White matter damage in frontotemporal dementia and Alzheimers disease measured by diffusion MRI

Frontotemporal dementia (FTD) and Alzheimers disease are sometimes difficult to differentiate clinically because of overlapping symptoms. Using diffusion tensor imaging (DTI) measurements of fractional anisotropy (FA) can be useful in distinguishing the different patterns of white matter degradation between the two dementias. In this study, we performed MRI scans in a 4 Tesla MRI machine including T-1-weighted structural images and diffusion tensor images in 18 patients with FTD, 18 patients with Alzheimers disease and 19 cognitively normal (CN) controls. FA was measured selectively in specific fibre tracts (including corpus callosum, cingulum, uncinate and corticospinal tracts) as well as globally in a voxel-by-voxel analysis. Patients with FTD were associated with reductions of FA in frontal and temporal regions including the anterior corpus callosum (P 0.001), bilateral anterior (left P 0.001; right P 0.005), descending (left P 0.001; right P 0.003) cingulum tracts, and uncinate tracts (left P 0.001; right P 0.005), compared to controls. Patients with Alzheimers disease were associated with reductions of FA in parietal, temporal and frontal regions including the left anterior (P 0.003) and posterior (P 0.002) cingulum tracts, bilateral descending cingulum tracts (P 0.001) and left uncinate tracts (P 0.001) compared to controls. When compared with Alzheimers disease, FTD was associated with greater reductions of FA in frontal brain regions, whereas no region in Alzheimers disease showed greater reductions of FA when compared to FTD. In conclusion, the regional patterns of anisotropy reduction in FTD and Alzheimers disease compared to controls suggest a characteristic distribution of white matter degradation in each disease. Moreover, the white matter degradation seems to be more prominent in FTD than in Alzheimers disease. Taken together, the results suggest that white matter degradation measured with DTI may improve the diagnostic differentiation between FTD and Alzheimers disease.