located in posterior brain regions. aMCI-C had a pattern of GM and WM changes similar to that seen in AD, whereas aMCI-NC showed DT MRI values similar to those of healthy subjects. DT MRI metrics that better distinguished aMCI-C from aMCI-NC were MD of total GM and WM, hippocampi, anterior insulae, frontal and parietal WM, and occipital GM and WM, and FA of temporal WM. Subtle brain diffusivity changes occur from the prodromal stages of AD, mainly in posterior brain regions, and spread over the course of the disease to involve the frontal lobe. In aMCI, the severity of tissue damage within and beyond the medial temporal lobe is associated with an increased short-term risk to develop AD.