White matter damage in frontotemporal dementia and Alzheimer's disease measured by diffusion MRI

Frontotemporal dementia (FTD) and Alzheimer's 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 T1-weighted structural images
and diffusion tensor images in 18 patients with FTD, 18 patients with
Alzheimer's 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 Alzheimer's 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 Alzheimer's disease, FTD was associated with greater reductions
of FA in frontal brain regions, whereas no region in Alzheimer's
disease showed greater reductions of FA when compared to FTD. In
conclusion, the regional patterns of anisotropy reduction in FTD and
Alzheimer's 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
Alzheimer's disease. Taken together, the results suggest that white
matter degradation measured with DTI may improve the diagnostic
differentiation between FTD and Alzheimer's disease.