Frontotemporal Dementia
Frontotemporal dementia (FTD) is a major constituent of early dementias and may be confused with early-onset Alzheimer disease. A comparison of FTD with Alzheimer disease not surprisingly revealed a greater reduction of FA within frontal regions in FTD (? Fig. 5.8)27; unlike Alzheimer disease, FTD entails more prominent white matter degeneration. More generally, increased diffusivity (MD) was seen throughout much of the frontal and temporal lobes in behavioral variant FTD compared to controls.28 Selective FA reduction has been demonstrated within the superior longitudinal fasciculus in frontal variant FTD, whereas this decrease occurred in the inferior longitudinal fasciculus for temporal variant FTD.29
Dementia with Lewy Bodies
Dementia with Lewy bodies (DLB) is another form of neurodegenerative dementia closely related to Alzheimer disease and may overlap clinically with other dementias. DTI is particularly well-suited to DLB because atrophy is not a leading component as in other dementias, and white matter indices may be more helpful than volumetric assessments of atrophy. DTI demonstrates preliminary utility in identifying differences between DLB and Alzheimer disease where DLB selectively involves substantially reduced FA in the precuneus and parieto-occipital tracts involved in visual association in comparison to more diffuse changes observed in Alzheimer disease (? Fig. 5.9).22'30 Dif- fusivity within the amygdala in DLB also corresponds well with a common measure of parkinsonism motor symptoms.22 There is a significant decrease in FA within the parahippocampal gyri in Alzheimer disease compared to DLB that aids in distinguishing between these two similar forms of dementia.30 Although bearing much overlap, early research suggests DTI is capable of differentiating between the neurodegenerative dementias.
